In this study, authors investigated a fatigue life prediction method for RC slabs considering effects of support condition and stepped incremental load based on experimental data of traveling wheel-type loading test. At first, to properly predict the fatigue life of RC slabs under constant cyclic loading test, a coefficient which represents influence of support condition was introduced to previous prediction method that authors had proposed. The modified method can cover three types of support conditions; simply support along longitudinal direction and elastic support along transverse direction, simple support along longitudinal direction and free ends along transverse direction, and simple support along all directions. Besides considering fatigue damage caused by preceding loading block as reduction of shear strength due to cyclic loading, a new evaluation method for stepped incremental loading test was proposed.

Studying about fatigue in RC beams without stirrup is one of valid approaches to investigate fatigue problem in RC slabs because the transverse cracked slab can be considered as plural RC beams lined up in parallel. Therefore, in this paper, authors tried to clarify the fatigue damage in RC beams keeping the problem of RC slabs in mind. Non-linear three-dimensional finite element analysis (3D-FEA) of RC beams without stirrup is conducted under three types of loading conditions; static load, fatigue load and variable amplitude fatigue load. By comparing static and fatigue analysis results, authors examine the principal compressive stress distribution and the stiffness reduction. This paper presents that static and fatigue loading showed different trends in both the stress distribution and stiffness reduction. It can be also revealed that when variable amplitude load with different two load blocks is given in fatigue analysis, the cyclic loading in the first load block influences on the decreasing rate of stiffness.

The authors conducted on-site load test and 3D Finite Element Analyses (3D-FEA) of an existing prestressed post-tensioned concrete bridge with four post-tensioned T-girders, whose span length was 36 m, constructed in 1960 so as to clarify structural behaviour and its capacity of the bridge superstructure. It was found that the 3D-FEA combined with the linear surface spring elements which represents restraint of adjacent members can well simulate the actual structural behavior, the capacity and failure mode. Besides it is also discussed about the reason why capacity of a girder in superstructure becomes greater than a single girder with same cross-sectional properties.

In this paper, a weakly singular boundary integral equation method is developed for the stress analysis of an anisotropic, linearly elastic, cracked whole space possessing a plane of symmetry. This study should offer an alternative powerful tool essential for the modeling of both near-surface and deeply embedded defects in a rock/soil medium. A system of governing equations is established using a pair of weakly singular, weakform, displacement and traction integral equations for the cracked whole space along with the symmetric condition. The final equations contain only unknown crack-face data in a lowerhalf of the whole space. In addition to their capability to treat cracks of arbitrary shape, material anisotropy and general loading conditions, all involved kernels are weakly singular allowing all integrals to be interpreted in the sense of Riemann. A symmetric Galerkin boundary element method together with the Galerkin approximation is implemented to solve the governing integral equations for the unknown crack-face data. To further enhance the accuracy and efficiency of the proposed scheme, special basis functions are introduced to approximate the near-front field and the interpolation technique is adopted to evaluate all kernels for generally anisotropic materials. The solved crack-face displacement data is then utilized to postprocess for the essential fracture information along the crack front. Various scenarios are employed to verify the proposed technique and a selected set of results is presented to demonstrate its accuracy and computational robustness.

An experimental program was carried out to investigate the shear capacity of High-Performance Fiber-Reinforced Concrete (HPFRC) I-beams. The main parameters were assigned as the fiber content and presence of shear reinforcement. To study the effect of these main parameters on the shear capacity, testing of six I-beams and other control specimens was conducted. It can be observed from the results of the experimental study that the presence of fibers and shear reinforcement significantly improves the ultimate capacity and structural behavior of HPFRC members. Finally, the experimental results are discussed, and the shear capacity of HPFRC can be estimated by extending the code provisions stated in AFGC-Sétra 2013.

The experimental and analytical study are attempted to clarify the static and fatigue behavior of mortar with blast furnace slag (BFS) sand as fine aggregates in compression in air and water. The cylindrical BFS mortar specimens were used for static and fatigue compression tests in air and water and results are compared with those of mortar using crushed sand (CS). The fatigue load was applied in the form of sine signal with a constant amplitude and the frequency of 5 Hz. The stress level is varied from 60%, 70% and 80% of the uniaxial compressive strength. The experimental results disclose that BFS mortar exhibits more fatigue life compared to CS mortar in air, while it is similar in water. Thereafter, the stress-strain relationships for each mortar under monotonic loading are formulated. Moreover, a simplified fatigue model for the assessment of plastic strain, total strain and fracture parameter at different number of loading cycles and for prediction of fatigue life is also proposed.

This study presents the experimental investigation carried out to evaluate the performance of non air-entrained concrete with blast furnace slag (BFS) sand as full amount of fine aggregates under freeze thaw cycles in comparison with conventional air-entrained normal concrete. Cuboidal specimens were used for freeze-thaw test. The concrete specimens were subjected to freeze-thaw cycles (FTC) in 3% NaCl solution at the age of about 4 months. The duration of each freeze-thaw cycle was 8 h with temperature variation between +20 °C and -25 °C. The strain variation during each FTC was recorded using strain gauges attached to the concrete surface and change of relative dynamic modulus of elasticity was measured at certain number of FTC using ultrasonic pulse velocity method. The damage progress is discussed based on plastic tensile strain accumulated during freeze-thaw cycles. A particular number of specimens were taken out from freeze-thaw chamber after 50, 125 and 225 FTC. Thereafter, the static compressive strength tests were performed to determine the change in mechanical properties of concrete with blast furnace slag fine aggregates compared with normal concrete at different number of FTC. BFS concrete showed more compressive strength and Young's modulus for same FTC number compared to normal concrete, however, the rate of reduction of mechanical properties of air-entrained normal concrete is slightly slow.

This paper aimed to assess structural performance of superstructures of typical RC bridge in Thailand. The static load test was performed to measure both horizontal and vertical displacement in Reinforced Concrete (RC) girder using Image Measurement System (IMS). The RC girder's stiffness obtained from the IMS results is compared with that obtained from 3D Linear Finite Element Method. The stiffness from IMS is smaller than that from 3D FEM, indicating deterioration of RC girder. Besides, to predict the failure mode and capacity of RC girder, 2D Non-linear Finite Element Method. It was founded that the RC girder occurred shear and anchorage failure. In this paper, furthermore, the Load and Resistance Factor Rating (LRFR) is conducted to evaluate the performance of the bridge which has been designed by old LRFD specification. The results show that the moment rating factor and the shear rating factor for the designed load rating is equal to 1.20 and 1.01, respectively. From LRFR, the bridge still has sufficient capacity to carry both the AASHTO LRFD-design live load HL-93 and the AASHTO legal loads.

This study presents a new bond model based on the deterioration mechanisms observed during uniaxial tensile tests of reinforced concrete prismatic specimens subjected to freeze-thaw cycles. The test results demonstrated that the bond stress reduced, even though the specimens were exposed only to temperature fluctuation without the damage in concrete cover. The proposed model considers the bond deterioration mechanism caused by the temperature fluctuation in addition to the damage in concrete cover. Finally, the proposed model shows good agreement with the test results regardless of the dominant deterioration mechanism.

An examination including an evaluation of mechanical properties of concrete that had suffered combined deterioration from fatigue and frost damage was done using cylindrical specimens. The order of deterioration and degree of deterioration of the specimens were used as variables. The examination clarified that certain mechanical properties of concrete that had undergone combined deterioration were able to be evaluated by measuring the propagation speed of ultrasonic waves. The decrease in the elastic modulus and the ultrasonic velocity that accompanies the increase in the number of freeze-thaw cycles was smaller in the specimens that experienced fatigue first and then frost damage than in the specimens that experienced frost damage only. The values for mechanical properties (e.g., compressive strength, elastic modulus, and shrinkage strain) of the specimen that experienced frost damage first and then fatigue had already greatly decreased after the application of freeze- thaw cycles. Therefore, the decrease in the mechanical properties was small even with increases in the number of loading cycles. The decrease in the fatigue life of the specimen in the fatigue test was proportional to the deterioration from the preceding frost damage.

Concrete structures can be deteriorated in extreme service conditions especially for fire incidents. For the evaluation of the post-fire performance, analytical methods are very powerful and useful. However, widely applicable mechanical models of fire-damaged material have not yet been proposed. To develop such models, the scale of control volume considering strength, stiffness and deformability is one of important factors. This paper presents an experimental study in which visual observations and mechanical properties of oven-dried mortar after exposed to the fire curves of ISO 834 and ASTM E119 for 90 minutes and to be left to cool down in air were conducted. Mortars were made from two different types of fine aggregate and cement. Experimental results indicate that the raw material made mortar is a prominent factor to introduce the different fire damage characteristics. Meanwhile, the mechanical properties of mortar in fire problem are strongly related to temperature that mortars were experienced to.

Bond performance of RC strengthened with polyurea resin and strand sheet depends on the concrete strength and the amount of polyurea resin. The present experimental study was undertaken in order to confirm the effect of above factors in the bond behaviour of concrete - strand sheet with a layer of polyurea resin by means of one side pull-out bond test method. Consequently, the specimen of the low strength concrete showed lower ultimate bond strength than that of the normal strength concrete at the same amount of polyurea resin regardless of presence or absence of the polyurea resin. However, the specimens with polyurea resin showed far higher ultimate strength than that of the specimens without polyurea resin regardless of the concrete strength. Furthermore, the bond strength was almost the same in the range of polyurea resin coating amount of 0.5-3kg/m2.

The fiber-reinforced polymers (FRP) were used over the past years to strength the reinforced concrete (RC) beams and slabs by attaching it to their tension face. Despite considerable research over the last decade, reliable model to simulate the performance of strengthened beams still need more research. In this paper, a nonlinear numerical analysis code based on the rigid body spring model (RBSM) was extended to simulate the behavior of (RC) beams strengthened with externally bonded (FRP). The code supports the nonlinear constitutive laws for the different materials and nonlinear bond stress-slip relationships for steel - concrete and FRP-concrete interfaces. Previous experimental programs were used to validate the the model and confirm its ability to simulate the experimental observations. In all cases, very good agreement between the analytical and the experimental observations is obtained in terms of deflections, strains, internal forces, and failure mode, showing the capabilities of the model to evaluate the efficiency of proposed strengthening solutions.

The purpose of this study is to grasp the change in mechanical behavior of meso-scale mortar specimens damaged by Ca leaching. Particularly, thin mortar specimens were immersed in demineralized water and NaCl solution for 0, 56, 112 and 168 days. After immersion tests, three points bending tests and double direct shear tests were carried out in order to determine elastic modulus, tensile strength, fracture energy and tensile softening curve from load displacement curves using back analysis and shear strength. In addition, chemical analysis was conducted so as to clarify how amount of calcium hydroxide and C-S-H and in the porosity quantitatively. Consequently, it was found that the change in mechanical behavior was strongly related to the change in the amount of cement hydrate and porosity. Furthermore, mechanical models that can consider the change in porosity were constructed and were evaluated adequacy itself.

This paper presents the flexural strengthening effect of CFRP sheets on prestressed concrete (PC) beams having strands ruptured at the midspan. The increase in the number of sheets resulted in the reduction of tensile stress of the remaining prestressing strands. However, the increase in the number of sheets with insufficient sheet lengths did not provide a higher flexural strength because of the debonding from the sheet ends. The increase in the sheet lengths not only prevented the latter failure but also significantly improved the beam stiffness. More importantly, the debonding of the sheets was avoided by wrapping the transverse sheets for the whole beam span.

Previously, beam bending tests had been conducted on strengthened RC beams with polyurea resin layer, which has low elastic modulus and high elongation, between the CFRP strand sheet (strand sheet for short) and concrete surface. It was found out that polyurea resin layer improves the bonding ability between the strand sheet and concrete surface. In this study, in order to examine the bonding ability of strand sheets with polyurea resin layer, a series of bonding test was carried out. Especially to verify the applicability of this method at elevated temperature for structure such as a chimney, bonding test at different temperature were selected. As a result, it was found out that bonding strength with polyurea resin was about 2.8 times more than that without polyurea resin at room temperature. Furthermore, it was found out that sufficient bonding performance can be achieved even at high temperature.

How volume change of the cement hydrates affects mechanical characteristics of mortar after calcium leaching are discussed and prediction equations for elastic modulus, tensile strength, fracture energy and shear strength are proposed. Furthermore an analysis of mass transfer with chemical reaction based on a finite volume method is developed and is coupled with a mechanical analysis based on the RBSM. The validity of the coupled analytical method is discussed.

A new bond model for reinforced concrete members considering material deterioration induced by freezing-thawing action has been developed. The developed model with the extensive applicability from non-damaged to severely damaged members can reasonably describe deterioration mechanism between steel bar and concrete.

Reinforced concrete T-beam is widely used in civil engineering structures and buildings. However, the evaluation method based on the shear resistance mechanism considering the effects of the top fange area has not been established in current structural design codes. The purpose of this study is to clarify the shear failure mechanism of RC T-beams with stirrups. The shear failure behaviours of the RC T-beams were investigated numerically with a three-dimensional nonlinear finite element method in which the width of the top flange, shear reinforcement ratio were varied. As a result, increasing in flange width of T-beam gives higher shear capacity with nonlinear relationship. The principal strain distribution and stirrups strain development of T-beams were different from the rectangular beam. In T-beams, the average shear stresses of web area in top flange were almost the same at the ultimate state, regardless of the flange width. In addition, the effect of shear reinforcement with respect to the increase of the average shear stress in fange area was not observed. The RC T-beam has a unique shear failure mechanism which is caused by T-shape cross-section and the horizontal crack.

On RC beam members damaged by freeze-thaw cycles, the authors performed nonlinear finite-element analysis using distributed reinforcement and smeared cracking models, toward evaluating the structural properties of such RC beams. We then compared the analysis results to test results. The comparison found that the accuracy of analysis depends on the severity of concrete deterioration. It was clarified that the test values do not agree with the analysis values for RC beams that experience shear rigidity reduction from freezing damage to the compressive area or for RC beams that experience decreased rebar-concrete bonding strength from freezing damage to the tensile area. It was also clarified that the analysis may enable the evaluation of the rigidity to yield the failure mode and the maximum load for RC beams that have experienced no major decreases in shear rigidity and bonding strength. © 2014 4th International Conference on the Durability of Concrete Structures.

A strengthened method using CFRP strand sheets, which consist of bunch of hardened continuous fiber strands, and polyurea resin (shortly polyurea) with low elastic modulus have been newly developed by authors. In the method, layer of polyurea is inserted between concrete surface and FRP with the aim of improving bonding ability of the strand sheet. In this study, two kinds of test, bonding test and flexural test, were performed to clarify those effects of the polyurea soft layer on bonding ability of the strand sheet. To clarify the influence affected by temperature, bonding tests were carried out at two different temperatures, -20°C and 23°C. It was proved that inserting a polyurea soft layer was effective for improving bonding ability between the strand sheet and concrete surface at low temperatures and room temperatures, and flexural capacity of concrete beams strengthened with the strand sheet.

Allowing for the tension stiffening effects resulting from the bond between steel reinforcement and surrounding concrete leads to effective deformation analysis of reinforced concrete (RC) members when using a nonlinear finite element analysis modeled on the smeared crack concept. Nowadays, externally bonded fiber reinforced polymer (FRP) composites are widely used for strengthening existing RC structures. However, it remains unclear to what extent the tension stiffening of postcracking concrete is quantitatively influenced by the addition of FRP composites, as a result of the bond between the FRP and the concrete substrate. This article presents a discrete model, which is based on rigid body spring networks (RBSN), for investigating the tension stiffening behavior of concrete in FRP-strengthened RC tensile members. A two-parameter fracture energy-based model was deployed to represent the bond-slip behavior of the FRP-to-concrete interface. The reliability of the RBSN model was verified through comparisons with previous test results. Further parametric analysis indicates that the tension stiffening of concrete is hardly influenced by the addition of FRP composites before the yield of steel reinforcement has occurred although concrete crack patterns and crack widths may be influenced by the bond-slip behavior of the FRP-to-concrete interface. © 2011 Computer-Aided Civil and Infrastructure Engineering.

Loading tests were performed on RC beams with the depth and location of frost damage as variables. The results showed which side of the beams was damaged by frost (i.e., the compression side or the tension side) and indicated that the maximum bearing capacity, deformation properties and failure mode varied significantly with the extent of the deterioration. Specifically, with respect to deterioration on the compression side, deeper frost damage resulted in impaired performance in terms of rigidity and displacement under the maximum load, and the failure mode was more likely to shift to that of diagonal compression. For deterioration on the tension side, it was found that shallower frost damage corresponded to better deformation performance, with the failure mode shifting to a tied arch mechanism due to bond deterioration. However, deeper frost damage caused brittle diagonal tensile failure and may have resulted in reduced deformation performance.

We have developed advanced CFRP strand sheets which consist of bunch of hardened continuous fiber strands. It is assumed that the bonding ability of the strand sheet can be improved by putting a soft layer in between the strand sheet and concrete surface. In this study, the polyurethane resin was used to form a soft layer. In order to clarify the effectiveness of the polyurethane soft layer on the bonding ability of the strand sheet, bonding tests and beam bending tests in which the strand sheet was attached on concrete surface using epoxy resin with or without the polyurethane soft layer were carried out. As a result, it was found out that the polyurethane soft layer was effective for improving bonding ability between the strand sheet and concrete surface and flexural capacity of concrete beams strengthened with the strand sheet.

A two-dimensional (2D) nonlinear numerical analysis code by using the rigid body spring method (RBSM) was developed by the writers at Hokkaido University to simulate the behavior of reinforced concrete (RC) members strengthened with fiber-reinforced polymer (FRP) sheets. The code supports the nonlinear constitutive laws for the different materials and nonlinear bond stress-slip relationships for steel-concrete and FRP sheet-concrete interfaces. This study uses the aforementioned code to examine the uniaxial tension behavior of RC members strengthened with carbon fiber sheets (CFS). Experimental results are compared with relevant numerical outputs to validate the model and confirm its ability to simulate the experimental observations. This study also assesses the influence of the amount of CFS strengthening on the tension-stiffening behavior of strengthened members. Finally, this research also suggests new analytical expressions for the average stress-strain relationships of concrete and steel in tension in the presence of stiffening contributions from internal steel reinforcement bars and externally bonded CFS reinforcement. DOI: 10.1061/(ASCE)CC.1943-5614.0000175. (C) 2011 American Society of Civil Engineers.

The purpose of the present study was to determine the change in tensile behavior of a meso-scalc mortar specimen immersed in a solution of NaCl. In particular, mortar specimcns were immersed in a NaCl solution for 2 months, and then three-point bending tests and chemical analyses were conducted to determine the influence of the cement hydrate (CH and CSH) concentration on the tension-softening behavior of the material. To this end, tension- softening curves were obtained from load-displacement curves via a back analysis. Wc found that tensile strength and fracture energy were reduced as the concentration of CH decreased. Furthermore, the tensile-softening model for the deteriorated mortar was proposed. ©2010 by Hokkaido University Press All rights reserved.

Concrete would be deteriorated by various factors in severe environment. Chemical erosion of concrete in acidity environment is one of important deterioration mechanism. It is not clarified, however, how chemical characteristic change affects mechanical characteristics. Meanwhile, a meso-scale approach in which both aggregate and mortar can be modeled is on the verge of becoming possible to apply to such durability problems. In this paper, the relationships between chemical characteristic change (amount of CH and CSH) and mechanical characteristic change are examined experimentally and then the mechanical behavior is simulated by Rigid Body Spring Method which is a typical meso-scale analysis. In particular, meso-scale constitutive laws are obtained from the bending tests of deteriorated mortar specimens after immersion test. Finally the applicability and availability of the analysis with the developed constitutive laws are discussed based on comparison with experimental. © 2010 Taylor & Francis Group, London.

When attaching continuous fiber sheets on concrete members on site, bonding defection of the continuous fiber sheets likely happens. FRP strips could solve the problem associated with the continuous fiber sheets, though they also have demerit due to less adhesion property caused by small adhesive area. To solve these problems, we have developed advanced FRP strand sheets which consist of bunch of individually hardened continuous fiber strands. The FRP strand sheets can be easily attached on the surface of concrete members with a single adhesive. Thus, the advanced strand sheets assure better construction quality and enable to cut down on application time and/or costs. Series of tensile, lap splice, and bonding tests were conducted in order to evaluate the material characteristics of CFRP strand sheets. Bending test of RC (Reinforced Concrete) beams was also conducted to evaluate strengthening effect of the CFRP strand sheets. In each test, specimens strengthened with CFRP strand sheets, with ordinal carbon fiber sheets or with CFRP strips were prepared. In the bending test, it was observed that both bending stiffness and capacity of RC beams were increased by strengthening with CFRP strand sheets. It was also observed that ultimate load, which was determined by delamination of strengthening material; of specimen strengthened with CFRP strand sheets was the greatest among all the specimens. Furthermore, the influence of concrete strength and depth of cover concrete on flexural strengthening effect of the FRP strand sheets were investigated.

Mesoscale constitutive models of frost-damaged concrete are developed in this study through numerical simulation using a two-dimensional rigid body spring model (RBSM). The aim of the simulation is to predict the macrobehavior of frost-damaged concrete subjected to mechanical loading. The models also clarify the difference in failure behavior of concrete with and without frost damage. Zero strength elements and the concept of mesoscale plastic tensile strain are introduced into the normal RBSM springs to consider the experimentally observed cracking and plastic deformation caused by frost damage. The difference in the effect of frost damage on compression and tension behavior as found in the experiments is clearly predicted. Finally, analysis of a notched beam subjected to bending after different degrees of frost damage is carried out. The resulting load-deflection curves agree well with those obtained in the experiments. These good correlations confirm the applicability of the mesoscale model for predicting the macrobehavior of frost-damaged concrete. © ASCE 2009.

Analytical system for mortar failure under time-dependent loading was extended to high strain rate range by improving the time-dependent constitutive model of Rigid Body Spring Model. Using the model, experimental results of mortar specimens subjected to high strain rate loading and fatigue loadings were well simulated. Furthermore, damage accumulation of mortar under fatigue loading was explained in terms of the degradation in residual strength. It was confirmed analytically that damage accumulation of mortar is not proportional to number of loading cycles but suddenly increase near the failure point.© 2009 Taylor & Francis Group.

Mesoscopic analyses of mortar failure under high-stress creep and low-cycle fatigue loading are presented using a newly developed time-dependent constitutive model for Rigid Body Spring Model, which is a discrete analysis method. The failure process over time was successfully expressed by adopting a four-component combined mechanical model as the time-dependent model of connected springs, and by developing a new method for determining the failure state for load-controlled analysis. The numerical model provides reasonable results not only for the stress-strain characteristics under cyclic loading but also for the inapplicability of Miner's law under varying stress levels. The mechanism of the time-dependent failure of mortar was clarified by investigating the local stress-strain behaviors. © 2008 Japan Concrete Institute.

This study attempted to develop a model for the stress-strain relationship in compression of frost-damaged concrete subjected to fatigue loading. Concrete specimens were prepared and exposed to freeze-thaw cycles followed by application of static and fatigue loading. The strains induced during the freeze-thaw test were carefully measured as well as during a mechanical loading test. It was found that the static strength and the fatigue life of concrete decreases as increasing irreversible tensile strain was induced by frost action. A stress-strain model for frost-damaged concrete under application of static and fatigue loading based on the degradation of initial stiffness caused by frost damage was presented. The degradation of initial stiffness for damaged concrete was empirically formulated as a function of remaining expansion caused by freeze-thaw cycles. The plastic strain under the application of mechanical static and fatigue loading for frost-damaged concrete is higher than that for original concrete. Therefore, plastic strain for damaged concrete was formulated as not only the function of strain level under mechanical loading, but also the function of irreversible strain caused by frost action. The unloading and reloading stiffness factors were introduced to explain the change of stiffness as increasing the number of loading cycles by considering the effect of the degree of frost damage. © 2008 ASCE.

As is well known, in the current design code, the shear strength of beams can be calculated based on the modified truss theory, which cannot take into account the effects of the top flange area of T-beams. Reported experimental data show that the top flange has an effect on the shear capacity of T-beams with shear reinforcement. To predict the shear capacity of T-beams more precisely, the effect of the concrete top flange area on the shear resisting mechanism must be clarified. Comparison of test results for rectangular and T-beams yielded insights into the shear resisting mechanism of T-beams. Verification and clarification of the shear resisting mechanism of T-beams were performed based on the 3D nonlinear finite element code (CAMUI). Finally, a simplified method for determining the failure criteria for shear of RC T-beams is proposed. Copyright © 2007 Japan Concrete Institute.

High Performance Fiber Reinforced Concrete (HPFRC), which has a high compressive strength of about 130 N/mm2 and a high tensile ductility by the addition of short steel fibers, was used in this study. Axial tensile tests on reinforced HPFRC members were conducted in order to investigate the influence of fibers on tension stiffening. Therefore the fiber content and the dimensions of the fibers (aspect ratio) were varied in the HPFRC mixture . The average concrete stresses, which were derived from the test results after correction for the initial shrinkage strain, showed that an increase e of the fiber content and a larger aspect ratio lead to a higher tension stiffening. Moreover, a simplified equation to determine the tension stiffening in HPFRC was proposed on the basis of the axial tensile test results.

Based on a series of experimental tests on notched concrete beams externally bonded with unidirectional fiber-reinforced polymer (FRP) sheets, this paper investigates the bond characteristics of FRP sheet-concrete interfaces under dowel load, which acts vertically on the FRP sheet and leads to a mix-mode interface peeling. The peeling properties of FRP sheet-concrete interfaces under the dowel load are evaluated in terms of their interface dowel load-carrying capacity, critical interface peeling angle, and interface peeling fracture energy. Experimental parameters include strength of concrete substrate, tension stiffness of FRP sheets, properties of bonding adhesives, concrete surface treatment methods, and length of precrack set between the FRP sheet and concrete substrate. Analytical models clarifying the relationships among the interface dowel load-carrying capacity, the interface peeling angle, and the interface peeling fracture energy are built up and also verified by test results. Further, this paper shows how to use the interface peeling fracture energy calibrated from the present dowel tests for the practical design of spalling prevention, which is now becoming a popular application of FRP sheets for the maintenance and repair of existing concrete structures in Japan. © 2007 ASCE.

FEM in combination with an appropriate material model may serve as a suitable tool to analyze the structural performance of UHPFRC. Some reported constitutive models considering the effect of steel fibers are installed into the 3D FE program. The comparisons between the numerical and the experimental results are performed to confirm the applicability of the proposed models from the view point of structural performance. Moreover, a sensibility analysis is conducted to evaluate the effect of the material parameters on shear behavior of beams with UHPFRC. A new concept for a combination of the constitutive models in FEM is introduced in the present study. In the analysis, the constitutive laws are varied for different fiber directions in a numerical specimen following the phenomenal fact that orientation number differs for different considering directions in 3D space. Finally, the advantage of simulation by the proposed technique compared with current FE methods and test results are demonstrated on the structural level. © 2006 Taylor & Francis Group.

The pullout test is a conventional test method for calibrating interfacial shear bond characteristics of Fiber Reinforced Polymer (FRP)-concrete interfaces. However, due to the small bending stiffness of FRP sheets/strips and the highly non-linear interface fracturing mechanism, a well-recognized analytical approach to the accurate interpretation of the pullout test results remains to be achieved despite extensive studies particularly when the aim is to calibrate a local bond stress-slip model, which is necessary for developing bond strength and anchorage length models avoiding the use of empirical formulations. This paper introduces a newly developed non-linear bond stress-slip model for analyzing full-range strain distributions in FRP and shear bond stress distributions in the interface bond layer during pullout tests, along with a new anchorage length model and bond strength model that were developed accordingly. Compared with other existing bond models, the bond model described here has two advantages besides its simplicity: (1) it incorporates the most important interface parameter, the so-called interfacial fracture energy, in all analytical processes and links it successfully with all other important bond parameters; (2) it is a general and unified approach that allows for the first time consideration of the effects of the adhesive bond layer in non-linear analysis of FRP-concrete interfaces. Further, a unified bond stress versus slip expression is formulated to show the differences in local bond stress-slip relationships at the loaded and free ends in pullout tests, so that the effects of the bond length used in a pullout test on the calibration of the interfacial bond stress-slip model can be clarified. The reliability of all proposed models is verified through a comprehensive comparison of the experimental and analytical results. Copyright © 2006 Japan Concrete Institute.

Both short and long-term performances of repaired or strengthened concrete structures using external FRP bonding are greatly affected by states of bonding substrates, which are covercrete and may have experienced various damages. One of them is frost damage in cold regions. This paper intends to investigate how the initial frost damages in concrete influence the static and fatigue bond performances of CFRP/concrete interfaces. Concrete specimens were exposed to freeze and thaw cycles before being bonded with CFRP sheets. The initial frost damage of concrete was controlled approximately at three different levels in terms of its relative dynamic modulus of elasticity, which was 100% (non frost damage), 85% and 70%, respectively. Test results showed that failure modes of CFRP/concrete bonded joints with initial frost damage in concrete were the delamination of covercrete. By contrast the joints without initial frost damage failed in a thin concrete layer as usual. Moreover, CFRP/concrete joints with and without initial frost damage showed different manners in their interface bonding strength and stiffness. If the initial frost damage existed in concrete substrate the effective bond length of CFRP/concrete joints was increased due to the decrease of the bonding stiffness and interfacial fracture energy. Fatigue testing results indicated that the linear slopes of S-N curves of CFRP/concrete bonded joints were not influenced by the initial frost damage. The initial frost damage did not shorten the fatigue life of CFRP/concrete joints if a same relative tensile stress level was kept in the FRP sheets, where the relative tensile stress level was defined as a ratio of the applied tensile force in FRP sheets for the fatigue tests to the maximum static pullout one achieved in each test series.

A new analytical method for defining the nonlinear bond stress-slip models of fiber reinforced plastics (FRP) sheet-concrete interfaces through pullout bond test is proposed. With this method, it is not necessary to attach many strain gauges on the FRP sheets for obtaining the strain distributions in FRP as well as the local bond stresses and slips. Instead, the local interfacial bond stress-slip models can be simply derived from the relationships between the pullout forces and loaded end slips. Based on a series of pullout tests, the bond stress-slip models of FRP sheet-concrete interfaces, in which different FRP stiffness, FRP materials (carbon FRP, aramid FRP, and glass FRP), and adhesives are used, have been derived. Only two parameters, the interfacial fracture energy and interfacial ductility index, which can take into account the effects of all interfacial components, are necessary in these models. Comparisons between analytical results and experimental ones show good accordance, indicating the reliability of the proposed method and the proposed bond stress-slip models.

Concrete is a heterogeneous material consisting of mortar and aggregate at the meso scale. Evaluation of the fracture process at this scale is useful to clarify the material characteristic of concrete. The authors have conducted meso scale analysis of concrete over a past few years by Rigid Body Spring Model (RBSM). In this study, three-dimensional analyses of mortar and concrete are carried out, which is necessary for the quantitative evaluation of concrete behavior especially in compression. Constitutive models at the meso scale are developed for the 3D RBSM analysis. Failure behaviors and strengths in compression and tension of mortar and concrete are predicted well by the analysis. In biaxial compression test of concrete, crack in normal direction to plane of specimen is simulated that cannot be presented by two-dimensional analysis. Copyright © 2005 Japan Concrete Institute.

In this study, a model for the interface between a concrete slab and a steel plate in composite slabs with studs is developed through a bending test for composite beams. A smeared reinforcing stud model is also implemented to consider the shear-reinforcing effect of taller studs. 3D nonlinear finite element analysis using the model for the interface and the reinforcing stud model developed in this study is found to predict punching shear behavior of composite slabs. Copyright © 2005 Japan Concrete Institute.

The mechanism of diagonal tensile failure of RC beams without shear reinforcement, which is difficult to solve by means of experimental and analytical study, is investigated. The close relationship between the fracture modes and the transfer stress at shear cracks is clarified, and the experimental results are verified by the finite element method taking into consideration the influence of a splitting tensile crack and dowel action. In RC members without shear reinforcement, the width of a shear crack increases owing to the occurrence of a splitting tensile crack along the main bars. As a result, the transfer stress of a shear crack cannot be generated and the shear crack grows and propagates rapidly. This paper also puts forth that FE analysis, in which not only shear crack but also splitting tensile crack are modeled discretely, can predict the size effect on diagonal tensile failure strength of RC beams without shear reinforcement.

Concrete is a heterogeneous material consisting of mortar and aggregate at the meso level. Evaluation of the fracture process at this level is useful to clarify the material characteristic of concrete. However, the analytical approach at this level has not yet been sufficiently investigated. In this study, two-dimensional analyses of mortar and concrete are carried out using the Rigid Body Spring Model (RBSM). For the simulation of concrete, constitutive model at the meso scale are developed. Analysis simulates well the failure behavior and the compressive and tensile strength relationship of mortar and concrete under uniaxial and biaxial stress conditions. Localized compressive failure of concrete is also simulated qualitatively.

This study investigates the dependence of the mechanical behavior of concrete, such as strength, stiffness, and deformation capacity on the damage caused by freezing and thawing cycles (FTC). A stress-strain model for concrete damaged by freezing and thawing prior to the application of mechanical loading was proposed based on plasticity and fracture of concrete elements. The FTC fracture parameter was introduced to explain the degradation in initial stiffness of concrete resulting from freezing and thawing damage. Based on experimental data, the FTC fracture parameter was empirically formulated as a function of plastic tensile strain caused by freezing and thawing with the assumption that the plastic strain was caused by the combined effects of FTC and mechanical loading damage. The stress-strain relationships obtained by the proposed model were compared with the experimental data.

The Mode II interlaminar fracture tests of hybrid composites with non-woven carbon tissue (NWCT) were carried out using the end-notched-flexure (ENF) specimen. The hybrid composites were made by interleaving NWCT prepreg between CFRP layers. CFRP specimen [0₂₄] as well as hybird specimen [0₁₂/T/0₁₂] were prepared to compare the Model II interlaminar fracture tough-ness. Here, the symbol "/T/" means that NWCT prepreg is located at a 0/0 mid-plane of the hybrid specimen. Three kinds of interlaminar cracks which have different positions in the NWCT layer were introduced to the hybrid specimen. It was found that the NWCT layer has the short fiber bridging effect due to in-plane random short carbon fibers and increases the interlaminar fracture toughness of laminated composites. The fracture surfaces and side-sections of the hybird specimens were observed with an optical microscope and a scanning elelctron microscope, and the failure mechanism was discussed.

This paper presents experimental results on the behavior in tension of reinforced concrete members strengthened with carbon fiber sheets (CFS). CFS reduced the crack spacing and brought about good crack width control as well as a significant change in the average bond stress and the average stress of steel reinforcing bars and concrete. The deterioration mechanism of the CFS bond properties near cracks was presented.

Continuous fiber such as carbon fiber, aramid fiber and glass fiber, have been accepted as a substitute for conventional steel reinforcement because of its good characteristics: high strength, lightness, anti-corrosiveness, anti-magnetism and flexibility. At the same time continuous fibers also show some major drawbacks when compared with steel. This article introduces new directions for continuous fiber to overcome its drawbacks and to utilize its unused advantage. The new directions necessitate the development of new materials.

Modeling of compression softening is essential to predict the ultimate behavior of RC members. In this study, constitutive laws of concrete under compression-tension state are extended according to the concept of the fracture energy and the influence of compression softening on ultimate behavior of RC members failing in shear compression mode was examined. It was found that the ultimate strength and deformation strongly depended on compression softening, namely compression fracture energy. It was also found that the analytical results agreed well with experimental ones, when compression fracture energy of 40 N/mm was used for normal concrete with compressive strength of 20 MPa.

The uniaxial tensile tests of Reinforced Concrete elements with Carbon fiber sheet (RCC) are conducted to clarify the basic mechanical characteristics which affect the tension stiffness of RCC. This paper mainly presents the difference between RCC and ordinary Reinforced Concrete member (RC) in the load carrying capacity, the average crack spacing, stress and/or strain distributions of steel, and the average stress - strain relationship of concrete. Crack spacing of RCC becomes smaller between 25% and 60% of that in RC as the amount of Carbon Fiber Sheet (CFS) increases. The strain distributions of steel in RCC before and after the yielding of steel differ from those in RC. The tension stiffness developed by the bond action of CFS increases as the amount of CFS increases but that of steel becomes less. With the steel and CFS contributions combined, the tension stiffness of concrete as a whole generally becomes greater than that in RC. There is, however, a case in which tension stiffness of concrete in RCC decreases more than that in RC, because the average bond stress of steel rapidly decreases after the yielding of steel.

An experimental study on bond strength of Continuous Fiber Sheet (CFS) was conducted. Based on the experimental results the bond strength and various factors are clarified. Bond strength does not increase with bond length for bond length longer than 100 mm. As CFS stiffness increases, the maximum local and average bond stresses at delamination increase and CFS strain gradient decreases. CFS with a narrower width has a bond strength greater than that with a wider width. Non-uniform loading decreases the bond strength, however anchor steel plate with tensioned bolt increases it due to the bond between steel plate and CFS and confmement from the bolt. From the observed bond stress in CFS, the equation to predict the maximum local bond stress was proposed.

The simple-supported concrete beams reinforced with aramid FRP (AFRP) rods and carbon FRP (CFRP) sheets were tested to failure using a symmetric two-point concentrated static loading system. AFRP rods were used instead of steel reinforcing bars, and CFRP sheets were epoxy bonded to the tension face of the concrete beams to enhance their flexural strength. Moreover, a 5-cm wide strip of CFRP sheet in some places were wrapped around the web (hereafter, called "U· jacket") after the CFRP sheets were bonded. The strain distributions on AFRP rods and CFRP sheets, and flexural behavior of the beams with AFRP rods and CFRP sheets were examined experimentally. The results showed that; 1) peeling of CFRP sheets occurred near the maximum flexural moment region, 2) ultimate load and deflection of the beam with U-jackets were higher, and 3) the U-jacket was a significant factor affecting the ductile behavior of beams with CFRP sheets.

The authors have developed a continuous fiber flexible reinforcement (CFFR) which has good workability and can be used as a reinforcement in concrete. It consists of a plastic tube containing continuous fiber bundles and resin. The salient feature of this new material is that it can be easily formed at the construction site. The authors have conducted a study of fabrication methods of the material and an evaluation of its mechanical properties. This paper introduces the material and fabrication methods, and details the tensile strength of a member formed from this material. A member bent into a U shape was subjected to a load test to examine its basic properties. As a result, it was found that even when the material was bent, the applied tensile load was transmitted through it. Also, the load-deflection characteristic of the material and the stress concentration due to bending were influenced by the wall thickness of the plastic tube.

This study shows how reducing the thickness of the tube enclosing continuous fiber flexible reinforcement (CFFR) and providing mechanical anchorage at the end of CFFR improve the shear capacity of a beam specimen. It is also clarified in this study that from tensile tests on U shaped specimen of CFFR the shear capacity in a concrete beam reinforced with CFFR is greatly influenced by the deformational characteristics of CFFR, i.e., a slippage at bent portion of fibers and deformation of tube covering the fibers.

The aim of this study is to clarify the strength and the deformational ability of recycled concrete. It was clarified that the deformational behavior of recycled concrete filled steel tube (RCFT) was similar to that of normal concrete filled steel tube (CFT). It was shown that the stiffness of RCFT could be predicted approximately with consideration of the Young's modulus of recycled concrete which were lower than that of normal concrete. It was also shown that of the dilatancy in the elasto-plastic range, which is related to the Poisson's ratio, is important to predict the strength.

Simple-supported concrete beams reinforced with aramid FRP (AFRP) rods and carbon FRP (CFRP) sheets were tested up to failure under a symmetric two-point load application. AFRP rods were used instead of steel reinforcing bars, and CFRP sheets were bonded on the tension face. Moreover, in one specimen, three 5-cm wide strips of CFRP sheeting were wrapped around the web (U-jacket) after the CFRP sheets were bonded. The results showed that; 1) both the ultimate load and deflection of the beam with U-jackets were highly improved, and 2) the calculated deflection and strain correlated well with the measured values before the peeling failure.

The property of recycled concrete column encased by steel tube subjected to axial compression was studied. It was found that the column, where progress of fracture is faster than the normal concrete, has enough capacity to be utilized though its rigidity and ultimate strength are smaller than those of the normal concrete.

In this study, the shear resisting behavior of reinforced concrete (RC) beams with carbon fiber sheet (CFS) was examined experimentally. Shear strength of RC beams with CFS attached to the sides is defined as the summation of the shear force carried by concrete and the shear forces carried by stirrup and CFS in shear cracking zone. The concept for calculation of the shear forces carried by stirrup and CFS is also discussed.

In this study splitting crack of cover concrete due to corrosion of reinforcing bar and the critical volume increment of the reinforcing bar which causes full penetration of the splitting crack to the concrete surface are analyzed by a nonlinear finite element method. As a result, relationships between the dimension of the surrounding concrete, which is the concrete cover and the bar spacing, and the characteristics of the splitting crack, which is its direction and the critical volume increment are clarified.

Based on the finite element analyses, the equation for shear strength of deep beams without shear reinforcement is modified to predict the shear strength of deep beams with horizontal and vertical shear reinforcement. It is confirmed that the modified equation can estimate the experimental results.

Experiment on Fiber Reinforced Plastic (FRP) rods as shear reinforcement with the intersection of a shear crack in a beam is carried out in order to clarify the failure criterion of the FRP rod at the bent portion. The finite element analysis in which anisotropy of the FRP rod and bond slip between concrete and the FRP rod are considered, is also conducted. Strain and bond stress distributions of the FRP rod with bent portions are investigated in detail.

Non-linear finite element analysis is conducted in order to clarify the shear resisting behavior of prestressed concrete beams reinforced with FRP rods. Prestressing force, stiffness of tendon and web reinforcement are chosen as parameters. It is discussed how prestressing force and mechanical properties of reinforcement influence the shear strength as well as the shear force components in the shear resisting behavior.

モルタルのメゾレベルの試験体を用いてイオン交換水，NaCl溶液，硫酸溶液による浸漬実験を行った。浸漬後，力学試験および物理化学的性質を同定することで，Ca溶脱および硫酸による劣化が生じた試験体の力学的性質の変化を評価した。具体的には，浸漬後の試験体を用いて曲げ試験を行うとともに，得られた荷重変位曲線から逆解析を行うことで力学的性質を同定した。加えて，同一試験体を用いて化学的劣化により変化する物理化学的性質を測定した。さらに，既往の曲げ強度の推定式を基に，化学的劣化に伴って変化する各力学的性質の関連性を評価した。

In this study, meso-scale thin mortar specimens were immersed in a sulfuric acid solution for 60 days and then subjected to three-point bending tests and shear tests to clarify the mechanical behaviors of mortar in containing cement hydrates transubstantiated under sulfate attack. In particular, tensile behaviors, namely elastic modulus, tensile strength and fracture energy, and shear strength, were determined from the load-displacement curves using back analysis and shear tests, respectively. Following the mechanical tests, chemical analyses were also carried out to clarify how the amount of hydrates, which were quantities of CH and C-S-H, the existence of precipitates, porosity and pore volume distribution affect mechanical characteristics. As a result, it was found that the relationships between physico-chemical properties and elastic modulus and tensile strength differ from the relationships between physico-chemical properties and fracture energy and shear strength. Furthermore, the applicability of the proposed model based on the relationships between porosity and strength was verified through comparison of the calculated and experimental results.

The purpose of this study is to develop the analytical method which can evaluate the change in physico-chemical property of mortar immersed in sulfuric acid solution. In this analytical approach, influences of sulfate acid attack were considered by diffusivity change of sulfate ions and physical change caused by chemical reaction of cement hydrate with sulfate ions. In the analysis, deposition condition of ettringite and gypsum was given by pH value and porosity which were calculated by the change in cement hydrate based on the experimental results. Finally, the validity of the analysis was discussed through parametric analyses in which the porosity value was varied.

In this study, thin mortar specimens were immersed in either ion exchanged water or NaCl solution for 360 days for the purpose of evaluating the relationships between changes in mechanical characteristics and physico-chemical properties caused by Ca leaching. Following the immersion test, bending and shear tests were carried out to determine the elastic modulus, flexural strength, tensile strength, fracture energy, tensile softening curve and shear strength. Furthermore, physico-chemical properties such as calcium hydroxide and porosity were also determined by chemical analysis. Based on these results, the relationships between the mechanical characteristics and physico-chemical properties were evaluated. Bending strength, tensile strength, fracture energy and shear strength were found to be strongly related to the amount of cement hydrate and porosity, both for the ion exchanged water immersed and the NaCl solution immersed specimens.

This paper presents some of the results achieved by Technical Committee on Systematization to Evaluate Structure and Durability Performance in Corroded RC Structure, which works to establish the use of numerical structural analysis as an evaluation method that allows numerical representation in space and time of durability of concrete structures with chloride induced damage（hereinafter, structural performance over time）, and an index of structural performance over time allowing the evaluation of total structural systems. This paper covers in particular methods to evaluate the spatial variability of the amount of corrosion that affects structural performance using probabilistic and statistical techniques, and constitutive models related to reinforcement corrosion and the bond between concrete and corroded reinforcement, which are essential for the finite element analysis of corroded concrete structures. Further, an index of structural performance over time is proposed and formulated, and trial calculation results for total structural systems are introduced.

This document outlines the revisions made to the “Design” volume of the Standard Specifications for Concrete Structures 2012. The aim of these revisions was to raise the level of performance assessment and verification methods, building on the basic organization of the 2007 version and drawing from advances in technology in the past few years. Specifically, various technical items, including chloride attack and steel corrosion, volume change of concrete (drying shrinkage, autogenous shrinkage, temperature change), prediction of cracking, shear strength formula, long-term deformation of structures, nonlinear analysis, restorability of structures and repairability of members, have been revised and mutual consistency has been enhanced.

The cement paste adhering to recycled aggregate increases the unit weight of water and reduces the confinement effect of aggregate. Therefore, the authors presented a method to estimate the increase in unit weight of water and the reduction of the confinement effect of aggregate by means of regression analyses using data in references. Next, a formula to predict dry shrinkage for concrete made with recycled coarse aggregate, based on the JSCE prediction formula for normal concrete, was developed by taking into account the increase in unit weight of water and the reduction of the confinement effect of aggregate. Since the proposed method does not require any tests to estimate the characteristics of the cement paste adhering to recycled aggregate, it allows easy calculation of shrinkage strain. As a result of verification using prior experimental results, it was concluded that the predicted value of dry shrinkage of recycled concrete has sufficient precision comparable to that of the prediction of dry shrinkage of normal concrete using the JSCE prediction formula.

This document outlines the revisions made to the "Design" volume of the Standard Specifications for Concrete Structures 2012. The aim of these revisions was to raise the level of performance assessment and verification methods, building on the basic organization of the 2007 version and drawing from advances in technology in the past few years. Specifically, various technical items, including chloride attack and steel corrosion, volume change of concrete (drying shrinkage, autogenous shrinkage, temperature change), prediction of cracking, shear strength formula, long-term deformation of structures, nonlinear analysis, restorability of structures and repairability of members, have been revised and mutual consistency has been enhanced.

Application example of recycled aggregate concrete is extremely few even though many studies on quality of recycled aggregates for the structural concrete have been conducted so far. Based on several experimental investigations, therefore, we have attempted an application of low quality recycled coarse aggregates, which are made from demolished concrete of an old hydroelectric power plant, to renovation work of the power plant. In this paper, both the characteristics of the recycled aggregate concrete and cost performance of this project are reported.

Frost damage, which is the deterioration due to freeze and thaw of pore solution is causes scaling, pop-out and cracks on surface of concrete members, is an important issue in the durability of concrete structures in cold regions. Deicing agents are sprayed in order to prevent frost damage. By contrast, it has been reported that chlorides of deicing agents accelerate the deterioration due to frost damage under freeze-thaw environment. It is generally known that phase changes of hydration products, such as formation of friedel's salt and ettringite, occur due to penetration of chloride ion. Ettringite formation leads volume expansion and cracks. Since the acceleration of frost damage due to chlorides penetration, the use of deicing agents which is not containing chloride ions, such as potassium acetate and calcium-magnesium acetate, has been proposing. However, it has not been shown that chemical alteration due to penetration of deicing agents influence on increase of strain and decrease of structural characteristic value with frost damage under freeze-thaw environment. Therefore, this study aimed to investigate the influence of deicing agents under freeze-thaw environment on 1）progress of frost damage, 2）phase changes of hydration products and 3）decrease of structural characteristic value. As the results, 1）penetration of deicing agents containing chloride ions influenced on the strain hysteresis and resulted in the increase of residual strain and water absorbing ratio, 2）ettringite formation with displacement and dissolution of monosulfate hydrates was a contributory factor for frost damage acceleration and 3）chemical alteration and increase of residual strain due to penetration of chlorides led decrease of tensile strength, elastic modulus and fractural energy.

This Paper presents experimental and numerical results on axial tensile tests of prism members with HPFRM (High Performance Fiber Reinforced Mortar) and conventional reinforcing bar. With increasing fiber content in the HPFRM, the tension stiffening effect was improved as well as cracks being distributed with finer crack width. In addition the orientation of the fibers affected both the tension stiffening and the crack distribution. To evaluate these structural behaviors the analytical simulation using 2D Rigid Body Spring Model was applied with some improvements on the material constitutive law for unique characteristics on the HPFRM.

Time-dependent constitutive law of Rigid-Body Spring Model (RBSM) was developed by separating mortar deformation into four components based on material information from micro to meso scale. In addition, the analysis could track residual strength up to the failure under creep and fatigue loading by installing a new method for determining failure state for load-controlled analysis. The analytical model could simulate mortar behavior under monotonic, creep and fatigue loading in terms of change in strength, stress-strain-time and S-N relationship. Furthermore, fracture mechanism of mortar under creep and fatigue loading was numerically explained. That is, failure happens when the material strength becomes less than the applied stress as a result of crack propagation with stress release-redistribution due to relaxation or unloading-reloading.

This paper represents a tension stiffening effect on a High Performance Fiber Reinforced Mortar (HPFRM), which has a compressive strength of 130 N/mm2 and high tensile ductility by the addition of short steel fibers. Uni-axial tensile tests on the reinforced HPFRM with various fiber content and fiber orientation were conducted. On basis of the experimental results and the analytical simulations using Rigid Body Spring Model (RBSM), a simplified equation to determine the tension stiffening effect on the HPFRM was proposed. The accuracy of the model was verified through simulations with non-liner FEM analyses on reinforced HPFRM members.

In this study, cement paste and mortar specimens were immersed in NaCl solution for 2 months. After that three points bending test of the specimens and chemical analyses were conducted so as to determine tension softening curves, which can be applicable to meso-scale analysis, from load-displacement curves using a back analysis and to clarify how amount of cement hydrates affects the tension softening behavior. It was found, as a result, that tensile strength, Young's modulus and fracture energy of mortar specimens become smaller as the amount of cement hydrate CH decreases. Furthermore tension softening model which can consider the change in amount of cement hydrates was proposed.

本研究委員会は,非線形有限要素解析法の信頼性の向上と利用の拡大を目的に調査・研究活動を行った。具体的には,非線形有限要素法の基礎・基本を手引書の形で整理した上で,その手引書に基づく実解析を通じ,解析上の留意点を分かりやすくまとめた。さらには,非線形有限要素法を活用した検討が,実構造物の施工性の改善や安全性の向上に大きく貢献できる事例を提示した。

100N/mm^2以上の圧縮強度を有し,鋼繊維を混入した高強度繊維補強モルタルを適用した鉄筋コンクリート部材の変形性能および耐荷性能を把握するため,薄肉の試験体による曲げ載荷試験を実施した。実験のパラメータとして,鉄筋量および鋼繊維の混入率,種類,配向性を変えることで,それらが部材の曲げ靭性やひび割れ性状に与える影響を定量的に把握した。さらに,直接引張試験より得られた引張応力下の力学モデルを適用した非線形EEM解析による検証解析により,鉄筋を有する高強度繊維補強モルタル部材の耐荷挙動のシミュレーションを可能とした。

著者が提案している剛体バネモデルの時間依存構成モデルを改良し,モルタルの時間依存破壊シミュレーションを高ひずみ速度域に拡張した。これにより,ひずみ速度の増加がモルタルの強度増進に与える影響,さらには,実際の疲労載荷速度下におけるモルタルの破壊過程が再現可能となり,実験結果を良好に表すことができた。また,残存強度変化を調べることで,疲労荷重下におけるモルタルの累積損傷度の評価を行った。モルタルの累積損傷は載荷回数に対して線形ではなく,ある時点を境に急激に増加することを確認した。

炭素繊維プレートにより曲げ補強された鉄筋コンクリートはりの破壊性状と耐力に関する実験的研究を行った。実験変数は,接着枚数(1枚,2枚,3枚),接着の仕方(積層と並列),接着長を変えることによる端部でのプレート剛性の低減の有無である。プレートを積層接着すると付着応力が増加し,はく離破壊が早期に発生すること,プレートを2もしくは3枚並列に接着すると,積層する場合よりも耐力が増加するものの,プレートを1枚だけ接着した場合の耐力を下回る可能性があることを明らかにした。また,はく離破壊を支配する端部の付着強度は,剛性が大きいほど増加するが,上限値が存在する可能性を示した。

連続繊維シート接着工法の施工性の改善やFRPプレート接着工法の補強性能の改善を日的として連続繊維ストランド1本ずつに樹脂を含浸・硬化させたFRPストランドシートを新たに開発した。このFRPストランドシートの引張試験,継手試験,付着強度試験を行ない材料特性を評価した。さらにFRPストランドシートで補強したRCはりの曲げ載荷試験を行いその補強効果について検討した。FRPストランドシートを接着することでRCはりの曲げ剛性および曲げ耐力は増加し,同種の連続繊維を用いた連続繊維シートに比べ剥離荷重が高くなった。FRPストランドシートの引張剛性の違いによって,破壊モードに違いが見られた。

本研究では,疲労荷重がコンクリートの耐凍害性に与える影響について検討するために,疲労荷重と凍結融解作用の組合せ方を変化させた実験を行った。すなわち,初期状態を軽微な乾燥状態としたコンクリートを対象とした,疲労と凍結融解を交互に作用させた複合劣化試験を行い,それら作用の順序や回数がコンクリートの相対動弾性係数と静弾性係数の推移及び残存強度に及ぼす影響を検討した

本研究は,コンクリート構造物の上面近傍に透水性の大きい層が存在することに着目し,上面近傍の透水性の差異が中性化の進行に及ぼす影響を明らかにすることを目的とする。まず,円柱試験体の上面近傍の透水係数を測定した。次に,材料内の熱水分移動と化学物質移動を考慮した中性化反応モデルを提案した。この解析モデルを用い,測定した透水係数の差異が,酸性雨に曝される条件下の中性化の進行に及ぼす影響を検討した。

本研究において,剛体バネモデル解析法を用いた,モルタルの凍結融解時の変形挙動の解析方法を開発した。その手法は,固相,液相,気相の3相を考えた熱水分同時移動方程式に基づきモルタル内の温度,水分量,氷の量(含氷率)を求め,得られた温度と氷の膨張によるひずみを初期ひずみとして剛体バネモデル解析法に引き渡し,モルタルの凍結及び融解時の変形挙動を求めるものである。

離散解析手法のひとつである剛体バネモデルの時間依存型構成則を構築し,持続および繰り返し荷重を受けるモルタルの破壊解析を行った。連結バネの時間依存モデルには,4成分系力学モデルを採用し,かつ,荷重制御解析における新しい破壊判定方法を用いることにより,破壊までの載荷時間及び終局ひずみの評価が可能となった。解析では,時間の経過に伴う変形挙動を表現することに成功した。また,連結バネの応力-ひずみ挙動を調べ,モルタルの時間依存破壊メカニズムに対する検証を行った。

現在,多種の高性能繊維補強セメント系複合材の開発が国内外で進められている中,材料単体の引張性能の実験的評価は多くなされているものの,鉄筋コンクリート部材としての引張性能の把握は十分になされていない。本論文では,鉄筋補強された高強度繊維補強モルタル部材の一軸引張試験結果より,銅繊維の混入量が多いほど,鋼繊維のアスペクト比が高いほど部材の引張剛性や耐荷力が向上することを確認した。さらに試験体製作時に違えた鋼繊維の配向性の差によってもこれら力学的特性に大きな差が生じることも示された。

RCはり下面に曲げ補強として2層のCFRPシートを貼付し(1層目のコンクリートに直接貼付されるシート長を変化させ,2層目のシート長は154mmで一定),さらに剥離防止のためのU字補強量を変化させたRCはりに静的二点対称荷重を作用させた載荷試験を行った。本研究では,1層目のCFRPのシート長を64cm,108cm,154cmと,シートの剥離制御を目的とし下面からウェブに渡るU字状の巻上げ補強(以下「U字補強」と呼ぶ)量を0,4,8,12,16本と変化させた。はりの最大荷重は,U字補強16本の場合,1層目シート長によらずほぼ同じ値を示した。また,U字補強量増加により終局変位が増加した。

再生細骨材を用いたコンクリートの強度低下の要因について,数値解析による検討結果を示した。また,数値解析に用いる主な構成則として再生細骨材を用いたモルタルの最大せん断応力および粗骨材と再生細骨材を用いたモルタルの界面の付着強度を実験により求めた。

鉄筋コンクリート梁下面に曲げ補強として貼付するCFRPシート幅の変化とシート層数との関係に着目し静的二点対称荷重を作用させた載荷試験を行った。本研究では,CFRPのシート幅(85mmと170mm)及び層数(1層～4層)と変化させ,さらにシートの剥離制御を目的とし下面からウェブに渡るU字状の巻上げ補強(以下U字補強と呼ぶ)を行った。はりの最大荷重は,シート幅85mmで4層貼付した場合とシート幅170mmで2層の場合とでは,ほぼ同じ値を示した。しかし,U字補強したシート幅85mm4層と幅170mm2層とではシート幅170mm2層の方が最大荷重は約17%の増加であった。

再生粗骨材を用いたコンクリートの凍結融解抵抗性を実験的に明らかにした。すなわち,原コンクリートがnon-AEコンクリートであっても再生コンクリートの平均吸水率を3%以下とすることで高い凍結融解抵抗性を確保できること,また,大きな収縮ひずみ(本実験では750μ以上)を経験した後の凍結融解抵抗性は著しく低下することを明らかにした。

本研究室で開発された3次元非線形有限要素プログラムを使用し,拘束筋として緊張されたPC鋼材を用いた角柱供試体の一軸圧縮試験を解析し十分な解析精度を得ることができた。そのプログラムを使用し補強筋比・緊張力量をパラメーターとした解析を行い,それらを変数とし終局耐力との関係を明らかにした。

せん断補強鉄筋の定着不良がRCはりのせん断抵抗機構に及ぼす影響を検討する目的で,せん断補強鉄筋の定着フック及び端部近傍の付着を除去したはりを製作し,せん断耐力の低下と破壊モードを実験的に検証した。せん断補強鉄筋によるせん断負担分がコンクリートの負担分と同程度に高く,トラス機構が顕著となるせん断スパン比に対しては,定着不良がトラス機構の保持を困難なものにする場合があることを確認した。さらに,せん断補強鉄筋の有効性は,鉄筋端部の付着劣化域を簡便に考慮した非線形ひび割れ解析で凡そ評価が可能であることを示した。

初期荷重をRCはりに作用させ,ある程度の損傷をRCはりに与え後にCFRPシートを下面に貼付し,再度静的曲げ載荷試験を行った。本研究では,CFRPのシート層数を変化させ(1層～3層),さらにシートの貼付方法としてはコンクリートとシートとの間に緩衝材を塗布した場合,さらにシートの剥離制御を目的とし下面からウェブ全高さに渡り5cm幅シートによりU字状に巻き上げたU字補強を行った場合について検討した。はりの最大耐力は,全てにおいて緩衝材を塗布し,さらにU字補強を行った場合が最大値を示した。また,シート層数の増加割合ほど耐力は増加しなかった。

The Mode II interlaminar fracture tests of hybrid composites with non-woven carbon tissue (NWCT) were carried out using the end-notched-flexure (ENF) specimen. The hybrid composites were made by interleaving NWCT prepreg between CFRP layers. CFRP specimen [0<SUB>24</SUB>] as well as hybird specimen [0<SUB>12</SUB>/T/0<SUB>12</SUB>] were prepared to compare the Model II interlaminar fracture tough-ness. Here, the symbol "/T/" means that NWCT prepreg is located at a 0/0 mid-plane of the hybrid specimen. Three kinds of interlaminar cracks which have different positions in the NWCT layer were introduced to the hybrid specimen. It was found that the NWCT layer has the short fiber bridging effect due to in-plane random short carbon fibers and increases the interlaminar fracture toughness of laminated composites. The fracture surfaces and side-sections of the hybird specimens were observed with an optical microscope and a scanning elelctron microscope, and the failure mechanism was discussed.

本研究では,再生粗骨材に付着するモルタルが再生コンクリートの力学特性に及ぼす影響を,付着モルタル及び界面の強度特性の差異を考慮できる剛体バネモデル(RBSM)により検討した。その結果,付着モルタルと原骨材間の界面強度(旧界面)及び付着モルタルの強度が大きければ圧縮強度は大きくなるが,モルタル付着率が小さく,旧界面と新モルタルと旧モルタルとの界面(新界面)との距離が狭いと,ばらつきが大きくなることが明らかとなった。

持続および繰返し荷重を受けるコンクリートの変形性状を明らかにするためにコンクリート平板の一軸圧縮試験を行った。各種荷重による変形性状の差異を比較する指標として,除荷時の弾性係数と残留ひずみを軸ひずみおよび軸直角ひずみとの関係に着目した。その結果,軸ひずみは作用荷重の影響を大きく受けること,コンクリートの損傷過程は,いずれの荷重に対しても,軸直角ひずみを指標として一義的に表せることを明らかにした。

初期荷重をRCはりに作用させ,ある程度の損傷をRCはりに与え後にCFRPシートを下面に貼付し,再度静的曲げ載荷試験を行った。本研究では,CFRPのシート層数を変化させ(1層～3層),さらにシートの貼付方法としてはコンクリートとシートとのに緩衝材を塗布しその有無による影響等について実験的に検討した。初期荷重による損傷をうけたはりの最大耐力は,初期荷重を受けなかったはりの最大耐力を上回ることはなかった。また,シート層数が3層で緩衝材を塗布した場合には初期荷重によるシートひずみへの影響は殆ど見られなかった。

This paper presents the experimental results on shear deformation of concrete beams with shear reinforcement, which was measured by laser speckle method. The results indicate that besides flexural deformation the significant amount of shear deformation occurred after shear cracking, which was caused by the localized shear deformation along shear cracks. Based on the experimental results, a rather simple mechanical model for prediction of the deformation is proposed. The model consists of a truss model that calculates the shear deformation and a modified Branson's model with the tension shift concept to calculate the flexural deformation. The model can predict the experimental results well.

本研究ではコンクリートを作製する際に用いた粗骨材として普通骨材,再生骨材,それらを混合したものを用いており(以降,それらを総称して使用骨材と呼ぶ),使用骨材の平均的な吸水率を変化させ,再生コンクリートの圧縮強度,凍結融解抵抗性,乾燥収縮特性を明らかにする目的で実験を行った.再生骨材は3種類用意しており,使用骨材の平均的な吸水率が等しくなるよう普通骨材と再生骨材の混合割合を調整した供試体も作製した.使用骨材の平均的な吸水率に着目した結果,平均吸水率がコンクリートの圧縮強度と凍結融解抵抗性に与える影響は見られなかったが,乾燥収縮ひずみの大きさに与える影響は顕著であった.

本研究では,過去に提案されている構成モデルを組み合わせた3次元非線形有限要素プログラムを開発し,鉄筋コンクリート棒部材の純ねじり解析を行い,本プログラムの検証とせん断流に着目した考察を行った。その結果,本プログラムによる解析結果は,概ね実験値に一致し,また,せん断流の幅は鉄筋比によって影響を受けないこと,中空断面鉄筋コンクリート棒部材において,せん断流路幅分の厚さがあればそのねじり耐力は中実断面の場合とほぼ同じに取り扱えることが解析的に確認された。

剥離抑制を目的として弾性係数が小さい緩衝材を用いた炭素繊維シート補強鉄筋コンクリートはりの静的及び疲労載荷試験を行った。静的試験結果より,接着端部から約300mmの区間における炭素繊維シートの平均付着応力の最大値は緩衝材を用いた方が大きく,その結果,剥離が抑制され耐力が増加すること,また,200万回の繰返し荷重を受けた後であっても,緩衝材を用いない場合と同等かそれ以上の残存耐力を有していることを明らかにした。

RCはりの下面に炭素繊維(CFRP)シートを貼付し曲げ試験を行った。実験供試体は全部で10体で,CFRPのシート層数をパラメータとし,シートの貼付方法としてコンクリートとシートとの間の緩衝材の有無とU字巻き上げ補強の有無について実験的に検討した。緩衝材を設けた供試体では,その最大荷重は緩衝材を設けなかった供試体に対し最大で46%増加した。また,供試体にU字巻き上げ補強を併用すことにより,終局変位の増加と若干の最大荷重の増加が確認できた。

本研究において、静的および繰返しの圧縮荷重を受けるコンクリートの破壊に至るまでの変形性状を実験的に明らかにした。すなわち、破壊に至るまでの軸ひずみと体積ひずみとの関係は、荷重条件によらずほぼ等しいこと、繰返し荷重下の弾性係数の変化は全ひずみのみによって表せ得ること、塑性ひずみは載荷時間の影響を大きく受けることを明らかにすると共に、クリープひずみを用いて繰返し荷重を受けるコンクリートの塑性ひずみの算定方法を提案した。

炭素繊維フレキシブル筋(以下CFFR)をせん断補強筋として用いたコンクリート橋脚模型の一方向繰返し載荷、正負交番繰返し載荷を行い,その変形特性について実験的に検討した。CFFRは、本実験のような大変形を起こす供試体においてその効果を十分に発揮し、補強部材の変形性能を大きく向上させ得ることが明らかとなった。また繊維のひずみは折り曲げ部を超えて生ずるが、その伝達率はひずみが増加するにつれ、既往のU字型引張試験で得られた値に収束する傾向があった。

鉄筋コンクリート(以下RCと略す)部材の終局挙動を数値解析によって予測,再現するためにはコンクリートのひずみ軟化特性のモデル化が不可欠である.本研究では,破壊エネルギーの概念に基づいた圧縮・引張場における圧縮軟化モデルを2軸圧縮場に拡張し,せん断圧縮破壊するRC部材の終局挙動に及ぼす影響について検討した.その結果,せん断圧縮破壊するRC部材の耐力および終局変形は圧縮軟化特性,つまり圧縮破壊エネルギーに大きく依存すると言え,圧縮強度20(MPa)のコンクリートを用いた場合,圧縮破壊エネルギーを40(N/mm)とすると耐力,終局変形,破壊モードおよび圧壊領域を概ね推定できることが確認できた.

本研究において、静的および繰返しの圧縮荷重を受けるコンクリートの破壊に至るまでの変形性状を実験的に明らかにした。すなわち、破壊に至るまでの軸ひずみと体積ひずみとの関係は、荷重条件によらずほぼ等しいこと、繰返し荷重下の弾性係数の変化は全ひずみのみによって表せ得ること、塑性ひずみは載荷時間の影響を大きく受けることを明らかにすると共に、クリープひずみを用いて繰返し荷重を受けるコンクリートの塑性ひずみの算定方法を提案した。

再生骨材を用いたコンクリートの耐凍害性に及ぼす水セメン比、置換率、および、粗骨材を繰り返し利用することによる影響について検討した.さらに凍結融解試験後の供試体を用いた曲げ試験および圧縮試験を行い、力学特性に及ぼす凍害の影響についても検討した、その結果、粗骨材吸水率が大きくても、水セメント比を小さくバージン骨材との併用率を大きくすることにより耐凍害性が改善されること、再生骨材、再々生および再々再生コンクリート間に大きな差異が認められないことを示した.

本研究において,上限応力および環境条件(水中と気中)を変えたコンクリートの圧縮疲労試験を行い,その基本的な変形特性を明らかにすることを試みた。破壊に至るまでに蓄積されるエネルギー量は,応力比(上限応力/圧縮強度)が大きいほど,また,気中よりも水中の方が小さくなること,塑性ひずみを疲労破壊直前の全ひずみで除した場合,蓄積エネルギーの増加に対する塑性ひずみの変化は,応力比のみの関数として表すことが可能であることなどを明らかにした。

コンクリートにエポキシ樹脂を用いて接着した炭素繊維シートの疲労荷重下における付着挙動に及ぼす炭素繊維シートの積層数と作用最大引張力の影響を実験的に明らかにした。また実験結果より、炭素繊維シートの付着応力-すべり関係の特徴を定性的に明らかにした。

相対する二辺が単純支持され、他の二辺が自由のRCスラブの下面に炭素繊維シートを貼付し,スラブ上面の中央及び自由縁に向かって荷重が偏心して作用した場合のスラブの破壊性状・たわみ性状・主鉄筋のひずみ性状・シートのひずみ性状・一部供試体においてはコンクリート表面のひずみ性状を実験的に検討した。実験に用いた供試体は全部で9体である。中央載荷の場合は押抜きせん断破壊であった。下面にシートを貼付することによりその最大荷重は,シート無し供試体の約1.3倍の値を示した。また,荷重が自由縁近傍に作用した場合,シートの補強効果は殆ど期待できない。

The aim of this study is to clarify the bond mechanism of Carbon Fiber Sheet (CFS) attached to concrete using epoxy resin and to propose the numerical methods which can simulate the bond behavior of CFS and its bond strength. A bond-slip-strain relation for CFS has been developed based on the bond characteristic which was clarified by means of experimental observation. A numerical method using the bon d-slip-strain relation can simulate the actual bond behavior. This paper also reports that a bond strength equation developed by the numerical analysis can predict the experimental results with good accuracy.

相対する二辺が単純支持され、他の二辺が自由のRCスラブの下面に炭素繊維シートを貼付し,スラブ上面の中央に静的集中荷重が作用した場合のスラブの破壊性状・たわみ性状・主鉄筋のひずみ性状・シートのひずみ性状について実験的に検討した。実験に用いた供試体は全部で6体である。その内1体は,シートを貼付しない供試体で基準供試体とした。他の5体の供試体の内訳は,下面全面にシートを貼付したもの3体,下面にシートを10cm間隔でゼブラ状に貼付したもの2体である。供試体全て押抜きせん断破壊であった。下面にシートを貼付することによりその最大荷重は,基準供試体の最大で1.58倍の値を示した。

本論文において、連続繊維フレキシブル筋の被覆チューブの厚さを薄くし、さらに、端部定着を施すことによりRCはりのせん断耐力が大きくなることを明らかにした。さらに、被覆チューブの厚さを実験変数としたU字型引張試験を通じて、折り曲げ部で繊維が滑り抜けていること、チューブの変形が引張荷重方向の変位を大きくし、繊維の効果を発揮させにくくしていることがせん断耐力に大きな影響を及ぼす要因であることを示した。

This paper presents the study results of a reinforced concrete pier with carbon fiber sheet (CFS) retrofitting. Plain reinforced concrete specimens were used for comparison. The experimental variables are: type of loading, ratio of CFS reinforcement. Specimens were subjected to static monotonic lateral loading or static cyclic lateral loading.

矩形断面はりの引張主鉄筋に降伏現象のないアラミドロッドを用い,はり下面に炭素繊維シートを貼付し,二点対称集中荷重を作用させ,ロッド及びシートのひずみ性状,はりの曲げ性状,及び破壊性状について実験的に検討した。その結果,曲げ補強のため供試体下面に貼付した炭素繊維シートの積層数の違い(一層と三層)による終局耐力の差はほとんど見られなかった。しかし,曲げ補強シート貼付後さらにシートでU字巻き上げ補強することにより下面シートの剥離進行が制御され,終局耐力及び終局変位が増加した。また,下面のシートが剥離する前までのはりの変形は,断面分割法により概ね予測することができた。

This paper presents the study results of a reinforced concrete pier with carbon fiber sheet (CFS) retrofitting. Plain reinforced concrete specimens were used for comparison. The experimental variables are: type of loading, ratio of CFS reinforcement. Specimens were subjected to static monotonic lateral loading or static cyclic lateral loading.

本研究では,再生骨材コンクリートの力学的特性として拘束下における強度および変形性能を把握することを目的としている.充填するコンクリートの一軸圧縮強度の変化にともなうコンクリート充填鋼管柱の変形性状は再生骨材コンクリートを用いた場合も普通骨材コンクリートを用いた場合と同様であることを明らかにした.また,再生骨材コンクリートのヤング係数は普通骨材コンクリートに比較して小さいことを考慮すれば,再生骨材コンクリート充填鋼管柱の剛性を概ね推定できることを示したが,強度の推定にはボアソン比と相関がある弾塑性域での体積膨張を考慮することが重要であることを示した.

本研究は、無筋の梁部材を用い、繰返し荷重を受けるコンクリートのひび割れ進展のメカニズムを明らかにすることを試みた。梁の曲げひび割れの下縁で、除荷時に圧縮力が作用することにより、ひび割れ先端部分に引張力が作用する。その結果、新たなひび割れが成長することを実験的に明らかにした。また、ひび割れが閉じようとする時に、ひび割れ面で圧縮力が作用することを考慮に入れた構成則を用いた有限要素解析により実験結果を反映することが可能となった。

本研究において,再生骨材を用いたコンクリート充填鋼管柱の軸圧縮特性を実験及び解析的に検討した.すなわち,再生骨材を用いたコンクリートは,普通骨材を用いたコンクリートに比べ,内部の損傷(破壊)速度がより大きく,このため,部材剛性及び終局耐力が若干低下するが,実用に耐えうる性能を有していることを明らかにした.

本研究において、鉄筋コンクリートはりの下面に炭素繊維シートを貼り付けた場合と、剥離破壊を抑制することを目的として、下面に貼り付けた炭素繊維シートにさらにその上から炭素繊維シートをU字に巻き付けた場合におけるRCはりの破壊性状、変形及び耐力の差異を明らかにした。

本研究において、炭素繊維シートで補強した鉄筋コンクリートはりのせん断性状を実験的検討により明らかにした。すなわち、炭素繊維シートを側面に補強した鉄筋コンクリートはりのせん断力は、コンクリートが受け持つせん断力と斜めひび割れ域での炭素繊維シート及びスターラップにより受け持たれるせん断力の和として表されることを明らかにするとともに、炭素繊維シート及びスターラップが受け持つせん断力の算定方法の考え方を提示した。

本研究では、主鉄筋が複数一列に配置されたはり部材における鉄筋腐食によるかぶりコンクリートのひび割れの性状とその発生までに要する鉄筋膨張率について有限要素法を用いた解析的な検討を行った。その結果、かぷり厚さ及びあき長さの差異による腐食ひび割れの発生方向と限界膨張率との関係を明らかにした。

本研究において、有限要素解析に基づき、せん断補強筋を持たないディープビームに対するせん断耐力式を、水平補強筋及びスターラップを有するディープビームに対して適用できるよう修正した。本研究で提示したせん断耐力式により、実験結果を概ね評価できることを確認した。

Concrete structures in hot spring area, underground structures, sewerage structures are suffered from mechanical actions such as earthquake and at the same time environmental actions. However, understandings on the mechanical characteristics of concrete under combined actions are not progressing. In this study, therefore, a mass transfer model; chemical reaction analysis method for prediction of cement hydrates and porosity change under environmental actions (Ca leaching and acid attach) and a fracture analysis method considering reduction in strength, Young's modulus and facture energy based on meso scale perspective are developed and those methods are integrated so as to predict the mechanical characteristics of semi-macro concrete.

In order to develop the unified design method for strengthening by external bonding and overlaying, the followings are presented: Prediction models for various debonding types at interface between substrate concrete and reinforcing materials, Influences of fatigue, moisture, freeze thaw cycles and interface roughness on interface bond strengths, Optimum reinforcing material properties and reinforcing methods (dimension and location), Experimental evidence of enhancement of ultimate member strength by overlaying under traffic loads, and (5) Applicability of 3D numerical analysis to simulate member strength after strengthening. After compiling all the results, latest guidelines for strengthening of concrete structures as well as strength prediction models after strengthening are presented.

In concrete structures in cold regions frost damage is occurred by freeze-thaw cycles of water in the concrete. This study presents the method to measure the degree of frost damage in actual structures using ultrasonic wave. The relationship between the frost damage degree and degraded material properties is observed. The deterioration mechanism under the combined effects of frost damage and wet-dry cycles/salt attack is clarified, and then the models to simulate the deterioration is proposed. The model for numerical analysis of structures with frost damage after being repaired by overlaying is also proposed.

The purpose of this study is to evaluate the durability of concrete through the nation-wide testing and local climate monitoring. The test has been started since 2003, and still continuing.
From these investigations, following conclusion was clarified.
A. For the first year
(1) The climate condition at Tsukuba was much severe than that at Kurihama in both summer and winter. In other word, Tsukuba was colder than Kurihama in winter season, and Tsukuba was hotter than Kurihama in summer season.
(2) Therefore, the compressive strength of concrete exposed in Tsukuba were remarkably influenced more than that in Kurihama.
B. For the fifth year
(1) From the results of climate condition at 17 places, several classifications could be done as the influent condition for the durability of concrete.
(2) The curing condition at early stage of concrete production is quite important for the long term durability of concrete.

The following conclusions can be drawn.
(1)A model for evaluating life cycle cost of pavements considering winter road traffic situation was proposed. An algorithm for the model which was developed by applying the sensitivity analysis of the probit stochastic user equilibrium (PSUE) was also proposed. Drivers' route choice behavior induced by deterioration of surface condition of pavements, change in traffic capacities brought by repair works in summer, and change in traffic capacities brought by antifreezing admixture dispersion in winter was endogenously expressed in the model. As a result, a plan for repair works and dispersion of antifreezing admixture which minimizes the life cycle cost by taking above mentioned driviers' behavior into account was obtained by carrying out a numerical experiment.
(2)The integrated database combining the data of varieties, such as the road surface condition, the drive condition, the weather information and so on was created. As a case study using this database, the research solved the relation between the road surface condition and the drive condition in winter, and showed that the useful information to the traffic administrator and the road user could be created. This result showed the validity of the anti-freezing agent in the case of many, and clarified further the conditions on which that effect fades.
(3)A calculation example of 2 dimensional Moving Element Method (MEM) with a vehicle model was introduced and it is verified that an interactive behavior between a vehicle and plate can be successfully analyzed by this method. The developed MEM has following advantages against conventional time-domain FEM for continuous structure under the loading due to a moving vehicle, (a) MEM can fix the loading position in the model regardless of time elapsingwhereas FEM needs large model corresponding to the moving range of the vehicle, (b) Since limited area or length near the loading point is finitely modeled for MEM, the degrees of freedom required for the analysis become smaller than those for a conventional FEM.
(4)Damage evaluation method for infrastructure based on fractal analysis was developed.
(5)A bond model for FRP sheet which can consider the influence of Young's modulus of resign and sheet was developed.
(6)Surface protective agent which can penetrate into 40 mm depth from concrete surface was developed.

本研究は,疲労と凍結融解を同時に受ける鉄筋コンクリートはり部材の寿命予測手法を構築することを目的として行った.すなわち,凍結融解による劣化と疲労荷重による損傷を考慮できるFEMプログラムを開発し,かつ,部材レベルでの促進試験を行い,実験結果と解析結果とを比較することにより本解析手法の妥当性を示すとともに,劣化メカニズムを解明する.3年間の研究成果を以下に列挙する.
・鉄筋コンクリートはり部材の凍結融解試験を実施した.その結果,凍結融解により劣化することにより,はりの破壊形式が曲げ降伏破壊からせん断圧縮破壊へ移行し,さらに大きな劣化度を有する場合には,せん断圧縮破壊から曲げ圧縮破壊へと移行することを明らかにした.
・鉄筋の定着強度が,凍結融解作用により大きく低下することを実験的に明らかにした上で,凍害による損傷を考慮できる付着構成則の開発を行った.
・静的荷重を作用させることでコンクリートに予め損傷(マイクロクラック)を与えた場合,凍結融解抵抗性が著しく低下することを明らかにした.さらに,初期損傷を有するコンクリートが凍結融解作用を受ける場合のコンクリートの応力ひずみ構成則を開発した.
・既往の実験結果に加え,温度や湿度を制御した疲労及びクリープ試験を通じて,コンクリートの変形性状を明らかにするとともに,静的荷重を対象として開発された弾塑性破壊モデル(前川モデル)を基本とした変形モデル,すなわち,持続荷重や疲労荷重を受けるコンクリートの破壊までの応力-ひずみ関係の定量化を行った.さらに,この変形モデルを2次元非線形有限要素解析プログラムに組み込んだ.
・本研究で開発した構成則を導入した有限要素解析を実施し,凍害による劣化が,鉄筋コンクリートはり部材の変形と耐力に及ぼす影響を明らかにした.

本研究は,バクテリアリーチングにおいて利用されてきた方法を基本とし,微生物を利用して再生骨材を製造し,その品質を明らかにすることで,再生骨材の製造に微生物を利用することの有用性を示そうとするものである.
本研究において,多種多様な微生物の中から硫黄酸化細菌と鉄酸化細菌に着目した基礎実験を行った.すなわち,細菌の有無,骨材の有無,コンクリート塊の大きさ,炭酸化の有無がペースト及びモルタルの劣化度に及ぼす影響を実験的に明らかにした.得られた知見を以下に列挙する.
・硫黄酸化細菌及び鉄酸化細菌が増加すると培地のPHを低下させ,モルタルをよく剥離させ,カルシウムイオンを溶脱させる.
・硫黄酸化細菌と鉄酸化細菌の活動は,コンクリート塊のサイズが5-20mmの範囲の方が,5mm以下の範囲よりも活発化した.これは塊のサイズが小さいと培地に溶け出すアルカリ量が多くなるためである.それゆえ,微生物を摂取する前に炭酸化させた方が良い.
・硫黄酸化細菌と鉄酸化細菌が骨材に及ぼす影響は工学的に無視できる.
・酸性硫黄温泉水を培地として利用した場合,効率よくカルシウムイオンを遊離させることができる.しかし,コンクリート塊の表面に生成される腐食性生物が硫酸イオンの浸透を阻止する為,反応速度が著しく低下する.

The influences from dispersion of antifireezing admixture, toward function of road transport and toward deterioration of road facilities, are analyzed in this study. This study aimes for the enhancement of systems of operation and maintenance for dealing with the influences. Firstly, an examination on the technologies of operation and maintenance for road network which support transport system is made. Then, a Web-based database system which can capture the real road traffic situation in winter, both temperaly and spatialy, is developed. Finally, an examination on the optimal amount of antifreezing admixture dispersion problem considering the changes in modal shares made by passengers is also carried out. An efficient usage of antifreezing admixture will be brought out by both technologies regarding the effective road maintenance, and regarding the control of passengers' travel behaviors determined by characteristics of transport network.
A detailed mechanism of deterioration in concrete structure caused by antifreezing admixture is captured. An examination on the strengthening resistibility to penetration of sodium into cement, which is known as main material of concrete, is carried out, new tangible method for that is then developed. An examination on priority decision making system for maintenance and repair works is carried out by taking steel structure as an example. Furthermore, a development of diversification risk system targeted to destruction of structure, by taking disaster as am example, is made an attemp. Those works will make it possible to develop both structures which are hard to be deteriorated by sodium, and well-designed structure management system.
Some important achievements, which could contribute to a development of road management system, have been made in this study by assuming usage of antifreezing admixture. However, a development of comprehensive management system comprised of technologies mentioned above are intended for in the first stage, only indication on the direction toward the comprehensive system is made against our objectives. Some examinations on what kinds of effects are botained by organizing the technologies dealt with in the present study will be made in the fixture.

The followings are summary of what have been obtained in the experimental research of the loop joint.
From static tension tests with loop joint, two types failure mode of yielding of longitudinal bar and crushing of core concrete in the loop joint are observed. In case of crushing the core concrete, ultimate strength is large as the loop height, the splice length and the bar diameter are increased Mechanical model for estimating the compressive stress of the core concrete is conducted. The capacity of the compressive stress can he estimated to define the limit stress determined form the concrete strength and the bar diameter From the fatigue tests using beam specimens, it is shown that the fatigue life may be decrease due to occur the local bending at the joint.
The followings are summary of what have been obtained in the experimental research of the bearing-type connection.
It is clarify that a cracking load is computed by using EC beam theory with the bond strength of the hearing-type connection and a compression zone at the connection resists to the shear force after cracking when the connection are subjected to bending moment. The equation for the shear transfer strength is conducted in such this case.

This study presents a unified local bond stress-slip model for interface between concrete and externally bonded reinforcing material (shear bond model). The shear bond model was derived based on a reinforcing material stress-slip relationship at loaded end of pullout bond test, so that necessary measurement was simplified and the data scatter problem was minimized. The shear bond model needs only two material constants, interfacial fracture energy and interfacial ductility factor. The shear bond model was expanded to be bond stress-slip-reinforcing material strain model to express cases with a short bond length. Both original and expanded shear bond models consider effects of mechanical properties of reinforcing materials, adhesive materials and concrete substrate. Besides the shear band model, the prediction formula for interfacial fracture energy, effective bond length and bond strength for given anchorage length are presented. Reliability of the proposed unified shear bond model together with the proposed formula for interfacial fracture energy, effective bond length and bond strength for a given bond length is presented by comparing the calculated results with experimental results.
Tension bond model is examined experimentally and it is disclosed that the bond strength (or interfacial fracture energy) is not affected by stiffness of adhesive materials, which is different from the cases of shear bond model. A test method to represent a mixed mode for bond (shear and tension bond) is newly developed. Using this method, an interaction diagram of shear bond strength and tension bond strength is presented, which shows that the shear bond strength is reduced only by 10% even under tension bond stress equal to 90% of the tension bond strength. The theoretical method to calculate punching out capacity of reinforcing material externally bonded in orthogonal direction is also presented.

本研究の目的は,コンクリート構造物の性能をライフサイクルを通じて適切にかつ合理的に維持するための管理技術の構築について,共同で行う研究計画に対して企画調査を行うことであった.そこで本研究では,コンクリート構造物の劣化・損傷,性能低下,対策,対策後の性能回復・向上,再劣化,性能の再低下における時間的なサイクルの過程を定量的にシミュレートするモデルの開発に対して,材料の専門家と構造の専門家が共同して,現状の技術レベルおよび課題の抽出,モデル開発の有効性を中心に企画調査を実施することとした.
本企画調査によって,補修材料のうち例えば,コンクリートの表面保護材料の耐久性が不明であり,補修後の維持管理やライフサイクルを通じたメンテナンスを考えた場合,早急にこれらの材料の耐久性の定量化が重要であることを明らかにした.これに対して,特に本研究では,シート接着鉄筋コンクリート供試体の電食試験結果と,シートの塩化物イオン拡散係数を仮定した数値解析結果とを比較することにより,シートおよび樹脂層の拡散係数を導出し,時間軸における評価手法の開発の妥当性を検討した.さらに,断面修復材のうち高耐久性のある材料についても電気泳動法によって塩化物イオン拡散係数を算出し,耐久性の合理的な評価の可能性を検討した.一方,特に厳しい海洋環境下や凍結融解作用下で劣化したコンクリート構造物の補修,補強や再劣化の実態調査では,補修後に再補修が必要となるケースが見られ,室内実験での材料評価に加えて,施工の要因を採り入れた総合的な対策が重要であることも明らかになった.
以上より本研究は,コンクリート構造物のライフサイクルマネージメントの合理化,高度化に必要となる具体的な研究計画を立案できる可能性や必要とされる要素技術を明らかにした.

The summary of conclusions obtained by experimental and numerical analyses in this study is as follows :
・The equation to predict the fracturing strength of Carbon Continuous Fiber Flexible Reinforcement (C-CFFR) at bent portion and the model to predict the transferred tensile force by C-CFFR at bent portion were proposed. Three dimensional finite element analyses, in which the proposed strength equation and the force transfer model for C-CFFR were introduced, could predict the mechanical properties of C-CFFR observed in the experiment.
・It was observed that the ultimate deformation of concrete columns with Polyacetal Continuous Fiber Flexible Reinforcement (P-CFFR) as tie reinforcement was greater than that of columns with steel tie reinforcement whose volume ratio is the same. This is because P-CFFR did not fracture even at ultimate deformation and because P-CFFR can be arranged inside the core concrete. The prediction formulae for P-CFFR strains were proposed based on the experimental results.
・The unified model for bond stress-slip relationship at the interface between continuous fiber sheet and concrete was proposed for finite element analysis of concrete members reinforced with continuous fiber sheet. Based on the finite element analysis of reinforced concrete prism with continuous fiber sheet subjected to uniaxial tension, it was found that the concrete tension stiffness is greater than the case without continuous fiber sheet.
・In order to obtain the precise prediction of the shear tension strength of reinforced concrete members, which is necessary for finite element analysis to predict shear and ultimate deformation of concrete members reinforced with various materials, it is necessary to model precisely the force transfer along the major shear crack.

The objective of this research project is to develop an analytical system that can predict performance of concrete structures subjected to various load and environmental actions. Following results were obtained.
1) A computer program for numerical simulation of time-dependent performance change of RC bridges subjected to chloride attack was developed. It can predict effectiveness of some rehabilitation techniques as desalination method and retrofitting of CF sheet on service life of structures.
2) Material models in the computational system mentioned above were improved, which are material transport models in cracked concrete, corrosion model of reinforcing bar in concrete and tension stiffening model for corroded RC members.
3) 3D nonlinear FEM program that can simulate post peak behavior of various types of RC structures was developed.
4) A testing apparatus to examine gas permeability in cracked concrete was developed. Using this apparatus, resistance of damaged concrete against ingress of aggressive agent was investigated.
5) Constitutive models for concrete were improved to ensure a damage analysis of concrete structures under various conditions. A constitutive model for plane concrete under cyclic tensile and compressive stress was formulated. A constitutive model for plane concrete damaged by freeze-thaw action was formulated. A constitutive model for bonding behavior of CF sheet and concrete under static and cyclic load was formulated.

The followings are summary of what have been obtained in this research.
/FE analysis considering strength and stiffness reductions caused by damage due to fatigue loading can predict fatigue life of RC beams without stirrups. However the analysis cannot evaluate its deformation precisely because time-dependent deformation is not considered.
/Longitudinal strain and volumetric strain curve observed under compressive stress does not differ from different loading conditions.
/Longitudinal strain and Young's modulus curve observed under compressive stress does not differ from different loading conditions.
/Plastic strain in fatigue test increases as applied maximum force becomes greater.
/A constitutive model which can consider influence of loading speed was developed. The plastic strain in the model consists of plastic strain caused by cracks and creep strain. The model can be applicable to the both cases of static and fatigue loading.
/It was clarified through the numerical analysis using the proposed model that creep strain greatly affects fatigue life, fatigue strength predicted by the model is slightly greater than that calculated by an empirical equation and ultimate strain decreases linearly as stress at failure becomes smaller.
/In static test after fatigue test in water, shear force carried by stirrups in a RC beam increases as applied shear force increases but shear force carried by concrete does not because redistribution caused by compression failure in concrete compression zone takes place.
/To develop fatigue design method of RC members in water, not only fatigue strength of plain concrete but also shear resisting forces in truss mechanism in RC member must be quantified.

The followings are summary of what have been obtained in this research.
・ Fatigue strength of prestressing strand under effect of fretting is apparently smaller than that under ordinary fatigue loading.
・ Fretting fatigue strength is influenced by stress range, slip range and contacting force. The greater stress range is, and the greater contacting force is, the smaller becomes the fatigue strength. The experimental fact indicates that how slip range influences fretting fatigue strength may depend on magnitude of slip range. Extent of influence of stress range and slip range is greater than that of contacting force.
・ It is necessary to consider effect of slip range in the direction normal to strand axis besides that in the direction of the strand axis.
・ Fretting fatigue occurs at contacting point between strands rather than between wires in the same strand. This fact indicates that there is the effect of slip range.
・ Although contacting force is considered greater at inner contacting points than at outer one at deviator, location of fretting fatigue fracture was found almost evenly. This fact indicates either that with magnitude of contacting force observed in the experiment fretting fatigue strength is hardly affected by change in contacting force, or that actual contacting force in the experiment did not change by the location.
・ Grouting in protection tube for cable and resin coating of strand can increase fretting fatigue strength, However, it is difficult to prevent fretting fatigue fracture by providing them only.
・ Restriction of grout movement by taper inside protection tube or spacer of strand for reduction of contacting can prevent fretting fatigue fracture.

本研究の主たる実績を以下に示す。
1.本研究において,静的荷重下における連続繊維シートの付着機構を実験的に明らかにし,得られた付着機構に基づき付着応力-すべり-ひずみ関係(以下「付着モデル」)を構築した。本付着モデルは,コンクリート強度,積層数,接着幅の影響を考慮できるものであり,実際の剥離発生・進展過程,さらには,剥離耐力を精度良く予測できるものである。
2.疲労荷重を受ける連続繊維シートの付着機構および疲労寿命を実験的に明らかにし,静的荷重に対して開発された付着モデルの疲労荷重を受ける場合への拡張を図った。一定の荷重比(上限荷重/静的付着耐力)で比べた場合,連続繊維シートの剛性が大きい方ほど,局部的な付着応力が静的荷重時の局部付着強度に比べ小さくなることにより,疲労寿命が長くなることを明らかにした。また,付着モデルを用いた数値計算より,局部付着応力比(局部付着応力の上限値/静的局部付着強度)と疲労寿命との関係は,剛性によらずほぼ一義的な関係で記述できることを示した。
3.本付着モデル及び鉄筋に対する既往の付着モデルを用いた,連続繊維シートで補強した鉄筋コンクリートの一軸引張挙動の数値シミュレーション手法を構築した。本手法は,連続繊維シートの剛性が大きいほどひび割れ間隔が小さくなることや鉄筋の付着応力が小さくなることなどの実験的事実を定量的に評価することができる。また,本手法を用い,連続繊維シート補強鉄筋コンクリートの平均応力-平均ひずみ関係をも構築した。本関係において,コンクリートの平均応力-平均ひずみ関係は,コンクリートの引張強度とともに鉄筋比およびシートの補強筋比により表される。

The purpose of this study is to investigate the characteristics of the dynamic behavior of submerged floating tunnels under wave and seismic action, which are critical forces in design. Moreover, effective beam model for discussion on the design of structure is also presented.
The most important findings under wave force are summarized as follows;
For leg arrangement Type-A :
1. Although lateral displacement is great, slack is least likely to occur with this arrangement.
2. The rigidity of the joints between tunnel elements has a major effect on the lateral displacement of the tunnel as a whole. The ideal type of joint for Type-A would be a pin joint. Lateral displacement and the maximum bending moment in rigid joints increases with the angle of wave incidence.
For leg arrangement Type-C :
1. Lateral displacement is much less than in type A, but slack is more likely to occur.
2. No significant variations in lateral displacement are found with different joint rigidities.
The results of analysis under seismic wave can be summarized as follows:
1. If the natural period of the structures is long enough comparing to the predominant period of seismic wave, maximum response of displacement or bending moment for design are approximately predictable by an analysis with simultaneous excitation. When the natural period of the structure is close to the predominant period of seismic wave, propagation velocity plays an important role for dynamic response and it should be taken into account.
2. For prediction of sectional force like the bending moment at the joints, propagation velocity should be carefully decided.
In order to discuss the global behavior of the structure, a beam model on elastic foundation is developed for submerged floating tunnel with tension legs spaced at equal interval. It Is shown that the approximation of a uniform continuous elastic foundation is reasonable whenever kィイD2vィエD2hィイD13ィエD1/(6EI)≦0.2.

Icicles and side wall ices in tunnels became a problem for transportation and maintenance. Recently a heat insulator for icicle prevention at the lining surface has been developed in the existing tunnels. The purpose of this study is to propose a simplified design procedure for heat insulator.
This project is summarized as follows :
(l) A simple practical equation for estimating the thickness of heat insulator is presented. The equation is obtained by using a one-dimensional tunnel-ground model and a non-steady periodic thermal analysis. A comparison with other solutions suggests that the proposed equation provide satisfactory accuracy. By using the equation presented, we can reasonably determine the optimum material of heat insulator and its optimum thickness. In addition, the equation is useful for a better understanding for the thermal characteristics of the tunnel-ground system.
(2)In order to identify unknown thermal parameters (thermal conductivity and heat capacity in ground) in appearing the proposed equation, the extended Kalman filter in combination with the one-dimensional finite element thermal analysis is used. A comparison of the temperatures calculated from identified parameters with the measured fild data shows that the method is sufficiently accurate for practical purposes.
(3)In order to estimate the unknown temperatures at a planning site of road tunnels, Semi-Yariogram is used on the basis of the a stochastic method. A comparison of the estimated temperatures with the measured fild data gives satisfactory results.

This study is carried out to develop the design method for strengthening of exsisting concrete structures using FRP sheets and FRP tendons. Results in this study are summarized on the following three points ; (1)Long term properties of reinforcing materials, (2)Ultimate capacity and deformation of concrete members retrofitted with FRP sheet, (3)Ultimate capacity and deformation of concrete structures retrofitted with FRP tendons.
(1) Long-term Properties of Reinforcing Materials
・The relaxation ratio represents the natural characteristics of each FRP tendon and varies in proportion to the logarithm of time throughout the entire loading time range.
・The tensile strength and bond strength of FRP sheet were not reduced even after FRP sheet is soaked in 10% sulfuric acid solution for six months.
(2) Ultimate Capacity of Deformation of Concrete Members Retrofitted with FRP Sheets
・It was clarified how concrete strength, and stiffness of FRP sheets affect the bond mechanism of FRP sheet. The bond strength equation was proposed.
・When peeling of FRP sheet which is attached to a lower face in a beam as flexural reinforcement does not occur, the bending capacity and deformation of the beam can be predicted by the layr-by-layr procedure.
・For failure mode with peeling of FRP sheet along a shear crack, the model of predicting the shear reinforcing effect of FRP sheet was proposed.
(3) Ultimate Capacity and Deformation of Concrete Structures Retrofitted with FRP Tendons
・The flexural behavior of externally prestressed beams can be estimated by a precise calculation method considering the compatibility of deformations and changes in location of cables.
・The ultimate strength of FRP tendons at deviators becomes less then the uniaxial tensile strength. The rate of reduction differs for different type of FRP tendons.
・When a cable tensile force was within the range of 40 to 50% of the nominal breaking load for AF rope, failure did not occur during the the 2,000,000-cycle loading.

In this study four topics are discussed. The major results obtained are as follows.
1) Effective Width for Shear Failure of RC Deep Slabs
The effective width to the shear capacity of RC deep slabs was discussed from the experimental results. The effect of the length of loading plate on the effective width is larger than that of the supporting plate. If it is considered that the effective width is related to the swell of the compressive concrete strut formed between the loading and supporting plates, the shear span ratio is a factor of great importance to the swell.
2) Effect of Shear Reinforcement on Local Shear Failure of RC Slabs
For one way and cantilever RC slabs, the shear reinforcing effects were experimentally investigated. In case of the slabs with a punching shear failure, the shear capacities increase with shear reinforcement. In case of the slabs with a beam shear failure, the capacities increase a little. The strain of the shear reinforcement starts to increase suddenly at a certain load, however, the strains do not reach its yield strain when the slabs reaches its ultimate state.
3)Modeling for Dowel and Bond Actions of Longitudinal Bars in Shear Failure of RC Members
Modeling for the longitudinal bars in a shear resisting mechanism was conducted. The cracking along a longitudinal bar is caused by a combined effect between the dowel and the bond actions. The deformation of the bars can be described by modeling the surrounding concrete as an elasto-plastic spring. The criteria of the cracking is related to a vertical and a slip displacements of the bars.
4)Analytical Study on Axisymmetrical RC Slabs
An effect of the shear reinforcement on the shear capacity of axisymmetrical RC slabs can be described by using a nonlinear finite element analysis. The effect of the tensile and shear reinforcing bars on the member stiffness is clarified by the analysis.

本研究において、連続繊維補強コンクリートはりのせん断疲労強度に関する実験及び解析的な検討を行った。まず、実験的検討により得られた主な知見を以下に示す。
(1)せん断補強筋を持たない連続繊維補強コンクリートはりのせん断疲労強度は、鉄筋コンクリートはりに対して提案されている疲労強度式により評価できる。
(2)せん断補強筋に連続繊維補強材を用いたはりにおいて、繰返し回数の増加に対するせん断補強筋の歪み及びひび割れ幅の増加割合は、鉄筋コンクリートはりに対する予測式により評価できる。
以上が、実験的検討により得られた結論である。すなわち、繊維と直角方向の剛性が繊維方向の剛性に比べ極端に小さいことによる付着の劣化はほとんど認められず、従来の鉄筋コンクリートはりの疲労強度式に基づき連続繊維補強コンクリートはり部材の疲労強度を評価できるのである。ただし、本研究では、曲げ成形部の疲労破断に関しては検討できておらず今後の課題として残る。
一方、解析的な検討により得られた主な知見を以下に示す。
(1)斜めひび割れ発生荷重が繰返し回数とともに低下することを解析的にシミュレートできる手法を構築した。すなわち、静的荷重問題用に開発されているひび割れ発生前及びひび割れ発生基準に繰返し荷重が作用することによる影響を組み入れた構成則を、非線形有限要素解析プログラムに導入し、斜めひび割れ発生荷重が繰り返し回数とともに低下する現象を評価することを可能とした。
(2)解析の妥当性を確認するために、本実験結果と比較した結果、的確に予測できることが明らかとなった。今後は、ひび割れ発生後の構成則に繰返しの影響を考慮し、部材の疲労寿命をも解析的に予測できるようにする必要がある。

Shear connector should be placed to assure the composite action between core concrete and skin steel plates in sandwich structures. The code for design of steel-concrete sandwich structures proposed by JSCE specifies how to arrange shear connectors considering its capacity for transferring shear force. However, the effects of existence and deformation characteristics of shear connector on member capacity, especially shear capacity, have not been clarified yet. In this study, having constitutive laws for finite element analysis of sandwich members in our mind, it was aimed to develop a mechanical model for prediction of deformation and capacity of shear connectors. The type of shear connector is shaped steel shear connector. The followings are the conclusions.
(1) A series of test for steel plates without shear connector indicated that there was a linear relation between capacity of shear force transfer and confining force and that the capacity of shear force transfer was reduced by 20 to 30% putting lubrication oil on the plate.
(2) Finite element analysis in which the part with shear connectors and the part between shear connectors were modeled differently as link elements expressing relationship between transferred shear force and slip could predict the deformation and ultimate capacity of open sandwich beams.
From a series of test in which height of shear connector was a parameter the shear connector was modeled as a cantilever together with surrounding concrete. The stiffness of the cantilever was found to be dependent on the height of shear connector, the transferred shear force and the confining force in the surrounding concrete. The transferred shear force at a sudden reduction of the stiffness could be modeled as well.

本研究では、はり部材中の連続繊維補強材の局部応力による破壊基準を、(1)連続繊維補強材直線部の斜めひび割れとの交差部での破断、(2)連続繊維補強材曲げ成形部での破断、に分けて検討した。以下にそれぞれに対して得られた知見を示す。
(1)直線部の破壊基準
連続繊維補強材直線部の破壊基準を明らかにすることを目的として、連続繊維補強材に引張力とせん断力を作用させたモデル供試体を用いた実験及び3次元非線形有限要素解析を行った。その結果、連続繊維補強材直線部の破壊モードは、曲げ支配型とせん断力支配型の2つに分けて考えることができることが明らかとなった。すなわち、曲げ支配型の場合、連続繊維補強材は一軸引張歪みに達したときに破断し、せん断支配型の場合には一軸引張歪みに達する前に限界のせん断歪みに達し破壊する。特に、炭素繊維補強材の限界せん断歪みはアラミド繊維補強材よりも非常に小さいことが明らかとなった。
(2)曲げ成形部の破壊基準
曲げ成形部における破壊基準を明らかにする目的で、はり部材中のせん断補強筋をモデル化した実験及び2次元非線形有限要素解析を行った。その結果、曲げ内半径が小さなものほど、曲げ成形部強度が小さく、特に、一軸引張強度に対する曲げ成形部強度との比、すなわち強度低下率は、アラミド繊維補強材に比べ炭素繊維補強材の方が大きいことが実験的に明らかとなった。有限要素解析より、曲げ内半径が小さなものほど応力集中率が大きくなることが明らかとなり、その結果、曲げ内半径が小さなものほど曲げ成形部強度が小さくなるものと考えられた。また解析において、一軸引張歪みに達したときに破断するとした破壊基準を用いた場合、本解析は、アラミド繊維補強材に対しては実験値を精度よく評価できたが、炭素繊維補強材に対しては実験値より曲げ成形部強度が大きくなる傾向にあった。これは、直線部同様、一軸引張歪みに達する前に限界のせん断歪みに達し破断しているものと考えられた。