<jats:p>Patch repair is one of the countermeasures for RC members with rebar corrosion. Patched materials often debond from the RC members due to a loss of bonding capacity, so appropriate treatment of the boundary between RC members and patch materials is required. This paper focuses on the characteristics of the boundary surface and the material properties of patch materials to clarify the bonding mechanisms. The influences of the materials and boundary surface conditions on the structural behavior were investigated by the experiment of the patch-repaired RC beams. As a result, the elastic modulus of the patched mortar should be smaller than that of the substrate concrete to prevent debonding, and chemical adhesion ensures a strong bond even with a relatively smooth boundary surface.

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本研究では，開発したGFRPシートが力を受けることによって透明な状態から白濁化する現象に着目し，シートの応力状態を可視化する手法について検討した。GFRPシートの引張試験と付着試験を実施し，引張試験では引張力に応じて緯糸が白濁化すること，また，付着試験においては，はく離前は経糸が白濁化し，はく離後に緯糸が白濁化することが明らかになった。モデル検証試験から経糸もしくは緯糸の白濁化は，繊維と直交する方向に引張応力が作用することで発生した繊維束内の内部損傷（き裂）による現象と推定された。デジタル画像解析によって，GFRPシートの白濁化面積から「白濁化率」を算出し，白濁化率とひずみには高い相関関係があることを示した。

コンクリートに接着したFRPシートの付着試験から得られる実験的な付着応力–すべり関係を用いずに，剥離機構に基づくことでFRPシートとコンクリートの付着応力–すべり関係を導出できる付着モデルを構築した．このモデルはFRPシートの剥離性状をコンクリート表層の鋸歯状の破壊として表現したもので，力のつり合い，変形の条件，エネルギー等価，材料構成則によって導かれる．構築した付着モデルを用いて付着試験の数値解析を行った結果，シート剛性や付着長，樹脂の種類に関わらず実験結果と良く一致した．また，剥離深さが未知の既往の付着試験に適用した結果，既往の付着モデルと同程度の精度であった．さらに，提案モデルの活用例として，材料特性の影響度評価と境界条件の異なる両引き状態への適用を行い，モデルの妥当性が示された．

Unlike plain concrete, frost damaged reinforced concrete (RC) exhibits anisotropy because of the presence of reinforcing bars. The resultant mechanical responses are influenced strongly by the loading direction. Therefore, to ascertain the mechanical behavior up to failure of RC beams subjected to freeze-thaw action and subsequent mechanical loading, anisotropic damage models of frost-damaged RC elements were assessed in this study using three-dimensional nonlinear finite element analysis (3D-NLFEA), which revealed that the anisotropic damage affected load-deflection responses and played a key role in failure modes that differed from those of an undamaged RC beam. This paper is the English translation from the authors' previous work [Kanazawa, T., Sato, Y. and Takahashi, R., (2019). "Frost damage of reinforced concrete beams and analytical evaluation of its static failure behavior." Journal of Japan Society of Civil Engineers. Ser. E2 (Materials and Concrete Structures), 75(4), 293-307. (in Japanese)].

This experimental study investigates the compressive fatigue behavior of air-entrained (AE) concrete with blast furnace slag (BFS) fine aggregates subjected to freeze-thaw cycles (FTC). The fatigue tests were carried out on cylindrical specimens of intact and frost-damaged AEBFS concrete and the results are compared with those of AE high strength (HS) normal concrete using crushed sand. The strain measurements are used to discuss the damage progress under fatigue loading. The results reveal that although the static compressive strength of AEBFS concrete is slightly less than AEHSN concrete, the fatigue life of AEBFS concrete is longer than that of AEHSN concrete. No significant effect of FTC is found on the fatigue behavior of each concrete due to very low frost damage. Moreover, it is found that overall the fatigue life of AEHS concrete is longer than that of non-AE high strength concrete from literature and this difference is pronounced with the reduction in maximum stress level.

This study is attempted to investigate the change in mechanical properties and to formulate the stress-strain models of air-entrained (AE) and non-air entrained high strength concrete with blast furnace slag (BFS) sand as fine aggregates under freezing and thawing. The freeze-thaw (FT) test was carried out on the concrete specimens followed by static compression tests and the results are compared with those of AE normal strength normal (AENSN) and AE high strength normal (AEHSN) concrete using crushed sand. The experimental results disclose that overall the rate of plastic strain development due to freezing and thawing in non-AE high strength concrete is higher than that of AE high strength concrete, but less than that of companion normal strength concrete. Consequently, the mechanical properties of non-AE concrete deteriorate at higher rate in comparison with AE concrete under freezing and thawing. However, no significant reduction in mechanical properties of AEBFS and AEHSN concrete is observed compared to AENSN concrete. Moreover, it is found that the Young's modulus of frost-damaged concrete degrades rapidly than the compressive strength. Thereafter, the stress-strain relationships for AE and non-AE high strength concrete under monotonic loading are formulated based on elasto-plastic and fracture concept. Based on the experimental data, the relationships for fracture parameter and plastic strain development of high strength concrete under monotonic loading are developed. The stres-strain relationships calculated by the proposed model are compared with the experimental ones.

This paper investigates experimentally how various bond configurations influence the flexural response of FRP-strengthened RC beams. A total of seven beams(200×200×2200mm) were tested. One was the reference without strengthening. Two were strengthened with CFRP sheets using hard and soft adhesive bonding, respectively, along the whole test span. The remaining four were applied a combination of hard and soft adhesives but in two different ways. One way is to use the soft adhesive at the flexure-dominating zone only and another is to use it for the shear-dominating zone only. Pair tests were conducted for these four specimens under both normal and low temperature (- 10°C). It is revealed that a sole use of soft adhesive improves the ultimate member strength and ductility but leads to a loss of stiffness. Using the soft adhesive at the flexure-dominating zone can not improve the member strength but improve the member ductility only. However, use of hard adhesive at the flexure-dominating zone and the soft one for the remaining parts can improve the member strength and ductility while avoiding loss of member stiffness. This test program provides an in-depth understanding of the debonding mechanisms in the FRP-strengthened RC beams. In addition, it is verified that that a low temperature of -10°C does not influence the global flexural response of FRP strengthened beams using the combined bonding system.

Aiming at improving bond strengths between FRP sheet and concrete, the FRP sheet bonding method using high elongation elastic resin as a buffer layer was developed. In this study, bonding tests was conducted to clarify the basic bond characteristics of FRP strand sheet-concrete interface with a polyurea resin. As a result of the bonding tests, it was found that the use of the polyurea resin as a buffer layer significantly improved the bond strength and the interfacial fracture energy between FRP sheets and concrete. In addition, bond stress-slip relationships with a polyurea resin were proposed. Finally, numerical analyses of bonding CFRP strand sheets and concrete were conducted so as to verify validity of the proposed bond stress-slip relationships. This paper is an extended version in English from the authors' previous work [Kobayashi, A., Ozaki, M., Sato, Y., Arazoe, M., Tateishi, A. and Komori, A., (2020). “Study on bonding behavior of FRP sheets and concrete bonded with high elongation elastic resin.” Journal of Structural Engineering, JSCE, 66A, 855-867. (in Japanese)].

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.

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.

<jats:p>Concrete structures can be damaged by various factors in extreme service conditions. Analytical methods that can predict the strength of structural concrete after exposure to fire are needed to facilitate decisions regarding whether to repair, strengthen, or demolish fire-damaged buildings. However, appropriate and widely applicable material models have not yet been proposed. This paper presents an experimental study in which we assess damage, including changes in flexural strength, porosity and residual cement hydrates, to oven-dried mortar that has been fired and immediately cooled in the air. Mortars were made from calcareous and siliceous aggregates, and one face of each specimen (100×100×400 mm) was exposed to fire curves of ISO 834 and ASTM E119. Specimens for quantitative assessment were hewed to ten layers from the originalspecimens. Experimental results indicate that the in-depth flexural strength of a thin specimen is substantially diminished by fire exposure, especially for specimens with existing fire cracks. In addition to the loss in strength, changes in porosity and chemical properties occur. Based on the experimental evidence obtained from this study, the relationships between each property are discussed.</jats:p>

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.

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。

硫酸溶液を用いたモルタルの薄片供試体による最大60日間における浸漬実験を行った。その目的は，浸漬後に曲げ試験およびせん断試験を行うことで，硫酸劣化によりセメント水和組織が変質した薄片供試体における力学的性質の挙動を抽出することにある。本研究において，曲げ試験から得られる荷重変位曲線から逆解析により引張特性（弾性係数，引張強度，破壊エネルギー，引張軟化曲線）を同定し，同一試験体を用いてせん断試験を行うことでせん断強度を測定した。加えて，物理的性質として力学試験後の薄片供試体の水和物量（CH，C-S-H），析出物，空隙率，細孔径分布を測定することで，物理的性質と力学的性質の変化を関連付けた。最終的に，硫酸劣化による物理的性質の変化が力学的性質に及ぼす影響は，弾性係数と引張強度および破壊エネルギーとせん断強度とで異なることを明らかにした。さらに，空隙と強度の関係に基づく既往の提案モデルの適用性を評価した。

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.

本研究は、硫酸溶液に浸漬したモルタルの物理化学的性質の経時変化を評価可能な解析手法を提案するものである。本解析手法では、硫酸による劣化を硫酸イオンの拡散および硫酸イオンと水和物との反応によってモデル化するとともに、pHを閾値としたエトリンガイトと二水セッコウの析出条件を導入した。また、実験値から回帰的にモルタル中の水和物量を求めることで、水和物量と析出物量に伴う固体体積の増減から空隙率を算出した。最終的に、空隙率の変化量を変数としたパラメトリック解析を行い、本解析手法の妥当性を検討した。

本研究では，モルタルを対象に，準微視的視点に立ち，Ca溶脱により変化する物理化学的性質と力学的性質との関係性を評価することを目的とした実験的検討を行った。すなわち，イオン交換水とNaCl溶液を用いたモルタルの薄片供試体による最大360日間の浸漬実験を行い，浸漬後に曲げ試験およびせん断試験を行うことで，力学的性質（弾性係数，曲げ強度，引張強度，破壊エネルギー，引張軟化曲線，せん断強度）を測定するとともに，物理化学的性質（CH，C-S-H，空隙率，細孔径分布）を定量的に把握した。その結果，弾性係数を除く力学的性質と物理化学的性質の相関関係が非常に高いことが明らかとなった。さらに，過去に著者らの提案した引張強度，弾性係数，破壊エネルギーの予測式の適用性を検証した結果，モデル式の妥当性を確認した。

<jats:p>Actual truck loads data is vital for bridge rating, and development of bridge design load. In Thailand, bridges have been designed using the HS20-44 design truck according to the AASHTO code; however, the actual truck loads are usually greater than the design truck load from the code. In addition, actual truck load are not available data to develop local truck load model for bridge design. This paper presents truck loads in Thailand that have been monitored using Bridge WeightIn-Motion (BWIM) system which innovated by author. Seven truck types are derived. Nominal analysis for simple span bridges shows that the heaviest Thai trucks induced forces are greater than that of the HS20-44 design truck.</jats:p>

本論は，再生粗骨材を用いたコンクリートの乾燥収縮ひずみの予測式を提案するものである。再生コンクリートは再生骨材における付着セメントペーストの存在により単位水量の増加と骨材の拘束効果の減少が考えられる。これらの点を考慮するため，再生コンクリートに関する既往の研究データを利用して単位水量の増分と骨材の拘束効果の減少分を求める手法を示した。これを土木学会コンクリート標準示方書における乾燥収縮ひずみの予測式に考慮することで，再生コンクリートの乾燥収縮ひずみの予測式として表した。ここで提案する方法は簡便さを備えたものであり，実験的に付着セメントペーストの量を求めるような作業工程を必要としない。既往の研究データを用いて検証を行った結果，土木学会コンクリート標準示方書式で普通コンクリートの乾燥収縮ひずみを求める場合と同等の精度が得られた。

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.

凍害環境下において、セメント硬化体の凍結防止剤成分の浸透に伴う化学的変質に着目した定量的な検討事例は稀少であり、上記の化学的な影響が凍害に及ぼす影響は不明確である。本論文では、凍結防止剤成分の浸透に伴うセメント硬化体中の水和生成相の変化が凍結防止剤の浸透および凍害の進行に伴う引張特性に及ぼす影響について検討した。その結果、凍結融解作用下における凍結防止剤および塩化物イオンの浸透による1）ひずみ履歴および融解時の残留ひずみの増加、2）モノサルフェート水和物の転移および分解、エトリンガイト生成に伴う凍害の促進、および3）引張強度、弾性係数等の力学特性値や破壊エネルギーの低下を確認した。

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.

本論文では，130N/mm2程度の圧縮強度を有し,鋼繊維を最大で1.6vol.%で混入した高性能繊維補強モルタルを適用したRC部材の変形特性とひび割れ性状の把握を目的に，両引き試験およびそれに対する数値解析を実施した．実験より，鋼繊維の混入率が高いほどひび割れ荷重や降伏荷重が向上し，ひび割れ分散性が高まるとともに，テンションスティフニングの効果も増加した．しかし，鋼繊維が同混入率であっても配向性の違いでその効果が低下することも明らかとなった．また,これらのRC部材の一軸引張挙動を数値解析的に把握することを目的に，材料特有の引張軟化特性を考慮した2次元剛体バネモデル解析手法を開発し，本解析法が所要の精度を有することを確認した上で，平均ひび割れ幅の評価法を検討した．

ミクロからメソスケールまでの材料の微細構造とそれらに対する現象論的仮定に基づき，モルタルの変形を，弾性，粘弾性，粘塑性特性を有する非ひび割れ成分とひび割れ成分とに分離した．さらに，各変形成分に対して実験的事実に基づいた力学モデルを導入し，剛体ばねモデルの時間依存型構成モデルを構築した．また，荷重増分法による構造解析に対する新しい破壊判定法により，疲労，クリープ荷重下で材料が破壊に至るまでのプロセスを追跡可能とした．本論文では，ひずみ速度を変数とした単調載荷解析，作用応力比を変数とした疲労およびクリープ解析を行った．その結果，時間依存荷重を受けるモルタルの種々の力学的挙動の再現，残存強度変化の評価に成功した．また，メソスケールにおける力学的挙動から，モルタルの時間依存破壊メカニズムを検証した．

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.

本研究では，NaCl溶液へのセメントペーストおよびモルタルの2ヶ月間の短期間浸漬実験を行った後，３点曲げ試験および化学分析を行った。その目的は，曲げ試験から得られた荷重－変位関係から逆解析により，メソスケール解析に適用可能な引張軟化曲線を同定し，化学分析により同定した供試体中の水和物量との両者の関連性を評価することにある。最終的に，水和物の減少に伴う，セメントペーストとモルタルの引張強度，弾性係数，破壊エネルギーの変化を捉えることができた。さらに，水和物の影響を含めた引張軟化曲線のモデル化を行った。

This paper presents numerical simulation of the tension behaviour of reinforced concrete (RC) members strengthened with externally bonded carbon fiber sheets (CFS) by using two dimensional (2D) rigid body spring model (RBSM). A non-linear RC model strengthened with CFS with bond-slip relations to model the concrete, steel reinforcement interface and concrete, externally bonded CFS interface, and simple models for bond deterioration due to cracking was embedded in the RBSM code that was developed by the authors. Comparison between the RBSM prediction and experimental results shows good agreement. The CFS has shown significant change in the bond stress and average stress of steel reinforcing bar and concrete. In addition the CFS has reduced the crack spacing and gave good crack width control.

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.

ひび割れがコンクリートの中性化の進行に及ぼす影響をについて,材料内の熱水分同時移動を考慮可能な中性化進行予測モデルを用いた2次元解析により,周期的に酸性雨を受ける条件下について検討した.幅04mm,深さ20mmのひび割れ近傍における解析の結果,ひび割れが含水率分布に及ぼす影響は,ひ囎1れの中心線から10mm以内の範囲であった。ひび割れの中心線から数mm以内の範囲における中性化の進行は,ひび割れも酸性雨もない場合に比して,2.38倍の促進される結果となった。

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.

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。

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.

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。

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.

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。

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.

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。

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.

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&lt;SUB&gt;24&lt;/SUB&gt;] as well as hybird specimen [0&lt;SUB&gt;12&lt;/SUB&gt;/T/0&lt;SUB&gt;12&lt;/SUB&gt;] were prepared to compare the Model II interlaminar fracture tough-ness. Here, the symbol &quot;/T/&quot; 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。

本論文では, 光学的手法であるレーザースペックル法によって測定された, せん断補強筋を有するはりのせん断変形の実験結果を示している. それによれば, 曲げ変形に加え, 無視できないほどの大きさのせん断変形が, せん断ひび割れ部に集中して生じた局部的なせん断変形により, 生じていた. 実験結果に基づき, 変形を推定するための簡便な力学モデルを提案している. 提案モデルは, せん断変形を算定するためのトラスモデルと, テンションシフトによる付加的な曲げ変形を算定するためのモデルとからなっている. モデルは, 実験結果を精度よく推定できている.

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.

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。

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。

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.

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。

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.

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。

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。

本論文は, 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付着性状を実験的に明らかにし, その挙動および強度を予測できる手法を提示するものである. すなわち, 炭素繊維シートの付着長, 積層枚数, 付着幅, を実験変数とした付着試験を行い, その付着機構を実験的に明らかにした. さらに, 実験結果に基づき, 炭素繊維シートの付着応力-すべり-ひずみ関係の構築を行った. また, 付着応力-すべり-ひずみ関係を用いた数値解析に基づき, 炭素繊維シートの付着強度式を提案した.

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.

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 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.

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.

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.

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。

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.

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。

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.

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。

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.