Calculation Method of Shear Behavior of Hybrid Fiber Reinforced High Performance Concrete Deep Beams

The static tests on hybrid fiber (steel fiber and polypropylene fiber) reinforced high performance concrete deep beams according to the orthogonal experimental design were conducted. The shear capacity and calculation method of deep beams were discussed as well. The contributory factors such as the characteristic parameters of steel fiber (types, volume fraction, aspect ratio), the volume fraction of polypropylene fiber, the ratio of web horizontal reinforcement and the ratio of web vertical reinforcement were analyzed. Results show that the shear failure mode of deep beams is changed with adding a reasonable volume of hybrid fibers, and hybrid fiber can greatly increase the diagonal cracking strength and shear strength of HPC deep beams. The diagonal cracking strength is increased by 45.2% averagely while the shear strength is increased by 25.6% averagely. A satisfied result is obtained when the plasticity theory is used to analyze shear behavior of hybrid fiber reinforced HPC deep beams. The contribution of web horizontal reinforcement and web vertical reinforcement to shear strength of deep beams is not obvious but the former plays a major role. After analyzing the strengthening mechanism of hybrid fiber, a formula to calculate the shear capacity of hybrid fiber reinforced HPC deep beams is presented based on spatial strut-and-tie mode and splitting failure.     

Computational Model and Influencing Factor Analysis of Reinforced Concrete Walls under Fire

The finite element software ABAQUS is used to calculate the deformation of reinforced concrete walls under fire. The calculated results agree well with previous experimental results. Based on the finite element model, the influences of such parameters as axial load level, lateral load level, height-to-thickness ratio, wall thickness, concrete compressive strength, steel reinforcement yield strength, steel reinforcement ratio and concrete protection thickness on deformation and fire resistance of walls are analyzed systematically. It is found that, under the conditions of big axial load level or wall thickness without lateral load and small height-to-thickness ratio, the reverse deflection of reinforced concrete walls in fire is apt to occur. Within the work range of parameters in common use, the fire resistance of walls decreases with the increase of axial load level, lateral load level, height-to-thickness ratio, steel reinforcement yield strength or steel reinforcement ratio, and increases with the increase of wall thickness or concrete compressive strength.     

Experimental Analysis on Shear Strengthening Capacity of Secondary Dapped end Beams

Because section steel can only be extended to the edge of the support, when a simple support RC beam is reinforced by bonded section steel, a notch comes into being at the end of the beam which is called a secondary dapped end beam, making the stress state of the beam more complex. Through experimental analysis on 21 dapped end beam specimens shear reinforced by steel plate bonded, the deformation process, performing characteristics and failure mechanism of the specimens were investigated. The result shows that two steel bonded forms, including horizontal steel plate and oblique steel plate with angle 45° bonded, delay the appearance of cracks significantly and improve the maximum bearing capacity by 102% and 93%. Due to the impact of stress concentration at the notch, the main modes of damage include concrete tensile or shear failure with the result of bonding failure of a steel plate. By changing the width of steel plates and analyzing different reinforcement effects, formula of bearing capacity of shear reinforcement was proposed based on the method of truss analogue, which provides a reference for engineering application.     

Finite Element Analysis of Shear Behavior of Super High Strength Reinforced Concrete Beam

On the basis of testing results of shear behavior from 18 super high strength reinforced concrete restrained beams with web reinforcement, with the cube compressive strength ranging from over 100Mpa, in this paper, the nonlinear finite element analysis procedure was formulated and the analysis of the specimen tests was carried out with the parameters obtained from the experiments and improved constitutive model and failure criteria of materials. Based on the simulated shear resistance test results and practical measured data of eighteen super high strength concrete restrained beams under point load, the equation to compute the shear resistance capacity of such beams was thus obtained by regression. The analytical results agree well with those of experiments.     

方形高强钢管混凝土叠合柱轴压极限承载力分析

对于新提出的方形高强钢管混凝土叠合柱的极限承载力,基于统一强度理论,考虑中间主应力和材料拉压比的影响,引入有效约束系数和非有效约束系数并考虑箍筋对钢管外混凝土约束作用的不同,把钢管外箍筋约束混凝土划分为有效约束区和非有效约束区,将方形截面等效为圆形截面以考虑钢管核心混凝土受到的钢管和外围钢筋混凝土的双重约束效应,提出了方形高强钢管混凝土叠合柱的一种新的轴压极限承载力计算方法。将所得理论计算结果与文献试验结果进行对比,吻合良好,证明了公式的正确性。对各参数的影响规律分析表明,方形高强钢管混凝土叠合柱的承载力随着侧压系数、中间主应力影响系数、材料拉压比和纵向配筋率的增大而增大,随着钢管径厚比的增大而减小。     

Design Method of Reinforced Concrete Sandwich Beam column Joints

The experimental results of reinforced concrete sandwich beam column joints were studied intensively and finite element method simulation of such joints were performed for the sake of design method.Basic design criterion and computation contents were provided according to failure mode of specimens and other experimental results.And the limits of parameters were proposed based on the analysis of seismic behavior influence factors and comparison of traditional joints and sandwich joints.Hence, formulas of load resistant capacity were acquired by the results of load resistant capacity of specimens and nonlinear finite element method simulation.It is found that three measures should be taken for sandwich joints in order to reach demanded ductility and load resistant capability.Firstly, several parameters should be limited, including shear compression ratio, axial load ratio, ratio of beam concrete strength to column concrete strength, and minimal amount of transverse reinforcement of joint.Secondly, shear load resistant capacity and axial compressive load resistant capacity should be computed to ensure load resistant capability of joint, and essential strengthen measures could be applied if necessary.Thirdly, appropriate construction details should be taken to avoid reducing of beam bar anchorage capacity.     

Modeling and Its Application of Reinforced Concrete Columns Considering Nonlinear Shear Effects

A fiber beam-column element in conjunction with zero-length elements attached to its ends was proposed to simulate the flexural and shear mechanism respectively. Based on the Limit State Material model and the Shear Limit Curve model provided by OpenSees, the nonlinear shear effect of reinforced concrete column and its coupling with the flexural effect were defined. The reliability of the proposed model was validated by means of comparisons with existing test results. Finally, a plane frame from in-situ pushover test was simulated. It is shown that the proposed method, by taking the nonlinear shear effect into account, produces satisfactory results for frame columns with shear strength and stiffness degradation, while the conventional fiber beam-column element can hardly simulate actual flexure-shear failure mechanism for columns characterized by insufficient transverse reinforcement. The proposed method is applicable for nonlinear analysis of reinforced concrete frame structures with shear deficiencies.     

600 MPa高强钢筋与混凝土的粘结锚固性能试验研究

为研究600 MPa高强钢筋与混凝土粘结锚固性能,设计了72个棱柱体试件进行拉拔试验,对600 MPa高强钢筋粘结锚固的破坏形态及粘结应力分布进行分析,通过建立基本粘结滑移关系及位置函数,确定600 MPa高强钢筋在混凝土结构中的粘结滑移本构关系。采用一次二阶矩法进行可靠度分析,提出锚固长度设计建议。研究表明：600 MPa高强钢筋粘结锚固的破坏形态及粘结应力分布与普通钢筋类似且粘结锚固性能良好,《混凝土结构设计规范》（GB 50010—2010）基本锚固长度计算公式依然适用于600 MPa高强钢筋。     

CFRP筋钢筋混凝土剪力墙自复位性能试验研究

通过对1片钢筋混凝土剪力墙和4片配有碳纤维增强聚合物(CFRP)筋的剪力墙的低周反复荷载试验,在分析试验中测得的裂缝宽度、裂缝的发展和分布形态、侧向变形的基础上,研究了在钢筋混凝土剪力墙的适当位置部分或全部配置CFRP筋对剪力墙的残余裂缝和残余变形等自复位性能的影响规律。研究结果表明:与普通钢筋混凝土剪力墙相比,配有CFRP筋的剪力墙的开裂荷载较低,裂缝较多,裂缝分布分布范围较广,墙体的最大裂缝宽度、残余裂缝宽度和侧向残余变形分别降低了60%、70%和90%,说明在剪力墙中合理配置CFRP筋能使剪力墙具有优异的自复位性能。     

改性竹筋混凝土受弯构件力学性能试验研究

针对竹筋混凝土结构存在的问题,提出了多种对竹筋的改性方法。在此基础上,对12根采用不同配筋和不同改性方法的受弯构件(11根竹筋混凝土梁和1根钢筋混凝土梁)进行了试验研究,分析了不同改性方法和不同配筋率竹筋混凝土受弯构件的力学性能、破坏形态及其影响因素。研究结果表明：竹筋能有效提高混凝土受弯构件的承载能力;经过适当方法改性后的竹筋能确保竹筋和混凝土之间的有效粘结,其正截面强度计算可以采用平截面假定;竹筋混凝土受弯构件的破坏均为脆性破坏,其破坏形态与其截面配筋率有关。     

钢筋混凝土无腹筋细长梁剪切破坏机理模型研究综述

根据现有关于钢筋混凝土无腹筋细长梁剪切破坏机理问题的研究成果,介绍了基于修正压力场理论的抗剪模型、临界剪切裂缝理论、塑性理论、压力路径理论、劈裂破坏理论和基于截面应变分析的抗剪模型的基本假设、核心观点及受剪承载力计算方法,并给出总结、归纳及评析;另一方面,利用相关试验数据和ACI-DAfStb无腹筋细长梁剪切破坏数据库,分别对不同理论模型的受剪承载力计算公式进行了设计参数的影响评估和统计评估;并展望了无腹筋细长梁剪切破坏机理研究的发展方向。研究结果表明：不同理论模型的部分假设缺少直接的试验依据支持,梁腹混凝土的受拉（劈裂）或受剪（骨料咬合）以及受压区混凝土对抵抗剪力的贡献成为抗剪机制的主要分歧;不同受剪承载力计算公式对不同影响因素的考虑方式的合理性和计算结果的准确度均有待进一步提高。后续深入研究应综合考虑剪切破坏问题的随机性和物理属性,利用先进测试技术、应力演化分析方法,进一步揭示剪切破坏机理。     

Shear Ductility of Hybrid Fiber Reinforced High Performance Concrete Deep Beams

The shear tests were conducted on 18 different groups of deep beams with steel fiber and polypropylene fiber and two groups high performance concrete deep beams without fiber according to the orthogonal experimental design. By a definition of shear ductility index shear ductility of deep beams was analyzed quantitatively. The influence of six factors on improving shear ductility of deep beams was compared by direct-viewing analysis of the orthogonal experiment. The contributory factors such as the species of steel fiber, the volume fraction of steel fiber, the length/diameter aspect ratio of steel fiber, the volume fraction of polypropylene fiber, the ratio of web horizontal reinforcement and the ratio of web vertical reinforcement were analyzed. Results show that the volume fraction of steel fiber plays the most important role in improving shear ductility of deep beams exceeding the ratio of web horizontal reinforcement and the ratio of web vertical reinforcement, whereas species of steel fiber has minimum effect. Hybrid fiber can be used to greatly increase shear ductility of deep beams and shear ductility is at the most increased by 40.7% although it can not change the brittleness of shear damage. The full-range shear behaviors of deep beams through ABAQUS are analyzed and the calculated results are in good agreement with test results.     

Effect of Longitudinal Reinforcement Rate on Shear Behavior of Beams without Web Reinforcement Restriction

Previous researches on shear behavior of inclined sections in reinforced concrete beams used to be carried out on a comparatively high longitudinal reinforcement ratio in the codes of various countries.However,the shear design methods based on the data obtained from these researches may have distinguished deviations.This paper studies the shear behavior on a comparatively low longitudinal reinforcement ratio.Research has indicated that different longitudinal reinforcement ratios have significant impact on the shear behavior and the development of cracks in the beams,and the shear design equation in the code applied to beams without wed reinforcement restrained maybe not safe enough.     

Seismic Shear Strength of Concrete Hollow Block Masonry

According to some problems existed in current Chinese codes for design of seismic shear strength of concrete hollow block masonry, the curve of shear strength of concrete hollow block masonry under shear-compression loading, including descent segment, was presented by theory of failure region and test results of 58 concrete block masonry walls under shear-compression loading. And the design seismic shear strength formula of concrete hollow block masonry, which has reliability guarantee, was deduced. Compared with current Chinese codes, the design seismic shear strength formula of concrete hollow block masonry not only can perfectly simulate the shear-friction, shear-compression and diagonal compression failure modes, but also avoid unreasonable and unsafe calculation of seismic shear strength of concrete hollow block masonry, which can be applied to design of tall reinforced concrete masonry structures.     

Effect of Varying Longitudinal Reinforcement Ratios on Shear Behavior of Reinforced Concrete Beams Without Web Reinforcement

Effect of varying longitudinal reinforcement ratios on shear behavior of reinforced concrete simply supported beams without web reinforcement was analyzed in this paper, with emphasis on both shear ultimate capacity and failure mode, on the basis of available testing data. Generic laws were thus obtained and codified methods, including ACI Code and China Design Code of Reinforced Concrete Structures, were evaluated as a result.     

Experimental Analysis of Time-dependent Shear Behavior on Stud Connectors

With regard to the long span continuous composite beams, the early composite shear stud strength at the joint surface between the steel girder and concrete slab at different concrete ages should be considered while the concrete slabs are casted by phases in construction stage. In this study, the push-out test of stud shear connectors were conduced at different concrete ages. Meanwhile, the change law of the ultimate shear strength, ultimate slip deformation, design shear strength, and shear stiffness of the stud shear connectors with concrete ages were analyzed, and the corresponding time-dependent calculation equations were presented. The results include that the main failure modes of stud shear connectors are the concrete slab splitting failure before 3-days concrete age. The load-slip laws of stud shear connectors at different concrete ages are basically the same, however, the shear strength and stiffness all increase with the concrete ages prolonging, and the increase degree is faster at early ages, but slower at later ages, which indicates that the early composite shear stud strength at the joint surface of composite beams should not be neglected.     

Analysis of Fiber Renforced Concrete Beam-Column Joints Model

Due to the large stirrup ratio and reinforcement congest in beam-column joints, the ordinary reinforced concrete beam-column joints take inconvenience to construction. Cracked fiber renforced concrete (FRC) has strong bridge ability and better tensile performance so that it can replace part or all of the stirrups. Based on previous researches on resistance mechanism of reinforced concrete joints, a new model using FRC materials in the core zone of beam-column joints is presented. It is a kind of model in which horizontal shear supported by the diagonal strut mechanism and softening truss mechanism with a certain percentage. The calculation results of the model is compared with the existing test results. It is a bit conservative to specimens with low axial load ratio. However, the results are in line with the specimens with high axial load ratio. Therefore, the results totally demonstrate the rationality of the proposed model in this paper. Meanwhile, according to the proposed model, the shear capacity of beam-column joints can be not only calculated, it also check whether FRC compressive strength in core zone of joints and horizontal stirrup ratio meets design requirements, which has a higher practicability.     

Experimental and Parametric Analysis of the Flexural Behavior of HRBF RC Beams

In order to investigate the flexural behavior of concrete beams reinforced with high strength hot rolled bars of fine grains, static bending test on four rectangle cross section HRBF400, HRBF500 RC beams was conducted. The results show that the experimental maximum crack width under short term load meets the requirement of current code while calculated value does not meet; mid span deflection of RC beams with HRBF400 under short term load still meets the requirement of current code while RC beams with HRBF500 does not meet. Bearing capacity calculating formula under conditions of crack/deflection control was proposed and conception of component's bearing capacity utilization coefficient (BCUC) was put forward. The influences of reinforcement strength, reinforcement diameter, concrete grade, reinforcement ratio, concrete cover thickness and high span ratio on BCUC were analyzed. Within the range of economic reinforcement ratio, ductility of HRBF RC beams meets the requirement. Energy dissipation capacity of HRBF RC beams is similar to that of normal RC beams at low reinforcement ratio but it decreases faster than normal RC beams with the increasing of reinforcement ratio. Energy dissipation capacity of HRBF RC beams is higher than that of normal RC concrete beams in elastic stage and it enhances with the increasing of reinforcement ratio.     

Impact of Temperature in Air-conditioned Room on Blood Rheological Characteristics

Based on the reversed cyclic loading tests of 21 nearly full-size interior joints in completed reinforced concrete frames,the law of bond deterioration of beam bars crossing the joint is tested and analyzed,which is influenced by the axial load ratio,shear-compression ratio,reinforced bar strength,concrete strength and the relative length of beam bars crossing the joint. By the nonlinear fitting method, the formula of the bond stress r between steel crossing interior joints and concrete under different loading step is obtained. According to the loading approach, the propositional formula of the relative length of beam bars crossing the joint hc/d is presented, which is influenced by axial load ratio, shear-compression ratio ,reinforced bar strength and concrete strength.     

Experimental study on the mechanical behavior of eccentrically loaded steel tubular columns filled with structural steel and concrete

Considered strength classes of concrete, ratio of structural steel to concrete, ratio of steel tube to concrete and eccentricity ratio of load, 6 test specimens of steel tubular columns filled with structural and concrete are designed. The damage phenomena of specimens are described in detail and the failure mechanism is analyzed. The results show the initial failure of the specimens are began from the yield of steel tube, the ultimate failure are ended from the buckling of steel tube caused by the expansion of core concrete. Due to the existence of structural steel, the ductility of specimens is superior to steel tubular columns. Before the yield of steel tube, the plane cross-section assumption of specimens can be put into use. The ultimate bearing capacity of specimens is increased with the increase of strength classes of concrete, ratio of structural steel to concrete and ratio of steel tube to concrete. But the ultimate bearing capacity and ductility are decreased with the increase of eccentricity ratio.