Primary Study of Applicability of Plane-section Assumption of Shaped RC Columns

Adopting the element SOLID65 and LINK8 in the general finite element analysis software ANSYS and fiber model beam-column element based on finite element flexibility method respectively, the comparative analysis of the cross, L and T-shaped RC columns under compression, bending, shear and torsion with flange width-thickness ratio of 4:1 is carried out. The applicability of plane section assumption in the nonlinear analysis is discussed primarily, which shows that it is feasible on the whole for shaped RC columns with flange width-thickness ratio equal to or smaller than 4:1.     

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.     

Experimental Study on Shear Strength of High Strength Concrete Columns

On basis of the experiment on sixteen high strength concrete columns, their shear behaviors are analysed. The effects of shear-span ratio and axial compression ratio on failure behavior, cracking shear and shear strength are analysed. The authors have discussed the suitability of the design equations for shear strength in the code. This experimental study on shear strength of high strength concrete frame columns is the first one in this field at home and the results can be served as reference for the code of high strength concrete design.     

Shear resistant performance of RC columns subjected to vertical near-fault velocity pulse-like earthquake actions

The aim is to evaluate the seismic properties of ancient timber structure after strengthening and analyze the failure process and corresponding failure state. Based on the hysteretic behavior and energy dissipation principle of the dovetail column-frame strengthened with CFRP and Arches Brackets under the low reversed cyclic loading, the “potential of destruction-resisting” of the two energy-consuming components is obtained. The dissipated energy of each energy-consuming component under the various earthquake conditions is calculated combining with the shaking table test of ancient timber structure. The model of seismic damage evaluation of the two energy-consuming components is established on the basis of the “potential of destruction-resisting” and the dissipated energy. By means of the energy distribution coefficient, the relationship of the failure state between energy-consuming components and overall strengthened structure is discovered, and the model of seismic damage evaluation of the overall structure under the various earthquake conditions is presented. With the derived model of seismic damage evaluation, the failure coefficient of the energy-consuming components and the overall strengthened structure is quantitatively calculated. According to the failure state, the corresponding damage grade of overall strengthened structure is obtained. The results can provide a reliable theoretical basis for predicting the destruction before earthquake and re-reinforcement to the strengthened ancient timber structures after earthquake.     

Analysis on Seismic Capacity for RC Specially Shaped Columns in Different Horizontal Direction

With fiber beam-column element based on flexibility method of finite element, the RC specially shaped columns of different axial compression ratio under cyclic loading have been simulated and the analysis results have been compared in aspects of strength, stiffness and ductility in order to provide some suggestions for seismic-resistant design of specially shaped columns. The strength, stiffness and ductility of L,T-shaped columns are apparently different in different horizontal direction, but those of t-shaped column are close.     

柱失效方程中荷载相关特性对承载力抗震设计可靠度的影响

以竖向荷载和水平地震作用组合下的钢筋混凝土柱和钢柱为对象,研究了失效方程中荷载相关特性对柱承载力抗震可靠性的影响。根据现行《混凝土结构设计规范》和《钢结构设计规范》分析了不同柱弯矩轴力相关曲线的特性。结合多个框架结构实例,对比了柱失效方程中荷载相关曲线与规范考虑情形的异同。实例分析表明:水平地震和竖向荷载组合作用下,小偏压RC柱和工字型钢柱的荷载相关曲线与规范考虑的情形较为符合,均近似为负相关的直线;水平地震和竖向荷载组合作用下,大偏压RC柱的荷载相关曲线则与规范考虑的情形有较大出入,存在明显的正相关段部分。在此基础上,考虑失效方程复杂特性,依据已有的荷载和抗力变量概率模型,采用Monte Carlo法分析了水平地震和竖向荷载组合作用下柱的可靠性。结果表明:钢柱和小偏压RC柱的承载力抗震可靠度随轴压力荷载效应比值的变化幅度较小,与规范模式计算结果较接近;大偏压RC柱的承载力抗震可靠度随轴压力荷载效应比值的变化会有较大幅度波动,与规范模式计算结果差异较大;当轴压力荷载效应比值为负时,大偏压RC柱的承载力抗震可靠度会低于规范计算值较多,现行柱可靠性设计方法会偏于不安全。     

Stability Behavior of Shuttle-Shaped Steel Lattice Columns With Bending Moment

The stability behavior of shuttle-shaped steel lattice columns subject to combined axial force and bending moment was examined through elastic buckling analysis and geometrically and materially nonlinear analysis. Firstly, the concept of section stiffness variation ratio is proposed for shuttle-shaped lattice columns and the elastic buckling behavior is discussed. Then, the effect of bending moment on the stability behavior of lattice columns is investigated, with the emphasis on the development of axial stress, bending stress and shear stress. The influence of column component spacing and diaphragm thickness on the stability bearing capacity is also analyzed. It is shown that the elastic buckling mode of the lattice column is dependent on its section stiffness variation ratio; for lattice columns with C-shaped buckling mode, the reduction in stability bearing capacity caused by bending moment is smaller than that of columns with S-shaped buckling mode; the maximum stability bearing capacity of the lattice column can be achieved by adjusting the column component spacing, and the spacing corresponding to the maximum capacity is basically consistent with the critical spacing for transformation of C-shaped buckling mode and S-shaped mode; and it is more effective to increase the thickness of columns with S-shaped buckling mode to get larger bearing capacity.     

Analysis of Failure Mechanism of RC Structures with Specially Shaped Columns Affected by the Diaphragm

With the flexibility-based fiber model,the seismic behaviors of RC structures with specially shaped columns,designed according to the current code,are analyzed under unidirectional rare earthquakes using nonlinear dynamic analysis method.The beam strength is calculated with or without consideration of the diaphragm and its reinforcement.The results are compared and the conclusion has been drawn that the bending capacity of beams would be increased due to the effect of diaphragm and its reinforcement,and which would change the failure mechanism of RC frames under rare earthquake,especially in high intensity areas.Therefore the influence of the diaphragm should be considered during the seismic design of the type of structure.     

混凝土密柱石膏复合墙板结构性能及简化分析模型

对混凝土密柱石膏复合墙板的水平剪力传递机理进行分析,发现石膏板肋能有效地在混凝土芯柱间传递水平剪力,对复合墙板结构性能有较大影响。在此基础上,提出混凝土密柱石膏复合墙板的等效带缝剪力墙简化分析模型,剪力墙竖缝布置以保证等效带缝剪力墙与复合墙板具有相同弹性抗侧刚度为原则确定。对混凝土密柱石膏复合墙板及等效带缝剪力墙的结构性能进行比较分析表明,混凝土密柱石膏复合墙板与带缝剪力墙受力机理相似,等效带缝剪力墙弹性及塑性阶段都能很好地反映混凝土密柱石膏复合墙板的结构性能。     

Strain rate effects on dynamic behavior of reinforcement concrete columns with various reinforcement ratio

The mechnical characteristics of concrete is sensitive to the strain rate and it is crucial to consider the effect of load rates on the behavior of reinforced concrete (RC) structures subjected to dynamic loads such as severe earthquakes. In this study, numerical simulations on the dynamic behavior of typical RC column specimens under dynamic loadings with different load rates were performed. Concrete constitutive model considering the strain rate effects proposed by the CEB code was employed with a fiber model to characterize the nonlinear strain rate dependent behavior of RC columns. The developed dynamic fiber element model was validated by comparing the simulated results of four RC column specimens with the fast loading test results. Results show that the developed fiber element model can predict the behavior of RC columns with acceptable accuracy. After valiating the proposed fiber elemen model considering the strain rate effect, the load carrying capacity of different RC columns with various longitudinal reinforcement ratios and volumetric stirrup ratios were simulated. Results show that the trends of the influences of longitudinal reinforcement ratios and volumetric stirrup ratios on the load carrying capacity of the RC columns under dynamic loadings are different.     

Influence Factors Study of Bearing Capacity of T Shaped RC Steel Reinforced Concrete Short-pier Shell Wall

In order to ensure that the T shaped steel reinforced concrete short-pier shear wall ductile shear failure occurs, the failure mechanism on the basis of experimental research, using ANSYS finite element analysis software to simulate the failure mode. In the process of analysis considered the influence factors of horizontal steel reinforcement ratio, concrete strength, axial compression ratio and the content of steel. The results show: the level of reinforced volume reinforcement ratio, concrete strength and the content of steel can obviously change the the bearing capacity and ductility of components.     

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.     

Yield Displacement Calculation Method of High-Strength Concrete Shear Wall

It is assumed that concrete compressive stress of the cross-section compression zone is linear distribution when the cross-section of high-strength concrete shear wall reaches yield situation. Based on the plane section assumption, the yield curvature formula of shear wall section is obtained by using moment - curvature analysis method. The parameters affecting yield curvature of high-strength concrete shear wall are studied by using the yield curvature formula. The results show that longitudinal reinforcement yield strain is the most vital factor of the yield curvature in addition to axial load ratio. When axial load ratio is larger, both wing walls of shear wall section have larger impact. The yield curvature formula is presented, considering the impact of axial load ratio, boundary reinforcement yield stress and both ends of wing walls of shear wall section based on the regression analysis of calculation results. On this basis, the vertex yield displacement formula of high-strength concrete shear wall is proposed, and the calculation results of formula correspond well to the vertex yield displacement experimental values of the 12 high-strength concrete cantilever wall. The formula is also suited for the vertex yield displacement of comment concrete shear wall.     

Effect of Shear Lag on Structural Behaviours in Indeterminate Box Girders

A finite element method considering interaction betwee bending and shear lag deformation was proposed and the finite element formulations including the effect of shear lag was deduced. The effect of shear lag on structural behaviours in indeterminate box girders was studied in detail based on the proposed method. Firstly, the shear lag effects on deflection and the shear lag coefficients were analyzed for both determinate and indeterminate beams. The results obtained by using the proposed method were compared with those by using the analytical method. Finally, the effect of shear lag on redistribution of internal forces including shear force, bending moment, and additional bending moment due to shear lag in indeterminate box girder bridges was studied. It is found that the effects of shear lag on deflection and stresses at a cross section are obvious for both determinate and indeterminate beams, while the effect of shear lag on internal forces in indeterminate box girder bridges is small and may be neglected.     

Bearing Capacity of Bar-Reinforced Concrete-Filled Square Steel Tubular Short Columns After Fire

Based on the determined stress-strain relationship of steel and concrete after fire, a temperature field and mechanical model of bar-reinforced concrete-filled square steel tubular columns after fire was set up with using ABAQUS, and the model has been validated by testing results. Then this paper analyzed the side of section, bar ratio, fire duration time, steel ratio and material strength parameters on the bearing capacity of bar-reinforced concrete-filled square steel tubular columns after fire. It is found that fire duration time and side of section is the dominant factor. Lastly this paper puts forward a theoretical formula of bearing capacity of bar-reinforced concrete-filled square steel tubular columns after fire, for the post-disaster restoration and provides references for the reinforcement.     

Axial Force Stiffness Interaction in Seismic Analysis of RC Double Column Bridges

Earthquake induced dynamic axial force in reinforced concrete (RC) bridge bent columns will not only change the yield strength of the columns but also change their stiffness, which is seldom considered by the common lumped plasticity line model. Based on the fiber element model results that taking into account the influence of dynamic axial force on strength and stiffness simultaneously, the axial force stiffness interaction effect on the seismic responses of RC double column bridges was analyzed. The results show that, axial force stiffness interaction has a large effect on the seismic responses of the double column bridge in the elastic range, and it does not alter the ultimate capacity of the columns. Since the stiffness of the columns under compression and tension dynamic axial forces offset each other, the global displacement of bridge bent with equal columns is relatively unaffected by the axial force stiffness interaction, however, the differences of the column member forces are manifest. For the short column controls the global stiffness, the axial force stiffness interaction has significant influences on both the global displacement and member force responses. The influences become larger as the irregularity of the bridge bent increases, so the interaction between axial force and member stiffness should be sufficiently considered in seismic analyses.     

X形配筋增强高强钢筋异形柱边节点抗震性能试验研究

通过对核心区应用X形配筋增强的高强钢筋异形柱边节点和同等条件下未被增强的高强钢筋异形柱边节点进行拟静力试验研究,对比分析异形柱边节点的破坏特征、滞回曲线、承载能力、位移及延性、刚度退化、耗能能力等抗震性能指标。研究结果表明,配置HRB500高强钢筋异形柱边节点比配置600 MPa级的边节点承载能低,但滞回性能好,变形能力强,刚度退化推迟,耗能能力强;在核心区加入X形配筋,均可以改善高强钢筋异形柱边节点的破坏特征,使边节点抗剪能力、变形能力、耗能能力增强,刚度退化推迟,提高异形柱边节点抗震性能,配置HRB500高强钢筋的试件核心区应用X形配筋加强后抗震性能提高效果更好。     

Experimental Study on a Prestressed Frame of Two Spans Under Unsymmetric Load

By the experimental study on a full-dimensioned prestressed frame of two spans, the relative factors are analyzed such as relative height of equivalent compression zone in critical section, secondary moment, ratio of beam rigidity to column and development of cracks in the top of columns etc., which influence the moment distribution of the post-tensioned prestressed concrete frame from the side of internal force redistribution. It is believed that that the factors of relative height of concrete equivalent compression zone and secondary moment influence the moment modulation in most degree, and ratio of column rigidity to beam also plays a part in the moment modulation to some extent. Second, the plastic joints of frame with excessive spans exit in the span which endure the whole load, at last the whole frame is destroyed because of the destruction of the loading frame, the influence to the non-loading span is little.     

THE EVALUATION OF SHEAR STRENGTH TAKING ACCOUNT OF SPAN-TO-HEIGHT RATIO OF SIMPLE BEAMS UNDER UNIFORM LOADS

By introducing the span-to-height ratio,this paper deduces wo evaluating equations of shear strength of simple reinforced concrete beamwith stirrups and under uniform loads.This makes the shear stressing concept consistent with the evaluating equations,thus improves the evaluating equationsof shear strength of the New Code.Two equations are provided with auto-regulating function on shear strength for a cross section of beam.They aresimple and convenient in evaluation.The working time used for design is not increased and 10% of stirrups is economized in frequent conditions of span-to-height ratio.     

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.