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.     

Experimental study on seismic behavior of beam-column sandwich joints with big beam-column eccentricity

Three specimens of sandwich joints with eccentricity being larger than a quarter of the column width in middle floor of frame are designed and loaded under cyclic loading. Their shear capacity, failure modes, and ductility, as well as energy dissipation are analyzed. The results show that the performance of sandwich joints with big eccentricity is good under cyclic loading. X-type reinforcements can be used to substitute for stirrups in the joint to bear shear forces. But the anchorage of longitudinal bars of beams in eccentric sandwich joints is relatively weak. Comparing to sandwich joints without eccentricity, the column longitudinal bars near the sandwich joints with big eccentricity are vulnerable to sudden change of strain.     

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.     

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.     

Design Approach on Flexural Load-carrying Capacity of Steel Beam to CFST Column Joints with External Stiffening Ring

A 3-D finite element model is established by ABAQUS to simulate the behavior of the joints with concrete-filled steel tubular (CFST) column to steel beam using external stiffening ring.The load versus deformation curves of this type of joints are compared between theoretical and experimental results,and in good agreement.Parametric analysis is performed to study the flexural load-carrying capacity of the joint.The width of external stiffening ring,the steel ratio of CFST column,the ultimate strength of steel beam,the strength of steel tube and beam,the concrete strength,the axial load ratio,and the beam to column linear stiffness ratio are considered as parameters.The simplified practical design approach is proposed based on parameter analysis of the flexural load-carrying capacity of these joints.The practical calculated values are in good agreement with the FEM results.     

Test Analysis on Prestressed Frames with Three Kinds of Beam-column Section Strength

"Strong column with weak beam","strong beam with weak column" and"column & beam with equal strength"can be existed in one-storey prestressed concrete frames and the top storey of mult-storey prestressed concrete frames.Through the test of four prestressed concrete frames under vertical load,three kinds of prestressed concrete frames performances are studied,such as ultimate load,deflection,displacement ductility,redistribution of internal force.When the relative height of equivalent compression zone is smaller enough,the test proves that three kinds of prestressed concrete frames can realize full redistribution of internal force and have better displacement ductility,the width of cracks and deflections can satisfy the rules of code for design of concrete structures.     

Test and Finite Analysis to Non-strong Column and Weak Beam Concrete Frames

Through the test of two concrete frames under vertical load and nonlinear finite programme analysis,the performances of strong beam with weak column and equal strength column and beam are studied,such as ultimate load,deflection,displacement ductility,redistribution of internal force.When the reinforcement is proper,the research proved that strong beam with weak column" and "equal strength column and beam" have better displacement ductility and can realize full redistribution of internal force,the width of cracks and deflections can satisfy the rules of code for design of concrete structures.     

Nonlinear Finite Element Analysis of Reinforced Concrete Transferring Joints with Inclined Columns

A nonlinear finite element analysis using ANSYS is applied to the vertical mechanical behaviors of three specimens of reinforced concrete transferring joints with inchned columns, which are used in high - rise buildings. A comparison is made between the analytical achievements and the test results, including the mechanical behaviors, load - transferring path and the failure modes, and a good agreement is obtained. The reliability of the software ANSYS in the nonlinear analysis of such reinforced concrete structures is verified and developed.     

Analysis on the Force-Transferring Mechanism of the Earthquake-Resistant Reinforced Concrete Frame Joints

On the basis of a summary of achievements from a large quantity of experimental studies both at home and abroad, in combination with the authors'experience in the experimental works on the reinforced concrete frame joints, their force-transferring characteristics are fully studied. The important fact that there is also a confined mechanism besides the inclined compressive strut and the truss mechanisms,is clearly pointed out. The influences of the three mechanisms upon the mechanical behaviors of the joint core concrete, the transverse and the vertical reinforcements,as well as upon the failure characteristics of the joint are also explored. Mechanical behaviors of the inclined concrete compressive strut and the factors causing its failure are specially discussed. These analyses provide theoretical bases for establishing more rational earthquake-resistant design criterion for reinforced concrete frame joints.     

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.     

RC加气混凝土砌块组合墙加固框架抗震性能试验研究

RC加气混凝土砌块组合墙（简称组合墙）是由混凝土梁柱网格与加气混凝土砌块组合形成的一种轻型网格式抗震墙,可用于框架结构的抗震加固。笔者进行了1/2比例空框架试件、组合墙试件和组合墙加固框架试件的低周反复荷载试验,分析了各试件的主要破坏过程,对比了组合墙加固框架前后试件承载能力、刚度等抗震性能变化。试验结果及分析表明：组合墙加固框架后承载力、抗侧刚度有较大幅度提高,中大震及大震阶段其承载力、等效刚度约为空框架和组合墙单独受力之和的0.9倍,两者具有良好的协同工作性能;加固试件的破坏过程基本上遵循填充砌块混凝土框格外框架的破坏顺序,能够发挥组合墙多重抗震防线的特点,采用RC加气混凝土砌块组合墙加固框架是一种较为经济实用的加固方法。     

粉煤灰对高强混凝土收缩徐变的影响试验研究及其修正模型

粉煤灰对高强混凝土收缩徐变的影响直接关系到结构长期性能的合理确定。制作粉煤灰掺量分别为0、12%和24%的100 mm×100 mm×400 mm的C50混凝土棱柱体试件,在试验室条件下进行收缩及不同加载龄期的徐变试验,研究了粉煤灰对高强混凝土收缩徐变的影响。根据试验结果评估了目前常用的4种相关规范公式对高强混凝土收缩徐变的适用性,并引入粉煤灰影响系数以综合反映粉煤灰掺量和加载龄期对高强混凝土收缩徐变的影响,根据试验结果和现有研究成果提出了其修正模型。分析结果表明,JTG D 62和GL 2000推荐的收缩徐变预测模式与基准试件实测结果较为吻合,验证结论亦说明所引入的粉煤灰影响系数可应用于掺粉煤灰高强混凝土的收缩徐变预测。     

Nonlinear Finite Element Analysis for Seismic Performance of High - Strength Concrete Beam -Column Joints with New Reinforcement Details

Because the factors that affect the behavior of the beam-column joints are complicated,an experimental study alone is not sufficient.Therefore,a nonlinear finite element analysis was conducted to provide better understanding of the performance of the beam-column joints.The authors intend to do the parameter study with nonlinear finite element method after a lot of high-strength concrete beam-column joints have been experimented.In this paper,the analytical model firstly was applied to simulate the experimental joint behavior and the comparison results were very well.Based on this,the parametric analysis of concrete strength on seismic performance of beam-column joints has been conducted.     

Experimental Analysis on the Behavior of Panel-to-lumber NailedJoints in Light Wood Frame Construction

To study their resistance performance, totally 222 specimens of panel-to-lumber nailed joints, in different configurations and used in light wood frame construction, were manufactured and tested under monotonic load. There are five kinds of destruction produced with nailed joints,which are model M-c1, rupture of panel, shear failure of panel, wood tear-off and push-through of nail. The resistance of nailed joints with vertical nailing is higher than that with toe-nailing, while the stiffness is almost the same. The angle between the panel orientation and dimension lumber wood grain affects the resistance and the stiffness of nailed joints little, while the angle between loading and dimension lumber wood grain affects the stiffness but not the resistance. The empirical equations to calculate the stiffness of the nailed joints are derived, thus providing reference for evaluating the performance of shear walls and diaphragm (floor and roof) in design of light wood frame structures.     

A Model Analysis to Beam Bar Slippage of Seismic Structure Joints

Many experimental results indicates, beam bar slippage within joints is a frequent local nonlinear response of reinforced concrete structures under the rare earthquakes. For the sake of modeling and evaluating seismic behaviors of reinforced concrete structures entirely and rational, the model way of the quantity and hysteresis order of beam bar slippage within joints, which was found in the elasto plastic earthquake response of structures, is discussed thoroughly. And the personal characteristics of several structure analysis ways to model the beam bar slippage within joints are evaluated respectively. Based on the results already gotten, a hysteresis model of beam bar slippage within frame joints is advanced, and the relative issues are also discussed. The beam bar slippage model suggested is convenience to the elasto plastic dynamic response analysis of whole reinforced concrete structures.     

内框架箱型混凝土结构施工活荷载实测分析

施工期早龄期钢筋混凝土结构与模板支撑系统组成临时承载体系为时变结构,其承担的荷载主要有新浇筑混凝土自重与包括施工人员和设备荷载以及混凝土浇筑时产生的冲击和振捣荷载在内的施工活荷载。将多层连续施工时变结构体系模拟成一组弹性支撑连续板,根据该模型分析了施工期现浇钢筋混凝土结构的受力特性。根据现场实测数据,以构件有效承载面积为统计对象,计算了混凝土施工荷载的统计参量,并参考相关研究成果,以95%的置信度对施工期活荷载标准值进行反演,建议施工活荷载标准值取2.5 kN/m 2。     

Seismic Characteristics of Widened Beam Flange Joints

In order to analyze the seismic behavior of widened beam flange joints, 16 specimens were derived from finite element models base on experiments. The effects of some parameters, such as the increased width and length, on ultimate load and ductility performance of joints were further discussed with ANSYS finite element method. According to specimen failure phenomenon of both experiment and finite element method, the weak link of the joints was found and the cracking possibility was evaluated. A theoretical analysis of the fracture mechanism of widened beam flange connection was conducted. In addition, design method of widened beam flange parameters was introduced, which will offer valuable information and reference for seismic design in steel frame joints.     

Failure Mechanism and Mechanical Properties of CFRP Strengthened Super-servicing Reinforced Concrete Poles

Super-servicing reinforced concrete poles (RCP) which come from a road section in a power grid, including six pole shafts and six specimens with a mid-span steel joint, were selected as samples to conduct a flexural strength test, in which three shafts and three poles with steel joint in the middle span were strengthened by CFRP in the longitudinal direction. The mechanical behavior and failure mechanism under different CFRP layers pasted were comparatively studied. Based on the measured test data, the calculation methods of strength and stiffness were investigated, and the mathematical expression of stiffness degradation mechanism was proposed. The result shows that the final failure mode of CFRP strengthened poles is the local bond failure between CFRP material and the external concrete, and the longitudinal CFRP is snapped. The process of damage is rapid and brittleness. The mean strain of cross-section is in accord with the assumption of plane cross-section. The strength degradation of shaft specimens without strengthened is throughly serious. As for the strengthened poles, the bearing capacity and stiffness under each forcing stage are improved with different levels. The damage of strengthened specimens develops faster and more intensive than that of none-strengthened ones. When multi-aspects are synthetically considered, there is a suggestion that double layers of CFRP should be pasted along the longitudinal in the joint of the site within a certain distance, and the single layer of CFRP should be adopted in the shaft.     

Study of Cracks on Rubber Concrete Beams Based on Fractal Theory

The flexural performances of a rubber concrete beam and a ordinary concrete beam are studied under concentrated load through the experiment. The influences of the content of the rubber powder in the rubber concrete beam on the bearing capacity and the crack width of beams are analyzed. The experimental results show that the crack distributions on two beam surfaces possess the characteristics of self-similar in statistical sense. The maximum crack width of the rubber concrete beam is less than that of the ordinary concrete beam under the same load level. The performance of anti-crack of the concrete beam is improved by adding the crumb rubber. Using the fractal theory, the fractal dimension values of the surface crack of the beams under different load grades are calculated and the relationship between the fractal dimension and the maximum crack width of the surface cracks is established.     

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.