Performance of cross-shaped concrete columns confined by stirrups

The stress-strain curves of confined concrete were obtained based on tests of seven cross-shaped columns confined by stirrups under axial load. The experiment results showed that the strength and deformation of confined concrete can be enhanced effectively by stirrups for cross-shaped columns. Compared with the non-confined concrete, when the stirrup characteristic value is in the range of 0.046--0.230, the confined concrete compressive strengths has an increase of 8%--43%, and the strain corresponding to the peak stress of confined concrete has an increase of 25%-- 195%. According to the test results, the effects of stirrup characteristic and stirrup spacing on the compressive strength and strain of confined concrete were analysed. It is shown that the compressive strength of confined concrete has a linear relationship with the product of stirrup characteristic value and stirrup effective restraint coefficient, and the strain corresponding to the peak stress of confined concrete has a nonlinear relationship with the product of stirrup characteristic value and stirrup effective restraint coefficient. The stress-strain curve equation of confined concrete was proposed for cross-shaped columns, and the calculated curves are in good agreement with the experimental curves.     

Seismic ductility of very-high-strength-concrete short columns subject to combined axial loading and cyclic lateral loading

The seismic ductility of reinforced very-high-strength-concrete (VHSC) short columns was studied by combinatively applying axial load and low cyclic lateral load on specimens to simulate seismic impact. Twelve specimens with concrete compressive strength ranging from 95.6 MPa to 118.6 MPa and a shear-span ratio of 2.0 were tested for shear failure pattern and fear force-displacement hysteretic responses. Combinative application of axial load and low cyclic lateral load to VHSC short columns incurs shear failure. The displacement ductility is much smaller when the axial load ratio is larger;whereas a larger stirrup ratio is accompanied with a better displacement ductility. The relationship of displacement ductility factor, μ?, with stirrup characteristic value, λv, and test axial load ratio, nt, is μ?=(1 8λv)/(0.33 nt). By this relationship and relevant codes for aseismatic design, the axial load ratio limits for aseismatic design of reinforced VHSC (C95 to C100) short columns for frame construction are respectively 0.5, 0.6, and 0.7 for seismic classes I, II, and Ⅲ;corresponding minimum characteristic values of stirrups are calculated according to the required characteristic values of at least 1.273 times of experimental results. These data are very useful to aseismatic engineering.     

混凝土异形柱构造配箍图的制作

《混凝土异形柱结构技术规程（JGJ149—2006）》提出按照最小配箍特征值确定箍筋加密区体积配箍率要求,相应箍筋配置方案需通过计算求得,应用不便。按《规程》要求,根据异形柱的抗震等级、截面形式与尺寸、混凝土强度等级、轴压比的大小,给出了具体的箍筋配置方案,并形成图表,方便设计人员设计、核查。     

高强砼框架柱抗震性能的试验研究

本文采用框架加荷系统对高强砼柱进行了反复荷载下的试验。以位移延性系数为指标,对影响高强砼柱延性的各因素进行了分析,提出了高强砼柱轴压比的限值和柱加密区箍筋最小体积含箍率的建议值,对高强砼偏心受压柱强度计算的基本假定进行了修正。供设计人员参考。     

Seismic behavior of steel reinforced ultra high strength concrete column and reinforced concrete beam connection

To investigate the seismic behavior of connections composed of steel reinforced ultra high strength concrete （SRUHSC） column and reinforced concrete （RC） beam, six interior strong-column-weak-beam connection specimens were tested subjected to reversal cyclic load. Effects of applied axial load ratio and volumetric stirrup ratio on ductility, energy dissipation capacity, strength degradation and rigidity degradation were discussed. It was found that all connection specimens failed in bending in a ductile manner with a beam plastic hinge. The ductility and energy dissipation capacity increased with the decrease of applied axial load ratio or increase of volumetric stirrup ratio. The displacement ductility coefficient and equivalent damping coefficient lay between those of steel reinforced ordinary concrete connection and those of reinforced concrete connection. The applied axial load ratio and volumetric stirrup ratio had less influence on the strength degradation and more influence on the stiffness degradation. The stiffness degraded sharply with the decrease of volumetric stirrup ratio or increase of applied axial load ratio. The experimental results indicate that SRUHSC column and RC beam connection exhibited better seismic performance and can provide reference for engineering application.     

焊接高强箍筋高强混凝土柱滞回特性研究

以2根焊接高强箍筋、高强混凝土柱试件为研究对象,进行低周反复水平荷载作用试验,研究体积配箍率的变化对柱滞回特性的影响.试验结果表明,高强混凝土柱体积配箍率较大的试件滞回曲线相对饱满,滞回环面积较大,累积滞回耗能大,吸收地震能量多,延性好.该研究结果对发展应用高强混凝土具有实际意义.     

Mechanical Behavior of Rectangular Steel-Reinforced ECC/Concrete Composite Column under Eccentric Compression

In order to improve the seismic performance, deformation ability and ultimate load-carrying capacity of columns with rectangular cross section, engineered cementitious composite(ECC) is introduced to partially substitute concrete in the edge zone of reinforced concrete columns and form reinforced ECC/concrete composite columns.Firstly, based on the assumption of plane remaining plane and the simplified constitutive models, the calculation method of the load-carrying capacity of reinforced ECC/concrete columns is proposed. The stress and strain distributions and crack propagation of the composite columns in different states of eccentric compressive loading are analyzed. Then, nonlinear finite element analysis is conducted to study the mechanical performance of reinforced ECC/concrete composite columns with rectangular cross section. It is found that the simulation results are in good agreement with the theoretical results, indicating that the proposed method for calculating the load-carrying capacity of concrete/ECC composite columns is valid. Finally, based on the proposed method, the effects of ECC thickness, compressive strength of concrete and longitudinal reinforcement ratio on the mechanical performance of reinforced ECC/ concrete composite columns are analyzed. Calculation results indicate that increasing the thickness of ECC layer or longitudinal reinforcement ratio can effectively increase the ultimate load-carrying capacity of the composite column with both small and large eccentricity, but increasing the strength of concrete can only increase the ultimate loadcarrying capacity of the composite column with small eccentricity.     

FRP加固RC圆柱正截面受弯承载力计算（英文）

运用数值计算方法对FRP加固钢筋混凝土（RC）圆柱截面特性进行计算,发现截面破坏时受压区高度主要受轴压比、FRP约束强度比和纵筋配筋特征值3个主要参数影响.根据数值计算的结果进行回归,提出了受压区对应圆心角θ的计算方法.数值计算结果显示,横向约束导致的混凝土应力提高以及纵筋屈服后的强化效应使RC柱破坏时截面受弯承载力远大于规范规定值.根据理论分析和36个大比例试件实测结果提出截面破坏时受弯承载力计算方法,计算结果与试验结果吻合很好.最后,对一个典型柱变形能力进行参数分析,研究轴压比,纵筋配筋特征值和FRP约束强度比对正截面变弯承载力的影响.结果显示FRP加固圆柱破坏时受弯承载力可以比规范规定的未加固柱受弯承载力提高50%左右.     

Replacing stirrups of self-compacting concrete beams with steel fibers

Based on the investigation of fiber influence on workability of self-compacting concrete (SCC), tests were carried out on two series of SCC rectangular simply supported beams, which were made of hooked steel fibers reinforced concrete with or without stirrups, subjected to four-point symmetrically placed vertical loads. The major test variables are steel fiber contents and stirrup ratios. The results indicate that the ultimate load significantly increases with the increase of fiber content; the addition of ...     

Shear behavior of novel prestressed concrete beam subjected to monotonic and cyclic loading

Prestressed steel ultrahigh-strength reinforced concrete (PSURC) beam is a new type of prestressed concrete beam, which not only has a considerable compressive strength attributed to the ultrahigh strength concrete, but also ensures a certain degree of ductility at failure due to the existence of structural steel. Five of these beams were monotonically tested until shear failure to investigate the static shear performance including the failure pattern, load-deflection behavior, shear capacity, shear crack width and shear ductility. The experimental results show that these beams have superior shear capacity, crack control ability and shear ductility. To study the shear performance under repeated overloading, seven PSURC beams were loaded in cyclic test simultaneously. The overall shear performance of cycled beams is similar to that of uncycled beams at low load level but different at high load level. The shear capacity and crack control ability of cycled beams at high load level are reduced, whereas the shear ductility is improved. In addition, the influences of variables including the degree of prestress, stirrup ratio and load level on the shear performance of both uncycled and cycled beams were also discussed and compared, respectively.     

碳纤维布约束高强混凝土的研究

基于 8个碳纤维布约束高强混凝土棱柱体试件的试验 ,研究了碳纤维布对提高高强混凝土抗压强度和改善其变形性能的作用 .试验发现 ,包裹碳纤维布可以提高试件的抗压强度 ,并有效地改善混凝土的变形性能 ,其效果随碳纤维用量的增加而更加显著 .在试验基础上 ,根据理论分析和对试验结果的整理 ,归纳出碳纤维布约束高强混凝土的应力 应变全曲线方程 .最后 ,利用提出的全曲线方程编制计算机程序 ,分析了包裹碳纤维布对提高高强混凝土压弯构件的强度和延性的作用     

钢管混凝土双肢格构墩梁桥抗震优化设计

以黄桷湾特大桥为工程背景,选取轴压比、梁墩刚度比、系梁布置形式及柱肢混凝土强度等级为设计参数,应用Midas Civil有限元软件构造了20座三跨对称桥梁计算模型。研究E1地震作用下钢管混凝土双肢格构墩连续梁桥主要控制截面参数地震响应,探讨各设计参数对钢管混凝土双肢格构墩连续梁桥抗震性能的影响规律,并对全桥进行优化验证。研究结果表明:轴压比对地震作用下结构内力和位移有一定影响,建议控制在0.15~0.25;梁墩刚度比对结构的抗震性能影响较大,控制在4.08~10.90时结构的内力分布更加合理;核心混凝土的强度在C40~C50时取值较为合理。     

Seismic behavior of confined RC column-composite beam joints

In order to evaluate the seismic behavior of confined RC column-composite beam joints, five interior joints were tested under low cyclic reversed load. The weakening extent of flanges, the number of studs, and whether to reinforce weakened flanges were used as parameters in designing these five joints. Failure characteristics, hysteretic curves, skeleton curves, ductility, energy dissipation, strength degradation, and stiffness degradation were analyzed. The test results revealed that the steel beam flanges in the joints were equivalent to the tie rod. Weakened flanges resulted in poor seismic behavior; however, the seismic behavior could be improved by increasing studs and reinforcing weakened flanges. The joint steel plate hoops, equivalent to stirrups, did not yield when the maximum load was reached, but yielded when the failure load was reached for the joints with shear failure. Increasing stud-type joints and reinforcing flange-type joints ensured good seismic behavior and met project requirements. Based on the experimental results, the failure mechanism of the joints was discussed, and the shear capacity equations of the joints was presented.     

Model Experiment on Integral Seismic Behavior of Reinforced Concrete Frame with Split Columns

Based on a series of previous studies, an experiment on the integral seismic behavior of a 1/3 scaled model of two-bay and three-story reinforced concrete frame with split columns at lower two stories is performed under cyclic loading. The original columns at lower two stories of the model frame are short columns and they are replaced by the split columns. The hysteresis curves between the horizontal cyclic load and the lateral displacement at the top of the model frame, indicate that under the cyclic loading, the model frame undergoes the process of cracking, yielding, and maxi-mum loading before being destroyed at the ultimate load. They also indicate that the model frame has better ductility, and the ratio of the ultimate displacement to the yielding displacement, reaches 6.0. The yielding process of the model frame shows that for the frame with split columns, plastic hinges are generated at the ends of beams and then the columns begin yielding while the frame still possesses the bearing and deformation capacity. The design idea of directly changing the short col-umn to long one in the reinforced concrete frame may be realized by replacing the short column with the split one.     

高强混凝土的研制及其抗压抗拉强度关系的建立

笔通过多次试探试验,配制出40组高强度等级混凝土立方体试块,并分别测定其抗压与抗拉强度数值,经回归分析得出高强混凝土立方休抗压强度fcu与抗拉强度ft．s的关系表达式：ft．s=0．1457 0．0678fcu。     

C90级粉煤灰高强混凝土的研制

本试验采用优质粉煤灰作为活性矿物掺合料代替等量水泥,通过低水灰比,成功研制出C90级高强混凝土,其流动性大,坍落度损失小,早期强度高,适合于高层建筑施工。     

Analysis and behaviour of FRP-confined short concrete columns subjected to eccentric loading

Fibre-reinforced polymer （FRP） composites were widely utilized in civil engineering structures as the retrofit of reinforced concrete （RC） columns. To design FRP jackets safely and economically, the behaviour of such columns should be predicted first. This paper is concerned with the analysis and behaviour of FRP-confined RC circular and rectangular short columns subjected to eccentric loading. A simple design-oriented stress-strain model for FRP-confined concrete in a section analysis was first proposed. The accuracy was then proved by two test data. Following that, a parametric study including amount of FRP confinement, FRP strain capacity, unconfined concrete strength and shape of column section is provided. Some conclusions were obtained at the end of the paper. The work here will provide a comprehensive understanding of the behaviour of FRP-confined concrete columns. The simplicity of the model also enables a simple equivalent stress block to be developed for direct use in practical design.     

关于钢筋混凝土框架短柱的几点讨论

框架柱因其剪跨比较小而多属于短柱甚至超短柱。本文准确给出短柱判定条件,分析了钢筋混凝土短柱和超短柱在水平地震荷载作用下的破坏模式,针对短柱的变形能力和延性差、从而导致框架结构的整体抗震性能下降的问题,建议改善其抗震性能的各种有效措施,其结论可为工程设计人员提供参考。     

型钢高强混凝土柱抗震性能的非线性有限元分析

采用ANSYS软件进行了数值模拟,分别对比了三种型钢截面形式和i种轴压比对型钢高强混凝土柱的延性和耗能性能的影响。从计算结果可以看出,轴压比越小,延性系数越大,抗震性能越好;带翼缘十字形型钢柱的延性比不带翼缘十字形型钢柱的延性好。     

Bearing capacity and failure mechanism of ground improved by deep mixed columns

Extensive research has investigated the bearing capacity of footings placed on leveled ground improved by deep mixed (DM) columns. However, few studies have focused on the effects of the embedment on the bearing capacity of footings on ground reinforced with DM columns. In geotechnical engineering practice underestimation of the limit load has occurred in China because of the increased use of conventional design methods for reinforced ground with embedment. In this investigation, a numerical model using a rigorous limit analysis tool, known as discontinuity layout optimization (DLO), is established. An equivalent area model is employed with an appropriate stress concentration ratio. Subsequently, a set of design charts of bearing capacity coefficients is produced with a special focus on the bearing capacity coefficient N_q and the failure mechanism. The results show that three failure patterns exist in the composite ground reinforced by DM columns. For cases without embedment, the bearing capacity coefficient N_c increases with the area replacement ratio to a certain value due to the occurrence of general shear failure mechanism. The bearing capacity coefficient N_γ decreases with the area replacement ratio, as the equivalent frictional strength of the reinforced region is reduced. When the embedment is considered, the failure mechanism of composite foundation has a significant influence on the coefficient N_q. Specifically, increase of column length leads to a larger value of N_q when block failure is observed. When a general shear failure pattern occurs, the effect of additional column lengths on the coefficient N_q can be neglected.