Earthquake simulation test of circular reinforced concrete bridge column under multidirectional seismic excitation

Structures behave multi-directionally when subjected to earthquake excitation. Thus, it is essential to evaluate the effect of multidirectional loading on the dynamic response and seismic performance of reinforced concrete bridge columns in order to develop more advanced and reliable design procedures. To investigate such effects, a 1/4 scaled circular reinforced concrete bridge column specimen was tested under two horizontal and one vertical components of a strong motion that has long duration with several strong pulses. Damage progress of reinforced concrete columns subjected to strong excitation was evaluated from the test. The test results demonstrate that the lateral force response in the principal directions become smaller than computed flexural capacity due to the bilateral flexural loading effects, and that the lateral response is not significantly affected by the fluctuation of the axial force because the horizontal response and axial force barely reached the maximum simultaneously due to difference of the predominant natural periods between the vertical and the horizontal directions. Accuracy of fiber analyses is discussed using the test results.

Seismic Performance of High-Strength Short Concrete Column with High-Strength Stirrups Constraints

The seismic performance of four short concrete columns was investigated under low cycle and repeated loads, including the failure characteristics, hysteretic behavior, rigidity degeneracy and steel-bar stress. The influences of reinforcement strength, stirrup ratio and shear span ratio were also compared. Test results reveal that the restriction effect of stirrups can improve the peak stress, so the bearing capacity of specimen can be improved; for the high-strength short concrete column with high-strength stirrups, it was more reasonable to use ultimate displacement angle to reflect the ductility of the specimen, and the yield strength of high-strength stirrups should be devalued when calculating the stirrup characteristic value; the seismic performance of short column would be improved with the increase of volume–stirrup ratio and shear span ratio; the high-strength stirrups and high-strength longitudinal reinforcements did not yield when the load acting on the specimen reached the peak value, which brought adequate safety stock to these short columns. © 2017, Tianjin University and Springer-Verlag Berlin Heidelberg.

Study of Short Column Behavior Originated from the Level Difference on Sloping Lots during Earthquake (Special Case: Reinforced Concrete Buildings)

The disorders originated from architectural design in buildings, show in different forms. One of them is the level difference originated from lot’s slope which affects structures through short column phenomenon. The great stiffness of short columns enables them to absorb large amounts of structural energy. Inattention of some manuals and regulations such as Earthquake regulations to this phenomenon necessitates paying further attention to it. On this basis, the present study employed experimental modeling and numerical modeling for a four-story reinforced concrete building that involves the analysis of simple 2-D frames of varying floor heights and varying number of bays using a very popular software tool STAAD Pro on both a sloping and a flat lot. Also Sap2000 software had been used to show that the displacement of floors is greater for a flat lot building than a sloping lot building. However, the increase in shear was found to be quite greater in short columns compared to common ones and an enormous moment should be tolerated by sloping lot structures. The greater stiffness of the structure was also revealed by non-linear static (Push-Over) analysis. According to the results, short column are required to have more resistant sections and are suggested to be reinforced with more bars. In addition, more steel should be used as stirrups than as longitudinal bars. Also for existing structures, shear capacity of short columns should be retrofitted by FRP, Steel Jacket or other materials.

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 maximum 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 column to long one in the reinforced concrete frame may be realized by replacing the short column with the split one.

Investigation of effect of near-fault motions on substandard bridge structures

The objective of this study was to investigate the effects of near-fault ground motions on substandard bridge columns and piers. To accomplish these goals, several large scale reinforced concrete models were constructed and tested on a shake table using near- and far-field ground motion records. Because the input earthquakes for the test models had different characteristics, three different measures were used to evaluate the effect of the input earthquake. These measures are peak shake table acceleration, spectral acceleration at the fundamental period of the test specimens, and the specimen drift ratios. For each measure, force-displacement relationships, strains, curvatures, drift ratios, and visual damage were evaluated. Results showed that regardless of the measure of input or response, the near-fault record generally led to larger strains, curvatures, and drift ratios. Furthermore, residual displacements were small compared to those for columns meeting current seismic code requirements.

Residual drift spectra for RC bridge columns subjected to near-fault earthquakes

Permanent displacement of a bridge column can be directly measured during the inspection after near-fault earthquakes.However,the engineer needs to estimate the expected residual drift at the design stage to determine if the bridge seismic performance is satisfactory.The most direct method to estimate the residual displacement is nonlinear response history analysis,which is time consuming and cumbersome.Alternatively,an attractive but indirect method is generating estimated residual displacement spectra that depend on displacement ductility demand,column period,site conditions,and earthquake characteristics.Given the period and the expected displacement ductility demand for the column,the residual drift response spectra curves can be utilized to estimate the residual drift demand.Residual drift spectra that are applicable to RC bridge columns in different parts of the United States were developed based on nonlinear response history analyses using a comprehensive collection of recorded and synthetic near-fault ground motions and were linked to one-second spectral acceleration(S1)of the AASHTO maps.It was also found that the residual drift ratio is below one percent when S1 is less than 0.6 g.

Axial compression tests and numerical simulation of steel reinforced recycled concrete short columns confined by carbon fiber reinforced plastics strips

To research the axial compression behavior of steel reinforced recycled concrete(SRRC)short columns confined by carbon fiber reinforced plastics(CFRP)strips,nine scaled specimens of SRRC short columns were fabricated and tested under axial compression loading.Subsequently,the failure process and failure modes were observed,and load-displacement curves as well as the strain of various materials were analyzed.The effects on the substitution percentage of recycled coarse aggregate(RCA),width of CFRP strips,spacing of CFRP strips and strength of recycled aggregate concrete(RAC)on the axial compression properties of columns were also analyzed in the experimental investigation.Furthermore,the finite element model of columns which can consider the adverse influence of RCA and the constraint effect of CFRP strips was founded by ABAQUS software and the nonlinear parameter analysis of columns was also implemented in this study.The results show that the first to reach the yield state was the profile steel in the columns,then the longitudinal rebars and stirrups yielded successively,and finally RAC was crushed as well as the CFRP strips was also broken.The replacement rate of RCA has little effect on the columns,and with the substitution rate of RCA from 0 to 100%,the bearing capacity of columns decreased by only 4.8%.Increasing the CFRP strips width or decreasing the CFRP strips spacing could enhance the axial bearing capacity of columns,the maximum increase was 10.5%or 11.4%,and the ductility of columns was significantly enhanced.Obviously,CFRP strips are conducive to enhance the axial bearing capacity and deformation capacity of columns.On this basis,considering the restraint effect of CFRP strips and the adverse effects of RCA,the revised formulas for calculating the axial bearing capacity of SRRC short columns confined by CFRP strips were proposed.

纤维织物增强高延性混凝土加固RC短柱抗剪性能试验研究

为研究纤维织物增强高延性混凝土(TR-HDC)加固钢筋混凝土短柱的抗剪性能,设计了6根钢筋混凝土柱,包括2个对比柱和4个TR-HDC加固柱.通过低周反复荷载试验,对比分析剪跨比、纤维织物层数对试件破坏形态、变形、承载力和耗能能力的影响.结果表明:采用TR-HDC加固钢筋混凝土短柱,可显著提高其抗剪承载力;TR-HDC与原混凝土柱协同工作性能良好,加固后的混凝土柱的变形、承载力和耗能能力明显提高;增加纤维织物的层数对钢筋混凝土短柱的抗剪承载力提高幅度较小,但可大幅增强柱的耗能和变形能力;剪跨比较大时,更有利于发挥TR-HDC加固材料的力学性能.基于桁架-拱模型,提出TR-HDC加固钢筋混凝土短柱的抗剪承载力计算方法,计算结果较准确.

高强型钢超高性能混凝土短柱轴压性能试验及其有限元分析

为研究高强型钢超高性能混凝土短柱的轴压性能,对试件进行了轴心受压试验,设计参数包括配钢率、箍筋间距和箍筋形式。观察了试件的轴压破坏过程,获得了破坏形态及轴向荷载-位移曲线,分析了承载能力、变形能力、刚度等轴压性能指标,以及超高性能混凝土、纵筋、箍筋和型钢的应变发展规律。在试验研究基础上,采用ABAQUS建立了高强型钢超高性能混凝土短柱轴压性能有限元分析模型,计算结果与试验结果吻合较好,进而进行了参数分析。结果表明:试件发生的是典型轴压破坏,中部表面出现“锯齿形”裂缝;轴向荷载-位移曲线会出现2次荷载峰值;箍筋间距减小时,试件的承载能力和变形能力均提高,但刚度退化速率没有显著变化;配钢率增大时,试件的承载能力提高,变形能力先增大后减小,刚度退化变缓;型钢强度增大时,试件的承载能力和变形能力均提高,提高速度先快后慢;超高性能混凝土抗压强度增大时,试件的承载能力提高,变形能力降低;超高性能混凝土受拉能够达到峰值应变;纵筋在极限点之前发生受压屈服;箍筋在极限点时应变不足屈服应变的1/3,但在破坏点前达到受拉屈服;型钢翼缘在极限点前后发生屈服,腹板屈服晚于翼缘。

地震作用下纵筋屈曲的研究进展

在地震作用下,钢筋混凝土结构中的墩柱在承受竖向力的同时,通常还会受到往复荷载作用下的水平力,若结构中横向约束不足,纵筋可能会发生明显的横向变形,使得结构承载力和延性显著降低,修复困难.因此,研究纵筋在受压时的屈曲机理对结构设计以及施工都有着重要的指导意义.鉴于此,对基于单根钢筋直压试验的纵筋屈曲研究进行总结,分析得出钢筋屈曲的主要影响因素是长细比和屈服强度;概括总结基于RC (reinforced concrete)短柱直压试验的纵筋屈曲问题的研究进展,阐述在复杂相互作用下纵筋屈曲可能受到的各种影响因素;结合土木发展现状,对使用新材料/新构造的墩柱中的纵筋屈曲研究进行讨论.现阶段对纵筋屈曲的研究中没有给出判断钢筋屈曲方向和范围的理论方法,对纵筋的整体屈曲以及新型结构中的纵筋屈曲问题仍有待进一步研究,且应在后续研究中综合考虑锈蚀、加载历程、截面形式以及各材料相互作用等因素对纵筋屈曲的影响.

截面尺寸和箍筋对RC短柱抗震性能的影响

为了研究钢筋混凝土(reinforced concrete,RC)短柱的抗震性能,通过低周反复破坏试验对其抗震性能的尺寸效应进行了分析。试验主要考虑了截面尺寸和箍筋形式的影响,RC短柱的截面分别设计为200 mm×200 mm、400 mm×400 m和600 mm×600 mm,箍筋主要分为普通方形箍筋和井字箍筋。结果表明:配有普通方箍筋的RC短柱均表现出斜拉破坏特征,脆性破坏特征明显,而配有井字箍筋较大尺寸的RC短柱(边长为400 mm和600 mm)为剪压破坏;随着RC短柱截面边长的增加,其名义抗剪强度、延性和平均耗能系数均逐渐减小,并且配有井字箍筋的RC短柱相对于配有普通方形箍筋的短柱,其减小的速率逐渐变小。通过考虑截面尺寸和箍筋的影响作用,提出了修正的RC短柱的抗剪承载计算模型,并建立了考虑尺寸效应的RC短柱恢复力模型,计算结果与试验结果较吻合。

大瑞铁路澜沧江大桥设计及关键技术研究

大瑞铁路澜沧江特大桥为双线铁路桥梁,大桥跨越澜沧江峡谷。结合桥位处的地质、地形及运输条件,经过方案比选,最终确定主桥结构为342 m上承式混凝土提篮拱桥,拱肋箱形混凝土截面由钢管混凝土桁架作为劲性骨架。围绕大桥的设计和施工技术开展一系列研究,采取梁-板单元模拟拱肋复合截面,对全桥进行静力、动力分析,确保全桥结构在列车活载、风荷载和地震荷载作用下受力安全;采取实体元建立拱肋内填外包钢管混凝土复合截面短柱模型,以全桥计算截面内力做外部荷载进行分级加载,最终确定拱肋拱顶复合截面受力安全系数为2.98,大于2.0;研发二次竖转的新型钢拱肋施工工艺,充分适应陡峭的地势,减少拱肋钢劲性骨架施工期间空中大悬臂状态时间。2022年7月22日,澜沧江大桥开通运营,围绕其开展的系列研究成果得以验证。研究成果中钢管混凝土参数体系与分析方法纳入《铁路桥梁钢管混凝土结构设计规范》;研发拱桥拱肋二次竖转施工新工艺,确保澜沧江大桥每岸质量2500 t的拱肋钢劲性骨架通过二次竖转实现合龙,为后期拱肋混凝土及桥面系的施工奠定基础。

矩形钢管混凝土短柱的轴心受压性能分析

采用考虑钢—混界面的接触的非线性有限元方法分析了内加劲肋矩形钢管混凝土短柱轴心受压性能。分析结果表明,矩形钢管混凝土短柱的轴压破坏过程表现出明显的弹塑性特征,短柱破坏时,钢管中部的纵向应力水平普遍较高,横向应力仅在壁板的角点处偏高;钢管内壁设置的开孔钢板加劲肋能够有效约束钢管壁板的鼓曲变形,改善钢管壁板的屈曲形态,提高钢管壁板的屈曲荷载;开孔钢板加劲肋还能起到提高钢管壁板对管内混凝土约束作用的效果。

玄武岩纤维与碳纤维加固短柱抗震试验研究

对5根采用玄武岩纤维布和碳纤维布加固的混凝土短柱和1根对比柱进行了低周反复荷载试验.试验表明,玄武岩纤维布环向包裹加固能显著改变混凝土短柱的破坏形态,提高混凝土短柱的抗剪承载力、延性和耗能能力.相同工况下,玄武岩纤维布加固短柱的抗震性能与碳纤维布加固的短柱相近.玄武岩纤维布因低廉的价格和较好的综合力学性能,在抗震加固领域将有较好的应用前景.

落石冲击对山区桥梁墩柱破坏的影响

为了研究落石冲击作用对山区桥梁墩柱破坏的影响规律,采用Holmquist-Johnson-Cook损伤本构模型构建了数值模型,并展开非线性显式动力分析,基于能量守恒原理检验了计算结果的数值稳定性。考虑了落石冲击高度、冲击速度、水平冲击角度和落石直径等影响因素,从体积损伤率和墩柱位移两个角度研究了各种因素对墩柱冲击破坏的影响。数值模拟结果和试验测试的加速度历程、破坏特征进行了对比,证明了数值模拟的合理性。研究结果表明,HJC本构模型能较好模拟钢筋混凝土墩柱在落石冲击作用下的破坏发展,在高能量冲击作用下,石块直径和冲击速度对墩柱破坏影响相对较大。

钢骨高强混凝土T形短柱偏心受压的试验

目的设计一种新型实腹式钢骨混凝土T形柱，研究不同含钢率对钢骨混凝土T形柱正截面承载力的影响．方法对3根钢骨高强混凝土T形短柱和1根钢筋高强混凝土T形短柱在偏心作用下的力学性能进行了试验研究，分析了不同含钢率对承载力的主要影响，得出了相应的关系曲线．结果钢骨高强混凝土T形短柱的承载力一般比不加钢骨的钢筋高强混凝土T形柱提高20％～34％．结论实验表明，在异形柱中加入钢骨对异形柱的承载力有很大的提高，这种新型实腹式钢骨混凝土T型柱可以在工程中使用．

钢骨混凝土T形截面短柱力学性能的试验研究

通过试验研究钢骨混凝土T形截面短柱的抗剪性能和抗震性能。制作14根钢骨混凝土T形截面短柱和2根钢筋混凝土T形截面短柱,主要考虑剪跨比、轴压力系数、体积配箍率及配骨率等参数对T形短柱抗剪承载力和位移延性的影响,提出钢骨混凝土T形截面短柱抗剪承载力计算公式,计算值与试验结果吻合较好。试验结果表明,钢筋混凝土T形截面短柱经加入钢骨抗剪承载力和位移延性均有较大程度的提高,且随配骨率、体积配箍率的增大而增大;另外,钢骨混凝土T形截面短柱的位移延性随轴压力系数的增大而降低,随剪跨比的增大而提高。研究成果为钢骨T形短柱应用于抗震烈度较高地区有一定的参考价值。

型钢高强混凝土短柱的抗剪机理与抗剪承载力

通过若干个型钢高强混凝土短柱的低周反复加载试验,对轴力和水平剪力共同作用下型钢高强混凝土短柱的受力性能进行了研究。由粘贴在箍筋和型钢表面的应变片和应变花,测到了柱中箍筋的应力-应变、型钢的剪应力-剪应变在不同受荷阶段的发展变化状况,分析了箍筋、型钢腹板以及混凝土在构件中的抗剪作用以及轴力在型钢与混凝土之间的分配关系,揭示了型钢高强混凝土短柱的抗剪机理,提出了型钢高强混凝土短柱不同破坏形态下的抗剪承载力计算公式,公式的计算结果与试验结果符合较好。

用碳纤维布改善钢筋混凝土极短柱抗震性能的试验研究

本文进行了５根钢筋混凝土极短柱（λ＝１．０）在周期反复荷载作用下的试验，研究了使用碳纤维布横向包裹钢筋混凝土极短柱以提高其延性这种加固方法的有效性．本文研究了碳纤维布横向包裹钢筋混凝土极短柱的受力特性，分析了碳纤维布抗拉强度对试件抗震性能的影响，并对碳纤维布加固钢筋混凝土极短柱使其延性提高的机理进行了探讨．试验结果表明，横向包裹碳纤维布可显著提高钢筋混凝土极短柱的变形性能．

工业与民用钢筋混凝土建筑中的短柱问题与分体柱技术

对工业与民用钢筋混凝土建筑中短柱的判断方法进行了介绍 ,并归纳了钢筋混凝土短柱的几种破坏形态以及目前国内外改善钢筋混凝土短柱抗震性能的各种方法 ,同时还对作为解决钢筋混凝土短柱问题最新方法之一的分体柱技术进行了简要概述 ,并提出了其中有待进一步研究的问题。