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.

Behavior of eccentrically loaded concrete-filled GFRP tubular short columns

The glass fiber reinforced polymer (GFRP) tube is an effective material that can increase the bearing capacity and ductility of concrete.To study the mechanical behavior of this composite structure,twenty-one concrete-filled GFRP tubular short columns were tested under an eccentric load.The principle influencing factors,such as the eccentricity ratio,concrete strength and ratio of longitudinal reinforcement were also studied.In addition,the course of deformation,failure mode,and failure mechanism were analyzed by observing the phenomena and summarizing the data.The test results indicated that the strength and deformation characteristics of core concrete increase as a result of the addition of the GFRP tube.However,the gain in strength due to the addition of the GFRP tube decreases as the ratio of e /d increases.An increase in the longitudinal steel ratio can improve the bearing capacity of the composite short column effectively.Furthermore,the study showed that the constraint effect of the GFRP tube on high-strength concrete is not as effective as that on common concrete.The reason is that the lateral deformation of the high-strength concrete is less than that of the common concrete when the concrete column was tested under the same axial compression ratio.

Experimental Study on the Axial Compression Behavior of Short Columns of Steel-Fiber-Reinforced Recycled Aggregate Concrete

In order to study the axial compression performances of short columns made of recycled aggregate concrete,four samples were designed with different recycled aggregate replacement rates and carbon fibre reinforced plastics(CFRP)sheets.Then,monotonic loading was implemented to assess the variation trends of their axial compression properties.The ABAQUS finite element software was also used to determined the compression performances.Good agreement between experimental and numerical results has been found for the different parameters being considered.As shown by the results,recycled coarse aggregates result in improved ductility and better deformation performance of the specimens.The failure of specimens caused by pre damage can be compensated by using CFRP sheets,by which both the resistance to deformation and the axial carrying capacity of columns can be increased.

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.

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.

Prediction of Axial Capacity of Concrete-Filled Square Steel Tubes Using Neural Networks

The application of artificial neural network to predict the ultimate bearing capacity of CFST （ concrete-filled square steel tubes） short columns under axial loading is explored. Input parameters consiste of concrete compressive strength, yield strength of steel tube, confinement index, sectional dimension and width-to-thickness ratio. The ultimate bearing capacity is the only output parameter. A multilayer feedforward neural network is used to describe the nonlinear relationships between the input and output variables. Fifty-five experimental data of CFST short columns under axial loading are used to train and test the neural network. A comparison between the neural network model and three parameter models shows that the neural network model possesses good accuracy and could be a practical method for predicting the ultimate strength of axially loaded CFST short columns.

高强钢管超高性能混凝土短柱轴压承载力性能试验研究

为研究高强钢管内填超高性能混凝土(UHPC)的钢管混凝土短柱轴压性能,该文设计22根高强钢管UHPC短柱进行轴压试验,从破坏模式、荷载-纵向应变关系对试件的轴压性能进行对比分析,旨在通过径厚比、混凝土强度、截面类型等变化来探究高强钢管UHPC短柱的实际承载力性能差异.试验结果表明:高强钢管UHPC短柱的轴压性能受径厚比、混凝土强度影响较大;试件承载力随钢管壁厚增加而增加,但相同钢管直径和不同钢管直径增幅呈现不同规律.该文从延性、核心混凝土强度提高程度两个角度进行分析并提出高强钢管混凝土试件的相关参数设计建议.最后,将高强钢管UHPC短柱的轴压试验承载力结果与国内外规范GB 50936—2014、AIJ计算承载力结果进行对比,并基于极限平衡理论推导出高强圆钢管UHPC试件的轴压承载力计算公式,同时结合该文试验数据对其进行验证,证明了公式的准确性.

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.

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.

预应力钢筒超高性能混凝土管套箍混凝土短柱的抗压性能研究

跨海大桥面临着严峻的耐久性问题,尤其是混凝土桥墩。提出以围套的形式保护海洋工程桥墩混凝土柱防止海水侵蚀,在钢管外壁设置剪力钉,然后浇筑超高性能混凝土(UHPC),并缠绕预应力钢丝,最后浇筑UHPC,形成预应力钢筒超高性能混凝土管(PUCCP)。制备了PUCCP套箍混凝土柱,并对其进行了抗压试验,并与素混凝土柱和UHPC套箍混凝土柱进行对比。此外,分析了PUCCP中预应力大小对PUCCP套箍混凝土柱抗压性能的影响。试验结果表明:相比素混凝土柱和UHPC套箍混凝土柱,PUCCP套箍可显著提高混凝土柱的抗压强度,且随着预应力的增加,混凝土柱的抗压强度相应增加;PUCCP套箍能对混凝土柱提供比UHPC套箍更充分的侧向约束,以实现应变硬化行为,从而显著提高混凝土柱的初始刚度和延性。

异形多腔钢管混凝土分叉短柱抗震性能试验及数值计算

针对某超高层巨型框架结构中异形截面多腔钢管混凝土(concrete-filled steel tube, CFT)分叉柱,为研究截面加强构造对分叉短柱抗震性能的影响,进行了4个试件在竖向轴压力及水平往复两次的低周反复荷载下的抗震性能试验研究,试件上部为五边形四腔体钢管混凝土双柱肢,下部为八边形十三腔体钢管混凝土单柱肢,以此形成分叉柱;研究的截面构造包括四种:基本构造,钢管钢板整体加厚构造,距中和轴较远的钢管角部钢板内表面贴焊等肢角钢的局部钢板加厚构造,距中和轴较远的钢管腔体内置圆钢管构造。基于试验结果及截面构造特点,进行了数值计算。试验及数值计算结果表明:异形截面多腔钢管混凝土分叉短柱的破坏主要发生在上柱根部分叉截面处,表现为距离中性轴较远处的钢板撕裂以及局部焊缝开裂引起的整块钢板撕裂;内置圆钢管的加强构造承载力提高7.6%、变形能力提高14.4%,综合耗能能力最强,局部钢板加强构造承载力提高9.2%、变形能力下降18.7%,钢管钢板整体加厚构造承载力略有提高、但变形能力下降较多;提出的异形多腔钢管混凝土柱简化建模方法计算效率较高,精度满足工程设计要求。

带对穿螺栓矩形钢管混凝土短柱轴压承载力计算方法研究

设置对穿螺栓可以提高钢管混凝土短柱的力学性能,以试件同参数的ANSYS模型为原始算例,研究对穿螺栓的直径和纵向间距、套箍系数、宽厚比、长宽比、材料强度等参数对其轴压力学性能的影响。结果表明:设置对穿螺栓可以提高钢管对核心混凝土的约束效应,核心混凝土的应力分布表现为以对穿螺栓为分界线形成两个有效约束区,且四个角部的应力值最大;随着对穿螺栓纵向间距的减小、直径的增大,试件的承载力、变形能力、延性提高;试件承载力可随着套箍系数的增加、宽厚比的减小、材料强度的增强有小幅度提高。提出带对穿螺栓矩形钢管混凝土短柱的轴压承载力的计算方法,得到的计算值和试验值吻合良好,该方法还同样适用于带约束拉杆矩形钢管混凝土短柱承载力计算,计算过程简便且准确度高。

方钢管超轻混凝土短柱轴压性能试验研究

对16个方钢管超轻混凝土短柱和8个空钢管短柱进行了轴压试验,以超轻混凝土强度和含钢率为变化参数,研究方钢管超轻混凝土短柱的破坏形态和受力性能。结果表明,随着超轻混凝土强度的降低,钢管对核心混凝土的约束效应越强;随着含钢率的增加,构件的承载力和变形能力提高,但当含钢率高于0.25时,超轻混凝土的存在对构件的承载力和变形能力已基本没有影响。基于叠加理论,提出了适用于方钢管超轻混凝土短柱承载力的计算公式。

带肋方钢管混凝土轴压短柱承载性能有限元分析

带肋方钢管混凝土是一种具有卓越性能被广泛应用的结构材料。使用ABAQUS有限元软件,对方钢管混凝土短柱进行了有限元分析,得出了方钢管混凝土短柱在轴向压力下的荷载-位移全过程关系曲线。增加加劲肋的设计,可以有效提高方钢管混凝土短柱的承载能力;随着加劲肋个数和钢管厚度的增加,构件的极限承载力也得到了提高。

浅谈智能机械立体车库结构设计

智能机械立体车库建筑设计除满足正常使用功能、消防、疏散等方面的要求,还要满足设备的运行安装要求。结构设计在满足建筑设计全部功能的前提下,还要保证结构安全、经济合理、施工简便。江西省南昌市渊明北路停车场项目采用垂直移动立体车库和巷道堆垛类立体车库两种停车方式,论文以该项目为例,分析智能机械立体车库结构设计的特点和可以采取的结构措施。

基于ABAQUS的圆钢管混凝土短柱受火力学性能研究

基于ABAQUS有限元软件建立了温度场和力学性能分析模型,将模拟结果与试验结果进行比对,验证了模型的可靠性。在此基础上建立了钢管混凝土短柱在高温火灾下的均匀受火和三面受火轴压的温度场模型,探讨了截面尺寸、钢管强度、混凝土强度、受火方式等因素与高温(受火)下钢管混凝土短柱的力学性能之间的关系。

Truss-arch model for shear strength of seismic-damaged SRC frame columns strengthened with CFRP sheets

Carbon fiber reinforced polymer(CFRP)materials are important reinforcing substances which are widely used in the shear strengthening of seismic-damage steel reinforced concrete(SRC)frame structures.To investigate the shear strength of SRC frame columns strengthened with CFRP sheets,experimental observations on eight seismic?damaged SRC frame columns strengthened with CFRP sheets were conducted at Yangtze University and existing experimental data of 49 SRC columns are presented.Based on the existing experiments,the theories of damage degree,zoning analysis of concrete,and strengthening material of the column are adopted.To present the expression formula of the shear strength of SRC frame columns strengthened with CFRP sheets,the contributions of strengthening material and transverse reinforcement to shear strength in the truss model are considered,based on the truss-arch model.The contribution of arch action is also considered through the analysis of the whole concrete and that of the three zones of the concrete are also considered.The formula is verified,and the calculated results are found to match well with the experimental results.Results indicate that the proposed whole analysis model can improve the accuracy of shear strength predictions of shear seismic-damaged SRC frame columns reinforced with CFRP sheets.

CFRP加固半高填充墙短柱框架抗震性能试验研究

设置半高填充墙的钢筋混凝土框架结构在地震中极易发生短柱破坏,进而引起结构整体倒塌,为改善半高填充墙框架结构的抗震性能,制作了3组半高填充墙框架结构试验模型,采用不同方法对短柱外包(Carbon fiber reinforced polymer,CFRP)加固,分析了CFRP布条带加固模型和全包加固模型的延性系数、滞回曲线、骨架曲线、刚度退化、耗能能力及破坏模式。试验结果显示:CFRP加固将半高填充墙框架结构的薄弱环节从短柱转移到填充墙,在填充墙完全破坏后框架结构表现为强柱弱梁型的节点破坏,外包CFRP加固将半高填充墙框架短柱破坏的脆性破坏模式转变为强柱弱梁型的框架延性破坏模式;全包加固后结构的初始刚度有所提高,条带加固可以大大提高结构的耗能能力,2种加固方法都能提高结构的延性和抗震性能。

截面短长轴比对椭圆钢管混凝土柱抗爆性能影响

目的 研究椭圆钢管混凝土柱抗爆性能,分析截面短长轴比对其抗爆性能的影响。方法 利用LS-DYNA有限元软件建立TNT炸药-空气-椭圆钢管混凝土柱-刚性地面整体三维实体有限元模型,分别从短轴和长轴两个方向进行起爆设置,探究椭圆钢管混凝土柱受爆炸荷载作用后冲击波传递特性。结果 与双向刚度相同的柱子相比,椭圆钢管混凝土柱抗爆冲击波反射、衍射作用更为复杂;椭圆钢管混凝土柱沿长轴迎爆的抗爆性能明显优于沿短轴方向;绘制短长轴比-柱中侧向位移曲线,根据短轴方向与长轴方向抗爆性能差异,提出了设计宜采用的短长轴比为0.6~1.0;沿短轴向施加爆炸荷载时,短长轴比设计值不应小于0.4。结论 得出了不同短长轴比下构件破坏形态,进一步提出了采用短长轴比0.4~0.6内的椭圆钢管混凝土柱时,应采取加固措施。