Numerical Analysis of Cold-Formed Thin-Walled Steel Short Columns with Pitting Corrosion during Bridge Construction

Pitting corrosion is harmful during bridge construction,which will lead to uneven roughness of steel surfaces and reduce the thickness of steel.Hence,the effect of pitting corrosion on the mechanical properties of cold-formed thin-walled steel stub columns is studied,and the empirical formulas are established through regression fitting to predict the ultimate load of web and flange under pitting corrosion.In detail,the failure modes and load-displacement curves of specimens with different locations,area ratios,and depths are obtained through a large number of non-linear finite element analysis.As for the specimens with pitting corrosion on the web,all the specimens are subject to local buckling failure,and the failure mode will not change with pitting corrosion,but the failure location will change with pitting corrosion location;the size,location,and area ratio of pitting corrosion have little influence on the ultimate load of cold-formed thin-walled steel short columns,but the loss rate of pitting corrosion section area has a greater impact on the ultimate bearing capacity.As for the specimen with flange pitting corrosion,the location and area ratio of pitting corrosion have less influence on the ultimate load of cold-formed thin-walled steel short columns,and the section area loss rate has greater influence on the ultimate bearing capacity;the impact of web pitting corrosion on the ultimate load is greater than that of flange pitting corrosion under the same condition of pitting corrosion section area.The prediction formulas of limit load which are suitable for pitting corrosion of web and flange are established,which can provide a reference for performance evaluation of corroded cold-formed thin-walled steel.

The Separation Efficiency of Biopolymers with Short Column in Liquid Chromatography

The separation efficiency of biopolymers with a short column in liquid chromatography has been investigated in this paper. It was found that the column length has slight effect on the resolution of biopolymers under gradient elution. The reasons have been explained by stoichiometric displacement model for retention of solute. The column 1.0 cm long was also used in the separation and purification of recombinant human granulocyte colony-simulating factor (rhG-CSF). It only took 40 min and the purity by one step was found to be almost 100%.

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.

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.

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.

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.

Axial compressive behavior and design method of tubed circular steel reinforced concrete short columns

To study the behavior and design of tubed circular steel reinforced concrete (TCSRC) short column under axial compressive loads, a nonlinear finite element model (FEM) has been developed to simulate this kind of structure. Depending on the FEM results, an elastic-plastic analysis was carried out to clarify the status of steel tube, then a simplified procedure was proposed to predict the compressive axial load strength. The results obtained from this procedure were compared with the test results. It is found that they agree well each other.

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.

The equivalent circuit of ultrasonic coupling vibration of a longitudinally-excited short column

On the basis of apparent elasticity method, we derived the equivalent circuit of coupling vibration of a short column and discussed its frequency equation and the effects of the load impedance on the resonant frequency of the short column. By the equivalent circuit, we calculated the input mechanical impedance of the longitudinally-excited short column and the curves of the apparent vibration velocity ratio versus the geometrical dimensions of the column. It shows that the equivalent circuit method is a simple and convenient one to analyze and calculate the coupling vibration of the short column.

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.

圆钢管超高性能混凝土短柱偏压力学性能研究

为研究钢管超高性能混凝土短柱的偏压性能,以荷载偏心率和钢管径厚比为变化参数,设计了12个圆钢管UHPC短柱试件并对其进行偏心受压加载试验,分析了该类构件的破坏模式、荷载-挠度曲线、钢管应变和变形系数等,考察了主要因素对短柱偏压性能的影响规律。结果表明:试件的破坏特征为钢管屈服和核心混凝土压坏;荷载-挠度曲线有较明显的峰值点,偏心率越大和径厚比越小,曲线的下降段越平缓;达到60%峰值荷载时,钢管开始产生明显的约束作用,达到90%峰值荷载时,截面变形不再符合平截面假定;偏心率增大使试件的承载力和刚度下降,而径厚比减小可降低这种不利影响。在试验基础上,结合数值模拟对短柱的N-M曲线进行分析,建立了临界偏心率和套箍系数的关系表达式,并基于此提出短柱偏压承载力实用计算方法,理论与试验结果吻合较好。

套筒强夯长短桩复合地基承载特性研究

【目的】随着大型海洋工程项目不断发展,对水下软土地基处理提出了新的挑战,水下挤密砂桩和水下水泥搅拌桩复合地基等传统方法具有定位难、制桩难、桩体质量差等问题,始终制约着其在海洋工程中的应用和发展。【方法】借鉴陆上孔内深层强夯施工方法,因地制宜地提出水下套筒强夯复合地基成桩技术,该技术使用套筒阻隔海水进入桩孔,具有定位准、加固深和强度高等优点,通过模型试验的方法对该技术进行研究。【结果】结果表明,在强夯碎石桩与传统碎石桩相结合的工况下,地基极限承载力提高50%以上,等长度群桩复合地基极限承载力比长短桩复合地基提升18%;在全部采用强夯碎石桩的工况下,地基极限承载力提高170%以上,等长度群桩复合地基极限承载力比长短桩复合地基提升3.7%。【结论】全部采用强夯碎石桩的复合地基比强夯碎石桩与传统碎石桩组合而成的复合地基承载力提高更多,在提高承载力方面,采用套筒强夯长短桩复合地基更加经济有效。

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。

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。

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。

设置型钢混凝土端柱短肢剪力墙的抗震性能试验研究

为了探究改善钢筋混凝土短肢剪力墙抗震性能的方法,制作了2个设置型钢混凝土端柱的短肢剪力墙试件,并对其进行低周反复循环加载试验。通过试验研究,比较2个试件的开裂荷载、屈服荷载和极限荷载的数值,设置核心型钢管混凝土端柱的短肢剪力墙的数值要高于拼合形型钢混凝土端柱的短肢剪力墙,其强度衰减也相对较为缓慢;2个试件的破坏形态都为弯剪型破坏,其承载能力较高,它们的延性、耗能大大优于一般钢筋混凝土短肢剪力墙结构,对于改善钢筋混凝土短肢剪力墙的抗震性能起到了很好的效果。

钢管混凝土短柱轴压承载力试验与规范计算方法对比研究

为研究钢管混凝土构件尺寸效应对其承载力与规范计算方法的异同,对含钢率和套箍系数相同,截面形式不同的三种钢管混凝土短柱构件进行轴压试验,分别获取了构件在轴心压力作用下的荷载-应变关系曲线和荷载-轴向位移全过程曲线。运用叠加原理理论分析了当套箍系数相等时,不同规格钢管混凝土构件的受力性能和极限承载力提高效果。将试验值与现行规范计算值对比,研究结果表明,现有规范CECS 28:2012和DBJ 13-51—2010对钢管混凝土短柱的承载力计算值与试验值最接近;当套箍系数相等,材料性能相同、构件几何尺寸近似的圆钢管混凝土短柱具有一定的尺寸效应。