The effects of axial tension on the sagging-moment regions of composite beams

This paper studies the effects of axial tension on the sagging moment regions of steel–concrete composite beams. The study comprised an extensive experimental programme and nonlinear finite element analyses. Six composite beams were designed and tested under the combined effects of axial tension and positive bending moment. The beams were loaded to their ultimate capacity and the experimental moment-axial tension interaction diagram was constructed. Following the tests, a finite element model was used to simulate the nonlinear response of the composite beams. The validity of the model was thoroughly assessed against the available experimental data and a parametric study was conducted to study different beam sizes and the effect of partial shear connection on the interaction diagram. It was found that the moment capacity of a composite beam is reduced under the presence of an axial tensile force acting in the steel beam section. In addition, the use of partial shear connection does not affect significantly the shape of the interaction diagram. The tensile capacity of the composite section, however, is limited by the axial capacity of the steel beam alone. Based on the experimental results and the finite element analyses, a simplified equation is proposed for the design of composite beams subjected to positive bending and axial tension.     

Block shear strength of coped beams with single-sided bolted connection

Block shear is one of the major failure modes for coped steel I-beams. While focus of previous studies on the block shear capacity of coped steel I-beam was mainly given to the connections with double clip angles, single-sided connections, which induce out-of-plane loading eccentricity, have not been adequately considered. Ten full-scale coped steel I-beam tests were conducted to examine the effects of two main test parameters, namely, out-of-plane loading eccentricity and web block aspect ratio (ratio of shear area to tension area). It was found that nine test specimens failed with tension fracture along the bottom bolt row of the web, and the remaining one failed in a whole block tear-out manner. Twisting of the web near the cope was observed for specimens with single-sided connection. More importantly, the test results showed that the out-of-plane loading eccentricity due to the single-sided connection did not have a detrimental effect on the block shear capacity of the specimens. Moreover, increasing the connection rotational stiffness could increase the block shear capacity. These effects are further discussed via a finite element analysis and a preliminary parametric study. Finally, the test results are compared with four major design standards. It is found that the Canadian Standards CAN/CSA-S16-09, which gives a test-to-predicted ratio ranged from 0.93 to 1.17, provided relatively good predictions for the specimens with single bolt line layout, while the predictions by other codes are too conservative. For those specimens with double bolt line layout, the capacities are underestimated by all the considered standards.     

火灾后栓接Q690角钢净截面受拉承载力研究

对栓接Q690角钢在火灾后的净截面受拉承载力展开研究,参考过火后高强钢Q690材性试验结果,利用ABAQUS建立栓接Q690角钢的有限元模型,分析面外偏心距、螺栓连接长度、过火温度对火灾后栓接Q690角钢净截面受拉承载力的影响; 将已有相关公式及规范公式的计算结果与模拟得到的角钢支撑受拉极限荷载进行比较; 基于最小二乘法,提出了Q690角钢净截面受拉承载力的有效截面系数公式,对比了数值结果及其他文献试验结果; 基于数值模拟数据库,进行了可靠度分析。结果表明:有效截面系数随着螺栓连接长度的增大而增大,随着面外偏心距的增大而减小,而过火温度对有效截面系数几乎没有影响; 美国规范AISC 360-16对不同过火温度下Q690角钢净截面受拉承载力预测结果偏于不安全,中国现行《钢结构设计标准》预测结果偏于离散; 提出的计算公式对于不同过火温度下的栓接Q690角钢净截面受拉承载力均能进行较好预测; 推荐所提出公式计算火灾后栓接Q690角钢净截面受拉承载力的抗力分项系数为1.061。     

弯剪受力下群锚有限元分析

采用型钢—混凝土后锚固连接方式,对弯剪受力下粘结型锚栓群的受力性能进行了试验研究和有限元分析。结果表明,该类连接的破坏形态为锚栓钢材破坏,仅锚栓周围混凝土发生锥体破坏,锚栓内力以拉应力为主。锚固承载力随着埋深的增加而提高,加载端至基材表面的水平距离较大时,弯矩起控制作用,承载力较小;水平距离较小时,则表现为弯剪共同作用,承载力较大。     

圆端形钢管混凝土构件纯弯力学性能

为研究圆端形钢管混凝土构件的纯弯力学性能,对4个构件进行了纯弯试验,分析了高宽比和含钢率对纯弯曲作用下圆端形钢管混凝土构件破坏形态、挠度曲线、截面应变、抗弯承载力的影响。基于ABAQUS建立有限元模型对圆端形钢管混凝土构件纯弯性能进行模拟,试验结果与模拟结果吻合良好,利用验证后的模型对圆端形钢管混凝土构件进行了受力全过程分析以及参数分析。最后基于ABAQUS参数分析结果提出了圆端形钢管混凝土构件抗弯承载力计算公式,公式计算结果与试验结果吻合良好。结果表明:圆端形钢管混凝土构件在纯弯曲作用下发生了明显的挠度变形,当跨中挠度达到L/25(L为试件长度)时,试件仍能承受较大的荷载,表现出良好的延性; 圆端形钢管混凝土构件的挠度曲线可假设为正弦半波曲线,其跨中截面基本保持为平截面; 当构件达到抗弯承载力时,钢管承受了大部分弯矩,圆弧段钢管相较于平直段钢管对混凝土的约束作用更强; 圆端形钢管混凝土构件的抗弯承载力随钢材强度的增大而增大,而混凝土强度的改变对其抗弯性能影响较小。     

圆锥形中空夹层钢管混凝土偏压构件受力性能研究

将圆锥形中空夹层钢管混凝土用于风电塔筒或输电塔架时,为满足在塔筒内设置设备等需求而将该类构件空心部分加大。为研究该类构件的偏压受力性能,进行了12个大空心率下的圆锥形中空夹层钢管混凝土偏心受压构件的试验研究,主要试验参数为荷载偏心率和长细比。利用ABAQUS软件建立有限元分析模型,对圆锥形中空夹层钢管混凝土偏心受压构件的典型破坏模态和荷载-变形关系曲线进行模拟,所得计算结果与试验结果基本吻合。通过典型算例分析了受力过程中钢管和混凝土各自所承担的荷载和纵向应力分布情况,同时分析了内、外钢管与混凝土之间相互作用力的变化情况。结果表明：偏心率和长细比对圆锥形中空夹层钢管混凝土偏心受压构件承载力及刚度有显著影响;该类构件力学行为与等截面圆中空夹层钢管混凝土偏心受压构件类似,锥度的存在使破坏位置从等截面柱的中部上移到锥形柱的3/4柱高处(柱顶处),因此在设计大空心率圆锥形中空夹层钢管混凝土偏压(压弯)构件时应考虑柱头处加强。同时,对该类构件压弯承载力计算方法给出了建议。     

钢管混凝土复合柱静力试验与偏心率折减系数计算方法

以偏心率为参数,对4根钢管混凝土复合柱和4根钢管混凝土格构柱进行了受压试验和有限元分析,对比分析了试件的破坏过程与特征、受压承载力和荷载-位移曲线以及荷载-应变曲线。试验结果表明：轴压复合短柱的破坏以钢筋混凝土板的压碎和纵筋屈服为特征,此时钢管混凝土柱肢没有充分发挥其自身的轴压承载能力;偏压复合短柱的破坏形态为近载侧钢筋混凝土板压碎同时柱肢钢管出现鼓曲,对应柱肢的受力状态与钢管混凝土格构柱的相似。当偏心率相同时,钢管混凝土复合柱的初始受压刚度和承载力均大于钢管混凝土格构柱,两者的初始抗弯刚度接近,但由于钢筋混凝土板在受力后期仍可有效传递截面剪力,钢管混凝土复合柱的侧向位移明显小于钢管混凝土格构柱。钢管混凝土复合柱的偏心率折减系数随偏心率的变化情况与钢管混凝土格构柱的基本相似。以钢管混凝土格构柱的基本计算式为基础,利用试验和有限元参数分析结果对其进行修正,得到钢管混凝土复合柱的偏心率折减系数计算方法,折减系数的计算结果与试验结果吻合良好。     

Bending behavior of grouted connections considering eccentricity errors

为研究偏心误差对海上风机灌浆连接段受弯性能的影响,完成了3根灌浆连接段四点弯曲静力加载试验,对比竖向荷载-挠度曲线、纵向应变分布等。同时采用ABAQUS进行有限元数值分析,通过比较破坏形态,荷载-位移曲线,验证模型的合理性。研究结果表明,在纯弯矩作用下,灌浆连接段最终破坏模式为套管受弯破坏并伴随局部屈曲,试件受拉侧浆体端部出现径向裂缝,同时还观察到浆体与钢管接触面张开。对该连接段进行有限元参数分析,考察灌浆材料强度、钢管材料屈服强度、偏心距和套管厚度对其受力性能的影响。试验与数值分析结果均表明在现有偏心距范围内,偏心误差对灌浆连接段受弯承载力影响有限。而钢管屈服强度和套管厚度会显著影响连接段的荷载-位移曲线。钢管屈服强度的增加会显著提高其承载力,而随着套管厚度的增加,破坏模式转为桩管受弯破坏,承载力小幅增长。     

Finite element modeling of block shear failure in coped steel beams

Block shear is a potential failure mode that is encountered in the connection regions of coped steel beams. Limited experimental studies completed so far have shown that the block shear failure in coped steel beams is a complex phenomenon, which is highly dependent on the number of bolt lines. In this paper, the use of the finite element method in predicting the block shear failure load was studied by making comparisons with experimental findings. The effects of numerical modeling details on load capacity predictions were investigated. In light of these investigations, a finite element analysis methodology has been developed and used to conduct a parametric study. Simplified load capacity prediction equations were developed based on the results of the parametric study and are presented herein.     

泡桐木芯材夹层梁抗弯性能试验研究

试验研究了复合材料泡桐木芯材夹层梁抗弯性能,考察了试验构件的破坏模式、荷载-位移曲线、抗弯承载力及受弯段的应变发展规律;开展试验构件抗弯承载力的有限元模拟,试验结果与有限元分析结果吻合较好,验证有限元模拟分析可行。基于试验及有限元分析可知:整个加载过程中复合材料泡桐木芯材夹层梁表现为线弹性受力,最后破坏发生脆性破坏;受弯承载力计算可以近似采用平截面假定。文章可供轻木芯材复合材料夹层结构的抗弯设计参考。     

Q460高强钢焊接箱形截面轴压构件整体稳定性能研究

为研究高强度钢材轴心受压钢柱的整体稳定性能,对5个国产Q460钢材焊接箱形截面柱进行了轴心受压试验研究。试验对试件的几何初弯曲、荷载初偏心以及截面的纵向残余应力分布均进行了测量。基于试验结果,分析了该类钢柱的失稳破坏形态和整体稳定承载力,建立了有限元分析模型并对试验结果进行模拟计算。研究结果表明：试件破坏模态均为整体弯曲失稳形态,大部分试件稳定承载力高于规范设计值;有限元分析模型能够准确地考虑几何初始缺陷和残余应力的影响,计算结果与试验结果吻合良好;通过与国内外钢结构设计规范的对比,提出了国产Q460高强钢焊接箱形截面轴压构件整体稳定设计的建议方法,即可以统一采用我国或欧洲规范的b类曲线进行设计,而不需要按板件宽厚比大小进行分类。     

钢管混凝土平缀管格构柱极限承载力试验研究

进行24根缀板式钢管混凝土格构柱轴心受压和偏心受压试验。试验参数为长细比、偏心率、柱肢间距和缀管间距。对试件的受力全过程、破坏特性与极限承载力进行分析,讨论了缀管的受力特性和缀管构造对试件极限承载力的影响。试验结果表明,钢管混凝土平缀管格构柱中缀管以受弯为主、应变较大,缀条式格构柱中缀管以受轴力为主、应变较小;柱肢间距和缀管间距对试件承载能力有较大的影响;随着长细比增加,试件破坏特性从局部压屈变为整体破坏;长细比和偏心率两个参数对缀板式钢管混凝土格构柱极限承载力的影响基本上是独立的,可以采用分项系数相乘来考虑二者的共同影响;稳定系数与偏心率折减系数可以采用与缀条式格构柱相同的方法计算,但其剪切变形对极限承载力的影响要大于缀条式格构柱;给出了应用图表法的换算长细比计算方法。     

拉-弯-剪组合作用下法兰连接方钢管柱受力性能研究

为研究多高层钢结构柱连接在拉-弯-剪组合作用下的受力性能,对4个不同法兰板厚度的法兰连接柱进行了足尺模型试验和有限元分析,并通过有限元模型分析了轴拉比对法兰连接柱性能的影响。结果表明：随着法兰板厚度增大,连接柱的侧向刚度和水平承载力增大,受拉区法兰接触面翘力减小;在拉-弯-剪组合作用下,法兰中性轴位置在受压侧第二排螺栓附近,且随着法兰板厚度的增大,中性轴位置由法兰受压区逐渐向其几何中心移动。轴向拉力对法兰产生的作用效应与水平荷载产生的作用同向。轴向拉力降低了法兰连接柱的水平屈服荷载,法兰转角随着轴拉比的增大而增大。     

The effects of axial tension on the hogging-moment regions of composite beams

Structural parts commonly comprised of composite members such as bridge approaches, inclined parking ramps and stadium beams, can be subjected to a combination of high axial loads and bending moments. Steel-concrete composite construction is a popular solution for these types of structures due to the numerous advantages that they offer. Although, current design codes (e.g. Eurocode 4, American code AISC, Australian codes AS2327 and AS5100) provide rules for the design of composite columns subjected to flexure and axial load, however the design of composite beams, which are asymmetric in nature under the combined effects of tension and bending, is not yet fully addressed. This paper investigates the ultimate strength of composite beams under the combined effects of axial tension and negative (hogging) bending moment. An experimental programme carried out in the laboratory of the University of Western Sydney comprised of a total of six specimens representing composite beams and subjected to various levels of axial tension and bending moment. Ultimate failure modes were identified and the resulting interaction diagrams were compared to the results of sectional rigid plastic analysis. Following the tests, three-dimensional finite element models were employed using the ABAQUS finite element software to further investigate the nonlinear behaviour of the composite beams and extend the experimental observations by studying the effects of parameters such as the span length and the effect of partial shear connection. Finally, simple design rules and formulae are proposed for use in engineering practice.     

Flexural performance of rectangular CFST members

This paper presents a finite element analysis (FEA) modeling to study the flexural performance of rectangular concrete filled steel tubular (CFST) members with compact, non-compact or slender element sections. Seventy test results are used to verify the FEA modeling. Generally good agreements were achieved in the ultimate bending capacity and the curvilinear trends of the moment versus mid-span deflection relations of the composite member between the experimental results and the FEA results. The FEA modeling is then used to investigate the residual failure patterns of the core concrete, the typical residual deformations of outer steel tube and the stress and strain distributions across the composite section in the whole loading procedure. Analysis results show that interaction of steel and concrete in the composite beam offers stress redistribution in steel and concrete which makes the rectangular CFST beam have high flexural capacity and ductility. Finally, the reliability analysis method is used to calibrate the existing design formulae on composite beam in EC4 (2004), AISC (2010) and DBJ/T13-51-2010 (2010). It was found that all the design formulae achieved adequate reliability index.     

冷弯薄壁C型钢绕强轴偏心受压构件的极限承载力

冷弯薄壁型钢结构多采用有效截面法对构件承载力进行计算,该方法计算繁杂且未考虑构件的畸变屈曲性能。直接强度法采用全截面计算各类参数,能够考虑各种单独屈曲模式及其相关屈曲对构件稳定性能的影响,但目前该方法并不能应用于压弯构件。对冷弯薄壁C形钢绕强轴偏压构件的稳定性能进行参数分析,探讨了构件长度、偏心距、腹板高厚比、翼缘宽厚比和卷边高厚比等因素对构件承载力的影响规律。结合有限元分析结果,基于轴压构件和纯弯构件的直接强度法公式,提出了冷弯薄壁型钢绕强轴偏压构件的极限承载力计算方法。     

椭圆形钢管混凝土构件纯弯力学性能分析

利用有限元软件ABAQUS建立椭圆形钢管混凝土构件纯弯力学性能分析的有限元计算模型,并通过6个椭圆形钢管混凝土构件纯弯试验验证有限元计算模型的准确性。在此基础上对其受力全过程中钢管及混凝土应力分布情况进行分析,同时给出钢管与核心混凝土之间的相互作用,并对剪跨比、钢管强度、混凝土强度、短轴长和长轴长等参数对纯弯时构件极限承载力及荷载-位移曲线的影响进行比较。结果表明:椭圆形钢管混凝土构件在跨中发生倾向弯曲破坏,钢管屈服强度、混凝土强度、长轴长、短轴长及钢管壁厚等参数对其力学性能影响显著,剪跨比对其力学性能影响不明显。     

圆锥形钢管混凝土长柱力学性能研究

利用有限元分析软件ABAQUS建立圆锥形钢管混凝土长柱力学性能分析的三维实体有限元计算模型,并与相应的试验结果进行对比。结果表明:有限元计算与试验所得的荷载-3H/4挠度曲线、承载力及破坏形态吻合较好。在此基础上,对圆锥形钢管混凝土长柱受力全过程中钢管与混凝土应力、应变分布情况进行分析,同时给出钢管与混凝土之间的相互作用规律,并对长细比、锥度、偏心距、材料强度及钢管壁厚等参数对圆锥形钢管混凝土长柱初始刚度、承载力及荷载-3H/4挠度曲线的影响进行比较。结果表明:圆锥形钢管混凝土长柱在3H/4处发生侧向挠曲破坏,长细比、锥度、偏心距、混凝土抗压强度及钢管壁厚等参数对其力学性能影响显著,钢管屈服强度对其力学性能影响不明显。     

An investigation of the block shear strength of coped beams with a welded clip angle connection — Part II: Numerical study

An experimental study of the block shear capacity of ten full-scale coped beams with a welded clip angle connection was presented in Part I. The test results were compared with predictions using block shear design equations in several current design standards. In general, the results showed that the existing design standards did not provide consistent predictions of the block shear capacity of coped beams with welded clip angles. In addition, the equations provided by the standards cannot accurately reflect the failure mode of the specimens observed in the tests. In order to gain a better understanding of the connection behavior, such as the stress distribution in the web near the periphery of the clip angles and the failure mechanism of the connection, an analytical study of the block shear capacity of coped beams with welded clip angles was carried out using the finite element method. Based on the limited test data and the results of the finite element analysis (FEA), a strength model was established and a design equation was proposed to evaluate the block shear strength of coped beams with welded clip angles. It was shown that the proposed design equation gave better predictions of the block shear capacity of the specimens.