Analysis of composite beams in the hogging moment regions using a mixed finite element formulation

Cracking of the concrete slab in the hogging moment region decreases the global stiffness of composite steel-concrete structures and also reduces the effect of continuity, thus making the structural behaviour highly nonlinear even for low stress levels. In this paper, the behaviour of continuous composite beams with discrete shear connection is investigated using a nonlinear mixed finite element model. The model includes appropriate nonlinear constitutive relationships for the concrete, the steel and tension stiffening effect. Furthermore, the discrete nature of the shear connection is embedded in the model and the tension stiffening effects are introduced in the analysis by using a concrete constitutive model proposed in the CEB-FIB Model Code 1990 which incorporates embedded steel. Special attention is paid to the hogging moment regions, where cracking occurs. Comparisons between the numerical analyses and experimental results in the current literature are undertaken to validate the accuracy of the model. Furthermore, a parametric study is carried out to study the influence of span length and degree of shear connection on the strength and ductility of continuous composite beams.     

Experimental investigation on inelastic behavior of composite box girder under negative moment

The mechanical behavior of negative bending moment zone in composite girder is very complex. The nonlinear characteristics due to the cracking of concrete slab need careful studies. In this experimental research, two specimens of steel-concrete composite box girder with inclined webs under hogging moment were cautiously conducted and tested. The relative slips between the steel and concrete, load-displacement relationship, the strain distribution of the steel girder, the reinforcements and the concrete slab, and the cracking behavior of the concrete slab were measured during the tests. The relatively small slips on the surfaces between the concrete slab and the top flange of the steel girder showed the full shear connection composite behavior of the girders. The initial cracking load was compared with the calculation results from linear analysis and nonlinear analysis based maximum strain. The strain of the steel web measured at different positions along the vertical direction showed the establishment of plane section assumption and the variation of neutral axis in the loading process. Moreover, shear lag effect was found in the strain distribution of the bottom flanges. The strain of concrete slab and the crack spacing showed the effect of the longitudinal reinforcement ratio on the cracking behavior of the concrete. The maximum crack width was observed in the loading process and compared with the calculation results according the design codes. The influence of reinforcement ratio on the strain of reinforcement and on the load capacity in serviceability limit state was studied in the context and it was found that the reinforcement ratio play an important role on the crack control of composite girder under hogging moment.     

Probabilistic analysis for design assessment of continuous steel-concrete composite girders

In the design of continuous steel-concrete composite girders, cross section plastic resistance can be exploited in the sagging regions, where the compressed flange of the steel beam is connected to the reinforced concrete slab. However, elastic verification of cross sections is normally adopted in the hogging regions, where the compressed portion of the steel beam is unrestrained by the concrete slab and more prone to buckling. In a combined design approach, which uses the cross section plastic resistance in the sagging regions and the cross section elastic resistance in the hogging regions, the design must satisfy the condition that the sagging plastic moment can develop while the hogging bending moment remains below the elastic limit. The objectives of this work are to present a framework for simplified probabilistic nonlinear analysis of steel-concrete composite bridges and to assess, through such framework, the combined elastic-plastic design as applied to a realistic three-span continuous steel-concrete composite road bridge. The methodology presented here is based on the First-Order Second-Moment (FOSM) approximation, adopted to compute the first- and second-order statistical moments (means, variances and covariances) of structural response quantities. Deterministic and probabilistic numerical results for the benchmark problem are illustrated and discussed.     

钢管混凝土梁柱连接形式及性能分析

指出钢管混凝土连接传递的内力主要包括梁端的剪力和弯矩,对钢梁—钢管混凝土柱连接和RC梁—钢管混凝土柱两类连接的形式及其受力性能进行了介绍,得出的结论可供设计人员参考。     

部分外包混凝土简支组合梁受弯性能试验研究

为了研究部分外包混凝土组合梁在正弯矩作用下的受力性能,考察钢梁腹部钢筋混凝土对组合梁承载力及刚度的影响,对4根简支梁试件进行了试验研究,其中包括1根普通钢-混凝土组合梁试件和3根钢梁腹板与腹部混凝土界面采用不同连接方式的部分外包组合梁试件。试验结果表明：钢梁腹板与腹部混凝土界面采用不同连接方式对部分外包组合梁的受弯承载力和刚度没有显著的影响;与普通钢－混凝土组合梁相比,由于钢梁腹部钢筋混凝土的贡献,部分外包组合梁的受弯承载力和抵抗变形的能力均有较大的提高;承载力极限状态时部分外包组合梁中钢梁与腹部混凝土之间的相对滑移值较小,其滑移效应对组合梁截面受弯承载力的影响可以忽略不计。在试验研究的基础上,推导了部分外包组合梁塑性受弯承载力的计算公式,计算结果表明,简化塑性理论可以较准确地预测该类组合梁的受弯承载力。     

组合效应对钢节点抗震性能的影响因素分析

钢—混凝土组合梁当前在钢框架结构中已经得到了广泛的应用,但是地震荷载作用下组合节点的设计方法却一直在完善和发展.基于组合节点的数值分析,着重研究钢框架梁柱节点的抗震性能,进行了有限元分析、模型参数分析,研究了不同变量条件下节点抗震性能与梁强度的平衡关系,并针对混凝土板中的配筋率、混凝土板板厚、钢节点类型等因素进行了分析和讨论.分析结果表明,在进行钢框架梁柱节点的抗震设计时,应该考虑混凝土板的组合效应.     

钢-混凝土组合梁截面组合抗剪性能的试验研究

对4根密实截面钢-混凝土组合梁的组合抗剪性能进行了试验研究。试件全部采用简支,跨中两点对称单调静力加载,考虑抗剪连接程度及正负弯矩的影响。试验结果表明,组合梁负弯矩区的界面滑移规律与正弯矩区的不同,其大小对组合梁的抗剪承载能力影响较小。不论混凝土翼板是处于组合梁截面的受压区还是受拉区,其对组合梁截面的抗剪承载能力均有明显的贡献,目前规范仅计算钢梁腹板的抗剪作用偏于保守。按叠加法建立了计算组合梁抗剪承载能力的计算式,计算值与实测值吻合良好。     

Experimental study on curved composite beams subjected to combined flexure and torsion

There are situations in which a composite steel–concrete beam is subjected to torsion, such as members that are curved in plan or straight edge beams. The concrete slab and steel beam contribute to the torsional strength and stiffness of a composite steel–concrete beam, but this composite action is usually ignored in design codes of practice, which leads to conservative designs. Therefore, this paper investigates the ultimate strength of curved in place composite steel–concrete beams. Eight curved in plan composite steel–concrete beams have been tested under a single applied load at mid-span. Partial shear connection has also been considered in these tests. The composite steel–concrete beams have been designed with different span/radius of curvature ratios. This paper further supports the view that, in the presence of flexure, there will be an increase in the torsional moment capacity, but the flexural moment capacity does not greatly increase in the presence of torsion. A model has also been presented to represent the bending–torsion interaction for curved in plan composite steel–concrete beams with full and partial shear connection.     

Experimental study of prestressed steel-concrete composite beams with external tendons for negative moments

Four groups of prestressed steel-concrete composite beams with external tendons in negative moment regions were tested, and the cracking behaviours and the ultimate negative moment resistances of the composite beams were investigated experimentally. It is found that in hogging moment regions, on adding prestressing to the composite beams with external tendons, the cracking resistance of the beams can be effectively increased; however, the incremental internal tendon forces of the prestressed composite beams are rather small, and therefore can be neglected in the evaluation of the negative moment resistance of the beams. In hogging moment regions, the ultimate resistance of a composite beam prestressed with external tendons is governed by either distortional lateral buckling or local buckling, or an interactive mode composed of the two bucklings. For a beam with a compact section, the negative bending moment can reach the plastic moment when the steel section is fully plastic, and for a non-compact section, the negative bending moment is limited to the yield moment at which the compression steel flange initiates yield. The method for evaluating the buckling resistance of the composite beams is discussed, and a tentative design method based on BS5400: Part 3 is proposed to assess the buckling resistances of the prestressed composite beams.     

从一桩工程质量司法鉴定案例引出的几点思考

从现浇混凝土楼板负弯矩钢筋偏位质量问题处理,引发对质量、安全问题界定的思考。从而发现板类设计中普遍按惯例将钢筋保护层厚度直接取为规范最小值,造成施工中实际楼板类构件负弯矩钢筋保护层厚度控制困难,普遍超设计要求,从而引发对过度加固问题的关注,以及如何通过荷载试验来解决。     

Shear strength of the connection between a steel coupling beam and a reinforced concrete shear wall in a hybrid wall system

No specific guidelines are available for computing the shear strength of the connection between a steel coupling beam and a reinforced concrete shear wall in a hybrid wall system. There were carried out analytical and experimental studies on the connection between a steel coupling beam and a concrete shear wall in a hybrid wall system. The bearing stress at failure in the concrete below the embedded steel coupling beam section is related to the concrete compressive strength and the ratio of the width of the embedded steel coupling beam section to the thickness of the shear walls. Experiments were carried out to determine the factors influencing the shear strength of the connection between a steel coupling beam and a reinforced concrete shear wall. The test variables included the reinforcement details that confer a ductile behaviour in the connection between a steel coupling beam and a shear wall, i.e., the auxiliary stud bolts attached to the steel beam flanges and the transverse ties at the top and the bottom steel beam flanges. In addition, additional test were conducted to verify the strength equations of the connection between a steel coupling beam and a reinforced concrete shear wall. The proposed equations in this study were in good agreement with both our test results and other test data from the literature.     

钢梁-混凝土墙铰结连接节点嵌固弯矩的分析与计算

近年来,外钢框架-混凝土核心筒混合结构在我国高层建筑中逐渐增多。钢梁-混凝土墙铰结连接节点是这种混合结构中常用的一种节点形式,在其预埋件的设计计算中,需要考虑节点连接处嵌固弯矩的影响。本文针对现有嵌固弯矩近似计算方法需求解超越方程的问题,首先基于螺栓连接的剪力-变形本构关系,给出了嵌固弯矩的理论计算方法,随后基于螺栓群连接的近似受力分布,提出了近似弹塑性计算方法,并根据塑性极限分析理论提出了近似极限计算方法。两种方法可直接计算嵌固弯矩,无需求解超越方程,其中近似极限计算方法更为简单。通过与收集到的20个试验结果的对比分析,讨论了理论方法和本文提出的近似方法准确性。结果表明,本文提出的近似弹塑性计算方法比试验值偏大约2%,近似极限计算方法比试验值偏大约20%,偏于保守较多。     

Loading capacity of composite slim frame beams

The estimation of the flexural stiffness and bending capacity of composite slim beams is rather complicated, because the influence of many factors should be taken into account. These factors include variable section dimensions, development of cracks and non-linear characteristics of concrete. This is especially true for the composite slim frame beam, in which the sagging moment region and the hogging moment region should both be considered. In this paper, experimental investigations have been conducted to investigate the flexural behavior of two specimens of composite slim frame beam with deep deck under monotonic loading. Based on the experimental results, formulas of calculating the bending capacity and flexural stiffness in the hogging moment region of the slim beam with deep deck has been proposed. Combining these formulas with existing formulas of sagging moment, formulas for the equivalent stiffness and the design method of the frame slim beam have been developed. The feasibility of the proposed formulas and design method has been verified by the test results.     

Design of semi-continuous composite steel-concrete beams at the fire limit state

A two-dimensional temperature analysis procedure based on the finite element method (FEM) is described and applied to steel-concrete composite beams. A computer program developed for the analysis is detailed. A strategy is also proposed for incorporating the influence of the partial resistance of the composite connections in reducing the sagging moment at central regions of the beam spans when the beam is calculated as semi-continuous. Finally, an example problem is discussed, comparing the design uniformly distributed loads that can be supported by a composite beam calculated as semi-continuous and with simply supported spans. The temperature distribution due to fire at the central region of the spans is taken as in the simplified procedure proposed in European Prestandard ENV 1994-1-2 [ENV 1994-1-2. Eurocode 4, Design of composite steel and concrete structures — Structural fire design. Brussels: European Committee for Standardization (CEN); 1994] and then obtained with the more rigorous calculation using the described numerical algorithm. It will be assumed that no ultimate limit state will occur due to shear force (web buckling) or due to bending moment at the hogging moment regions of the beam (web and bottom flange buckling or distortional lateral buckling).     

负弯矩区部分充填混凝土对窄幅钢箱-混凝土组合梁受力性能影响试验研究

为了研究充填混凝土对窄幅钢箱-混凝土组合梁负弯矩区的荷载-挠度特征、截面应变分布、抗弯刚度、钢箱梁的约束机理以及承载能力的影响,对5根部分充填混凝土窄幅钢箱-混凝土简支组合梁试件和1根全充填混凝土试件进行了静力加载试验。试验结果表明：在负弯矩作用下,配筋率和剪力连接程度对窄幅钢箱-混凝土组合梁的受力性能影响显著,配筋率从1%增加到2%,承载力提高22%;剪力连接度从0.75增加到1.25,承载力提高13%。半充填和全充填混凝土对窄幅钢箱-混凝土组合梁试件的承载力和刚度影响很小。充填混凝土对钢箱梁的屈曲约束作用明显,所有试件最终破坏时均未发生内凹屈曲。由于充填混凝土有效地限制钢箱变形,从而提高了组合梁的承载力和结构的稳定性。基于简化塑性理论提出了部分充填混凝土窄幅钢箱-混凝土组合梁的承载力计算方法,且计算值与试验值吻合较好。     

浅析钢管混凝土柱-钢梁节点形式

介绍了目前钢管混凝土柱—钢梁框架常用节点的构造形式和受力特点,按照柱贯通式节点和梁贯通式节点的分类,分析了钢管混凝土柱—钢梁框架节点形式的一些研究,并提出了简洁合理的端板螺栓连接新型节点形式,以供钢管混凝土柱—钢梁结构体系的节点设计参考。     

钢-混凝土组合梁在负弯矩作用下抗剪性能的试验研究

通过3根钢-混凝土组合梁在负弯矩作用下的试验,研究了其变形发展及破坏过程,得到了组合梁的跨中剪力-挠度曲线、交界面滑移曲线和沿截面高度分布的应变变化曲线,分析了剪切连接程度、截面尺寸、剪跨比、材料强度、钢筋配置等因素对组合梁承载力和延性的影响。对钢梁进行了塑性分析,得出在负弯矩作用下钢-混凝土组合梁抗剪承载力的提高不是由于钢梁腹板的硬化效应所致,而是由于混凝土翼板的贡献,并提出了考虑混凝土翼板影响的组合梁在负弯矩作用下抗剪承载力计算公式。将计算结果与实测结果进行了比较,二者吻合良好。     

钢-混凝土连续组合梁桥负弯矩区抗裂设计

为进一步验证抗拔不抗剪连接件对组合梁桥负弯矩区抗裂的效果,并研究采用该连接件时负弯矩截面的设计方法,利用考虑滑移效应的组合梁负弯矩区受力模型,推导了采用抗拔不抗剪连接时组合梁负弯矩截面承载力的计算模型,计算结果与有限元分析结果吻合良好.通过理论推导,进一步证明了抗拔不抗剪连接件对负弯矩截面承载力的折减不大,且能有效延缓...     

Behaviour of a Moment Resisting Composite Steel and Concrete Joint Under Alternate Loading

The authors show the results of a study conducted on a joint connecting a concrete column to a composite steel concrete floor, subjected to tension on the beams as a result of the decomposition of sagging bending moment. The beam to column connection is achieved by means of headed studs welded to the beam and embedded in the concrete cast. Five different configurations have been tested at failure and the results are compared to formulae proposed in literature. Different degrees of ductility, reliability and strength have been obtained varying geometry and reinforcement ratio on the joints tested.     

钢梁与混凝土墙铰接节点嵌固弯矩的计算方法

钢梁与混凝土墙铰接节点是外钢框架-混凝土核心筒结构中常见的一种节点连接形式,在其预埋件的设计计算中,需要考虑节点连接处嵌固弯矩的影响。该文讨论了钢梁与混凝土墙的铰接节点嵌固弯矩的形成原因及受力特点,介绍了嵌固弯矩的理论计算方法、Crawford计算方法及规范建议方法,并对三类方法进行了对比。研究表明,采用规范建议的方法可得到偏于安全的结果。