Behavior of steel-concrete composite cantilever box beams under negative moment

Four steel-concrete composite cantilever beam specimens were tested to investigate their mechanical behavior under negative moment induced by concentrated loads at the ends of the beams. The failure modes, serviceability and ultimate bearing capacities of the composite beams with full shear connection were studied. The crack initiation and propagation were investigated with consideration of two types of shear connectors. Three kinds of longitudinal reinforcement ratios were also examined. The experimental results indicate that an increase in the reinforcement ratio is beneficial to the bearing capacity of the composite beams to some extent and that the shear stud connector is superior to the steel block connector with regards to the serviceability of the beams. Two numerical models, which were based on a concrete material model and an elasto-plastic material model, were employed to simulate the behavior of steel-concrete composite beams. The numerical calculation results show that the combination of the two models can be used to predict the longitudinal cracking load and ultimate bearing capacity of composite cantilever beams. Based on the experimental and numerical results, it was found that the ultimate bearing capacity of a steel-concrete composite beam under negative moment can be significantly affected by longitudinal cracks in the concrete slabs. An equation to predict the longitudinal cracking load of a composite cantilever beam under negative moment by concentrated load was proposed and found to have good accuracy.     

Experimental study on inelastic mechanical behaviour of composite girders under hogging moment

Negative bending moments acting on the support regions of continuous composite girders generate tensile stresses in the concrete slab and compressive stresses in the lower steel profile. As a result, the mechanical behaviour of these girders becomes strongly nonlinear, which needs special study. In this paper, static experimental tests on four half-scale models of steel and concrete composite girders with different shear connectors such as studs and Perfo-Bond Strips (PBLs) under hogging moments are cautiously conducted in order to investigate the reduction of flexural stiffness and the inelastic behaviour after cracking. In the test results, crack development, crack widths and strains of the composite section before and after cracking were observed. The crack width evaluation methods based on design codes for steel and concrete composite girders under negative bending moment were compared. Crack widths should be controlled appropriately within an allowable value in the slab under service load. The strains in reinforcing bars obtained through the static tests agreed well with the values calculated through the application of the existing tension stiffening theory. The test specimens could be assumed to be a full composite section until the ultimate state on the basis of load and slip relationship results of shear connectors. It follows that analytical and experimental studies can be served as a basis for the design of continuous composite bridges.     

Experimental study on double composite action in the negative flexural region of two-span continuous composite box girder

In the negative flexural region of continuous composite girder, cracking of concrete slab results in a reduction in the sectional stiffness and may affect the durability of reinforcement. Double composite action defined as attaching additional concrete to steel bottom flange to improve local buckling strength can be a way to increase the sectional stiffness. It has many advantages for construction while disadvantages also exist. In this case, two continuous composite girders, both of which had two 9 m long spans with 300 mm extension at each edge support and were 0.55 m high, were designed to study the mechanical properties in concrete crack, formation of sectional plastic hinge, load-carrying capacity, etc. One was a conventional composite girder named CCG and the other one was designed with double composite action in the negative flexural region named DCG. Moreover, evaluations of concrete crack width, based on different design codes, and cracking moment were compared with test results and agreed with each other. It indicated double composite action made concrete crack development slower in service load stage. The evaluation of sectional bending-carrying capacity of CCG in the negative flexural region based on the mechanical model with full plastic section of Euro Code 4 and an analogous method was found to evaluate that of DCG. The evaluation results coincided with test results proved the summation which can be drawn from test results.     

箱梁施工中负弯矩施工质量的控制

根据多年的工作经验,针对箱梁施工中存在的负弯矩波纹管定位、漏浆严重、压浆不饱满、张拉槽口后期封堵,以及锚垫板加强筋处理等问题,提出了相应的预防和处理措施,解决了箱梁施工的质量问题。     

钢—混凝土组合节点在正弯矩作用下的试验研究

针对钢—混凝土组合柱组合节点在正弯矩下受力性能进行了试验研究,并探讨了混凝土组合柱对组合节点受力性能的影响。试验结果表明：组合节点在正弯矩作用下,受拉部件主要为中和轴下面的螺栓,受压部件主要为混凝土板。其他条件相同时,柱翼缘内填充混凝土的组合节点,在节点延性略有减小的同时,初始强度得到提高。     

Behavior of steel-concrete composite cantilever beams with web openings under negative moment

The effect of web openings on the mechanical behavior of composite beams under negative moment was studied through monotonically loading tests. Nonlinear finite element method based analysis was also conducted for cantilever composite beams. The test and the finite element analysis results indicated that the initial cracking loads of composite beams with web opening are lower than that without web opening. The first crack initiated from the concrete slab on the top of the opening. The beams with web opening failed due to shear failure of concrete slab upon the opening. It was also found that the load carrying capacity of beam decreases with the increase of the moment-to-shear ratio at the central line of the opening and the mechanical behavior of beam can be improved significantly by applying stiffening steel plates around the opening. To quantify the reduction of load carrying capacity, a method for calculating the load carrying capacity of beams with web openings under negative moment was derived with consideration of the interaction between moment and shear. Good consistency was obtained between the proposed method, the finite element method and the test results.     

基于碳化的预应力组合箱梁桥可靠性分析

为了研究预应力混凝土结构在混凝土碳化后,结构在服役期间的可靠度,分析讨论了混凝土碳化及其影响因素.将混凝土强度、保护层厚度、计算模式不确定性系数以及荷载增长系数作为随机变量,以混凝土的碳化深度作为一个随时间变化的随机过程,建立了一般大气环境下,混凝土碳化的时变概率随机模型.在此基础上,对五跨预应力组合箱梁进行了研究,从可靠度方面给出了在服役期间结构的可靠度水平.     

组合式钢桥弧形箱梁跨铁路安装施工工艺

介绍了遥控液压调平技术的特点及使用范围,以阳煤集团棚户区改造工程麻地巷组合钢箱梁桥安装工程为依托,对组合式钢桥弧形箱梁跨铁路安装施工工艺流程及操作要点进行了阐述,指出应用该工艺取得了良好的社会和经济效益。     

钢-混凝土组合梁在负弯矩下的承载力计算

介绍了在负弯矩作用下钢—混凝土连续梁的特点,在理论分析的基础上,阐述了塑性中和轴位于钢梁上翼缘内和钢梁腹板内的两种情况,并给出在这两种情况下正截面的受弯承载力公式。     

Available rotation capacity of composite bridge plate girders under negative moment and shear

This paper presents a study of the behaviour of slender composite plate girders under negative bending moment and shear. It is known that at composite bridge intermediate supports, the slender composite beams have very limited ductility, which has led to the adoption of elastic methods for the design of these members. However, this elastic design is time-consuming and does not correspond with real beam behaviour. In order to propose a simpler and more intuitive design method which corresponds better with real beam behaviour, the support region limited ductility must be quantified. In this study, slender composite beam ductility under shear and negative bending is investigated, using a numerical model developed specifically for this purpose. On the basis of the parametric analysis results, a simple analytical model for quantifying the slender composite beam support region ductility is proposed and verified.     

简支钢——混凝土组合箱梁有限元分析

为研究简支钢—混凝土组合梁在荷载作用下的受力性能,采用有限元软件ANSYS对某钢—混凝土组合箱梁进行数值模拟,对此类组合梁进行研究和分析,研究表明:在弹性范围内,钢混组合梁荷载与挠度基本上呈线性关系;采用ANSYS软件可以准确的模拟组合梁的受力过程。     

Experimental and analytical studies on a streamlined steel box girder

A new type of streamlined girder (lenticular cross-section) bridge with a thin-walled steel box girder is proposed. In order to deal with the problem of increasing traffic congestion, this bridge is designed with a large width-to-span ratio, which results in significant shear lag effects and causes non-uniform stress distribution in the three-cell thin-walled box girder, especially along the flanges of the girder. The aim of this study is to investigate the effect of shear lag in thin-walled box girder bridges with large width-to-span ratios through both experimental and numerical studies. A large-scale Plexiglas model is tested under different loading cases. The material parameters are obtained from physical characteristics tests and tensile tests. In addition, a computational model is presented for a comprehensive simulation of a girder bridge including the orthotropic top/bottom/web plates and their ribs, which leads to accurate modeling of structural properties of the girder. The simulation of the computation results compared well with the experimental results. It is illustrated that the finite element analysis is an effective method to predict properties of this class of bridges.     

简支钢混组合箱梁界面相对滑移性能研究

为研究简支组合梁中钢梁与混凝土板之间界面的相对滑移,采用有限元软件ANSYS对某钢—混凝土组合箱梁进行有限元模拟,分析了荷载大小和混凝土强度对界面相对滑移的影响。研究表明:钢梁与混凝土板之间的相对滑移量随荷载的增大而增大;相对滑移量随混凝土强度的增大而略微减小。     

Experimental investigation of composite shear walls under shear loadings

One of the efficient methods for improving the seismic behaviour of high-rise buildings is using Composite Steel Plate Shear Wall (CSPSW). In this paper, extensive experimental studies of one and three-story CSPSWs with the scale of 1:3 and 1:4, together with stress equations of each element are reported. The experimental results indicate that this system has reliable behaviour if the columns have high bending stiffness. Also bolts spacing to plate thickness ratio has direct relationship with system ductility. However, plate yield load has an inverse relationship with this ratio. In this system, plate stiffening requirement is obtained with minimum reinforcement for reinforced concrete, though for damage prevention high strength concrete is preferred. Also, the results show a good agreement for the recommended values of (b/t) by an AISC code for preventing plate buckling.     

Experimental investigation of composite shear panels under cyclic loading

The paper reports the experimental investigation of composite shear panels, composed of steel columns incorporated in concrete panels by means of headed shear studs, under reversible cyclic loading. Results are presented for push-out tests on small specimens and for whole panels. The response of two composite panels is compared to that of a conventional reinforced concrete panel of similar design parameters, serving as control. The results indicate that while ductility of the composite panel with unmodified connection is somewhat lower than that of the control panel, damage to the panel is substantially reduced. Composite panel with voids at studs’ roots displays enhanced ductility and energy absorption capacity. Other means of enhancing these parameters are discussed. An approximate, simplified analytical model based on push-out tests, yields a good qualitative prediction of panel response with conservative values of capacity, ductility and energy absorption.     

Experimental investigation on fatigue behavior of steel reinforced concrete composite beam-to-girder joints

Fatigue behavior and failure mechanism of steel reinforced concrete (SRC) beam-to-girder joints is discussed in this paper, which is intended for use in high-speed railway station structures due to their high stiffness and load capacity. Three identical SRC beam-to-girder joint specimens were designed and tested under static loading and two stages of fatigue loading. In the first stage of fatigue loading, the specimens were subjected to design fatigue load for 2 million cycles, while during the second stage, the specimens were loaded to failure under increased fatigue loading amplitude in order to know its fatigue strength and failure mechanism. The constructional details of SRC beam-to-girder joint specimen and the method of loading and testing are presented. The comparison in structural behavior of the joint is made between under static and fatigue loading. Fatigue failure characteristics of the joint are described in detail. It is found that the SRC beam-to-girder joints remained in their elastic range and the concrete surface crack did not exceed 0.1 mm when subjected to design static loading and 2 million cycles of design fatigue loading. There was no significant difference in structural behavior of each component of SRC composite beam between static and fatigue loading. Fatigue failure occurred after these joints were applied higher-level fatigue loading for another 0.70 to 0.91 million cycles. Fatigue crack was initiated at the tension flange of I-shape steel of beam connected by welding to the flange of I-shape steel of girder or at the hole in tension flange of I-shape steel of beam, and then the crack propagated along flange width and web height of the I-shape steel in beam until the I-shape steel lost loading capacity due to lack of enough cross section. The fatigue behavior of constructional detail of the I-shape steel played a key role in the fatigue strength of the SRC beam-to-girder joints. Discussions on improving the fatigue strength of SRC beam-to-girder joints and future research aspects are presented finally.     

S350冷弯薄壁型钢龙骨式复合墙体抗震性能试验研究

对12面S350冷弯薄壁型钢龙骨式复合墙体试件进行抗剪试验研究。试件尺寸为宽2400mm、高3000mm;覆面板组合分为2组,分别为石膏板加OSB板、石膏板加带肋波纹钢板;加载方式包括水平单调加载和低周反复加载。试件共设计3种洞口形式,以研究开洞尺寸及位置对墙体抗剪性能的影响。试验结果表明:龙骨式复合墙体试件的破坏模式主要表现为石膏板的局部挤压碎裂、带肋波纹钢板的剪切屈曲和墙体边立柱脚部的屈曲。试验得到墙体试件在不同加载方式下的抗侧移刚度、抗剪承载力、位移延性系数和能量耗散系数等性能指标。最后,结合国内外研究成果,对龙骨式复合墙体考虑开洞因素的抗剪承载力分析方法进行研究。     

高速公路预应力混凝土组合箱梁裂缝加固技术

以省内组合梁裂缝加固施工项目为研究案例,分析了预应力混凝土组合箱梁结构体系的构造及优缺点,指出了预应力混凝土组合箱梁裂缝特点,针对性提出了加固处理措施,以提高省内组合梁的裂缝处治总体水平。     

高速公路预应力混凝土组合箱梁裂缝加固技术

简要介绍了组合箱梁裂缝的类型,从原材料选用、设计、施工等方面,分析了组合箱梁裂缝产生的原因,并详细阐述了组合箱梁裂缝的加固技术,旨在避免裂缝发生扩张、恶化、保证组合箱梁的坚固耐久性能。