Ultimate negative bending-moment capacity of outer-plated steel-concrete continuous composite beams

Static load tests and bearing capacity analyses are carried out for two outer-plated steel-concrete continuous composite beams. The load-deflection curve and the load-strain curve of specimens are obtained and analyzed. The test results indicate that effective cooperation can be achieved by the shearresistant connection between the reinforcement in the negative moment area and the outer-plated steel beam, and the overall working performance of the composite beams is favorable. At the load-bearing limiting state, the plastic strain on the maximum negative and positive moment section becomes fully developed so as to form relatively ideal plastic hinges. With the increase in the reinforcement ratio, the moment-carrying capacity of the composite beams improves significantly, but the ductility of the beams and the rotation ability of the plastic hinges decrease. The formulae for calculating the limit bending capacity in the negative moment area of outer-plated steel-concrete composite beams are proposed based on the test data. The calculated results agree well with the test results.

Closed-form solution for shear lag effects of steel-concrete composite box beams considering shear deformation and slip

Based on the consideration of longitudinal warp caused by shear lag effects on concrete slabs and bottom plates of steel beams,shear deformation of steel beams and interface slip between steel beams and concrete slabs,the governing differential equations and boundary conditions of the steel-concrete composite box beams under lateral loading were derived using energy-variational method.The closed-form solutions for stress,deflection and slip of box beams under lateral loading were obtained,and the comparison of the analytical results and the experimental results for steel-concrete composite box beams under concentrated loading or uniform loading verifies the closed-form solution.The investigation of the parameters of load effects on composite box beams shows that:1) Slip stiffness has considerable impact on mid-span deflection and end slip when it is comparatively small;the mid-span deflection and end slip decrease significantly with the increase of slip stiffness,but when the slip stiffness reaches a certain value,its impact on mid-span deflection and end slip decreases to be negligible.2) The shear deformation has certain influence on mid-span deflection,and the larger the load is,the greater the influence is.3) The impact of shear deformation on end slip can be neglected.4) The strain of bottom plate of steel beam decreases with the increase of slip stiffness,while the shear lag effect becomes more significant.

Nonlinear finite element analysis of steel-concrete composite beams

Proposes a simplified finite element model for steel-concrete composite beams. The effects of slip can be taken into account by creating a special matrix of shear connector stiffness and using the iteration method. Meanwhile, the effect of material non-linearity of steel and concrete on rigidity and strength of composite beams is considered. With the age-adjusted effective modulus method, the analysis for the whole process of shrinkage and creep under long-term load can be performed. The ultimate load, deflection, stress and slip of continuous composite beams under short-term and long-term load are computed using the proposed finite element model. The numerical results are compared with the experimental results and existing values based on other numerical methods, and are found to be in good agreement.

Mechanical performance of shear studs and application in steel-concrete composite beams

This work experimentally investigates the effects of shear stud characteristics on the interface slippage of steel-concrete composite push-out specimens. ABAQUS is used to establish a detailed 3D finite element(FE) model and analyze the behavior of push-out specimens. The modeling results are in good agreement with the experimental results. Based on parametrical analysis using the validated FE approaches, the effects of important design parameters, such as the diameter, number, length to diameter ratio, and yield strength of studs, concrete strength and steel transverse reinforcement ratio, on the load-slip relationship at the interface of composite beams are discussed. In addition, a simplified approach to model studs is developed using virtual springs with an equivalent stiffness. This approach is demonstrated to be able to predict the load-displacement response and ultimate bearing capacity of steel-concrete composite beams. The predicted results show satisfactory agreement with experimental results from the literature.

Double-layer model updating for steel-concrete composite beam cable-stayed bridge based on GPS

In order to establish the relationship between the measured dynamic response and the health status of long-span bridges, a double-layer model updating method for steel-concrete composite beam cable-stayed bridges is proposed. Measured frequencies are selected as the first-layer reference data, and the mass of the bridge deck, the grid density, the modulus of concrete and the ballast on the side span are modified by using a manual tuning technique. Measured global positioning system （GPS） data is selected as the second-layer reference data, and the degradation of the integral structure stiffness EI of the whole bridge is taken into account for the second-layer model updating by using the finite element iteration algorithm. The Nanpu Bridge in Shanghai is taken as a case to verify the applicability of the proposed model updating method. After the first-layer model updating, the standard deviation of modal frequencies is smaller than 7%. After the second-layer model updating, the error of the deflection of the mid-span is smaller than 10%. The integral structure stiffness of the whole bridge decreases about 20%. The research results show a good agreement between the calculated response and the measured response.

Distortional buckling analysis of steel-concrete composite box beams considering effect of stud rotational restraint under hogging moment

Restrained distortional buckling is an important buckling mode of steel-concrete composite box beams(SCCBB)under the hogging moment.Rotational and lateral deformation restraints of the bottom plate by the webs are essential factors affecting SCCBB distortional buckling.Based on the stationary potential energy principle,the analytical expressions for the rotational restraint stiffness(RRS)of the web upper edge as well as the RRS and the lateral restraint stiffness(LRS)of the bottom plate were derived.Also,the SCCBB critical moment formula under the hogging moment was derived.Using twenty specimens,the theoretical calculation method is compared with the finite-element method.Results indicate that the theoretical calculation method can effectively and accurately reflect the restraint effect of the studs,top steel flange,and other factors on the bottom plate.Both the RRS and the LRS have a nonlinear coupling relationship with the external loads and the RRS of the web’s upper edge.Under the hogging moment,the RRS of the web upper edge has a certain influence on the SCCBB distortional buckling critical moment.With increasing RRS of the web upper edge,the SCCBB critical moment increases at first and then tends to be stable.

Bending Stiffness of Truss-Reinforced Steel-Concrete Composite Beams

This paper is concerned with a special steel-concrete composite beam in which the resisting system is a truss structure whose bottom chord is made of a steel plate supporting the precast floor system. This system works in two distinct phases with two different resisting mechanisms: during the construction phase, the truss structure bears the precast floor system and the resisting system is that of a simply supported steel truss;once the concrete has hardened, the truss structure becomes the reinforcing element of a steel-concrete composite beam, where it is also in a pre-stressed condition due to the loads carried before the hardening of concrete. Within this framework, the effects of the diagonal bars on the bending stiffness of this composite beam are investigated. First, a closed-form solution for the evaluation of the equivalent bending stiffness is derived. Subsequently, the influence of geometrical and mechanical characteristics of shear reinforcement is studied. Finally, results obtained from parametric and numerical analyses are discussed.

A new 3-D element formulation on displacement of steel-concrete composite box beam

Slip of a composite box beam may reduce its stiffness, enlarge its deformation and affect its performance. In this work, the governing differential equations and boundary conditions of composite box beams were established. Analytic solutions of combined differential equations were also established. Partial degree of freedom was adopted to establish a new FEA element of three-dimensional beam, taking into account the slip effect. Slip and its first-order derivative were introduced into the nodes of composite box beams as generalized degree of freedom. Stiffness matrix and load array of beam elements were established. A three-dimensional nonlinear calculation program was worked out. The results show that the element is reliable and easy to divide and is suitable for special nonlinear analysis of large-span composite box beams.

Analysis and seismic tests of composite shear walls with CFST columns and steel plate deep beams

A composite shear wall concept based on concrete filled steel tube （CFST） columns and steel plate （SP） deep beams is proposed and examined in this study. The new wall is composed of three different energy dissipation elements： CFST columns; SP deep beams; and reinforced concrete （RC） strips. The RC strips are intended to allow the core structural elements - the CFST columns and SP deep beams - to work as a single structure to consume energy. Six specimens of different configurations were tested under cyclic loading. The resulting data are analyzed herein. In addition, numerical simulations of the stress and damage processes for each specimen were carried out, and simulations were completed for a range of location and span-height ratio variations for the SP beams. The simulations show good agreement with the test results. The core structure exhibits a ductile yielding mechanism characteristic of strong column-weak beam structures, hysteretic curves are plump and the composite shear wall exhibits several seismic defense lines. The deformation of the shear wall specimens with encased CFST column and SP deep beam design appears to be closer to that of entire shear walls. Establishing optimal design parameters for the configuration of SP deep beams is pivotal to the best seismic behavior of the wall. The new composite shear wall is therefore suitable for use in the seismic design of building structures.

Dynamic Characteristics of Long -Span Steel -Concrete CompositeBeam Bridge Based on Vehicle -Bridge Coupling Effect

In order to investigate the effect of vehicle-bridge coupling on the dynamic characteristics of the bridge,a steel-concrete composite beam suspension bridge is taken as the research object,and a three-dimensional spatial model of the bridge and a biaxial vehicle model of the vehicle are established,and then a vehicle-bridge coupling vibration system is constructed on the basis of the Nemak-βmethod,and the impact coefficients of each part of the bridge are obtained under different bridge deck unevenness and vehicle speed.The simulation results show that the bridge deck unevenness has the greatest influence on the vibration response of the bridge,and the bridge impact coefficient increases along with the increase in the level of bridge deck unevenness,and the impact coefficient of the main longitudinal girder and the secondary longitudinal girder achieves the maximum value when the level 4 unevenness is 0.328 and 0.314,respectively;when the vehicle speed is increased,the vibration response of the bridge increases and then decreases,and the impact coefficient of the bridge in the middle of the bridge at a speed of 60 km/h achieves the maximum value of 0.192.

Experimental and analytical study on seismic behavior of steel-concrete multienergy dissipation composite shear walls

In this paper, a steel-concrete multi-energy dissipation composite shear wall, comprised of steel-reinforced concrete （SRC） columns, steel plate （SP） deep beams, a concrete wall and energy dissipation strips, is proposed. In order to study the multi-energy dissipation behavior and restorability after an earthquake, two stages of low cyclic loading tests were carded out on ten test specimens. In the first stage, test on five specimens with different number of SP deep beams was carried out, and the test lasted until the displacement drift reached 2%. In the second stage, thin SPs were welded to both sides of the five specimens tested in the first stage, and the same test was carried out on the repaired specimens （designated as new specimens）. The load-bearing capacity, stiffness, ductility, hysteretic behavior and failure characteristics were analyzed for both stages and the results are discussed herein. Extrapolating from these results, strength calculation models and formulas are proposed herein and simulations using ABAQUS carried out, they show good agreement with the test results. The study demonstrates that SRC columns, SP deep beams, concrete wall and energy dissipation strips cooperate well and play an important role in energy dissipation. In addition, this study shows that the shear wall has good recoverability after an earthquake, and that the welding of thin SP＇s to repair a deformed wall is a practicable technique.

Experimental study on seismic behaviors of steel-concrete composite frames

Steel-concrete composite frames are seeing increased use in earthquake region because of their excellent structural characteristics, including high strength, stiffness, and good ductility. However, there exist gaps in the knowledge of seismic behavior and the design provisions for these structures. In order to better understand the seismic behaviors of composite frame systems, eight steel-concrete composite frames were designed. These composite frames were composed of steel-concrete composite beams and concrete filled steel tube columns. The axial compression ratio of column, slenderness ratio and linear stiffness ratio of beam to column were selected as main design parameters. The low reversed cyclic loading tests of composite frame system were carried out. Based on test results, the seismic behaviors of composite frames such as failure mode, hysteresis curve, strength degradation, rigidity degradation, ductility and energy dissipation were studied. Known from the test phenomenon, the main cause of damage is the out-of-plane deformation of steel beam and the yielding destruction of column heel. The hysteretic loops of composite frame appear a spindle shape and no obvious pinch phenomenon. The results demonstrate that this type of composite frame has favorable seismic behaviors. Furthermore, the effects of design parameters on seismic behaviors were also discussed. The results of the experiment show that the different design parameter has different influence rule on seismic behaviors of composite frame.

The Study of Force and the Mechanical Characteristic of Incremental Launching Construction Method on a Steel-Concrete Continuous Beam Bridge

The usage of steel-mixed composite beams is quite extensive today.During an event of constructing steel-mixed composite bridges,the incremental launching construction method is generally adopted.This paper mainly analyzes the force of incremental launching construction on a steel-concrete continuous beam bridge,the classification of incremental launching construction,the application of incremental launching construction in steel-mixed composite beams,the temporary facilities existing in incremental launching construction as well as their existing problems.Lastly,the analysis of the stress of composite beams in incremental launching construction is described by using the reference for the construction of mixed composite continuous beam bridges provided.

Identification of Connection Flexibility Effects Based on Load Testing of a Steel-Concrete Bridge

In the case of composite girders, an effective cooperation of both parts of the section is influenced by deformability of connectors. Limited flexural stiffness of welded studs, used commonly in bridge structures, does not provide full interaction of a steel beam and a concrete slab. This changes strain distribution in cross-sections of a composite girder and results in redistribution of internal forces in steel and concrete element. In the paper partial interaction index defined on the basis of a neutral axis position, which can be used for verification of steel-concrete interaction in real bridge structures rather than in specimens is proposed. The range of the index value changes, obtained during load testing of a typical steel-concrete composite beam bridge, is presented. The investigation was carried out on a motorway viaduct, consisting of two parallel structures. During the testing values of strains in girders under static and quasi-static loads were measured. The readings from the gauges were used to determine the index, characterizing composite action of the girders. Results of bridge testing under movable load, changing position along the bridge span is presented and obtained in-situ influence functions of strains and index values are commented in the paper.

Field validation of UHPC layer in negative moment region of steel-concrete composite continuous girder bridge

Improving the cracking resistance of steel-normal concrete(NC)composite beams in the negative moment region is one of the main tasks in designing continuous composite beam(CCB)bridges due to the low tensile strength of the NC deck at pier supports.This study proposed an innovative structural configuration for the negative bending moment region in a steel-concrete CCB bridge with the aid of ultrahigh performance concrete(UHPC)layer.In order to investigate the feasibility and effectiveness of this new UHPC jointed structure in the negative bending moment region,field load testing was conducted on a newly built full-scale bridge.The newly designed structural configuration was described in detail regarding the structural characteristics(cracking resistance,economy,durability,and constructability).In the field investigation,strains on the surface of the concrete bridge deck,rebar,and steel beam in the negative bending moment region,as well as mid-span deflection,were measured under different load cases.Also,a finite element model for the four-span superstructure of the full-scale bridge was established and validated by the field test results.The simulated results in terms of strains and mid-span deflection showed moderate consistency with the test results.This field test and the finite element model results demonstrated that the new configuration with the UHPC layer provided an effective alternative for the negative bending moment region of the composite beam.

基于等效梁长法的组合深梁临界预紧力计算模型

为确定合理的临界预紧力,保证预紧组合结构横梁的整体性,提出采用等效梁长法修正传统Airy应力函数计算结果,从而得到更准确的临界预紧力。基于平面应变理论,建立临界预紧力的理论计算模型,通过叠加原理,分别得到弯曲模型和压缩模型中间截面x方向应力的傅里叶三角级数形式解,分析误差原因;采用等效梁长法进一步修正,结合临界开缝判据,得到临界预紧力理论计算公式。试验结果表明:等效梁长法修正的临界预紧力理论计算结果与试验结果最小误差为10.1%,最大误差为13.5%,与试验结果吻合较好,能够为大型成形设备的预紧组合结构横梁的设计提供理论依据。

组合深梁填充钢框架的恢复力模型

为实现结构刚度可在一定范围内渐变,同时充分发挥组合钢板的性能,介绍一种新型高层抗震加固结构体系—组合深梁。通过在水平低周反复荷载下,2个组合深梁填充钢框架结构模型试验,得到内填组合深梁钢框架结构的滞回曲线。试验过程中,混凝土板限制了钢板失稳变形,钢板塑性得以发展;组合深梁最后耗能破坏,随后钢框架发生破坏。试验结果显示:组合深梁主要由钢板部分来承担水平剪力和弯矩,混凝土板并不承担水平荷载;试件的滞回曲线饱满且骨架曲线有明显的塑性流动阶段,试件的延性和耗能能力较好,证明内填组合深梁钢框架结构抗震性能良好。最后,利用得到的试验数据进行回归分析,建立该结构恢复力模型,可用于组合深梁结构的弹塑性反应分析。

框架深肋组合扁梁的抗弯承载力研究

为提出一种简单可行的框架深肋组合扁梁的抗弯承载力计算方法,通过试验研究塑性受力阶段深肋组合扁梁的截面应力状况,提出框架深肋组合扁梁的承载力极限状态的破坏机制;推导出简化的深肋组合扁梁负弯距区的抗弯承载力公式,并利用已研究的正弯距区抗弯承载力公式,得到框架抗弯承载力的计算公式.计算公式的合理性和正确性得到了试验的验证.

钢管混凝土边框内藏钢板剪力墙抗震试验与损伤加固

提出了一种钢管混凝土边框内藏钢板深梁剪力墙。为研究其抗震性能及损伤后的加固性能,进行了两阶段试验。第I阶段低周反复荷载试验进行到位移角为1/50,试件明显屈服损伤,然后在墙体两侧钢管间贴焊薄钢板进行加固,进行第II阶段低周反复荷载试验,直至试件严重破坏。分析了各试件的承载力、刚度及退化过程、延性、耗能和破坏特征。研究表明:钢管混凝土边框和型钢中柱,有效约束了混凝土条带裂缝的开展,提高了剪力墙的延性;加设内藏钢板深梁,可明显提高剪力墙承载力和后期刚度;混凝土条带与钢管混凝土柱、型钢混凝土柱的连接界面区域,隐含形成了竖向耗能条带,往复变形过程中充分发挥了耗能性能;这种剪力墙明显屈服损伤经加固后,仍具有足够的抗震承载力和良好的耗能能力,便于震后修复。

简支深肋组合扁梁受弯性能试验

目的研究简支深肋组合扁梁的受弯性能,考察粘结力变化对其抗弯刚度和承载力的影响.方法对两根尺寸相同但钢梁与混凝土交界面处理状况不同的试件进行静力单向加载试验.结果得出荷载变形关系及截面应变分布特征,由荷载-跨中挠度关系曲线知粘结力的削弱没有影响到组合扁梁的承载力.弹性受力阶段钢梁和受压区混凝土的横向应变分布均匀,截面竖向中线的应变近似成线性分布.结论粘结力的变化对其抗弯刚度和承载力的影响很小,钢梁与受压区混凝土在弹性受力阶段能够近似保持平截面,板肋处混凝土分担的荷载很小.