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.

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.

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.

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.

碳纤维布加固锈蚀钢筋混凝土梁疲劳性能试验研究

通过10根碳纤维布加固锈蚀钢筋混凝土梁和2根锈蚀钢筋混凝土梁的弯曲疲劳试验,研究了钢筋锈蚀率、碳纤维布加固量、荷载比、加固前损伤等因素对碳纤维布加固锈蚀钢筋混凝土梁弯曲疲劳性能的影响。试验结果表明,碳纤维布加固锈蚀钢筋混凝土梁的典型疲劳破坏过程仍具有三阶段发展规律,但其第二阶段在整个发展过程中所占的比例有所下降。钢筋的疲劳性能是控制加固梁疲劳破坏的主要因素,随着钢筋锈蚀率的增加,梁的疲劳寿命急剧缩短,其破坏形式为受拉钢筋脆性断裂,外贴碳纤维布加固则能明显改善锈蚀钢筋混凝土梁的弯曲疲劳性能、提高梁的疲劳寿命,避免锈蚀钢筋疲劳断裂后梁突然失去承载力。基于此,提出了采用粘贴碳纤维布提高锈蚀钢筋混凝土梁疲劳性能的设计步骤。荷载水平提高以及加固前的损伤均会降低混凝土梁的疲劳寿命,因此在钢筋混凝土结构使用过程中应尽量避免超载现象,并应及时对损伤结构进行修复、加固。

锈蚀栓钉钢−混凝土组合梁的疲劳寿命预测模型

采用有限元分析软件ANSYS和理论公式相结合的方法,提出一种预测锈蚀栓钉钢−混凝土组合梁疲劳寿命的模型。根据钢−混凝土组合梁在实际试验中发生疲劳破坏的原理,提出组合梁在疲劳加载过程中栓钉依次退出工作的假设,同时把栓钉疲劳寿命预测模型和栓钉剩余承载力计算公式与数值分析相结合,综合考虑疲劳加载幅、疲劳加载上限、栓钉极限承载力、栓钉直径以及栓钉初始缺陷等因素对组合梁疲劳寿命的影响,计算分析组合梁的疲劳寿命。首先预测未锈蚀栓钉钢−混凝土组合梁的疲劳寿命,在验证模型的有效性基础上,综合考虑锈蚀率对栓钉极限强度、屈服强度、弹性模量、截面直径和本构关系等因素的影响,修正组合梁有限元分析模型,并结合锈蚀栓钉的疲劳寿命预测模型,对锈蚀栓钉钢−混凝土组合梁的疲劳寿命进行模拟计算。研究结果表明:采用本文提出的模型预测组合梁试件FSCB-4和FSCB-5的疲劳寿命,计算结果与试验结果的相对误差分别为12.30%和6.95%,较利用传统S-N曲线的分析方法具有更高的精度,与试验值更吻合;栓钉的锈蚀对钢−混凝土组合梁的疲劳寿命影响较大,当栓钉的锈蚀率分别为5%,10%,15%和20%时,组合梁的疲劳寿命分别下降11.51%,25.27%,48.08%和79.65%。

碳纤维布加固锈蚀钢筋混凝土梁的疲劳性能试验

完成了粘贴碳纤维布加固锈蚀钢筋混凝土梁的疲劳试验。试验结果表明,碳纤维布加固可以明显提高梁的疲劳寿命,减小梁的变形,提高梁的疲劳抗裂性能。因此,粘贴碳纤维布可以较大提高锈蚀钢筋混凝土梁的疲劳性能,延长锈蚀钢筋混凝土结构的使用寿命,为碳纤维布加固锈蚀钢筋混凝土结构的长期疲劳性能研究提供了试验依据。

碳纤维布加固锈蚀钢筋混凝土梁抗弯刚度的衰减规律

在对碳纤维布加固锈蚀钢筋混凝土梁进行四点弯曲疲劳试验的基础上，研究了加固梁抗弯刚度和损伤变量、荷载加载次数与疲劳寿命比之间的关系。试验结果表明：加固梁抗弯刚度的衰减曲线包括初始的快速减小阶段、稳定衰减阶段和梁临近破坏的快速减小阶段。分析结果表明：加固梁的线性刚度比介于0．6～0．9之间，平均值为0．75，破坏刚度比介于0．4～0．8之间，平均值为0．6，加固梁疲劳破坏时损伤变量约为0．4，此值可作为碳纤维布加固锈蚀钢筋混凝土梁疲劳破坏的失效判据。

栓钉锈蚀钢-混凝土组合梁在负弯矩作用下的力学性能研究

基于受弯性能试验和数值分析,研究栓钉锈蚀钢-混凝土组合梁在负弯矩作用下的力学性能。对5根梁进行试验,其中4根梁采用恒定电流通电加速锈蚀方法(CCAC)使其抗剪栓钉锈蚀,栓钉锈蚀率为0%~40%。加载结果表明:随着栓钉锈蚀率的增加,组合梁抗弯承载力轻微减小,但其抗剪承载力则明显减小。根据试验结果,建立一个新的计算分析模型,以研究负弯矩下栓钉锈蚀组合梁的力学性能。该数值分析模型能够相当准确地预测试验结果。

长期荷载作用卸载后的锈蚀钢-混凝土组合梁抗弯性能试验研究

为研究长期荷载卸载后锈蚀简支组合梁的抗弯性能,进行了6片钢-混凝土简支组合梁的抗弯性能试验,采用电化学腐蚀方法对组合梁进行加速腐蚀,使用5%浓度的NaCl溶液作为电解液。对钢梁和钢筋进行防腐处理,以达到仅使试件指定部位生锈的目的。腐蚀速率通过调节腐蚀电流来控制。在腐蚀和长期荷载作用200天后卸载,测试组合梁的抗弯性能。研究了腐蚀与长期荷载共同作用对组合梁挠度、滑移、应变及极限承载力的影响。试验结果表明:(1)在长期荷载作用下,组合梁的截面应变和界面相对滑移前期得到增长,但对试件的最大应变和最大滑移值影响甚微。(2)栓钉锈蚀导致组合梁整体刚度降低,延性变差;(3)经过栓钉锈蚀,组合梁的抗剪连接程度下降,混凝土板与钢梁工作协同性变差,组合梁抗剪连接程度降低导致滑移量增长,钢材塑性得不到充分发挥,试件的受弯承载力降低;(4)栓钉锈蚀导致栓钉与混凝土的有效接触面积减少,截面组合程度减弱,混凝土压应力提高,应变增大;(5)栓钉锈蚀导致栓钉抗剪切变形能力减弱,试件的滑移增长速率明显增大,相同荷载下,栓钉锈蚀率越高,组合梁相对滑移的最大值越大;(6)栓钉锈蚀更严重的组合梁在同一荷载等级下应变量更大。