预应力混凝土T梁桥设计中需要考虑剪力滞效应,而预应力轴压作用和材料非线性对剪力滞效应的影响目前仍有待研究,采用非线性有限元程序对预应力混凝土T梁进行全过程分析不失为一种较精确的方法.考虑混凝土和钢筋的材料非线性,采用降温法模拟预应力,利用Abaqus软件建立了不同翼缘宽度的预应力混凝土T梁有限元模型,对T梁在恒载、集中荷载和均布荷载下加载至破坏的全过程受力性能和剪力滞效应进行了分析.结果表明:T梁在集中荷载和均布荷载下均达到承载能力极限状态;在线弹性受力阶段,T梁在恒载和均布荷载下的剪力滞效应不明显,在集中荷载下T梁跨中加载点附近区域内呈正剪力滞;进入非线性受力阶段后,受沿梁长内力重分布和截面上应力重分布的影响,T梁加载全过程的剪力滞效应区别于其线弹性状态,均布荷载下,全过程剪力滞系数较线弹性值变化较小,集中荷载下,全过程剪力滞系数相对于线弹性值的最大增幅为 12%～15%;集中荷载下,T梁跨中截面的最大剪力滞效应发生于其纵向普通钢筋受拉屈服对应荷载;临近破坏时,随着沿梁长不同位置的纵向钢筋相继屈服,T梁剪力滞效应呈沿梁长正、负剪力滞交替分布状态.

曲线梁桥因其在经济与美学上的优势,在现代公路立交系统中得到广泛应用.由于结构上的特点,曲线梁的竖向弯曲和扭转耦合,使曲线梁桥的分析相对直梁桥较为复杂.本文对曲线梁桥分析理论的相关研究进行总结,着重对混凝土曲线梁桥的力学性能进行介绍,并提出下一步研究的方向.

三维空间曲梁有限单元模型是模拟曲梁结构的有效数值方法,可以考虑曲梁的弯扭耦合特性,最为符合曲梁的几何和受力特征.由于有限元法采用梁理论的平截面假定,空间曲梁单元上的扭转剪应力分布与实际曲梁截面上的扭转剪应力不同,从而会导致扭转刚度和扭转变形的计算失真.本文基于剪切应变能等效原理,推导了不同长宽比的矩形截面空间曲梁单元的扭转刚度修正系数η和截面边中点处扭转剪应力的修正系数λ,并采用曲线悬臂梁进行了验证.验证结果表明,根据本文提出的η作为校正因子的空间曲梁单元模型,对任意矩形截面曲梁计算的扭转变形均与实体单元模型的结果吻合良好;且只有截面为正方形时,扭转剪应力修正系数η才恰好与弯曲剪应力修正系数(1.2)一致.

Horizontally curved concrete bridges are widely used in urban viaducts and overpasses all over the world. A box cross-section is often used in curved concrete girders because of its high resistance to both bending and torsion. This study focuses on the development of a new finite element analysis (FEA) methodology incorporating a novel formulation for curved box sections using orthotropic constitutive models for reinforced concrete, along with a layered shell theory approach. In the new approach, the box section is treated as a frame consisting of curved shell elements modeling webs and flanges and curved beam elements in the web-flange junctions. The use of shell and beam elements in the formulation significantly reduces the number of elements needed to model the box-section girder while maintaining the accuracy of the model. A degenerate superparametric shell element with reduced integration is used to avoid shear-locking, membrane-locking, and zero-energy problems. Prestrain effects are considered in the formulation to account for prestressing forces. The simulation results are compared to the available experimental results on four straight and curved, reinforced and prestressed, concrete box -section girders, with good agreement in terms of the deflections, twist angles, and strains in the prestressed reinforcement. Some critical issues in the analysis of concrete box girders, such as postpeak-strength behaviors, distortion of box section, are also discussed. (c) 2020 American Society of Civil Engineers.

In recent years, failings of girders due to overturning in continuous girder bridges have repeatedly occurred in China. To investigate the overturning collapse mechanism and also to evaluate the rationality of anti-overturning design method using beam element models that are commonly adopted in practical design, detailed 3D finite solid element models of a typical single-column pier three-span continuous box girder bridge were built and a full-range numerical analysis of the models was conducted. The solid models included the prestressing effect and diaphragms. Both boundary and geometric nonlinearities were taken into consideration. Bearings were modeled considering the actual construction and dimensions of pot rubber bearings, the material characteristics and boundary conditions of rubber pads, and the contact properties between each part of the bearings. The analysis results revealed that the behavior of the bridge approached the nonlinear state at the onset of first bearing disengagement; the rotation (overturning) mechanism of the girder was gradually transitioned from deformable-body rotation to rigid-body rotation; all the end and middle bearings had been disengaged totally or locally at ultimate overturning failure. The analysis results also showed that bearing disengagements would lead to the ineffectiveness of the constraint in the transverse direction, which significantly reduced the overturning ultimate load and structural ductility before the final collapse. Prior to the first bearing disengagement, the vertical reactions calculated from the beam model were in good agreement with those from the solid model, while the transverse reactions were not. The behaviors were inaccurate after bearing disengagement in the beam models in which the movement of the rotation axis and transition of rotation mechanism failed to be realized. Reliable transverse stoppers and tensile anchors at bearing sections were recommended to efficiently improve anti-overturning stability and ductility in practical design.

Horizontally curved concrete girder bridges have been widely used in urban viaducts and overpasses across the world. When designing these structures, it is necessary to estimate the maximum deflections under service loads to satisfy requirements of the serviceability limit state. Because of twist due to torsion in curved concrete girders, the maximum deflection needs to take into account the effect of torsional twist, which has not been considered in previous research. Based on the concept of effective torsional stiffness, a new method is proposed for calculating post-cracking twist angles in curved concrete girders. The proposed method in combination with the effective moment of inertia method can accurately predict maximum deflections in curved concrete girders. The simplicity of the proposed method is illustrated in an example. The calculated central deflections and twist angles are compared with experimental data obtained from previous tests that cover curved box-section and solid-section non-prestressed and prestressed concrete beams. The proposed method provides satisfactory predictions in terms of twist angles until the first yielding of reinforcement. The variations between the calculated and measured twist angles and maximum deflections are within +/- 10% and +/- 20%, respectively. The results of this study indicate that deflection formulas from the ACI 318-14 Code and the AASHTO LRFD Bridge Design Specifications may produce non-conservative results for curved concrete girders under certain loading conditions.

Moment redistribution is important in the ductile design of concrete structures, but moment redistribution in externally prestressed concrete (EPC) continuous curved beams has not yet been studied. Neutral axis depth approaches to moment redistribution in current design codes are based on the test results of straight beams, which are not applicable to continuous curved beams. This paper presents experimental results for three three-span EPC curved box beam specimens, including their failure processes and modes, the strains in the reinforcement and concrete, and the full-range behavior of the neutral axis depth. The test results show that moment redistribution occurred from cracking of the specimens to their failure. The test results also reveal a significant difference in the mechanical behavior of the inner and outer sides of the specimens. A method for conversion of the neutral axis depth is proposed, and the calculated results, which are typically conservative, are compared with the test results. The test results show that flexural yielding in curved beam specimens did not induce a sudden increase in torsion before moment redistribution as the European standard would predict. (C) 2017 American Society of Civil Engineers.

The similarities between the reduced scale structural model and the proto type in experiments relate directly to the accuracy of the experiment results,and the determination of similar loads is always a difficulty in the similarity conditions.This article focuses on the optimization design method of similar loads on reduced scale structural models,and proposes the concept of similar errors to quantify the errors between the similar loads and the ideal reduced scale loads.Based on the limited multi-point centralized loading method commonly used in model experiments to express the similar errors of characteristic quantities as an optimized objective function,this article presents the basic idea and the work flow of the optimization design for similar loads.The analytical solutions of the optimal similar load designs for simple supported beams and continuous beams are put forward.On the basis of the basic idea,some multi-dimensional difficulties during the optimization design are discussed with the preliminary solutions given.Finally,according to the space finite element method,an optimal design on the similar dead loads of curved continuous beam is given.

为了抵抗曲线箱梁桥的扭转效应、改善结构的受力状态,在不增加预应力钢束数量的前提下,提出一种利用体外预应力钢束形成空间抗扭作用的方法.基于空间解析几何关系推导了体外预应力扭矩计算公式,以此建立了以最小扭矩为目标的体外预应力钢束的抗扭设计流程,并利用非线性规划方法给出钢束最优平面线形参数的数值解法.分析结果表明,与体内预应力钢束相比,通过合理的体外预应力钢束空间布置,能大幅降低扭矩峰值,抗扭效果明显,且不影响抗弯、抗剪能力;扭矩计算数值解与有限元分析结果吻合良好,能方便地用于实际设计.

A radius of curvature 20 times greater than the deck width of the bridge (R≥20b) is required as a specification in the regular bridge simplification conditions of the seismic response of curved girder bridges. Selecting benchmark bridges and employing parameter analysis method, this article studies on the effect of R/B value of the curved girder bridge on the response ratio of the seismic response calculated using the finite element model and that using a regular girder bridge. This study shows that on conditions that the deck width of the bridge is constant, the smaller the radius of curvature and the larger the B/R value (i.e., the smaller the R/B value) of the curved girder bridge are, the greater the difference between the seismic response of the curved girder bridge and the result calculated with a regular girder bridge is, and the difference is more significant under traverse seismic effect than that of longitudinal seismic effect. On conditions that the radius of curvature is constant, the impact of the change of B/R value due to the deck width change of the bridge on the difference between the seismic response of the curved girder bridge and the result calculated with a regular girder bridge is insignificant. Compared with the deck width of the bridge, the difference between the seismic response of the curved girder bridge and the result calculated with a regular girder bridge is more sensitive to the radius of curvature.