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.

Lateral-torsional buckling of box beam with corrugated steel webs

Corrugated steel web is folded along the longitudinal direction and has the mechanical properties such as axial compression stiffness corrugation effect, shear modulus corrugation effect, similar to that of an accordion. In order to study the lateral-torsional buckling of box beams with corrugated steel webs (BBCSW) under the action of bending moment load, the neutral equilibrium equation of BBCSW under the action of bending moment load is derived through the stationary value theory of total potential energy and further, along with taking Kollbrunner-Hajdin correction method and the mechanical properties of the corrugated web into consideration. The analytical calculation formula of lateral-torsional buckling critical bending moment of BBCSW is then obtained. The lateral-torsional buckling critical bending moment of 96 BBCSW test specimens with different geometry dimensions are then calculated using both the analytical calculation method and ANSYS finite element method. The results show that the analytical calculation results agree well with the numerical calculation results using ANSYS, thus proving the accuracy of the analytical calculation method and model simplification hypothesis proposed in this paper. Also, compared with the box beams with flat steel webs (BBFSW) with the same geometry dimensions as BBCSW, within the common range of web space-depth ratio and web span-depth ratio, BBCSW’s lateral-torsional buckling critical bending moment is larger than that of BBFSW. Moreover, the advantages of BBCSW’s stability are even more significant with the increase of web space-depth ratio and web depth-thickness ratio.

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.

Shear deformable finite beam elements for composite box beams

The shear deformable thin-walled composite beams with closed cross-sections have been developed for coupled flexural, torsional, and buckling analyses. A theoretical model applicable to the thin-walled laminated composite box beams is presented by taking into account all the structural couplings coming from the material anisotropy and the shear deformation effects. The current composite beam includes the transverse shear and the restrained warping induced shear deformation by using the first-order shear deformation beam theory. Seven governing equations are derived for the coupled axial-flexural-torsional-shearing buckling based on the principle of minimum total potential energy. Based on the present analytical model, three different types of finite composite beam elements, namely, linear, quadratic and cubic elements are developed to analyze the flexural, torsional, and buckling problems. In order to demonstrate the accuracy and superiority of the beam theory and the finite beam elements developed by this study,numerical solutions are presented and compared with the results obtained by other researchers and the detailed threedimensional analysis results using the shell elements of ABAQUS. Especially, the influences of the modulus ratio and the simplified assumptions in stress-strain relations on the deflection, twisting angle, and critical buckling loads of composite box beams are investigated.

Restrained Torsion of Thin-walled Box Beam with Honeycomb Core

Restrained torsion of thin-walled box beam with honeycomb core is analyzed on the basis of rigid profile assumption. The method of variable separation is applied and two ordinary differential governing equations are established and solved. The boundary conditions are satisfied rigorously and the solutions are expressed by means of eigen function expansions. The diagram of torque is formulated by trigonometric series and used to determine the coefficients in above expansions. The results of computation provide the chord-wise and span-wise distributions of normal and shear stress in the face plate along with shear stress in the honeycomb core.

Restrained Bending of Thin-Walled Box Beam with Honeycomb Core

Restrained bending of thin-walled box beam with honeycomb core is analyzed on the basis of rigid profile assumption. The method of variable separation is applied and two ordinary differential governing equations are established and solved. The boundary conditions are satisfied rigorously and the solutions are expressed by means of eigen function expansions. The diagram of shearing force is formulated by trigonometric series and used to determine the coefficients in above expansions. The computational resuits give the chord and span wise distributions of nomal and shear stress in the cover plate and the honeycomb core. At the same time, the attenuation of additional stress from fixed end to free end along the length of beam is shown clearly.

Optimal Design for Thin-Walled Box Beam Based on Material Strength Reliability

According to the reliability of material strength,the optimal design for the cross sectional size of thin walled box beam was studied.Firstly the cross sectional size as design random variable was determined,then its stochastic nature was researched,with which the objective function is to seek the maximum reliability of the beam under given constraint conditions.This way is not the same as the conventional optimal design for the minimum weight of the material.With establishing the optimal objective,the reliability of the material under conditions of static and fatigue was considered.The corresponding calculated expressions are given.Normally the cross section sizes are fitted to the normal distribution,for the simplification of the design variable,the variation of the section size is assumed as a dependent variable proportional to the mean of the size.The way is different not only with the conventional optimal design but also with the common reliability design.The maximum reliability of material is obtained,meanwhile the area of the cross section is reduced,i.e.,the weight of the material is decreased.

Numerical Investigation on the Ultimate Strength of Box Beams with Impact Damage

The objective of this paper is to study the residual ultimate strength of box beams with impact-induced damage,as a model of what may occur in ship hulls.The bottom and side plates of ship hulls can suffer denting or fracture damage due to grounding,collision and other contacts during the ship’s service life and these impact-induced damages could result in considerable strength degradation.Box beams are firstly subjected to impact loading and then four-point bending loading is imposed on the damaged structures to assess the residual strength using ANSYS/LS_DYNA.The ultimate moment and collapse modes are discussed considering the effect of impact location.The impact-induced deformation is introduced in the four-point bending simulation,and the impact-induced stress is included or not to determine the effect of residual stress and distortion after impact.It is shown that impact location has significant influence on the residual ultimate bending moment of the damaged box beam providing that the impact energy is kept constant.The collapse modes also change when the impactor strikes on different locations.Damaged hard corner and inclined neutral axes might explain the reduction of ultimate strength and diverse collapse modes.The residual stress in the box beam after impact may increase or decrease the ultimate strength depending on impact location.

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.

Optimization and analysis of composite sandwich box beam for solar drones

Solar drones have garnered considerably research attention in recent years due to their continuous cruising capability,and the feasibility of design schemes is sensitive to the weight of structure.Sandwich box beam composed of carbon fiber and polymethacrylimide(PMI)foam is conducive to realize the lightweight of structure.In this study,a two-stage optimization design methodology for sandwich box beam is proposed.This methodology is primarily based on a low-order analytical method for evaluating stress/deflection and the linear buckling analysis method combined with experimental correction factor for predicting the buckling eigenvalues.Subsequently,a case study was conducted using an 18-m wingspan solar drone,where the results of mechanical test verified the optimization results.For validating the use of sandwich box beam in solar drones of other scales,additional analysis was conducted based on three aspects:(A)effects of stiffness and stability constraints on the design of sandwich box beam;(B)crucial role of the weight of foam inter layer and application scope of sandwich box beam;(C)best method to improve the buckling eigenvalue of sandwich box beam.Overall,the methodology and general rules presented in this paper can support the design of light wing beam for solar drones.

Application of stiffness matrix of a beam element considering section distortion effect

According to the stationary principle of potential energy and the generalized coordinate method, a stiffness matrix of a beam element considering distortion effects is derived. Using the stiffness matrix of the beam element, a finite element program for computing thin-walled box steel beams is developed. And the program can take the section distortion and warping effects into account. The influences of diaphragm spacing on the mechanical behavior of thin-walled box beams are analyzed by the program. The numerical analysis shows that setting diaphragms have the greatest influence on the distortion normal stress, while there is very little influence on the bending normal stress. Only when the distance of adjacent diaphragms decreases to a certain value, will the distortion normal stress in the thin-walled box beam obviously reduce under the distortion load. Finally, a distortion-warping coefficient γ is introduced for simplifying the calculation of the longitudinal normal stress of thin-walled box beams. When the ratio of diaphragms adjacent space L to the maximum section dimension H is less than 2, the distortion-warping coefficient γ tends to one, which means that the distortion normal stress of the thin-walled box beam tends to zero, and the effect of the section distortion can be ignored.

部分充填式窄幅钢箱-UHPC组合梁抗剪试验研究

目的为研究部分充填式窄幅钢箱-UHPC组合梁的抗剪性能,方法对4根倒置组合梁试件通过三点加载方式进行了静载试验,通过研究其负弯矩作用下的破坏形态及变形特征,得到了组合梁的荷载-挠度曲线、应变分布、荷载-滑移曲线、最终破坏形态等。结果试验研究结果表明:UHPC翼板显著提升了组合梁的变形能力和极限承载力;相较于试件SUCB-3(NC翼板),试件SUCB-1(1/2UHPC翼板和SUCB-4(全UHPC翼板))的承载力分别提高了18.2%和27.3%,变形能力则分别增强了38.02%和41.2%;钢纤维的添加能有效地抑制翼板裂缝的开展,钢纤维掺量从0提高到2%,试件的最大裂缝宽度从1.06 mm降低到0.92 mm,变形能力增强了23.61%,承载力则提高了4%。结论提出了考虑钢箱、UHPC翼板和充填混凝土贡献的组合梁抗剪承载力计算公式。

配筋率对钢箱-UHPC组合梁裂缝特征的影响

为研究钢箱-超高性能混凝土(UHPC)组合梁负弯矩区裂缝特征,设计制作了3根配筋率分别为1%、2%和3%的UHPC翼板部分充填砼窄幅钢箱组合梁,通过对不同配筋率的试验梁进行反向加载试验研究组合梁的裂缝发展特征,并对最大裂缝宽度、裂缝间距及开裂荷载进行对比分析。研究结果表明:试验梁在不同配筋率条件下,UHPC面层裂缝发展明显不同,配筋率越高最大裂缝宽度越小,裂缝越密集,开裂荷载越大;与配筋率为1%的试验梁相比,配筋率为2%和3%的试验梁的开裂弯矩分别提高了30.3%和65.2%;可根据《公路钢筋混凝土及预应力混凝土桥涵设计规范》(JTG 3362—2018)中的裂缝宽度计算公式乘以0.78的修正系数,来计算窄幅钢箱-UHPC组合梁负弯矩区的裂缝宽度。

收缩徐变对高速铁路斜拉桥单箱单室混合梁位移的影响及调控

以某主跨300 m的高速铁路无砟轨道混合梁斜拉桥为背景,运用Midas/Civil有限元软件建立其数值模型,进行桥塔、桥面板、箱梁等混凝土构件收缩徐变对主梁位移影响研究,并提出主梁位移调控措施。结果表明:成桥10年后,混凝土收缩徐变引起的跨中主梁向下位移共计79 mm,桥塔、桥面板、箱梁收缩徐变的影响占比在施工阶段分别为58%,32%和10%,在运营阶段分别为48%,38%和14%;跨中主梁向下位移的主要原因是桥塔和桥面板变形,混凝土收缩徐变缩小了桥塔竖向及桥面板纵桥向尺寸,改变了斜拉索锚点位置及索力,导致主梁在施工阶段和运营阶段分别产生56和18 mm的向下位移;预抬高斜拉索的桥塔锚点位置10 mm,可消除混凝土收缩徐变引起的钢梁架设初始误差;混凝土桥面板预制后存放6个月、桥塔采用低徐变混凝土、成桥后延迟90 d铺轨等措施,能改善混凝土收缩徐变对单箱单室混合梁位移的不利影响,可减小跨中主梁向下位移3%~38%。

窄幅钢箱-UHPC组合梁负弯矩下抗弯性能试验研究

为改善钢-混凝土组合梁负弯矩下的受力性能,提出一种新型窄幅钢箱-超高性能混凝土(UHPC)组合梁。通过6根试验梁的反向静力加载试验,得到试验梁受力全过程跨中荷载-挠度、荷载-应变、荷载-最大裂缝宽度关系曲线、裂缝发生发展及破坏形态等,基于简化塑性理论推导出了组合梁极限抗弯承载力计算公式。结果表明:窄幅钢箱-UHPC组合梁在负弯矩下具有良好的受力性能;提高配筋率、钢纤维掺量和UHPC相对板厚都可在一定程度上改善组合梁延性,提高其极限抗弯承载力;翼板配筋率对承载力影响较大,配筋率由1%增加至2%时,其极限抗弯承载力提高了15%;钢纤维掺量和UHPC相对板厚对初始开裂荷载影响较大,钢纤维掺量从1%增加到2%时,初始开裂荷载提高32%,UHPC相对板厚由0增加到0.5时,初始开裂荷载提高56%;增加钢纤维掺量和UHPC相对板厚可有效控制裂缝宽度,减少结构主裂缝数量,改善组合梁耐久性;组合梁极限抗弯承载力计算公式计算值与试验值吻合较好,表明塑性理论适用于窄幅钢箱-UHPC组合梁的承载力计算。

CFRP-钢箱混凝土变截面新型跨座式轨道梁设计优化

为满足新型跨座式单轨系统需求,提出一种碳纤维复合材料(CFRP)-钢箱混凝土组合轨道梁形式。通过数值模拟试验,探究钢箱上室混凝土厚度对荷载作用下的钢箱混凝土轨道梁跨中顶面、底面、上室混凝土最大应力及竖向挠度的影响,得出钢箱上室混凝土的适宜厚度;在此基础上考虑运行维护阶段轨道梁抗弯性能需求,通过梁底粘贴预应力CFRP提高其抗弯性能,经分析得出钢箱混凝土变截面组合轨道梁跨中竖向挠度随梁底粘贴CFRP长度的变化趋势并给出CFRP-钢箱混凝土轨道梁的设计建议。研究结果表明:该CFRP-钢箱混凝土变截面新型跨座式单轨轨道梁抗弯性能良好,可满足实际工程需要。

曲线钢箱梁桥面板力学行为及构造优化研究

研究目的:小半径曲线钢箱梁桥正交异性钢桥面板构造繁复,弯扭耦合作用下受力特性极为复杂。为了探究该类型桥面板力学特性,并提出合理构造优化建议,本文依托西安市某立交小半径曲线钢箱梁匝道桥,采用数值分析方法研究局部荷载作用下曲线钢箱梁桥面板力学行为,并基于正交试验方法,利用IntelliJ IDEA软件开发曲线钢箱梁桥面板构造优化程序,实现桥面板多目标构造参数优化。研究结论:(1)边跨最大正弯矩截面为大多数控制细节的最不利荷载控制截面,其中车轮荷载作用于边跨最大正弯矩位置时控制细节3(横隔板过焊孔圆弧位置)的主应力明显大于最大负弯矩和零弯矩位置,且车轮荷载作用于曲线钢箱梁外侧会增大桥面系应力;(2)车轮荷载作用于纵肋正上方和中间时产生的各控制细节主应力较相近,但作用于横隔板中间与正上方造成的局部应力具有显著差异,进而确定曲线钢箱梁正交异性桥面板各控制细节的最不利荷载作用位置;(3)通过多目标优化构造运算确定的曲线钢箱梁正交异性组合桥面板的合理构造,可显著改善桥面板力学特性;(4)本研究成果可为曲线钢箱梁正交异性桥面系构造设计和养护方法提供优化建议。

钢桥面沥青铺装车辙研究

钢桥面沥青铺装层车辙病害问题日益凸显,已不容忽视。综合近年来钢桥面沥青铺装车辙的研究现状与发展趋势,针对钢桥面沥青铺装层车辙类型与形成机理、车辙预估研究及车辙主要影响因素进行了详细剖析与总结,结果表明:较之于沥青路面,钢桥面沥青铺装层车辙主要为材料抗剪切能力不足引起的流动性车辙,不同铺装材料的车辙形成机理不同;在车辙预估研究方面,以Bailey-Norton与修正Burgers蠕变模型表征高温下铺装材料非线性行为的有限单元法已取得了一定的成果,但仍有诸多需改进之处;国内已形成了以“上层环氧+下层浇注”和“上层SMA+下层浇注”为主流的优良抗车辙性能铺装结构,影响铺装层车辙发展的最主要因素有铺装材料性能、铺装层结构、温度、车辆荷载及施工质量,因此优化铺装材料与结构设计、严控重超载车辆及改善施工工艺质量应为今后延缓铺装层车辙发展的重要措施。研究结果可为钢桥面铺装层的抗车辙设计与后期维养工作提供参考依据。

大跨度悬挂式单轨钢箱组合梁总体设计及关键技术研究

悬挂式单轨是一种轻型、中速、低成本的新型轨道交通方式,结构轻盈、美观,但是当跨越河流、沟壑等障碍时,存在明显短板。从结构受力、运行安全角度出发,提出一种在斜拉桥的主梁上架设轨道墩柱和轨道梁的新型组合梁结构方案,突破常规悬挂式单轨跨越能力受限的壁垒。为研究斜拉桥主梁与轨道梁墩柱结合部位复杂的受力情况和传力路径,采用ANSYS软件分别建立钢箱梁区段和混凝土箱梁区段有限元模型。结果表明:钢箱梁区段,墩柱荷载主要传递给与之直接相连的横隔板以及中腹板,其中,横隔板受力比较均匀,中腹板受力主要集中在以墩柱为中心,半径约2 m的范围内,基本可以传递至钢梁底板。墩柱轴力的58%传递给与之直接相连的横隔板;墩柱横桥向弯矩的传递过程中,58.8%的剪力传递给与之直接相连的横隔板;墩柱顺桥向弯矩的传递过程中,53.4%的剪力传递给中腹板;混凝土箱梁区段,墩柱荷载主要传递给与之直接相连的混凝土腹板、横隔板。混凝土受力主要集中在以结合面为中心,半径约2 m的范围内,墩柱荷载在结合面以下约0.5 m的范围内基本完成传递,墩柱轴力的68.8%传递给与之直接相连的横隔板;墩柱横桥向弯矩的传递过程中,86.4%的剪力传递给与之直接相连的横隔板;墩柱顺桥向弯矩的传递过程中,44.6%的剪力传递给中腹板。

窄幅钢箱连续组合梁受力性能有限元分析

为了解决钢-混凝土组合梁负弯矩区开裂以及钢箱受压屈曲问题,提出采用窄幅钢箱连续组合梁对钢-混凝土组合梁进行优化,并在窄幅钢箱连续组合梁桥面翼板的负弯矩区采用超高性能混凝土材料部分替代强度等级为C40的混凝土,形成超高性能混凝土-窄幅钢箱连续组合梁,进一步优化窄幅钢箱连续组合梁受力性能;采用有限元分析软件ABAQUS建立超高性能混凝土-窄幅钢箱连续组合梁有限元模型,在验证模型适用性的基础上,分析窄幅钢箱连续组合梁的受弯过程,并对窄幅钢箱连续组合梁翼板、钢筋、钢箱云图进行对比。结果表明:窄幅钢箱连续组合梁中混凝土的充填跨度对窄幅钢箱连续组合梁刚度存在一定的影响,超高性能混凝土材料显著改善了翼板的抗裂性能,翼板受拉区损伤面积减小95%以上;当采用超高性能混凝土材料完全替代普通混凝土材料时,窄幅钢箱连续组合梁的刚度、开裂荷载、极限荷载等性能得到较大改善。