Closed-form solution to thin-walled box girders considering effects of shear deformation and shear lag

Considering three longitudinal displacement functions and uniform axial displacement functions for shear lag effect and uniform axial deformation of thin-walled box girder with varying depths,a simple and efficient method with high precision to analyze the shear lag effect of thin-walled box girders was proposed.The governing differential equations and boundary conditions of the box girder under lateral loading were derived based on the energy-variational method,and closed-form solutions to stress and deflection corresponding to lateral loading were obtained.Analysis and calculations were carried out with respect to a trapezoidal box girder under concentrated loading or uniform loading and a rectangular box girder under concentrated loading.The analytical results were compared with numerical solutions derived according to the high order finite strip element method and the experimental results.The investigation shows that the closed-form solution is in good agreement with the numerical solutions derived according to the high order finite strip method and the experimental results,and has good stability.Because of the shear lag effect,the stress in cross-section centroid is no longer zero,thus it is not reasonable enough to assume that the strain in cross-section centroid is zero without considering uniform axial deformation.

Lateral static and dynamic characteristics of thin-walled box girder

To analyze the static and dynamic behaviors of the thin-walled box girder in its lateral webs in consideration of shear lag effect and shear deformation, an approach based on the minimum potential principle is introduced in this paper. Both static and dynamic response equations as well as the corresponding natural boundary conditions of the box girder are deduced. Meanwhile, three generalized displacement functions： w （x） , U（x） and O（x） are employed and their differences in the calculus of variation are quantitatively investigated. The comparison of finite shell element results with analytical results of calculation examples validates the feasibility of the proposed approach.

A comparative study on the hull strength of a ship with thin-walled box girders

Based on the Finite Element Analysis and Thin Walled-Box girder Mechanics, two design concepts of adding box girders under main deck in order to increase the hull strength of ship are presented. By comparison and analysis on the longitudinal strength, torsion strength and deck buckling between designed concepts and the original concept, it is found that by adding box girders under the main deck, the weight of hull structure is increased by lower than 10%, but the stress on the plate of the main deck is reduced by about 10%, the stress on the plating of the second deck is reduced about 20%. The shear stress on the plating of both of the main deck and second deck is reduced, but the shear stresses in several nodes are increased. Also the capability of resisting damage to ship is obviously increased by adding box girders under the main deck. The deck buckling is also increased by more than 90%. Consequently, the box girders added under the main deck are useful and effective to increase the strength of hull and ship survivability.

Powell's optimal identification of material constants of thin-walled box girders based on Fibonacci series search method

A dynamic Bayesian error function of material constants of the structure is developed for thin-walled curve box girders. Combined with the automatic search scheme with an optimal step length for the one-dimensional Fibonacci series, Powell＇s optimization theory is used to perform the stochastic identification of material constants of the thin-walled curve box. Then, the steps in the parameter identification are presented. Powell＇s identification procedure for material constants of the thin-walled curve box is compiled, in which the mechanical analysis of the thin-walled curve box is completed based on the finite curve strip element （FCSE） method. Some classical examples show that Powell＇s identification is numerically stable and convergent, indicating that the present method and the compiled procedure are correct and reliable. During the parameter iterative processes, Powell＇s theory is irrelevant with the calculation of the FCSE partial differentiation, which proves the high computation efficiency of the studied methods. The stochastic performances of the system parameters and responses axe simultaneously considered in the dynamic Bayesian error function. The one-dimensional optimization problem of the optimal step length is solved by adopting the Fibonacci series search method without the need of determining the region, in which the optimized step length lies.

Finite element failure analysis of continuous prestressed concrete box girders

In order to analyze the load carrying capacity of prestressed concrete box girders, failure behaviors of in-situ deteriorated continuous prestressed concrete box girders under loading are experimentally observed and a finite failure analysis method for predicting behaviors of box girders is developed. A degenerated solid shell element is used to simulate box girders and material nonlinearity is considered. Since pre-stressed concrete box girders usually have a large number of curve prestressed tendons, a type of combined element is presented to simulate the prestressed tendons of box girders, and then the number of elements can be significantly reduced. The analytical results are compared with full-scale failure test results. The comparison shows that the presented method can be effectively applied to the failure analysis of in-situ continuous prestressed concrete box girders, and it also shows that the studied old bridge still has enough load carrying capacity.

Fatigue Performance of Orthotropic Steel Decks in Super-Wide Steel Box Girder Considering Transverse Distribution of Vehicle Load

This study presents an investigation on the fatigue analysis of four types of details on orthotropic steel decks(OSDs)for a cable-stayed super-wide steel box girder bridge based on finite-element analysis(FEA)with vehicle transverse distribution model(VTDM).A high-fidelity 3D FE model verified by the static load test is established to satisfy the fatigue analysis accuracy.The stress behavior of super-wide steel box girders under the vehicle load at different lane locations is investigated.Then,considering the effect of VTDM,the fatigue life analysis of four typical details is performed using the Miner cumulative damage rule.The results show that the vehicle transverse location has a great influence on the stress behavior of details with sharp influence surface,and the stress ranges in the outermost lane are larger than those in other lanes,indicating that the details of OSD in the outermost lane are prone to fatigue.The fatigue life analysis indicates that the diaphragm cutout is more prone to fatigue than other details,which should be carefully treated in bridge maintenance.

Weakening effect of vertical prestress ducts on web sections in prestressed concrete box girder bridges

Based on experimental study result of two simply supported beams,which were prestressed by vertical tendons,the research on the weakening effect of vertical prestress ducts on web sections of prestressed concrete box girder was carried out. The test result shows that in the condition without grouting into the ducts,the cracking load is evidently lower than that with full grouting,and stirrup stress and principal tension stress at the surface of concrete will increase obviously. Meanwhile,the finite element analysis has been done to the test beams. The research is consistent with the analysis of finite element. The research tells that strengthening the detection and management for the vertical prestress grouting quality have an important meaning to prevent cracking of the prestressed concrete box girder bridge and provide one theoretical and testing basis for analyzing the cracking reason of such bridges.

大吨位箱梁曲线段梁上运梁承压箱梁受力分析

研究目的:杭甬高速复线宁波段一期工程S1标段采用大吨位预应力混凝土箱梁(50 m/1650 t),使用YL1800型运梁车采用单车跨双幅梁上运梁方案,为研究大吨位箱梁在小半径曲线段(R=1800 m)进行梁上运梁时下部承压箱梁的受力性能,验证运梁方案的可行性,对下部承压箱梁进行了测试与分析。研究结论:(1)大吨位箱梁在梁上运梁过程中,承压箱梁跨中截面顶板、底板沿纵向均处于受压状态,顶板沿横向处于受压状态,箱梁的受力满足规范要求;(2)随着运梁车偏载距离的增大,承压箱梁的应力和跨中挠度逐渐增大,运梁车向低侧偏载时对箱梁应力和跨中挠度影响较大,建议在梁上运梁时运梁车向高低两侧偏载不应超过1000 mm;(3)本研究成果可为大吨位箱梁梁上运梁施工提供参考。

极地冰撞载荷作用下船体典型箱型结构极限强度分析方法研究

船舶在极地航行的过程中船体可能受到冰载荷的撞击,北极地区海域的温度最低可达-68℃,因此航行于极地的船舶将面临严重的冰载荷环境和低温环境.由于船体结构是典型的加筋板组合的变截面箱型梁结构,故将船体模型简化为箱型梁模型.基于LS-DYNA对箱型梁-冰碰撞的收敛性分析,在不同温度下对箱型梁-冰碰撞进行非线性有限元数值仿真,得到不同低温下箱型梁结构在冰载荷作用下的极限强度.引入冰厚、速度等敏感性参数,得到一般结论,箱型梁的极限强度随着温度的降低而升高,随着冰厚、温度的增大而增大.研究结果对低温下箱型梁-冰在碰撞的极限强度研究具有一定意义,为极地船舶船体结构的设计提供参考.

单箱双室变截面波形钢腹板组合梁剪应力分析

为了研究单箱双室变截面波形钢腹板组合箱梁(CBBCSW)的剪应力分布规律,分析了单箱双室变截面CBBCSW的顶底板与波形钢腹板(CSW)的承剪问题。基于微元体平衡和切应力互等定理推导了变截面CSW的剪应力计算公式,并与等截面CSW剪应力计算公式进行了对比。对各项剪应力的性质展开了研究,针对变截面CBBCSW的顶底板和参与承剪机理进行了分析,提出了底板承剪比例计算公式。以室内模型试验梁和一座单箱双室变截面CBBCSW为例,采用ANSYS有限元软件分别建立了试验梁与实桥的有限元模型,研究了不同约束体系下,剪应力在CSW上的分布以及顶底板与CSW参与承剪的规律。对比不同荷载情况下,有限元计算结果与理论公式计算结果的差异,分析不同荷载工况对顶底板与CSW参与承剪的影响。此外,分析了横隔板对单箱多室CBBCSW剪力分配的影响。研究结果表明:所提公式的理论结果与试验实测结果和有限元结果吻合较好,且底板参与承剪的比例不可忽视;变截面引起的“附加剪应力”是影响剪力传递的直接原因,弯矩的大小会直接影响底板参与承剪的比例;对称荷载下中腹板与边腹板的剪力分布几乎相同,而横隔板会改变CSW上剪力分配,靠近横隔板处的部位剪应力分布更均匀。研究结果可以为实际工程中变截面CSW的剪应力和承剪比的分析提供参考依据。

混凝土连续组合小箱梁桥温度效应有限元分析

以亚沟枢纽互通G匝道桥作为依托工程,采用有限元数值分析方法对混凝土小箱梁桥在各国规范规定的温度梯度模式下进行仿真模拟,研究混凝土小箱梁桥在不同温度梯度模式作用下顶板、腹板和底板温度效应的分布规律,得出各国规范对于桥梁温度梯度模式方面规定的差异性。研究结果表明:在不同的温度梯度模式下,混凝土小箱梁桥的顶板、腹板和底板产生的正截面法向温度效应差异较大;沿梁长方向,边跨各截面产生的温度应力波动幅度较大,而中跨各截面产生的温度应力趋于相同;各国规范规定的竖向温度梯度荷载对混凝土小箱梁桥作用后产生的温度效应曲线之间存在规律性。可对类似混凝土连续组合小箱梁桥温度效应的计算提供参考。

30 m预应力UHPC箱梁抗弯性能试验及结构优化研究

为了解大尺寸预应力UHPC箱梁的抗弯性能,以预应力UHPC公路桥——河北石磁跨线桥为背景,设计、制作1片长30 m的足尺预应力UHPC箱梁模型进行四点弯曲试验,结合有限元计算结果,分析试验现象及裂缝分布、跨中荷载~位移曲线、受拉区UHPC及筋材应力~应变曲线。在此基础上分别考虑普通钢筋配筋情况、预应力筋数、腹板厚度和底板厚度等参数对预应力UHPC箱梁进行结构优化设计研究。结果表明:箱梁破坏时受压区UHPC未压溃、受拉区钢纤维被拔出,裂缝贯通底板;根据荷载~位移曲线,箱梁受力可分为弹性阶段、裂缝发展阶段、裂缝快速发展阶段和破坏阶段;根据应力~应变曲线,受拉区UHPC在纵筋屈服时仍能贡献抗拉能力;试验现象及力学指标实测值均说明了预应力UHPC箱梁抗弯能力还有很大富裕空间,可进一步优化。完全不配置普通钢筋的预应力UHPC箱梁仍能满足抗弯承载能力极限状态设计要求;底部预应力筋数增多可有效提高受压区UHPC的抗压强度利用率;腹板厚度过薄会造成腹板主拉应力过大问题,不宜薄于8 cm;采用体外预应力的方法可有效减薄底板所需厚度。

钢箱梁横隔板优化布置对顶推施工力学性能的影响分析

针对斜交连续钢箱梁的横隔板布置方式,提出在钢箱梁斜交支撑位置处加密设置正交横隔板,通过建立钢箱梁的有限元全桥模型,对不同横隔板布置方案进行了对比分析。在顶推最不利工况下,分析了不同横隔板布置方案下的结构内力、挠度、支座反力、局部应力及扭转变形,验证了新型横隔板布置方案的可行性。结果表明,新型横隔板布置方案与常规布置方案在支座反力及弯矩分布上基本一致,优势主要体现在易于加工制造、整体自重较小且能显著减小支撑区域应力水平。新型斜交连续钢箱梁横隔板优化布置方式在顶推施工中满足强度设计要求。

跨越既有线路钢箱梁顶推施工有限元仿真分析

崔家崖特大桥钢箱梁项目是当地一项重要的民生工程,该项目跨越既有中川铁路,与既有线中线交角为75°,施工具有一定的难度和危险性。为顺利地完成施工任务,采用顶推的方式进行钢箱梁的施工作业,并采用多种施工模拟软件对崔家崖特大桥钢箱梁项目进行施工仿真模拟分析,来保证结构的刚度、强度、稳定性。分析表明,在整个顶推施工过程中,钢箱梁最大组合应力为31.0 MPa<265 MPa,发生在钢箱梁支点处,导梁最大组合应力为62.7 MPa<250 MPa,发生在导梁的中间部位,钢箱梁挠度最大值21.8 mm、导梁挠度最大值48.0 mm,且都发生在导梁最大悬臂长度为33.3 m时,均小于L/400=83.2 mm,强度、刚度、稳定性均满足相关要求;钢箱梁局部受力分析,最大应力为137.5 MPa<265 MPa,发生在钢箱梁与垫梁接触位置的端部,满足相关规范要求;导梁局部受力分析,最大应力为176.5 MPa<265 MPa,发生在导梁与垫梁接触位置的端部,满足相关规范要求。

深中通道中山大桥主桥超宽大节段钢箱梁吊装匹配技术

深中通道中山大桥主桥为主跨580 m的双塔双索面钢箱梁斜拉桥,主梁采用流线型扁平钢箱梁,梁宽46 m(含风嘴),主梁共划分69个节段,标准段长18 m、最大吊重约429 t,采用桥面吊机双悬臂吊装。由于钢箱梁节段自重大、宽度较大、横桥向竖向刚度较小等,在桥面吊机悬臂吊装过程中,会出现钢箱梁匹配面高差过大(最大约63 mm)的问题。为解决该问题,实现梁段精确匹配安装,提出3种钢箱梁吊装匹配方案:“门架+拉索”方案、“牛腿反力架”方案、“一字梁锁定+C形焊缝+部分张拉斜拉索”方案。经有限元仿真分析综合比选,最终选择“一字梁锁定+C形焊缝+部分张拉斜拉索”方案。该方案以箱梁竖腹板为定位点,提前焊接一字梁,采用法兰连接后锁定待拼梁段,部分焊接拼接面内箱梁形成C形焊缝;通过提前挂索并张拉部分斜拉索,减小匹配面已拼梁段横桥向竖向变形,达到箱梁匹配要求。施工中采取了匹配高差调节、局部应力控制、拼接缝宽控制等关键技术,最终将该桥钢箱梁匹配面高差减小至9.8 mm以内,钢箱梁局部应力可控,斜拉索初张过程中钢箱梁应力增量小于10 MPa,且各箱梁节段拼接缝宽可控制在1 cm以内。

梁端预制拼接箱梁桥抗剪性能模型试验

针对预应力混凝土箱梁桥施工质量不易保证的问题,提出梁端预制拼接的施工方法;采用精细化加工的箱梁锚固端节段,通过剪力键与混凝土箱梁的现浇节段纵向拼接,从而避免由于施工原因造成的预应力箱梁桥长期性能退化.作为拼接箱梁桥受力的关键构件,梁端承受剪力作用的结合面的受力最为不利,因此本研究采用足尺模型试验和有限元计算的方法,对新型节段拼接混凝土箱梁桥抗剪性能进行研究.试验、有限元计算和参数分析结果表明,所建立的有限元模型能较好地模拟节段拼接箱梁桥在试验荷载作用下的抗剪性能;带剪力键的箱梁节段结合面是该类型桥梁受力最薄弱的部位;试验模型在试验荷载的作用下,其主要破坏模式是在箱梁节段之间传递剪力的剪力键发生破坏;桥梁抗剪极限承载力与剪力键尺寸成正比,与腹板剪力键和顶板剪力键的数量成正比,但与底板剪力键的数量关系不大.

某钢筋混凝土弯箱梁桥承载力评估

为了研究连续箱梁桥承载力及裂缝开展情况,评定桥梁的各项指标,为桥梁的运营养护提供可靠资料,采用现场加载试验及有限元数值模拟分析相结合的方法,基于静载试验测定各工况下桥梁应力和变形,利用动载试验测定桥梁自振特性及车辆对桥梁的冲击系数。对比实测值与有限元计算结果得出结论,该桥梁卸载后的残余位移和应变满足相关规范要求,结构动刚度能满足正常使用要求,桥梁正常使用条件下的车辆冲击效应满足设计要求。裂缝开展方面满足相关规范最大裂度的限值要求,该桥梁承载力不满足设计要求。建议对该桥梁上部结构进行加固补强,以满足正常运营条件。

UHPC箱梁桥面体系主要设计参数优化及试验研究

为获取UHPC箱梁桥面体系主要设计参数的合理取值范围,以某单跨跨径102 m的UHPC简支箱梁桥为背景,通过单参数影响效应分析和ANSYS优化设计模块分析对桥面板厚度h_(1)、上弦板高度h_(2)、上弦板厚度b及上弦板间距L的合理取值进行优化设计,并对优化后的UHPC箱梁桥面体系开展1∶2缩尺模型试验和有限元模拟,最后对UHPC箱梁桥面体系抗裂性能参数(上弦板受拉钢筋直径和上弦板高度)进行分析。结果表明:h_(1)、h_(2)、b和L合理取值范围分别为UHPC单箱室顶板(不含翼缘)横向跨度的1/40~1/35、1/10~1/8、1/37~1/31和1/2.8~1/1.4,对于背景工程h_(1)、h_(2)、b应分别不小于14、55、15 cm,L应不大于4 m;ANSYS优化结果与力学特性指标优化结果参数取值较为接近,优化后背景工程全桥UHPC体积减少约11.0%;试验梁上弦板发生面内受弯破坏,为UHPC箱梁桥面体系最不利受力部件;试验梁开裂应力值是正常使用极限状态设计值的2.14倍,具有较高安全储备,优化方案能满足工程应用要求;增大上弦板受拉钢筋直径及上弦板高度整体上可有效提高UHPC箱梁桥面体系的抗裂性能。

提篮式拱梁组合体系桥梁拱梁结合段受力特性研究

为了解提篮式拱梁组合体系桥梁拱梁结合段的受力特性,以福州至长乐机场城际铁路乌龙江大桥为背景,建立该桥拱梁结合段精细化有限元模型,考虑几何大变形、材料非线性等效应进行全过程非线性分析,得到不同荷载阶段下拱梁结合段的应力分布,研究拱梁结合段的破坏模式和受力特性。结果表明:随着荷载增加,中拱拱脚外侧加劲肋与底板交界处最先屈服,最不利截面位于拱肋壁板与拱脚横隔板交界处;拱梁结合段的弹性承载力系数为2.32,塑性承载力系数为4.71。当荷载达3.57倍最不利荷载组合时,最不利截面拱肋壁板与拱脚横隔板相交的角点先达到屈服;当荷载达4.25倍最不利荷载组合时,1/2最不利截面屈服,屈服区域由角点屈服向拱肋上部区域扩展;当荷载达4.71倍最不利荷载组合时,最不利截面大部分屈服,拱肋壁板屈服区域向整个截面扩展,拱肋因屈服区域过大而丧失承载力。拱肋壁板屈服区域扩展过程中,内、外侧加劲肋逐步屈服;设置外侧加劲肋有利于推迟拱肋壁板的屈服。

大幅变宽连续箱梁桥受弯性能研究

为研究大幅变宽度连续箱梁桥的宽跨比对其力学特性的影响,以湖南省长益高速公路互通匝道变宽预应力混凝土连续梁桥为工程背景,分别建立梁格模型与单梁模型,对其弯矩、挠度及应力进行分析。研究结果表明:在仅考虑自重与二期荷载作用下,随着宽跨比的增加,各纵梁沿横截面承担的弯矩逐渐趋于均匀,各纵梁承担的应力相对平均偏差增大,空间效应明显;与增加箱室宽度而变宽的主梁相比,通过增加箱室数量而变宽的主梁的挠度与弯矩分布更加均匀。