A 3-Node Co-Rotational Triangular Finite Element for Non-Smooth,Folded and Multi-Shell Laminated Composite Structures

Based on the first-order shear deformation theory,a 3-node co-rotational triangular finite element formulation is developed for large deformation modeling of non-smooth,folded and multi-shell laminated composite structures.The two smaller components of the mid-surface normal vector of shell at a node are defined as nodal rotational variables in the co-rotational local coordinate system.In the global coordinate system,two smaller components of one vector,together with the smallest or second smallest component of another vector,of an orthogonal triad at a node on a non-smooth intersection of plates and/or shells are defined as rotational variables,whereas the two smaller components of the mid-surface normal vector at a node on the smooth part of the plate or shell(away from non-smooth intersections)are defined as rotational variables.All these vectorial rotational variables can be updated in an additive manner during an incremental solution procedure,and thus improve the computational efficiency in the nonlinear solution of these composite shell structures.Due to the commutativity of all nodal variables in calculating of the second derivatives of the local nodal variables with respect to global nodal variables,and the second derivatives of the strain energy functional with respect to local nodal variables,symmetric tangent stiffness matrices in local and global coordinate systems are obtained.To overcome shear locking,the assumed transverse shear strains obtained from the line-integration approach are employed.The reliability and computational accuracy of the present 3-node triangular shell finite element are verified through modeling two patch tests,several smooth and non-smooth laminated composite shells undergoing large displacements and large rotations.

The mechanical response of multi-tower continuous-span suspension bridge deck pavement based on whole bridge analysis

The effect of multiple span suspension structure on the mechanical response of bridge deck pavement was studied, and finite element analysis (FEM) of stress and strain of pavement according to the bridge floor system features of super-long and high flexibility was made. Meanwhile, the FEM results were compared with those of the single span suspension structure. Three-stage analytic hierarchy process (AHP) is developed to analyze the mechanical response including whole bridge analysis, partial beams section analysis and orthotropic plate analysis. The most unfavorable load position was determined by the numerical solutions acquired from each stage to study the main mechanical index of multiple span suspension structure. The FEM results showed that the mechanical response numerical solutions by using the three-stage AHP are greater than those by simplified boundary condition, and the force condition of multiple span suspension structure is worse than that of the single span suspension structure.

Contrastive analysis and crashworthiness optimization of two composite thin-walled structures

For the safety protection of passengers when train crashes occur, special structures are crucially needed as a kind of indispensable energy absorbing device. With the help of the structures, crash kinetic-energy can be completely absorbed or dissipated for the aim of safety. Two composite structures(circumscribed circle structure and inscribed circle structure) were constructed. In addition, comparison and optimization of the crashworthy characteristic of the two structures were carried out based on the method of explicit finite element analysis(FEA) and Kriging surrogate model. According to the result of Kriging surrogate model, conclusions can be safely drawn that the specific energy absorption(SEA) and ratio of specific energy absorption to initial peak force(REAF) of circumscribed circle structure are lager than those of inscribed circle structure under the same design parameters. In other words, circumscribed circle structure has better performances with higher energy-absorbing ability and lower initial peak force. Besides, error analysis was adopted and the result of which indicates that the Kriging surrogate model has high nonlinear fitting precision. What is more, the SEA and REAF optimum values of the two structures have been obtained through analysis, and the crushing results have been illustrated when the two structures reach optimum SEA and REAF.

Numerical Simulation-Based Analysis of the Impact of Overloading on Segmentally Assembled Bridges

Segmentally assembled bridges are increasinglyfinding engineering applications in recent years due to their unique advantages,especially as urban viaducts.Vehicle loads are one of the most important variable loads acting on bridge structures.Accordingly,the influence of overloaded vehicles on existing assembled bridge structures is an urgent concern at present.This paper establishes thefinite element model of the segmentally assembled bridge based on ABAQUS software and analyzes the influence of vehicle overload on an assembled girder bridge struc-ture.First,afinite element model corresponding to the target bridge is established based on ABAQUS software,and the load is controlled to simulate vehicle movement in each area of the traveling zone at different times.Sec-ond,the key cross-sections of segmental girder bridges are monitored in real time based on the force character-istics of continuous girder bridges,and they are compared with the simulation results.Finally,a material damage ontology model is introduced,and the structural damage caused by different overloading rates is compared and analyzed.Results show that thefinite element modeling method is accurate by comparing with on-site measured data,and it is suitable for the numerical simulation of segmental girder bridges;Dynamic sensors installed at 1/4L,1/2L,and 3/4L of the segmental girder main beams could be used to identify the dynamic response of segmental girder bridges;The bottom plate of the segmental girder bridge is mostly damaged at the position where the length of the precast beam section changes and the midspan position.With the increase in load,damage in the direction of the bridge develops faster than that in the direction of the transverse bridge.Thefindings of this study can guide maintenance departments in the management and maintenance of bridges and vehicles.

Parameter analysis of composite pile foundation in bridge foundation

In the current theory of bridge foundation design,all of the loads above the cap are loaded by the pile,and the bearing capacity of the soil among piles is not taken into account.In order to analyze the bearing capacity of the soil among piles in bridge pile foundation,a model of pile foundation is established based on a bridge foundation which is under construction,and by the finite element analysis software ANSYS.According to the results of finite element analysis(FEA)and current bridge foundation design theory,a feasible composite pile foundation which can be applied in the design of bridge foundation,is recommended.Additionally,a number of modifications are made to the original design.It was confirmed that these modifications derived from numerical simulations can improve the performance of the foundation.

Analysis of a New Composite Material for Watercraft Manufacturing

In this paper, we investigate the properties of an alternative material for use in marine engineering, namely a rigid and light sandwich-structured composite made of expanded polystyrene and fiberglass. Not only does this material have an improved section modulus, but it is also inexpensive, light, easy to manipulate, and commercially available in various sizes. Using a computer program based on the finite element method, we calculated the hogging and sagging stresses and strains acting on a prismatic boat model composed of this material, and determined the minimum sizes and maximum permissible stresses to avoid deformation. Finally, we calculated the structural weight of the resulting vessel for comparison with another structure of comparable dimensions constructed from the commonly used core material Divinycell.

Displacement and force analyses of piles in the pile-caisson composite structure under eccentric inclined loading considering different stratum features

A novel anchorage for long-span suspension bridges,called pile-caisson composite structures,was recently proposed by the authors in an attempt to reduce the construction period and costs.This study aims to investigate the displacement and force behavior of piles in a pile-caisson composite structure under eccentric inclined loading considering different stratum features.To this end,both 1g model tests and three-dimensional numerical simulations were performed.Two groups of 1g model tests were used to validate the finite-element(FE)method.Parametric studies were then performed to investigate the effects of groundwater level,burial depth of the pile-caisson composite structure,and distribution of soil layers on the performance of the pile-caisson composite structure.The numerical analyses indicated that the influence of the groundwater level on the stability of the caisson was much greater than that of the piles.In addition,increasing the burial depth of the pile-caisson composite structure can assist in reducing the displacements and improving the stability of the pile-caisson composite structure.In addition,the distribution of soil layers can significantly affect the stability of the pile-caisson composite structure,especially the soil layer around the caisson.

Influence of Random Track Irregularities on Dynamic Response of Bridge/Track Structure/High-Speed Train Systems

Random vertical track irregularities are one of essential vibration sources in bridge, track structure and high-speed train systems. The common model of such irregularities is a stationary and ergodic Gaussian process. The study presents the results of numerical dynamic analysis of advanced virtual models of composite BTT （bridge/ballasted track structure/high-speed train） systems. The analysis has been conducted for a series of types of single-span simply-supported railway composite （steel-concrete） bridges, with a symmetric platform, located on lines with ballasted track structure adapted for high-speed trains. The bridges are designed according to Polish bridge standards. A new methodology of numerical modeling and simulation of dynamic processes in BTT systems has been applied. The methodology takes into consideration viscoelastic suspensions of rail-vehicles, nonlinear Hertz wheel-rail contact stiffness and one-side wheel-rail contact, physically nonlinear elastic-damping properties of the track structure, random vertical track irregularities, approach slabs and other features. Computer algorithms of FE （finite element） modeling and simulation were programmed in Delphi. Both static and dynamic numerical investigations of the bridges forming the series of types have been carried out. It has been proved that in the case of common structural solutions of bridges and ballasted track structures, it is necessary to put certain limitations on operating speeds, macadam ballast and vertical track roughness.

Stability Analysis of Space Compcoite Structore and Its Ultimate Bearing Capacity

In this paper, using incremental equilibrium equation, the authors have studiedthe effeet of ultimate bearing capacity of every component on structuralstability, and discussed the stability analysis method for space compositestructures. With the help of the test results for the concrete filled ateel tubeskeleton of the long-spen RC arch bridse, it is proved that the proposed methodis accurate and reliable.

Bridge Engineering-Oriented Parametric Model

A new model is proposed to improve the efficiency of structural modeling. In this model, the bridge structural components are expressed with component description, parametric description and geometric description in a software system. This model provides both convenience and flexibility for users in structural modeling process. The object-oriented method is applied in the model implementation. A bridge analysis preprocessor is developed on the basis of this model. It provides an effective way for bridge modeling.

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.

常泰长江大桥组合索塔锚固结构钢-混传剪构造足尺模型试验研究

常泰长江大桥索塔锚固结构采用钢箱-核芯混凝土组合结构,为研究该新型组合索塔锚固结构钢-混传剪构造的受力特性,进行钢-混传剪构造足尺模型试验研究。制作2个锚固结构足尺节段试验模型,通过压剪试验研究锚固结构的荷载~滑移曲线及应力、应变分布等受力特性,并通过有限元模型分析锚固结构的传力机理和各组件的内力分配比例,推导剪力钉剪力计算方法。结果表明:在2.14倍单索最大索力荷载作用下,锚固结构保持弹性状态,钢壁板未产生明显滑移,钢-混界面最大滑移不超过0.25 mm,该锚固结构中钢-混传剪构造至少具有2.14倍的安全系数;荷载作用下,剪力钉剪力从上至下逐渐增大,锚腹板附近底部3排剪力钉剪力较大,钢-混传剪构造至少存在剪力钉和界面摩擦力2种传剪机制,钢-混传剪构造的承载能力显著提高;钢-混传剪构造受力过程分为粘结力传力阶段和局部滑移阶段,剪力钉剪力分布不仅与沿剪切方向长度分布有关,也与荷载的大小线性相关。

梁桁组合结构高铁斜拉桥的收缩徐变分析——以西十高铁汉江特大桥为例

梁桁组合结构高铁斜拉桥中,混凝土收缩徐变对桥面线性的平顺性及行车的舒适性有直接影响,是桥上能够铺设无砟轨道的关键因素。因此,为分析收缩徐变对梁桁组合结构受力和变形的影响,依托新建西安至十堰高铁汉江特大桥工程,采用CEB-FIP90徐变计算模型,通过建立有限元模型分析收缩徐变影响下主要构件的内力和变形,评价各主要受力构件刚度变化对徐变变形的贡献程度,研究改善收缩徐变变形措施。结果表明:(1)收缩徐变引起主梁跨中下挠、桥塔向跨中侧偏移,同时引起主梁和桥塔的压缩变形,5年完成的收缩徐变变形占前10年的70%以上,且主梁产生的收缩徐变贡献超过50%;(2)收缩徐变引起斜拉索索力松弛,运营30年的最大变化率在5%以内;(3)收缩徐变引起主梁应力及上下缘应力差变化,随着运营时间增加主梁跨中区域应力差增大明显,主要表现在下缘压应力储备降低;(4)随着桥塔刚度、主梁刚度、加劲钢桁刚度增大,收缩徐变引起的变形有所减小,而斜拉索刚度则产生相反的趋势。(5)延长铺轨时间、适当增加底板钢束面积、增加斜拉索索力以及在跨中加劲钢桁上弦灌注混凝土可有效降低主梁跨中徐变下挠。

钢-混组合结构群钉连接件的连杆效应试验研究

钢—混组合结构连接件中栓钉式群钉连接件存在单钉承载力折减及群钉中栓钉的剪力分布不均匀的情况,本文提出一种带连杆的群钉连接件,旨在通过在栓钉之间设置连杆使群钉中栓钉之间的剪力分布更加均匀,并提高构件的整体承载能力。利用推出试验结合有限元模拟,揭示了带连杆群钉连接件的作用机理,并通过参数分析给出群钉构件合理的连杆布置位置以及尺寸。研究结果表明:在构件达到极限承载力时,合理的设置连杆能够减少83.76%的栓钉底部剪力分布的不均匀程度,对构件承载能力的提升能达到8.56%。本文研究可为带连杆群钉连接件的结构优化提供一定的理论基础,推动新型连接件的发展。

波纹钢-混凝土复合结构高温压弯性态研究

波纹钢-混凝土复合结构因其强度较高且施工高效已逐渐应用于隧道支护中,但波纹钢板由于无混凝土的保护,在高温下性能劣化严重。依托云南省普洱市高山寨隧道,利用ABAQUS软件建立有限元模型进行数值模拟分析,研究波纹钢-混凝土复合结构在不同温度和不同偏心距正负弯矩作用下的多工况高温压弯性态。研究结果表明,随着温度的升高,波纹钢-混凝土复合结构中和轴逐渐上移,初始抗弯刚度和极限荷载逐渐下降;当温度>500℃时,结构性能降低幅度最大,宜将500℃作为结构重点关注温度。

钢-混凝土组合简支桥面连续结构横向应力分析

针对钢-混组合简支梁桥的桥面连续结构开裂等病害,围绕桥面连接板的横桥向应力问题,采用线弹性理论和板的偏微分方程进行分析,得出了桥面连接板挠度和应力的分布函数,建立非线性有限元模型,并进行实桥荷载试验.通过比较理论解、有限元解和实测试验结果,证实了理论解和有限元的有效性.根据得到的分布函数,发现横桥向和纵桥向上的最大拉应力出现在钢梁端部位置的连接板的上缘.此外,还分析了连接板区域尺寸变化对横桥向应力峰值的影响,包括纵梁端部距支座的长度、纵梁的间距以及连接板区域整体尺寸变化.结果表明:较小的纵梁间距和较长的纵梁端部与支撑之间的距离会导致连接板中的横向拉应力峰值增加,并提高横向拉应力在总应力中的占比,从而导致桥面连接板早于设计荷载开裂.因此对于纵梁间距较小、梁端长度较长的钢-混组合简支梁桥桥面连续结构,仅计算其纵桥向受力性能会导致计算结果偏危险,建议按照本文方法考虑横桥向应力对桥面连接板的影响.

东津黄河大桥主桥总体设计

东津黄河大桥主桥为(50+180+420+180+50) m双塔钢-混组合梁斜拉桥,采用半飘浮结构体系;主梁采用宽34 m的双边钢箱-混凝土桥面板组合梁;桥塔采用无下横梁的A形桥塔+分离式承台,承台间设横向系梁,塔梁交接处设置牛腿支承主梁,塔柱底部设置破冰体;基础采用?2.0 m钻孔灌注桩,最大桩长117 m;斜拉索采用标准抗拉强度1 860 MPa平行钢丝拉索,按空间双索面扇形布置,塔端采用钢锚梁+混凝土齿块锚固,梁端采用钢锚箱锚固于主梁边钢箱外腹板。计算结果表明,该桥结构静、动力性能良好,各项指标满足规范要求。

斜拉桥V形钢塔-混凝土基座结合构造方式比选

某人行景观桥为空间异型钢塔斜拉桥,主塔中2根箱型钢柱在四棱台混凝土基座上方交汇呈非对称V形,钢柱轴线与其底端钢-混连接面不垂直,基座尺寸严格受制于河道防洪要求,使塔根-基座结合部构造方式设计具有挑战性。按照造价相当的标准初步拟定3种结合方案,采用ABAQUS软件分别建立相应的有限元模型,选取塔底支座反力中平面内外弯矩绝对值相加最大的组合进行模拟计算及其结果比较和对标检验。研究结果表明:承压-传剪组合式结合部可以大幅度减小桥塔根部、基座及其中锚箱的应力,使其合理满足相关规范要求。就塔根最大位移和应力幅而言,均为传剪式最大、组合式最小。组合式方案中承压板厚度较承压式减小1/3,应力虽有上升却未超限,材料利用率提高。承压式、特别是传剪式构造方案中,混凝土基座最大主拉应力远超规范限值,无法满足抗裂要求。传剪式方案中锚箱钢板Mises应力也超限22%,且与其竖向压应力和混凝土主拉应力的最大值处于同一位置。传剪式方案不适用的原因是,锚箱中侧面竖板间距太小,矩形板与柱壁连接屈从于不利构造特点,形成大转折。无论应力大小还是变形控制,组合式方案都值得优先选择。研究成果直接服务于本工程,对类似工程也有一定的参考价值。

基于施工全过程健康监测的装配式部分包覆钢-混凝土组合结构体系动力特性研究

为研究装配式部分包覆钢-混凝土组合结构的动力特性,基于世博文化公园双子山项目,采用全过程健康监测手段对装配式PEC结构体系施工全过程的应力、加速度进行监测,研究其阻尼比和自振频率在施工过程中的变化情况,将实测结果与有限元计算结果进行对比。结果表明:结构应力计算值、自振频率计算值等均与实测值吻合较好,验证了结构施工全过程仿真模拟计算的合理性。施工过程中PEC框架梁柱及节点后浇区的型钢及混凝土应力实际监测结果均满足强度要求。节点后浇区混凝土浇筑前后,结构自振周期和阻尼比差别较小;结构顶部覆土恒载施加完成后,结构的自振周期和阻尼比均较之前有所增大。结构设计时阻尼比取0.04,小于施工完成后的阻尼比实测值最小值0.046,阻尼比取值偏于安全,设计阻尼比取值合理。

考虑水-结构-土相互作用的桥墩自振频率半解析解

建立考虑水-结构-土相互作用的桥墩结构自振频率半解析解,并通过实测数据进行验证。以单个桥墩为研究对象,将“桥墩-承台-桩基”结构体系简化为Bernoulli-Euler梁,采用附加质量模型模拟水-结构相互作用,采用弹性Winkler地基模型模拟桩-土相互作用,建立考虑水-结构-土相互作用的桥墩结构振动控制方程。使用分离变量法得到结构振型函数,根据边界条件建立矩阵方程,通过求解方程的特征值得到结构自振频率。以福州浦上大桥E11桥墩为例,将海底地震仪(ocean bottom seismometer,OBS)核心地震计安装在承台处,采集桥墩的振动响应并提取结构自振频率。同步安装陆地地震仪验证OBS水下监测的有效性,通过对比半解析解、有限元解和实测值验证桥墩结构半解析解的合理性。在此基础上,分析土-结构相互作用、水-结构相互作用对结构自振频率的影响。结果表明,OBS能够满足桥墩自振频率水下测试的环境要求;建立的考虑水-结构-土相互作用的桥墩结构自振频率半解析解合理;土-结构、水-结构相互作用会降低结构的一阶自振频率,其中土-结构相互作用的影响比水-结构相互作用更显著。