Spatial embedded reinforcement of 20-node block element for analysis PC bridges

The formula for the contribution of prestressed reinforcement on embedded reinforcement element is derived according to the mechanical behavior of PC bridges and the foundational principle of finite element method. Mechanical concept is definite and examples validate the calculation results. Reinforcement element model allows generating a finite element mesh without taking into consideration the layout of reinforcements. Furthermore, the prestressing tendon may pass through the concrete elements in an arbitrary manner. It is an effective approach that the no-node loads are diverted from the tendons to the adjacent concrete elements. A useful arithmetic analysis of the spatial curved tendon PC Bridges is provided.     

基于视觉关注度与审美偏好的城市景观 元素感知特征研究

视觉关注度与审美偏好是衡量城市景观元素感知属 性的2个独立变量。这2个概念往往易被混淆,且鲜有研究探 究两者之间的关系,并甄选出既受人关注又受人喜爱的景观元 素。通过将城市景观照片作为测试媒介,结合眼动分析法与审 美偏好测试,量化分析了城市景观元素的视觉关注度与审美 偏好。结果显示：1)相比自然景观元素(山体、树林、水体、 草地),人工景观元素(现代建筑、传统建筑、桥梁、道路)更 易受到关注;2)不同自然景观元素对审美偏好的贡献差异显 著,水体审美偏好显著,而山体偏好表现负向;3)在易受到 关注的各类景观元素中,传统建筑、桥梁等偏好显著,现代建 筑偏好表现负向。该研究结果可为城市景观规划设计实践提供 理论参考。     

预应力混凝土梁CFRP加固设计研究

以实际工程为背景,针对预应力混凝土梁CFRP加固的抗弯受力性能进行了研究。研究中运用了基于材料非线性本构关系的有限元分析及参照现有加固规范的计算分析,并对不同的分析结果进行了比较。经分析对比,参照规范得出计算结果具有足够的安全余量,可用于实际工程的设计计算,但此方法对预应力梁的裂缝、挠度等特性无法描述,需要进一步研究。     

Special braced stairs versus typical braced frames. New architectural-structural-seismic approach to stair design

This paper presents a new approach to the project of steel buildings, mainly focused on the architectural, structural, and seismic design of stairs. The objective is to design a structural stair system capable of controlling seismic damage and contributing to the bracing system of the building. The article begins with a review of the seismic standard (ATC, FEMA, and EC8) on which the current design criteria for new buildings with stairs are based. The research is based on two spatial building models (A–B) with the same bracing elements but placed differently. Reference Model A follows classical design approaches. It means, stairs are considered nonstructural elements that do not influence the seismic behavior of the building. This structure corresponds to typical braced frames (IV-CBF and EBF) according to EC8. Model B includes a stair system designed to help control the effects of inter-story drifts and inertia forces. In this case, the same bracing elements of Model A were integrated into the stair structure of Model B. A comparative seismic behavior analysis of typically braced frames (A) versus specially braced stairs (B) is presented. The research was based on the static nonlinear (pushover) analysis and the capacity spectrum method (ATC-40) according to the seismic performance levels (FEMA) and damage limitation (EC8). Finally, the braced stairs was verified via nonlinear time-history analysis in order to better capture the structural safety of the evacuation routes and their influence on the behavior of the building. This deterministic analysis of the braced stairs verified satisfactory results compared to reference bracing systems.     

Seismic assessment of masonry arch bridges

In this paper, the seismic performance of existing masonry arch bridges is evaluated by using nonlinear static analysis, as suggested by several modern standards such as UNI ENV 1998-1 2003, OPCM 3274 2004, and FEMA 440 2005. The use of inelastic pushover analysis and response spectrum approaches becomes more difficult when structures other than the framed ones are investigated. This paper delves into the application of this methodology to masonry arch bridges by presenting two particular case studies. The need for experimental tests in order to calibrate the materials and the dynamic properties of the bridge is highlighted, in order to correctly model the most critical regions of the structure. The choice of the control node in the pushover analysis of masonry arch bridges and its influence on seismic safety evaluation is investigated. The ensuing discussion emphasizes important results, such as the unsuitability of the typical top node of the structure for describing the bridge seismic capacity. Finally, the seismic safety of the two bridges under consideration is verified by presenting an in-depth vulnerability analysis.     

Probabilistic optimal safety with minimum life-cycle cost based on stochastic finite element analysis of steel cable-stayed bridges

This study was intended to efficiently perform the probabilistic safety and optimal design assessment of steel cable-stayed bridges (SCS bridges) using stochastic finite element analysis (SFEA) and expected life-cycle cost (LCC) concept. To that end, advanced probabilistic finite element algorithm (APFEA) which enables to execute the static and dynamic SFEA considering aleatory uncertainties contained in random variable was developed. APFEA is the useful analytical means enabling to conduct the reliability assessment (RA) in a systematic way by considering the result of SFEA based on linearity and nonlinearity of before or after introducing initial tensile force. Appropriateness of APFEA was verified in such a way of comparing the result of SFEA of a simple structure and the result of numerical analysis using Monte Carlo Simulation (MCS) program. The probabilistic method of SCS bridges was set, taking into account of analytical parameters. The dynamic response characteristic by probabilistic method was evaluated using ASFEA, and RA was carried out based on analysis result, thereby quantitatively calculating the probabilistic safety. The optimal design of SCS bridges was determined based on the expected LCC according to the results of SFEA and RA of alternative designs. Moreover, given the potential epistemic uncertainty contained in safety index, failure probability and minimum LCC, the sensitivity analysis was conducted and as a result, a critical distribution phase was illustrated using a cumulative-percentile.     

System reliability of suspension bridges

Provisions for the design of existing suspension bridges often rely on a deterministic basis. Consequently, the reliability of these bridges cannot be assessed if current provisions are applied. In order to develop cost-effective design and maintenance strategies for suspension bridges a system reliability-based approach has to be used. This is accomplished by a probabilistic finite element geometrically nonlinear analysis approach. This study forms part of an investigation into the system reliability evaluation of geometrically nonlinear large span bridges recently undertaken at the University of Colorado. A brief review of reliability analysis of geometrically nonlinear elastic structures allows for the determination of its relevance to the assessment of suspension bridges. A probabilistic finite element geometrically nonlinear elastic code is used for system reliability evaluation of suspension structures. The allowable stress design procedures used by the Honshu Shikoku Bridge Authority for the design of suspension bridges are presented along with their application to the design of an existing bridge. This bridge is studied from a system reliability viewpoint to evaluate its reliability under different loading and damage scenarios. Such information calls attention to the fact that the reliability of cables, hanger ropes and girders are very different. Therefore, optimal maintenance decisions for suspension bridges designed according to allowable stress method are not consistent with those based on equal component reliability values.     

斜拉桥的空间非线性静力分析

针对斜拉桥高次超静定复杂结构,建立了合理的有限元模型。采用大型有限元软件ANSYS对结构整体进行了空间非线性静力分析,以彩色图给出了桥梁结构的弯矩图,斜拉索拉力图,提出了预应力布设的修改建议。分析结果为设计提供了重要的参考依据。     

沪蓉西四渡河悬索桥抗震性能研究

大跨度悬索桥必须进行可靠的抗震性能研究。以一座在建的山区悬索桥为研究对象,采用基于迭代拟合规范设计反应谱法合成一致激励、行波效应以及多点激励3种工况下的位移时程,并作为该桥地震动输入。采用两水准设防二阶段抗震设计方法,分别按纵向+竖向、横向+竖向对其进行线性和几何非线性地震时程分析。分析结果表明:多点激励的影响较大,线性与几何非线性分析结果较接近;经抗震强度、变形验算,该桥抗震性能满足要求。     

缆索承重桥梁的非线性分析方法综述

论述了缆索承重桥梁的非线性分析的几种计算方法,并指出每种方法的适用范围,以使整个结构的分析精度达到新的水平,为同类桥梁结构计算建立了指导。     

自适应模型缩放非线性动力分析方法

提出一种基于模型损伤的自适应模型降阶动力分析方法。该方法在动力分析的每个分析步中根据损伤分布和损伤程度自适应地定义和调整模型子区域的缩放属性。针对模型缩小子区域，采用模态综合方法对其进行动力缩聚；针对模型放大子区域，采用精细化单元替换原有单元，最终形成混合坐标空间内的结构运动方程，通过求解缩减自由度之后的运动方程来提高计算效率。最后通过一个20层钢框架来验证该方法的有效性和适用性，数值结果表明，自适应模型缩放动力分析方法能够在满足模拟精度要求的同时，显著地提高非线性动力分析的计算效率。     

用于悬索桥非线性分析的鞍座-索单元

悬索桥是跨越能力最大的一种桥型,鞍座是使主缆转向的一个重要构件,直接约束着主缆的变形。然而,鞍座及其顶推的模拟一直是悬索桥非线性分析时的一个难点,现有方法存在一定的不足之处。为此,本文提出了一种基于弹性悬索精确解的二节点新单元———鞍座-索单元,这种单元隐含了主缆与鞍座相切及主缆无应力长度保持不变这两个重要条件,同时将鞍座及其顶推的模拟融为一体,提出了基于NewtonRaphson法的状态求解方法,并推导了其切线刚度矩阵和等效节点力。计算表明,状态求解方法精确而有效,切线刚度矩阵推导正确。采用这种单元,既可使悬索桥非线性分析的计算模型更接近实际结构,也能显著提高计算精度和计算速度,并且具有很好的通用性。     

厦门时代广场复杂连体隔震结构整体分析

针对厦门时代广场商业区这一复杂连体顶托一网架的环形建筑采用整体建模方法,分别进行了水平两方向多遇地震和罕遇地震作用下的非线性动力时程计算及分析,并与无连体结构进行了对比研究。整体模型的动力分析结果表明,连廊与主体之间组合隔震系统后,连廊的滑动端平均滑动距离的减震效果自下而上逐渐显著;各单体建筑楼层剪力由于连廊与顶部网架的动力影响,底部两层出现楼层剪力放大,但其余楼层剪力明显减小;网架与托柱之间采用柱顶组合隔震系统后,网架柱底总剪力减震效果极为显著,底部剪力分布更均匀,对调整下部结构内力分布,减小结构在动力作用下的反应是显著的。     

混凝土砌块砌体结构弹塑性地震反应分析方法

基于地震工程模拟开放系统OpenSees,提出了混凝土砌块砌体结构三维弹塑性地震反应数值分析方法,用带刚域的等效框架模型模拟混凝土砌块砌体结构,空间杆单元采用以力为基础的非线性梁、柱单元。数值模拟结果与试验结果较为吻合,验证了分析方法和计算模型的合理性。     

大跨度两铰钢拱桥面内结构设计计算方法

大跨度拱桥具有显著的几何非线性力学行为,按线性设计理论不能满足安全要求,考虑由拱肋变形产生的附加弯矩和精确推算结构的稳定强度是设计中的重要课题。以两铰钢拱桥为对象,提出了考虑非线性影响以及高精度稳定强度的拱桥结构设计方法,以跨度160 m和200 m的两桥计算模型为例,验证了按非线性理论设计的必要性以及本设计方法的合理性,分析结果表明按线性计算方法和弹性稳定理论不能精确评价结构的受力特性和强度。     

A Numerical Method for the Analysis of Rheologic Effects in Concrete Bridges

A method is presented for the numerical analysis of creep, shrinkage, and relaxation in concrete bridges. The method is based on an incremental analysis of the behavior of a viscoelastic composite member and on the use of a classic finite beam element. One of the main advantages of the method is its ability to take the structure constitution and the material behaviors into account in a very precise manner for low calculation cost—limited numbers of finite elements and calculation steps. Also, the processes of construction, prestressing, and free strain development are easily taken into account. The method is compared with test results for two prestressed concrete beams. Finally, the method is applied to the time analysis of a cable-stayed footbridge.     

Safety formats for nonlinear analysis tested on concrete beams subjected to shear forces and bending moments

Safety formats for nonlinear analysis have mainly been tested on beams and columns subjected to normal forces and bending moments. Therefore, it is unclear, whether available safety formats lead to the intended reliability when they are applied to structures that fail due to shear loading. To test available safety formats for nonlinear analysis, a tool was developed which allows a full probabilistic nonlinear analysis of beam sections subjected to arbitrary combinations of normal and shear forces as well as bending moments. Applying this tool to test the safety format according to EN 1992-2 on beams subjected to a combination of shear forces and bending moments showed that EN 1992-2 led to a reliability level that was lower than the target reliability. The safety format according to Schlune et al. (submitted for publication) [1] led to better agreement with the target reliability.     

基于规范车辆荷载模型的三塔悬索桥中间塔鞍座抗滑安全评估

中间塔鞍座抗滑安全是三塔悬索桥设计的关键问题之一,其特点与传统两塔悬索桥不同.根据鞍座与主缆间的抗滑力学模型,中间塔两侧的不平衡车辆荷载是导致主缆与鞍座滑移的主要因素.由于三塔悬索桥体系存在明显的几何非线性特性,通过分析明确了对于中间塔抗滑问题,不考虑车辆荷 .载的几何非线性是偏安全的,于是可选用基于叠加原理的线性理论计算车辆荷载效应.基于规范车辆荷载模型的中间塔鞍座抗滑安全评估表明,不同规范标准下的车辆荷载都能保证中间塔鞍座的抗滑安全,但相应的抗滑安全水平存在差异.因此为获取更加精细化的评估结果,有必要在桥梁实际工作状态下开展进一步的研究.     

碳纤维索(CFRP)斜拉桥的抗震性能分析

为研究特大跨度碳纤维索(CFRP)斜拉桥的抗震性能,以主跨为1700m的钢斜拉桥为例,运用三维非线性有限元理论进行抗震性能分析。分析结果表明,特大跨度斜拉桥采用碳纤维索后:(1)减小了桥梁的最大内力值,改善了结构的受力状态;(2)桥梁的变形特征基本接近。因此,从抗震性能方面考虑,特大跨度斜拉桥采用碳纤维索是可行的,斜拉索截面的确定建议采用等刚度的方法。     

铁路四线桥梁曲线计算方法研究

针对目前铁路桥梁设计中四线桥曲线计算困难的情况,考虑T梁+箱梁+T梁、8片T梁和两片箱梁等多种上部结构模式,求解梁宽-线间距-里程构成的强耦合体系,得出曲线计算结果,并扩展到N线并置的情况。另外对于边置的T梁,如何保证其严格按平分中矢布置,以确保梁体横向的受力均衡,也是研究过程中的另一个难点。