Deterministic and reliability analysis of prestressed concrete bridge girders: comparison of the Chinese, Hong Kong and AASHTO LRFD Codes

This paper compares the prestressing requirements and reliability indices of prestressed concrete bridge girders designed using three codes: the Chinese Code, the Hong Kong Code and the AASHTO LRFD Code. Typical post-tensioned concrete girders of spans ranging from 25 to 40 m are considered. Deterministic analysis indicates that the service limit state governs the design according to the Chinese Code and the AASHTO LRFD Code. However for the Hong Kong Code, only those with longer spans are controlled by the service limit state. The actual number of strands needed by the AASHTO LRFD Code is quite close to that needed by the Chinese Code, while that required by the Hong Kong Code is about 18–33% higher than that required by the AASHTO LRFD Code. Disparity between reliability indices for flexural capacity based on the requirements of the service and strength limit states exists in all three codes. However, the disparity does not follow the same trends as that of the required number of strands for service and strength limit states in the three codes. In addition, the reliability index for flexural capacity according to the requirements of the service limit state is always higher than that of the strength limit state in the three codes. The actual reliability indices for flexural capacity of the girders considered according to the three codes, which are governed by the service limit state, are close to one another.     

Spatial time-dependent reliability analysis of corroding pretensioned prestressed concrete bridge girders

Accelerated pitting corrosion tests have been performed to obtain spatial and temporal maximum pit-depth data for prestressing wires. This data is then used to develop probabilistic models of pitting corrosion and strength capacity of 7-wire strands. The probabilistic model of pitting corrosion for strands is then combined with a non-linear Finite Element Analysis and probabilistic models of corrosion initiation and propagation to study the spatial and temporal effects of pitting corrosion on a typical pretensioned prestressed concrete bridge girder. The limit states considered are flexural strength and serviceability. The spatial time-dependent reliability analysis takes into account the uncertainties and variabilities related to material properties, dimensions, loads and corrosion parameters as well as the spatial variability of pitting corrosion of prestressing strands. Including the spatial variability of pitting corrosion in the reliability analysis increased both the probability of strength and serviceability failure when compared with a mid-span sectional analysis.     

预应力混凝土曲线连续刚构桥结构行为分析

研究了悬臂施工的高墩大跨预应力混凝土曲线连续刚构桥在施工阶段和成桥阶段的结构行为,讨论了由于主梁平面弯曲对结构变形和应力的影响,为曲线刚构桥提供相应的设计建议和施工控制思路,具有现实意义。     

基于碳化的预应力组合箱梁桥可靠性分析

为了研究预应力混凝土结构在混凝土碳化后,结构在服役期间的可靠度,分析讨论了混凝土碳化及其影响因素.将混凝土强度、保护层厚度、计算模式不确定性系数以及荷载增长系数作为随机变量,以混凝土的碳化深度作为一个随时间变化的随机过程,建立了一般大气环境下,混凝土碳化的时变概率随机模型.在此基础上,对五跨预应力组合箱梁进行了研究,从可靠度方面给出了在服役期间结构的可靠度水平.     

既有预应力混凝土空心板桥校核分析

依据现行新规范对既有预应力空心板桥进行了分析校核,计算出既有旧桥荷载横向分布系数,按照新规范进行荷载统计分析,求得各种工况下荷载组合情况,对空心板桥中的单梁按照规范进行复核验算,结果表明:不考虑空心板运营中强度等劣化时,其各项指标仍满足新规范要求可继续使用,因而,旧桥加宽改造时可根据桥梁实际运营情况和计算分析决定是否更换旧板,以节约资源。     

在役混凝土桥梁结构的动态可靠性评估分析

介绍了钢筋混凝土桥梁构件的动态可靠性评估方法,初步分析了荷载效应概率模型、结构抗力概率模型以及抗力的影响因素,提出动态可靠性理论也可以作为可靠性的预测方法,可以使人们获得任意时点的可靠度,从而应用于桥梁结构的可靠性评估.     

Reliability of composite steel bridge beams designed following AASHTO''s LFD and LRFD specifications

Composite steel beam bridges designed following AASHTO's Load Factor Design (LFD) method and the newly developed Load and Resistance Factor Design method (LRFD) are proportioned for different loading conditions. They need to satisfy these conditions at maximum design load, an overloading condition, and fatigue load. The ultimate strength of compact composite steel beams is based on the fully plastic stress distribution. The capacity of non-compact beams is based on the yield or partially-plastic moment, depending on whether the beam violates all or few of the compactness or ductility requirements. In this paper, the reliability for the ultimate flexural capacity limit state of composite steel beams is investigated. The structural reliability is measured in terms of the reliability index. The statistical data on strength are generated starting from statistics on material properties and using the Monte Carlo simulation method. Statistical data on load components are compiled from the available literature. The scope of the study covers a wide range of rolled beams, span lengths, beam spacings, and two yield strengths. The deterministic study showed that the design of composite steel beams is usually not governed by the maximum design load combination, but rather by the overloading condition. The results of the reliability study indicate non-uniformity in the safety of steel bridges that are designed by the AASHTO LFD code. This is also true for AASHTO's LRFD code since it is not calibrated for the overloading condition. The value of the reliability index is a function of the compactness classification, method of design, beam spacing, span length, and section size.     

Assessment of prestressed concrete bridge girders with low shear reinforcement by means of a non-linear filament frame model

The safety of existing bridges and the efficiency of strengthening measures can be accurately studied through non-linear numerical models, assisting decisions of dismantle, repair or change of use and avoiding unnecessary or inappropriate interventions. In this ambit, filament beam models due to their inherent simplicity and low computational demand are adequate for the engineering practice. Accordingly, in this paper, the structural assessment of a prestressed concrete bridge presenting low shear reinforcement, the Wassnerwald Viaduct in Switzerland, is presented. The bridge was dismantled due to, among other reasons, not complying with the safety standards related to shear. The girders of the bridge, which were submitted to full-scale in situ load tests, were numerically simulated by means of a non-linear filament beam model considering axial force (N)–shear (V)–bending (M) interaction. Hypothetical strengthening solutions for this bridge were also numerically studied: a shear strengthening through vertical prestressing and a bending strengthening through external longitudinal prestressing.     

大跨预应力混凝土梁桥下挠的成因及措施

以某特大预应力混凝土梁桥为工程背景,着重从混凝土的收缩徐变、预应力损失、结构刚度等方面分析了各参数对挠度的影响,最后提出了控制结构长期下挠的相关防治措施,从而为同类型研究积累经验。     

预应力混凝土桥梁质量控制及其耐久性研究

针对预应力混凝土桥梁建设中的质量和耐久性问题,详细探讨了问题产生的原因并提出了一套能够有效解决这些问题的施工以及质量控制方法,以推动我国桥梁建设事业稳步健康发展。     

高墩大跨预应力混凝土曲线连续刚构桥位移分析

在介绍高墩大跨预应力混凝土曲线连续刚构桥结构特点的基础上,分析主梁自重、预应力、混凝土徐变以及平曲线等对结构应力和变形的影响。结合某工程实例,建立有限元模型计算分析高墩曲线刚构桥的受力和位移规律,研究此类桥梁在施工阶段和成桥阶段的空间结构行为,为高墩大跨曲线刚构的设计与施工提供参考。     

高墩大跨预应力混凝土曲线连续刚构桥内力分析

在介绍高墩大跨预应力混凝土曲线连续刚构桥结构特点的基础上,分析了主梁自重、预应力、混凝土徐变以及平曲线等对结构应力和变形的影响.结合某工程实例,建立有限元模型计算分析高墩曲线刚构桥的受力和位移规律,研究此类桥梁在施工阶段和成桥阶段的空间结构行为,为高墩大跨曲线刚构的设计与施工提供参考.     

大跨度预应力混凝土刚构桥施工计算分析

大跨度预应力混凝土连续刚构桥是公路、市政桥梁常采用的主要桥型,通过对施工过程进行有效的计算分析,有利于对桥梁施工过程进行合理的控制,同时确保桥梁施工过程安全。本文通过对一跨径组合为55 m+100 m+55 m进行计算分析,对桥梁持久状况承载能力极限状态、持久状况正常使用极限状态、持久状况构件的应力、短暂状况构件的应力、结构预拱度进行了详细的计算,为同类工程提供参考。     

某预应力混凝土连续梁桥内力计算分析

采用桥梁专用有限元软件MIDAS/Civil对某大跨度预应力混凝土连续梁桥的上部结构建立桥梁实体模型,并对其进行了内力计算分析,得出了不同荷载效应作用下桥梁的内力数据,同时对不同荷载效应按照正常使用极限状态和承载能力极限状态进行内力组合,绘出内力包络图,从而为大跨度预应力连续梁桥的配筋设计提供了理论依据。     

下承式钢管混凝土无风撑系杆拱桥设计与施工

介绍了温州市划龙桥西路南塘河大桥的设计和施工工程概况，对该桥的构成、设计和施工均作了简要介绍，提出了确定吊杆合理张拉力的方法及其施工要点。     

预应力混凝土箱梁桥的预应力损失成因及控制

结合具体工程实例,对预应力混凝土箱梁桥的预应力损失原因进行了分析,探讨了预应力损失的组成,阐述了预应力张拉施工时扁锚体系出现伸长值不足的原因,并提出了相应的控制措施,以期指导实践。     

大跨预应力混凝土连续刚构桥优点及施工控制

主要阐述了大跨预应力混凝土连续刚构桥的优点及施工控制措施,分别从应力控制、线形控制、安全控制、稳定控制和温度控制五大方面展开了论述,以期确保桥梁建设的安全运行。     

独塔单索面预应力混凝土斜拉桥施工控制分析

以安徽省怀远县涡河四桥为背景,对其施工过程进行了详细模拟,分析了小跨径独塔单索面预应力混凝土斜拉桥的施工特点,并提出了相应的施工控制对策及施工控制目标.     

混凝土空心板桥病害分析及加固措施

结合广东省清远至连州一级公路高速化改造桥梁加固工程,介绍了混凝土空心板桥病害特征,分析了病害产生原因,提出了桥梁加固措施和施工工艺,对同类桥梁病害处置有一定的参考借鉴作用。     

桥梁结构物耐久性与混凝土配合比的相关分析

针对桥梁混凝土构造物对耐久性的要求 ,介绍了影响混凝土耐久性的三方面因素 ,并从混凝土配合比的角度 ,提出了结构物耐久性需注意的问题