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.     

Reliability-based optimization of steel truss arch bridges

A reliability-based optimization approach is developed and applied to minimize the weight of steel truss arch bridges subject to probabilistic (the overall probability failure of the structure) and deterministic (stress and deflection) constraints. The method intelligently integrates the genetic algorithm (GA), the finite element method and the first order reliability method. A real-coded/integer-coded method is used to realistically represent the values of the design variables. Three GA operators consisting of constraint aggregate selection procedure, arithmetic crossover, and non-uniform mutation are proposed. The finite element method (FEM) and the first order reliability method are used to compute the value of the probabilistic and deterministic constraint functions. A numerical example involving a detailed computational model of a long span steel arch bridge with a main span of 550 m is presented to demonstrate the applicability and merits of the present method. Finally, several important parameters in the present method are discussed.     

A review of experimental investigations and assessment methods for masonry arch bridges

Masonry arch bridges constitute a significant proportion of European road and rail infrastructures. Most of them are well over 100 years old and are supporting traffic loads many times above those originally envisaged. The inherent variation in their constituent materials, the traditional design criteria and methods used for their construction, their deterioration over time caused by weathering processes and the development of other defects, significantly influence the mechanical response of these historic structures. A deep understanding on the numerous factors that affect the structural behaviour of masonry arch bridges and on the analysis methods to assess the life expectancy of such bridges and inform maintenance and strengthening strategies is essential. This paper provides a critical review of the experimental studies that have been carried out and of the assessment approaches that have been developed in the last three decades to these aims. The current knowledge is established and areas of possible future research work are identified, with the aim of providing students and researchers, asset managers and bridge owners, and practitioners with a guidance for research activities and maintenace strategies.     

Terrestrial laser scanning and limit analysis of masonry arch bridges

Masonry arches are one of the most common and extended structural shapes present in the worldwide architectural heritage. When handling with these structures at least two demands are addressed to the scientific community: (i) development of reliable and affordable methods for documenting historic infrastructures and (ii) improvement of structural analysis for appraising the actual structural condition of the bridge. In relation to the first item, 3D laser scanning is an exponent of the evolution of the non contact techniques for built up structures survey and documentation. In relation to the structural stage, the limit analysis is still the most extended method among engineers and technicians and some of the most common software package for masonry arch bridges work within the assumptions of limit analysis. However computations should be adapted to work on the base of the real geometry instead of on idealized geometry in order to benefit from the advanced 3D surveying techniques and get more reliable results. In this article we describe a methodology based on using TLS to obtaining the real 3D geometry of the whole bridge and the arches. The collapse load value and position, as well as the hinges position and reaction forces are obtained within the assumptions of the limit analysis but on the base of the resulting survey. The methodology is applied in a mediaeval bridge.     

Reliability-based condition assessment of deteriorating concrete bridges considering load redistribution

A wide variety of models have been proposed for estimating the reliability of highway bridges. For reinforced concrete bridges subjected to environmental attack, time-variant reliability methods have to be used. In this study, the condition of reinforced concrete girder bridges is assessed using a time-variant system reliability approach in which both load and resistance are time-variant quantities. Several system models are considered, including failure of any girder (series system) and failure of a specified number of adjacent girders (series-parallel system). Adaptive importance sampling is used to determine the cumulative-time system failure probability. An existing reinforced concrete T-beam bridge located near Pueblo, Colorado, is investigated. The influence of resistance degradation and post-failure load redistribution is included. A comparison of reliability estimates for several system models is given, including the influence of correlation among initial girder strengths. The results can be used as a guide for the selection of system models for bridge reliability analysis, identification of critical girders in a bridge system, and for the development of optimal reliability-based maintenance strategies for reinforced concrete highway bridges.     

Assessment of masonry arch railway bridges using non-destructive in-situ testing methods

The paper presents methods of inspection and testing for masonry arch railway bridges. An overview of a selection of available non-destructive, minor-destructive and monitoring methods is given and their efficacy for the assessment of masonry arch bridges is discussed. The principles of in-situ load tests are described and a methodology for the assessment of masonry arch railway bridges is shown through case studies. Results of a testing programme are demonstrated where the efficiency of various non-destructive testing methods has been studied. It is shown that non-destructive investigation and non-destructive in-situ load-testing can provide valuable information on the condition of bridges and help verify basic input parameters for structural analysis and assessment.     

Longitudinal and transverse effects in masonry arch assessment

Recent advances in the analysis of masonry arch bridges, substantiated by extensive testing programs in the United States and Europe, provide bridge engineers and inspectors with increasing confidence that reasonable estimates can be made of the capacity of these structures. Observations of ultimate strength testing indicate that spandrel walls and fill contribute greatly to the strength and stiffness of these structures, and that loads approaching the plastic collapse load can often be obtained. Observations from service load testing indicate that the development of cracking and non-linearity under service loads can be a significant indicator of the capacity of the structure. Modeling of these structures has shown the importance of restraint of the abutment to the overall resistance of the structure, and has recently shown the importance of transverse effects in diminishing the strength of structures with high spandrel walls or thin arch rings.     

Assessment of the load-carrying capacity of multi-span masonry arch bridges using fibre beam elements

An approach that makes use of non-linear beam elements with fibre cross-section has been used for modelling the ultimate behaviour of multi-span masonry arch bridges. The proposed approach proves able to take into account the interaction among the spans and the non-linear material behaviour with low computational effort. In order to validate the use of the model for the assessment of masonry arch bridges, the load-carrying capacity for typical multi-span railway bridges has been evaluated and the results compared to experimental results and to currently used limit analysis methods. It is shown that, by parity of constitutive assumption, the method provides the same results as limit analysis, both in terms of maximum load prediction and hinges position at collapse; however, taking the effective ductility capacity into account, a strong reduction in load-carrying capacity with respect to classical limit analysis was found, depending on rise-to-span arch ratio, piers slenderness and backfill height. The approach is then applied to a seven span viaduct of the Italian railway network, for which the effective mechanical properties of masonry were identified through an experimental campaign on brickwork samples according to the effective material properties surveyed on site.     

Decision support software approach to the assessment of stone masonry bridges

This paper identifies the need for a formalized approach to the assessment of the integrity of stone masonry bridges and develops the concept of the use of a computer database and suitable software to support the practising bridge engineer in the decision-making process (decision support software, DSS).

The different standard techniques of assessment of masonry bridges are outlined and their limitations described. The common faults associated with masonry structures are discussed and the problems of identifying these faults are described. The part played by the individual components of a masonry arch bridge is outlined and the significance of faults on the individual components of the structure is discussed.

Database development and operation of the DSS are detailed and their value to the bridge engineer is discussed. The system is illustrated with a demonstration run.     

Reinforced concrete and masonry arch bridges in seismic areas: typical deficiencies and retrofitting strategies

In recent years, appraisal of the condition and rehabilitation of existing bridges has become an ongoing problem for bridge owners and administrators in all developed countries. Reliable methodologies are therefore needed in the assessment and retrofit design phases, to identify the vulnerability of each bridge class. The specific problems of common arch bridge types are discussed herein, for both reinforced concrete and masonry structures, proper interventions for their static and seismic retrofitting are illustrated and several examples of applications are provided. Retrofitting is usually coupled with functional refurbishment, according to a methodological approach that takes into account bridge characteristics, state of maintenance and functional requirements, and environmental aspects connected with repair and strengthening systems.     

Reliability-based strength limit state for steel railway bridges

Railway bridges require special attention to provide safe and economical service. To assess the reliability of a structure, all critical parameters need to be specified. Load and resistance are random in nature; hence, the probabilistic approach is the best method for accurate evaluation of the performance of a bridge. In this study, identification of critical parameters was conducted on a typical through-plate girder, riveted, open deck railway bridge. This type of structure is a weakest link system. In such a system, the failure of one component can lead to failure of the entire structural system. This research involved identification of the basic load and resistance parameters and the development of analytical procedures for modelling the structural behaviour. The finite element method (FEM) was used to investigate the structural performance characteristics of the evaluated bridge. A three-dimensional structural model was developed to determine stress distribution in the members and connections. Based on the results of FEM analysis, the reliability indices were calculated for critical components.     

浆砌石双曲拱坝施工技术

结合工程实例 ,介绍了浆砌石双曲拱坝的施工技术 ,阐述了其施工工艺和作业方法 ,指出双曲拱坝已成为近年来较普遍采用的一种坝型 ,值得推广应用     

某圬工拱桥的承载力评估

以某圬工拱桥为工程背景,建立了有限元计算模型,对其承载能力进行评估研究,得出评估结论,并结合荷载试验综合评定该桥的承载力,对同类桥梁的承载力评估有借鉴意义。     

拱桥的维修与加固方法

介绍了拱桥的发展,针对拱桥在使用过程中出现的病害,提出了拱桥维修和加固的几种方法以及这些方法所适用的条件,以提高拱桥的维修与加固技术水平,从而提高拱桥的社会经济效益。     

Optimum rise design of steel arch bridges

The subject of this paper is the preliminary estimation of the optimum rise of the arch rib in the case of steel arch bridges. This optimum rise is defined in relation to the weight of the construction material used for the arches and columns, while the cost of erection is ignored. A series of arch bridges, having various spans are examined. These bridges have a flexible deck and a stiffened arch rib. For each span the optimum rise is obtained, when the weight of the arches and columns is minimized. The results are given in diagrams in which the variation of the optimum rise with respect to various characteristic parameters, is shown.     

Reliability-based bridge assessment using risk-ranking decision analysis

Information about present and anticipated bridge reliabilities can be used in conjunction with decision models to provide a rational decision-making tool for the assessment of bridges and other structural systems. The present paper presents a broad overview of reliability-based assessment methods and will then focus on decision-making applications using updated time-dependent estimates of bridge reliabilities considering a risk-ranking decision analysis. A practical application of reliability-based safety assessment is illustrated herein which relates the effects of bridge age, current and future (increasing) traffic volume and loads, and deterioration on the reliability and safety of ageing RC bridges.     

Reliability-based optimisation design of post-tensioned concrete box girder bridges considering pitting corrosion attack

Since the mid-twentieth century, prestressed concrete (PC) bridges have been significantly developed to become the most important type of bridge in the world. However, only a few studies have dealt with the reliability-based design optimisation (RBDO) of PC bridges despite the fact that RBDO demonstrates the real behaviour of structures. Moreover, the corrosion of post-tensioned tendon in PC bridges seriously caused sudden failures which have been recorded in the world. Since then, this study presents the probabilistic model and approach to formulate and analyse the RBDO of PC box girder bridges which consider the pitting corrosion phenomenon of shear, torsion reinforcements and post-tensioned tendon. A practical example of a typical PC box girder bridge is presented and discussed. Sensitive analyses are performed to evaluate the influence of ultimate target reliability index on the optimal solution. For the simple support PC box girder bridge, the ultimate target reliability index should be in the range of β_ult: 3.5–5 in order to produce the optimal design.