Long-term structural health monitoring of the Cleddau bridge: evaluation of quasi-static temperature effects on bearing movements

This paper illustrates how long-term measurements can be analysed to understand bridge behaviour under changing environmental conditions and how the developed understanding can help explain the performance of its critical components. Measurements from the Cleddau bridge, a structure that has been continuously monitored for more than two years, are used to investigate thermal effects in steel box-girder bridges and, in particular, their bearings. Observed temperature distributions are very different to the recommended distributions in design codes (BS EN 1991-5: 2003). These temperature distributions create plan bending of the box girder, which in turn impose forces at the bearings that have contributed to its wear. This paper investigates bearing movements of the bridge using numerical models, and estimates the resulting forces at the supports. A physics-based model of the bridge is created to which temperature distributions inferred from in situ measurements are supplied as input. Model predictions are validated against measured deformations at the bearings. Subsequently the model is used to predict forces at the bearings due to plan bending and bearing locking. Results quantify the impact that thermal effects have on the performance of the bearings. They also highlight the significance of considering a range of temperature distribution scenarios that go beyond those given in the design codes in order to reliably evaluate thermal effects at the design stage.     

Seismic vulnerability assessment of wall pier supported highway bridges using nonlinear pushover analyses

Pushover analyses were conducted to assess the seismic vulnerability of wall pier supported highway bridges on southern Illinois priority emergency routes. Three-dimensional finite element models were developed to reflect typical hammerhead and regular wall pier bridges from a random sample of the bridge inventory. The models incorporated expected nonlinear structural and material behavior of all the bridge components—superstructure, expansion joints, approach embankments and/or abutments, bearings, wall piers, footings and/or pile caps, and pile and/or mat foundations (plus soil effects)—as well as defining failure measures for each component. Both transverse and longitudinal pushover analyses were conducted on ninety wall pier bridge models reflecting the sample population variation in bridge characteristics such as wall pier type, number of piers, skew, type of foundation, concrete reinforcement ratio, bearing type, and wall height. It was found that the population of wall pier bridges studied was generally vulnerable to wall bearing and abutment bearing failures, wall pier ductility failures, and footing shear and/or bending failures, with bridge skew leading to a coupling of the failure mechanisms from the two pushover directions.     

Reduction of traffic-induced vibration of two-girder steel bridge seated on elastomeric bearings

Reinforcing end-cross beam and removing bumps at expansion joints of bridges are proposed to reduce the traffic-induced vibration and to enhance the deck resistance near the expansion joint of a two-girder steel bridge with elastomeric bearings at each support. The reduction effect is investigated by means of a three-dimensional traffic-induced dynamic analysis. This study indicates that traffic-induced acceleration responses as well as dynamic reaction force of the bridge with the elastomeric bearings are greater than those of the bridge with steel pin bearings. It is observed that reinforcing the end-cross beam reduces traffic-induced vibrations regardless of bearing types, and also removing bumps is the most effective in reducing the dynamic reaction force of the bridges. Especially, for the bridge with elastomeric bearings, the maintenance of bumps near expansion joints is very important to improve not only expanding life span of the expansion joint but also the vibration serviceability of bridges.     

Seismic response of a continuous bridge with bearing protection devices

Unseating of bridges during earthquakes results from the failure of bearings and insufficient seat length. In case of elastomeric bearings, large deformations of the superstructure occur, under severe earthquake ground motions and additional protection measures are necessary. The combination of a displacement restraining device with the elastomeric bearing can prevent bearing failure. This paper evaluates the performance of four different types of protection devices to limit the displacement of the superstructure during earthquakes: (1) rigid stopper device, (2) yielding stopper device, (3) steel restrainer, and (4) superelastic shape memory alloy (SMA) restrainer. Analytical models for all the protection devices have been developed and seismic response of an existing bridge with elastomeric bearings and different protection devices has been evaluated for five strong ground motion records scaled in the frequency domain. The results show that all the protection devices have comparable performance in preventing the failure of bearing during an earthquake.     

Design of Rupture Strength of Side Blocks in Elevated Steel Girder Bridges with Elastomeric Bearings

Elastomeric rubber bearings with side blocks have been extensively used as a seismic response-control device in steel girder bridges in Japan. In real scenarios, the behavior of the girder bridges with elastomeric bearings are usually complex because of the complex mechanism by which the seismically induced inertia forces at concrete deck transmits to the girder bearings. Therefore, it is important to carry out seismic response analysis of a whole bridge system considering the interaction between different structural components in order to check the performance of the side blocks during an event of severe earthquakes. The objectives of the present study are to develop a detailed three-dimensional finite element (FE) model of an elevated girder bridge system and to propose a design rupture strength for the side blocks. The FE-model is constructed based on an existing plate girder bridge considering the effect of concrete slab, girders, stiffeners, rubber bearing, pier and the damage control by the side blocks. A sequence of seismic response analysis is then performed using four different rupture forces of the side blocks by considering the Level-2 design earthquake, the 1995 Kobe earthquake and the 2016 Kumamoto earthquake. The analytical investigation reveals that the side blocks should be designed to withstand a horizontal force of at least 1200 kN in order to prevent the rupture of the side blocks and to mitigate damage of bridge piers. Moreover, the damage to the critical parts of bridge superstructure can be mitigated by strengthening the side blocks. Based on the analysis results, a retrofit plan to strengthen the side blocks of existing girder bridges is proposed.

     

A numerical investigation on the fire response of a steel girder bridge

The response of bridges subject to fire is an under researched topic despite the number of bridge failures caused by fire. Since available data shows that steel girder bridges are especially vulnerable to fire, this paper delves into their fire response by analyzing with a 3D numerical model the response of a typical bridge of 12.20 m span length. A parametric study is performed considering: (1) two possibilities for the axial restraint of the bridge deck, (2) four types of structural steel for the girders (carbon steel and stainless steel grades 1.4301, 1.4401, and 1.4462), (3) three different constitutive models for carbon steel, (4) four live loads, and (5) two alternative fire loads (the hydrocarbon fire defined by Eurocode 1 and a fire corresponding to a real fire event). Results show that restraint to deck expansion coming from an adjacent span or abutment should be considered in the numerical model. In addition, times to collapse are very small when the bridge girders are built with carbon steel (between 8.5 and 18 min) but they can almost double if stainless steel is used for the girders. Therefore, stainless steel is a material to consider for steel girder bridges in a high fire risk situation, especially if the bridge is located in a corrosive environment and its aesthetics deserves special attention. The methodology developed in this paper and the results obtained are useful for researchers and practitioners interested in developing and applying a performance-based approach for the design of bridges against fire.     

Seismic performance of isolated curved steel viaducts equipped with deck unseating prevention cable restrainers

This paper presents an in-depth analysis to evaluate the efficiency of using cable restrainers connecting isolated and non-isolated spans for preventing unseating of curved steel viaducts. For this purpose, the overall three-dimensional non-linear bridge response is examined in detail under the action of strong earthquake ground motions. The expected seismic vulnerability of bridge structures with curved deck geometries has been demonstrated, providing a refined estimation of seismic demands on most critical bridge components. The advantage of using a precise three-dimensional model has revealed the concentration of large seismic forces on specific steel bearing supports and cable restrainer units that greatly increase their failure possibility. Moreover, the unbalanced distribution of pounding forces found across the expansion joint is able to cause local damage to colliding girders and transmit high impact forces to bearing supports. In general, restrainers perform effectively to minimize the possibility of deck unseating and reduce the pounding forces at the expansion joint. Special attention should be paid to the non-linear bridge dynamic response in order to avoid failure of restrainers and ensure the adequate proportioning of the cables according to the characteristics of isolation bearings.     

Comparative structural response of two steel bridges constructed 100 years apart

This paper presents a comparative numerical analysis of the structural behaviour and seismic performance of two existing steel bridges, the Infiernillo II Bridge and the Pinhão Bridge, one located in Mexico and the other in Portugal. The two bridges have similar general geometrical characteristics, but were constructed 100 years apart. Three-dimensional structural models of both bridges are developed and analysed for various load cases and several seismic conditions. The results of the comparative analysis between the two bridges are presented in terms of natural frequencies and corresponding vibration modes, maximum stresses in the structural elements and maximum displacements. The study is aimed at determining the influence of a 1 century period in material properties, transverse sections and expected behaviour of two quite similar bridges. In addition, the influence of the bearing conditions in the global response of the Pinhão Bridge was evaluated.     

Seismic effects of elevating bridges with steel pedestals in the southeastern United States

Steel pedestals have been used in the southeastern parts of the United States to elevate highway bridges and decrease the likelihood of vehicle collisions with bridge decks. However, the seismic performance of bridges elevated with steel pedestals is still unknown. To investigate the effect of elevating bridges with steel pedestals, this paper uses the results of previously conducted experimental tests to model the hysteretic behavior of three types of steel pedestals in a detailed 3D finite element model of a representative bridge. One short pedestal (with a height of 500 mm) and two tall pedestals (with a height of 850 mm) are studied. The structural responses of the studied bridge with the addition of steel pedestals are compared to the structural responses of the same bridge before elevation, where elastomeric bearings support the deck. This study considers five different locations in the southeastern United States and for each of them selects 20 artificial ground motions at two hazard levels of 2% and 10% probability of exceedance in 50 years. The selected artificial ground motions are applied to the representative bridge model in four cases: one case with elastomeric bearings and three cases with three studied pedestals. Because of the large amount of resulting data, a statistical effects model is employed. The statistical effects model is a statistical tool that uses the statistics of the data to investigate the effect of each studied parameter such as bearing type, bridge location and hazard level on the structural responses. Results show that elevating bridges with the studied steel pedestals decreases longitudinal and transverse deck displacements, longitudinal shear and moment in columns, cap beam moment and pounding force. In the transverse direction, elevating the bridge leads to an increase in the abutment force. Also, results show that the studied tall steel pedestals are more effective than the studied short steel pedestal in decreasing longitudinal shear and moment in columns and decreasing transverse deck displacements while offering a height advantage. A study of the stability of the pedestals in this paper shows that the three types of studied pedestals may become unstable in earthquakes, thereby serving as a means to help determine where the installation of steel pedestals would not seem detrimental.     

地震作用下双曲面球型减隔震支座在铁路#br# 简支梁桥中的动力行为

为研究双曲面球型减隔震支座在铁路简支梁桥中的减隔震效果,采用ABAQUS软件建立8m及25m墩高的铁路简支梁桥有限元模型,进行地震荷载作用下的非线性动力时程分析。通过对有限元计算结果与振动台模型试验结果进行对比,验证有限元模型的正确性。与普通球型钢支座作对比,分析地震作用下双曲面球型减隔震支座的水平滑动位移、竖向位移和竖向荷载变化等动力行为。研究得到双曲面球型减隔震支座在不同地震烈度下的水平滑动位移范围。研究结果表明：相对于普通支座,双曲面球型减隔震支座在大多数情况下,能明显减小顺桥向地震作用造成的简支梁固定端与滑动端之间的竖向相对位移,对轨道结构造成的不利影响更小;双曲面球型支座能显著降低横桥向地震作用造成的支座竖向荷载变化幅值,并有效避免支座滑动面发生脱离碰撞。     

Ermüdungsbeanspruchungen von Betonbrücken unter zunehmendem Schwerverkehr

Fatigue Life of Concrete Bridges under Consideration of Increasing Traffic Loads Increasing traffic loads lead to higher fatigue stresses on bridge structures. The effects on the stresses of the main load‐bearing structure depend on the load models representing weight and the ratio of the load model length to the bearing distance of the superstructure. Within a research project carried out on behalf of the Federal Ministry of Transport, Building and Urban Affairs several different bridge constructions (box girder bridge, skew slab construction, girder bridge with T‐beam elements) were analysed with respect to their fatigue strength. Hence, the stresses in concrete and steel components are examined on extensive numerical models in longitudinal and transversal direction. The fatigue investigations of these existing bridges are performed by specified load combinations according to the German Standard for the design of concrete bridges. Furthermore the future development of heavy traffic loads is included by calculating the effects of a 60to‐heavy traffic vehicle.     

简支梁桥采用减隔震装置后抗震性能分析

介绍了桥梁隔震的概念。以3座不同柱高的城市高架桥工程为实例,分别采用板式橡胶支座和铅芯橡胶支座隔震装置。研究采用隔震装置的高架桥地震反应计算表明:随着立柱的高度增加,结构的柔性增大,桥梁的抗震性能也越好;采用铅芯橡胶支座后,桥梁地震响应明显降低,桥梁抗震性能显著增强。以上海软土地基为基准刚度,研究了基础弹性刚度对采用铅芯橡胶支座桥梁地震响应的影响。结果表明:当基础弹性刚度小于基准值的5倍时,应考虑基础的弹性影响;当刚度大于基准值的5倍时,其影响甚微。     

Uplift of elastomeric bearings in isolated bridges subjected to longitudinal seismic excitations

Bearings are used to isolate bridge substructures from the lateral forces induced by creep, shrinkage and seismic displacements. They are set in one or two support lines parallel to the transverse axis of the pier cap and are typically anchored to the deck and to the pier cap. This detailing makes them susceptible to possible tensile loading. During an earthquake, the longitudinal displacements of the deck induce rotations to the pier caps about a transverse axis, which in turn cause tensile (uplift) and compressive displacements to the bearings. Tensile displacements of bearings, due to the pier rotations, have not been addressed before and questions about the severity of this uplift effect arise, because tensile loading of bearings is strongly related to elastomer cavitation and ruptures. An extended parametric study revealed that bearing uplift may occur in isolated bridges, while uplift effect is more critical for the bearings on shorter piers. Tensile displacements of bearings were found to be significantly increased when the isolators were eccentrically placed with respect to the axis of the pier and when flexible isolators were used for the isolation of the bridge. The results of this study cannot be generalised as bridge response is strongly case-dependent and the approach has limitations, which are related to the modelling approach and to the fact that emphasis was placed on the longitudinal response of bridges.     

考虑板式支座滑移的中小跨度梁式桥振动台试验

基于汶川地震中小跨度梁式桥普遍出现的板式橡胶支座滑移典型震害,采用大比例全桥振动台试验手段探究了考虑板式支座滑移对该类桥梁抗震性能影响。以一座25m跨径的标准简支T梁桥为例,设计了1/4缩尺比的全桥试验模型,选取一条近场脉冲型实际地震动记录作为振动台试验输入,对不同墩梁横向约束体系的结构开展了一系列振动台试验研究。试验结果表明：①强震作用下板式橡胶支座与梁底间会出现摩擦滑移效应,从而在一定程度上对下部结构起到隔震作用;②在地震动较小时,常规横向混凝土挡块可以起到一定限位效果,但在强震作用下,随着板式橡胶支座开始发生滑移,混凝土挡块的限位效果逐渐减弱,同时混凝土挡块还会造成下部结构较大的地震损伤;③新型弹塑性挡块具有良好稳定的滞回耗能能力,可有效控制强震作用下墩梁间最大相对位移需求,减低其震后残余位移,同时弹塑性挡块的屈服还可避免下部结构造成严重地震损伤。     

钢桁架结构次应力问题的探讨

近年来钢桁架结构桥梁的建造逐渐增加,相比于其他类型桥梁,钢桁架结构具有跨度大、承载能力强、构造轻巧简洁的特点。但钢桁架结构桥梁设计中次应力的分析计算比较困难,特别是随着大跨度桥梁的建造,如何考虑次应力对桥梁结构设计的影响很重要。应用有限元软件,以广州新光大桥钢桁结构拱设计方案为例,探讨引起钢桁架结构中次应力的因素,同时根据次应力大小决定是否考虑其影响,并就减小钢桁架结构次应力给出了一些建议措施。     

支座摩擦滑移和挡块力学性能退化影响下#br# 桥梁易损性研究

为探究支座摩擦滑移和挡块力学性能退化的共同作用对桥梁墩柱及支座在地震作用中的影响,通过板式橡胶支座往复荷载试验,建立可以考虑摩擦滑移的支座计算模型,并结合挡块模型,对同时考虑支座摩擦滑移和挡块力学性能退化的桥梁进行地震损伤分析。利用易损性曲线的方法对近、远场地震作用下,桥梁墩柱和支座的损伤概率进行分析,结果表明：板式橡胶支座摩擦滑移会降低支座的力学性能;仅考虑支座摩擦滑移而不考虑挡块限位作用时墩柱损伤概率较低,支座的损伤概率较高;当支座摩擦与挡块退化共同作用时,会增加支座的损伤概率,降低墩柱的损伤并且由于挡块力学性能退化的特性,可能造成挡块和梁体的损坏。     

箱型连续梁桥复合加固效果动力特性评定

箱型桥梁复合加固的效果是工程中比较关注的课题。本文结合典型箱型连续梁桥-连霍高速公路仁存沟高架桥病害情况,采用复合加固手段提高桥梁承载能力。针对该桥复合加固的效果评定,采用了比较加固前后桥梁动力特性的变化方法进行。建立了该桥的数值模型,分别研究了体外预应力、铆粘钢板、增大截面及粘贴碳纤维布和复合加固法等多种加固措施对桥梁动力特性的影响。计算结果表明,铆粘钢板法、增大截面法等加固法明显影响了桥梁振动频率,可采用频率的变化来评估加固效果;体外预应力加固法、外贴碳纤维和复合加固方法对桥梁动力特性的影响比较复杂,可以通过联合动力特性和静力测试分析加固效果。     

Finite element investigation of the structural behaviour of deck slabs in composite bridges

This research studies the structural behaviour of bridge deck slabs under static patch loads in steel–concrete composite bridges and investigates compressive membrane action (CMA) in concrete bridge decks slabs, which governs the structural behaviour. A non-linear 3D finite element analysis models was developed using ABAQUS 6.5 software packages. Experimental data from one-span composite bridge structures are used to validate and calibrate the proposed FEM models. A series of parametric studies is conducted. The analysis results are discussed and conclusions on the behaviour of the bridge decks are presented.     

Management system for road bridge structural bearings

Support bearings used in road bridges frequently account for a major part of the maintenance budget of the corresponding bridges. In addition, there are considerable indirect costs and inconveniences resulting from rehabilitation operations and consequent interruption of traffic. This paper presents an innovative management system for support bearings used in road bridges. The system encompasses the development of a classification system of bridge support bearings, their anomalies and possible causes, inspection and diagnosis methods, and maintenance and rehabilitation techniques, linked by appropriately validated correlation matrixes. Based on a set of parameters that define degradation levels, the system allows evaluating each defect in terms of physical and functional deterioration and social impact. Priorities for action can then be set according to the parameter considered most critical: anomaly, bearing, bridge or road section.     

Dynamical identification and modelling of steel–concrete composite high-speed railway bridges

In the last few years, the construction of new high-speed (HS) railways across Europe, as well as in many other countries, has required many different bridges and viaducts. Together with classical concrete solutions, new steel–concrete composite typologies have been developed, giving light and cheap structures. Despite these studies and applications, some concerns still remain about the definition of reliable models for the evaluation of their actual dynamical behaviour under HS train passage. In particular, the influence of many structural and non-structural components, such as cross-girders and ballast, are still not well recognised. In this paper, open problems related to the dynamical assessment and modelling of new steel–concrete four-parallel-girder and box-girder solutions are exposed and analysed. A suitable procedure, based on operational modal analysis, model updating and train–bridge interaction analysis is applied to two bridges, recently built in the new Italian HS network, in order to assess and verify their dynamic behaviour under operative conditions.