板式橡胶支座对斜交连续梁桥地震反应的影响

为充分了解板式橡胶支座对斜交连续梁桥地震反应的影响,利用OpenSees软件建立简化的斜交桥计算模型进行时程分析,研究板式橡胶支座摩擦滑移效应,以及支座动摩擦系数、剪切刚度、局部脱空等参数对斜交桥地震反应的影响。结果表明:板式橡胶支座考虑摩擦滑移后,不仅桥面位移和转角显著增大,而且出现残余位移和残余转角;随着支座剪切刚度的增大,桥面位移和转角均明显减小;随着桥墩处支座动摩擦系数的增大,桥面位移、转角均呈增长趋势,然而桥台处支座动摩擦系数的影响与之相反;桥墩处局部支座脱空对斜交桥的影响明显大于桥台支座。     

Direct displacement‐based seismic assessment procedure for multi‐span reinforced concrete bridges with single‐column piers

In Italy, as in other high seismic risk countries, many bridges, nowadays deemed ‘strategic’ for civil protection interventions after an earthquake, were built without antiseismic criteria, and therefore their seismic assessment is mandatory. Accordingly, the development of a seismic assessment procedure that gives reliable results and, at the same time, is sufficiently simple to be applied on a large population of bridges in a short time is very useful. In this paper, a displacement‐based procedure for the assessment of multi‐span RC bridges, satisfying these requirements and called direct displacement‐based assessment (DDBA), is proposed. Based on the direct displacement‐based design previously developed by Priestley et al., DDBA idealizes the multi DOF bridge structure as an equivalent SDOF system and hence defines a safety factor in terms of displacement. DDBA was applied to hypothetical bridge configurations. The same structures were analyzed also using standard force‐based approach. The reliability of the two methods was checked performing IDA with response spectrum compatible accelerograms. Copyright © 2012 John Wiley & Sons, Ltd.     

无缝桥抗震性能的对比研究

本文以一座三跨总长60 m的整体桥为案例桥,分别试设计了同跨径的半整体桥、延伸桥面板桥和常规连续梁桥。通过Midas/Civil软件建立四种桥型的有限元模型,并对其进行了E1和E2反应谱分析和时程分析,对比了四种桥型的结构反应峰值（墩顶位移、桥墩及桩基剪力与弯矩、台底位移、桥台桩基剪力与弯矩）。计算结果表明:当桥梁存在15°的斜交角,整体桥、半整体桥在地震动沿平行于桥台长边方向及其垂直方向输入时更不利,而延伸桥面板桥和常规连续梁桥在地震动沿顺桥向和横桥向输入时更不利。四种桥型在地震作用下:整体桥抗震性能最优异,但其台底位移、桥台桩基的剪力和弯矩最大;半整体桥台底位移、桥台桩基的剪力和弯矩最小,其墩顶位移、桥墩及桩基的剪力和弯矩仅比整体桥大;延伸桥面板桥和常规连续梁桥的墩-梁相对位移远大于整体桥和半整体桥,不适用于地震基本烈度高的区域。     

Further development of a multimodal pushover analysis procedure for seismic assessment of bridges

An improvement is first suggested to the modal pushover analysis (MPA) procedure for bridges initially proposed by the writers (Earthquake Engng Struct. Dyn. 2006; 35 (11):1269–1293), the key idea being that the deformed shape of the structure responding inelastically to the considered earthquake level is used in lieu of the elastic mode shape. The proposed MPA procedure is then verified by applying it to two actual bridges. The first structure is the Krystallopigi bridge, a 638 m‐long multi‐span bridge, with significant curvature in plan, unequal pier heights, and different types of pier‐to‐deck connections. The second structure is a 100 m‐long three‐span overpass bridge, typical in modern motorway construction in Europe, which, although ostensibly a regular structure, is found to exhibit a rather unsymmetric response in the transverse direction, mainly due to torsional irregularity. The bridges are assessed using response spectrum, ‘standard’ pushover (SPA), and MPA, and finally using non‐linear response history analysis (NL‐RHA) for a number of spectrum‐compatible motions. The MPA provided a good estimate of the maximum inelastic deck displacement for several earthquake intensities. The SPA on the other hand could not predict well the inelastic deck displacements of bridges wherever the contribution of the first mode to the response of the bridge was relatively low. Copyright © 2009 John Wiley & Sons, Ltd.     

Extension of direct displacement‐based design methodology for bridges to account for higher mode effects

An improvement is suggested to the direct displacement‐based design (DDBD) procedure for bridges to account for higher mode effects, the key idea being not only the proper prediction of a target‐displacement profile through the effective mode shape method (wherein all significant modes are considered), but also the proper definition of the corresponding peak structural response. The proposed methodology is then applied to an actual concrete bridge wherein the different pier heights and the unrestrained transverse displacement at the abutments result in an increased contribution of the second mode. A comparison between the extended and the ‘standard’ DDBD is conducted, while further issues such as the proper consideration of the degree of fixity at the pier's top and the effect of the deck's torsional stiffness are also investigated. The proposed methodology and resulting designs are evaluated using nonlinear response‐history analysis for a number of spectrum‐compatible motions. Unlike the ‘standard’ DDBD, the extended procedure adequately reproduced the target‐displacement profile providing at the same time a good estimate of results regarding additional design quantities such as yield displacements, displacement ductilities, etc., closely matching the results of the more rigorous nonlinear response‐history analysis. However, the need for additional iterations clearly indicates that practical application of the proposed procedure is feasible only if it is fully ‘automated’, that is, implemented in a software package. Copyright © 2012 John Wiley & Sons, Ltd.     

Nonsmooth dynamics prediction of measured bridge response involving deck‐abutment pounding

Earthquake‐induced deck‐abutment contact alters the boundary conditions at the deck level and might activate a different mechanical system than the one assumed during the design of the bridge. Occasionally this discrepancy between the assumed and the actual seismic behavior has detrimental consequences, for example, pier damage, deck unseating, or even collapse. Recently, an insightful shake‐table testing of a scaled deck‐abutment bridge model 1 , showed unexpected in‐plane rotations even though the deck was straight. These contact‐induced rotations produced significant residual displacements and damage to the piers and the bents. The present paper utilizes that experimental data to examine the validity and the limitations of a proposed nonsmooth dynamic analysis framework. The results show that the proposed approach satisfactorily captures the planar rigid‐body dynamics of the deck which is characterized by deck‐abutment contact. The analysis brings forward the role of friction on the physical mechanism behind the rotation of the deck, and underlines the importance of considering the frictional contact forces during deck‐abutment interaction even for straight bridges, which typically are neglected. Finally, the paper investigates the sensitivity of the rotation with respect to macroscopic contact parameters (i.e., the coefficient of friction and the coefficient of restitution). Copyright © 2017 John Wiley & Sons, Ltd.     

Seismic performance evaluation of steel arch bridges against major earthquakes. Part 1: dynamic analysis approach

In this study the inelastic behavior of steel arch bridges subjected to strong ground motions from major earthquakes is investigated by dynamic analyses of a typical steel arch bridge using a three‐dimensional (3D) analytical model, since checking seismic performance against severe earthquakes is not usually performed when designing such kinds of bridge. The bridge considered is an upper‐deck steel arch bridge having a reinforced concrete (RC) deck, steel I‐section girders and steel arch ribs. The input ground motions are accelerograms which are modified ground motions based on the records from the 1995 Hyogoken‐Nanbu earthquake. Both the longitudinal and transverse dynamic characteristics of the bridge are studied by investigation of time‐history responses of the main parameters. It is found that seismic responses are small when subjected to the longitudinal excitation, but significantly large under the transverse ground motion due to plasticization formed in some segments such as arch rib ends and side pier bases where axial force levels are very high. Finally, a seismic performance evaluation method based on the response strain index is proposed for such steel bridge structures. Copyright © 2004 John Wiley & Sons, Ltd.     

Axially equilibrated displacement‐based beam element for simulating the cyclic inelastic behaviour of RC members

Distributed plasticity beam elements are commonly used to evaluate limit state demands for performance‐based analysis of reinforced concrete (RC) structures. Strain limits are often preferred to drift limits because they directly relate to damage and are therefore less dependent on member geometry and boundary conditions. However, predicting accurately strain demands still represents a major simulation challenge. Tension shift effects, which induce a linear curvature profile in the plastic hinge region of RC columns and walls, are one of the main causes for the mismatch between experimental and numerical estimates of local level quantities obtained through force‐based formulations. Classical displacement‐based approaches are instead suitable to simulate such linear curvature profile. Unfortunately, they verify equilibrium only on an average sense due to the wrong assumption on the axial displacement field, leading to poor deformation and force predictions. This paper presents a displacement‐based element in which axial equilibrium is strictly verified along the element length. The assumed transversal displacement field ensures a linear curvature profile, connecting accurately global displacement and local strain demands. The proposed finite element is validated against two sets of quasi‐static cyclic tests on RC bridge piers and walls. The results show that curvature and strain profiles for increasing ductility demands are significantly improved when axially equilibrated rather than classical displacement‐based or force‐based elements are used to model the structural members. Copyright © 2017 John Wiley & Sons, Ltd.     

Pseudo‐dynamic testing of bridges using non‐linear substructuring

Pseudo‐dynamic tests on a large‐scale model of an existing six‐pier bridge were performed at the ELSA laboratory using the substructuring technique. Two physical pier models were constructed and tested in the laboratory, while the deck, the abutments and the remaining four piers were numerically modeled on‐line. These tests on a large‐scale model of an existing bridge are the first to have been performed considering non‐linear behavior for the modeled substructure. Asynchronous input motion, generated for the specific bridge site, was used for the abutments and the pier bases. Three earthquake tests with increasing intensities were carried out, aimed at the assessment of the seismic vulnerability of a typical European motorway bridge designed prior to the modern generation of seismic codes. The experimental results confirm the poor seismic behavior of the bridge, evidenced by irregular distribution of damage, limited deformation capacity, tension shift effects and undesirable failure locations. Copyright © 2004 John Wiley & Sons, Ltd.     

钢筋混凝土圆截面桥墩抗震加固方式对比分析

为研究不同加固方式对钢筋混凝土(RC)圆截面桥墩抗震性能的影响,利用OpenSees有限元软件建立了普通RC桥墩以及分别采用钢套管、碳纤维增强聚合物(CFRP)、体外预应力筋进行加固的桥墩数值分析模型,对模型输入远断层地震动,进行增量动力分析。以墩顶峰值位移角与震后残余位移角为指标,对比分析了桥墩加固前后的地震响应。结果表明:采用钢套管、体外预应力筋和CFRP加固后,RC桥墩的峰值位移与震后残余位移均减小,钢套管加固方式对桥墩峰值位移的降低幅度最大,体外预应力筋加固方式对抑制桥墩震后残余位移的效果最好;随着剪跨比的增大,3种加固方式对桥墩在地震动作用下位移响应的抑制作用均逐步减小;随着轴压比的增大,3种加固方式对RC桥墩峰值位移的抑制作用逐步降低。     

基于模糊理论的高铁连续梁桥地震风险评估

以某高速铁路线上一座连续梁桥为例,运用模糊综合评判法,结合基于位移的支座损伤分析和截面曲率的桥墩损伤分析,以全概率理论地震损失模型为基础,提出了基于模糊理论的桥梁系统地震经济风险评估方法。结果表明:综合考虑桥梁系统的模糊地震经济风险分析方法能更全面地计算出连续梁桥在地震作用下的经济损失,仅以桥墩构件代表全桥所得地震经济损失误差较大。基于模糊理论的年预期损失风险框架方法通过结构抗震性能的概率特征可对高速铁路连续梁桥的地震直接经济风险进行全面评估,为该类桥梁的抗震设计、维修加固和灾后重建等方案做出合理评价。     

Life‐cycle reliability of RC bridge piers under seismic and airborne chloride hazards

Over the last two decades, the probabilistic assessment of reinforced concrete (RC) structures under seismic hazard has been developed rapidly. However, little attention has been devoted to the assessment of the seismic reliability of corroded structures. For the life‐cycle assessment of RC structures in a marine environment and earthquake‐prone regions, the effect of corrosion due to airborne chlorides on the seismic capacity needs to be taken into consideration. Also, the effect of the type of corrosive environment on the seismic capacity of RC structures has to be quantified. In this paper, the evaluation of the displacement ductility capacity based on the buckling model of longitudinal rebars in corroded RC bridge piers is established, and a novel computational procedure to integrate the probabilistic hazard associated with airborne chlorides into life‐cycle seismic reliability assessment of these piers is proposed. The seismic demand depends on the results of seismic hazard assessment, whereas the deterioration of seismic capacity depends on the hazard associated with airborne chlorides. In an illustrative example, an RC bridge pier was modeled as single degree of freedom (SDOF). The longitudinal rebars buckling of this pier was considered as the sole limit state when estimating its failure probability. The findings show that the life‐cycle reliability of RC bridge piers depends on both the seismic and airborne chloride hazards, and that the cumulative‐time failure probabilities of RC bridge piers located in seismic zones can be dramatically affected by the effect of airborne chlorides. Copyright © 2011 John Wiley & Sons, Ltd.     

限制位移桥墩的连续刚构桥抗震性能研究

沿着摇摆桥墩的概念提出一种限制位移桥墩连续刚构桥体系。该体系通过对连续刚构桥墩底和承台之间采取一定措施,使桥梁在地震发生时能够在限制的位移量内活动,减小输入到桥梁结构中的能量,达到减震的目的。通过对一座铁路连续刚构桥的分析,发现这种限制位移桥墩连续刚构桥体系能大幅减小桥墩的延性和强度地震需求,减震效果明显,在选择合适的限制位移量的情况下,可保证桥墩在高烈度罕遇地震作用下几乎保持弹性工作状态,震后经简单处理即可保证使用功能,为震后救援工作带来极大便利,也大大减少了修复成本。     

Effect of torsional stiffness of prestressed concrete box girders and uplift of abutment bearings on seismic performance of bridges

Uplift of certain abutment bearings during earthquake may be utilized as a safety mechanism for the protection of the bridge against excessive stress. For this reason design codes such as Eurocode 8 permit the uplift of such bearings under certain conditions. Uplift of an abutment bearing occurs when the torque at the deck end exceeds a critical value. Therefore the torsional stiffness of the deck, before or after concrete cracking, is an important factor. In this work realistic values for the cracked torsional stiffness of the bridge deck are estimated from a parametric study of typical thin-walled prestressed box girders, based on non-linear analysis of softened space truss models proposed in the literature. Moreover the interaction between bearing uplift and pier flexural response is investigated and recommendations for the seismic design of bridges are proposed, taking into account the possibility of uplift of abutment bearings before or after yielding of the piers.     

Hybrid simulation of a multi‐span RC viaduct with plain bars and sliding bearings

This paper deals with the seismic response assessment of an old reinforced concrete viaduct and the effectiveness of friction‐based retrofitting systems. Emphasis was laid on an old bridge, not properly designed to resist seismic action, consisting of 12 portal piers that support a 13‐span bay deck for each independent roadway. On the basis of an OpenSEES finite element frame pier model, calibrated in a previous experimental campaign with cyclic displacement on three 1:4 scale frame piers, a more complex experimental activity using hybrid simulation has been devised. The aim of the simulation was twofold: (i) to increase knowledge of non‐linear behavior of reinforced concrete frame piers with plain steel rebars and detailing dating from the late 1950s; and (ii) to study the effectiveness of sliding bearings for seismic response mitigation. Hence, to explore the performance of the as built bridge layout and also of the viaduct retrofitted with friction‐based devices, at both serviceability and ultimate limit state conditions, hybrid simulation tests were carried out. In particular, two frame piers were experimentally controlled with eight‐actuator channels in the as built case while two frame piers and eight sliding bearings were controlled with 18‐actuator channels in the isolated case. The remaining frame piers were part of numerical substructures and were updated offline to accurately track damage evolution. Copyright © 2015 John Wiley & Sons, Ltd.     

Relative displacement response spectra with pounding effect

To avoid unseating of a deck, an adequate seat width must be provided. The seat width is basically determined from maximum relative displacement between two bridge segments. Under a strong ground excitation, pounding between two decks may occur at a joint. The pounding will affect the response of two bridge segments. This research is conducted to investigate the effect of pounding on the relative displacement between two adjacent bridge segments. A simplified analytical model of two linear single‐degree‐of‐freedom systems is employed. To take into account the pounding, the laws of conservation of momentum and energy are applied. The analytical results are represented in the form of relative displacement response spectra with pounding effect. It is found that due to the pounding the relative displacement can be amplified, resulting in the requirement of a longer seat width to support a deck. The formulation of normalized relative displacement response spectra is presented together with an application example. It is found that the seat width determined from the relative displacement response spectra with pounding effect becomes close to the value specified in the Japanese design specifications for structures with large difference of natural periods. Copyright © 2001 John Wiley & Sons, Ltd.     

Accuracy of nonlinear static procedures for the seismic assessment of shear critical structures

The nonlinear behavior of reinforced concrete (RC) members represents a key issue in the seismic performance assessment of structures. Many structures constructed in the 1980s or earlier were designed based on force limits; thus they often exhibit brittle failure modes, strength and stiffness degradation, and severe pinching effects. Field surveys and experimental evidence have demonstrated that such inelastic responses affect the global behavior of RC structural systems. Efforts have been made to consider the degrading stiffness and strength in the simplified nonlinear static procedures commonly adopted by practitioners. This paper investigates the accuracy of such procedures for the seismic performance assessment of RC structural systems. Refined finite element models of a shear critical bridge bent and a flexure‐critical bridge pier are used as reference models. The numerical models are validated against experimental results and used to evaluate the inelastic dynamic response of the structures subjected to earthquake ground motions with increasing amplitude. The maximum response from the refined numerical models is compared against the results from the simplified static procedures, namely modified capacity spectrum method and coefficient method in FEMA‐440. The accuracy of the static procedures in estimating the displacement demand of a flexure‐critical system and shear‐critical system is discussed in detail. Copyright © 2015 John Wiley & Sons, Ltd.     

Simplified method for real‐time seismic damage assessment of motorway bridges: Transverse direction—Accounting for abutment stoppers

In the context of developing a real‐time seismic damage assessment technique, this paper proposes a simplified model that accounts for abutment stoppers, focusing on the transverse direction. Detailed 3D finite element models of 4 bridges of the Attiki Odos motorway are developed and used as benchmarks to assess its efficiency. The selected bridges vary in length, pier typologies, clearances, and pier‐deck connections. The simplified model entails a SDOF system of a pier, with assemblies of gap elements, lateral and rotational springs, and dashpots (top and bottom), representing the deck, the bearings, the abutment stoppers, and the foundation. The effect of stoppers is initially studied, focusing on the response of the abutment‐embankment system. To shed more light on the role of abutment stoppers, a parametric study is conducted, considering a wide range of clearances. Subsequently, the effect of variabilities in span length and pier height is examined. The simplified method is extended to nonideally symmetric systems and verified against the 3D benchmarks. Finally, the model is modified to account for multicolumn piers. The extended simplified model offers a reasonable prediction of the seismic damage state, reducing significantly the computational cost, and allowing detailed parametric studies. The latter are used to develop nonlinear regression model equations correlating a selected damage index with statistically significant intensity measures. Such equations offer a viable alternative for network‐wide seismic damage assessment as part of a real‐time emergency response framework. A pilot implementation is presented, illustrating the applicability of the proposed methodology.     

Identification of yield drift deformations and evaluation of the degree of damage through the direct sensing of drift displacements

Inter‐story drift displacement data can provide useful information for story damage assessment. The authors' research group has developed photonic‐based sensors for the direct measurement of inter‐story drift displacements. This paper proposes a scheme for evaluating the degree of damage in a building structure based on drift displacement sensing. The scheme requires only measured inter‐story drift displacements without any additional finite element analysis. A method for estimating yield drift deformation is proposed, and then, the degree of beam end damage is evaluated based on the plastic deformation ratios derived with the yield drift deformation values estimated by the proposed method. The validity and effectiveness of the presented scheme are demonstrated via experimental data from a large‐scale shaking table test of a one‐third‐scale model of an 18‐story steel building structure conducted at E‐Defense. Copyright © 2016 John Wiley & Sons, Ltd.