Thermal signature of in situ soil damping under severe seismic actions

This paper gives a synthesis on a series of studies demonstrating the possibility to have a direct access to in situ soil damping, exploiting the thermal dissipation due to irreversible mechanical phenomena under severe seismic conditions. The introduction provides a background to the three steps of such a study: instrumentation, modelling and inverse identification problem. Section 2 recalls the principle of the Seismic Harmonic System, equipment able to generate powerful in situ soil accelerations in the vicinity of a well. Evidence of a significant in situ soil temperature elevation is given under such seismic conditions. Section 3 reviews the mechanical and related thermal simulations for the prediction by a direct problem procedure of the mean temperature elevation in the vicinity of the borehole, using a two- or three-parameter behaviour model depending on the intensity of the actions. Section 4 is a synthesis of the possibilities offered by thermal in situ measurements to contribute, in parallel with mechanical measurements, to the identification and/or the validation of the damping characteristics of an in situ soil.     

地震作用下曲线梁桥结构响应及敏感性分析

为研究不同设计参数对曲线梁桥地震响应的影响以指导结构抗震设计,对不同支承约束曲线梁桥地震响应及地震需求敏感性进行分析。采用增量动力分析（IDA）方法对比分析了不同支承约束曲线梁桥的结构地震响应变化趋势;采用Tornado图形法对不同结构参数影响程度进行了排序,找出了对结构地震需求影响显著的参数。结果表明:采用板式橡胶支座桥梁因支座易发生滑移而导致上部结构位移较大,但降低了下部结构响应,设置固定墩后,下部结构损伤显著增加;对于采用板式橡胶支座和铅芯橡胶支座的曲线梁桥,墩高及跨径对墩底曲率需求影响较大,而对于固定墩为墩梁固结形式和采用盆式橡胶支座的曲线梁桥,跨径及跨数对墩底曲率需求影响较大;对于采用不同支承约束的曲线梁桥,墩高和曲率半径对桥台位移需求影响较大,仅次于地震动参数PGA。     

Structural upgrading strategy for electric power networks under seismic action

This paper presents a procedure to identify an optimal retrofitting strategy for electric power networks (EPN) subjected to seismic events. The optimization consists of the minimization, under economic constraints, of the probability of power cut‐off at the nodes where electric energy is most needed in the post‐earthquake situation; these nodes are referred to as critical nodes. The EPN model used herein has been presented earlier and is briefly reviewed in the text. The method to individuate the critical nodes, based upon the value of an index proposed in this study, is presented first; then the optimization procedure to select which elements of the EPN to upgrade is examined based upon a standard reliability study. Its effectiveness is tested against routinely used upgrading schemes for an existing EPN (the one of Sicily in Italy). It is shown that the optimization procedure is effective and leads to a significant saving of economic resources. Copyright © 2000 John Wiley & Sons, Ltd.     

Concentrically braced steel frames under seismic actions: Non-linear behaviour and design coefficients

The paper deals with the non-linear dynamic analysis of concentrically braced pinned frames under earthquake conditions. A model is first presented for the behaviour of bars subjected to cyclic axial force, which takes into account the overall and local buckling phenomena, section shape, residual stresses, material behaviour and damage accumulation due to low-cycle fatigue and fracture. Dynamic analyses of bracing systems are then described: these have been performed, on the basis of the axially loaded bar model, within the framework of a simplified procedure for the determination of optimal design factors. The results obtained are first reported for the case of one-storey systems; an example of the behaviour of a four-storey system is given finally.     

地震作用下曲线梁桥双向碰撞作用影响分析

碰撞作用直接影响到桥梁不同构件的地震响应,是桥梁抗震研究中一直关注的问题。针对地震作用下曲线梁桥因主梁面内转动而发生主梁与切向桥台和径向挡块碰撞的现象,以1座3跨预应力混凝土连续梁桥为例,采用非线性时程分析方法,对曲线连续梁桥的双向碰撞作用影响进行研究,并分析了不同减撞措施的效果。结果表明:考虑双向碰撞作用后,下部结构响应有明显增加,主梁转动现象变得复杂,曲线梁桥地震响应分析中应通过建立精细化模型来考虑主梁双向碰撞作用的影响;在切向桥台处设置限位拉锁装置能起到较好的减轻双向碰撞作用的影响,以及采用减隔震设计后,减撞效果更明显,桥梁抗震性能明显改善,但合理减撞措施设计参数应结合曲线梁桥约束体系及结构设计参数进行体系分析确定。     

Structural performance of a base-isolated reinforced concrete building subjected to seismic pounding

The effects of seismic pounding on the structural performance of a base-isolated reinforced concrete (RC) building are investigated, with a view to evaluate the influence of adjacent structures and separation between structures on the pounding response. In particular, seismic pounding of a typical four-story base-isolated RC building with retaining walls at the base and with a four-story fixed-base RC building is studied. Three-dimensional finite element analyses are carried out considering material and geometric nonlinearities. The structural performance of the base-isolated building is evaluated considering various earthquake excitations. It is found that the performance of the base-isolated building is substantially influenced by the pounding. The investigated base-isolated building shows good resistance against shear failure and the predominant mode of failure due to pounding is flexural. Copyright © 2012 John Wiley & Sons, Ltd.     

Mechanics and performance of a tied-back wall under seismic loads

In this paper the stability of a tied-back wall subjected to seismic loads is analysed for a predetermined mode of failure (rotation about the top of the wall) and the analysis is compared with data from tests on this type of wall using the seismic simulator at the State University of New York at Buffalo. We carried out a pseudo-static analysis of the problem using the Mononobe-Okabe earth pressure coefficients, wherein the dynamic effects due to the seismic loading are converted into equivalent static loads. The acceleration ratio at which the wall fails by rotation about the top was obtained by considering the moments due to the various lateral earth pressure resultants and the inertial forces induced in the soil due to the seismic loading. We found that the presence of wall friction on the passive side significantly enhances the stability of the flexible retaining wall under seismic loads. Thus, flexible retaining walls supporting dry cohesionless soil can be very efficient during earthquakes. Under moderate earthquakes, an increase in the depth of embedment increases the dynamic factor of safety significantly. However, beyond a certain acceleration ratio for a soil with a particular value of ø, any increase in the depth of emdedment has no effect in impeding failure, irrespective of any change in the geometry of the system. Seismic design charts are presented to evaluate the stability of, and to design, flexible retaining walls embedded in dry cohesionless soils under seismic loading.     

International standard (ISO) on seismic actions for designing geotechnical works–An overview

The seismic performance of geotechnical works is significantly affected by ground displacement. In particular, soil–structure interaction and effects of liquefaction play major roles and pose difficult problems for engineers. An International Standard, ISO23469, is being developed for addressing these issues in a systematic manner within a consistent framework. The objective of this paper is to give an overview of this International Standard.In this International Standard, the seismic actions are determined through two stages. The first stage determines basic seismic action variables, including the earthquake ground motion at the site, the potential for earthquake-associated phenomena such as liquefaction and induced lateral ground displacement. These basic variables are used, in the second stage, for specifying the seismic actions for designing geotechnical works. In the second stage, the soil–structure interaction plays a major role. Types of analyses are classified based on a combination of static/dynamic analyses and the procedure for soil–structure interaction classified as follows:

– simplified: soil–structure interaction of a global system is modeled as an action on a substructure;

– detailed: soil–structure interaction of a global system is modeled as a coupled system.

钢桁架(ST)约束混凝土组合柱抗震性能研究

目前,组合柱在建筑结构中进行了广泛应用和研究,研究表明:截面形式对组合柱的抗震性能有很大影响。首先,对钢桁架(ST)约束混凝土组合柱进行了试验研究。并在此基础上,利用有限元软件ABAQUS建立了数值分析模型;其次,基于数值分析模型,分析了组合柱中各部件的应力应变状态,分别考察了轴压比、缀板排列方式、体积配箍率、角钢肢宽与肢厚等因素对柱抗震性能的影响;最后,给出了组合柱在不同抗震等级下轴压比限值的建议值,可为后续组合柱的研究提供参考。研究表明:随着轴压比的增大,组合柱的延性变差,承载力先增大后减小;合理的缀板排列方式可有效抑制角钢的局部屈曲;随着体积配箍率的增大,组合柱的承载力有一定提升,延性提高较为显著;随着角钢肢宽和肢厚的增加,组合柱的承载力和延性均有显著提升。     

Evaluation of the structural response under seismic actions using non‐linear static methods

The paper investigates the degree of accuracy achievable when some non‐linear static procedures based on a pushover analysis are used to evaluate the seismic performance. In order to assess the significance of different sources of errors, three types of structural systems are analysed: (i) single‐degree‐of‐freedom (SDOF) systems with different hysteretic behaviour; (ii) shear‐type multi‐degree‐of‐freedom (MDOF) systems with elastic–perfect plastic (EPP) shear force–interstorey drift relationships; (iii) a steel moment‐resisting frame with rigid joints and EPP moment–curvature relationship. In SDOF systems, the source of approximation comes only from the calibration of the demand spectrum, while in MDOF systems some further errors are introduced by the schematization with an equivalent SDOF system. The non‐linear static procedures are compared with rigorous time‐history analyses carried out by considering ten generated earthquake ground motions compatible with the Eurocode 8 elastic spectra. It was found that SDOF systems with longer periods satisfy the equal displacement approximation regardless of the hysteretic model, while hysteresis loops with smaller energy dissipated indicate lower response for shorter periods. This is the opposite of what predicted by the ATC‐40 capacity spectrum method, which underestimates and overestimates, respectively, the actual response of low‐ and high‐ductility systems. Conversely, the inelastic spectrum method proposed by Vidic, Fajfar and Fischinger leads to the most accurate results for all types of structural systems. The analyses carried out on EPP shear‐type frames point out a large concentration of the ductility demand on some storeys. However, such a concentration markedly reduces when some hardening is accounted for. Copyright © 2006 John Wiley & Sons, Ltd.     

地震作用下盾构隧道变形性能试验研究

地震作用下,盾构隧道的抗震变形性能限值是个重要指标。采用盾构区间隧道为原型,设计1/20的相似模型,考虑管片接头以及土体-结构相互作用,采用隧道结构加载试验系统,对盾构管片结构在不同的拼装方式和埋深下的变形行为进行了研究,测得了管片环的内力和位移。通过对6组试验结果进行分析对比,得出结论:埋深和拼装方式对盾构隧道结构变形有影响,对通缝结构的影响大于错缝结构;弹塑性分界点直径变形率限值,对通缝结构为0.56‰~1.00‰,对错缝结构为0.42‰~1.09‰;临界失稳点直径变形率限值,对通缝结构为16.87‰~21.44‰,对错缝结构为15.22‰~19.52‰。     

强震下水闸结构抗震性能分析

强震下的水闸结构抗震性能尚待深入研究,结合实际工程案例,运用UC-WCOMD有限元分析软件建立精细化的水闸计算模型,并分别采用Pushover法和时程分析法讨论水闸在强震作用下的抗震性能,结果表明:结合抗震设防目标,采用Pushover分析法评估水闸的抗侧能力,并采用弹塑性时程分析方法进行强震下的抗震性能校核,是值得推荐的研究方法。     

城市高架桥合理抗震体系选择与经济性对比

探讨了基于两水准设防的城市高架桥的合理抗震设防标准与相应的结构性能目标.选取两座典型的城市高架桥结构,包括一座正线桥和一座匝道桥,分别采用延性抗震体系和减、隔震体系进行结构抗震设计.对比了不同结构抗震体系所对应的结构在各水准地震作用下具体抗震性能表现,结果表明减、隔震体系具有更优的抗震性能.在此基础上,进一步从经济性的...     

Numerical investigation of seismic performance of high modulus columns under earthquake loading

Earthquake Engineering and Engineering Vibration - This paper presents the result of two-dimensional finite element modeling studies in order to investigate the seismic behavior of high modulus...     

Polynomial friction pendulum isolators (PFPIs) for seismic performance control of benchmark highway bridge

The seismic response of a benchmark highway bridge isolated with passive polynomial friction pendulum isolators (PFPIs) is investigated and subjected to six bidirectional ground motion records. The benchmark study is based on a lumped mass finite-element model of the 91/5 highway overcrossing located in Southern California. The PFPI system possesses two important parameters; one is horizontal flexibility and the other is energy absorbing capacity through friction. The evaluation criteria of the benchmark bridge are analyzed considering two parameters, time period of the isolator and coefficient of friction of the isolation surface. The results of the numerical study are compared with those obtained from the traditional friction pendulum system (FPS). Dual design performance of the PFPI system suppressed the displacement and acceleration response of the benchmark highway bridge. The dual design hysteresis loop of the PFPI system is the main advantage over the linear hysteresis loop of the FPS. The numerical result indicates that the seismic performance of the PFPI system is better than that of the traditional FPS isolated system. Further, it is observed that variations of the isolation time period and coefficient of friction of the FPS and PFPI systems have a significant effect on the peak responses of the benchmark highway bridge.     

Precast industrial buildings in Southern Europe: loss of support at frictional beam-to-column connections under seismic actions

This paper presents the evaluation of the loss-of-support conditions in frictional beam-to-column connections of industrial precast concrete buildings under seismic actions. This type of connection is widespread throughout Southern Europe in non-seismically designed industrial precast buildings. First, geometric properties of industrial precast buildings and of the frictional beam-to-column connections, together with reference values for the friction coefficient, are reviewed. Then, earthquake time histories taken from the European Strong-Motion sets and recordings of the two major shocks of the 2012 Emilia-Romagna events are presented and discussed showing the importance of the vertical component. Two dynamic models of increasing complexity are used to ascertain loss-of-support conditions under seismic action. The first model is an elastic one, representing a single frame of the industrial buildings. Results are obtained according to: (1) 2D analyses, disregarding the time correlation between the response peaks along the horizontal and vertical directions, (2) 2D analyses taking into account time correlation, and (3) 3D analyses to evaluate also directionality effects. The second model is a 2D non-linear planar frame developed within the OpenSees framework. Results show that simplified (linear) models are a good proxy to more refined (non-linear) ones. However, one must resort to non-linear models if differential displacements between beam and column are of interest. The non-linear numerical investigations show that friction coefficient, horizontal and vertical periods and damping, and column reinforcement ratio are the key variables in estimating the loss-of-support conditions.     

RC剪力墙结构小震与中震设计对比及其抗震性能研究

近年来,国内学者强调对于复杂和超限结构需进行中震性能设计,即在小震弹性设计后进行中震下的承载力复核及调整,然而中震设计能否提高结构整体抗震性能仍存在争议.为探究中震设计与小震设计方法的差异,本文依据现行规范,以设防烈度、结构高度和场地类别为变化参数,建立了48个典型RC剪力墙模型,并分别以"小震"、"高规中震"、"广东...     

强震下斜交桥地震反应与减隔震性能分析

针对斜交桥在破坏性地震中发生破坏和损伤的突出问题,采用铅芯橡胶支座(LRB)进行隔震和滞回耗能。基于OpenSees平台建立了不同斜度的传统非隔震和全桥采用LRB隔震的4跨斜交连续梁桥动力分析模型,沿2个水平方向输入远场地震动和具有向前方向性效应、滑冲效应以及无速度脉冲效应的近断层地震动,并进行非线性时程计算,研究桥墩和挡块的损伤状态、主梁旋转度、碰撞力与斜交桥斜度的关系以及LRB对斜交桥抗震性能的影响。结果表明:向前方向性效应和滑冲效应的脉冲型地震动作用下的斜交桥地震反应和损伤明显大于无速度脉冲近断层和远场地震动作用; 采用LRB隔震后,明显降低了固定墩的地震损伤,桥墩位移减震率可达到50%以上; LRB隔震桥主梁与挡块的间隙宜结合桥梁的地震风险和设计位移进行确定。