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1.
Offshore structures, such as composite breakwaters, are generally vulnerable to strong seismic wave propagating through loose or medium-dense seabed foundation. However, the seismically induced failure process of offshore structures is not well understood. In this study, seismic dynamics of a composite breakwater on liquefiable seabed foundation is investigated using a fully coupled numerical model FSSI-CAS 2D. The computation results show that the numerical model is capable of capturing a variety of nonlinear interaction phenomena between the composite breakwater and its seabed foundation. The numerical investigation demonstrates a three-stage failure process of the breakwater under seismic loading. In this process, the far-field seabed can become fully liquefied first, inducing excessive settlement of the structure, followed by significant lateral movement and tilting of the structure when the near-field soil progressively liquefies. The study demonstrates great promise of using advanced numerical analysis in geotechnical earthquake design of offshore structures. 相似文献
2.
Many surviving ancient monuments are freestanding stone masonry structures, which appear to be vulnerable to horizontal dynamic loads such as earthquakes. However, such structures have stood for thousands of years despite numerous historic earthquakes. This study proposes a scaled-down dynamic centrifuge modelling test to study how these masonry structures resist seismic loading. The test is proposed for seismic risk assessments to evaluate risk of damage from a future seismic event. The seismic behaviour of a 3-storey, freestanding stone block structure has been modelled and tested within a centrifuge. Models were made at 3 different scales and dynamic tests were conducted using different centrifugal acceleration fields so that the behaviours could be transformed to an equivalent full-scale prototype and compared. Data from 2 earthquakes and a sweeping signal were used to simulate the effects of earthquake ground motion within the centrifuge. The acceleration and frequency responses at each storey height of the model were recorded in different centrifugal acceleration fields. Similar behaviours appeared when the results of the small-scale models were transformed to a full-size prototype scale. This confirms that the seismic behaviour of stone masonry structures can be predicted using scaled-down models. 相似文献
3.
Verifying adequacy of the seismic deformation method by using real examples of earthquake damage 总被引：1，自引：0，他引：1
In a seismic design, the dynamic loads are generally dependent on the inertial interaction caused by earthquake. But for the foundations embedded in soil, the dynamic loads are influenced by both the inertial and kinematic interactions among superstructure, foundation and soil. Especially, when a foundation is embedded in soft surface ground, the effects due to the kinematic interaction increase and should be considered in seismic design. For this reason, a method called seismic deformation method (SDM), which is suitable for an intensive earthquake motion (level 2 earthquake motion), has been stipulated recently in a new design code called Seismic Design Code for railway structures (the Railway Code, drawn up by Railway Technical Research Institute, Japan, 1999) [Railway Technical Research Institute. Seismic Design Code for railway structures. Tokyo: Maruzen; 1999]. In order to grasp the suitability of the SDM to actual structures, pile foundations, which experienced the Hyogoken-Nanbu earthquake, were taken as the objects for investigations. Comparison studies between the SDM analysis and reconnaissance were conducted. As a result, the adequacy of the SDM to actual foundations was confirmed to prove good agreement between the two results from the viewpoint of engineering practice.In addition, determination of indices for seismic-performance evaluation and speculation of damage mechanism of the foundations are also discussed in this paper. 相似文献
4.
使用ANSYS软件对一大直径预应力混凝土圆形储煤筒仓结构建立了有限元模型,以储料质量沿高度分布不变为原则,采用施加质量单元的方法模拟储料的分布,通过对预应力混凝土筒仓进行地震作用下的受力、变形分析,研究了预应力混凝土筒仓结构的受力性能及整体抗震性能,同时分析了筒仓结构地震作用简化计算方法的可行性.分析结果表明,水平地震作用对筒仓预应力结构部分的环向力无显著影响,预应力筒仓结构具有良好的抗侧力性能;同时,在结构基本振型指数选取合理时,采用底部剪力法估算筒仓水平地震作用是可行的.所得结果可为同类筒仓结构的地震反应分析提供参考. 相似文献
5.
地震作用下贮料对筒仓产生的超压是造成筒仓损伤破坏的原因之一。为研究地震作用下贮料的地震响应特性及变化规律,对缩尺比例为1∶25的柱承式筒仓模型开展了单向和双向地震作用下的振动台试验,揭示了筒仓仓壁动态侧压力分布规律和超压系数,建立了仓壁动态侧压力的计算方法。研究表明:（1）地震时筒仓内贮料的运动滞后于仓壁,随着地震动持续滞后逐渐明显,且沿仓壁顶部至底部滞后不断减弱;（2）动态侧压力分布规律与测点布置位置、地震波的输入方式相关;（3）仓体顶部范围内超压系数试验值大于规范采用值,现行规范中采用的修正系数偏小;（4）仅依据单向地震激励,尚不足以真实反映地震作用下筒仓贮料的动力学特性,筒仓结构强度设计时不应忽略双向地震作用。研究成果可为柱承式筒仓的抗震设计提供参考和依据。 相似文献
6.
An improved pseudo-static method for seismic resistant design of underground structures 总被引：1，自引：0，他引：1
This paper describes a commonly used pseudo-static method in seismic resistant design of the cross section of underground structures. Based on dynamic theory and the vibration characteristics of underground structures, the sources of errors when using this method are analyzed. The traditional seismic motion loading approach is replaced by a method in which a one-dimensional soil layer response stress is differentiated and then converted into seismic live loads. To validate the improved method, a comparison of analytical results is conducted for internal forces under earthquake shaking of a typical shallow embedded box-shaped subway station structure using four methods： the response displacement method, finite element response acceleration method, the finite element dynamic analysis method and the improved pseudo-static calculation method. It is shown that the improved finite element pseudo-static method proposed in this paper provides an effective tool for the seismic design of underground structures. The evaluation yields results close to those obtained by the finite element dynamic analysis method, and shows that the improved finite element pseudo-static method provides a higher degree of precision. 相似文献
7.
The seismic response of one section of a 23 km strategic urban overpass to be built in the so‐called transition and hill zones in Mexico City is presented. The subsoil conditions at these zones typically consist on soft to stiff clay and medium to dense sand deposits, randomly interbedded by loose sand lenses, and underlain by rock formations that may outcrop in some areas. Several critical supports of this overpass are going to be instrumented with accelerometers, inclinometers and extensometers, tell tales and end pile cell pressures to assess their seismic performance during future earthquakes and to generate a database to calibrate soil–structure interaction numerical models. This paper presents the seismic performance evaluation of the critical supports located in one section of the overpass. Sets of finite elements models of the soil–foundation–structure systems were developed. Initially, the model was calibrated analyzing the seismic response that an instrumented bridge support exhibited during the June 15th, 1999 Tehuacan (Mw = 7) Earthquake. This bridge is located also within the surroundings of Mexico City, but in the lake zone, where highly compressible clays are found. The computed response was compared with the measured response in the free field, pile‐box foundation and bridge deck. Once the model prediction capabilities were established, the seismic response of the critical supports of the urban overpass was evaluated for the design earthquake in terms of transfer functions and displacement time histories. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
8.
The basic aspects of testing small-scale masonry building models on simple earthquake simulators are discussed. Since the scale effects represent a difficult problem to solve, the overall seismic behaviour of structural systems, and not the behaviour of structulal details, has been studied by testing the reduced-sized models on a simple earthquake simulator. Accurate results regarding the dynamic behaviour and failure mechanism of the tested structures have been obtained by means of testing the relatively simple, adequately designed small-scale masonry building models. A simple earthquake simulator capable of simulating the uni-directional earthquake ground motion has been developed to study the seismic behaviour of masonry building models. Although a multipurpose programmable actuator was used to drive the shaking table, the comparison of the dynamic characteristics of the generated shaking-table motion and the earthquake acceleration records used for the simulation of seismic loads showed an acceptable degree of correlation between the input and output seismic motion. 相似文献
9.
Masoud Moghaddasi Misko Cubrinovski J. Geoff Chase Stefano Pampanin Athol Carr 《地震工程与结构动力学》2011,40(2):135-154
Complex seismic behaviour of soil–foundation–structure (SFS) systems together with uncertainties in system parameters and variability in earthquake ground motions result in a significant debate over the effects of soil–foundation–structure interaction (SFSI) on structural response. The aim of this study is to evaluate the influence of foundation flexibility on the structural seismic response by considering the variability in the system and uncertainties in the ground motion characteristics through comprehensive numerical simulations. An established rheological soil‐shallow foundation–structure model with equivalent linear soil behaviour and nonlinear behaviour of the superstructure has been used. A large number of models incorporating wide range of soil, foundation and structural parameters were generated using a robust Monte‐Carlo simulation. In total, 4.08 million time‐history analyses were performed over the adopted models using an ensemble of 40 earthquake ground motions as seismic input. The results of the analyses are used to rigorously quantify the effects of foundation flexibility on the structural distortion and total displacement of the superstructure through comparisons between the responses of SFS models and corresponding fixed‐base (FB) models. The effects of predominant period of the FB system, linear vs nonlinear modelling of the superstructure, type of nonlinear model used and key system parameters are quantified in terms of different probability levels for SFSI effects to cause an increase in the structural response and the level of amplification of the response in such cases. The results clearly illustrate the risk of underestimating the structural response associated with simplified approaches in which SFSI and nonlinear effects are ignored. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
10.
Khoshnoudian Faramarz Shahreza MehdiPaytam Farzane 《Soil Dynamics and Earthquake Engineering》2012,34(1):25-36
The earthquake responses of structures are usually analyzed under the assumption that the foundation is firmly bonded to the soil (fixed at their base). Such analyses often predict a base overturning moment that exceeds the available overturning resistance due to gravity loads, which implies that a portion of the foundation mat or some of the individual column footings, as the case may be, would intermittently uplift during the earthquake. In addition, p-delta phenomena are another valuable parameter that influence the response of structure with foundation uplift. Therefore it is a vital subject to investigate the influence of uplift on earthquake response of structures with including the p-delta effects. In the current paper, the investigation has been performed using finite element method with considering nonlinear material behavior. The computer program used already incorporates foundation uplift in a more realistic approach than structural models available in literature. The response of structures was compared in four cases: 1—with foundation uplift, 2—without foundation uplift, 3—with including the p-delta effects and 4—without including the p-delta effects. Some additional parametric studies have been conducted such as slender of structure, elastic modulus of soil and bi-directional input ground motion. These studies show the importance of uplift foundation on the seismic behavior of structures and the beneficial effects of foundation uplift in computing the earthquake response of structures are demonstrated. In addition, p-delta effects are the main reason to resonate the differences between the four cases. 相似文献
11.
In this investigation, the seismic torsional response of a multi-storey concentrically braced frame (CBF) plan irregular structure is evaluated numerically and experimentally through a series of hybrid tests. CBF structures have become popular in seismic design because they are one of the most efficient types of steel structures to resist earthquake loading. However, their response under plan irregular conditions has received little focus mostly in part due to their complex behaviour under seismic loading conditions. The majority of research on the seismic response of plan irregular structures is based purely on numerical investigations. This paper provides much needed experimental investigation of the seismic response of a CBF plan irregular structure with the aim of characterising the response of this class of structure. The effectiveness of the Eurocode 8 torsional effects provision as a method of designing for low levels of mass eccentricity is evaluated. Results indicate that some of the observations made by purely numerical models are valid in that; torsionally stiff structures perform well and the stiff side of the structure is subjected to a greater ductility demand compared to the flexible side of the structure. The Eurocode 8 torsional effects provision is shown to be adequate in terms of ductility and interstorey drift however the structure performs poorly in terms of floor rotation. Importantly, stiffness eccentricity occurs when the provision is applied to the structure when no mass eccentricity exists and results in a significant increase in floor rotations. 相似文献
12.
许多学者对软土在动力作用下的变形特性进行了大量的研究,并提出了相应的经验公式,但其经验公式参数较多且试验复杂,不易被一般工程技术人员掌握运用。本文采用天津滨海地区软土为研究对象,进行钻探取样、波速测试、室内静力学和动三轴试验,获取该地区软土的静、动力学参数,并利用相对简单的模型对残余应变和软化指数随振次的变化规律采用最小二乘法进行拟合,取得很好的效果。成果表明,利用简单的模型对软土的动力特性进行区域性研究是可行的。该成果可为今后软土动力特性和软土震陷计算方法研究提供参考和基础性资料。 相似文献
13.
Fragility curves constitute the cornerstone in seismic risk evaluations and performance-based earthquake engineering. They describe the probability of a structure to experience a certain damage level for a given earthquake intensity measure, providing a relationship between seismic hazard and vulnerability. In this paper a numerical approach is applied to derive fragility curves for tunnel shafts built in clays, a component that is found in several critical infrastructure such as urban metro networks, airport facilities or water and waste water projects. The seismic response of a representative tunnel shaft is assessed using tridimensional finite difference non-linear analyses carried out with the program FLAC3D, under increasing levels of seismic intensity. A hysteretic model is used to simulate the soil non-linear behavior during the seismic event. The effect of soil conditions and ground motion characteristics on the soil-structure system response is accounted for in the analyses. The damage is defined based on the exceedance of the concrete wall shaft capacity due to the developed seismic forces. The fragility curves are estimated in terms of peak ground acceleration at a rock or stiff soil outcrop, based on the evolution of damage with increasing earthquake intensity. The proposed fragility models allows the characterization of the seismic risk of a representative tunnel shaft typology and soil conditions considering the associated uncertainties, and partially fill the gap of data required in performing a risk analysis assessment of tunnels shafts. 相似文献
14.
隧道可液化土层围岩对地震动作用非常敏感,可液化土层动孔压的产生和发展使得地下结构受到上浮作用,从而影响地下结构的稳定性.通过对可液化土层中隧道动力响应计算,研究了不同静应力场隧道围岩动孔压场分布、围岩液化区域分布以及衬砌结构仰拱底与拱顶的动孔压差变化.研究结果表明,不同静应力场对围岩可液化土的动孔压分布、液化区域分布及... 相似文献
15.
Christopher Bode Reinhold Hirschauer Stavros A. Savidis 《Soil Dynamics and Earthquake Engineering》2002,22(4)
A time-domain formulation is proposed for the transient response analysis of general, three-dimensional structures resting on a homogeneous, elastic halfspace subjected to either external loads or seismic motions. The formulation consists of two parts: (a) the time domain formulation of the soil behaviour and (b) the coupling of the corresponding soil algorithms to the Finite Element Code ANSYS. As far as the structure is concerned, this coupling opens the way for the analysis of non-linear soil–structure interaction. The approach is based on halfspace Green's functions for displacements elicited by Heaviside time-dependent surface point loads. Hence, the spatial discretisation can be confined to the contact area between the foundation and the soil, i.e. no auxiliary grid beyond the foundation as for conventional boundary element formulations is required. The method is applied to analyse the dynamic response of a railway track due to a moving wheel set by demonstrating the influence of ‘through-the-soil coupling’. 相似文献
16.
通过砂土的一系列动三轴实验,研究不规则地震荷载作用下与定次数等幅荷载作用下土体变形间的关系,给出砂土相对密实度对二者间关系的影响规律。结果表明:真实地震荷载下土的变形发展与等幅正弦荷载明显不同,应变发展时程的形态主要受地震动的形态控制;应变比C与砂土相对密度间关系具有规律性,随相对密度增大而降低,若采用以20周作为标准作用次数、0.65倍地震波峰值为等幅荷载代替不规则的地震荷载,修正真实地震应力下的残余变形,其应变比C随砂土密实度的增大而减小。同时,冲击型荷载的应变比C`要远大于振动型荷载。 相似文献
17.
The purpose of this study is the evaluation of dynamic behavior induced by seismic activity on a silo system, containing bulk material, with a soil foundation. The interaction effects between the silo and bulk material, as well as the effects produced between the foundation of the silo and the soil, were taken into account. Proposed simplified approximation, as well as the finite model, were used for analysis. The results, from the presented approximation, were compared with a more rigorous obtainment method. Initially, the produced simplified approximation, with elastic material assumption for the grain, could determine the pressures on the dynamic material along with displacements along the height of the silo wall and base shear force, etc., with remarkable precision. Some comparisons, via a change of soil and/or foundation conditions, were also made regarding the seismic pressure of the dynamic material pressure, displacement and base shear forces for both squat and slender silos. Comparing the analytical predictions to results from the numerical simulations produced good results. It can be concluded that the model can be used effectively to perform a broad suite of parametric studies, not only at the design stage but also as a reliable tool for predicting system behavior under the limit state of the system. The results and comprehensive analysis show that displacement effects and base shear forces generally decreased when soil was softer; however, soil structure interaction (SSI) did not have any considerable effects on squat silos and therefore need not be taken into practice. 相似文献
18.
在隧道的施工和运营中,隧道衬砌不可避免会产生裂纹。裂纹和地震荷载的相互作用将加剧隧道的破坏,因此研究带裂纹隧道衬砌地震荷载作用下的破坏具有重要的意义。为了证明本文二维有限元数值模拟计算结果的正确性,首先用相互作用积分的方法计算动载作用下的静态裂纹,并与解析解进行比对,发现二者的吻合性很好。计算结果表明相互作用积分法可以用来精确地计算动载作用下带裂纹结构的动应力强度因子。用这种经过验证的方法来计算带裂纹重载铁路隧道衬砌的动应力强度因子和动承载力安全系数,可以看出在地震荷载作用下,I型裂纹的动应力强度因子在隧道结构的安全中起控制作用。当裂纹的长度大于某特定值时,隧道处于很危险的状态。 相似文献
19.
As high‐rise buildings are built taller and more slender, their dynamic behavior becomes an increasingly critical design consideration. Wind‐induced vibrations cause an increase in the lateral wind design loads, but more importantly, they can be perceived by building occupants, creating levels of discomfort ranging from minor annoyance to severe motion sickness. The current techniques to address wind vibration perception include stiffening the lateral load‐resisting system, adding mass to the building, reducing the number of stories, or incorporating a vibration absorber at the top of the building; each solution has significant economic consequences for builders. Significant distributed damage is also expected in tall buildings under severe seismic loading, as a result of the ductile seismic design philosophy that is widely used for such structures. In this paper, the viscoelastic coupling damper (VCD) that was developed at the University of Toronto to increase the level of inherent damping of tall coupled shear wall buildings to control wind‐induced and earthquake‐induced dynamic vibrations is introduced. Damping is provided by incorporating VCDs in lieu of coupling beams in common structural configurations and therefore does not occupy any valuable architectural space, while mitigating building tenant vibration perception problems and reducing both the wind and earthquake responses of the structure. This paper provides an overview of this newly proposed system, its development, and its performance benefits as well as the overall seismic and wind design philosophy that it encompasses. Two tall building case studies incorporating VCDs are presented to demonstrate how the system results in more efficient designs. In the examples that are presented, the focus is on the wind and moderate earthquake responses that often govern the design of such tall slender structures while reference is made to other studies where the response of the system under severe seismic loading conditions is examined in more detail and where results from tests conducted on the viscoelastic material and the VCDs in full‐scale are presented. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
20.
Though rocking shallow foundations could be designed to possess many desirable characteristics such as energy dissipation, isolation, and self-centering, current seismic design codes often avoid nonlinear behavior of soil and energy dissipation beneath foundations. This paper compares the effectiveness of energy dissipation in foundation soil (during rocking) with the effectiveness of structural energy dissipation devices during seismic loading. Numerical simulations were carried out to systematically study the seismic energy dissipation in structural elements and passive controlled energy dissipation devices inserted into the structure. The numerical model was validated using shaking table experimental results on model frame structures with and without energy dissipation devices. The energy dissipation in the structure, drift ratio, and the force and displacement demands on the structure are compared with energy dissipation characteristics of rocking shallow foundations as observed in centrifuge experiments, where shallow foundations were allowed to rock on dry sandy soil stratum during dynamic loading. For the structures with energy dissipating devices, about 70–90% of the seismic input energy is dissipated by energy dissipating devices, while foundation rocking dissipates about 30–90% of the total seismic input energy in foundation soil (depending on the static factor of safety). Results indicate that, if properly designed (with reliable capacity and tolerable settlements), adverse effects of foundation rocking can be minimized, while taking advantage of the favorable features of foundation rocking and hence they can be used as efficient and economical seismic energy dissipation mechanisms in buildings and bridges. 相似文献