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1.
具有埋入基础的土-结构系统的非线性地震响应分析 总被引：3，自引：0，他引：3
本文使用7S-Ⅱ计算机程序,在两个不同大小的地震力作用下,对具有埋入基础的土-结构系统进行了地震响应分析。分析中不但考虑了地基土的材料非线性,而且考虑了接触界面的非线性。为了估计这些非线性性能对结构和土的响应值影响的大小,文中定义了非线性时间比,β_J和β_J。接触界面的动力性能在文中也得到了详细的讨论。在中等地震的作用下,界面上的滑移和剥离对其邻近区域的响应值就有了很大的影响。随着激震力的增大,结构物基础的侧面和地基土会完全剥离,使得系统的基频发生漂移,从而引起结构物顶端的线性和非线性结构内部反应谱之间在共振频率区段内有明显的差别。 相似文献
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土与结构动力相互作用(简称SSI)存在于大多数的建筑物,在普通结构设计中,并没有考虑SSI,这和缺少一种简单有效的计算方法有关.通过调整结构的自振周期,可以很好地考虑SSI,实际情况是,一般的计算方法都偏于保守,计算结果与实测结果的误差离散性比较大.土是非线性很强的材料,结构振动过大,土容易进入非线性状态,使得计算变得复杂.找出由于土的非线性导致结构自振周期的增大的规律,对于实际工程很有意义.本文通过对刚性基础与土槽中柔性地基上的钢框架模型进行激振,分别测得上部结构在不同刚度以及不同激振加速度时的结构自振周期.并根据实验结果,拟合结构自振周期与激振加速度、上部结构与地基相对刚度比的关系.通过拟合后的公式对两个文献中的试验模型的自振周期进行计算,结果显示,本文拟合的公式能很好的考虑土的非线性,有效地减少简化模型计算与实测的差别. 相似文献
3.
高层钢框架-支撑结构二阶非线性随机地震响应分析 总被引：1，自引：0，他引：1
针对常用的高层钢框架－支撑结构，考虑材料非线性和几何非线性，建立了框架部分、支撑部分的二阶动力分析模型。用等效线性方法对结构进行非线性随机地震响应分析，结合工程算例，论述不同场地土、不同层数、不同支撑情况下，二阶效应对结构地震响应统计量的影响。 相似文献
4.
《地震工程与工程振动》2016,(3)
目前在高耸混凝土烟囱结构抗震设计和抗震性能评估中,由于缺乏合适的计算模型,一般采用刚性地基假定而忽略土-结构相互作用效应,或者采用传统的集中参数模型而忽略土的非线性特性。针对此不足,本文选用240 m高的钢筋混凝土烟囱作为研究对象,采用OpenSees程序,基于非线性文克尔地基梁模型和基于柔度法的分布塑性梁柱单元,建立了土体-基础-上部结构共同工作的整体非线性有限元分析模型,详细介绍了非线性文克尔地基梁模型主要参数的确定方法;研究了地基土非线性对高耸烟囱结构地震反应的影响,给出了考虑土-结构相互作用效应后结构周期、上部结构的内力和变形分布的变化规律。分析结果表明:考虑土-结构相互作用后,结构的自振特性、内力及节点位移都发生了不同程度的改变;考虑土体非线性特性的土-结构相互作用模型,峰值截面弯矩、剪力及截面曲率延性系数与不考虑土-结构相互作用时的结果之比分别介于0.921~1.219、0.732~1.29和0.822~1.536;而不考虑土体非线性特性的土-结构相互作用模型,峰值截面弯矩、剪力及截面曲率延性系数与不考虑土-结构相互作用时的结果之比分别介于0.838~1.578、0.92~1.76和0.656~2.831。不考虑土体非线性特性的土-结构相互作用模型的峰值截面弯矩、剪力及截面曲率延性系数的取值总体上较大,高估了烟囱结构在地震荷载作用下的内力需求。 相似文献
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土-结构体系的分枝模态与约束模态混合二步法 总被引：1，自引：0，他引：1
为了在结构设计过程中考虑土-结构非线性相互作用的影响,在线性-非线性混合的约束模态法以及分枝模态法的基础上,提出了适用于土-结构非线性相互作用体系的分枝模态与约束模态的混合方法,该方法既可考虑土体和结构的非线性特性又便于考察土-结构相互作用对上部结构的影响。在分枝模态与约束模态混合方法的基础上,进一步提出了混合二步分析法,并将其应用到地基土-框架结构地震响应分析中,算例结果表明,混合二步分析法在实现上部结构和地基土分开计算的同时,还能够考虑结构与地基土的材料非线性特性,有利于采用专业设计软件仅通过对上部结构进行分析来考虑土-结构相互作用的影响,为实际工程计算考虑土-结构相互作用的影响提供了便利的条件。 相似文献
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目前结构的抗震分析主要是采用刚性地基假定,忽略了土-结构相互作用,而在实际情况中结构的地震破坏与刚性地基假定的预期结果并不相同。为了对比差异,本文以一6层混凝土框架结构为例,分别进行了Pushover分析和非线性时程分析。结果表明:当考虑土-结构相互作用时,结构的基底剪力减小,周期增大,顶点位移增大且结构的破坏主要集中在首层,柱端出现了塑性铰,更符合实际的震害情况。并将Pushover分析与非线性时程分析的结果进行对比,验证了Pushover分析的可靠性。 相似文献
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浅平基桥墩在承受强震作用时其基础与地基之间会发生提离,地基土会进入塑性状态。同时,当结构遭遇设防烈度地震或罕遇地震时,结构往往处于非线性状态,这都会导致桥梁的严重破坏。本文以兰州小西湖黄河大桥为工程背景,采用场地超越概率为10%人工地震波,研究了在弹塑性Winkler地基上同时考虑桥墩塑性时的结构地震反应。通过非线性时程反应分析得到:考虑地基和桥墩的非线性使得桥墩墩顶的位移增大,墩底弯矩减小,这对保护桥墩是有利的;同时得到,小西湖黄河大桥当遭遇罕遇地震(大震)时桥墩已进入屈服,但其屈服曲率不到破坏曲率的1/2,该桥能够满足“小震不坏、中震可修、大震不倒”的设计目标。 相似文献
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多层框架结构弹性和弹塑性动力响应比较分析 总被引：2，自引：0，他引：2
结构在静荷载作用下,考虑材料塑性变形所得到的结构某点的位移响应大于不考虑塑性变形(即认为结构为完全弹性)所得到的位移响应。通过基于LSDYNA程序的计算分析发现,相同的结论并不适用于结构在动力荷载作用下的响应。进入弹塑性阶段后,可以认为结构的动力响应受两个因素影响:(1)刚度降低引起结构振动特性的改变;(2)塑性变形引起的位移增长。这两个因素的影响程度决定了结构在动力荷载作用下由弹性阶段过渡到塑性阶段后的各种响应的改变。 相似文献
10.
现有的基础隔震理论大多沿用刚性地基假定,忽略土-结构相互作用。由于地基土的柔性和无限性,土-结构相互作用会对基础隔震体系的隔震机理产生直接影响。因此,考虑土-结构动力相互作用对隔震结构体系隔震效果影响的研究十分必要。本文把地基土视为匀质、各向同性的黏弹性半空间,用等效双线型恢复力模型模拟铅芯橡胶支座的非线性,建立基础隔震体系单质点力学模型和运动方程。通过ANSYS软件进行数值模拟,用D-P材料考虑土的材料非线性,用接触单元模拟土与结构的接触非线性,分析土-结构动力相互作用对铅芯橡胶支座隔震效果的影响。 相似文献
11.
大跨度悬索拱桥极限承载能力研究 总被引：4，自引：0，他引：4
首先介绍了悬索拱桥的特点和极限承载能力计算方法,然后基于有限元理论,考虑施工阶段的位移和应力的叠加效应、几何非线性、材料非线性以及拱肋等构件的初始缺陷的影响,对某铁路悬索拱桥的极限承载力进行了分析,计算得出结构在施工阶段弹性稳定安全系数为5.2~5.8,非弹性稳定安全系数为2.0~2.6;在运营阶段其弹性稳定安全系数为4.9~5.1,非弹性稳定安全系数为1.7~1.9,表明该桥弹性稳定性和非弹性稳定性都是足够的。其计算方法和结果对于悬索拱桥的计算及设计理论有一定的借鉴价值。 相似文献
12.
Nonlinear finite element analysis of three‐dimensional free and harmonically forced vibrations of stranded conductor cables 
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下载免费PDF全文 The 3D finite deformation beam model originally developed by Simo is appropriately modified to derive a finite element formulation for the static and dynamic analysis of flexible electrical conductors. In contrast to what is currently carried out in the literature, a linear viscoelastic constitutive equation and an additional mass proportional damping mechanism are introduced to account for energy dissipation in a physically consistent way. The model is used for simulation of free and forced vibration tests performed on an actual electrical conductor. Energy balance calculations illustrate the reliability of the computations. The experiments reveal amplitude dependence of both stiffness and damping, pointing out the presence of material nonlinearity in the cable. The development of numerical models that can account for the amplitude dependence of bending stiffness and energy dissipation capacity is subject of current computational and experimental work. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
13.
B. K. Maheshwari K. Z. Truman M. H. El Naggar P. L. Gould 《Soil Dynamics and Earthquake Engineering》2004,24(4):343-356
A three-dimensional method of analysis is presented for the seismic response of structures constructed on pile foundations. An analysis is formulated in the time domain and the effects of material nonlinearity of soil on the seismic response are investigated. A subsystem model consisting of a structure subsystem and a pile-foundation subsystem is used. Seismic response of the system is found using a successive-coupling incremental solution scheme. Both subsystems are assumed to be coupled at each time step. Material nonlinearity is accounted for by incorporating an advanced plasticity-based soil model, HiSS, in the finite element formulation. Both single piles and pile groups are considered and the effects of kinematic and inertial interaction on seismic response are investigated while considering harmonic and transient excitations. It is seen that nonlinearity significantly affects seismic response of pile foundations as well as that of structures. Effects of nonlinearity on response are dependent on the frequency of excitation with nonlinearity causing an increase in response at low frequencies of excitation. 相似文献
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以实际港珠澳大跨度连续梁隔震桥为研究对象,采用纤维塑性铰单元模拟钢筋混凝土桥墩的非线性状态,建立其三维全桥有限元模型,对隔震及非隔震桥梁进行时程分析,采用桥墩曲率延性比和支座极限容许位移作为桥梁损伤破坏指标,定量评价隔震及非隔震桥梁在罕遇和极罕遇地震作用下的抗震性能,探讨隔震桥梁和非隔震桥梁的破坏模式;并研究材料非线性对桥梁结构地震响应的影响。研究结果表明：是否考虑材料非线性,对非隔震桥梁结构地震响应影响较大,对隔震桥梁影响较小;强震下隔震桥梁抗震性能明显高于非隔震桥梁,且破坏模式也不同于非隔震桥梁;隔震桥梁很好地保护桥墩构件,桥墩未发生任何损伤,而非隔震桥梁其桥墩在极罕遇地震作用时进入了严重破坏状态,且桥墩构件先于盆式支座发生损伤破坏。 相似文献
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Shantanu Joshi Amit Prashant Arghya Deb Sudhir K. Jain 《Soil Dynamics and Earthquake Engineering》2011
Presently available simplified analytical methods and semi-empirical methods for the analysis of buried pipelines subjected to fault motion are suitable only for the strike-slip and the normal-slip type fault motions, and cannot be used for the reverse fault crossing case. A simple finite element model, which uses beam elements for the pipeline and discrete nonlinear springs for the soil, has been proposed to analyse buried pipeline subjected to reverse fault motion. The material nonlinearities associated with pipe-material and soil, and geometric nonlinearity associated with large deformations were incorporated in the analysis. Complex reverse fault motion was simulated using suitable constraints between pipe-nodes and ground ends of the soil spring. Results of the parametric study suggest that the pipeline's capacity to accommodate reverse fault offset can be increased significantly by choosing a near-parallel orientation in plan with respect to the fault line. Further improvement in the response of the pipeline is possible by adopting loose backfill, smooth and hard surface coating, and shallow burial depth in the fault crossing region. For normal or near normal orientations, pipeline is expected to fail due to beam buckling at very small fault offsets. 相似文献
16.
A new modeling for the seismic response assessment of free-standing, rigid or flexible, pure rocking systems is presented. The proposed modeling is based on equivalent single degree-of-freedom (SDOF) oscillators that can be implemented with common engineering software or user-made structural analysis codes. The SDOF models adopted use beam elements that are connected to a nonlinear rotational spring with negative stiffness that describes the self-centering capacity of the rocking member. The loss of energy at impact is treated with an “event-based” approach consistent with Housner's theory. Different variations pertinent to rigid blocks are first presented, and then the concept is extended to the flexible case. The implementation of the method requires some minor programming skills, while thanks to the versatility of the finite element method, it is capable to handle a variety of rocking problems. This is demonstrated with two applications: (a) a vertically restrained block equipped with an elastic tendon and (b) a rigid block coupled with an elastic SDOF oscillator. The accuracy and the efficiency of the proposed modeling is demonstrated using simple wavelets and historical ground motion records. 相似文献
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Murat Emre Kartal Alemdar Bayraktar Hasan Basri Başağa 《Soil Dynamics and Earthquake Engineering》2010
In this study, failure probability of the concrete slab on concrete-faced rockfill (CFR) dams with welded and friction contact is investigated under earthquake effects by reliability analysis. For this purpose, Torul CFR dam is selected as an example and numerical solutions are performed by considering combination of reliability analysis–finite element method. 1992 Erzincan earthquake acceleration record is used in the finite element analysis considering deconvolved-base rock input model. In this model, the ground motion to be applied to the foundation base rock is obtained by deconvolution of the free-field surface record. In the materially nonlinear analysis, Drucker–Prager model is used for concrete slab and multi-linear kinematic hardening model is utilized for rockfill. Geometrically nonlinearity is also taken into account. Viscous boundary conditions are defined in the finite element model for both foundation soil and reservoir water. The hydrodynamic pressure of the reservoir water is considered using 2D fluid finite elements based on the Lagrangian approach. Both welded contact and friction contact based on the Coulomb’s friction law are defined in the structural connections. Improved Rackwitz–Fiessler method is used with response surface method in the reliability analysis. The tensile and compression strengths of the concrete slab are utilized in the implicit limit state functions considering various thicknesses. The probability of failure of the most critical points in the concrete slab is obtained. According to this study, the probabilities of failure obtained from the CFR dam including friction contact are lower. When the welded contact is considered in joints, the probability of failure of the concrete slab is 1 due to tensile stress limit state and compression stress limit state only if concrete slab is linear. The most critical probability of failure of the concrete slab appears in the case that the concrete slab is linear and rockfill is materially nonlinear. The probability of failure of the concrete slab decreases if the nonlinearity of the concrete is considered. Also, hydrodynamic pressure decreases the reliability of the concrete slab. 相似文献
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A study on the seismic response of massive flexible strip-foundations embedded in layered soils and subjected to seismic excitation is presented. Emphasis is placed on the investigation of the system response with the aid of a boundary element–finite element formulation proper for the treatment of such soil–structure interaction problems. In the formulation, the boundary element method (BEM) is employed to overcome the difficulties that arise from modeling the infinite soil domain, and the finite element method (FEM) is applied to model the embedded massive flexible strip-foundation. The numerical solution for the soil–foundation system is obtained by coupling the FEM with the BEM through compatibility and equilibrium conditions at the soil–foundation and soil layer interfaces. A parametric study is conducted to investigate the effects of foundation stiffness and embedment on the seismic response. 相似文献
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In order to estimate the distribution, as well as the magnitude, of dynamic material pressures on ground-supported silos a simplified seismic analysis procedure was utilized. The seismic analysis of silos can be complex, as the evaluation of several parameters must be taken into consideration, including the properties of bulk materials used and how the bulk materials and silo wall are joined together. It is therefore useful to develop an analytical approximation in order to better assess results. In addition to a simplified model for the seismic analysis of a silo–bulk material system being utilized, a three-dimensional finite element model was also incorporated. Using the finite element method, a more realistic representation of the structure is possible. Moreover, the finite element method also takes into consideration contact problems between the bulk material and the silo wall, which results in easier analyses. Both a squat and a slender silo were selected for this study. The results obtained in the study of selected examples were compared with those findings obtained via EN1998-4. Modified Veletsos and Younan approximations, which are commonly used for the analysis of grain silos, were also used. Results and analysis concluded that the proposed analytical model provided, overall, a good outcome, especially in regards to the analysis of dynamic material pressure. It should be noted that using the analytical method as proposed in Eurocode, the dynamic material pressure for squat silos can be underestimated, but the results for slender silos are stronger. 相似文献