Evaluation of the seismic behavior of reinforced concrete structures with flat slab-column gravity frame and shear walls through nonlinear analysis methods

This paper presents an investigation of the seismic behavior of reinforced concrete(RC)structures in which shear walls are the main lateral load-resisting elements and the participation of flat slab floor systems is not considered in the seismic design procedure.In this regard,the behavior of six prototype structures(with different heights and plan layouts)is investigated through nonlinear static and time history analyses,implemented in the OpenSees platform.The results of the analyses are presented in terms of the behavior of the slab-column connections and their mode of failure at different loading stages.Moreover,the global response of the buildings is discussed in terms of some parameters,such as lateral overstrength due to the gravity flat slab-column frames.According to the nonlinear static analyses,in structures in which the slab-column connections were designed only for gravity loads,the slab-column connections exhibited a punching mode of failure even in the early stages of loading.However,the punching failure was eliminated in structures in which a minimum transverse reinforcement recommended in ACI 318(2019)was provided in the slabs at joint regions.Furthermore,despite neglecting the contribution of gravity flat slab-column frames in the lateral load resistance of the structures,a relatively significant overstrength was imposed on the structures by the gravity frames.

Adaptive Neural Network Dynamic Surface Control for Perturbed Nonlinear Time-delay Systems

This paper proposes an adaptive neural network control method for a class of perturbed strict-feedback nonlinear systems with unknown time delays. Radial basis function neural networks are used to approximate unknown intermediate control signals. By constructing appropriate Lyapunov-Krasovskii functionals, the unknown time delay terms have been compensated. Dynamic surface control technique is used to overcome the problem of ＂explosion of complexity＂ in backstepping design procedure. In addition, the semiglobal uniform ultimate boundedness of all the signals in the closed-loop system is proved. A main advantage of the proposed controller is that both problems of ＂curse of dimensionality＂ and ＂explosion of complexity＂ are avoided simultaneously. Finally, simulation results are presented to demonstrate the effectiveness of the approach.

A study on the seismic behavior of a retrofitted building based on nonlinear static and dynamic analyses

This study describes the seismic performance of an existing five storey reinforced concrete building which represents the typical properties of low-rise non-ductile buildings in Turkey. The effectiveness of shear walls and the steel bracings in retrofitting the building was examined through nonlinear static and dynamic analyses. By using the nonlinear static analysis, retrofitted buildings seismic performances under lateral seismic load were compared with each other. Moreover, the performance points and response levels of the existing and retrofitting cases were determined by way of the capacity-spectrum method described in ATC-40 (1996). For the nonlinear dynamic analysis the records were selected to represent wide ranges of duration and frequency content. Considering the change in the stiffness and the energy dissipation capacities, the performance of the existing and retrofitted buildings were evaluated in terms of story drifts and damage states. It was found that each earthquake record exhibited its own peculiarities, dictated by frequency content, duration, sequence of peaks and their amplitude. The seismic performance of retrofitted buildings resulted in lower displacements and higher energy dissipation capacity depending mainly on the properties of the ground motions and the retrofitting strategies. Moreover, severe structural damage (irreparable or collapse) was observed for the existing building. However, buildings with retrofit alternatives exhibited lower damage levels changing from no damage to irreparable damage states.

IDENTIFICATION OF NONLINEAR DYNAMIC SYSTEMS:TIME-FREQUENCY FILTERING AND SKELETON CURVES

The nonlinear behavior varying with the instantaneous response was analyzed through the joint time-frequency analysis method for a class of S. D. O. F nonlinear system. A masking operator an definite regions is defined and two theorems are presented. Based on these, the nonlinear system is modeled with a special time-varying linear one, called the generalized skeleton linear system (GSLS). The frequency skeleton curve and the damping skeleton curve are defined to describe the main feature of the non-linearity as well. Moreover, an identification method is proposed through the skeleton curves and the time-frequency filtering technique.

Application of strength reduction method to dynamic anti-sliding stability analysis of high gravity dam with complex dam foundation

Considering that there are some limitations in analyzing the anti-sliding seismic stability of dam-foundation systems with the traditional pseudo-static method and response spectrum method, the dynamic strength reduction method was used to study the deep anti-sliding stability of a high gravity dam with a complex dam foundation in response to strong earthquake-induced ground action. Based on static anti-sliding stability analysis of the dam foundation undertaken by decreasing the shear strength parameters of the rock mass in equal proportion, the seismic time history analysis was carried out. The proposed instability criterion for the dynamic strength reduction method was that the peak values of dynamic displacements and plastic strain energy change suddenly with the increase of the strength reduction factor. The elasto-plastic behavior of the dam foundation was idealized using the Drucker-Prager yield criterion based on the associated flow rule assumption. The result of elasto-plastic time history analysis of an overflow dam monolith based on the dynamic strength reduction method was compared with that of the dynamic linear elastic analysis, and the reliability of elasto-plastic time history analysis was confirmed. The results also show that the safety factors of the dam-foundation system in the static and dynamic cases are 3.25 and 3.0, respectively, and that the F2 fault has a significant influence on the anti-sliding stability of the high gravity dam. It is also concluded that the proposed instability criterion for the dynamic strength reduction method is feasible.

On the Dynamic Behavior of Town Gas Pipelines

Pipelines have been acknowledged as the most reliable, economic and efficient means for the transportation of gas and other commercial fluids such as oil and water. The designation of pipeline system as “lifelines” signifies that their operation is essential in maintaining the public safety and well being. A pipeline transmission system is a linear system which traverses a large geographical area, and soil conditions thus, is susceptible to a wide variety of hazards. This pa-per is concerned with the dynamic behavior of buried town gas pipelines. A computer model with a finite number of nodes is created to simulate the behavior of the real gas pipeline. The dynamic susceptibility method is applied for twenty mode shapes of this model, which utilizes the stress per velocity method and is an incisive analytical tool for screening the vibration modes of the system. It can be readily identified, which modes, if excited, could potentially cause large dynamic stresses. This paper discusses also two of the piping dynamic analyses, namely the effect of the response spectrum of an earthquake and the time history analysis of a truck crosses the pipeline.

Earthquake Analysis for the System of RC Building with a Steel Tower

A steel tower topping an RC building comprises a non-proportional damping structural sys- tem with different damping ratios. To compare the results from the non-proportional damping model and the equivalent damping model.the structural system was calculated with the two damping mod- els during earthquake respectively, using earthquake time history analysis computer program devel- oped by the authors. Differences in the calculated results of inner forces and displacements using the two damping models were observed. It is found that if the equivalent damping model is used in design, the consequence will be unsafe for the steel tower and too safe for the RC building at the same time.

Study of Nonlinear Seismic Response and TMD Primary Control of the Cable-Stayed Bridge Section of the Third Macao-Taipa Bridge

The practical design of the cable-stayed bridge of the 3rd Macao-Taipa bridge is investigated by the finite element analysis program ANSYS, and 3-D elements BEAM188 and BEAM4 are adopted to create a dynamic calculation model. In order to analyze the material nonlinear seismic response of the cable-stayed bridge, the nonlinear behaviors of the ductile plastic hinges of the bridge towers are taken into account by employing the nonlinear rotational spring element COMBIN40. To simulate a major earthquake, three earthquake records were chosen using a wave-choosing program and input into the bridge structure along longitudinal and transversal directions. Comparisons of the linear and nonlinear seismic responses of the cable-stayed bridge are performed. In addition, a study of TMD primary control is carried out using element MASS21 and element COMBIN14, and it is indicated that the effects of mitigation monitoring are evident.

Simplified Full Dynamic Analysis of a Railway Tunnel in Ethiopia

This paper presents an effective means of analyzing the safety of a tunnel under dynamic loading in areas with seismic records. A particular case of the railway tunnel in the earthquake-prone regions of the escarpment seismic zone of Ethiopia was the specific focus area of the research. Probabilistic seismic hazard analysis (PSHA) and deaggregation have been conducted to determine the design earthquake required as an input for the dynamic analysis. The PSHA performed by considering the operating design earthquake with conservative assumptions of the local geological features resulted in a peak ground acceleration of 0.36. Two pairs of design earthquake have been obtained from the deaggregation process, which were used to filter acceleration time histories for the selected design earthquake from the ground motion database of Pacific Earthquake Engineering Research Center. Finally, full dynamic analyses of the tunnel have been performed by applying the scaled acceleration time histories corresponding to the structure in the specific site. It was demonstrated how to prove the stability of the tunnel located in difficult ground conditions by performing plane strain analyses with the possible minimum computational efforts.

附设黏滞阻尼器的RC框架结构抗震韧性评估

为研究黏滞阻尼器对钢筋混凝土(reinforced concrete,RC)框架结构抗震韧性影响,基于增量动力时程分析方法,对附设黏滞阻尼器的RC框架结构开展抗震韧性能力评估。结合FEMA P-58以及我国抗震韧性评价标准,将主要受损构件的修复费用、修复时间曲线以及易损性信息按实际情况进行相应修正,并对无控结构和有控结构的修复费用、修复时间和人员伤亡等主要抗震韧性指标进行对比分析,明确了黏滞阻尼器对RC框架结构抗震韧性的影响。研究表明,在RC框架结构中适当设置黏滞阻尼器不仅能够减小结构地震响应、降低结构破坏概率,还能有效提升结构抗震韧性。

四主缆大跨悬索桥抗震性能分析及减震措施优化

以燕矶长江大桥为工程背景,首先,采用动力非线性时程法分析了燕矶长江大桥抗震性能,并研究了设置电涡流-摩擦组合型阻尼器和黏滞阻尼器对大跨悬索桥抗震性能的影响;然后,对附加电涡流-摩擦组合型阻尼器摩擦力、阻尼系数和阻尼指数开展了参数敏感性分析;最后,从耗能角度分析地震作用下电涡流-摩擦组合型阻尼器减震特点.结果表明:在E2地震作用下,桥塔关键截面抗弯能力均大于弯矩需求;在“纵向+竖向”地震作用下梁端纵向位移较大.设置塔梁处纵桥向阻尼器后,可有效降低主桥梁端纵向位移;增大摩擦力、阻尼系数与降低阻尼指数均可提升梁端纵向地震响应的控制效果,但参数变化对桥塔控制截面的地震响应影响较小.阻尼系数较大时,电涡流阻尼主导了电涡流-摩擦组合型阻尼器耗能,相较于黏滞阻尼器,电涡流-摩擦组合型阻尼器对梁端纵向位移控制效果更好.

某高层木混合结构抗震分析与性能测试

木混凝土混合结构在多高层木结构建筑中应用广泛,但此类结构的整体抗震性能以及楼盖动力特性有待研究。本文以江苏省康复医院医技楼为例,应用反应谱法与弹性时程分析法分别开展木混合结构的抗震性能分析,并对局部正交胶合木(CLT)楼盖通过原位测试,开展力学性能、动力特性以及人致振动研究。结果表明:结构抗震指标符合规范要求;CLT楼盖荷载位移关系呈双折线,挠度、应力理论计算时,建议板两端按简支考虑;CLT楼盖竖向自振频率均值约15.49 Hz,满足建筑楼盖限值要求,但在单人快走、单人小跑以及多人随机人致振动工况下,楼盖的峰值加速度偏大,应考虑增加现浇建筑面层,改善纯CLT楼盖舒适度不足的问题。可见,木混合结构通过设计可满足抗震要求,但轻质楼盖应注意舒适度构造措施。

浅水浮式风电结构非线性波浪荷载及动力响应特性研究

浮式风电结构在浅水海域中承受的波浪荷载及运动响应表现出非线性特征,对浮式风电安全性提出很高要求。本文建立了风机-浮式基础-系泊系统耦合分析模型,对于不同水深、不同波浪荷载计算方法下的频域水动力系数和时域计算结果分别进行了对比,讨论了水深以及波浪荷载计算方法对浮式风电结构响应和系泊张力的影响。结果表明:浮式风电结构的水动力性能和动力响应随水深变化显著。水深较浅时,浮体响应和系泊张力的低频部分明显增大,二阶波浪荷载的影响更加显著。同时,Newman近似方法与全二次传递函数方法相比,在浅水条件下会明显低估二阶波浪荷载效应,进而影响平台响应和系泊张力的分析。

基于地下结构整体损伤表征的复合地震动参数构造及其性能验证

在地下结构抗震设计中,不同的输入地震动引起的地下结构响应有显著差异,因此,合理通过地震动参数选择输入地震动是正确开展地下结构抗震设计的重要前提。针对单一地震动参数难以表征地下结构地震动潜在破坏势问题,文章构造了能更好表征地下结构损伤破坏的复合地震动参数。具体开展了以下工作:提出基于变形与滞回耗能的地下结构整体损伤指标作为结构需求参数,以定量化评估地下结构的整体破坏状态。选取64条真实地震动记录作为输入地震动,开展四层三跨地铁车站地震弹塑性动力时程分析。基于分析结果提供的数据样本,采用偏最小二乘法从统计角度构造复合地震动参数。最后,选用100条真实地震动记录开展两层三跨地铁车站弹塑性动力时程分析,对文章所构造的复合地震动参数进行验证。对比分析复合地震动参数、12个常用地震动参数与地下结构整体损伤指数的回归统计特征。结果表明:复合地震动参数与结构需求数之间具有更好拟合优度值,其Pearson相关性、有效性也优于单一地震动参数。

地下管廊抗震研究现状综述

针对地下管廊工程建设高速发展、抗震减灾需求愈发凸显的现状,综述地下管廊抗震研究现状.首先,通过国内外以往的震害实例,对地下管廊的震害形式、震害影响因素及震害机理进行了系统性总结.其次,从拟静力试验和振动台试验两个方面总结了地下管廊抗震性能的试验研究现状.再次,总结了地下管廊抗震分析的简化分析方法、动力时程方法、地震易损性评估及减隔震技术的研究现状.最后,基于文献综述提出了目前地下管廊抗震研究亟待解决的问题并做出展望,以期促进地下管廊抗震研究的发展.研究表明:地下管廊在地震作用下的破坏形式主要有混凝土剥落、裂缝贯通、接缝错位或张开、管廊受剪断裂等;地震作用下地下管廊穿越非均匀场地时动力响应的放大效应显著,地下管廊穿越软硬交互等非均匀场地时的抗震性能研究值得重视;交叉节点是地下管廊的薄弱环节,交叉管廊的抗震设计方法研究值得关注;预制管廊接头易受到地震破坏,不同类型预制管廊接头的抗震性能研究需深入探索;城市大型地下管廊系统抗震性能受到不同交叉节点和不同管廊之间的交互影响,高效的地下管廊系统建模方法和高效的简化分析方法亟待研究;城市大型地下管廊系统地震易损性分析是重要的发展方向;地下管廊的减隔震技术值得发展.

节点域承载力对半刚性钢框架地震易损性影响研究

目的 通过考察节点域承载力变化与地震易损性曲线间的关系,获得半刚性钢框架地震易损性曲线,量化节点域屈服承载力对半刚性钢框架地震易损性的影响。方法 采用OpenSEES抗震分析软件建立以节点域承载力比为主要参数的半刚性钢框架模型,通过地震需求分析和抗震能力分析,绘制不同节点域屈服承载力比(0.5~1.0)对应的半刚性钢框架地震易损性曲线。结果 节点域屈服承载力比的取值为0.7时,半刚性钢框架地震易损性曲线在四种极限状态下均小于其他半刚性钢框架,且形成包络趋势。结论 在水平地震作用下,允许节点域屈服,可显著降低钢框架的失效概率,结构的抗震性能也得到了明显改善;节点域屈服承载力比取0.7时,结构抗震性改善效果最显著。

双向地震作用下崩塌堆积体边坡动力模糊可靠性分析

考虑崩塌堆积体边坡岩土体参数随机性和模糊性,以及地震力双向性,建立一种边坡地震动力模糊可靠度计算方法,针对竖向地震力对崩塌堆积体边坡稳定可靠性的影响进行进一步研究。首先,选用动力有限元时程分析法计算出双向地震工况下崩塌堆积体边坡的响应特征,并运用模糊理论对强度参数进行模糊性处理;然后,根据Mohr-Coulumb强度准则构建边坡安全系数与可靠度的时程计算模型;最后,采用边坡地震可靠性评价新方法,通过MATLAB编写相应程序,实现计算和分析结果的快速输出。案例结果表明:新方法计算结果更加合理,对工程而言也更加安全;竖向地震作用均对崩塌堆积体边坡整体可靠性存在影响,但影响程度需根据工程实际情况进行分析。在算例工况下,竖向地震对崩塌堆积体边坡的可靠性影响很小,仅使得可靠度降低3.55%,因此,可仅考虑水平地震的影响。

考虑SSI效应的带地下室RC框架结构抗震性能研究

土-结构相互作用效应(Soil-Structure Interaction,SSI)是带地下室钢筋混凝土(Reinforced Concrete,RC)框架结构抗震性能分析的重要因素。基于模态和动力时程分析,通过有限元分析软件系统探究了地下室顶板嵌固、基础顶面嵌固和考虑SSI效应地下室周围土体嵌固等3种不同嵌固方式的RC框架结构抗震性能。结果表明:考虑SSI效应带地下室RC框架结构的自振周期明显延长,其中心柱剪力、各层加速度和层间位移角均有所减小;基础顶面嵌固模型未考虑SSI效应,其计算结果较为保守;SSI效应对带地下室RC框架结构会产生较大的减震影响。

远场水下爆炸冲击作用下重力坝动力稳定性的简化时程分析方法

高坝大库的抗爆与防护是国防安全的重要研究课题。该文针对远场水下爆炸冲击作用下混凝土重力坝的稳定安全评价问题,研究了远场水下爆炸冲击波的传播及其与坝体的相互作用过程;基于波动理论和平面波假设,建立了重力坝爆炸动应力场的简化理论计算模型,最终建议了一种远场水下爆炸冲击波作用下重力坝动力稳定性的简化时程分析方法;同时结合工程实际,采用该方法对某混凝土重力坝的动力稳定性进行了分析。结果表明:在远场爆炸冲击荷载作用下,重力坝的稳定安全系数呈现出先增后减再增并最终保持恒定的变化规律;下游坝面反射形成的拉伸波与剪切波的共同作用是导致建基面稳定安全系数降低的主要原因。

考虑柱体摇摆效应的殿堂式木结构古建筑非线性地震反应分析

为了准确描述半刚性榫卯连接柱架在地震作用下的动力性能,采用非线性转动弹簧以模拟柱体在地震作用下的摇摆行为,基于柱体、榫卯节点及斗栱的非线性恢复力模型,提出了单层殿堂式木结构地震分析的集中质量简化分析模型,进行了地震作用下的结构动力响应时程分析。通过计算时程曲线与振动台试验结果的对比分析发现,未考虑柱体摇摆的计算值与试验值的误差较大,考虑摇摆效应的整体结构时程曲线计算峰值与柱架的实际位移峰值误差相对较小,且峰值出现的时间基本相同。基于简化模型进一步进行了参数分析,结果表明:竖向荷载可以显著降低殿堂式木结构的地震位移响应;柱高越大,结构的地震位移响应越大;结构的地震位移响应随着榫卯节点转动刚度的增大而显著降低;斗栱数量的增加提高了整体结构的抗侧刚度,从而降低了结构的地震位移响应。研究结果可为木结构古建筑在地震作用下的性能评估提供计算依据。