近场地震下竖向刚度不同的混合结构动力性能分析

近场地震的动力特性明显不同于远场地震,因此有必要对结构在近场地震作用下的动力性能展开研究。以上部钢结构-下部混凝土结构这类竖向刚度不同的加层混合结构为研究对象,对其在近场脉冲型地震、近场无脉冲型地震及远场地震作用下的动力响应进行研究。结果表明:在多遇、设防、罕遇地震作用下,近场脉冲型地震会使结构的层间位移角、层间剪力、加速度等动力响应均放大并出现超限的情况,而且都比罕遇地震作用下结构的响应增大更明显;在进行近场区加层混合框架结构的设计和建设时,近场脉冲效应会使结构存在不满足规范的情况,有必要对竖向刚度不同的加层混合结构在近场区的适用性进行深入研究。     

山西地区远震P波到时残差分布

收集2008—2016年山西地震台网记录的震中距30°—90°范围内1 253个远震事件波形,拾取7 600余条高质量P波初至到时,使用IASP91模型计算相对到时残差,分析残差水平分布特征,结果显示:①以山西地区中部的山西断裂带为界,西部地震台站记录的P波初至主要表现为早到时,东部位于大同火山区的地震台站记录则主要表现为晚到时;②位于山西断裂带内部的地震台站记录的P波初至主要表现为早到时,残差水平显著低于西部地震台站;③研究区P波到时整体呈现自西向东逐渐由早到晚的分布特征。推测山西断裂带西部地区下方可能存在高速异常结构,山西断裂带内部及大同火山区下方可能存在低速异常结构。     

关于土层地震反应分析中阻尼矩阵建模方式的讨论

阻尼矩阵的选择对土层时域内地震反应计算的准确性有重要意义。本文构造了质量比例阻尼、刚度比例阻尼、Rayleigh阻尼、Caughey阻尼和Clough阻尼矩阵,研究各阻尼对土层地震反应分析精度的影响。以苏通大桥5号桥塔基础处的工程场地为例,分别以人工合成基岩波,Northridge波、Parkfield波和汶川波为输入,得到不同阻尼模型下土层的地震反应,结果表明Clough阻尼在计算精度和误差稳定性上要优于其他阻尼模型,针对Clough阻尼的不足之处提出了改进方法,算例表明改进后的Clough阻尼能在保证计算精度的前提下减少计算机的存储量和计算量。     

高烈度区公路隧道横通道地震响应分析

双洞隧道主隧道与横通道交接部位是隧道抗震中的薄弱位置,以穿越高烈度区隧道为背景,采用MIDAS GTS-NX有限元分析软件,对在汶川地震动作用下的公路隧道横通道进行地震响应分析。在X方向和Y方向地震动荷载的共同作用下,通过对围岩和衬砌的计算结果研究,得出以下结论:隧道整体的最大相对位移主要发生在主隧道与横通道拱顶和连接处;衬砌相对位移随埋深增加而减小;隧道产生的横向变形更大;横通道边墙位置更容易受到剪切破坏,主隧道与横通道连接处拱脚的弯矩、剪力、最大主应力和最大剪应力最大,应重点采取设防措施。     

互联网+社区地震应急桌面演练的设计与实施——以青海省海西州为例

地震灾害应对实践表明,社区作为社会治理的基本单元,在抢救生命、安置群众生活等方面发挥着重要作用。应急演练是有效提升民众防灾减灾意识和社区应对灾害能力的重要途径。近年来,社区开展了不同程度的地震应急演练,但在专业性和实效性方面仍存在很大提升空间。本文基于互联网+应急演练理念,提出基于互联网云服务的分布式、多社区、不限人数、同步或异步开展的应急桌面演练新模式,并在青海省海西蒙古族藏族自治州进行了试点应用。实践表明,互联网+社区地震应急桌面演练融合了传统桌面演练与实战演练的优势,可针对社区管理层开展地震灾害全过程桌面推演,能有效促进社区管理层应急组织协调能力的提升。     

移动荷载对桥梁动力响应的影响研究——以开裂预应力混凝土简支梁为例

混凝土桥梁在工作过程中会产生裂缝,为分析移动荷载对开裂混凝土桥梁结构刚度的影响,对开裂梁动力响应进行分析。建立简支T梁桥有限元模型,并将移动荷载施加至有限元模型中。根据简支T梁桥破坏横向分布位置和强度的不同,研究不同工况下各梁荷载横向分布及不同移动速度对裂缝扩展宽度的影响。结果表明,数值模拟结果能较好地验证计算模型的准确性;在较大的移动荷载作用下,混凝土开裂,导致结构刚度减小、位移增大;随着移动荷载和速度的增加,开裂时间增加,结构刚度降低,持续时间增加,位移增大,使结构响应呈现明显非线性。     

Seismic effectiveness of tuned mass dampers considering soil–structure interaction

This paper presents how soil–structure interaction affects the seismic performance of Tuned Mass Dampers (TMD) when installed on flexibly based structures. Previous studies on this subject have led to inconsistent conclusions since the soil and structure models employed considerably differ from each other. A generic frequency-independent model is used in this paper to represent a general soil–structure system, whose parameters cover a wide spectrum of soil and structural characteristics. The model structure is subjected to a stationary random excitation and the root-mean-square responses of engineering interest are used to measure the TMD's performance. Extensive parametric studies have shown that strong soil–structure interaction significantly defeats the seismic effectiveness of TMD systems. As the soil shear wave velocity decreases, TMD systems become less effective in reducing the maximum response of structures. For a structure resting on soft soil, the TMD system can hardly reduce the structural seismic response due to the high damping characteristics of soil–structure systems. The model structure is further subjected to the NS component of the 1940 El Centro, California earthquake to confirm the TMD's performance in a more realistic environment. Copyright © 1999 John Wiley & Sons Ltd.     

Predictive optimal control for seismic analysis of non-linear and hysteretic structures

In this paper, an effective active predictive control algorithm is developed for the vibration control of non-linear hysteretic structural systems subjected to earthquake excitation. The non-linear characteristics of the structural behaviour and the effects of time delay in both the measurements and control action are included throughout the entire analysis (design and validation). This is very important since, in current design practice, structures are assumed to behave non-linearly, and time delays induced by sensors and actuator devices are not avoidable. The proposed algorithm focuses on the instantaneous optimal control approach for the development of a control methodology where the non-linearities are brought into the analysis through a non-linear state vector and a non-linear open-loop term. An autoregressive (AR) model is used to predict the earthquake excitation to be considered in the prediction of the structural response. A performance index that is quadratic in the control force and in the predicted non-linear states, with two additional energy related terms, and that is subjected to a non-linear constraint equation, is minimized at every time step. The effectiveness of the proposed closed-open loop non-linear instantaneous optimal prediction control (CONIOPC) strategy is presented by the results of numerical simulations. Since non-linearity and time-delay effects are incorporated in the mathematical model throughout the derivation of the control methodology, good performance and stability of the controlled structural system are guaranteed. Copyright © 1999 John Wiley & Sons, Ltd.     

Statistical study of spatial variation of response spectrum using free field records of dense strong motion arrays

Spatial variation of acceleration response spectra is examined using strong motion records for a large number of events from dense accelerometer arrays at Chiba in Japan and SMART-1 in Lotung, Taiwan. The effects of earthquake component, structural damping, earthquake magnitude, focal depth, epicentral distance, structural time period, and station separation on the intra-event variation of response spectra are examined first through an empirical analysis and then through a least-square regression fit for parametric study. A very large scatter of the response spectra ratio is observed for both arrays, especially for SMART-1 array. The mean values of the ratio vary from 10 to 20 per cent for Chiba array while they vary from 25 to 50 per cent for SMART-1 array. The coefficients of variation of the ratio range from 5 to 25 per cent for Chiba array and 30 to 50 per cent for SMART-1 array. The correlation among response spectra is found to be inversely proportional to station separation and shows frequency dependence. For larger time periods, the correlation is lower and not higher. The correlation is also lower for UD earthquake component as compared to the two horizontal components. For higher damping ratio, the correlation among spectra is higher. The effect of the earthquake magnitude, focal depth and epicentral distance on the spatial variation is complex. The three parameters having implicit interdependence, considering their combined effect, a positive contribution to the value of ratio of response spectra is observed in the case of larger earthquake events. Furthermore, as mentioned above, the spatial variation for SMART-1 array is much larger than that for Chiba array. This difference can be attributed mainly to the difference in distance between the instruments in the two arrays. However, some of the difference is considered to be due to site specific characteristics. Copyright © 1999 John Wiley & Sons, Ltd.     

Optimal instrumentation of structures on flexible base for system identification

A criterion previously developed by Heredia-Zavoni and Esteva for selecting optimal sensor locations is used to analyse the optimal instrumentation of structures on soft soils. The stochastic response of a linear structural system on a flexible base is formulated for use of the criterion. The case of MDOF shear systems on flexible base, with uncertain lateral stiffness and subjected to random earthquake ground motions, is studied. The optimal location of accelerometers, the reduction of prior uncertainty on the lateral stiffness, the effects of the base flexibility, the relative influence of translation and rocking of the base, and the influence of recording noise are assessed and discussed. Copyright © 1999 John Wiley & Sons, Ltd.