Active TLCGD control of plane asymmetric buildings under earthquake excitation

The sealed,tuned liquid column gas damper （TLCGD） with gas-spring effect extends the frequency range of application and efficiently increases the modal structural damping.Active tuned liquid column gas damper （ATLCGD） is developed for the vibration control of plane asymmetric buildings subjected to earthquake excitation,improving the performance of the passive control scheme.The active behaviour is obtained by adjusting the pressure at the end of the liquid column using a pressurised reservoir.The classical linear quadratic regulator （LQR） design is presented as a straightforward approach to optimal control.Numerical simulations indicate a significant vibration reduction of plane asymmetric buildings by active control within the strong motion of the dynamic response.

Study on the Sliding Displacement of a Sliding Structure Subjected to Multi directional Earthquake Excitation

Transient dynamic analysis is used to study the effect of the bidirectional interaction of friction on the response of sliding displacement of a sliding structure subjected to bidirectional earthquake ground motion. The analysis varies the parameters of amplitude ratio of earthquake excitation, the period of the superstructure, and the coefficient of friction in the sliding support. Numerical results show that the sliding structure is significantly influenced by the interaction of frictional forces. So the sliding displacement may be underestimated and the acceleration of the superstructure may be overrated if the bidirectional interaction of frictional forces is neglected.

Karhunen-loéve expansion for random earthquake excitations

This paper develops a trigonometric-basis-fimction based Karhunen-Loeve （KL） expansion for simulating random earthquake excitations with known covariance functions. The methods for determining the number of the KL terms and defining the involved random variables are described in detail. The simplified form of the KL expansion is given, whereby the relationship between the KL expansion and the spectral representation method is investigated and revealed. The KL expansion is of high efficiency for simulating long-term earthquake excitations in the sense that it needs a minimum number of random variables, as compared with the spectral representation method. Numerical examples demonstrate the convergence and accuracy of the KL expansion for simulating two commonly-used random earthquake excitation models and estimating linear and nonlinear random responses to the random excitations.

The Study of Excitation of the Earthquake to Earth's Rotation

Usingthefaultplaneparameters,thelocationofepicenterandtheexpressiongivenby Dahlenaswellasthestepfuction ,theaccumulativechangeoftheaxialandequatorialmomentof inertiaoftheearthfor 1 977～ 1 994dataisestimatedinthispaper .Resultshaveshownthat changeofpolemotiondirectioninducedbysingleearthquakeisindependentofthesizeofearth quake .Theearthquaketendstomaketherotationalpoledrifttowardsthedirectionof 1 2 5～ 1 5 0 E .Thisdirectionisroughlydifferenttothatoneinferredfromobservations.Accumulative changesofthetwoequatorialprincipalmomentsandaxialmomentofinertiaoftheearthexhibit secularbehaviour.Thechangedependstoalargeextentupontheslipangleofthefaultmove ment.

Comparison of base-isolated liquid storage tank models under bi-directional earthquakes

Seismic response of ground supported baseisolated liquid storage tanks are evaluated under bi-directional earthquakes. The base-isolated liquid storage tanks are modeled using mechanical analogs with two and three lumped masses (Model 1 and Model 2). Two types of isolation systems, such as sliding system and elastomeric system, are considered for the present study. The isolation systems are modeled using Wen’s equation for hysteretic isolation systems. Response of base-isolated liquid storage tanks, evaluated through two different modeling approaches, is compared. Both the models predict similar sloshing displacement. The effect of interaction between the mutually perpendicular seismic responses of the isolator is investigated for both the models. It is observed that interaction affects the peak seismic response of the base-isolated liquid storage tanks significantly, under the bi-directional earthquake components.

DYNAMIC ANALYSIS OF DAMPER CONNECTED ADJACENT BUILDINGS UNDER EARTHQUAKE

A formulation of the multi degree of freedom equations of motion for damper connected adjacent multi story buildings under earthquake excitation is presented.The ground acceleration due to earthquake is regarded as a stochastic process,and a pseudo excitation algorithm in frequency domain is implemented in a computer program to handle the non orthogonal damping properties of the system.The effectiveness of joint dampers is then investigated in terms of the reduction of displacement,acceleration and shear force responses of adjacent buildings.

EARTHQUAKE RESPONSE OF SEMI RIGID FRAME WITH ROTATIONAL DAMPER

The seismic behavior of frames with semi rigid connections and rotational dampers is examined.The ground acceleration due to earthquake is regarded as a stochastic process,and a pseudo excitation algorithm in frequency domain is implemented in a computer program to handle non orthogonal damping properties of the system.The computer program which incorporates detailed connection models and rotational damping models is used to investigate the effect of the connection of the semi rigid frame.It is shown from analytical studies that semi rigid frames with rotational dampers improve the seismic response of the building and may provide an effective and reliable earthquake resistant design solution.

Seismic Response Analysis of Long-Span Suspen-Dome under Multi-Support Excitations

A practical suspen-dome project, Changzhou Gym roof, is adopted as an example and its transient analysis based on the multi-support excitations of the earthquake wave is carried out. Compared with the single support excitation, the position and value of the maximum stress under multi-support excitations both change and the amount of elements with obvious changes is large and more than 70% of the total. Moreover, when other terms are not changed, this influence will decrease as the span decreases, but increa...

Orientation effect on ground motion measurement for Mexican subduction earthquakes

The existence of the principal directions of the ground motion based on Arias intensity is well-known. These principal directions do not necessarily coincide with the orientations of recording sensors or with the orientations along which the ground motion parameters such as the peak ground acceleration and the pseudo-spectral acceleration （PSA） are maximum. This is evidenced by the fact that the maximum PSA at different natural vibration periods for horizontal excitations do not correspond to the same orientation. A recent analysis carried out for California earthquake records suggests that an orientation-dependent ground motion measurement for horizontal excitations can be developed. The main objective of this study is to investigate and provide seismic ground motion measurements in the horizontal plane, including bidirectional horizontal ground motions, for Mexican interplate and inslab earthquake records. Extensive statistical analyses of PSA are conducted for the assessment. The analysis results suggest that similar to the case of California records, the average behavior of the ratio of the PSA to the maximum resulting PSA can be approximated by a quarter of an ellipse in one quadrant; and that the ratio can be considered to be independent of the value of the maximum resulting PSA, earthquake magnitude, earthquake distance and the focal depth. Sets of response ratios and attenuation relationships that can be used to represent a bidirectional horizontal ground motion measurement for Mexican interplate and inslab earthquakes were also developed.

A Study on the Seismic Velocity Changes before and after the 2016 M_S6.4 Menyuan Earthquake Using the Active Source Data in the Qilian Mountain

The Qilian Mountain active source network data was processed using the methods of stacking, cross-correlation and interpolation, and the airgun travel time variation characteristics of P and S waves around the January 21,2016 MS6. 4 Menyua,Qinghai earthquake. The results show that about 6 months before the earthquake,the relative travel time of three stations near the epicenter showed a declined change( travel time decrease),and such a change of low value anomaly was recovered about 3 months before the earthquake. The travel time decrease then appeared again, and the earthquake occurred during the recovery process. The maximum decrease of the S-wave travel time was 18 ms,and the change in travel time returned to normal after the earthquake. The variation trend of the 3 stations is consistent,including the S-wave travel time change of station ZDY38,which is nearest to the epicenter and changed obviously,and the variation range of the travel time is smaller at the stations afar. This variation pattern is related to the position of the seismic source. The shorter travel time means the velocity increase,which may be related to the regional stress accumulation.

地震行波激励下单层对称框架结构扭转响应的时域解析解

针对单层对称框架结构,利用地震行波激励研究地震波中频率成分对框架结构扭转响应的影响。给出了单层对称框架结构在地震行波激励下的动力平衡方程,利用相对运动法对方程进行求解,给出了地震行波激励下扭转响应级数形式的时域解析解。计算了框架结构分别在低频成分丰富和低频成分不丰富地震波行波激励下的峰值柱剪力,进而分析了地震波中低频成分对框架结构行波效应的影响。研究表明:地震行波激励下柱剪力解析解不但与固有频率和激励频率有关,还与时间延迟以及结构基频和激励频率比值的平方有关。地震波加速度幅值谱中存在小于结构基频的主要频率时,框架结构易于产生行波效应,幅值谱中主要频率均大于结构基频时,不存在行波效应。框架结构地震行波效应除取决于时间延迟外,还取决于地震波中的低频成分。在低频成分和时间延迟的共同作用下,框架结构将产生地震行波效应。低频成分越丰富的地震波,行波效应越显著。

行波激励下单层单跨结构地震响应解析解

目的研究地震波中频率成分对小跨度结构响应行波效应的影响,以探究小跨度结构地震行波效应的产生机理。方法给出地震行波激励下单层单跨结构的动力平衡方程,使用相对运动法对方程进行求解;推导地震行波激励下屋面绝对位移和柱剪力的解析解,分别研究低频成分丰富和低频成分不丰富地震波激励下的峰值柱剪力。结果地震行波激励下柱剪力解析解不仅与时间延迟有关,还与结构基频和激励频率比值的平方有关;对于低频成分丰富的地震波,行波激励下峰值柱剪力大于一致激励下峰值柱剪力;相反,对于低频成分不丰富的地震波,行波激励下峰值柱剪力要小于一致激励下峰值柱剪力。结论结构响应地震行波效应除取决于时间延迟外,还取决于地震波中的低频成分;在低频成分丰富的地震波激励下,小跨度结构会产生行波效应,且低频成分越丰富的地震波,行波效应越显著;在低频成分不丰富的地震波激励下,不会产生行波效应。

水平-纵向双地震动作用下桥梁桩基地震响应研究

基于FLAC 3D有限差分软件,建立了场地土-桩基-结构体系三维数值分析模型;然后,在松砂层采用SANISAND液化土本构,密砂层采用Mohr-Coulomb本构的基础上,将数值分析结果与离心机试验结果进行对比,验证了数值分析模型的可靠性;最后,选取水平单向和水平-竖向双Kobe地震波对土体孔压、加速度、位移、桩身弯矩等进行分析,进一步探究了双地震动作用对桩基地震响应的影响。研究结果表明:1)竖向地震动作用的存在会增大土体加速度响应,加剧孔压的振荡;2)与水平单向地震动相比,松砂层在水平-竖向双地震动作用下的土体位移差异更明显,这可能与竖向地震动作用下松砂层土颗粒之间的粘结性更易变弱有关;3)竖向地震动作用增大了桩身的弯矩响应,并于土层交界面处弯矩达到最大,易发生桩身的弯曲破坏。以上结论可为今后考虑竖向地震动作用下桥梁桩基易损部位加固施工提供参考。

列车移动荷载与非一致地震动作用下轨道-路基系统动力响应

为研究列车移动荷载与非一致地震动耦合作用下轨道-路基系统动力响应规律,以京沪高铁和CRH3型列车为研究对象,建立了三维精细化有限元模型,进行了耦合荷载作用下轨道-路基系统动力响应分析。通过平稳地震动时程乘以包络函数合成了非一致地震动,参数化分析了列车运营时速、轴质量及非一致地震动震级对轨道-路基系统动力响应影响规律。结果表明:轨道-路基系统响应幅值并非随列车运行速度提升而增大,存在一个包括临界速度的范围,在此范围内列车移动荷载与非一致地震动耦合作用下轨道-路基系统将会出现强烈振动;随着列车轴质量或地震动PGA(peak ground acceleration)增大,轨道-路基系统出现更显著的震动响应。与一致激励相比,非一致激励下轨道板竖向位移峰值和竖向加速度峰值的出现时间更早。

Behavior of composite rigid frame bridge under bi-directional seismic excitations

Pushover analysis and time history analysis are conducted to explore the bi-directional seismic behavior of composite steel-concrete rigid frame bridge, which is composed of RC piers and steel-concrete composite girders. Both longitudinal and transverse directions excitations are investigated using OpenSees. Firstly, the applicability of pushover analysis based on the funda- mental mode is discussed. Secondly, an improved pushover analysis method considering the contribution of higher modes is proposed, and the applicability on composite rigid frame bridges under bi-directional earthquake is verified. Based on this method, an approach to predict the displacement responses of composite rigid frame bridge under random hi-directional seismic excitations by revising the elasto-plastic demand curve is also proposed. It is observed that the developed method yield a good estimate on the responses of composite rigid frame bridges under bi-directional seismic excitations.

泸定6.8级地震公路地质灾害链效应分析

省道S217是2022年9月5日泸定6.8级地震中灾毁最为严重的公路,沿线灾害链生效应明显。通过实地踏勘,收集地质资料和前人研究成果,总结了公路沿线崩塌群、滑坡、泥石流次生地震地质灾害的分布规律及特征,并从灾害链的角度对地震诱发次生地质灾害进行剖析,归纳出地震—震裂山体—崩塌(滑坡)、地震—崩塌(滑坡)—堰塞湖—水流(冲刷)—泥石流、地震—滑坡—崩塌等灾害链模型,且通过对灾害链成灾机理和发展趋势的分析判断:部分灾害链已趋于稳定,但仍有部分灾害正在发展、或将形成隐患。为此,针对灾害链的孕灾环和激发环,建议通过监测、控制、消除激发环和改变新孕灾环的方式实现断链,提出了相应的断链措施,为灾后重建提供参考。

多期地震作用的台阶式顺层岩质边坡震裂破坏机制

高烈度区斜坡震裂变形体广泛存在,为理清台阶式顺层岩质边坡在多期地震作用下的震裂破坏机制,以三清高速路堑斜坡为原型,开展大型振动台试验。引入加速度放大系数比(ratio of acceleration amplification factor,RAAF)研究不同台阶位置加速度动力响应差异性,利用希尔伯特−黄变换和边际谱识别边坡震裂累积损伤及失稳破坏过程,结合边坡失稳破坏现象阐明台阶式边坡震裂破坏机制。结果表明:边坡具有高程放大效应,加速度放大系数随输入地震波峰值增加呈现先增加再降低的趋势。RAAF在输入地震波峰值为0.6g前后出现正负突变,表明输入地震波峰值为0.6g是改变两种类型边坡动力响应差异性的“临界值”。多期地震作用下,希尔伯特谱低频部分减小,高频部分增加,岩体和夹层表现出滤波作用。水平地震作用下,台阶阴角极易产生动拉应力集中,造成阴角处被拉裂。不均匀台阶宽度边坡的渐进破坏过程为第2级台阶首先出现拉裂缝→上部岩层沿软弱夹层滑动→坡顶后缘拉裂→第1级台阶拉裂并脱离坡体。均匀台阶宽度边坡各级台阶阴角均出现拉裂缝,边坡未出现明显滑动面。模型试验揭示了台阶式岩质边坡的震裂破坏机制,针对勘察设计和施工应加强各级台阶阴角变形量的监测,阴角处可做圆弧处理降低应力集中现象。坡脚处可设置抗滑桩,提高边坡出现震裂破坏的阈值,增强边坡稳定性。

2021年5月21日青海玛多M_(W)7.4地震及余震序列应力降时空分布与孕震环境

2021年5月21日发生在青藏高原巴颜喀拉块体内部的玛多M_(W)7.4地震是继2008年M_(W)7.9汶川地震之后在中国陆区发生的最大地震.由于玛多地震发生在板块内部滑移速率较缓慢的次级断裂上,该地震成为研究巴颜喀拉块体内部地震危险性的典型震例.通过计算2021年玛多地震序列中震级大于2.5的地震应力降,我们调查了该地震序列应力释放的时空演化规律.首先,利用已有的青藏高原及其周边地区宽频带Lg波衰减模型,对玛多地震序列产生的地震Lg波观测数据进行了传播路径衰减校正,获得119个地震事件的Lg波震源谱;然后,通过将理论震源函数与观测数据拟合,获得对Lg波标量地震矩、拐角频率和高频下降率的估计;最后,根据标量地震矩和拐角频率计算了2021年玛多地震序列的应力降.结果表明,2021年5月21日玛多地震主震应力降为22 MPa,余震序列的应力降分布范围为0.08~7.5 MPa、中位数为0.39 MPa,平均值为0.88 MPa.应力降与震级具有较强的正相关关系,说明该地区的地震活动可能并不遵从地震自相似理论.换言之,大小地震具有不同的破裂动力学性质.玛多地震序列应力降变化反映了断层面上的应力释放过程具有强烈的非均质性.主震发生之后余震应力降显著降低,但其间仍夹杂着少数具有较高应力降的事件.这些高应力降事件所在区域与主震后破裂面上的闭锁和应力集中区域相对应.

水平及竖向地震作用下多高层RC框架混合试验

以往混合试验方法大多只考虑水平地震作用,为进一步拓展混合试验方法的应用,本文提出一种水平及竖向地震共同作用下多高层钢筋混凝土(RC)框架混合试验方法。该方法对框架结构计算模型和子结构边界条件进行合理简化,框架结构水平振动和竖向振动分别采用串联质点系模型和串并联多质点系模型进行模拟。在此方法基础上开发出一套完整的混合试验程序,该程序利用Matlab编写运动方程求解模块,采用OpenSees模拟数值子结构,并结合加载设备HNU-MUST开发出混合试验控制程序。为验证本方法和程序,设计并制作一根足尺RC框架柱作为试验子结构,并以一榀七层三跨RC框架作为整体结构进行混合试验,试验的顺利进行和良好稳定的试验控制效果验证了本方法的可行性与有效性。试验结果表明:在水平和竖向地震共同作用下RC框架柱轴力会发生剧烈变化,该轴力变化会使试件的受力状态和破坏形态变得较为复杂,同时可能会降低试件的强度和延性,并最终导致滞回曲线呈现不对称性和一定的“捏缩”现象。

某国际会展中心地震多点激励时程分析

广东佛山潭洲国际会展中心底部支撑结构东西向长度约为292 m,南北向长度约为323.8 m(屋盖总长度约为380 m),南北向结构超长,属超限大跨空间结构。本文采用大质量法对其进行考虑行波效应的地震多点激励时程分析,并对多点激励与一致地震输入下结构的扭转效应、重要构件的内力情况进行对比分析。结果表明:多点激励作用下,地震输入方向与地震传播方向垂直时结构的扭转效应明显,地震输入方向与地震传播方向一致时结构的扭转效应不明显;不同部位的杆件,地震多点激励作用的影响程度不同,文中给出了考虑地震多点激励作用影响的调整系数,构件设计时,可将反应谱分析结果乘以多点激励调整系数,以此来考虑地震多点激励作用的影响;总体上,地震多点激励对本结构的影响不大。