Nonlinear analysis of pounding between decks of multi-span bridge subjected to multi-support and multi-dimensional earthquake excitation

The nonlinear analysis of pounding between bridge deck segments subjected to multi-support excitations and multi-dimensional earthquake motion was performed.A novel bottom rigid element(BRE)method of the current displacement input model for structural seismic analysis under the multi-support excitations was used to calculate structural dynamic response.In the analysis,pounding between adjacent deck segments was considered.The seismic response of a multi-span bridge subjected to the multi-support excitation,considering not only the traveling-wave effect and partial coherence effect,but also the seismic non-stationary characteristics of multi-support earthquake motion,was simulated using finite element method(FEM).Meanwhile,the seismic response of the bridge under uniform earthquake was also analyzed.Finally,comparative analysis was conducted and some calculation results were shown for pounding effect,under multi-dimensional and multi-support earthquake motion,when performing seismic response analysis of multi-span bridge.Compared with the case of uniform/multi-support/multi-support and multi-dimensional earthquake input,the maximum values of pounding force in the case of multi-support and multi-dimensional earthquake input increase by about 5 8 times;the absolute value of bottom moment and shear force of piers increase by about50%600%and 23.1%900%,respectively.A conclusion can be given that it is very necessary to consider the pounding effect under multi-dimensional and multi-support earthquake motion while performing seismic response analysis of multi-span bridge.

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.

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.

New indexes and methods in earthquake prediction research

This paper gives a brief introduction to a few new indexes and methods published in recent issues of seismological literature which have been explored especially by the authors and many of their collaborators for applying in earthquake prediction research. The new indexes include the statistical indexes of seismicity (Morishita index Iδ, the parameters C and b-value spectrum derived from the magnitude-frequency relation, etc. )and indexes describing the dynamical characteristics of seismic waves obtained from digitized seismologicrecords (wave form linearities, spectral characteristics, etc. ). The new methods fall into two categories:namely the methods of non-linear sciences (fractal analysis, self-similarity and self-organization structure,neural network) and graphical analysis methods of multi-dimensional data (face analysis, projection pursuit,chronogeometric analysis ).

Experimental and numerical studies on new multi-dimensional earthquake isolation and mitigation device:Horizontal properties

Earthquake is a complex multi-dimensional excitation. Counter-measures of such multi-dimensional excitation on many critical structures,such as long-span structures and high-rise buildings,must be taken into account to avert the structural failure. Many types of earthquake mitigation or isolation devices for mitigating earthquake-induced effects in the horizontal direction have been proposed and applied to real applications. However,study on multi-dimensional earthquake isolation and mitigation devices for structures has been received much less attention. In this paper,a new multi-dimensional earthquake isolation and mitigation device was developed and tested. Effects of excitation frequency and environmental temperature on horizontal properties of this device were considered. At the same time,fatigue properties of the device under different amplitude horizontal excitations were also studied experimentally. The equivalent standard solid model which can effectively describe the effect of frequency and temperature on the horizontal properties of the device was proposed and verified. From the experimental results,it may be concluded that the multi-dimensional earthquake isolation and mitigation device owns fine energy dissipation and fatigue resistance capabilities.

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。

利用连接装置控制两相邻结构的地震动响应

运用连接单元来减小平行结构的振动一直是结构振动控制领域的重要课题。该文将两平行结构简化为两单自由度体系 ,用 Voigt粘弹性阻尼器模型表示被动的连接单元 ,运用 Kuhn- Tucker优化原理导出了在地面随机激励下被动连接单元的优化刚度和阻尼值的一般表达式 ,优化控制目标是在保证两平行结构的平均振动能量均得到控制的条件下 ,使两平行结构的总平均振动能量为最小。研究表明优化刚度和阻尼值仅与两平行结构的相对自振频率和相对质量有关 ,同时 。

多维地震激励下工程结构隔减震技术研究进展

地震地面运动是一种复杂的多维激励,结构在单维与多维地震作用下的反应是不同的,特别是对一些复杂或重要的工程结构,只考虑单分量的地震作用是不够的,结构多维抗震是一个非常重要的研究课题。文章系统介绍多维地震激励下结构响应分析方法,比较反应谱法、时程分析法和随机振动法的优缺点;综合国内外研究成果,对结构多维隔减震装置进行详细的描述;对多维隔减震结构的试验研究和工程应用也作了相关介绍。最后,提出结构多维隔减震需要进一步研究的问题。

超大型冷却塔结构风振与地震作用影响比较

超大型冷却塔属于典型风及地震敏感结构,随着塔高的日益增大这两种作用成为设计的控制因素,为了研究这两种作用在不同部位的控制程度,对某超大型冷却塔进行风洞刚体测压和气弹测振试验,通过加载试验获得的塔筒表面风压分布模式和风振系数进行风载作用下结构响应计算,和冷却塔在七度地震作用下的响应进行比较.对比结果表明:环基和塔筒响应完全受风振控制,其在风载作用下的内力数值远大于地震作用下的数值,其中子午向和环向内力从塔底到塔顶逐渐变小,子午向和环向弯矩最大值均出现在塔筒的中部区域.两者对于人字柱的内力影响相差较小,和自重作用共同控制人字柱响应;采用振型分解法计算结构响应需要考虑前300阶的振型影响,而对于风振作用的频域分析只需考虑前30阶模态数即可满足.

强震后基于泄流激励的映秀湾水电站拦河闸动态检测与损伤评估研究

以泄流荷载作为激励源,基于泄流激励对结构产生的动力响应,在模态参数识别的频域分解法的基础上,提出模态一致性函数(MCF),解决通过CMIF指示函数拾取峰值是结构真实模态频率还是噪声引起的虚假模态频率(如水流噪声频率)的主观性难题,有效地提高了泄流激励下结构模态识别精度;在此基础上,对遭受汶川大地震的映秀湾水电站拦河闸结构进行了泄流激励条件下的现场动力测试与模态识别,同时对拦河闸结构在不同部位和不同损伤程度条件下的耦合动力特性进行了数值模拟,建立了拦河闸结构损伤评估样本库,最后进行了拦河闸结构损伤评估;通过拦河闸现场围堰检查结论与本检测结果的比较,两者吻合较好。所提出的方法可为泄流结构的灾后检测与评估提供一种新的便捷手段。