Optimal design for rubber concrete layered periodic foundations based on the analytical approximations of band gaps and mapping relations

The seismic performance of rubber concrete-layered periodic foundations are significantly influenced by their design,in which the band gaps play a paramount role.Aiming at providing better designs for these foundations,this study first proposes and validates the analytical formulas to approximate the bounds of the first few band gaps.In addition,the mapping relations linking the frequencies of different band gaps are presented.Furthermore,an optimal design method for these foundations is developed,which is validated through an engineering example.It is demonstrated that ensuring the superstructure’s resonance zones are completely covered by the corresponding periodic foundation’s band gaps can achieve satisfactory vibration attenuation effects,which is a good strategy for the design of rubber concrete layered periodic foundations.

Generalized Rydelek-Sacks test for distinguishing between periodic and randompatterns in seismicity

For distinguishing the periodicity of strong earthquakes on the time scale of decades, we generalized the Rydelek-Sacks test (R) delek. Sacks. 1989) to explore whether a time series is modulated by a periodic process or not. Thetest is conducted by comparing the total phasor of seismicity with that produced by a random Brownian motion.The phdse angle is defined by the origin time of earthquakes relative to a reference time scale. Using this methodwe tested two hypotheses in geodynamics and earthquake prediction study. One is the hypothesis of Romanowicz( 1993 ) who proposed that the great earthquakes alternate in a predictable fashion between strike-slip and thrustingmechanisms oil a 20~30 years cycle. The other hypothesis is that the strong earthquakes in and around China havean active period of about ten years. The test obtains a negative conclusion for the former hypothesis and a positiveconclusion for the latter at the 93% confidence level.

Spectra of seismic force reduction factors of MDOF systems normalized by two characteristic periods

Seismic force reduction factor(SFRF) spectra of shear-type multi-degree-of-freedom(MDOF) structures are investigated. The modified Clough model, capable of considering the strength-degradation/hardening and stiffnessdegradation, is adopted. The SFRF mean spectra using 102 earthquake records on a typical site soil type(type C) are constructed with the period abscissa being divided into three period ranges to maintain the peak features at the two sitespecific characteristic periods. Based on a large number of results, it is found that the peak value of SFRF spectra may also exist for MDOF, induced by large high-mode contributions to elastic base shear, besides the mentioned two peak values. The variations of the stiffness ratio λk and the strength ratio λF of the top to bottom story are both considered. It is found that the SFRFs for λF ≤λk are smaller than those for λF > λk. A SFRF modification factor for MDOF systems is proposed with respect to SDOF. It is found that this factor is significantly affected by the story number and ductility. With a specific λF(= λk0.75), SFRF mean spectra are constructed and simple solutions are presented for MDOF systems. For frames satisfying the strong column/weak beam requirement, an approximate treatment in the MDOF shear-beam model is to assign a post-limit stiffness 15%-35% of the initial stiffness to the hysteretic curve. SFRF spectra for MDOF systems with 0.2 and 0.3 times the post-limit stiffness are remarkably larger than those without post-limit stiffness. Thus, the findings that frames with beam hinges have smaller ductility demand are explained through the large post-limit stiffness.

Simulation of the active and quiet periods of seismicity

In this paper we simulate the repeated occurrence of strong earthquakes along a strike-slip fault by using a finite element model. The fault valve mechanism is included in the model in order to take into account the effeCt of POre fluid pressure variation. Five parameters are used to characterize the rheology of the fault, POre pressure variation, and fracture criteria. By Systematically varying these parameters and calculating a large number of models we carried out a preliminary investigation on the alternatively quiet and active periods of seismicity and their relation to model Parameters and loading conditions. Under the action of a constant-rate boundary movement, in the case of intermediate stress and pore pressure, the models display a regular quiescence-activity phenomenon with a cycle length of 1/3-1 of the recurrence pened. When the model is under high stress or high pore pressure, this phenomenon becomes irregular or inexplicit. When the model is subject to periedic boundary forces and the amplitude of force variation is not too small, it results in an alternatively quiet and active seismicity Pattern with the same Period Of the force variation.

Influence of long period seismic waves induced by the Taiwan large earthquake on Shanghai area

In this paper a group of long period seismic waves in Shanghai area induced by Taiwan large earthquake is presented by using the method of semi empirical Green function, the period is up to 20 s. Such seismic waves can be used as a reference curve to test the strength of long period structures and their aseismic design. The long period part of seismic influence curve presented in 'Architecture Aseismic Design Code'(GBJ11 89) is less than 3 s, and uncertainties exist in the effects of earthquake safety evaluation. This research will be able to eliminate these shortages.

Seismic pounding and collapse behavior of neighboring buildings with different natural periods

Seismic pounding phenomena, particularly the collision of neighboring buildings under long-period ground motion, are becoming a significant issue in Japan. We focused on a specific apartment structure called the Nuevo Leon buildings in the Tlatelolco district of Mexico City, which consisted of three similar buildings built consecutively with narrow expansion joints between the buildings. Two out of the three buildings collapsed completely in the 1985 Mexican earthquake. Using a finite element code based on the adaptively shifted integration (ASI)-Gauss technique, a seismic pounding analysis is performed on a simulated model of the Nuevo Leon buildings to understand the impact and collapse behavior of structures built near each other. The numerical code used in the analysis provides a higher computational efficiency than the conventional code for this type of problem and enables us to address dynamic behavior with strong nonlinearities, including phenomena such as member fracture and elemental contact. Contact release and recontact algorithms are developed and implemented in the code to understand the complex behaviors of structural members during seismic pounding and the collapse sequence. According to the numerical results, the collision of the buildings may be a result of the difference of natural periods between the neighboring buildings. This difference was detected in similar buildings from the damages caused by previous earthquakes. By setting the natural period of the north building to be 25% longer than the other periods, the ground motion, which hada relatively long period of 2 s, first caused the collision between the north and the center buildings. This collision eventually led to the collapse of the centerbuilding, followed by the destruction of the north building.

Correlation of Structural Seismic Damage with Fundamental Period of RC Buildings

The sufficient estimation of the natural period of vibration constitutes an essential step in earthquake design and assessment and its role in the development of seismic damage is investigated in the current research. The fundamental period is estimated for typical reinforced concrete building types, representative of the building stock of Southern Europe, according to existing relationships. The building typologies also represent groups of 180,945 existing damaged buildings of an observational database created after the Athens (7-9-1999) near field earthquake. The estimated fundamental periods are correlated to several degrees of the recorded damage. Important conclusions are drawn on the parameters (height, structural type, etc.) that influence the seismic response and the development of damage based on the wide database. After conducting a correlation analysis, noticeable is the difference between the seismic demand of the elastic spectrum of the first (1959), the contemporary (2003) Greek Seismic Code and the values of peak ground accelerations of several Athens earthquake records. Moreover, PGAs in most records are often between the lower and the upper bound of the estimated fundamental periods for RC buildings with regular infills (n-normal) and with ground levels without infill panels (p-pilotis) regardless the height. A disparity is noticed when the estimated fundamental period is based on EC8 provisions for the considered as “high” buildings in S. Europe regarding the referring earthquake. The majority of buildings that developed several degree, type and extent of damage are considered of “low” height with estimated fundamental periods close to the PGA values of Athens earthquake ground motions. However, the developed damage was the result of the combination of parameters based on geological, tectonic and morphological characteristics of the affected area. In addition, a damage scale for the measurable recording, beyond the qualitative characterization of seismic damage in Greek post-earthquake surveys, is presented wherein the performance levels are defined according to the physical description of the seismic damage and, as well, in terms of structural and economic damage index.

A Seismic Facies Analysis to Determine the Relative Age and History of the Al Idrissi Mud Volcano from Offshore Larache Located in the NW Moroccan Atlantic Margin

Formed on top of the Gulf of Cadiz, the Al Idrissi mud volcano is the shallowest and largest mud volcano in the El Arraiche mud volcano field of the northwestern Moroccan margin. The development and morphology of mud volcanoes from the El Arraiche mud volcanoes group have been studied at a large scale. However, the time interval related to their formation period still needs to be better understood. In this regard, we interpreted and analyzed the seismic facies from the 2D reflection data of the GEOMARGEN-1 campaign, which took place in 2011. The aim was to identify the seismic sequences and draw the Al Idrissi mud volcano system to determine the formation period of the Al Idriss mud volcano. And as a result, the Al Idrissi mud volcano system is made of both buried and superficial bicone and was identified along with the Upper Tortonian to Messinian-Upper Pliocene facies. As the initial mud volcano extrusive edifice, the buried bicone was formed in the Late-Messinian to Early-Pliocene period. However, the superficial bicone, as the final extrusive edifice, was included in the Late Pliocene. In this case, the timing interval between the buried and superficial bicone is equivalent to the Late-Messinian to Upper-Pliocene period. Therefore, the latter corresponds to the Al Idrissi mud volcano formation period.

鲁东—黄海地块西部中强地震活动特征及周边地震对该地区的影响

鲁东—黄海地块西部为华北地块东侧的次级地块,其地震活动具有显著的周期特征,地块内部的中强地震活动特征和周边大震对该地区的影响对研究该地区地震活动状态有重要意义。采用小波分析方法定量计算了鲁东—黄海地块西部历史地震的活动周期,并结合中强地震活动的定性分析、时空演化、能量释放及周边大震等资料,探讨了该地区的地震活动特征。结果显示:(1)鲁东—黄海地块西部M5.0以上地震活动存在着60.6—78.6 a的长周期,该周期反映了地震活跃—平静的韵律特征,据此M≥5.0地震可划分为活跃时段Ⅰ(1844—1879年)、活跃时段Ⅱ(1905—1949年)和活跃时段Ⅲ(1974年至今)。1997年以来,该地区处于活跃时段末期的弱释放阶段;(2)在三个活跃时段,地震活动的主体地区不同,活跃时段Ⅰ,Ⅱ以海域地震活动为主,并且地震活动水平海域强、陆域弱。活跃时段Ⅲ陆域、海域均有M≥6.0地震活动;(3) 1815年以来,鲁东—黄海地块西部M≥5.0地震与华北M≥6.0地震活动大致同步,当鲁东—黄海地块西部中强地震恰好处于较强活跃时段时,华北地块M6.0地震显著平静后,M≥6.0地震先从鲁东—黄海地块西部开始活动,然后向华北地块中西部地区活动;(4)当太平洋板块西侧的俯冲带上M_(W)≥5.0中深源地震活跃,并发生M_(W)≥7.0地震时,鲁东—黄海地块西部易于发生M_(S)≥6.0地震,这可能是太平洋板块西侧深部俯冲构造动力作用增强导致的结果。

2022年泸定M_(s) 6.8级地震发震构造与鲜水河断裂带强震迁移规律

2022年9月5日12时52分在四川甘孜州泸定县发生Ms6.8级地震,震源深度16 km。这是继2014年康定地震后,发生在鲜水河断裂带上的又一次强震。笔者等通过已有文献资料,结合鲜水河断裂带南段野外地质调查,统计了滑动速率及历史地震资料,并总结了近代鲜水河断裂带强震迁移规律,对认识鲜水河断裂带活动特征及未来地震危险性具有重要意义。主要得出以下几点认识:①鲜水河断裂带各段滑动速率差异较大,以乾宁为界,从NW至SE段整体上呈现出“先减速后加速”的滑动特点;②泸定地震发震构造磨西断裂,为一次左旋走滑事件;③川滇地区近代历史强震活跃期具有“跳跃性”迁移的特点。自1981年道孚地震后,鲜水河断裂带断进入相对平静期,持续了33 a。自2014年康定地震发生,鲜水河断裂带再次进入地震活跃期;④鲜水河断裂带的强震破裂并非单次地震的“贯通型”模式,而是多次地震的渐进式。断层间相互作用尤其是大地震的发生对断裂带强震复发间隔具有重大影响,相同断裂带的强震也会对后续地震的发生概率产生变化。

装配式轻钢框架-轻钢骨架轻混凝土墙板结构抗震性能

为研究装配式轻钢框架-轻钢骨架轻混凝土墙板结构抗震性能,对1个足尺轻钢框架结构试件和3个足尺轻钢框架-轻钢骨架轻混凝土墙板结构试件进行了低周反复荷载下的抗震性能试验及理论分析,试件变量包括:2种装配构造,即内嵌式装配墙板、外贴式装配墙板;2种轻钢骨架轻混凝土墙板,即框架式轻钢骨架轻混凝土墙板、桁架式轻钢骨架轻混凝土墙板。研究了各试件的破坏特征和损伤演化过程,分析了结构滞回特性、承载力、变形能力、刚度退化、耗能性能和应变。结果表明:装配式轻钢框架-轻钢骨架轻混凝土墙板结构共同工作性能良好,其水平承载力相比轻钢框架提高了204.7%~210.4%,抗侧刚度提高了257.3%~512.5%,结构变形及耗能能力有显著提高;内嵌墙板的自攻钉连接构造以及外贴墙板的螺栓连接构造传力性能可靠,结构具备2道抗震防线的受力特征;基于简化塑性分析模型以及拉压杆软化桁架模型,对试件承载力进行了计算,计算结果与试验符合较好。

木构架古建筑基本周期的分析方法

针对现行规范近似公式存在的不足,结合单层、两层砖围护墙木构架古建筑的构造特征,构建了设有集中质量和连续分布质量的悬臂杆分析模型,以考虑屋顶、楼盖的质量和位置,以及围护墙、木构架的质量和刚度分布规律。依据结构动力学原理,采用等效质量法将分析模型等效为单质点悬臂杆模型,推导了中部集中质量和连续分布质量的等效公式,以及基本自振周期的计算公式。所研制的分析模型较好地反映了古建筑的大屋顶、楼盖及围护墙对结构自振周期的影响,相应的计算公式可以得出结构的横向和纵向基本周期。结合3座典型古建筑的动力特性试验研究,介绍了计算公式的运用方法,并将基本周期的计算值与实测值进行了对比,表明提供的分析方法适用于围护墙在横向、纵向不同布置的木构架古建筑的基本周期分析。

Joint observation of long period tremor signals with broadband seismometer,tiltmeter and gravimeter

We report here the observation result of joint observation of long period tremor signals with broadband seismome-ter,tiltmeter and gravimeter at the HUST(Huazhong University of Science and Technology)station.The observed data were compared and analyzed.Since 2005,the several tens of abnormal tremor signals which are weak,com-plex and duration of 2 to 3 days have been synchronously recorded by the different instruments.The tremor signals have the periodic domain in the range of 3 to 5 minutes,20 to 30 minutes and even more than 1 hour.The observa-tion shows such tremors are a physical existence.The analysis indicates that a part of the tremors caused by the typhoon from the western Pacific Ocean.These tremors have a close relationship with wind velocity of typhoon and distance between the typhoon center and the station.Except these,the cause of others is still unclear.

斜入射情形场地基本周期的计算

场地基本周期是场地效应模型的重要变量,是场地分类的重要指标。已有基本周期的计算假定基岩地震波为垂直入射,常用方法包括利用垂直入射情形下场地内SH波竖向一维传播模型建立的模拟与经验方法,其中逐层单自由度法这一经验方法因计算简易、结果与模拟方法相当而被日本抗震设计规范所采纳。然而垂直入射假定大多与实际不符,为此给出可考虑基岩地震波斜入射的场地基本周期计算方法。首先利用Snell定律将基岩斜入射地震波作用下场地内的SH波二维传播表征为一维竖向视传播建立了斜入射情形场地内SH波传播模型。其次利用这一模型给出了斜入射情形基本周期计算的模拟和修正逐层单自由度法并应用于KiK-net台站场地,结果表明基本周期随入射角的增加而变小,就统计所得平均入射角57°而言,基本周期将缩减11%;修正逐层单自由度法可准确考虑斜入射的影响且计算简易度和原方法相当。最后,讨论了基岩面选取对基本周期计算的影响,结果表明,若依据土体首次达到给定剪切波速以确定基岩面,当剪切波速大于700m/s时,不同基岩面所对应的基本周期具有高度线性相关性。

考虑周期折减的结构弹性时程分析调整方法

针对结构弹性时程分析时无法考虑周期折减的问题展开研究,通过对比结构时程分析的过程中,地震波的选取是否考虑周期折减的差异,提出采用增大系数放大时程分析法输入地震波有效峰值加速度以及地震响应;考虑弹性时程分析过程中,周期折减对结构地震作用的增大效应。理论分析增大系数取值的影响因素,并基于单自由度体系对比两种调整方法的效果及差异,采用实际算例以验证所提出弹性时程分析中考虑周期折减调整方法的有效性。结果表明:增大系数的取值与周期折减系数、结构自振周期及场地特征周期等因素有关;对于单自由度体系,两种调整方法具有完全相同的调整效果;按文章提出方法考虑周期折减的算例结构,弹性时程分析所得各楼层地震剪力及层间位移角与考虑周期折减的反应谱(CQC)计算结果均较为接近。

基于结构等效周期选择和谱匹配地震动记录对RC框架结构地震易损性分析的影响

选择合适的地震动记录和地震动强度指标是结构地震易损性分析的基础。首先,分别以加速度反应谱S_(a)(T_(1))值和S_(a)(T_(eq))值为强度指标选取两组地震动记录各20条,并运用谱匹配方法对其进行基于目标设计谱的匹配;其次,输入匹配前后4组地震动记录分别对一个5层和一个11层钢筋混凝土(RC)框架结构模型进行增量动力分析,进而分析谱匹配方法以及不同强度指标对最大层间位移角、结构地震易损性、最大残余层间位移角和抗倒塌储备系数的影响。分析结果表明:输入谱匹配后的两组地震动记录,结构地震易损性结果的离散性明显降低且各损伤状态下50%超越概率对应的谱加速度S_(a)(T_(1),5%)和S_(a)(T_(eq),5%)未发生明显偏差;随着结构损伤程度的增大,以S_(a)(T_(eq))为强度指标可以更有效地减小易损性分析结果的离散性;以抗倒塌储备系数为参考指标,S_(a)(T_(1),5%)作为强度指标进行地震动记录的选取有可能高估结构抗倒塌能力,应考虑以S_(a)(T_(eq),5%)为强度指标更优。

榆神矿区多层厚硬顶板强矿压显现及覆岩破断运动规律研究

针对榆神矿区多层厚硬顶板条件下工作面强矿压和邻空侧巷道变形严重问题,综合采用理论分析、数值计算和微震监测方法,分析了多关键层结构下顶板覆岩破断和邻空侧巷道围岩应力特征。研究结果表明:多层厚硬岩层条件下,顶板破断垂向位移和能量均呈现明显的“低、中、高”分区特征,中高位岩层破断明显滞后于低位岩层,这构成了工作面“大、小周期”的重要结构基础;本工作面开采时,相邻采空区破碎顶板大能量微震事件增多、破断强度较高,并可对邻空回风巷围岩形成强二次采动影响,这是邻空侧回风巷高应力、强变形的主要诱因。同时,高低位多关键层组合破断可导致“大周期”来压发生强度和风险上升,对关键层顶板破断运动规律进行控制是降低“大周期”强度和频率的有效途径之一。

跨走滑断层大跨度桁架悬索桥地震响应分析

跨越断层的长大跨度桥梁难免会受到断层错动作用,为探究跨走滑断层地震动参数对大跨度悬索桥地震响应的影响,以某主跨为538 m的钢桁架悬索桥为例,利用ABAQUS建立考虑桩-土相互作用(“m”法)的全桥有限元模型。通过叠加人工低频地震成分和实际高频地震成分,合成了跨走滑断层地震动,采用非一致激励位移时程法,重点分析永久位移、脉冲周期和跨断层角度对大跨度悬索桥的动力响应影响。结果表明:随着永久位移增大,桥塔动力响应呈不同幅度的增长,特别是横桥向位移、剪力,以及顺桥向弯矩增幅比较明显,分别增大97%、88%和95%,且剪力的增大加剧了桥塔发生剪切破坏的风险;随着脉冲周期减小,桥塔沿顺桥向和横桥向的动力响应增幅差距较大,当脉冲周期小于4 s时,桥塔横桥向位移、剪力,以及顺桥向弯矩相较于另一方向增幅更为明显,其增幅分别为492.5%、170%和189.2%;跨断层角度对桥塔的动力响应影响较大,且沿顺桥向和横桥向的响应变化趋势相反,跨断层角度为90°时,桥塔横桥向位移、剪力取得最大值,而弯矩取得最小值,且桥塔动力响应均在合理范围内,为最佳跨越角度。

RC框架结构基本自振周期个体间不确定性量化

钢筋混凝土(RC)框架结构是城市区域地震风险评估重要对象,其基本自振周期存在明显个体间变异性,如相同高度周期不同。通常采用的确定性结构高度-周期经验公式主要面向新结构设计,未能考虑既有RC建筑物周期的个体间变异性,影响区域地震风险评估的准确性,因此需要合理量化。该研究通过大量文献检索,收集了不同地区的641栋RC框架结构实测长轴、短轴方向基本周期以及高度、结构形式等信息,开展了严格的数据库清洗,并采用物理准则-数据驱动相结合的方式,建立了高度相依基本周期随机函数模型描述个体间变异性。与经典统计回归基本周期随机模型相比,新模型可以更好地反映结构间基本周期的物理机制差异以及观测数据的联合概率特性,便于在区域地震风险评估中应用。

基于等效线性化隔震结构设计周期折减系数研究

《建筑隔震设计标准》提出的隔震设计是基于复振型分解反应谱等效线性化的一体化直接设计方法,但未提及隔震结构周期折减系数如何取值。基于此,根据刚度串联关系推导等效单自由度隔震体系周期折减系数简化计算公式,探讨隔震结构周期折减系数因素的影响规律,建立不同填充材料、不同填充率的有限元数值模型,并利用数值模拟结果验证隔震结构周期折减系数简化计算公式。结果表明:隔震结构周期折减系数与名义周期比、非隔震结构周期折减系数存在函数关系;墙体开洞与通高墙体的隔震结构的周期折减系数均随着填充率的增大而减小,当填充率相同时,呈现出随填充材料弹性模量增大而减小的趋势,墙体开洞会增大隔震结构周期折减系数,且隔震结构的周期折减系数的取值范围相对较窄,为0.915~0.965;数值有限元模拟与理论结果偏差小于3%,吻合度高,以验证隔震结构周期折减系数简化计算公式的正确性,说明该简化计算方法对隔震工程设计具有一定指导意义。