Influences of nonassociated flow rules on seismic bearing capacity factors of strip footing on soil slope by energy dissipation method

Seismic bearing capacity factors of a strip footing placed on soil slope were determined with both associated and nonassociated flow rules. Quasi-static representation of earthquake effects using a seismic coefficient concept was adopted for seismic bearing capacity calculations. A multi-wedge translational failure mechanism was used to obtain the seismic bearing capacity factors for different seismic coefficients and various inclined angles. Employing the associated flow rule, numerical results were compared with the published solutions. For bearing capacity factors related to cohesion and equivalent surcharge load, the maximum difference approximates 0.1%. However, the difference of bearing capacity factor related to unit weight is larger. With the two flow rules, the seismic bearing capacity factors were presented in the form of design charts for practical use. The results show that seismic bearing capacity factors related to the cohesion, the equivalent surcharge load and the unit weight increase greatly as the dilatancy angle increases, and that the nonassociated flow rule has important influences on the seismic bearing capacity.

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.

SEISMIC RANDOM VIBRATION ANALYSIS OF STOCHASTIC STRUCTURES USING RANDOM FACTOR METHOD

Seismic random vibration analysis of stochastic truss structures is presented. A new method called random factor method is used for dynamic analysis of structures with uncertain parameters, due to variability in their material properties and geometry. Using the random factor method, the natural frequencies and modeshapes of a stochastic structure can be respectively described by the product of two parts, corresponding to the random factors of the structural parameters with uncertainty, and deterministic values of the natural frequencies and modeshapes obtained by conventional finite element analysis. The stochastic truss structure is subjected to stationary or non-stationary random earthquake excitation. Computational expressions for the mean and standard deviation of the mean square displacement and mean square stress are developed by means of the random variable＇s functional moment method and the algebra synthesis method. An antenna and a truss bridge are used as practical engineering examples to illustrate the application of the random factor method in the seismic response analysis of random structures under stationary or non-stationary random earthquake excitation.

Seismic design factors for RC special moment resisting frames in Dubai,UAE

This study investigates the seismic design factors for three reinforced concrete （RC） framed buildings with 4, 16 and 32-stories in Dubai, UAE utilizing nonlinear analysis. The buildings are designed according to the response spectrum procedure defined in the 2009 International Building Code （IBC＇09）. Two ensembles of ground motion records with 10% and 2% probability of exceedance in 50 years （10/50 and 2/50, respectively） are used. The nonlinear dynamic resPonses to the earthquake records are computed using IDARC-2D. Key seismic design parameters are evaluated; namely, response modification factor （R）, deflection amplification factor （Cd）, system overstrength factor （Ωo）, and response modification factor for ductility （Rd） in addition to inelastic interstory drift. The evaluated seismic design factors are found to significantly depend on the considered ground motion （10/50 versus 2/50）. Consequently, resolution to the controversy of Dubai seismicity is urged. The seismic design factors for the 2/50 records show an increase over their counterparts for the 10/50 records in the range of 200%-400%, except for the D~ factor, which shows a mere 30% increase. Based on the observed trends, perioddependent R and Cd factors are recommended if consistent collapse probability （or collapse prevention performance） in moment frames with varying heights is to be expected.

Seismicity Factor A-Value and Its Application to Mid-Term Earthquake Prediction in North China

The seismicity factor A-value is defined by synthesizing the seismicity precursors in time, space and magnitude in this paper. The seismicity data of moderate or small earthquakes during 1972 ~ 1996 in North China are used to perform spacial scanning of seismicity factor A-value. The result shows that there are obviously anomaly zones of A-value with better prediction effect in the mid-term of 2~3 years before most moderately strong earthquakes. Some problems regarding the mid-term prediction using A-value have been discussed.

Assessment of seismic design response factors of concrete wall buildings

To verify the seismic design response factors of high-rise buildings, five reference structures, varying in height from 20- to 60-stories, were selected and designed according to modern design codes to represent a wide range of concrete wall structures. Verified fiber-based analytical models for inelastic simulation were developed, considering the geometric nonlinearity and material inelasticity of the structural members. The ground motion uncertainty was accounted for by employing 20 earthquake records representing two seismic scenarios, consistent with the latest understanding of the tectonic setting and seismicity of the selected reference region （UAE）. A large number of Inelastic Pushover Analyses （IPAs） and Incremental Dynamic Collapse Analyses （IDCAs） were deployed for the reference structures to estimate the seismic design response factors. It is concluded that the factors adopted by the design code are adequately conservative. The results of this systematic assessment of seismic design response factors apply to a wide variety of contemporary concrete wall buildings with various characteristics.

山东平原M5.5地震区域的地震活动性参数因子分析

引入因子分析方法,对平原地震区域中小震序列的16种地震活动性参数进行降维综合,发现目前综合指数W处于平静幕的最高值区。通过进一步单因子分析结果推测,平原地震区域地下介质可能发生变化,未来华北地区地震活动性有增强趋势。

基于持时-条件谱双准则选取地震动的RC框架结构地震损伤分析

采用持时-条件谱双准则选择地震动记录,以损伤指数为性能指标对结构进行地震损伤分析。首先,根据选择的性能目标,确定不同水准地震加速度反应谱S_(a)(T_(1),5%),通过概率地震危险解聚分析确定不同水准S_(a)(T_(1),5%)对应的设计震级和设计震中距,结合地震动重要持时预测模型,通过调节持时预测模型标准差系数的范围,构建满足重要持时要求的待选地震动记录库。其次,建立地震动条件谱,从待选地震动记录库中选择地震动,并验证持时-条件谱双准则选择地震动记录方法的有效性。最后,以选择地震动为输入对一钢筋混凝土框架结构进行增量动力分析,结合考虑构件重要性系数的变形-滞回耗能双参数损伤模型,以损伤指数为性能指标分析结构的地震损伤。研究表明,与仅利用条件谱作为目标谱选择地震动相比,基于持时-条件谱双准则的地震动选取方法对结构变形和滞回耗能响应的离散性均可控且效果良好;对结构进行地震损伤分析发现,滞回耗能引起损伤的占比随S_(a)(T_(1),5%)的增大明显增大,同时滞回耗能可使结构的损伤模式发生改变,在地震损伤分析中不可忽略。

煤田震电协同勘探技术研究与应用

近年来煤田震电协同勘探技术在设计、处理分析方面都取得了较大的发展,从采区最常使用的三维地震勘探、瞬变电磁勘探方法入手,对采集到的各种数据运用主成分分析(PCA)进行融合处理,解译煤矿采区工作面的异常地质体及富水性等隐蔽致灾因素。该技术实现了三维地震、瞬变电磁勘探在数据层面的综合勘探,提高了物探解释煤矿采区工作面地质异常体(富水性)的准确性,为震电协同勘探技术体系的构建提供了新思路,为煤矿安全、高效、绿色生产提供了保障。

基于等效钢筋连接的连梁和剪力墙节点抗震性能研究

目的 研究基于等效钢筋连接的连梁和剪力墙节点的抗震性能,为装配式混凝土连梁和剪力墙的连接设计提供依据。方法 采用WCOMD有限元软件建立现浇连梁及装配连梁模型,对比分析二者的受力破坏过程。结果 未考虑连梁端部破坏向墙内扩展时,装配连梁与现浇连梁相比,屈服荷载、峰值荷载和极限荷载分别提高3.98%、15.19%和12.76%,延性和能量耗散系数分别提高3.83%和15.84%;未考虑连梁端部破坏向墙内扩展与考虑连梁端部破坏向墙内扩展的装配连梁相比,屈服荷载、峰值荷载和极限荷载分别提高5.97%、0.84%和3.57%,延性和能量耗散系数分别提高1.07%和23.76%。结论 采用等效钢筋连接连梁和剪力墙的方法具有可行性,且等效钢筋面积比、装配区灌浆长度及装配位置对结构的承载力影响较大。

积石山Ms6.2级和泸定Ms6.8级地震地质灾害发育规律对比

2023年积石山Ms6.2级地震是继2022年泸定Ms6.8级地震后在青藏高原东缘—东北缘地区发生的又一次强震事件。2次地震均诱发大量地震地质灾害,但由于发震断层类型、地质和地貌等条件的差异,2次地震地质灾害发育分布规律呈现显著的差异性。为揭示不同震区地震地质灾害发育规律,本研究采用地面调查、遥感解译和空间叠加统计等方法,对比分析了积石山和泸定地震地质灾害发育分布特征和控灾因子。结果表明:断层类型控制了同震地质灾害的发育优势坡向和垂向空间展布,即“背向坡效应”和“上下盘效应”;地貌条件是影响同震地质空间分布的主要因子,即川西高山峡谷地貌中“线状”分布和陇西黄土地貌中“面状”分布;特殊土体类型、气候、植被覆盖等差异性是同震地质灾害调查与应急处置中需要重点关注的因子。本次研究可为不同断层类型和不同地貌区同震地质灾害重点防范区范围划定、趋势预测和灾后重建提供科学参考。

三心拱断面地下管廊结构地震动力响应分析

针对地下管廊抗震的问题,以郑州市耿河变电站到博文变电站之间的三心拱断面地下管廊为研究对象,利用ANSYS Workbench软件建立三维实体模型,对其进行前6阶的模态分析,发现该管廊存在纵向振动、竖向振动、横向振动以及转动。基于模态分析,对管廊在水平地震和竖向地震作用下的位移响应、加速度响应和主应力响应进行分析。结果表明:最大的水平和竖向位移峰值分别为-24.222 mm和-8.954 mm;最大加速度峰值分别为3354.2 mm/s^(2)和1646.0 mm/s^(2);第一主应力峰值分别为514.7 kPa和244.15 kPa;第三主应力峰值分别为-608.15 kPa和-256.71 kPa,可得出水平地震占主导作用。对管廊的横向地震动力时程进行分析,改变频谱特性、结构材料强度、结构埋深等参数,分析其对管廊抗震性能的影响。得到研究的管廊结构在地震波频谱特性约为1.1 Hz时最为敏感;混凝土强度的改变对管廊结构的动力响应影响不大;随管廊埋设深度的增加,周边土压力加大,使其内力逐步上升。

被动陆缘深水海底限制性水道三维地震表征及沉积演化——以纳米贝盆地为例

【目的】被动陆缘盆地深水浊积砂体已成为深海油气勘探突破及储量发现的新领域。【方法】以典型被动陆缘纳米贝盆地深水高分辨率三维地震资料为研究基础,以受构造活动和沉积压实影响较小而保持原始水道沉积构型的海底第四纪沉积地层为目标,精细描述和解析了目标层内限制性水道沉积的剖面和平面地震响应特征。【结果与结论】限制性浊积水道侵蚀作用总体大于沉积作用,单一水道的沉积模式以凹岸侵蚀、凸岸“S”型加积为主,该过程使“V”型河谷展宽并充填形成“U”型水道沉积;多期叠置水道沉积体系分为侧切叠置和垂切叠置的两种模式,以侧切叠置模式为主;窄陆架、宽缓陆坡的海底地形控制限制性水道的延伸方向及长度规模,陆缘盆地的沉降中心控制着各期水道的迁移方向,古气候事件发生频率控制着水道体系内部浊积砂体发育的期次。该研究成果能够给予限制性水道沉积构型认识及砂体储层预测启发。

Application of fluid modulus inversion to complex lithology reservoirs in deep-water areas

It has been a challenge to distinguish between seismic anomalies caused by complex lithology and hydrocarbon reservoirs using conventional fluid identification techniques,leading to difficulties in accurately predicting hydrocarbon-bearing properties and determining oil-water contacts in reservoirs.In this study,we built a petrophysical model tailored to the deep-water area of the Baiyun Sag in the eastern South China Sea based on seismic data and explored the feasibility of the tri-parameter direct inversion method in the fluid identification of complex lithology reservoirs,offering a more precise alternative to conventional techniques.Our research found that the fluid modulus can successfully eliminate seismic amplitude anomalies caused by lithological variations.Furthermore,the seismic databased direct inversion for fluid modulus can remove the cumulative errors caused by indirect inversion and the influence of porosity.We discovered that traditional methods using seismic amplitude anomalies were ineffective in detecting fluids,determining gas-water contacts,or delineating high-quality reservoirs.However,the fluid factor Kf,derived from solid-liquid decoupling,proved to be sensitive to the identification of hydrocarbon-bearing properties,distinguishing between high-quality and poor-quality gas zones.Our findings confirm the value of the fluid modulus in fluid identification and demonstrate that the tri-parameter direct inversion method can significantly enhance hydrocarbon exploration in deep-water areas,reducing associated risks.

2023年12月18日甘肃积石山6.2级地震及启示

介绍了2023年12月18日甘肃积石山6.2级地震的发生、震前预测、震后趋势判断、地震动参数设定,震区构造、震害特征和周边地震活动的基本情况,对地震发生日期的调制,相互构造影响作用进行了分析,对此影响未来发震的可能性也做了简单分析,认为与之相交的南边和北边断裂危险性会增加,尤其西秦岭北缘断裂处在甘肃东部段地震可能性增大。对地震区历次烈度区划(地震动区划)的设定进行了阐述和回顾。重点在此次地震产生灾害的基础上针对地震科学与社会政策提出建议。

基于粒子群优化算法的地震数据品质因子及混合相位子波同时估计

非稳态地震数据高分辨率处理及反演是通过求解包含地震子波滤波效应及地层吸收衰减效应的反演方程,获得地下反射界面的地震响应。为实现高分辨率处理及反演中初始地震子波及数据品质因子Q模型的实施条件,结合地震子波Z变换的根移动编码及等效Q模型的二进制—十进制转换策略,引入粒子群全局优化算法,建立非稳态地震数据混合相位初始地震子波及数据品质因子同时估计的方法。利用井旁道与数据的互相关作为准则函数,判定粒子群是否收敛至最大,输出最佳初始地震子波及Q。应用理论合成数据和实际数据测试进行验证。结果表明:相较于传统常相位地震子波估计及反Q滤波,该方法在复杂干扰条件下能更精确捕获真实的子波波形及衰减参数。利用输出的地震子波及Q进行时变反褶积处理得到高分辨率剖面,说明方法具有准确性、计算效率高且输出结果优,估计的地震子波和Q更符合实际地震波传播特征,为后续高分辨率地震数据处理提供基本参数。

基于强震记录的大阪盆地竖向地震动的放大效应研究

文章基于日本KIK-net强震观测台网,分离大阪盆地水平向与竖向分量S波和盆地次生波,并为研究竖向地震动与水平向的关系,采用井上井下谱比法分析。研究表明,盆地中竖向分量S波和盆地次生波放大倍数虽整体小于水平分量,但在不同周期内不同盆地深度竖向S波、次生波放大均有超抗震设计时,竖向地震动峰值取水平峰值的最大值2/3;盆地S波与次生波对浅层土层竖向地震动的影响明显大于深层土层,并且在长周期中影响逐渐增大。

应用遗传算法估计非稳态地震数据的混合相位子波及Q值

地震高分辨率处理或反演的目的是获得精确的反射系数或弹性参数模型。然而地层滤波效应模糊了地震记录中的地层反射信息,因此有必要消除这种滤波效应。现有的大部分提高分辨率方法并不能完全摒弃关于地震子波和Q模型的一些假设。为了获得更为切合实际的地震子波,同时自适应获取Q模型,文中将地震子波相位估计与Q模型估计相结合,提出了基于遗传算法的非稳态地震数据混合相位子波及Q值估计方法。首先通过井旁道记录拟合得到初始地震子波的振幅信息,然后依据子波Z变换的根关于单位圆移动与否构建用于遗传算法的编码链条。另一方面,十进制Q模型对应的二进制表示形式同样能够利用编码链条表征,因此利用全局优化算法能够同时估计地震混合相位子波以及Q模型。结合根变换和遗传算法不断改变子波相位的同时自适应生成Q模型,利用子波和Q模型构造的时变子波矩阵与测井反射系数得到合成地震记录,并与井旁道记录进行匹配,最终得到合理的混合相位子波和地层Q模型,进而构造时变子波矩阵进行时变反褶积。通过井旁道记录与测井数据拟合得到的混合相位子波,与实际地震子波相位更为接近,理论数据和实际数据处理结果证实了该方法的有效性。

柔性连接AAC填充墙钢框架抗震性能影响因素数值分析

为分析不同因素变化对柔性连接蒸压加气混凝土(autoclaved areated concrete,AAC)砌体填充墙钢框架抗震性能影响的趋势和显著性,基于拟静力试验结果验证了建模方式及参数选取的可行性,采用ABAQUS建立9个有限元正交模型,对模型轴压比、预留缝宽、耗能材料刚度和高跨比进行变参分析。研究结果表明:预留缝宽、耗能材料刚度、高跨比和轴压比对结构抗震性能指标影响的显著性依次降低。整体上,增大预留缝宽,减小耗能材料刚度、高跨比以及轴压比对提高结构的抗震性能有利。实际应用中建议柔性连接AAC墙框间缝宽取值在40 mm左右,缝间填充材料的刚度宜在100~500 N/mm之间。

风与地震作用下平面索网幕墙系统的动力性能研究

平面索网幕墙被广泛应用于大型公共建筑中,因具有阻尼小、刚度低、非线性强等特点,其在强风与地震作用下易出现索力突变、变形过大、面板损伤等不利现象。建立了索网幕墙系统的精细化数值模型,量化了风、地震作用下相邻主结构对幕墙动力性能的影响,分析了两种灾害共同作用下的索网动力响应及面板、密封胶安全状态,计算了幕墙的风振系数并与规范参考值进行对比。研究结果表明:考虑主结构影响的索网幕墙的频率平均减小了12%,地震作用下中部拉索的峰值位移比为6.5,远大于风致响应,计算索网幕墙的地震响应时不可忽略主结构的影响。两种灾害共同作用时,索网位移的增幅大于索力的增幅,位移响应对外部激励变化更加敏感,且位于幕墙顶部的玻璃面板与密封胶的应力均超过设计强度,应在运维过程中予以重点关注。此外,对索网幕墙风致响应结果进行数理统计,得到了可供工程设计参考的风振系数。