基于HHT变换瞬时能量谱的长周期结构地震反应分析

基于HHT变换得到瞬时能量谱,并以简谐地震反应为理论基础进行多自由度体系在地震动作用下的瞬态反应计算。通过对一个长周期(十五层)结构工程实例的地震瞬态反应计算分析,揭示长周期结构有别于短周期结构动力响应的独特特性:长周期结构位移响应的瞬时能量峰值的时间滞后于地震动能量峰值的时间,且主要受到瞬态振动的控制,并以低阶振型的控制为主,第一阶振型峰值位移滞后的时间最长,滞后的时间主要取决于结构的第一阶自振周期。研究结果表明,长周期结构在强烈地震动作用下,地震动强度出现的最大时刻并不总是对应于结构破环与倒塌的时间。     

基于SDOF体系和高层结构的地震动强度指标研究

合理的地震动强度指标是预测和评价结构抗震响应的重要基础。选取24个周期点的单自由度体系和一个高层框架核心筒长周期结构,基于不同震源机制的100条地震动记录时程分析结果,研究16种地震动强度指标与结构地震响应的相关性,并提出考虑高阶振型影响的改进反应谱相关型地震动强度指标。研究表明：（1）不同地震动强度指标与结构地震响应的相关性差别较大,随着单自由度体系自振周期的增大,地震动强度指标与单自由度体系地震响应的相关性大致呈减小的趋势;（2）对于高层长周期结构,综合对比分析各地震动强度指标分别与顶点最大位移、最大基底剪力、最大层间位移的相关性,从工程实用角度出发,推荐地面运动峰值速度为最佳地震动强度指标;（3）由于高层长周期结构受高阶振型影响显著,采用含有高阶振型因素的反应谱强度指标可提高与结构地震响应的相关性。     

超大型冷却塔随机地震响应分析

为全面掌握核电超大型冷却塔的抗震性能,首先进行结构的模态分析,然后采用振型分解反应谱法和弹性时程分析方法,计算结构在多遇地震作用下的响应,并对结构进行考虑材料和几何非线性的动力弹塑性时程分析,得到结构在罕遇地震作用下的响应。由于超大塔支柱跨度达到170m,还首次对结构进行了考虑行波效应的多点激励分析。结果表明:结构前8阶振型以局部振动为主,直到第9阶出现整体倾覆振型。在多遇地震作用下,支柱的最大位移和基底剪力均满足规范要求,且水平地震反应远大于竖向地震反应。在罕遇地震作用下,支撑结构位移角远小于规范限值,出现的塑性铰数量较少,且主要分布在支柱与壳体的连接处。多点输入对支柱内力影响较为不利,而对支柱位移和塔筒内力影响较小,塑性铰出现的数量稍多且破坏程度更加严重。     

远场长周期地震下基于规范设计隔震结构的抗震性能研究

隔震结构具有较长自振周期,且容易受地震动长周期特性的影响,因此其在长周期地震动作用下的抗震性能值得研究。以某基于规范设计的基础隔震结构为例,通过对该结构在规范规定地震作用和远场长周期地震作用下的地震响应进行分析和对比,研究长周期地震动对结构地震响应的影响;通过对钢筋和混凝土的损伤状态进行定义和标识,探讨长周期地震作用下基础隔震结构的损伤分布规律。研究结果表明,长周期地震动作用下隔震结构发生破坏的概率远大于具有相同峰值地面加速度的普通地震动,其中长周期地震动反应谱的谱峰值"后移"被认为是造成这种情况的主要原因,且长周期地震动作用下隔震结构的损伤分布并不均匀,其主要集中在结构的底层。     

远场地震动长周期特性对基础隔震结构地震响应影响研究

与普通强地震动相比,长周期地震动的低频分量丰富,对长周期结构影响显著。隔震结构作为一类具有较长自振周期的结构,其在长周期地震动作用下的动力行为值得研究。选取远场长周期地震记录和远场普通地震记录作为外部激励,以某基础隔震结构作为研究对象,研究了远场地震记录的长周期特性,及其对隔震层和上部结构地震响应的影响。研究结果表明:远场地震动长周期特性对结构地震响应的影响显著,远场长周期地震记录下结构的地震响应明显大于远场普通地震记录,在隔震结构设计中应考虑其不利影响;地震动功率谱与结构地震响应之间存在明显联系,应进行深入研究。研究结果可为长周期地震动作用下隔震结构的抗震设计提供参考。     

旋转地震合成及其在大跨度悬索桥中的应用

为探究旋转地震动在大跨度悬索桥中的应用,首先,从线弹性理论和功率谱角度基于随机振动理论提出了6维地震动加速度功率谱模型;其次,基于MATLAB编制旋转地震动人工地震合成程序,从反应谱角度对合成地震动进行了正确性验证和拟合精度迭代调整;最后,分析了旋转地震动与地震动入射角对桥梁结构地震响应的影响。研究表明：人工合成的地震动平动分量反应谱与实测地震动的平动分量反应谱吻合度较高;六维地震动的主梁跨中竖向位移越是三维平动地震动的3倍,而主缆轴力峰值接近2.25E+05kN,约是三维平动地震动的1.3倍;旋转地震动和地震动入射角将会加大桥梁结构的位移响应和内力响应,且会减小塔底截面和桩最不利截面的安全性。     

地震动速度脉冲对巨型结构体系地震响应影响研究

以巨-子结构抗震体系、隔震体系以及智能隔震体系为研究对象,选择4组具有速度脉冲特性的实际地震动加速度记录及人工模拟的具有相同加速度反应谱而无速度脉冲的地震动时程分别作为地震动输入,采用数值分析方法分别计算在有、无速度脉冲的地震动激励下三种结构体系的地震响应,探讨地震动的速度脉冲对巨型结构体系在不同控制策略下地震响应的影响。研究结果表明:三种结构体系在速度脉冲型地震动作用下的地震响应大部分要大于无速度脉冲型的地震响应,近断层地震动的速度脉冲对巨-子结构抗震体系、隔震体系以及智能隔震体系的地震响应均有一定的不利影响。智能隔震体系对速度脉冲地震动较为敏感,但能有效地减小隔震层位移。     

大跨度公铁两用斜拉桥群桩基础地震响应研究

为了解大跨度公铁两用斜拉桥群桩基础的地震响应行为,总结了该类桥梁基础的总体结构特征,探讨了基础的抗震分析模型,提出了估计高桩承台基础地震响应的实用性方法,分析了该类型基础的抗震安全度和地震响应特征。研究表明:承台等效振型参与度大小与地震动长周期成分的频谱特性有关,当忽略该因素影响时其取值分布较为平稳; E2与E1地震作用下桩基抗震安全度的比值平均大小为0. 65左右;高桩承台基础最不利位置一般在桩头处,且通常表现为大偏心受压;一般冲刷线以上桩身内力呈线性分布;自一般冲刷线以下,桩身轴力基本保持不变,剪力和弯矩呈先增大后减小的曲线分布规律。     

大跨度空间网格结构在地震行波作用下的响应

本文对地震行波三向正交分量分别独立作用和联合作用下的大跨度空间网格结构的地震响应（包括结构控制点的位移，杆件内力，柱底弯矩等）进行了数值分析，结果表明，与一致地震振动相比，地震动的行波效应可使大跨度空间网格结构的控制点位移增大21%，柱脚弯矩增大79%，杆件内力增大100%，因此，在大跨度空间结构的抗震分析中必须进行详细的抗震分析。     

最不利设计地震动研究

实际记录到的真实地震动在工程结构的抗震研究、分析和设计中往往作为一种施加到结构上使结构振动，直至破坏的地震荷载．如何合理选择真实的地震动记录作为研究结构地震反应的输入，一直是国内外抗震研究和设计中引人关注的重要问题．本文首先提出了最不利设计地震动的概念；然后在收集到的国内外5000余条被认为有重要意义的地震动记录基础上，利用综合估计地震动潜在破坏势的方法，对４种场地类型分别给出了长周期、短周期和中周期结构的国内外最不利设计地震动；最后通过几类不同结构的地震反应分析，初步验证了本文所确定的最不利设计地震动的可靠性和合理性．      

Shaking table test and numerical analysis of offshore wind turbine tower systems controlled by TLCD

A wind turbine system equipped with a tuned liquid column damper(TLCD) is comprehensively studied via shaking table tests using a 1/13-scaled model. The effects of wind and wave actions are considered by inputting responseequivalent accelerations on the shaking table. The test results show that the control effect of the TLCD system is significant in reducing the responses under both wind-wave equivalent loads and ground motions, but obviously varies for different inputs. Further, a blade-hub-tower integrated numerical model for the wind turbine system is established. The model is capable of considering the rotational effect of blades by combining Kane’s equation with the finite element method. The responses of the wind tower equipped with TLCD devices are numerically obtained and compared to the test results, showing that under both controlled and uncontrolled conditions with and without blades’ rotation, the corresponding responses exhibit good agreement. This demonstrates that the proposed numerical model performs well in capturing the wind-wave coupled response of the offshore wind turbine systems under control. Both numerical and experimental results show that the TLCD system can significantly reduce the structural response and thus improve the safety and serviceability of the offshore wind turbine tower systems. Additional issues that require further study are discussed.     

Study on the severest real ground motion for seismic design and analysis

How to select the adequate real strong earthquake ground motion for seismic analysis and design of trucures is an essential problem in earthquake engineering research and practice.In the paper the concept of the severest design ground motion is proposed and a method is developed for comparing the severity of the recorded strong ground motions.By using this method the severest earthquake ground motions are selected out as seismic inputs to the structures to be designed from a database that consists of more than five thousand significant strong ground moton records collected over the world.The selected severest ground motions are very likely to be able to drive the structures to their critical response and thereby result in the highest damage potential.It is noted that for different structures with diffferent predominant natural periods and at different sites where structures are located the severest design ground motions are usually different.Finally.two examples are illustrated to demonstrate the rationality of the concept and the reliability of the selected design motion.     

运行状态下海上单桩风机系统自振频率分析

系统自振频率限制是海上风机结构设计中的一个关键因素。运行状态下风机动力荷载会引起基础的水平侧移,较大的水平侧移会导致基础刚度的降低,进一步影响风机系统的自振频率。该文基于有限元软件ABAQUS平台,建立单桩式海上风机结构系统的自振频率数值模型,并讨论运行状态下基础水平侧移对大直径海上风机系统自振频率的影响。模型中考虑了塔筒的变截面特性;桩-土相互作用通过p-y曲线方法模拟;桩和塔采用梁单元模拟;通过Pushover分析汇总出水平侧移引起的桩顶水平刚度。研究结果表明:桩基侧向位移会降低风机结构体系的自振频率;桩基侧向位移对基频的影响较小,对高阶频率的影响显著;大直径海上风机的频率计算中可忽略风机运行状态对体系自振频率的影响。     

一种改进后的海上风机动力特性理论分析方法研究

海上风机是一种高柔性海洋结构物,其支撑结构的动力响应对风、浪、流等环境因素、风机荷载及基础刚度的影响异常敏感。建立基础-塔架-顶部集中质量为一体的风机简化计算模型,在底部弹性约束条件下考虑水平刚度和转动刚度之间的耦合。基于改进后的计算模型、经典微分方程及其边界条件,通过对方程的求解,系统研究底部基础刚度和顶部竖向轴压等设计参数对结构前四阶自振频率的影响规律。本文研究结论在一定程度上可揭示风机运行过程中因基础刚度变化而引起的支撑结构动力特性变化规律,可为今后实际工程中风机基础、支撑结构的选型及设计提供相关启示。     

脉冲型地震动作用下隔震结构动力响应的影响参数研究

通过对隔震结构进行非线性动力响应分析,分别研究地震动参数和支座参数对结构地震响应的影响。首先,建立铅芯橡胶支座基础隔震结构的非线性运动方程;然后,以人工合成脉冲型地震动作为输入,运用MATLAB进行编程并求解结构在脉冲型地震动作用下的地震响应;最后,分别研究速度脉冲周期、支座屈服力、屈服后与屈服前的刚度比对隔震支座最大位移和上部结构层间位移的影响。研究结果表明,脉冲周期对结构地震响应影响很大,在进行隔震设计时应使结构自振周期远离脉冲周期;支座刚度比对结构地震响应影响较大,在进行支座选型时应重点关注;支座屈服力对支座位移的影响显著,屈服力越大,支座位移越小。     

An assessment of seaonc draft code for resilient sliding isolators

The displacement responses of rigid structures supported on resilient sliding isolation systems with various frictions to six different ground motions normalized to ground velocity levels from 1 to 25 in per sec are evaluated. Through the application of an equivalent damping procedure, the minimum required displacement capacities as dictated by the SEAONC draft code are also estimated. It is concluded that, even though the code displacement requirement is on the conservative side, the displacement capacity requirement is not excessive.     

双向地震动作用的拟等延性系数谱

首先建立了以强度折减系数表述的恢复力特性满足二维屈服面模型的理想弹塑性单质点系统(它在2个相互垂直的主轴方向上分别具有水平平动自由度)在双向地震动作用下的归一化运动方程。然后引入单向地震动作用下等延性系数的强度折减系数谱,给出了双向地震动作用的拟等延性系数谱(定义为系统分别承受双向和单向地震动作用,在同一主轴方向上的最大位移反应之比)最后通过硬土场地10组双向地震动记录拟等延性系数谱的统计平均结果,分析了结构周期、位移延性系数和阻尼等因素对谱值及结构双向地震反应的影响。结果表明,双向地震动作用与单向地震动作用相比主要增加结构较长周期方向的最大位移反应。若在基于位移的抗震设计中降低结构较短周期方向的设计位移延性系数,可在一定程度上降低双向地震动的不利影响。因定义的谱为比值形式,阻尼对其影响不大。     

Kinematic soil-structure interaction effects on maximum inelastic displacement demands of SDOF systems

This paper presents a statistical study of the kinematic soil-foundation-structure interaction effects on the maximum inelastic deformation demands of structures. Discussed here is the inelastic displacement ratio defined as the maximum inelastic displacement demands of structures subjected to foundation input motions divide by those of structures subjected to free-field ground motions. The displacement ratio is computed for a wide period range of elasto-plastic single-degree-of-freedom (SDOF) systems with various levels of lateral strength ratios and with different sizes of foundations. Seventy-two earthquake ground motions recorded on firm soil with average shear wave velocities between 180 m/s and 360 m/s are adopted. The effects of period of vibration, level of lateral yielding strength and dimension of foundations are investigated. The results show that kinematic interaction will reduce the maximum inelastic displacement demands of structures, especially for systems with short periods of vibration, and the larger the foundation size the smaller the maximum inelastic displacement becomes. In addition, the inelastic displacement ratio is nearly not affected by the strength ratio of structures for systems with periods of vibration greater than about 0.3 s and with strength ratios smaller than about 3.0. Expressions obtained from nonlinear regression analyses are also proposed for estimating the effects of kinematic soil-foundation-structure interaction from the maximum deformation demand of the inelastic system subjected to free-field ground motions.     

Centrifuge modeling of offshore wind foundations under earthquake loading

The construction of large offshore wind turbines in seismic active regions has great demand on the design of foundations. The occurrence of soil liquefaction under seismic motion will affect the stability of the foundations and consequently the operation of the turbines. In this study, a group of earthquake centrifuge tests was performed on wind turbine models with gravity and monopile foundations, respectively, to exam their seismic response. It was found that the seismic behavior of models was quite different in the dry or saturated conditions. Each type of foundation exhibited distinct response to the earthquake loading, especially in the offshore environment. In the supplementary tests, several remediation methods were evaluated in order to mitigate the relatively large lateral displacement of pile foundation (by fixed-end pile and multi-pile foundation) and excessive settlement of gravity foundation (by densification, stone column, and cementation techniques).