An extended multiple-support response spectrum method incorporating fluid-structure interaction for seismic analysis of deep-water bridges

The effects of ground motion spatial variability(GMSV)or fluid-structure interaction(FSI)on the seismic responses of deep-water bridges have been extensively examined.However,there are few studies on the seismic performance of bridges considering GMSV and FSI effects simultaneously.In this study,the original multiple-support response spectrum(MSRS)method is extended to consider FSI effect for seismic analysis of deep-water bridges.The solution of hydrodynamic pressure on a pier is obtained using the radiation wave theory,and the FSI-MSRS formulation is derived according to the random vibration theory.The influence of FSI effect on the related coefficients is analyzed.A five-span steel-concrete continuous beam bridge is adopted to conduct the numerical simulations.Different load conditions are designed to investigate the variation of the bridge responses when considering the GMSV and FSI effects.The results indicate that the incoherence effect and wave passage effect decrease the bridge responses with a maximum percentage of 86%,while the FSI effect increases the responses with a maximum percentage of 26%.The GMSV and FSI effects should be included in the seismic design of deep-water bridges.

A simplified multisupport response spectrum method

A simplified multisupport response spectrum method is presented.The structural response is a sum of two components of a structure with a first natural period less than 2 s.The first component is the pseudostatic response caused by the inconsistent motions of the structural supports,and the second is the structural dynamic response to ground motion accelerations.This method is formally consistent with the classical response spectrum method,and the effects of multisupport excitation are considered for any modal response spectrum or modal superposition.If the seismic inputs at each support are the same,the support displacements caused by the pseudostatic response become rigid body displacements.The response spectrum in the case of multisupport excitations then reduces to that for uniform excitations.In other words,this multisupport response spectrum method is a modification and extension of the existing response spectrum method under uniform excitation.Moreover,most of the coherency coefficients in this formulation are simplified by approximating the ground motion excitation as white noise.The results indicate that this simplification can reduce the calculation time while maintaining accuracy.Furthermore,the internal forces obtained by the multisupport response spectrum method are compared with those produced by the traditional response spectrum method in two case studies of existing long-span structures.Because the effects of inconsistent support displacements are not considered in the traditional response spectrum method,the values of internal forces near the supports are underestimated.These regions are important potential failure points and deserve special attention in the seismic design of reticulated structures.

Response Spectrum Method for Extreme Wave Loading With Higher Order Components of Drag Force

Response spectra of fixed offshore structures impacted by extreme waves are investigated based on the higher order components of the nonlinear drag force. In this way, steel jacket platforms are simplified as a mass attached to a light cantilever cylinder and their corresponding deformation response spectra are estimated by utilizing a generalized single degree of freedom system. Based on the wave data recorded in the Persian Gulf region, extreme wave loading conditions corresponding to different return periods are exerted on the offshore structures. Accordingly, the effect of the higher order components of the drag force is considered and compared to the linearized state for different sea surface levels. When the fundamental period of the offshore structure is about one third of the main period of wave loading, the results indicate the linearized drag term is not capable of achieving a reliable deformation response spectrum.

Comparison between Response Spectrum and Time History Method of Dynamic Analysis of Concrete Gravity Dam

Dam structure built to store water has failed with resulting loss of life, social, economic and environmental losses due to seismic vibrations. These vibrations are dynamic in nature. These vibrations must be reduced with proper application of engineering principles and for estimating the behavior of concrete gravity dam dynamic analysis plays an extraordinary role. This paper presents the dynamic time history analysis and response spectrum method of a concrete gravity dam by using STAAD-PRO. Here Finite Element Approach is used to analyze the dam. A concrete gravity dam model is prepared in STAAD-PRO to perform the time history analysis and response spectrum analysis and a comparison is done between both these methods. Concrete gravity dam is a large structure which retains a very large amount of water on its upstream side and it is very crucial for a dam to survive against vibrations of earthquake. So it is a matter of study to check the behaviour of a dam during and after the application of the loading.

Efficient simulation of spatially correlated non-stationary ground motions by wavelet-packet algorithm and spectral representation method

Although the classical spectral representation method(SRM)has been widely used in the generation of spatially varying ground motions,there are still challenges in efficient simulation of the non-stationary stochastic vector process in practice.The first problem is the inherent limitation and inflexibility of the deterministic time/frequency modulation function.Another difficulty is the estimation of evolutionary power spectral density(EPSD)with quite a few samples.To tackle these problems,the wavelet packet transform(WPT)algorithm is utilized to build a time-varying spectrum of seed recording which describes the energy distribution in the time-frequency domain.The time-varying spectrum is proven to preserve the time and frequency marginal property as theoretical EPSD will do for the stationary process.For the simulation of spatially varying ground motions,the auto-EPSD for all locations is directly estimated using the time-varying spectrum of seed recording rather than matching predefined EPSD models.Then the constructed spectral matrix is incorporated in SRM to simulate spatially varying non-stationary ground motions using efficient Cholesky decomposition techniques.In addition to a good match with the target coherency model,two numerical examples indicate that the generated time histories retain the physical properties of the prescribed seed recording,including waveform,temporal/spectral non-stationarity,normalized energy buildup,and significant duration.

Comparison of Design Response Spectrum for Long Period Structures Based on Scenario Earthquakes

Two kinds of determining methods for scenario earthquakes are presented in this paper,namely the weighted average method and maximum probability method. This paper briefly introduces the two methods,then taking a high-rise building in the Yantai area as a case study,we use the weighted average method and maximum probability method to realize seismic hazard analysis, determine earthquake magnitude, the epicenter and specific space position,and then give two response spectrums of the two methods. By comparing the differences of response spectrums between the two methods,we find that the weighted average method is more suitable for long period structures,while considering long period safety. The maximum probability method is more suitable for short period structures. It is reasonable to choose a corresponding different method when the structures have different natural vibration periods.

Stochastic Response Analysis of Piled Offshore Platforms to Earthquake Load

In this paper, using the theory of stochastic analysis of the response to earthquake load, a stochastic analysis method of the response of piled platforms to earthquake load has been established. In the method, the strong ground motion is considered as three dimensional stationary white noise process and the pile-soil interaction and water-structure interaction are considered. The stochastic response of a typical platform to earthquake load has been computed with this method and the results compared with those obtained with the response spectrum analysis method. The comparison shows that the stochastic analysis method of the response of piled platforms to earthquake load is suitable for this kind of analysis.

Dynamic modeling of ultra-precision fly cutting machine tool and the effect of ambient vibration on its tool tip response

The dynamic performances of an ultra-precision fly cutting machine tool(UFCMT)has a dramatic impact on the quality of ultra-precision machining.In this study,the dynamic model of an UFCMT was established based on the transfer matrix method for multibody systems.In particular,the large-span scale flow field mesh model was created;and the variation in linear and angular stiffness of journal and thrust bearings with respect to film thickness was investigated by adopting the dynamic mesh technique.The dynamic model was proven to be valid by comparing the dynamic characteristics of the machine tool obtained by numerical simulation with the experimental results.In addition,the power spectrum density estimation method was adopted to simulate the statistical ambient vibration excitation by processing the ambient vibration signal measured over a long period of time.Applying it to the dynamic model,the dynamic response of the tool tip under ambient vibration was investigated.The results elucidated that the tool tip response was significantly affected by ambient vibration,and the isolation foundation had a good effect on vibration isolation.

An alternative approach for computing seismic response with accidental eccentricity

Accidental eccentricity is a non-standard assumption for seismic design of tall buildings. Taking it into consideration requires reanalysis of seismic resistance, which requires either time consuming computation of natural vibration of eccentric structures or finding a static displacement solution by applying an approximated equivalent torsional moment for each eccentric case. This study proposes an alternative modal response spectrum analysis （MRSA） approach to calculate seismic responses with accidental eccentricity. The proposed approach, called the Rayleigh Ritz Projection-MRSA （RRP-MRSA）, is developed based on MRSA and two strategies： （a） a RRf＂ method to obtain a fast calculation of approximate modes of eccentric structures; and （b） an approach to assemble mass matrices of eccentric structures. The efficiency of RRP-MRSA is tested via engineering examples and compared with the standard MRSA （ST-MRSA） and one approximate method, i.e., the equivalent torsional moment hybrid MRSA （ETM-MRSA）. Numerical results show that RRP-MRSA not only achieves almost the same precision as ST-MRSA, and is much better than ETM-MRSA, but is also more economical. Thus, RRP-MRSA can be in place of current accidental eccentricity computations in seismic design.

Pushover analysis procedure for systems considering SSI effects based on capacity spectrum method

This paper presents a new procedure to transform an SSI system into an equivalent SDOF system using twice equivalence. A pushover analysis procedure based on the capacity spectrum method for buildings with SSI effects （PASSI） is then established based on the equivalent SDOF system, and the modified response spectrum and equivalent capacity spectrum are obtained. Furthermore, the approximate formulas to obtain the dynamic stiffness of foundations are suggested. Three steel buildings with different story heights （3, 9 and 20） including SSI effects are analyzed under two far-field and two near-field historical records and an artificial seismic time history using the two PASSI procedures and the nonlinear response history analysis （NLhRHA） method. The results are compared and discussed. Finally, combined with seismic design response spectrum, the nonlinear seismic response of a 9-story building with SSI effects is analyzed using the PASSI procedures, and its seismic performance is evaluated according to the Chinese ＇Code for Seismic Design of Buildings. The feasibility of the proposed procedure is verified.

Comparative analysis of seismic response characteristics of pile-supported structure

In order to analyze the seismic response characteristics of pile-supported structure,a computational model considering pile-soil-structure interaction effect was established by finite element method.Then,numerical implementation was made in time domain.At the same time,a simplified approximation for seismic response analysis of pile-soil-structure system was briefly presented.Furthermore,comparative study was performed for an engineering example.Through comparative analysis,it is shown that the results obtained by the simplified method well agree with those achieved by the finite element method.These results show that spectrum characteristics and intensity of input earthquakes are two important factors that can notablely influence the seismic response characteristics of superstructure.When the input ground motion acceleration amplitude gradually increases from 1 to 4 m/s2,the acceleration of pier top will increase,but it will not be simply proportional to the increase of input acceleration amplitude.

Simplified Analysis of the Effect of Soil Liquefaction on the Earthquake Pile Response

The time-history response of a structure-pile system during soil liquefaction is highly complicated and several analytical methods have been proposed through the accuracy verification based on the comparison with the experimental works. However, the analytical methods with higher accuracy often require large computational loads and are not necessarily preferred in the actual design practice. On the other hand, while the response spectrum method is not accurate compared to the aforementioned methods, it can provide useful design guidelines in the preliminary stage for structure-pile systems under soil liquefaction with acceptable accuracy. In this paper, the previously proposed response spectrum method for a structure-pile-soil system is used where the effect of soil liquefaction is taken into account by introducing the so-called p-multiplier method. It is shown that, while in the case of inner partial liquefaction with a non-liquefied layer at the top, the demand on the pile moment is large due to the inertial effect of that non-liquefied layer at the top, in the case of overall liquefaction near the ground surface, the demand is smaller than the case of inner partial liquefaction.

冲击响应谱在炮击振动环境的谱编制应用研究

机载航炮是军机结构振动/冲击最严酷的载荷源之一,基于实测数据得到真实的环境谱,对于军机结构及机载设备的设计与考核非常重要。基于某飞机航炮实测响应数据,采用数字滤波法得到炮振环境下单点单次响应的冲击响应谱,并结合国军标和相关标准的要求,提出了基于不同统计数据类型的机载设备炮振环境分类方法,对每一组炮振实测数据进行归纳,得到了炮击振动环境实测谱和规范谱,最后通过某飞机舱段地面试验进行了验证。结果表明该方法相较于常用的位置区域分类和极值包络区域归纳方法更正确合理,且比行业内普遍采用的随机炮振通用谱更符合炮击真实环境。该方法可直接用于军机结构与机载设备的地面试验验证,具有较好的科学性和工程实用价值。

大型空泡水洞试验设施结构有限元分析

大型空泡水洞试验设施是目前中国规模最大的水洞系统,为评估其整体结构强度和抗震设计安全性,对空泡水洞结构进行三维有限元数值分析,考虑正常工作工况和地震载荷作用极限工况下的结构刚强度,基于振型分解反应谱法计算了地震惯性加速度载荷,并对结构地震位移响应进行校核。结果表明:空泡水洞的结构变形在正常工作工况主要表现为水洞内壁的膨胀变形,在极限工况下主要表现为由地震载荷引起的水洞顶部水平位移;空泡水洞高应力区域主要位于结构角隅处的筒壁和加强筋。这对中国自主研发大型空泡水洞具有重要的借鉴意义。

基于TMD的大跨度斜拉桥风致随机振动控制研究

本文开展基于TMD的大跨度桥梁风致随机振动控制研究.建立了随机风荷载作用下桥梁—TMD系统随机振动响应分析的虚拟激励分析程序.提出了随机振动响应控制的TMD参数优化方法.以西固黄河大桥为背景,开展了实际桥梁的风致振动控制分析.结果表明:基于本文方法TMD参数优化后振动控制效率可提高近9倍,横向随机位移响应的控制效率可达到28.83%,横向随机加速度响应的控制效率可达到28.8%.

基于多层框架结构的楼层阻尼比修正的仿真研究

附加有效阻尼比的确定是消能减震结构设计的关键。为探究布置消能器楼层数的不同对结构设计安全性的影响,以新疆地区某多层钢筋混凝土框架结构为研究对象,采用非线性时程分析方法和等效结构模型的振型分解反应谱分析方法,基于各楼层剪力计算结果,引入楼层阻尼比修正系数k mn,对等效结构模型的附加有效阻尼比进行迭代修正。结果表明:采用小震时程分析阻尼比的等效结构模型,其楼层阻尼比修正系数随着阻尼器布置楼层数的逐渐增加呈现出先增后减的趋势,当阻尼器布置层数为楼层总数的3/5时折减率最低;采用中震时程分析阻尼比的等效结构模型,当阻尼器布置楼层数不少于2/5时,可满足设防要求;对于多层框架结构,考虑综合成本,黏滞阻尼器的布置楼层数可不采用满布的形式。

随机脉动风场作用下输电塔线体系的动力响应分析

输电杆塔及塔线体系(简称塔线体系)是整个电力系统中输电环节的核心部分,沿海地区的强风对塔线体系有着重要影响。为研究在随机脉动风场作用下塔线体系的动力响应特性,文中以广东某地区的1W2C9型鼓型自立式输电杆塔为研究对象,建立输电杆塔的单塔及一塔两线的塔线耦联有限元模型,结合Davenport风速谱与四阶自回归法模拟具有空间相关性的单塔9节点及塔线体系49节点的脉动风场,研究在此脉动风场下的单塔及塔线体系的动力响应,并探究不同风向角对其动力响应的影响。研究结果表明:单塔及塔线体系的动力响应最大值大于其拟静力响应;由于塔线耦联效应的存在,输电线会增加塔线体系的稳定性,降低其动力响应;90°是输电杆塔单塔及塔线体系动力响应的最不利风向角。

武汉某超高层建筑对台湾花莲6.9级地震的结构响应分析

为研究2022年台湾花莲6.9级地震对武汉市某超高层建筑结构的影响,初步分析了该建筑结构4个加速度测点记录的各向PGA放大效应、傅立叶谱及反应谱,分别利用互功率谱法和基于协方差的随机子空间法分别识别结构在频域和时域上的一阶模态。结果表明:结构的峰值加速度随楼层的增高而有显著的放大效应,最大放大倍数达7.322倍;各向傅立叶谱峰值均集中在0.275 Hz和1.171 Hz;加速度响应反应谱远小于该地区Ⅵ度设防地震设计谱;两种方法识别的结构一阶模态频率基本一致,均接近数值分析值。台湾花莲6.9级地震没有对该高层建筑结构造成损伤。

南郭寺南山佛法身舍利塔抗震性能研究

南郭寺南山佛法身舍利塔是一幢新建于高设防烈度地区山坡平地上的仿古塔建筑,设计使用年限为100年,其建筑造型和结构体系比常规建筑稍复杂。首先通过动力特性分析得到塔的自振周期和振动模态,而后基于振型分解反应谱法和时程分析法,采用有限元软件midas Gen对结构在小震、中震和大震作用下的地震响应进行了数值分析。因为在结构总说明中,只用到了设计使用年限为50年的地震作用,而未将其调整为100年,所以分析中均取2组地震动参数,即设计使用年限50年和100年。小震和中震的地震响应计算均采用弹性法,分析结果满足结构抗震性能要求。大震响应计算时,振型分解反应谱法中将特征周期提高了0.05 s,弹塑性时程分析采用塑性铰滞回模型,最大层间位移角均小于限值1/100。弹塑性时程分析还表明,内核心筒剪力墙的塑性铰发展和屈服程度均比外框架严重,但结构总体处于存在明显塑性变形至不严重破坏的状态,满足“大震不倒”的抗震性能要求。总的来说,南郭寺南山佛法身舍利塔抗震性能安全可靠,其结构体系对于类似仿古塔建筑的结构选型和设计富有借鉴意义。

基于改进多目标布谷鸟算法的拦沙重力坝结构抗震优化

混凝土重力坝在强震作用下易出现结构安全问题,因而需采用合理经济的工程措施加以防护。将西北地区某拦沙重力坝作为研究对象,基于振型分解反应谱法分析大坝自振特性与动力响应,并综合考虑坝踵拉应力和抗震措施可变造价,采用改进多目标布谷鸟算法(MOCS)进行抗震设计方案的优化。此外,为提高算法性能,通过调整拥挤度距离计算公式、引进多项式变异算子以及动态步长和发现概率等方式进行改进。通过与其他多目标算法在不同测试函数上的对比试验,证明改进MOCS算法具备计算高效和解集均匀等优点。最后,根据Pareto最优解集,对重力坝的设计方案进行合理性评价,并提出工程建议。相关方法与结论对高烈度地震区混凝土重力坝的结构设计具有参考价值。