复阻尼多自由度系统动力分析的模态叠加法

工程实际中,复阻尼多自由度系统的瞬态响应过去一直是通过频域方法求解的。频域方法的一个突出问题是求传递函数矩阵的计算工作量过大。本文给出一种有效而实用的时域解法———实模态叠加法,此外还介绍了复模态叠加法。实模态叠加法是基于一个事实,即n维复向量空间中的复向量可以在n维实向量空间中的一组线性无关的实向量构成的基下表出;另外,就此方法还讨论了复阻尼多自由度系统初始运动条件的给出和转换问题。复模态叠加法则是通过变量替换的方法,变其中的复特征值问题为形式上的一个实特征值问题来解决的。     

力平衡加速度计在线动态测试方法的实验研究

为了提高强震观测系统中力平衡加速度计动态测试的效率并降低成本，本文提出了利用力平衡加速度计内的自标定机构进行在线动态测试的方法。通过对比力平衡加速度计的绝对测试和在线测试实验结果，证明自标定机构可以代替超低频标准振动台来进行力平衡加速度计的动态测试。     

剪切型多自由度体系瞬时输入能量的分布

通过对剪切型多自由度体系的地震能量反应分析,提出了描述多自由度体系整体脉冲能量反应的参数,瞬时输入能量等效平均速度,并在此基础上建立了瞬时输入能量分布系数的概念,提出了估计瞬时输入能量分布的方法。     

基础隔震房屋模型振动台试验研究

本文结合日本在建的基础隔震实际工程,采用中国有关工厂生产的铅芯橡胶支座的作为基础隔震支座,进行了基础隔震房屋模型和基础固家房屋模型模拟地震动台试验,并引入能量分析方法对两种试验结果进行了分析比较。结果表明,基础隔震模型隔震效果明显,隔震层滞回变能有效吸收地震动入能量,减小模型结构的塑性变形和累积损伤。     

短柱隔震模型与非隔震模型模拟地震振动台对比试验研究

本文取一栋四层转混住宅的标准单元为模型。在两种情况下：即房屋模型底部加设钢管混凝土短柱隔震支座和不加设钢管混凝土短柱隔震支座,分别进行了模拟地震动台试验。通过试验结果的对比,了解了钢管混凝土短柱支座隔震模型的隔震效果及其抗震性能。     

弹性能量半径演化谱及其在多自由度体系地震反应计算中的应用

目前用于结构抗震设计的反应谱仅能反映峰值反应,无法体现反应值随时间的变化。文中提出一种弹性能量半径演化谱,可反映线性单自由度体系弹性能量(即动能与弹性势能之和)随地震持时的变化,且其峰值近似等于结构峰值位移。文中给出了利用地震动演化功率谱得到该演化谱的方法并进一步发展了一种计算线性多自由度体系地震位移反应的新方法。通过两座框架结构的地震反应计算,将新方法与传统振型组合法及时程分析法的计算结果进行对比,发现对于振型稀疏结构,新方法计算结果与SRSS法接近;而对于振型密集结构,新方法计算结果较CQC法更精确,且避免了CQC法相关系数的复杂计算。     

Effect of structural characteristics distribution on strength demand and ductility reduction factor of MDOF systems considering soil-structure interaction

It is known that structural stiffness and strength distributions have an important role in the seismic response of buildings.The effect of using different code-specified lateral load patterns on the seismic performance of fixed-base buildings has been investigated by researchers during the past two decades.However,no investigation has yet been carried out for the case of soil-structure systems.In the present study,through intensive parametric analyses of 21,600 linear and nonlinear MDOF systems and considering five different shear strength and stiffness distribution patterns,including three code-specified patterns as well as uniform and concentric patterns subjected to a group of earthquakes recorded on alluvium and soft soils,the effect of structural characteristics distribution on the strength demand and ductility reduction factor of MDOF fixed-base and soil-structure systems are parametrically investigated.The results of this study show that depending on the level of inelasticity,soil flexibility and number of degrees-of-freedoms(DOFs),structural characteristics distribution can significantly affect the strength demand and ductility reduction factor of MDOF systems.It is also found that at high levels of inelasticity,the ductility reduction factor of low-rise MDOF soil-structure systems could be significantly less than that of fixed-base structures and the reduction is less pronounced as the number of stories increases.     

Full‐scale shaking table test for examination of safety and functionality of base‐isolated medical facilities

A series of full‐scale shaking table tests are conducted using the E‐Defense shaking table facility on a base‐isolated four‐story RC hospital structure. A variety of furniture items, medical appliances, and service utilities are placed on the hospital specimen in as realistic a manner as possible. Four ground motions are adopted, including recorded near‐fault ground motions and synthesized long‐period, long‐duration ground motions. The test results show that the base‐isolated system performed very effectively against near‐fault ground motions due to significant reduction in the floor acceleration response, and operability and functionality of the hospital service is improved significantly as compared with the case observed for the corresponding base‐fixed system. Against the long‐period ground motion, however, the hospital service is difficult to maintain, primarily because of the significant motion of furniture items and medical appliances supported by casters. Resonance accentuated large displacements and velocities on the floors of the base‐isolated system, which causes such furniture items and medical appliances to slide, sometimes more than 3 m, resulting in occasional collision with other furnitures or against the surrounding partition walls. It is notable that a key to maintaining the function of the medical facilities is to securely lock the casters of furniture and medical appliances. Copyright © 2011 John Wiley & Sons, Ltd.     

区域数字地震台网实时速报系统试运行情况分析

研制了一套区域数字地震台网实时速报系统,并于2005年7月在福建数字地震台网试运行.本文对系统在2005年7月至2006年5月间处理的网内震和网缘震进行了统计与分析.结果表明,系统对90%以上网内ML≥2.0地震的处理结果达到中国地震局地震速报评比满分的要求;系统对网内线以外100 km区域范围内ML≥2.5的网缘地震也有一定监控能力.本文对系统处理其他网缘震、网外震与人工爆破的不足之处也进行了分析与讨论.     

Numerical modeling of MDOF structures with sliding supports using rigid‐plastic link

In this paper, the responses of multi‐degree‐of‐freedom (MDOF) structures on sliding supports subjected to harmonic or random base motions are investigated. Modeling of the friction force under the foundation raft is accomplished by using a fictitious rigid link which has a rigid–perfectly plastic material. This will result in identical equations of motion for the sliding structure, both in the sliding and non‐sliding (stick) phases which greatly simplifies the implementation of the method into a numerical algorithm. In this model the phase transition times are determined with high accuracy. This has two advantages: first, it prevents the so‐called high‐frequency oscillation of the relative velocity at the end of the sliding phase, and second, the time steps can be selected so that each falls exactly within one phase of motion. In this case, the stiffness matrix of the structure remains constant throughout each phase and thus any method for solving the non‐linear differential equations of motion (e.g. Newmark method) can be used without iteration. The proposed method, besides its simplicity, is numerically very efficient and considerably reduces the required analysis time compared with most of the other methods. Copyright © 2001 John Wiley & Sons, Ltd.     

Optimal design of SDOF envelope systems for the responses of MDOF dynamic systems

The concept of envelope system for a given dynamic system is proposed in this paper which refers to those systems whose module of transfer function in the whole range of frequency domain is always bigger than that of a given system. This concept opens a new way to study the problems of robust design and modelling for dynamic systems. The condition that an envelope system has to satisfy is rendered as the determination of the positiveness of a real polynomial function and Sturm's sequence method is used to establish an easily implemented criterion for evaluating the positiveness of the polynomial in terms of its coefficients. The optimization for the envelope system is expressed as the minimization of the 2-norm of its transfer function and simplex method is employed to search for the optimal solution. Two dynamic systems are used to illustrate the optimal design for the envelope systems of some of their responses. © 1998 John Wiley & Sons, Ltd.     

Modified fish-bone model: A simplified MDOF model for simulation of seismic responses of moment resisting frames

This paper presents a simplified Multi-Degree-Of-Freedom (MDOF) model through modification of fish-bone model (or generic frame). Modified Fish-Bone (MFB) model is developed through three enhancements: (i) the moment of inertia for half-beams is reduced slightly to modify the assumption of equal rotation at each story joints, (ii) a number of truss elements are inserted to the fish-bone model to simulate flexural deformation of moment frames due to axial elongation and contraction of columns, and (iii) moment–rotation relationship of representative rotational springs is supposed to be bilinear instead of trilinear in order to consider simultaneous yielding at both ends of the beam in moment frames. The proposed model is evaluated with respect to nonlinear dynamic analysis results of three classic moment resisting frames subjected to 94 records of FEMA-440 ground motion data set. Moreover, the adequacy of this model is compared with the fish-bone model and two predictors of nonlinear seismic demand. The statistical study of predicted interstory drift demonstrates the superiority of the proposed model over the fish-bone model and both seismic demand predictors.     

A base isolation system for bridges subjected to seismic disturbances

The study reported in this paper investigates the feasibility of developing an active base isolation system for the protection of bridges subjected to earthquakes. The proposed system incorporates spherical supports, cams and springs which can be optimally designed to minimize the transmissibility of the seismic disturbances to the bridge. The considered example shows that the proposed design is implementable and can provide an order of magnitude reduction in the maximum stress resulting from seismic waves acting on the bridge in the transverse or longitudinal direction. Since the system performance is highly dependent on the rapid unlocking of the cams in the event of a seismic disturbance, careful consideration should be given to the design of a reliable cam release control. This can be achieved by spring loading each cam such that it would be normally unlocked. A hydraulic actuator would be used to force it to rotate to the locking position under fluid pressure which would be constantly maintained at the design level during normal conditions. The actuator would be equipped with a quick response release valve for rapidly releasing the pressure and consequently unlocking the cam as soon as an earthquake is detected. Copyright © 2002 John Wiley & Sons, Ltd.     

区域数字地震台网实时速报系统研究

目前,安徽台网正在运行的自动地震定位系统包括中国地震局自动地震速报系统（AU）、江苏省地震局自动定位系统、福建省地震局自动定位系统和安徽区域地震预警系统。以2015—2019年安徽及周边省份发生的地震实例为研究对象,将上述4套系统产出的结果分别与中国地震局统一正式目录对比,结果表明这4套系统产出的结果均在地震速报要求所允许的误差范围内,在安徽区域具备适用性和实用性,但在识别双震等方面存在缺陷。同时,这几套系统之间的对比结果表明,安徽区域预警系统产出结果参数的平均发震时刻差、平均震中位置差和平均震级差都相对较小。     

Online test using displacement–force mixed control

This paper proposes an online test technique that employs mixed control of displacement and force. Two types of mixed control, ‘displacement–force combined control’ and ‘displacement–force switching control’ are proposed. In displacement–force combined control, one jack is operated by displacement‐control, and another is operated by force‐control. Validity of the combined control technique is demonstrated by a series of online tests applied to a base‐isolated structure subjected to horizontal and vertical ground motions simultaneously. The substructuring technique is employed in the tests, and the base‐isolation layer is tested, with the rest of the structure modeled in the computer. Displacement‐control and force‐control were adopted for simulating the horizontal and vertical response, respectively. Both displacement‐ and force‐control were implemented successfully despite interference between the two jacks. Earthquake responses of the base‐isolated structure involving the effects of varying axial forces on the horizontal hysteretic behavior of the base‐isolation layer were simulated. In the displacement–force switching control, the jack was operated by displacement‐control when the test specimen was flexible but switched to force‐control once the specimen became stiff. Validity of the switching control technique was also checked by a series of online tests applied to the base‐isolated structure subjected to vertical ground motions. Switching between displacement‐control and force‐control was achieved when the axial force applied to the base‐isolation layer changed from tension to compression or from compression to tension. Both the displacement‐ and force‐control were successful even with many rounds of switching. The test revealed that large accelerations occurred on the floor immediately above the base‐isolation layer at the instants when the axial force of the base‐isolation layer changed from tension to compression. Copyright © 2005 John Wiley & Sons, Ltd.     

Response of structures supported on SCF isolation systems

Aseismic base isolation is an effective method used to protect structures and their contents against earthquakes. An isolated structure may be designed to remain elastic throughout major ground motions as a result of the efficiency of the isolation systems. In this paper, the equations of motion of two‐dimensional elastic structures supported on a new base isolation system called the Sliding Concave Foundation (SCF) are presented and a procedure for their solution is suggested. The responses of a number of structures subjected to different earthquake records are evaluated and the results are compared with those of the same structures supported on two other famous isolation systems and also a fixed base condition. The results indicate the effectiveness of the SCF in protecting the supported structures even during very strong and/or long period earthquakes. Copyright © 2003 John Wiley & Sons, Ltd.     

Full‐scale shaking table test of a base‐isolated medical facility subjected to vertical motions

Base isolation is a well known technology that has been proven to reduce structural response to horizontal ground accelerations. However, vertical response still remains a topic of concern for base‐isolated buildings, perhaps more so than in fixed‐base buildings as isolation is often used when high performance is required. To investigate the effects of vertical response on building contents and nonstructural components, a series of full‐scale shaking table tests were conducted at the E‐Defense facility in Japan. A four‐story base‐isolated reinforced concrete building was outfitted as a medical facility with a wide variety of contents, and the behavior of the contents was observed. The rubber base isolation system was found to significantly amplify vertical accelerations in some cases. However, the damage caused by the vertical ground motions was not detrimental when peak vertical floor accelerations remained below 2 g with three exceptions: (1) small items placed on shelves slid or toppled; (2) objects jumped when placed on nonrigid furniture, which tended to increase the response; and (3) equipment with vertical eccentricities rocked and jumped. In these tests, all equipment and nonstructural components remained functional after shaking. Copyright © 2013 John Wiley & Sons, Ltd.     

建筑抗震实时混合试验时滞补偿方法研究综述

时滞补偿是建筑抗震实时混合试验的重要问题。文章对时滞补偿方法的研究进行总结,将时滞补偿方法分为基于时间的位移预测时滞补偿方法、基于反馈力的位移预测时滞补偿方法、基于加载系统模型求逆的时滞补偿方法、基于控制理论的时滞补偿方法和基于集成理念的综合补偿方法。     

On‐line hybrid test combining with general‐purpose finite element software

A new on‐line hybrid test system incorporated with the substructuring technique is developed. In this system, a general‐purpose finite element software is employed to obtain the restoring forces of the numerical substructure accurately. The restart option is repeatedly used to accommodate the software with alternating loading and analysis characteristic of the on‐line test but without touching the source code. An eight‐storey base‐isolated structure is tested to evaluate the feasibility and effectiveness of the proposed test system. The overall structure is divided into two substructures, i.e. a superstructure to be analysed by the software and a base‐isolation layer to be tested physically. Collisions between the base‐isolation layer and the surrounding walls are considered in the test. The responses of the overall structure are reasonable, and smooth operation is achieved without any malfunction. Copyright © 2006 John Wiley & Sons, Ltd.     

On precise time integration method for non-classically damped MDOF systems

In the complex mode superposition method, the equations of motion for non-classically damped multiple-degree-of-freedom （MDOF） discrete systems can be transferred into a combination of some generalized SDOF complex oscillators. Based on the state space theory, a precise recurrence relationship for these complex oscillators is set up; then a delicate general solution of non-classically damped MDOF systems, completely in real value form, is presented in this paper. In the proposed method, no calculation of the matrix exponential function is needed and the algorithm is unconditionally stable. A numerical example is given to demonstrate the validity and efficiency of the proposed method.