振动衰减测试方法确定高能级强夯对已有建（构）筑物的影响距离

某大型新建工程场地为近期吹砂填海方式形成,根据有关资料及勘察揭露,上部吹填层及原有细砂层存在地震液化及承载能力差的问题,设计采用高能级强夯进行处理。在地基处理区域处有一道永久防浪堤,根据设计要求,在进行强夯试夯过程中应采用一定的方法对振动影响进行测试,为设计提供相应的数据,进而确定强夯施工的范围。为解决上述问题,采用了振动衰减测试方法进行了强夯振动影响测试,对后期的大面积强夯施工提供了支持。通过该工程实例,介绍了振动衰减测试及其测试结果分析的方法。     

A method for assessing kinematic bending moments at the pile head

The conventional design methods for seismically loaded piles still concentrate in providing adequate resistance from the pile to withstand only the inertial bending moments generated from the oscillation of the superstructure, thus neglecting the effect of kinematic interaction between pile and soil. By contrast there has been extensive research on kinematic effects induced by earthquakes and a number of simplified methods are available for a preliminary evaluation of kinematic bending moments at the interface between two soil layers. Less attention has been paid to the effects of kinematic interaction at the pile‐head. The paper summarizes recent research work on kinematic response analysis of fixed‐head piles aimed at the performance evaluation of a piled foundation. Results from an extensive parametric study, undertaken by means of three‐dimensional FE analyses, suggest a new criterion to predict kinematic bending effects at the pile head, where the combination of kinematic and inertial effect may be critical. Copyright © 2010 John Wiley & Sons, Ltd.     

Natural vibration characteristics of gravity structures

A forced vibration procedure is presented to estimate fundamental and higher frequencies of vibrations and associated mode shapes of gravity structures. The gravity structures considered are retaining walls and gravity dams. The validity of the proposed procedure is tested on three test problems of varying complexity for which the natural vibration frequencies and mode shapes either have known analytical solutions or have been determined via numerical means/field tests by others. Also included are the results of natural vibration frequencies and associated mode shapes for a spillway control structure located near the abutment end of an embankment dam obtained using the proposed procedure. For all problems considered, fundamental frequency and mode shape results using the proposed procedure are compared with the results obtained using an alternative procedure in which static deflections due to the structure's own weight are used as the starting point for free vibrations by setting the gravity vector to zero. All results compare well. The merits of the proposed procedure are discussed. Published in 2006 by John Wiley & Sons, Ltd.     

抗震结构的阻尼减振效果分析

研究了抗震结构的阻尼减振效果。首先，考虑了单自由度体系在不同频率简谐干扰作用下阻尼比对结构反应的减小效果；然后，考虑了阻尼比对结构地震反应谱的影响，分析了我国现行建筑抗震设计规范反应谱，并讨论了不同阻尼比对水平地震影响系数的修正公式。     

Gray box identification of flexible structures: application to robust active vibration suppression control

The paper deals with gray box identification of flexible structures and active vibration suppression from a robust control perspective. First, the linearized mathematical model of an N‐storey flexible structure is presented. Next, the generalized mathematical model is particularized for the investigated three‐storey flexible structure. The considered flexible structure is identified based on black box and gray box identification methods and the model's parametric uncertainties are deduced. Furthermore, control constraints are presented for the design problem, in case of velocity as well as acceleration feedback, from a robust control perspective. Finally, the effectiveness of the control system is tested through experiments, when the input disturbance is assumed to be a sinusoidal one as well as a historical earthquake record (1940 El Centro record). Copyright © 2001 John Wiley & Sons, Ltd.     

Probabilistic critical excitation for MDOF elastic–plastic structures on compliant ground

Earthquake ground motions and their effects on structural responses are very uncertain even with the present knowledge. It is therefore desirable to develop a robust structural design method taking into account these uncertainties. Critical excitation approaches are promising and a new random critical excitation method is proposed for MDOF elastic–plastic shear‐building structures on compliant ground. The power (area of power spectral density (PSD) function) and the intensity (magnitude of PSD function) are fixed and the critical excitation is found under these restrictions. In contrast to linear elastic structures, transfer functions and simple expressions for response evaluation cannot be defined in elastic–plastic structures and difficulties arise in describing the peak responses except by laborious elastic–plastic time‐history response analysis. Statistical equivalent linearization is used to estimate the elastic–plastic stochastic peak responses approximately. The critical excitation responses are obtained for several examples and compared with those of the corresponding recorded earthquake ground motion. Copyright © 2001 John Wiley & Sons, Ltd.     

Resonance and criticality measure of ground motions via probabilistic critical excitation method

Resonant characteristics of recorded ground motions are investigated and a new measure of criticality of ground motions is proposed. Four classes of recorded ground motions, i.e., (i) near fault motions (rock records), (ii) near fault motions (soil records), (iii) long duration motions (rock records) and (iv) long duration motions (soil records), are taken from Abrahamson N, Ashford S, Elgamal A, Kramer S, Seible F, Somerville P, Proc of First PEER Workshop on Characterization of Special Source Effects, 1998. It is shown that resonant characteristics of recorded ground motions can be captured appropriately by means of the probabilistic critical excitation method due to the present author regardless of the type of ground motions and the distance between the critical response and the actual one can be a new measure of criticality of ground motions. The time-averaged approximate treatment of nonstationary ground motions as stationary ones is shown to be adequate for structures with shorter natural periods subjected to long duration ground motions.     

大庆台网观测效果分析与振动事件研究

应用周期－频度谱和复查分析等方法对大庆台网观测资料进行详细研究，从而取得了对台网的监测能力，其些小事件的性质等问题的明确认识。     

Lateral response of dams in semi-elliptical rigid canyons

An analytical closed-form solution is developed for the lateral response of earth and rockfill dams built in semi-elliptical canyons. The dam is idealized as a linearly hysteretic elastic body deforming only in shear, whereas the canyon is assumed to be rigid. The solution for the dam response is given in terms of prolate spheroidal radial and angular functions of the first kind and zero order. Results are presented for natural frequencies, modal displacement shapes, participation factors, and response to transient and steady-state harmonic base excitation for various dam length-to-height ratios. Comparisons are made of the effects of the length-to-height ratio and the canyon shape on the response of dams built in semi-elliptical and rectangular canyons. A subsequent study (Dakoulas, P. & Hsu, C.H., Response of earth dams in semi-elliptical flexible canyons to oblique SH waves, Report, Rice University, Houston, Texas, 1993) extends this model to a semi-elliptical canyon consisting of flexible elastic rock, subjected to obliquely incident harmonic SH waves.