摘要:

AbstractComprehensive analyses are made of the differences in the responses of simple models of offshore structures computed by the standard and extended versions of Morison's equation for the hydrodynamic forces, and of the effects and relative importance of the numerous parameters involved. The responses also are evaluated by the equivalent linearization technique and Penzien's decoupling technique, and the interrelationship and accuracy of these approaches are elucidated. The results are displayed graphically in the form of response spectra for absolute maximum displacement employing dimensionless parameters that are easy to interpret and use. In addition, the decoupling technique is generalized to include consideration of a current of constant velocity, and a simple modification is proposed which improves the accuracy of this approach. A particularly simple approximation is included for the hydrodynamic modal damping values of multi‐degree‐of‐freedom, stick‐like

ISSN:0098-8847    

DOI:10.1002/eqe.4290160502

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractA study on the dynamic response of three‐dimensional flexible foundations of arbitrary shape, embedded in a homogenous, isotropic and linear elastic half‐space is presented. Both massive and massless foundations are considered. The soil‐foundation system is subjected to externally applied forces, and/or to obliquely incident seismic waves. The numerical method employed is a combination of the frequency domain Boundary Element Method, which is used to simulate the elastic soil medium, and the Finite Element Method, on the basis of which the stiffness matrix of the foundation is obtained. The foundation and soil media are combined by enforcing compatibility and equilibrium conditions at their common interface. Both relaxed and completely bonded boundary conditions are considered. The accuracy of the proposed methodology is partially verified through comparison studies with results reported in the literature for rigid embedded founda

ISSN:0098-8847    

DOI:10.1002/eqe.4290160503

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractA series of strong ground motions was recorded during a set of earthquakes which occurred in the North Nahanni River area of the Northwest Territories of Canada in late 1985. The strongest of these motions were recorded within 10 km of the epicentre of a magnitude 6.9 event; peak accelerations were well above 1gand peak velocities exceeded 0.4 m/s.This paper describes a study of the engineering characteristics of the Nahanni strong motions, particularly as they affect the response of building structures. The response characteristics are analysed in terms of the response spectra and the unit velocity base shear coefficients for multi‐degree‐of‐freedom elastic frame structures. An analysis of the strong motion durations of the records and several measures of intensity is also included. The characteristics of the Nahanni records are compared with those of typical strong seismic ground motions and an ensemble of epicentral region seismic motions recorded under similar conditions. Comparisons are also made with the equivalent parameters in the 1985 edition of the National Building Code of Canada.It is concluded that the Nahanni records are very strong seismic ground motion records with relatively unusual response characteristics, even when compared with those of other records obtained within the epicentral region. The impact of these characteristics on engineering design is most significant for low period structures in epicentral regions. The specifications of typical design codes do not adequately describe the response to such records for very low pe

ISSN:0098-8847    

DOI:10.1002/eqe.4290160504

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractAn approximate procedure is introduced to analyse non‐linear multistorey structures within the framework of the conventional response spectrum method. Its derivation is based on the use of non‐linear response spectra and an approximate decomposition of the equation of motion for multi‐degree‐of‐freedom non‐linear systems. The decomposition is attained by considering the non‐linear terms in this equation of motion as additional external forces and, thus, by interpreting it as the equation of motion of linear systems with the initial properties of the non‐linear ones when subjected to a modified set of inertia forces. For simplicity, the procedure is herein limited to elastoplastic systems of the shear‐beam type. Its accuracy is evaluated by comparing the approximate and step‐by‐step integration solutions of systems with three and ten degrees of freedom when subjected to three different eart

ISSN:0098-8847    

DOI:10.1002/eqe.4290160505

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractDynamic instability of single storey frames having thin‐walled columns has been investigated. The lateral loads sustained by the frame are dynamic in character, while the axial loads are deemed to be quasi‐statically applied. The analytical model employed by the authors has the capability of modelling the combined action of the two ‘companion’ local modes whose amplitudes are variable along the length of the column and any type of end conditions of the members.For given levels of axial loads sustained by the columns, the magnitudes of lateral loads causing instability can be significantly smaller than those corresponding to static buckling, provided the dynamic load is of sufficient duration. There exists, however, a threshold value of axial force carried by the columns, below which there is no elastic instability—static or dynamic.For columns with overall critical loads several times greater than the local critical load, there is no danger of elastic instability, but the deflections under dynamic lateral loads of less than 1 per cent of the axial load may reach such huge values that there is a serious danger of localized plastic collapse. It is also shown that moment frames having thin‐walled columns such as those fabricated out of cold formed steel are extremely vulnerable to moderate seismic

ISSN:0098-8847    

DOI:10.1002/eqe.4290160506

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractAlthough the prediction of seismic damage is primarily a probabilistic problem, deterministic analysis can nevertheless be a valuable tool. This paper reviews the concepts which have been used in damage prediction, and identifies and classifies several specific techniques. Techniques of two types are considered, the first based on the balance between some demand on the structure and its corresponding capacity, and the second on the degradation of some structural property. For each technique, one or more damage parameters can be computed, and from these a damage index can be estimated. Several alternative choices for the damage parameters are identified. Procedures for computing values for these parameters, and relating them to damage indices, are suggested.

ISSN:0098-8847    

DOI:10.1002/eqe.4290160507

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractThe paper is concerned with the study of the effect of the randomness of material parameters on mean wave propagation in a semi‐infinite viscoelastic medium. The medium considered in this paper is a configuration of a randomly non‐homogeneous layer overlying a homogeneous half‐space and is loaded harmonically on the top surface. The method used is that of Karal and Keller and is based on the idea of fundamental matrix and Bourret approximation. The integro‐differential equation obtained in this paper is solved by the Laplace transform method. By using boundary and continuity conditions the mean wave solution is obtained. Numerical results show that the correlation functions, which introduce long‐range interactions, can be the source of the wave ampl

ISSN:0098-8847    

DOI:10.1002/eqe.4290160508

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractThe paper deals with the evaluation of non‐stationary spectral moments of multi‐degree‐of‐freedom (MDOF) line systems subjected to seismic excitations. The spectral moments of the response are evaluated in incremental form solution by means of an unconditionally stable step‐by‐step procedure.As an application, the statistics of the largest peak of the response are als

ISSN:0098-8847    

DOI:10.1002/eqe.4290160509

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractTwo processes using the Newmark implicit integration scheme are presented for the analysis of the earthquake response of a three‐dimensional model for arch dam‐reservoir systems including the effect of compressibility of the water. The solid structure and fluid regions are modelled separately, and the forcing functions at the interface are due to the hydrodynamic pressures from the reservoir acting on the upstream face of the dam wall, and the accelerations from the dam wall acting in turn on the reservoir.For the purposes of an initial investigation, elastic properties are assumed for the material of the dam, whilst in the reservoir radiation damping at the upstream boundary has been included, but bottom absorption has not. The excitation is provided by means of a combisweep which is fashioned so that its continuously varying frequencies pass through the fundamental frequencies of both the arch dam‐reservoir system and the reservoir alone. Consequently the response is highly resonant, thus providing a severe test for the numerical procedures. From the numerical results obtained for an example problem it is concluded that both schemes provide an acceptable solution to the problem posed, and the possibility of enhancement to cater for more complex situations is disc

ISSN:0098-8847    

DOI:10.1002/eqe.4290160510

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractDraft Eurocode 8 (Common Unified Rules for Structures in Seismic Regions1) is open for study and comment until the latter part of 1989. This paper presents sample seismic force calculations for an idealized building, to illustrate the differing forces which result from the alternative calculation methods allowed. It is tentatively suggested that part of the Draft be revised as a result of the above.

ISSN:0098-8847    

DOI:10.1002/eqe.4290160511

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY