摘要:

AbstractA procedure for vibration suppression of elastic structures and systems is introduced in this paper. First, the equations of the response of the system to external forces, based on a discretized linear model, are developed. Next, the vibration suppression is formulated as a minimization problem with control (external) forces as unknowns. Then, the optimality condition is applied to this problem and a set of linear simultaneous equations is obtained for the unknown forces. The scheme is applied to a number of simple examples for illustration. The results show that the procedure is very effective and, at the same time, very flexible compared to methods that are based on continuous models (partial differential equations). The actual (hardware) implementation can be achieved by means of either passive absorbers or active forces (actuators).

ISSN:0098-8847    

DOI:10.1002/eqe.4290180103

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractA comparative study of performances of different base isolators for shear beam type structures is carried out. Several leading base isolation systems, including the laminated rubber bearing with and without lead plug, the resilient‐friction base isolator with and without sliding upper plate, and the EDF system are considered. Displacement and acceleration response spectra for a shear beam structure subject to the accelerograms of the N00W component of El Centro 1940 and the N90W component of Mexico City 1985 earthquakes and their magnified forms are evaluated. A series of parametric studies is carried out and advantages and disadvantages of various base isolation systems are identified. Comparisons of the results with the response spectra of a fixed‐base structure show that the base isolation systems are, in general, highly effective in reducing the peak acceleration transmitted to the superstructure. Thus, the deflections and stresses generated in a base‐isolated structure are significantly lower than those of a fixed‐base one. Furthermore, the results of the study also show that the friction‐type base isolators are less sensitive to severe variations in frequency content and amplitude of the ground acc

ISSN:0098-8847    

DOI:10.1002/eqe.4290180104

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe equivalent base horizontal acceleration concept was developed for calculating the response of test structures to shaking table excitations, to account for pitching interaction effects of the table. Using the procedure, analysis‐experiment comparisons were made of the shaking table tests of a 0–3‐scale model of a six‐storey concentrically K‐braced steel structure. The correlation of the analytical and experimental results was excellent in both the elastic and inelastic ranges of structural

ISSN:0098-8847    

DOI:10.1002/eqe.4290180105

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe stationary response of base‐isolated buildings subjected to earthquake excitation is studied. The frequency content of earthquake input is described by the Clough‐Penzien spectral model. The response parameters of interest are (1) the root‐mean‐square (RMS) displacement σxof the basement relative to the foundation (i.e. shear deformation of the isolation system) and (2) the ratio (σa/σa0) of the RMS value of the absolute acceleration at the roof of the isolated structure over the corresponding value when the isolation system is locked. The variation of these response parameters with the effective frequencyf0of the base‐isolated structure is investigated. As input, earthquakes with moment magnitudesM= 7‐3 andM= 6‐0 are considered. The acceleration spectra corresponding to these two earthquake sizes have pronouncedly different frequency content over the frequency range 0–1‐1–0 Hz which is of primary importance for base‐isolated structures. An important conclusion that comes from these analyses is that confidence in the effectiveness of a base‐isolated system should be based primarily on its capacity to absorb/dissipate energy and less on its influence in shifting the fundamental period of the structure out of the range of

ISSN:0098-8847    

DOI:10.1002/eqe.4290180106

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractA simplified procedure for the analysis of single‐storey base‐isolated structures on a viscoelastic halfspace is extended to multistorey structures. Results of displacements and base shear obtained by this procedure compare favourably to exact results obtained by a computer program that has been develo

ISSN:0098-8847    

DOI:10.1002/eqe.4290180107

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe large amplification experienced at Mexico City during the earthquake of September 1985 is shown to be due to a standing shear wave set up in the clay layer. The frequency and amplitude of this wave were controlled by the properties of the clay which led directly to such high accelerations. The response curve due to the clay layer is calculated from field and laboratory measurements of the properties of the clay. There is good agreement with that obtained from field observations of ground motion.

ISSN:0098-8847    

DOI:10.1002/eqe.4290180108

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe result of a theoretical study on the rocking response of rigid blocks subjected to sinusoidal base motion is presented. The study indicates that, for a given excitation amplitude and frequency, a rigid block can respond in several different ways. Based on analysis, the regions of different classes of steady state symmetric response solutions are mapped on the excitation amplitude‐frequency parameter space. The steady state response solutions (both harmonic and subharmonic) are classified into two classes, out‐of‐phase and in‐phase with respect to the excitation. Only out‐of‐phase solutions are found to be stable. A parametric study shows that steady rocking response amplitude is highly sensitive to the size of the block and the excitation frequency in the low frequency range. It is relatively insensitive to the excitation amplitude and the system's coefficient of restitution of impact. For two blocks of the same aspect ratio and coefficient of restitution subjected to the same excitation, the larger block always responds in smaller amplitude than the smaller block. Computer simulation is carried out to study the stability of the symmetric steady state response solutions obtained from analysis. It is found that as the excitation frequency is decreased beyond the boundary of stable symmetric response, the response becomes unsymmetric where the mean amplitude of oscillation is non‐zero. Further decrease in excitation frequency beyond the stable unsymmetric response boundary causes instability in the form o

ISSN:0098-8847    

DOI:10.1002/eqe.4290180109

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe results of an experimental investigation on the rocking response of rigid blocks subjected to sinusoidal base motion is presented. It is shown that two common types of steady state response are harmonic and 1/3 subharmonic response. The measured steady state response amplitudes correlate well with theoretical predictions for both harmonic and 1/3 subharmonic responses. Within each type of steady state response, theoretical studies show that the system may respond in either a symmetric or an unsymmetric mode. A symmetric mode denotes that the block oscillates about a mean zero position while an unsymmetric mode implies the mean position of oscillation is at an inclined position. One form of unsymmetric response was observed in the experiment. In addition, almost periodic responses were also observed in the experiment, although their existence has not been reported in theoretical studies.

ISSN:0098-8847    

DOI:10.1002/eqe.4290180110

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractA solution technique based on the sequential linear programming (SLP) method is presented for the optimum design of braced and unbraced steel frames in seismic regions. First, the optimum rigidity distribution of the frames under static loading is computed, then the optimization procedure is repeated under the combined loading, setting lower bounds on the optimum static cross‐sectional areas and increasing allowable stresses.The stiffness, stress, displacement and side constraints are included in the optimization problem. As a result, a highly non‐linear mathematical programming problem is produced. A non‐linear programming algorithm is offered for the solution which is based on the successive linearization of non‐linear expressions and employs the simplex routine in an iterative manner.Design variables are chosen to be the free nodal displacements and the cross‐sectional areas of the members, while the objective function is taken to be the minimization of the total volume of the structure.As numerical applications, optimum weights of several frames (unbraced, concentrically and eccentrically braced) under static and combined loading cases are computed and the results are compared with those available in the l

ISSN:0098-8847    

DOI:10.1002/eqe.4290180111

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

ISSN:0098-8847    

DOI:10.1002/eqe.4290180112

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY