Earthquake Engineering and Structural Dynamics

VELETSOS, A. S.; PRASAD, A. M.; WU, W. H.

doi: 10.1002/(SICI)1096-9845(199701)26:1<5::AID-EQE619>3.0.CO;2-Xpmid: N/A

Closed‐form expressions and comprehensive numerical solutions are presented for the transfer functions of surface‐supported, rigid, rectangular foundations excited by horizontally polarized, incoherent shear waves for which the motions are parallel to one of the foundation sides. The free‐field ground motion is specified stochastically in terms of a local power spectral density function and an orthotropic incoherence function which decays exponentially with the square of the excitation frequency and the separation distance. The response quantities examined include the lateral and torsional components of the foundation motion. Displayed graphically, the results elucidate the effects and relative importance of the numerous parameters involved. For vertically incident incoherent wave fields, the lateral transfer function of a rectangular foundation is related to that of a judiciously selected square foundation, and the interrelationship of the results is examined. © 1997 by John Wiley & Sons, Ltd.

ZERVA, A.; ZHANG, O.

doi: 10.1002/(SICI)1096-9845(199701)26:1<19::AID-EQE620>3.0.CO;2-Fpmid: N/A

A methodology for the investigation of the spatial variation of seismic ground motions is presented; data recorded at the SMART‐1 dense instrument array in Lotung, Taiwan, during Events 5 and 39 are used in the analysis. The seismic motions are modeled as superpositions of sinusoidal functions, described by their amplitude, frequency, wavenumber and phase. For each event and direction (horizontal or vertical) analysed, the approach identifies a coherent, common component in the seismic motions at all recording stations, and variabilities in amplitudes and phases around the common component sinusoidal characteristics, that are particular for each recording station. It is shown that the variations in both the amplitudes and the phases of the motions at the station locations around the common component characteristics contribute significantly to the spatially variable nature of the motions, and, furthermore, they are correlated: increase in the variability of the amplitudes of the motions recorded at individual stations around the common amplitude implies increase in the variability of the phases around the common phase. The dispersion range of the amplitude and phase variability around their corresponding common components appear also to be associated with physical parameters. The spatially variable arrival time delays of the waveforms at the stations due to their upward travelling through the site topography, in addition to the wave passage delays identified from signal processing techniques, constitute another important cause for the spatial variation of the motions; their consideration in the approach facilitates also the identification of the correlation patterns in the amplitudes and phases. © 1997 by John Wiley & Sons, Ltd.

GENTILE, C.; MARTINEZ Y CABRERA, F.

doi: 10.1002/(SICI)1096-9845(199701)26:1<41::AID-EQE622>3.0.CO;2-Upmid: N/A

The theoretical and experimental investigation of a cable‐stayed bridge after major repair is described in this paper. Strengthening mainly involved the suspension system (originally with prestressed concrete stays) which was retrofitted by means of external tendons. Full‐scale tests were conducted to measure the dynamic response of the repaired system; the experimental program included both traffic‐induced and free vibration measurements. A total of 16 vertical frequencies and mode shapes were identified in the frequency range of 0–10 Hz. In the theoretical study, vibration modes involving deck, towers and cables were determined by using finite element models which accounted for the strengthening effects. Two‐ and three‐dimensional models were used so that the importance of three‐dimensional modes was estimated as well. The experimental results were compared to natural frequencies and mode shapes computed using theoretical models. For most modes the measured and predicted modal parameters compare well, especially for the vertical modes involving in‐phase motion of the stays. © 1997 by John Wiley & Sons, Ltd.

LU, L. Y.; YANG, Y. B.

doi: 10.1002/(SICI)1096-9845(199701)26:1<61::AID-EQE623>3.0.CO;2-Ppmid: N/A

The dynamic behaviour of a single degree‐of‐freedom (DOF) equipment mounted on a sliding primary structures subjected to harmonic and earthquake ground motions is studied numerically. To deal with the discontinuity nature of sliding structural systems, in this work the fictitious spring model is adopted. With the problem formulated in a state space form, an incremental numerical scheme capable of dealing with multi‐DOF sliding structural systems is proposed for solving the time history responses. Numerical examples excited by harmonic and real earthquake ground motions are considered in order to study the following three effects: (1)the variation of the frictional coefficient of the sliding support, (2)subharmonic resonance and (3)effect of tuning (i.e. when the frequency of the equipment is coincident with or close to the fundamental frequency of the primary structure) on the mounted equipment. The dynamic characteristics of the mounted equipment are highlighted in the analysis of the numerical examples. © 1997 by John Wiley & Sons, Ltd.

CABAÑAS, LUIS; BENITO, BELEN; HERRÁIZ, MIGUEL

doi: 10.1002/(SICI)1096-9845(199701)26:1<79::AID-EQE624>3.0.CO;2-Ypmid: N/A

The quantification and prediction of damage due to different seismic actions to structure types of different strength is an important problem not yet solved in the Earthquake Engineering field. In addition, owing to the fact that macroseismic information cannot be used directly in dynamic calculations, a new problem appears when these are the only kind of data available. Thus, there is a need to estimate a parameter to relate the energy of the ground motion and the damage occurrence, and eventually achieve a better seismic risk assessment. After the study and review of some representative potential damage parameters, attention has been paid to the Arias intensity (unfiltered and filtered in certain frequency ranges) and the Cumulative Absolute velocity (CAV) as the parameters to evaluate the energy of movement, and to relate them with the observed damage. The data used to infer these correlations have been provided by the ENEA‐ENEL (Italy). The information consists of strong motion records from the Campano Lucano (1980), Umbria (1984) and Lazio‐Abruzzo (1984) earthquakes, and data of damage to buildings in the vicinity of recording instruments (within a maximum radius of 300 m, where the soil conditions remain constant). In this paper, some relations have been obtained to quantify the damage level for different seismic inputs. The results suggest that unfiltered Arias intensity and CAV (for calculation threshold 20 cm/s2) correlate well with the macroseismic information used. Best fits are obtained between the quoted parameters and the observed damage in type A structures. © 1997 by John Wiley & Sons, Ltd.

ZHAO, J. X.

doi: 10.1002/(SICI)1096-9845(199701)26:1<93::AID-EQE625>3.0.CO;2-Apmid: N/A

For the one‐dimensional analysis of soft‐soil layers on an elastic half‐space, a general form of analytical solution is developed for converting radiation damping due to energy leaking back to the half‐space into equivalent modal damping, allowing the modal analysis technique to be extended to a site where radiation damping has to be accounted for. Closed‐form solutions for equivalent modal damping ratios and effective modal participation factors are developed for a single layer with a shear wave velocity distribution varying from constant to linearly increasing with depth. Compact and recursive forms of solutions for equivalent modal damping ratios are developed for a system with an arbitrary number of homogeneous layers on an elastic half‐space. Comparisons with numerical solutions show that the modal solutions are accurate. The nominal frequency of a site, i.e. the inverse of four times the total shear wave travel time through the layers, is an important parameter for estimating the high mode frequencies. A parameter study shows that for the same impedance ratio of the bottom layer to the elastic half‐space, a system of soil layers with an increasing soil rigidity with depth has, in general, larger peak modal amplifications at the ground surface than does a single homogeneous layer on an elastic half‐space, while a system with a decreasing soil rigidity with depth has smaller modal peak amplifications. © 1997 by John Wiley & Sons, Ltd.

ZHAO, J. X.; CARR, A. J.; MOSS, P. J.

doi: 10.1002/(SICI)1096-9845(199701)26:1<115::AID-EQE626>3.0.CO;2-0pmid: N/A

Apart from some special cases, calculating the dynamic stiffness matrix of foundations on a layered half‐space, especially for embedded foundations, is computationally expensive. An efficient method for two‐dimensional foundations in a horizontally layered soil media is presented in this paper. This method is based on indirect boundary element methods and uses discrete wave number solution methods for calculating Green's functions for displacements and analytical methods for the integrations over the boundary. For surface foundations, the present method applies at all frequencies. For embedded foundations or for constructing energy transmitting boundaries, because the free‐field part is modelled by boundary elements and the excavated part is modelled by finite elements, the present method applies only at low frequencies for the spring coefficients (the real parts of the dynamic stiffness matrix) but applies at all frequencies for the damping coefficients (the imaginary part of the dynamic stiffness matrix) for undamped sites. The novelty of the method can be used for three‐dimensional foundations. © 1997 by John Wiley & Sons, Ltd.

LIN, JIAHAO; LI, JIANJUN; ZHANG, WENSHOU; WILLIAMS, F. W.

doi: 10.1002/(SICI)1096-9845(199701)26:1<135::AID-EQE633>3.0.CO;2-6pmid: N/A

An efficient approach is proposed for analysing the non‐stationary random responses of complex structures located in an evolutionary inhomogeneous stochastic field. The approach is a kind of complete CQC method because the cross‐correlation terms both between the participant modes and between the ground joint excitations are included in the response calculations. The effect of the loss of coherency between ground joints is also taken into account. For non‐proportionally damped structures with many degrees of freedom, the order of the equations of motion can be reduced by using only real modes while structural non‐stationary random responses can still be computed conveniently and accurately. © 1997 by John Wiley & Sons, Ltd.

GAZETAS, G.

doi: 10.1002/(SICI)1096-9845(199701)26:1<147::AID-EQE635>3.0.CO;2-Upmid: N/A

The title of the book should be: FOUNDATION VIBRATION ANALYSIS USING SIMPLE PHYSICAL MODELS, by John P. Wolf, Prentice‐Hall, Englewood Cliffs, NJ07632, 1994. The omision of the word VIBRATION in the title as printed in the review is regretted.