Seismic displacement response spectrum estimated from the frame analogy soil amplification model

doi:10.1016/S0141-0296(01)00049-9

Engineering Structures

Volume 23, Issue 11, November 2001, Pages 1437-1452

https://doi.org/10.1016/S0141-0296(01)00049-9 Get rights and content

Abstract

This paper describes the development of a simple and rational manual procedure, termed the “frame analogy soil amplification” (FASA) model, which can be used to construct realistic seismic soil response spectra that account completely for the effects of soil resonance. FASA is based on the analogy of the dynamic response behaviour of a building to represent the dynamic behaviour of a horizontally layered soil column, when subject to earthquake excitations transmitted from bedrock. The theoretical foundation of FASA requires relatively few data for verification and calibration purposes. Thus, it is particularly suited to applications in regions of low and moderate seismicity where field data are typically limited. The procedure becomes even more powerful when its capability is extended to predict the response spectral displacement (RSD). This paper presents (1) a summarised account of the conception and development of the FASA-RSD model, (2) a comparison of the model predictions with response spectra computed from shear wave analysis (using the computer program SHAKE) and with response spectra recorded from the 1989 Loma Prieta earthquake, and (3) the application of FASA including commentaries and an illustrative example.

Section snippets

Background and introduction

The displacement-based (DB) approach of assessing seismic performance has attracted intensive research attention in the world arena over the past decade, and is slowly gaining acceptance in practice. Fig. 1 shows some classical examples of situations in which displacement is clearly the governing criterion of seismically induced ultimate failure. The cited examples are a building responding into the inelastic range, which is prone to failure by a soft-storey mechanism [Fig. 1(a)], a bridge

General conceptual development

The modifications of seismic shear waves by soil overlying bedrock are dominated by a number of mechanisms, including multiple reflections of waves from interfaces of high impedance contrast, causing resonance. Resonance of the seismic waves trapped within the soil layer develops narrow-band periodic waves in certain soft soil columns (Fig. 2). The periodic waves are then translated into a prominent amplification at a distinct “site period” in the soil response spectrum. Such a resonance effect

Verification of the FASA-RSD procedure

The seismic displacement demand predicted by the FASA-RSD procedure, introduced in this paper, has both random and modelling uncertainties. Random uncertainties have been introduced by the use of the ensemble average rock response spectrum, since the characteristics of the individual earthquake accelerograms have been eliminated by the averaging. Modelling uncertainties have also been introduced by numerous simplifications in each step of the procedure. For example, FASA accounts for the effect

Application of the FASA-RSD procedure

The determination of the RSD utilising FASA comprises the following steps:

Step One: determination of site natural period, T_g [Eq. (1)];
Step Two: identification of RSV_{(T_g)} from the design rock response spectra;
Step Three: determination of the soil response spectral velocity, RSV_max [Fig. 7 and , , ]; and
Step Four: determination of the bi-linear displacement response spectrum (RSD) based on the estimated T_g from Step One and the estimated RSV_max from Step Three (Fig. 11).

Commentaries relating to

Conclusions

1.
The displacement, velocity and acceleration response spectra of a soil site experiencing resonance are dependent mainly on the value of the site natural period (T_g). Such period dependence has been incorporated into the bi-linear compatible response spectrum model, as defined in Fig. 11.
2.
FASA draws the analogy between the vibrational behaviour of an MRF and that of a soil column in developing relationships to predict the peak ground velocity (PGV) on the soil surface [Eq. (5a) and Eq. (6a)] and

Acknowledgements

Invaluable contributions by Raymond Koo, Michael Cheng and Neaz Sheikh in providing results from SHAKE analyses for the purpose of Fig. 8, Fig. 10 and Appendix A are gratefully acknowledged. Contributions by information exchange in related investigations with Associate Professor T. Balendra of the National University of Singapore and by Associate Professor Pennung Warnitchai of The Asian Institute of Technology are also acknowledged.

The FASA model described in this paper has been developed as

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Seismic displacement response spectrum estimated from the frame analogy soil amplification model

Abstract

Section snippets

Background and introduction

General conceptual development

Verification of the FASA-RSD procedure

Application of the FASA-RSD procedure

Conclusions

Acknowledgements

J. Asian Earth Sci.

A computer program for earthquake response analysis of horizontally layered sites

Earthquake Engineering Research Centre Report EERC 72-12

Substitute structure method for seismic design in R/C

J. Struct. Div., ASCE

A global analysis of earthquake displacement response spectra

Displacement spectra for seismic design

J. Earthquake Eng.

Response spectral relationships for rock sites derived from the component attenuation model

Earthquake Eng. Struct. Dyn.

Response spectrum modelling for rock sites in low and moderate seismicity regions combining velocity, displacement and acceleration predictions

Earthquake Eng. Struct. Dyn.

Generation of synthetic earthquake accelerograms using seismological modelling: a review

J. Earthquake Eng.

Site response studies for purpose of revising NEHRP seismic provisions

Earthquake Spectra

Estimates of site-dependent response spectra for design (methodology and justification)

Earthquake Spectra

Introduction to a new procedure to construct site response spectrum

International building code, 2000 (IBC-2000)