Shape Of Response Spectra Research Articles

Hazard-Consistent Ground Motions: Generation on the Basis of Uniform Hazard Fourier Spectra

Design seismic forces depend on peak ground acceleration (PGA) values and on the shape of response spectra (RS) dictated by building codes or that need to be evaluated on a site-specific basis. The PGA values and RS strictly depend on earthquake magnitude and distance, style of faulting and in cases, near-source effects (e.g., rupture directivity), as well as on the regional and local geological conditions. At present, there is no doubt that it is necessary to construct so-called site- and region-specific building code provisions reflecting the influence of different magnitude events at different distances that may occur during the lifetime of the construction, as well as the variety of local ground conditions. A scheme of Uniform Hazard Response Spectra and PGA estimation considering local site response is described in this article. The assessments of these design parameters are obtained on the basis of Uniform Hazard Fourier spectra using the concept of “dominant earthquakes”. The effect of local geology is included by means of the soil/reference site spectral ratios. The results of using the method are presented for the regions characterized by different seismicity and tectonics and compared with the data obtained during the recent strong earthquakes: the Caucasus (Armenia, the 1988 Spitak earthquake region) and the Turan Plate (Central Asia, the 1979 and 1984 Gazli earthquakes region).

Amplification Factors for Equipment Design Subjected to Seismic Loading

A mathematical technique is developed to evaluate the seismic response of primary equipment supported directly by the main structure and also the response of secondary equipment supported by the primary equipment. The method can be used for structures ranging from the simple to the complex, and is amenable to calculations based on standard spreadsheet or numerical software or, if desired, can be programmed. The technique can be used to develop amplification factors for seismic motion between ground, structure, and equipment. Alternatively, the method can be utilized to develop the ground response (or structure motion) spectra for various structural damping ratios and also floor response (or equipment response) spectra directly from a ground motion spectrum given as datum. The results are compared with the results from other well-established methods. The proposed method has an advantage over the other methods in that it enables direct computation of the third level response, i.e., response of the secondary equipment supported by the primary equipment; also, the method can be readily applied to any shape of ground motion response spectrum given as datum.

Behaviour of near‐source vertical and horizontal response spectra at smart‐1 array, Taiwan

AbstractOver 700 accelerograms recorded from 12 earthquakes in northeast Taiwan have been analysed for investigating the behaviour of the vertical and horizontal peak and spectral ground motion in the near‐source region. Pseudo‐relative spectral velocities (PSV), at 5 per cent critical damping for 23 frequencies in the range of engineering interest have been subjected to non‐linear regression procedures in terms of magnitude and hypocentral distance. Predicted response spectra for several discrete distances and magnitudes are presented. The results show that the shape of response spectra for both vertical and horizontal components of ground motion is magnitude‐ as well as distance‐dependent.The 2/3 ratio of vertical to horizontal ground motion, commonly used in engineering applications, appears unconservative in the very near field for high frequency ground motion. However, it falls below 1/2 at distances greater than 50 km. The same ratio for peak ground velocity (PGV) and peak ground displacement (PGD) tends to increase with distance—the latter at a faster rate.

On reliability-based structural optimization for earthquakes

A formulation is presented for the minimum-weight design of a structure subjected to an earthquake ground motion and constrained by a specified upper bound on overall probability of failure. The formulation includes a probabilistic representation of earthquake response spectrum shape and structural stiffness characteristics. Examples are presented which provide insight into basic features of reliability-based earthquake-resistant designs, and also illustrate the effects of different material characterizations and different assumptions regarding parameter distributions. In addition, designs based on the probabilistic representation of response spectrum are compared to designs based on deterministic response spectra which correspond to particular levels of probability of occurrence.

Effect of soil properties on earthquake response

It is recognized that the nature of Earthquake motions, and hence their effect on structures is dependent to a large degree on the subsoils through which they pass, This paper presents the results of a computer investigation into the effects of surface layering at the site of a proposed motorway bridge. Dynamic strain controlled triaxial tests were conducted to determine the stress-strain relationships of the soils encountered. It is concluded that the site characteristics determine the seismic response and thus control the shape of the surface motion response spectrum.