Probabilistic Seismic Hazard Assessment and Seismic Design Provisions for Sudan

Abstract

Seismic hazard can be evaluated by calculating the different factors of seismic design such as seismic acceleration, velocity or displacement, which are the necessary factors to be used in designing buildings and structures in a region. This thesis deals with seismic hazard in Sudan and its vicinity to fill the gap between seismicity studies and engineering studies in designing earthquake-resistant buildings by providing designers with the expected peak ground acceleration (PGA) at any location in Sudan. A comprehensive review of previous work in engineering applications of seismic hazard analysis in the world since 1975 was made, then the analytical method based on probability approach was applied. An updated catalogue of earthquakes in Sudan covering the period 1632 – 2007 was used. A modified version of Earthquake Risk Program (EQRISK) was used and the whole region was divided into seismic sources based on the prevailing tectonics and seismicity of the region. The seismic hazard analysis for Sudan and vicinity was performed to calculate the maximum expected seismic acceleration at any site in Sudan. This analysis was carried out by assuming 10% probability of exceedance of peak ground acceleration (PGA) for exposure time periods of 50, 100, 200 and 500 years. From this analysis seismic hazard curves for main Sudanese cities were prepared. In addition, seismic hazard contour maps for Sudan and vicinity were prepared and plotted. Seismic hazard curve represents seismic ground acceleration at a site and its probability of occurrence. Contour maps are used to determine the required acceleration to design all types of structures to resist the expected ground motion during the exposure time periods of buildings. To overcome the traditional problem of incomplete and inhomogeneous earthquake data, a sensitivity study was carried out to evaluate the different assumptions on the final results, and then the appropriate parameters were determined according to data type and study nature.

In this thesis, seismic provisions for Sudan were proposed and seismic factors were suggested to help in designing earthquake-resistant structures in Sudan. Seismic codes worldwide were reviewed to propose these regulations. Such regulations are needed for the development of a Sudanese seismic code. In order to test the accuracy of these regulations compared with other seismic regulations, a reinforced concrete frame was seismically analyzed using the equivalent static lateral force procedure. From the calculation of base shear and lateral forces in the frame, the results obtained by the proposed regulations show good agreement with those obtained by other regulations.

Finally, a multi-story RC frame in Khartoum city was analyzed and designed under moderate earthquake loads as an application of seismic hazard in Sudan and to investigate the performance of our existing buildings if exposed to seismic loads. The design revealed the inadequacy of sections and reinforcement areas which need to be increased to resist stresses generated from seismic loads. This frame was analyzed and designed in accordance with the seismic provisions proposed in this study. The results obtained, clearly, show the importance of taking the proposed provisions into account when designing multi-storey buildings in Khartoum area.