Civil and Architectural Engineering Civil and Architecural Engineering Department-College of Engineering-Sultan Qaboos University

Comparison Of Omani Seismic Code With International Counterparts

Hasan Abdul Saeed

Abstract

Seismic codes represent the guidelines on how simple buildings should be designed to ensure

that they can adequately resist seismic force during earthquake. Oman have been working

towards preparing its own seismic code for buildings. The code defines the Sultanate to have

two seismic zones (Zone 1 and Zone 2). This research focuses on the comparison of this Omani

Seismic code (OSC draft version) with International seismic codes (UBC97 and IBC2006) to

address the fundamental difference in terms of lateral forces distribution, maximum lateral

storey displacement, base shear and bending moments in structural components with three

building heights using three different analysis methods. The results have been compared on the

basis of international design practice and then based on seismic hazard level. From the design

perspective, Muscat which belongs to Zone-I according to OSC is defined as Zone-2A in UBC

and Zone-II in IBC, while from the seismic hazard perspective it actually is comparable with

Zone-1 and Zone-I of UBC and IBC respectively. For all the scenarios (building type and

analysis method) investigated, the UBC is found significantly more conservative than OSC &

IBC based on International design practice. The values of base shear obtained using UBC97

code are 40 to 70% higher and those from IBC are 30 to 65% more than the value obtained by

using the OSC for all buildings. The difference on base shear values between OSC and UBC &

IBC decreases as the building height increases. The UBC design response spectra have higher

spectral acceleration over the entire period range, and as a result, the response spectrum analysis

provides a much higher base shear, displacement and moment in the structural members as

compared to IBC and OSC. Similar results pattern is observed in dynamic analysis. Further,

comparison between the codes based on seismic hazard, the OSC is found slightly more than

UBC & IBC. Finally, a brief comparison is made to do the cost benefit analysis for mostly

constructed low rise building under seismic and without seismic design using UBC and OSC

code. It is found that the strength and stiffness requirements for OSC is much lower compared

with UBC97 currently implemented design practice. Therefore, Omani Seismic Code is

preferable and more economical alternative for seismic design of low rise buildings in Oman.