A REVIEW OF THE ADEQUACY OF THE UGANDAN SEISMIC CODE (US 319:2003 CLAUSE 8) FOR ESTIMATION OF THE FUNDAMENTAL PERIOD OF VIBRATION OF BUILDINGS

Abstract

The determination of the fundamental period of vibration of a structure is essential to earthquake design. Current code equations (US 319:2003) provide formulas for the approximate period of generalized earthquake-resistant building systems, which are dependent on the height of the structure. Such a formulation is inadequate for various structures with lateral support mechanisms, inadequate for heights of structures above 20m for steel and heights above 30m for concrete frames. Additionally, its unable to account for structures with differing geometric irregularities. This study investigated the fundamental periods of different types of steel and concrete earthquake-resistant building structural models: steel moment resisting frames (MRF), steel concentrically braced frames (CBF), reinforced concrete (RC) structures with and without shear walls with varying geometric irregularities. A total of 24 MRFs, 12 CBFs, and 18 RCs were designed and analyzed with ETABS v.17. The fundamental periods based on vibration theory (Rayleigh equation) for each model were compared with empirical equations provided in the current code (US 319:2003). Based on the results obtained from vibration theory, equations for the approximate fundamental periods are put forth for MRFs, CBFs, RCs with shear walls and without shear walls which consider vertical and horizontal irregularities. Through statistical analysis (regression) using Datafit v.9.00 and comparison, it was found that a coefficient single-variable power model with consideration for irregularities resulted in a better fit to the Rayleigh data than the code provided empirical equations. The proposed equations were validated through a comparison of available measured period data against results based on vibration theory. Finally, conclusions from our observations of results and recommendations were recorded down.