Vulnerability Assessment of Structures Subjected To Earthquakes (VASE) In Pakistan

Abstract

The threats and damages of Earthquakes are intense and Pakistan is located in one of the most seismically active zones of the world. Historic earthquakes like Taxila earthquake of 25 AD, Quetta earthquake of 1935, Kashmir earthquake of 2005, Ziarat Earthquake 2008 and recent Dalbandin Earthquake 2011 bear testimony to the seismicity of the country. Quetta is located in seismic zone 4 according to Building Code of Pakistan (BCP) 2007 and is surrounded by a number of faults. The seismicity of the area is studied and compiled for better understanding and preparation for future hazards. Current practices for construction in Quetta are conservative and development is slow paced. Traditionally Peak Ground Acceleration (PGA) is used in design calculations for lateral loads on structures. However alone PGA does not amply define the seismic load and modern international building codes emphasize on use of spectral acceleration values. But such parameters don’t exist for any city of our country. In order to derive these parameters probabilistic seismic hazard analysis has been carried out for Quetta city. Short period spectral acceleration at 0.2 second (Ss) and one second spectral acceleration (S1) were calculated and plotted for the entire district of Quetta and surrounding areas. Seismic analysis of buildings is generally carried out by applying an equivalent lateral load. However dynamic analysis is required for important buildings or those of irregular geometry. Dynamic load can be defined as a response spectrum function or time history function. Response spectrum function was created for typical soil type D. Results of PSHA were de aggregated and a maximum earthquake scenario was defined for Quetta. Time history functions of real recorded events matching with the scenario earthquake were selected and scaled to match the design spectrum. A suite of three accelerograms each with two horizontal components were selected for time history analysis. In order to check the adequacy of defined loading, a five story building was modeled and analyzed using static, response spectrum and time history load cases, the results were found comparable. Testing in Engineering Dynamics and Earthquake Engineering is still an area of exploration. Experimental Setup using Shake table is initiated at SCEE, NUST programs for Quetta time histories were written in MATLAB/SIMULINK to scale different excitations. The aim was to develop an operational SIMULINK simulation which can effectively be used to operate the Shake table and the single storey model. The scaled accelerograms suit developed was used to excite the shake table and response was observed. The work is extended to dampen the vibrations using active and passive mass damping approach.