Seismic Retrofitting of Non-Ductile Reinforced Concrete Moment Resisting Frame Structures

摘要

Many reinforced concrete frame structures built before the 1970's can be classified as non-ductile and seismically deficient. The objective of the current research project is to investigate innovative, yet cost effective seismic retrofit methodologies for seismic upgrading of non-ductile reinforced concrete frame buildings. A 10-storey reinforced concrete moment-resisting frame building was first designed for Ottawa using the 1963 practice as a representative of seismically deficient older building. The building was then investigated analytically. Three retrofit schemes were considered, consisting of adding: shear walls, diagonal steel braces, and diagonal prestressing cables. The analyses were carried out with 2-D models using SAP2000 and 3-D models using ETABS. Both Equivalent Static Force Procedure (ESFP) and dynamic analyses were employed. The dynamic analyses were based on modal response spectrum method using Ritz vector analysis. The numerical results demonstrated that seismic forces imposed on the structure computed by dynamic analysis is consistent with the ESFP; while the displacements predicted by ESFP were overestimated and hence conservative. The retrofitting schemes considered were effective in reducing roof drift demands by approximately 1/2. The steel bracing techniques proved to be effective while adding shear walls resulted in substantially more structural stiffness, leading to a decrease in building period, thus attracting higher seismic forces. The analysis results of 2-D and 3-D models were found to be in good agreement. The numerical analyses described herein are used to develop effective retrofit techniques for verification through large-scale testing under simulated seismic loading.