A STUDY ON DUCTILITY AND SEISMIC INDICES FOR SEISMIC EVALUATION OF EXISTING REINFORCED CONCRETE BUILDINGS IN THE PHILIPPINES
Supervisor: Masanori TANI
The metropolitan region of the Philippines is expecting a large magnitude earthquake that will greatly affect the area and may lead to over 34,000 deaths and destroying 40% of structures. With this risk, a seismic evaluation of existing structures should be applied to identify the buildings which need retrofitting for effective disaster mitigation. The common characteristics of RC columns in the Philippines are smaller sections, high steel ratio and large axial load ratio. In this research, the Japanese seismic evaluation procedure developed by JBDPA was examined to determine its suitability for adaptation to the Philippines. The effect of confinement of RC columns on the ductility was analyzed by section analysis, in order to identify the characteristics of column sections in the Philippines. To consider the common design strength and deterioration of existing buildings in the Philippines, 20.7 MPa and 14.0 MPa concrete strengths were applied for six sample models. Additional evaluation considering the spalling of concrete cover, was performed to check its effects on the ductility of the columns. It verified that the confinement increased the ductility of RC columns and the capacity of the core concrete decreased after the cover concrete spalled. A seismic demand index for RC buildings in the Philippines was proposed, based on the results of the section analysis and the Philippine structural code. It is proposed to be the basis for judgment of the seismic capacity of existing RC buildings in the country. An existing sample building in the country was evaluated using the JBDPA standard and was compared to the proposed seismic demand index. It shows that the building is not adequate at a certain level of safety and needs retrofitting. A pushover analysis was also performed to have a confirmatory investigation.