Seismic Vulnerability Assessment of Strengthened RC Structures

Abstract

The objective of this research work is to assess the seismic vulnerability of a retrofitted RC frame. An analytical curve is developed for that purpose. The confinement behavior in RC columns is explained in detail. The confinement mechanism in Fiber Reinforced Polymer (FRP) confined concrete is discussed in particular. The critical areas in a frame are near joint regions of columns which are critical in withstanding earthquake forces. Similar phenomena were observed in the Kashmir (2005) earthquake (Ali, 2005). The provision of confinement to these critical areas can improve the overall performance of the structure. The bar pullout mechanism is also discussed, which is not taken care of while modeling the structures (Harajili, 2007.). The provision of confinement also improves the bond strength of members. Different methods of seismic vulnerability assessment along with their advantages and disadvantages are discussed. An experimental program was carried to see the effect of CFRP confined concrete as compared to un-confined concrete. Small scale specimen were tested using different layers of CFRP and their results were used in analytical modeling of a typical deficient RC frame using an appropriate analysis program. The results of experimental work done on a typical deficient RC structure by Chaudat et. al, (2005) were available. Therefore, a simple analytical model of this experimental work is developed to observe and compare the overall behavior of the deficient RC structure with the FRP strengthened frame. An analytical tool based on finite element modeling (Graham et. al., 2006) was used in this research work. The improved properties of four different levels CFRP confined concrete were modeled in the software and the bar pullout effect was also incorporated to see the effect of CFRP on seismic performance. After the analysis, the results are used to derive seismic vulnerability curve for reference and retrofitted frames for comparison. Seismic vulnerability curve is derived using seismic vulnerability assessment framework proposed by Kyriakides (2007). The curves show improvement in overall performance of the deficient RC structure after being retrofitted with CFRP.