Seismic performance of soft storey structures retrofitted with FRP wraps

Abstract

Design of seismic resistant structures is based on the assumption that real structures yield when subjected to design level ground acceleration. Assessment of seismic vulnerability of reinforced concrete buildings in the earthquake prone regions is a challenging task. The traditional approach to seismic design of a building is a force-based design. In this approach, there is no measure of the deformation capability of a member or of a building. Structural failures of soft-storey structures in recent earthquake have exposed the weakness of current design procedures and shown the need for new concepts and methodologies for building performance evaluation to enable necessary retrofit measures. Pushover-based seismic evaluation is now able to directly calculate the nonlinear seismic demand and evaluate its consequences on the structures. Applied Technology Council-40 (ATC-40), 1996 and Federal Emergency Management Agency (FEMA), 2002 proposed a simplified nonlinear static analysis (Pushover Analysis) procedure. The central focus of the simplified nonlinear procedure is the generation of the “Pushover” or Capacity curve. The nonlinear static (Pushover) analysis has become increasingly popular in structural applications around the world. Numerical tools like SAP 2000 developed by Computers and Structures Inc., which can perform the pushover analysis. In this thesis the main focus is to evaluate the seismic performance of soft storey structures retrofitted with FRP wrap in the plastic hinge region. Structural deficiencies of the soft storey buildings have been determined to demonstrate how their performance can be improved under seismic action. Eight Soft-Storey Building models located at Dhaka city are studied by pushover analysis using SAP 2000. The results obtained from analysis show that all the structures contain seismic deficiencies and require seismic retrofitting. Fiber reinforced polymer (FRP) composites have found increasingly wide applications in civil engineering due to their high strength-to-weight ratio and high corrosion resistance. One important application of FRP composites is as wraps or jackets for the confinement of reinforced concrete (RC) columns for enhanced strength and ductility. In this thesis, GFRP (Glass Fiber reinforced polymer) is considered for FRP wraps which is quite expensive. However, additional cost involvement are estimated as per standard rates and found within 0.49% to 3.75% of the total project cost for getting desired level of seismic performance as per ATC 40 and FEMA 356.