SEISMIC PERFORMANCE AND VULNERABILITY ASSESSMENT OF MASONRY INFILLED STEEL AND CONCRETE FRAMES

Abstract

Construction of masonry infilled frame structures is common practice in countries like Pakistan. Infills contribute to the performance of structures which is generally neglected in analysis and design by considering it as non-structural element. However the infill panels have significant in-plane stiffness that contribute to the frame stiffness and as a result presence of the infills significantly increases the strength, stiffness and frequency of the frame structures. The purpose of this study is to evaluate and compare the seismic behaviour of bare and masonry infilled steel and concrete frames. Different types of infill materials have been considered in this study. These infill materials include brick masonry, solid concrete block masonry and hollow concrete block masonry. Experimental testing has been performed to determine the compressive strength of the masonry infill. Three, five, seven and nine story, steel and concrete frames designed under gravity loads have been considered in this study. Seismic performance assessment and seismic vulnerability assessment has been conducted for detailed evaluation of seismic behaviour of masonry infilled frames. Seismic performance assessment is concerned with the evaluation of local and Global parameters of a structure when it is subjected to seismic loads. Key performance parameters evaluated are Fundamental time period, roof displacement, base shear, Interstory drift, infill stresses and member forces. A time history analysis has been performed for the evaluation of these global and local parameters of infilled frames. SAP2000 has been used as an analytical tool for seismic performance assessment of structures considered in this study. Infill panels have been modelled using both macro modeling (diagonal strut) and micro modeling (Finite element modeling) techniques. Effect of location of openings (doors, windows) on seismic behavior of infilled frames has also been discussed in detail. Seismic Vulnerability assessment is conducted to evaluate the seismic hazards corresponding to various levels of damage in the building. Perform-3D has been used as an analytical tool for this purpose. Cyclic pushover analysis followed by the capacity spectrum method and seismic vulnerability assessment framework proposed by Kyriakides (2007) have been used to derive the vulnerability curves for bare and masonry infilled frames. The vulnerability curves show an improvement in overall performance of frames with the inclusion of infill panel. In view of the results of this study, it can be concluded that brick masonry has the best earthquake performance than the other two types of infills considered in this study. Then comes the hollow concrete block and last is the solid concrete block masonry. It is also concluded that masonry infills have a significant effect in altering the seismic behavior of building frames. They increase the stiffness of the structure which ultimately results in an increase in earthquake resistance of the structure. However presence of openings in infill panel makes the seismic behavior of infilled frames very complex. Finally designers must be cautious about the role of infill panel during an earthquake to avoid soft story and weak story failures of structures.