¹M.E. Student (Structural Engg.) Civil Engineering Department Jabalpur Engineering College Jabalpur India

²Associate Professor Civil Engineering Department Jabalpur Engineering College Jabalpur India

A common type of construction in reinforced concrete (RC) buildings involves filling the vertical spaces created by the adjoining RC beams and columns with unreinforced masonry walls. The walls usually referred to as infill walls, in most instances are built as partitions or as cladding after the frame is constructed. The infill masonry is usually about 230-250mm thick and is mostly composed of burnt clay bricks, burnt clay tiles or hollow concrete blocks, in cement mortar. In such structures, the infill's often control the global response and performance, especially when acted upon by lateral loads. Experience from past earthquakes shows that strong infill's, although non engineered, often provide most of the lateral resistance and prevent collapse of relatively flexible and weak reinforced concrete frames, that are necessarily designed for the seismic forces. 

Role of infill's in altering the behaviour of moment resisting frames and their participation in transfer of loads has been established by decades of research. The surveys of buildings damaged in earthquakes further reinforce this understanding. The positive aspects of the presence of infills are higher strength and higher stiffness of the infilled frames. Nevertheless, it may not be appropriate to neglect their presence and declare the resulting design as conservative. Observed infill induced damage in the buildings in the past earthquakes exposes the shortcomings of the current bare -frame approach. The non-uniform distribution of infill walls along the plan and elevation of the buildings is on of the main reasons for the damage to such structures. 

Two opposing approaches exist in the design practice. According to the first, infills induce a significant source of uncertainty in
the seismic response, negate the efforts of the designer to control the seismic response and performance of the structure, and overall have more negative effects than positive. Accordingly infills are rendered non structural through proper isolations from surrounding structural members. But on the contrary, the other encourages the infills to be made integral with the frame and their strength and stiffness to be included in the design of the building. Because of economical considerations and uncertainty in the peak seismic demand on structure, including every element that contributes to earthquake resistance in both necessary and beneficial. 

The present study shows that infill's reduce the drift capacity and structural damage, and significantly increase the strength and stiffness of the structure. The column, beams and infill walls in the lower stories are more vulnerable to damage than those on the upper stories. The role of plinth beam is found to be significant when the contribution of infills is taken in to account in the building design. The structural ductility is reduced but the over strength is increased with the presence of infill's.