Masonry Infill RC Frames with Openings: Review of In-plane Lateral Load Behaviour and Modeling Approaches

Sachin Surendran

doi:10.2174/1874836801206010126

Abstract

Un-reinforced masonry walls are commonly used as infills in reinforced concrete (RC) buildings. These build- ings have high in-plane stiffness and strength, and therefore, the lateral load behaviour of such RC frames is different than that of the frames without infill walls. Openings in walls significantly reduce the lateral strength and stiffness of RC frames, and alter their failure modes. Past researchers have tried to find out experimentally and analytically the influence of several parameters, like opening size and location, aspect ratio of openings, connection between frame and infill wall, ductile detailing in frame members, material properties, failure modes, etc. on behavior of masonry infill RC frames. Ac- cordingly, several analytical models have been proposed in the literature and seismic codes of some countries to model the stiffness and strength properties of infill walls. Most of the past studies and seismic codes recommend modeling the infills as equivalent diagonal struts, and cross-sectional area of the struts are reduced appropriately to account for openings in the walls. Analytical methods have also been proposed to estimate the possible mode of failure and lateral load carrying ca- pacity of infill frames with and without openings. The current article is intended to review and compare past relevant stud- ies and seismic codes of different countries on in-plane lateral load behaviour and modeling approaches for masonry infill RC frames with openings. The comparative study may help designers and code developers in selecting and recommending suitable analytical models for estimating strength, stiffness, failure modes, and other properties of infill RC frames with openings.

Highlights

Reinforced concrete (RC) frames infilled with unreinforced masonry walls are quite commonly constructed all across the globe since many decades
Large number of experimental and analytical studies has been undertaken in the past by many researchers all over the world to investigate the effect of openings on the lateral stiffness, strength, failure modes, and other properties of infilled frames with openings
Positions and sizes were included to study the behaviour of infilled frames under the action of lateral loads

Summary

INTRODUCTION

Reinforced concrete (RC) frames infilled with unreinforced masonry walls are quite commonly constructed all across the globe since many decades. Twenty DCDTs measured total length changes across main and off diagonals of the masonry, and across window opening and a hydraulic actuator of capacity 245 kN was used to apply story displacements.Free vibration and static flexibility tests were performed on the concrete frame before the infill was built and repeated again after construction of the infill to estimate modal frequencies and natural damping ratios. The test results give good insight into the behaviour of masonry infilled RC frames with openings in walls under dynamic loads, and subsequently to develop methods to improve the lateral load performance of such buildings. The lateral stiffness of the equivalent trusses can be calculated as:

AdEt cos3!

Findings

SUMMARY AND CONCLUDING REMARKS