Analysis and Design Methods for Infilled Frames with Confined Openings

Abstract

Openings in the walls of infilled frame structural systems are very common. Reinforcement around the wall openings confines and strengthens the wall, making an infilled frame with a confined opening (IFcO) a reliable structural system for seismically active regions. To encourage the application of IFcO, an analysis method is proposed by introducing a simple equivalent diagonal strut formula with reduced width due to the wall opening. Finite element models using shell elements were used as reference to develop strut width formula for IFcO with varying opening ratios (r) and diagonal angles (?). The formula was verified against previous test results and then applied for the design of 3 and 5-story buildings, consisting of IFcOs with r of 30, 60 and 80% to represent medium, large and very large openings. The seismic responses of the strut models were then compared to those of the shell and the bare frame models. The effect of the opening on internal forces, frame reinforcement, wall stresses and soft story mechanisms were also investigated.

Keywords

• Confined opening
• Diagonal strut
• Infilled frame
• RC frame design
• Seismic load