Development of diagonal strut width formula for infill wall with reinforced opening in modeling seismic behavior of RC infilled frame structures

Abstract

The numerical study was conducted to determine equation of diagonal strut width to model infilled reinforced concrete (RC) frame structures with reinforced opening. The equation is necessary because, despite the opening, infill masonry wall in RC frame is capable of strengthening existing structures. Validation models of diagonal strut (ST) and shell elements (SH) were first made in SAP2000 to mimic the behavior of tested infilled frame RC structures with opening reported by others. The valid models were then used to predict the equivalent width of diagonal strut for the infill wall with opening percentage of 10, 20, 30, 40, 50 and 60%. The fitted data were then plotted and simple regression analysis was used to obtain equation that correlate between the opening percentage (r) and the stiffness reduction coefficient (c) associated with the wall opening. The proposed equation was then applied to model 2-6 storey infilled frames together with the shell element models for the wall opening ratios of 10, 20, 30, 40, 50 and 60%. It was revealed that the ST and SH models can mimic the true behavior of tested infilled RC frame with reinforced opening up to the maximum load. The equivalent strut width formula is then proposed in the form of wds = (d/4).c and c = (1.0565r2 - 2.281r + 1.3764). The d is diagonal length of the strut. Interestingly enough, the model with door opening is stronger than the model with window opening of equal opening ratio. More interestingly, the model with door opening is stronger than the model with solid infill due to the contribution of lintels to stiffen the structure. The data obtained from these models suggest that despite the opening, the infill wall should be considered in modeling the structure to have more accurate response.