Comparison of available expressions in predicting the flexural strength of self-centering masonry walls

The restoring nature of the post-tensioning (PT) force in self-centring masonry walls (SMWs)returns the wall to its original vertical position and minimizes the residual displacement. While strain compatibility equations can be used to determine strains in structural elements having bonded reinforcement, it cannot be applied to SMWs. The current approach of the Masonry Standards Joint Committee (MSJC 2013) ignores the stress increase in PT bars beyond initial post tensioning.However, several experimental and finite element studies have shown that under lateralloads the post-tensioning force increased, and the stress in the PT bars is a function of wall rotation and neutral axis depth. In this study, the accuracy of different expressions to predict the flexural strength of SMWs is investigated using experimental results of 18 SMWs tested under in-plane loading as well as finite element analysis results. The walls of the experimental database were all fully grouted and had heights ranging from 2800 mm to 5250 mm, lengths ranging from 1000 mmto 3000 mm, compressive strengths ranging from 13.3 MPa to 20.6 MPa and axial stress ratios ranging from 0.04 to 0.2. In this study four different available methods are considered to predict the in-plane flexural strength of SMWs, including MSJC 2013 (no PT bar elongation) and methods A, B and C proposed in other studies. Comparing the prediction obtained from MSJC 2013 and other available methods, with experimental results and finite element analysis result revealed that ignoring the elongation of PT bars in strength prediction resulted in a considerable underestimation of the flexural strength of SMWs. Using other methods, such as Method C, could significantly improve the prediction.