In-plane flexural strength of unbonded post-tensioned concrete masonry walls

The target of this paper is to develop a design equation to predict the in-plane flexural strength of unbonded post-tensioned masonry walls (PT-MWs). Using validated finite element models, a parametric study was performed to investigate the effect of different parameters on the wall rotation and compression zone length. Multivariate regression analysis was performed to develop an equation to estimate the rotation of the unbonded PT-MWs at peak strength. Using the drift capacity of the walls and the proposed equation, a design expression and a related step-by-step design method have been developed to estimate the flexural strength of unbonded PT-MWs. The accuracy of the procedure was examined using experimental and finite element model results. Ignoring the elongation of the PT bars in the strength prediction resulted in an underestimation of about 40%, while using the proposed approach the prediction improved significantly. It was found that the wall length and axial stress ratio are the most influential factors contributing to the rotation and compression zone length of unbonded PT-MWs. According to the results presented in this study it is recommended to limit the axial stress ratio to a value of 0.15. In addition, limiting the maximum spacing between PT bars to a distance of six times the wall thickness is recommended to prevent local shear failure and vertical splitting cracking.