Reza Hassanli1, Mohamed ElGawady2, and Julie E. Mills1
1)  University of South Australia
e-mail: {reza.hassanli, Julie.Mills}
2)  Missouri University of Science and Technology

Keywords: Rocking response, In-plane, Pre-stressed masonry, Simplified approach, Neutral
axis depth, Ductility.

Abstract. The accuracy of the MSJC (2016) code in predicting the lateral in-plane strengthof unbonded post-tensioned masonry walls (PT-MWs) was investigated, and a simplified method was proposed. The accuracy of the ductility criteria for PT-MWs provided in the MSJC (2016) was also discussed and some recommendations were provided. In order to develop the simplified method, the accuracy of an analytical model was first verified against experimental test results. This was followed by a parametric study and multivariate regression analysis to develop an empirical equation to estimate the neutral axis depth at the wall peak strength. The proposed neutral axis depth equation was then incorporated into the flexural analysis of PT-MWs to develop a new simplified expression to estimate the stress developed in the post-tensioned tendons, and accordingly to calculate the lateral strength of PT-MWs. Using experimental results, it was shown that the proposed method could significantly improve the prediction. As is discussed in this paper, it seems that the limit of a/d= 0.38 provided in MSJC 2016 (determined originally for conventional reinforcement masonry), cannot reflect the ductility response in either bonded or unbonded pre-stressed masonry walls, and hence a better design method is required. It was suggested that the a/d limitation could be removed from the code, and instead the designer should be required to control the yielding of the outermost tensile steel using strain compatibility conditions for the case of bonded PT masonry walls. It was also suggested that for unbonded masonry walls the ductility should not be attributed to the yielding of the PT steel, and also, in design, it might be better to prevent the yielding of the post-tensioning steel, to ensure a self-centering response.