<p>Using post-tension (PT) slabs as the floor system has become one of the common trends in concrete high-rise buildings (HRBs) construction. The traditional practice for the design of these slabs is to use a separate analytical model for each floor independent of the complete building model. The effect of this practice on analysis of PT slabs is investigated in the current paper considering different scenarios found in previously built HRBs. Based on the numerical validation of results against previous research on existing buildings, the current paper provides a recommended criteria to conduct a more accurate estimation of the analysis outcome. One of the investigated scenarios is the interaction between PT and non-PT slabs within the same HRBs when using staged-construction analysis. Interaction between PT and non-PT slabs is usually neglected as this interaction could only be investigated using a complete three-dimensional model. Another scenario is the effect of vertical irregularity of HRBs on the PT slabs due to the excessive differential axial shortening between vertical elements. Structural behaviour of three representative office buildings, including both PT and non-PT floors, is investigated. It is found that three-dimensional modelling shall be adopted to account for actions such as diversion of slab precompression (upon application of prestress) through flexure and shear in vertical elements to the adjacent non-PT slab. In addition, staged-construction was found an accurate method to evaluate the overall deformations of the structure during and after construction.</p>