A STUDY TO DETERMINE OPTIMAL THICKNESS FOR POST-TENSIONED CONCRETE FLAT SLAB WITH 3D PLATE FINITE ELEMENT USING RAM CONCEPT PROGRAM

Abstract

This research presents optimal thicknesses for post-tensioned concrete flat slabs based on construction costs in Thailand including concrete, prestressing stand, rebars and formworks and labors. The trial designs were performed for various thicknesses to determine the optimal ones that give lowest total cost per area. RAM Concept program based on 3-dimensional plate finite element analyses were used. There are three studied column layouts including (1) square (2) rectangular and (3) zigzag having short to long span ratios 0.5, 0.75 and 1.0 with long span length 6, 7.5 and 9 m, 200, 300 and 400 kg/m2 live loads and 320 and 400 kg/cm2 ultimate compressive strength concrete. Punching shear reinforcement or necessary drop panel are required to add at the columns where the concrete cannot resists the punching shear. The results from the designs were used to determine the predicted equations for the optimal slab thicknesses. This guideline could help engineers and other interested with their preliminary designs and the construction cost estimations. From this study, the predicting equations have correlation coefficient R2 between 0.84 to 0.99. The ratio of length slab thickness from Post-Tensioning Institute has ranged from 45 to 50, but while the ratio from this study are between 49 to 52. The comparison with similar studies but CSI SAFE V12.3.2 shown that the optimal thicknesses are +3%, +7% and +2% different from this study in case of square, rectangular and zigzag respectively.