Study of Productivity rate in Construction of Post-Tension slab in high rise building Projects.

Abstract

This research studies labor productivity and cost in construction of post-tension slabs in high-rise buildings. Construction of post-tension slabs involves six steps : table-form installation, side-formwork installation, bar reinforcement, wire rope installation, concrete pouring, and stressing and grouting. In the study, field works at two construction sites were observed and workers’ actions were collected for further analysis. These actions were classified into three different categories including effective work, essential contributory work, and not useful work. Once these actions were classified, they were used to calculate the labor utilization factor (LUF) and the labor productivity in each step. The results show that the labor productivity in construction of post-tension slabs ranges from 6.5 sq.m./man:day to 14.8  sq.m./man:day  with LUF rated between 48% to 92%, depending on various factors such as complexity of building designs, the use of wire mesh as a replacement of conventional rebar reinforcement, appropriate concrete pouring method and arrangement of labors that are suitable for the size and type of work. Besides the productivity, this research examines and compares two approaches by which contractors use to determine labor costs in construction of post-tension slabs. The first approach that is calculating a lump-sum labor cost based on weight of wire ropes. This approach is widely used by post-tension subcontractors to determine bidding costs to charge main contractors or owners. The other approach is calculating costs based on the number of man-days used to finish the entire works. These costs may be considered subcontractors’ actual costs. The results of this research show that a lump sum cost based on weight of wire ropes is 26-37 bath/sq.m. of slabs while a labor cost based on the number of man-days is 10-12 bath/sq.m.  Hence, the difference of labor costs calculated by these two approaches is most likely a profit margin for subcontractors.