Investigation of NERDC composite floor slab system

Abstract

NERD composite floor slab system is widely used in Sri Lanka to construct concrete floors specially by the low and middle income families. The system has considerable advantages over the traditional construction methods. One of the major drawback of this cost effective slab system is the unavailability of sound theoretical basis for the structural behavior of the system. Even though the slab system is used in this country over the past twenty years, this drawback has not yet been fulfilled. The aim of this research is to fill this timely needed gap by investigating the structural behavior of this slab system and optimize the system. The proposed method of structural analysis using first principle and the subsequent spread sheet calculation is presented. The spread sheet can be used to select the depth of the prestressed beam required, if the customer knows the imposed load and the span of the slab. According to the results of the spread sheet analysis, the present detailing of prestressed beams is to be changed. The new detailing can be implemented at the existing licensed prestressing yards in operation all over Island without much difficulties. The slab is presently constructed as unpropped construction. However it was identified '. that, by constructing as a propped construction, the moment carrying capacity can be increased significantly. However, by using props, the advantage "bottom space is available to use on the following day" will be lost. The customer can decide whether to use propped or unpropprd construction by considering the advantages and disadvantages of the method selected. The most important outcome of this research is the discovery of under utilization of strength of prestressing wires. The strength of wires cannot be fully utilized until the facilities available at the rural yards are improved up to the required standard. The capital investment to improve the facilities of the prestressing yards can be recovered very quickly as one third of the cost of prestressing steel can be saver by fully utilizing the strength of the prestressing steel