EXPERIMENTAL INVESTIGATION OF CHANGE IN PARTIAL FACTOR OF SAFETY OF CONCRETE WITH CHANGE IN STRENGTH

Abstract

The strength of any material obtained in a structure is always less than the characteristic strength of the material. It is because of the workmanship or quality control in the manufacture of materials. The reduced value of strength which is obtained by applying partial safety factors to the characteristic strength is called as design strength of the material. A higher value of partial safety factor for concrete i.e., 1.5 has been adopted in IS 456:2000 because of the fact that there are greater chances of variation of strength of concrete due to improper compaction, inadequate curing and variation in the properties of ingredients. The chances of variation in the properties of steel are small, as it is fabricated in the factories where good workmanship and better quality control can be an achieved. Hence, a lower value of 1.15 has been adopted. In this study, the influence of various parameters affecting the compressive strength of concrete such as type of materials used, water-cement ratio, aggregate size and curing period are experimentally studied. Also how the change in compressive strength affects the value of partial safety factor is studied. For the experimental research, M20 grade of concrete is chosen with coarse aggregate size of 12 mm, 20 mm and 40 mm with a water-cement ratio of 0.4 and 0.5 respectively. A set of specimens containing 9 cubes, 3 cylinders and a beam of each combination of selected material properties are cast and cured for a period of 7, 14 and 28 days. The study aims at decreasing the value of partial safety factor of concrete by experimental study of change in strength with respect to change in factors affecting the strength. The experimental results are validated using STAAD Pro. Keywords: Concrete, strength, partial safety factor, design strength, compaction, water-cement ratio