Assessment of Strength Evaluation and Structure Stability of Building Destroyed in Fire by Using Techniques of Non-destructive Testing

Abstract

The two-storey industrial building with area of 41,000 sq. ft on each floor was framed structure. The machinery in the building was used for the manufacturing of cotton and synthetic fabric. Concrete of M20 grade and steel of Fe 415 grade were used for construction. A fire incident was occurred for 42-50 h after one year of construction. Visual examination of columns, slabs and beams of ground floor showed cracks on the concrete surface. At many places, concrete had fallen off, and reinforcement was exposed. At few places, colour of concrete had also been changed from its natural grey to reddish brown which indicated that the temperature during fire might had crossed 600°C. In some of the circular columns, the thickness was reduced by about 25 % and fallen off concrete in between circular columns are a resulted in reducing the thickness of the slab by about 40 %. Due to inadequate circumstances for core extraction at some sections, decision of non-destructive testing like ultrasonic pulse velocity (UPV), rebound hammer (RH) were used to evaluate the elements. The quality of concrete was assessed by UPV. In situ strength of R.C.C. members, integrity and homogeneity of concrete help to evolve repair/strengthening/rehabilitation measures. Load test was also conducted to ascertain the actual load-carrying capacity of structural members. It was concluded that due to fire and excessive increase in temperature, the column concrete surface gets hardened, causing increase in value of rebound number. Further, results of concrete core test are more reliable when compared with rebound hammer test.