Enhancing Performance of RC Columns Exposed to High Temperature

Abstract

High temperature represents a signi cant hazard in construction industry. Concrete is a good high temperature resistance material. Due to high temperature exposure spalling of concrete as well as cracks are developed in concrete. In RC columns due to high temperature load bearing capacity is reduced. Properties of concrete are improved by using composite materials in concrete like steel bres, polypropylene bres, hybrid bres etc. Di erent types of composite concrete has excellent properties. For instance, exural tensile and shear strength, toughness, impact resistance, crack resistance etc. can be improved by the use of steel bre, polypropylene bre etc. in concrete. Strengthening of existing concrete columns has become more common during the last decade due to the increasing knowledge and con dence in the use of bre rein- forced polymer, as well as the economical and environmental bene ts of strengthening of columns compared to demolition and rebuilt. Experience from real res shows that it is rare for a concrete building to collapse as a result of re and most re damaged concrete columns can be successfully repaired or strengthened. One method of repair or strengthening comprises the simple and rapid approach of applying FRP wrapping. Total 30 RC column specimens are cast. 16 columns are of dimensions 150 mm; and 450 mm height. Another 14 columns are of dimensions 150 mm; and 300 mm height. Columns are designed using IS provisions All columns are cast using M25 grade of concrete. 8 columns are cast in plain reinforced concrete, 4 columns are cast using steel bre reinforced concrete, 4 columns are cast using polypropylene bre reinforced concrete and another 4 columns are cast using hybrid bre reinforced con- crete.10 column specimens are strengthened using FRP wrapping. 5 specimens are strengthened using GFRP wrapping and 5 specimens are strengthened using CFRP wrapping. All columns are place in oven and are heated upto 200 C temperature for 6 hours for duration of 75 days. All oven heated columns are tested for ultimate load carrying capacity, displacement, strain, failure modes, crack patterns, etc. 76 plain concrete specimens including cubes, cylinders and beams are cast. Testing vi of these specimens is carried out after applying high temperature. All plain concrete specimens are placed in oven and are exposed to 200 C temperature for 6 hours for total 25 days. Di erent parameters like change in compressive strength, modulus of rupture, split tensile strength and bond strength are measured after addition of bres in plain concrete and results are compared with plain concrete. Plain concrete specimens Compressive strength is reduced by 9.39% to 46.13% after applying 200 C temperature. Decrease in split tensile strength of 17.12% to 37.17% is observed for bre concrete specimens at 200 C temperature compared to room tem- perature. steel bre concrete and hybrid bre concrete have exhibited more exural strength compared to polypropylene bre concrete exposed to 200 C temperature. Decrease in bond strength of 26.34% to 40.89% for bre concrete specimens exposed to 200 C temperature is observed compared to bond strength at room temperature. Steel bre reinforced column has exhibited more failure load compared to other bre reinforced columns exposed to high temperature. Decrease in failure load of 7.35% to 23.36% is observed for heated FRP wrapped columns compared to unheated FRP wrapped reinforced columns. Displacement of Fibre reinforced columns is observed lesser compared to control columns after exposure of 200 C temperature. Displace- ment of FRP wrapped reinforced columns is higher compared to control columns after 200 C temperature exposure. Thus use of various type of bre reinforced concrete and FRP wrapping is strongly recommended for increase load carrying capacity and strengthening of elements especially for columns exposed to high temperature. Keywords: High temperature, Steel bre, Polypropylene bre, Hybrid bre, GFRP, CFRP, Compressive strength, Split tensile strength, Flexural strength, Bond strength