STRENGTHENING OF LOADED R.C. FRAMES AFTER FIRE EXPOSURE USING F.R.P

Abstract

One of the most common defects encountered in reinforced concrete structures is the fire exposure. Therefore, strengthening investigations that attempt to increase the ultimate load capacity of the defected structural elements have become an important topic in the field of reinforced concrete studies, specially, for reinforced concrete frames as a whole structure. Recently, composite material such as fiber-reinforced polymer (FRP) started to become a good replacement for strengthening of reinforced concrete elements to compensate the losses in ultimate capacity and energy dissipation due to fire exposure. In the last decade, many researchers and construction applications in industry showed great interest in this field and intensive researches were performed to begin the practical use of these materials in strengthening reinforced concrete structures. In this paper nine reinforced concrete frames have characteristic strength 22.5 MPa of one sixth scale were tested and examined. These frames are divided into three groups, group (A) control frames, group (B) exposed to 600 0C and cooled with air, while the last three frames, group (C) exposed to 600 0C and cooled using water. Each group consists of three frames with different beam to column inertia. Group (A) control frames loaded till to failure to determine the ultimate capacity of sections, while groups (B) and group (C) are loaded to about 0.3 its ultimate load, the load kept constant at this value, then each frame exposed to fire of 600 0C, for at least two hours , then cooled such that with air or using water. After totally cooling each frame strengthened using glass fiber reinforced polymers laminates (GFRP). After strengthening, the load increased gradually up to failure. The ultimate loads, crack pattern, strain progress, mode of failure and energy absorption were here recorded and analyzed.