DIFFERENT TECHNIQUES IN STRENGTHENING T-REINFORCED CONCRETE BEAMS UNDER NEGATIVE BENDING MOMENTS

Abstract

Abstract Deterioration is one of the laws of nature that effect on building structure that from the first structure were established until the modern structures Therefore, the needs for upgrading and strengthening is growing worldwide in recent decades. Strengthening of reinforced concrete is very common and important functions in civil engineering, becoming obtainable options for those structures which are more economical to strengthen than to demolish, and therefore techniques of strengthening have been proposed and developed over years of practical and laboratory works. There are many strengthening methods for RC beams and different materials, each with different advantages, disadvantages and practical limitations. In this study suggest using different techniques (external bonded, hybrid strengthening and near surface mounted) for strengthening T reinforced concrete beam by steel plate and CFRP sheet. Strengthening of specimens were using two percentage of length of span and width of flange (40% and 80%), Also thickness is different (2mm when percentage 40% and 1mm when percentage 80% )so that the mount used for strengthening is the same. Eleven reinforced concrete T beams were cast T-beams divided into five groups were cast and tested under negative bending moment. First group strengthened by external bonded with percentage 40%, second group strengthened by external bonded with percentage 80%, third group strengthened by hybrid strengthening with percentage 40%, forth group strengthened by hybrid strengthening with percentage 80% and fifth group strengthened by near surface mounted. All beams had the same amount of reinforcement and dimensions of 2300 mm length, overall depth of 265 mm (200mm web depth and flange thickness of 65mm), an effective flange width of 390 mm and a 130 mm web width. II The experimental result showed that, the presence of strengthened beams with external bonded by using steel plate and CFRP sheet with 40% increase in ultimate load about 4.34% and 10.43% and decrease of deflection about 47.8% and 46%, respectively, when compared with the reference solid beam. While when increase the percentage to 80% increase in ultimate load about 20%and 16%, decrease of deflection about 42.25% and 33%. while specimens strengthened by hybrid strengthening (steel plate +CFRP) with percentage 40%of length of span and width of flange, once put steel plate on sides of flange and CFRP sheet put on middle and others put CFRP sheet on sides of flange and steel plate on middle, increase in ultimate load about 7.39% and 4.95% and decrease of deflection about 43.34% and 36.7%. when increase percentage of 40% of length of span and width of flange to 80% with decease of thickness from 2mm to 1mm, increase in ultimate load about 25.65% and 16% and decrease of deflection about 29.17% and 45.87%. while specimens strengthened with near surface mounted with two groove and three groove, increase of ultimate load about 10.43% and 31.3% and decrease in deflection. The near surface mounted (NSM) technique and hybrid strengthening give approximate and better result from the external bonded (EB) technique in ultimate load capacity and first crack load ,while deflection at first crack for specimens strengthened with hybrid strengthening and external bonded techniques was lower near surface mounted ,but deflection at ultimate load from specimens strengthened with near surface mounted was lower than hybrid strengthening and external bonded method. The strengthening by percentage 40%( two layer CFRP sheet or 2mm thickness of steel plate )lead increasing in the first cracking load and decrease in deflection at ultimate load is better than when strengthening by percentage 80%( one layer CFRP sheet or 1mm steel plate ).The strengthening by percentage 80%( one layer CFRP sheet or thickness 1mm of steel plate )lead increasing in the ultimate load and decrease in deflection at first crack load is better than when strengthening by percentage 40%(two layer CFRP sheet or 2mm steel plate ). When strengthening two beam by 40% ,but the material is different .one beam strengthened by steel plate while other beam by CFRP sheet .CFRP sheet has first crack load and ultimate load. While strengthening two beam by 80% ,but the material is different .one beam strengthened by steel plate while other beam by CFRP sheet .steel plate has first crack load and ultimate load.