An Experimental Study on Flexural Strengthening of Structural Steel Angle Sections Using Carbon Fiber-Reinforced Polymer (CFRP) Composites

Globally, there is need for strengthening of steel structures due to increased load carrying requirements, changes in earthquake / wind codes and rehabilitation due to corrosion degradation. Advanced composites have become one of the most popular techniques of repairing and/or strengthening civil infrastructure in the past couple of decades. The use of FRP material for the repair and rehabilitation of steel members has numerous benefits over the traditional methods of bolting or welding of steel plates. Carbon FRPs (CFRPs) have been preferred over other FRP material for strengthening of steel structures due to CFRPs possess higher stiffness. The emergence of high modulus CFRP, with an elastic modulus higher than that of steel, enables researchers to achieve substantial load transfer in steel beams before the steel yields.\ud In the present work, experimental investigation is carried out to analyze the behavior of steel angle sections wrapped with carbon fiber reinforced polymer (CFRP) to increase flexural strength and stiffness of parent structural member steel angle section due to CFRP wrapping. A total of 4 tensile coupon tests are conducted to determine the engineering properties of structural steel used. A novel flexural strengthening technique using bonded CFRP wrapping to enhance the strength and stiffness of existing steel angle sections has been developed. This is carried out by varying the CFRP wrap configurations and keeping adhesive properties constant. The experimental program consists of two sets each with 15 specimens to test a total of 30 specimens. Each set has five subsets as four different strengthening configurations and a set representing reference control specimens. The parameters studied include the slenderness ratio (b/t) of steel angles, the thickness and orientation of the CFRP wrap, comparative study on behavior of strengthened specimens, investigation on stiffness enhancement and strain variation across the section in relation with load.\ud This research investigated experimentally the behavior transformation of open sections into closed section, stiffening enhancement in elastic region and strength enhancement in both elastic and post yield regions of high strength CFRP\ud vi\ud strengthened structural steel angles tested under four point bending system in comparison with bare steel angles. Proposed external wrapping (bonded) CFRP reinforcement has been clearly established as a promising alternative to existing strengthening technique for steel structures. This proves that CFRP strengthening can be employed with proposed strengthening configuration to achieve desired degree of effectiveness and efficiency. The new strengthening approach has resulted in novel wrapping technology which has been first time applied to structural steel angle section (open section).\ud KEYWORDS: Carbon Fiber Reinforced Polymers (CFRP), Adhesive, Structural steel angle section, Wrapping, Strengthening