Fibre reinforced polymer grids as shear reinforcement in fabric formed concrete beams

Steel reinforced concrete is perhaps our most widely used man-made material (approximately 1.5m3 of concrete [1] and 23kg of deformed steel bar [2] were produced for every person on the globe in 2008) and whilst its constituent materials are widely and readily available, cement manufacturing is estimated to account for some 3% of global carbon dioxide emissions [3]. Recent research [4] has suggested that as much as 40% of the concrete used in new office buildings does little but increase structural deadweight, adding credence to the motion that concrete should be cast in optimised elements whose final form is determined by the requirements of their loading envelope. Using fabric formwork, it is possible to cast architecturally interesting, structurally optimised shapes based on simple design rules and research has shown that material savings up to and in excess of 30% can be achieved [5]. Whilst fabric formwork offers unique opportunities for the design of low embodied energy concrete structures, the provision of transverse reinforcement in non-prismatic elements can be complex and may lead to increased construction cost. This paper reports on recent research in which fully and partially resin coated carbon fibre reinforced polymer (CFRP) grids have been used in place of conventional steel stirrups as shear reinforcement. The results of both feasibility studies and full scale structural testing are presented, wherein the concept is successfully demonstrated. The application of current shear design methods to advanced composite reinforcement is discussed before opportunities for further work are highlighted