Experimental Investigation on Un-reinforced Bottle Shaped Struts in Glass Fiber Reinforced Concrete

The strut-and-tie method (STM) is a rational methodology for the design of D (Discontinuity) regions in structural concrete. D-regions are those portions of a structure in which there is a complex non-linear variation in strain and beam bending theory cannot be used. The flow of forces within a D-region can be modelled using a network of struts and ties, called as a strut-and-tie model, which serves to transfer the applied loads to the supports or to adjacent B(Beam or Bernoulli) regions. Bottle-shaped struts are formed within a D- region when the external load is applied to a relatively small area of the member and the stresses disperse as they flow through the member. As the compression disperses along the length of a bottle-shaped strut, tensile stresses perpendicular to the axis of the strut are developed to counteract the lateral component of the angled compression forces. An experimental investigation was carried out to determine the performance of concrete under compression and tension for different amounts of glass fibers in concrete. Fibers are added in the amounts of 0%, 0.5%, 1.0%, 1.5%, 2% and 2.5% of weight of cement. It is observed that characteristic compressive strength of concrete is increased by 10% and 14 % and split tensile strength was increased by 18% and 10 % for M25 and M40 grade concrete respectively for 1 % of fibers. As the transverse tension is the main problem in bottle-shaped struts, addition of fibers in concrete will increase the performance of bottle-shaped struts. Performance of the strut is assessed from the efficiency factor#. Test specimen consisted of 400mm X 400 mm X 100 mm panels, tested for in plane loading under compression for two different grades of concrete and different amounts fiber contents. From the test results, it was observed that efficiency of bottle shaped struts increased up to 34% and 28% for M25 and M40 grade concrete respectively for 1% fibers in cement weight. Also addition of fibers to the concrete delayed the occurrence of main crack in the bottle-shaped strut. Therefore it can be concluded that addition of glass fibers to the concrete is an economical solution to increase the performance of the concrete in terms of capacity and serviceability.