Testing of Fibre Reinforced Concrete Structures: Shear Capacity of Beams with slender Webs
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Steel fibres in concrete beams have proven to be efficient with regards to take shear forces,and could become a competitor to today?s stirrups. This master?s thesis evaluates positiveand negative effects of having fibre reinforced cross sections with different web widths. I-beams are often used in the precast concrete industry to slimmer the structure and production cost. Using fibres as shear reinforcement instead of stirrups would rationalize the production, resulting in less labour needed and decreased production costs. A total of five beams have been used in the experiment and for the comparison. Each beam has been tested in two sections, giving two sets of data for each beam in the analysis. All beams were 400mm high, 250mm wide and 4000mm long. One of the beams were reinforced with conventional stirrups, the rest had a fibre amount of 1,0 vol% of the type Dramix 65/50. The web width for the beams varied from 250mm to 80mm. Each beam was reinforced with longitudinal reinforcement such that it would withstand twice the loading in bending than for shear. On this basis, the effect of having different web widths were examined and evaluated. The making of moulds and casting went out in Spenncon?s factory in Verdal. The testing afterwards took place on NTNU at Gløshaugen. In addition to the I-beams, standard beams and cylinders were casted and tested according to the design rules to find the correct concrete and fibre properties. This report is mainly related to the four main chapters Literature Theory, Beam Compilation, Laboratory Activity and Results and Discussion. Literature Theory examines various relevant topics related to the comprehension of fibre reinforced concrete. The chapter Beam Compilation describes how the final test beams are put together based on calculation models from the literature theory. The casting and testing procedure is described in Laboratory Activity, while the outcome from the Laboratory Activity is thoroughly reviewed in the chapter of Results and Discussion. Different design rules have been presented in this study. They have been evaluated up against the test results and against each other, with the aim of finding similarities and differences between them. The results show that a concrete beam with 1vol% fibres can withstand higher shear forces than a corresponding beam with stirrups that meets the requirements of minimum shear reinforcement in EC2. The tested beams generated satisfactory results to the hypothesis of increased shear efficiency for slim webs. Fibre counting indicates a linear increased trend of fibres as the web becomes slimmer.