Flexure and Shear Study of Deep Beams using Metakaolin Added Polypropylene Fibre Reinforced Concrete

Structural elements like walls of bunkers, load bearing walls in buildings, pile caps, plate elements in folded plates behave as deep beams. Beams whose span (L) to depth (D) ratio is reasonably small can be said as a deep beam. Beams with large depth, supported by individual columns, often used as transfer girders in tall buildings, long span structures etc are commonly referred to as deep beams. Deep beams are used for architectural buildings where the span is very large without any intermediate columns such as marriage halls, assembly halls, auditoriums, theatres etc. According to IS456-2000, a beam is said to be as a deep beam when the ratio of effective span to overall depth (L/D) is less than 2.0 for simply supported members and 2.5 for continuous members. The design of such structural elements requires innovative procedures to serve the functionality coupled with durability. In deep beams, the bending stress distribution across any transverse section deviates appreciably from the straight line distribution assumed as in the simple beam theory. So, assumption of “Plane section before bending remains plane after bending” does not become valid and the neutral axis does not lies at the mid depth. In deep beams, the ultimate failure due to shear is generally brittle in nature, in disparity to the ductile behavior and progressive failure with large number of cracks as observed in normal beams. In this paper, flexural strength of M20 and M30 graded concrete deep beams with the addition of a combination of 0%,10%,20% metakaolin as a partial replacement for cement and 0%,2.5%,5% polypropylene fibre is found out and mode of failure is observed for each case. Mix designs for M20 and M30 graded concrete are carried out in worksheets and the proportions of cement, sand, coarse aggregate are calculated based on the tests conducted on cement and aggregates. Cubes are casted and 7 days compressive strengths for those cubes are tested using compressive testing machine and the mix proportions are used.