STUDIES ON R. C. MANHOLE COVERS

Abstract

The work relates principally to the behaviour of Medium duty H.C. Manhole Covers, R.C. covers with 0.57. volume fraction of monofilament polypropylene fibres, R.C. covers with single G.1. wire mesh in tension zone, under static and impact loading. The meshes used are 19 x 19 mm, 22 gauge and 13 x 13 mm, 24 gauge. The experimental programme included test for compressive strength for plain and fibre concrete with 0.57. volume fraction of P.P. fibres. The flexural strength test was done to find the effect of Galvanised Iron woven wire mesh and P.P. fibre inclusion in the concrete. Twenty six Medium duty R.C. Manhole covers were cast. The covers were 600 mm dia x 65 mm thick and were provided with 3 mm thick Mild Steel flat edging to which reinforcing bars were welded. Thirteen covers were tested under monotonic loading up to failure and central deflection, crack width and strain in M.S. edging were measured, other thirteen were tested under impact, by dropping a 0.5 kN weight through a height of 0.5 m at the centre of cover. The blows were applied repeatedly, till the cover failed due to spalling of concrete on tension face. Crack widths were measured at different stages of loading. The test results shows that with the addition of 0.57. volume fraction of P.P. fibres there is small decrease in compre-ssive and flexural strength. By providing meshes in beam, there is improvement in flexural strength of concrete. The increase is found to be iv between 7 to 167.. Under static loading, the load at first visible crack and ultimate load has improved slightly by inclusion of P.P. fibres and mesh in concrete. Under impact loading, the impact resistance is found to increase by 2.47 times when 13 x 13 mm, 24 gauge mesh is used and 1.79 times when P.P. fibre concrete is used. From analysis of static test data it is observed that initially the load is supported by bending action of cover but as cracks appear, it is supported