STEEL FIBRE REINFORCED CONCRETE UNDER CYCLIC LOADING

Abstract

In recent years, it has been recognised that addition of small closely spaced and uniform dispersed discrete steel fibres in concrete substantially improve its static and dynamic properties. The addition of steel fibres from 0.5 to 2.0 per cent by volume in concrete are found to impart superior strength characteristics i.e. compressive strength, flexural strength, shear strength, fatigue strength and impact resistance. Recently, the use of steel fibres has increased in flexural members and columns of concrete structures subjected to cyclic loading such as bridge decks, highway roads, runways of airports, offshore platforms and buildings. It is necessary to obtain more information on the mechanical behaviour of steel fibre • reinforced concrete under cyclic loading in attempting applications of SFRC in structural members. The present investigaiton was planned to study the plain and steel fibre reinforced concrete under cyclic loading. The basic parameters of the study were fibre contents expressed as volume fraction and stress levels expressed as a percentage of the maximum flexural strength. The fibre contents used were 0.5 and 1.0% by volume of concrete. The beams were tested at three stress levels i.e. 85%, 90% and 95%. Straight mild steel fibres were used in the study with an aspect •ratio of 70. The physical properties of the basic constituent material viz, cement, sand, coarse aggregate, steel fibre were obtained as per relevent Indian standard specification. The compressive strength of concrete was obtained at 28 days. The mix proportion used was 1: 1.52:1.88 by weight with a water cement ratio of 0.47. In fresh state properties of SFRC, workability tests were carried out with indicators of workability i.e, slump, compaction factor and inverted cone test. From the present study, it was found that the addition of fibres to the concrete affects the cyclic loading life significantly under flexural cyclic loading. The variability in the cyclic loading life of specimen is quite large as expected in any cyclic loading test programme. The ultimate failure followed almost immediately after the first crack. (