Behaviour of over reinforced HSC helically confined beams

Abstract

The technology of high strength concrete and high strength steel have improved over the last decade although high strength concrete is still more brittle than normal strength concrete. As this brittleness increases, particularly with the use of over reinforced sections, they may, suddenly fail without any warning. The research reported in this thesis deals with the installation of helical confinement in the compression zone of over-reinforced high strength concrete beams. This study is divided into three parts as follows: 1) State of the Art & Literature Review This part deals with state of the art and literature review. Helical confinement is more effective than rectangular ties, compression longitudinal reinforcement and steel fibres in increasing the strength and ductility of confined concrete. Helical reinforcement upon loading increases the ductility and compressive strength of axially loaded concrete due to resistance to lateral expansion caused by Poisson’s effect. Based on this concept helical reinforcement could be used in the compression zone of over-reinforced high strength concrete beams. The effectiveness of helical confinement depends on different important variables such as helical pitch and diameter. Thus there is a need for an experimental programme VI to prove that installing helical confinement in the compression zone of an overreinforced concrete beam enhances its strength and ductility and to study the behaviour of over-reinforced high strength concrete beams subjected to different variables. 2) The Experimental Programme & Test Analysis This part deals with an experimental programme and analysis of test results. Extensive experimental work was done because the beams should be full size in order to accurately represent real beams. Twenty reinforced concrete beams, 4 m long &#;&#;200 mm wide &#;&#;300 mm deep were helically confined in the compression zone and then tested in the civil engineering laboratory at the University of Wollongong. In this programme the following areas were studied: the effect of helical pitch, helical diameter, concrete compressive strength and longitudinal reinforcement ratio, on the behaviour of over-reinforced HSC helically confined beams. 3) Analytical Models to Predict the Strength & Ductility This part deals with the analytical models used to predict the strength and ductility of over-reinforced high strength concrete beams based on the findings of this study. A comparison between the experimental and predicted results shows an acceptable agreement. This study concludes that helical reinforcement is an effective method for increasing the strength and ductility of over-reinforced high strength concrete beams