The structural use of synthetic fibres : thickness design of concrete slabs on grade

[摘要] ENGLISH ABSTRACT: Concrete is used in most of the modern day infrastructure. It is a building material for which thereexist various design codes and guidelines for its use and construction. It is strong in compression, butlacks tensile strength in its fresh and hardened states and, when unreinforced, fails in a brittle manner.The structural use of synthetic fibres in concrete is investigated in this study to determine its effect onenhancing the mechanical properties of concrete. Slabs on grade are used as the application for whichthe concrete is tested. The material behaviour is investigated in parallel with two floor design theories.These are the Westegaard theory and the Yield-Line theory. The Westegaard theory uses elastictheory to calculate floor thicknesses while the Yield-Line theory includes plastic behaviour.Conceptual designs are performed with the two theories and material parameters are determined fromflexural tests conducted on synthetic fibre reinforced concrete (SynFRC) specimens. Large scale slabtests are performed to verify design values from the two theories.Higher loads till first-crack were measured during tests with concrete slabs reinforced withpolypropylene fibres than for unreinforced concrete. It is found that the use of synthetic fibres inconcrete increases the post-crack ductility of the material. The Westegaard theory is conservative inits design approach by over-estimating design thicknesses. This was concluded as unreinforced slabsreached higher failure loads than predicted by this theory. The Yield-Line theory predicts designthicknesses more accurately while still accounting for the requirements set by the ultimate- andserviceability limit states. By using SynFRC in combination with the Yield-Line theory as designmethod, thinner floor slabs can be obtained than with the Westegaard theory.

[发布机构] Stellenbosch University