The structural use of fibrous-cement in partially prestressed composite concrete construction

A new concept in composite construction has been developedat the University of Salford, involving the use offibre-reinforced cement channels, combined structurallywith partially prestressed composite concrete T-beams.The British Standards Institution Code of Practice,CP110: 1972, "The Structural Use of Concrete", permits theuse of Class 2 and Class 3 (partially prestressed) concretemembers in structural design'. The limiting design criteriafor such members are usually the limit'states of deflectionand cracking and therefore, an improvement in theirflexural behaviour would be beneficial. This improvementmay be brought about by the addition of fibre-reinforcement,in the form of two or three dimensionally randomlydistributed fibres. The Code of Practice, CP110: 1972, doeshot, however, give any guidance on the use of fibres instructural members and it is also apl. arent that the methodsoutlined in the code for the calculation of the limitstates are limited and can be improved.The flexural behaviour of twenty-two partially prestressedcomposite concrete T-beams was investigated.Each beam consisted of a precast partially prestressedX-joist web, combined with a cast-insitu lightweightaggregate concrete flange. Alkali-resistant glass fibrereinforcedcement channels were placed at the soffits ofsix beams and steel fibre-reinforced concrete was used inthe webs of two beams. The T-beams were subjected toshort-term, long-term and fatigue loading and their structuralperformance was considered in terms of strength,cracking and deformation.Theoretical relationships are derived between theapplied moment and the depths of the neutral axes of stressand bending, enabling a design equation relating appliedmoment to the steel stress to be developed. Subsequently,design equations for the calculation of the limit states ofdeflection and cracking are developed, which are directlyapplicable to both conventional and fibre-reinforcedstructural members.The use of a fibre-reinforced cement channel as anintegral structural part of a concrete member results inmany important advantages when compared with conventionalconcrete members and the test results show that they considerablyimprove the structural performance of thepartially prestressed composite concrete T-beams