Experimental and theoretical investigation of the shear resistance of steel fibre reinforced prestressed concrete X-beams - Part I: Experimental work

This is the first part of two papers on the experimental (Part I) and theoretical (Part II) resistance of steel fibre reinforced precast concrete beams. Short steel fibres have been introduced into prestressed concrete X beams in order to study their behaviour under shear loads. The X beams, which have circular web profiles, were chosen to represent longitudinal sections from 215 mm deep prestressed precast hollow cored floor units, which are known to fail in shear in a brittle manner. No shear links were used. Round hooked end high strength steel (HS), and thin amorphous metal (AM) fibres were used in volume fractions up to 2.0%. The maximum flexural strength of fibre reinforced concrete (FRC) was 10.28 N/mm(2), some 50% greater than plain concrete. In the plain concrete beams the ratio eta of the ultimate shear resistance to the cracking resistance was 1.0, as expected. For the fibre beams eta = 1.43 to 1.52 for the HS fibres and eta = 1.23 for the AM fibres. Theoretical and empirical equations were developed using modified FRC principal tensile stress methods to predict ultimate shear strength and are given in Part II.