Hybrid UHPFRC thin walled "¶" beams for flat roofing applications

Abstract

The main hybrid UHPFRC properties are the high tensile strength it can achieve with a ductile behaviour and the close cracks it can develop during the strain-hardening, whereby its durability is improved. Those characteristics make this material especially suitable for carry tensile and flexural efforts in more slightly and new shapes elements, dispensing of conventional reinforcement. In this research, several hybrids UHPFRC mix compositions were designed and characterized for different levels of requirement in cost or strength, achieving values from 35 MPa to more than 45 MPa of equivalent linear elastic flexural tensile strength. The material composition includes high elastic limit steel fibres of two different sizes. Silica fume, aggregates type and qualities were also variables for this study in order to obtain different cost concretes. The workability of the mixture was designed for being high in order not to be compacted. A flat roof with similar purposes than conventional unidirectional flats was designed using thin walled ¿ cross section beams made with UHPFRC. Advantages on minimizing materials consumption, reducing self weight, construction procedures, transport facilities and other improvements make of this solution an interesting alternative to conventional solutions. To analyze the structural behaviour three thin walled ¿ cross section beams were made at actual dimensions in laboratory with different hybrid UHPFRC. Beams were tested in flexural four point bending tests. The load and associated deflection, the maximum load and cracking pattern were analysed and evaluated.