Experimental and analytical study of new hybrid beams constructed from high performance materials

The research work presented in this thesis is concerned with the experimental and analytical investigation of the behaviour of a hybrid beam. The hybrid beam is composed of a Glass Fibre Reinforced Polymer (GFRP) box section with a thin slab of Ultra High Performance Concrete (UHPC) cast on top to carry the compressive stresses induced by bending. The wet UHPC was bonded to the top flange of the GFRP box section using a moisture-insensitive epoxy in addition to GFRP shear studs. To carry the flexural tensile loads on the hybrid section, different types of Carbon Fibre Reinforced Polymer (CFRP) and Steel Reinforced Polymer (SRP) sheets were bonded to the lower flange of the GFRP box using a moisture-tolerant epoxy. Thus, all the components of the hybrid beam studied are high performance, high strength materials, while studies of beams previously reported in the literature examined combinations of traditional and high performance materials.;Seven long and three short beams were tested to study both the flexural and shear behaviour of the hybrid beams. Two of the long beams were exposed to cyclical temperature and humidity environmental conditions to assess the endurance of the hybrid section. In addition, five beams were tested under fatigue loading to study the behaviour of the hybrid beam under cyclic loading. Finally, Finite Element modelling for the hybrid beams was implemented to corroborate the results of the experimental tests.;Good bonding was achieved between the different hybrid beam components. The research revealed the high capacity of the hybrid beam relative to its weight, and showed a significant increase in the capacity of the GFRP box section through the addition of the UHPC and SRP/CFRP sheets. Fatigue failure of the GFRP box section was the control limit for the capacity of the hybrid beam. The flexural behaviour of the hybrid beams can be approximated to be linear. Linear compatibility and finite element analysis can predict values very close to experimental longitudinal strains and deflections at the mid-span section of the beam.;Since all the materials used have almost linear stress-strain relationships, different failure scenarios were investigated in order to determine the safest failure mode with the least brittle nature. Some beams were designed to fail by crushing of the UHPC, while others were designed to fail on the tension side. The failures on the tension side were controlled to occur either due to the tensile failure of the bonded CFRP sheets or due to the tensile failure of the lower flange of the GFRP box section. The early warning signs of failure were closely watched in each case before the complete collapse of the beam. The tensile failure of the beams was generally quieter and not sudden like the compressive failure of the beams.