Experimental and numerical analysis of concrete slabs prestressed with composite reinforcement

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The behaviour of concrete slabs prestressed with glass fibre reinforced polymer (GFRP) composite bars is investigated in this paper. The main advantage of GFRP bars is their high strength/self-weight ratio. On the other hand, Young’s modulus is very low compared to steel reinforcement, which is the main cause for unacceptable deflections. To eliminate such deflections and to utilize the high tensile strength of GFRP bars it is very useful to pretension the bars. During the experimental work a set of three concrete slabs 4.5 m long was casted. Each slab was prestressed with four GFRP bars. The slabs were subjected to four points bending. Each specimen was subjected to ten tow-load cycles and afterwards loaded until failure. Deflection under each loading point and in the middle of the beam span was recorded. Moreover, stress at the lower and upper surface was measured. The experimental procedure was modelled numerically in finite element nonlinear software. Brick elements were used for meshing and the full Newton-Raphson method was used for calculation. Special bond slip-law (GFRP-concrete) is involved based on the experimental results of pull-out tests. A stress-strain diagram and the stress and crack development were plotted. The experimental and numerical results show a statistically important relationship. A large deflection typical for GFRP reinforced slabs is observed, as well as very early crack propagation. The serviceability limit state (SLS) is exceeded much earlier than bar rupture is observed. For this reason, it is recommended that the design of GFRP reinforced structures is governed by SLS criteria.