Nonlinear transient analysis of reinforced concrete slabs subjected to blast loading and retrofitted with CFRP composites

Computational models using the finite element method for nonlinear transient analysis of reinforced concrete (RC) two-way slabs subjected to blast loading are presented. Both as-built and retrofitted slabs with carbon fiber reinforced polymer (CFRP) composite strips are analyzed. The models are used to investigate different parameters including (a) loading duration, and (b) effect of CFRP retrofit on damage accumulation. In this study, damage is globally quantified by the amount of reduction of the first two vibrational frequencies of the slabs. Local representation of damage in terms of reinforcing steel strains is also discussed. The computational models for both the as-built and the retrofitted slabs are verified using experimental results. In these experiments, a slowly increasing uniform pressure is applied to the bottom surface of large-scale RC slab specimens using high-pressure water bag. Experimental results showed that an increase up to 200% in the load carrying capacity is achieved when using the CFRP composite retrofit system. Transient nonlinear analysis results proved the efficiency of the CFRP composite retrofit in improving the slab behavior under blast loading for different loading durations, i.e. for small, medium, and large charge weights at the same applied maximum pressure. In particular, less than 50% reduction of the fundamental frequency due to concrete damage is obtained for the retrofitted slab compared to more than 85% reduction for the as-built slab. Moreover, the maximum displacement is reduced by 40–70% with the CFRP retrofit compared to the as-built slab. As for reinforcing steel strains, the application of CFRP retrofit significantly limited the spread of yielding in time and space. The improved slab behavior with CFRP is best when retrofitting is applied to both sides of the slab.