In 1981, many detached houses collapsed owing to the earth quake which took place at the coast of Miyagi Prefecture in Japan because ferroconcrete was not used as the base of the most of collapsed houses. Therefore, the earthquake-proof design criterion in Japan was revised and it obliged newly constructed houses to use ferroconcrete as the base of detached houses since then. However, there are still more than ten million detached houses using aged concrete as the base in Japan. In this paper, a reinforcement method for the aged concrete is demonstrated by using the high performance CFRP strips. Three kinds of concrete beams reinforced with the CFRP strips with different vertical insert positions and different numbers of the CFRP strips were tested by a four point bending test method. In order to clarify the effects of CFRP strips, a concrete beam without reinforcement was also tested. The results of the experiment showed that the maximum deflections of the concrete beams reinforced with the CFRP strip were more than one hundred times larger compared with that of the concrete beams without reinforcement. Although the concrete beam without the CFRP strips collapsed instantly, the concrete beam with the CFRP strips gradually failed similar to the plastic behavior of metals. This result means that the residents can afford to escape safely from the houses in the event of possible earthquakes. The experimental results were compared with the analytical ones obtained from the composite beam theory and the failure criterion. Bothresults showed good agreement and the effectiveness of base concrete reinforced with CFRP strips was demonstrated.
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