There exist in Japan a large number of old R/C buildings requiring reinforcement against the possible destructive effects of seismic activity. Responding to this, the authors of this paper propose an innovative reinforcing method that utilizes steel portal frames: the Portal-Grid Method. Based on the fact that for steel the modulus of elasticity and yield strength are respectively approximately 10 times and 20-25 times that of concrete, it is posited that steel portal frames - smaller in size than the respective R/C sections - are able to provide sufficient rigidity and strength to reinforce relatively weak R/C frames without braces. The steel portal frames - connected to exterior of R/C buildings - are composed of reinforcing H-sections whose rigidity can be adjusted to that required for complementing the respective R/C sections. In the process of their research, the authors have experimentally proved that the Portal-Grid Method suitably improves the strength of R/C frames - that the strength and rigidity of the reinforced frames can be calculated by summing up the strength and rigidity of the steel portal frames together with that of the R/C frames.
