The structural characteristics of new seismic retrofitting methods for existing RC columns, which were wrapped with the divided thin steel plates and continuous fiber sheets, was discussed in the previous papers. It was confirmed that the flexural resistance was significantly improved. Therefore, the proposed methods in our previous paper is expected as an useful repairing and strengthening methods for the columns damaged by earthquakes.
In this research, to examine the ultimate flexural strength of RC columns wrapped by the same means, repairing and re-retrofitting specimens were tested again. The test results indicated that the calculated value by current ultimate flexural capacity formula was underestimate these results, because the lateral confinement caused by steel plates and fiber sheets effect on the design of a column was generally unconsidered. Then, authors obtained a one solution of increasing effect of flexural strength based on the arch mechanism model by plane stress fields theory.
