An Application of Seismic Retrofit Technique of Thick Hybrid Wall Using Additional Concrete Sandwiched by Steel Plates and PC Bar Prestressing

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A seismic retrofit concept of thick hybrid wall using additional concrete sandwiched by steel plates and PC bar prestressing was introduced first in the annual meeting of AIJ in 2005. This technique was proposed for RC pilotis frame, which was retrofitted by installing cast-in-site thick hybrid opening type wing wall or non-opening type panel wall; and for RC framed shear wall or concrete block wall which was retrofitted by converting its thin wall into thick hybrid wall. To ascertain the effectiveness of the proposed retrofit technique, the cyclic loading tests under a constant vertical load were carried out on one-story one-bay RC pilotis frames, RC framed shear walls and concrete block walls, and two-story one-bay RC pilotis frames. Experimentally it was verified that the proposed retrofit technique enhanced both the lateral strength and ductility. Moreover, in non-opening type panel wall specimen, the necessary stress transfer mechanism to protect the punching shear failure through the top and bottom connections were confirmed by strengthening the top connection with casting additional concrete sandwiched by steel plates and PC bar prestressing up to beam, and the bottom connection by providing post-installed anchors. However, the ductility was obtained until a drift angle of about 2% due to the successive breakage of longitudinal rebars caused by the high local strain concentration at large drift angles. Moreover, by allowing the rebars as unbonded in column at the first story of two-story one-bay pilotis frame, the ductility was obtained a little more than 2% only. However, in the context of practical design drift angle of 1%, the proposed retrofit technique can be recommended for large seismic excitations.