Strengthening of Low Ductile Reinforced Concrete Frames Using Steel X-Bracings with Different Details

Abstract eng:
Many existing reinforced concrete (RC) frame buildings located in seismic zones, designed according to the past seismic codes are often found to have inadequate lateral strength to withstand major earthquakes. In this paper, the use of steel bracings in concrete framed structures is experimentally presented. A series of tests conducted on eight, one bay-one story, with 1:2.5 scale RC model frames. The object of the tests was to determine the effectiveness of cross bracings with various details of bracing connections to the concrete frames, to increase the in-plane shear strength of the concrete frames. The braces connections in model frames were selected to represent most easy, quick and economical techniques to strengthen RC frames by steel cross bracing system. Hence, two frames were not strengthened (un-braced) and were used as control specimens and six others were strengthened by X-bracings, and with five details of connection between frames and bracings. The details were: (i) using bolts and nuts (in two ways for two frames); (ii) using steel jackets around the columns (in two ways for three frames); (iii) using embedded plates (for welding gusset plates) in frame corners before placing the concrete (for studying possible use of steel bracing system in new concrete frames). Model frames were tested under constant vertical and cyclic lateral loadings. The tests results indicate considerable increase in the lateral strength and/or displacement ductility of strengthened frames upon bracing details.

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