SUDDEN CHANGE OF THE CROSS - SECTION OF REINFORCED CONCRETE COLUMN AT SLAB LEVEL: EXPERIMENTAL INVESTIGATION

Architects prefer the square or circular cross - section of the reinforced concrete (RC) columns in the garages or commercial floors in building. However in the upper residential floors, they prefer the elongated rectangular sections to be embedded in the partition walls. Therefore, the cross section of the RC columns may change suddenly between the floors. This study introduce a first attempt to investigate the behavior under compression of R C columns with sudden change of the cross section at the slap level. Five RC column specimens were tested under concentric loading. The columns have square cross - sections at the lower part and change to rectangular cross section with the same area at the u pper part. Some specimens have short cantilevers at the top head of the lower columns Variable parameters were studied as the slab confining effect, the reinforcement, and the short cantilever depth . Load s, axial displacement , strains, and failure patterns were studied for each column specimen . The results indicate that this system can be used in construction with some provisions about the steel ties distribution and the overlap length. The presence of the slab and steel ties are very effective to increase the axial capacity of the connection. Also, increasing the short cantilever depth is able to increase the ultimate capacity up to a certain depth equal s the offset of the upper column edge from the lower column edge .