Behaviour and strength of hidden beams' within slabs

Overhangs formed due to beams for architectural concerns on the ceiling of buildings are undesirable. In such cases alternative methods are applied for providing an esthetic view. One of which is forming a hidden beam with equivalent strength instead of the removed one. It is observed from the many existing structure that this situation may cause significant deformation problems in slabs and beams connected to them. Although it is an important issue, no studies directly related to this have been encountered in the literature. The main aims of this study are to determine the behaviour and strength of hidden beams formed within slabs and to compare these beams with traditional reinforced concrete beams. Therefore an experimental study consisted of 14 specimens was planed. Slab thickness and reinforcement ratio were chosen as the parameters. It was found that, objective strengths of hidden beams were achieved only after huge deformations infact some of them never reached the objective strengths. It was also proved that the measured deflections were much more than the servicibility limits provided in codes. For some hidden beams, measured instantaneous deflections were 8 times larger than the deflections encountered in beams with equivalent strength. It should not be forgotten that, when time dependent deflections are taken into account, instantaneous deflections may increase about 2 times and this makes the subject even more important.