Experimental behaviour of anchored smooth rebars in old type reinforced concrete buildings

Modelling of existing reinforced concrete (r.c.) frames designed without specific seismic rules is a key problem for maintenance, structural upgrading and seismic assessment. In many European countries a very large percentage of reinforced concrete buildings are 40 years old, or even older; thus reinforcement consists of smooth rebars, since only in the 1970's did early applications of deformed rebars appear. Technical literature on mechanical performances of anchored smooth rebars is non-comprehensive, mainly from the deformation standpoint, despite the relevance of this aspect to the response of critical regions, i.e. beam to column joints and column bases. In the present paper a series of experimental tests on smooth rebars are presented; they are aimed at describing in detail the force-slip relation for the bond mechanism for straight rebars and for anchoring end details, i.e. circular hooks with a 180∘ opening angle.