Seismic response of r.c. columns with smooth reinforcement. Part II: Cyclic tests

Evaluation of rotation capacity of reinforced concrete (r.c.) members is a key issue in the seismic performances evaluation of the existing buildings. In the framework of the modern safety assessment procedures, a comparison between a seismic demand (D) and seismic capacity (C) measure is required. However, available capacity models reflect experimental results representative of new constructions, where deformed bars are used. Consequently, deformation and strength mechanisms do not necessarily reflect response of old-type members. It is well known that r.c. members designed according to obsolete codes of practice are characterised by very different structural detailing, inadequate confinement, poor bond between smooth bars and concrete, so that very different post-yielding mechanisms compared to new constructions take place. This is the background of the present paper that reports the results of the second phase of the experimental program carried out on reinforced columns with smooth rebars designed according to guidelines available in Italy between 1940 and 1970. Results on specimens subjected to cyclic loading clearly point out the role of poor bond in the development of rotation capacity and in general on the local and global response of members. Relevant aspects of the research are discussed with reference to the monotonic response of columns analysed in a companion paper and to chord rotation given by empirical formulae, i.e. Eurocode 8 provisions.