Experimental test on a three storey reinforced concrete frame designed for gravity only
The seismic behaviour of reinforced concrete frame systems designed for gravity load only, as typical of the Italian construction practice between the 1950’s and the 1970’s, is addressed. The results of an experimental quasi-static cyclic test on a three storey reinforced concrete frame system with structural inadequacies typical of pre-seismic code provisions, performed at the Laboratory of the Department of Structural Mechanics of the University of Pavia, are herein presented. Use of smooth bars, inadequate reinforcing detailing (i.e. total lack of transverse reinforcement in the joint region), deficiencies in the anchored solutions (hookended bars) and the absence of any capacity design principle resulted in hybrid brittle local and global damage mechanisms. Particularly critical failure mechanisms, with no alternative sources for gravity-load bearing capacity, were observed in the exterior joints. An overview of damage observations and local and global behaviour is provided. Based on the experimental global response, the concept of “shear hinge”, due to the joint damage, is also introduced as alternative to flexural plastic hinge and the expected implications on global behaviour are briefly discussed.