Seismically induced one-sided rocking response of unreinforced masonry façades

Investigated in this paper is the earthquake response of typical unreinforced masonry façades of the historical centre of Gaeta, a town in Central Italy. The façades are assumed to undergo one-sided rocking, due to the presence of internal restraints, such as transverse walls and horizontal structural elements. The dynamic model accounts, in a simplified way, for geometrical imperfections. Two sets of excitations are considered, one developed from considerations of the actual seismic hazard of the area, the other based on code provisions. The overturning frequencies are compared against different parameters, such as aspect ratio, imperfection level, energy damped due to impact against vertical restraint, ground motion variability and direction of the rotation. Surprisingly, if no additional energy damping is assumed, one-sided rocking proves more dangerous than two-sided rocking. Results of dynamic analyses are compared to those of code-suggested static responses. It is established that static results can be overly conservative, thus requiring unnecessary retrofitting, against architectural heritage minimum intervention criterion. It is further determined that it is possible to transfer the results of dynamic analyses into existing static procedures, by means of simplified corrective coefficients, accounting for one-sided rocking and expected increased energy damping.