Effect of diaphragm flexibility on seismic response of unreinforced masonry out-of-plane walls

Current research is presented on response and behavior of unreinforced concrete masonry walls subjected to earthquake motions. Dynamic test data from a series of shake-table tests is presented that reveal response patterns for slender bearing walls excited normal to their plane and subjected to distortions at their top from an attached flexible floor diaphragm. These slender walls performed well at even large earthquake intensities. Each wall cracked at the mortar bed-joint at the base of the wall forming a hinge at that location which allowed the walls to remain stable while rocking and supporting substantial gravity loads. Observations from the shake-table test series imply that allowable limits on wall slenderness (h/t) as prescribed by the current seismic guidelines for rehabilitation of buildings (FEMA 273 or FEMA 356) are conservative and can be increased.