Brittle punching failure can occur due to the transfer of
shear forces combined with unbalanced moments between
slabs and columns. During an earthquake, significant
horizontal displacement of a flat plate-column connection
may occur, resulting in unbalanced moments that induce
additional slab shear stresses. As a result, some flat plate
structures have collapsed by punching shear in past earthquakes
(Berg and Stratta 1964, Yanev et al. 1991, Mitchell
et al. 1990, 1995). During the 1985 Mexico earthquake
(Yanev et al. 1991), 91 waffle-slab and solid-slab buildings
collapsed, and another 44 buildings suffered severe damage.
Hueste and Wight (1999) studied a building with a posttensioned
flat plate that experienced punching shear failures
during the 1994 Northridge, CA, earthquake. Their study
provided a relationship between the level of gravity load and
the maximum story drift ratio that a flat plate-column
connection can undergo without punching shear failure. The
displacement-induced unbalanced moments and resulting
shear forces at flat plate-column connections, although
unintended, should be designed to prevent brittle punching
shear failure. Even when an independent lateral-forceresisting
system is provided, flat plate-column connections
should be designed to accommodate the moments and shear
forces associated with the displacements during earthquakes.