Seismic response of multistory frames having elastic-plastic-brittle columns was numerically investigated. The columns were assumed to lose their restoring forces thoroughly after some plastic excursions. The plastic deformation capacity limited by such brittle fracture was regarded random. It was observed that the fracture of the brittlest column in a particular story causes consequent fracture of the remaining columns in the same story, resulting in dynamic progressive failure of the story like the pancake-type crash. Such fracture instability is enhanced by the randomness involved in the column-ductility. In order to make the safety of such brittle frames equivalent to the ordinary elastic-plastic frames, overstrength or overductility must be assigned to the columns according to the damage concentration escalated by brittle fracture.
