BEHAVIOR OF GRAVITY LOAD DESIGNED REINFORCED-CONCRETE BUILDINGS SUBJECTED TO EARTHQUAKES

Two small-scale reinforced concrete building models were tested on the Cornell University shake table. The models were a 1/6 scale two-story office building and a 1/8 scale three-story one-bay by three-bays off ice building. Both structures were designed to resist purely gravity l ends without regard to lateral loads (wind or earthquake forces). The reinforcement details were based on typical reinforced concrete frame structures constructed in the central and eastern United States over t he past 50 to 60 years, as characterized by (a) low reinforcement rati o in the columns, (b) discontinuous positive moment reinforcement in t he beams at the column locations, (c) little or no confining reinforce ment in the joint regions, and (d) lap splices located immediately abo ve the floor level. Both models were tested using the time-compressed Taft 1952 S69E ground motion scaled to increasingly large peak ground accelerations. Test results indicated that gravity load design (GLD) r einforced concrete buildings without walls will experience very large deformations associated with a considerable stiffness degradation duri ng a moderate earthquake. The high flexibility produced significant P- Delta effects in the three-story building model. Although the nonseism ic details associated with the gravity load design philosophy forms a source of damage, the experiments indicate that these details will not necessarily lead to collapse or to a complete failure mechanism. Comp arison with analytical results indicated that inclusion of the slab co ntribution to beam flexural strength is a vital step in the assessment of the performance of GLD reinforced concrete structures since it has the potential of altering the relatively ductile strong column-weak b eam mechanism to a more brittle soft-story mechanism.