Strength and Drift Characteristics of Steel Frames

The strength and drift characteristics of unbraced multistory steel frames subjected to combined loads are studied with emphasis on P-Δ effect. Seven frames having dimensions and loads typical of those found in apartment and office structures were selected. Four designs are made for each frame: three stress-controlled designs and one drift controlled design. The frames are then analyzed for their response under proportioned and nonproportioned loads. Results show that even though the strength of the structures is reduced by P-Δ effect, all stress designs can achieve a wind load factor equal to or greater than 1.40 under proportional loads, 2.06 under nonproportional loads with gravity load maintained at working value. The stress design having columns proportioned to satisfy AISC provisions does not show significant increase in strength when compared with the design neglecting instability effect. The drift designs have large wind load-carrying capacity, ranging from 1.45 to 4.0, depending on the amount of gravity load.