Abstract:
This research presents a first-order method for elastic-plastic analysis and design of steel rigid frames. The method considers the interaction between axial force and bending moment and permits concentrated and uniformly distributed loads to be placed on the frames. The method utilizes the AISC(4) interaction formulae in setting up conditions of plastic hinge formation. Both strength and in-plane stability effects are considered. In addition, the change in the effective length of each member due to modified member size is also taken into consideration. Following the AISC Specifications, member sizes are obtained from load factors corresponding to the formation of the first plastic hinge and the last plastic hinge at collapse with due regard to the effects of strength, in-plane stability, yield stresses and the limit on deflection at working loads, shear forces and local buckling. It was shown that the predicted maximum loads using the proposed method are about 0-52 % less than those obtained by elastic-plastic analysis while using effective length under the CRC guide line. With the proposed design, the total weight of steel is about 27-138 % more than that obtained by optimum plastic design.