Bending and shear stiffness optimization for rigid and braced multi-story steel frames

The response of multi-story building structures to lateral loads, mainly due to earthquake andrnwind, is investigated for preliminary design purposes. Emphasis is placed on structural systems consisting ofrnrigid and braced steel frames. An attempt to gain a qualitative understanding of the influence of bending andrnshear stiffness distribution on the deformations of such structures is made. This is achieved by modeling thernstructure with a stiffness equivalent Timoshenko beam. It is observed that the conventional stiffnessrndistribution, dictated by strength constraints, may not be the best to satisfy deflection criteria. This isrnparticularly the case for slender structural systems with prevailing bending deformations, such as flexiblernbraced frames. This suggests that a new approach to the design of such frames may be appropriate whenrnserviceability governs. A pertinent strategy for preliminary design purposes is proposed.