Steel Frames with H Section Columns and Capacity Designed Welded Beam-to-Column Connections

With production of H sections by Isfahan Steel and formation of new steel fabrication yards, multi-storey frames will become a desirable method of construction in Iran. The quality of the design and detailing of beam-to-column connection which is a critical regions of structure assure the desirable characterisitic of seismic tolerance with respect to the inevitable crudeness of predicting earthquake imposed displacements. Capacity design for welded beam-to-column connections in steel seismic moment resisting frames will be the future direction. Beam-to-column connections adjoining plastic hinges in beams are required to be designed for the overstrength plastic moment of the beam and the associated equilibrium shear force. Three factors influence this overstrength plastic moment in the beam, namely uncertainty in yield stress of steel, effect of strain-hardening on the beam cross-section, and local instability of the beam flanges and web due to slenderness. The effect of strainhardening is different in non-seismic and seismic moment frames due to different plastic rotation demands on them. This paper presents an explicit procedure for the capacity design of welded beam- to-column connections, which accounts for the expected strain hardening for any desired level of plastic rotation. An idealised shearmoment interaction boundary is used as a guide to estimate the maximum probable bending moment expected to be developed in the beam during strong earthquake shaking, and a step-wise procedure for design of a beam-to-column moment connection is presented through a specific example of a cover-plated and ribbed connection.