Seismic toughness and failure mechanisms of reduced web-section beams: Phase 1 tests

•Large openings in the webs of steel I-beams can be used to limit stresses at the beam-column connections and to avoid fracture of the welded beam-column connections.•The strength of the Reduced Web-Section specimens was reduced at story drifts of around 5%, although the specimens were able to sustain story drifts of at least 8%.•The web posts of the Mode-B specimens buckled at story drifts of 1–1.5%, and caused a reduction in lateral resistance of between 21 and 33%. The post-buckled strengths were maintained to story drifts of 5–6%.•The web posts fractured by ductile tearing, and the gradual failure of a post had a small effect on the lateral resistance, because load transfer could be maintained by other web posts acting in parallel.•Simple analytical approaches used to size web openings were effective in achieving the intended mechanisms.•The web post slenderness ratio, s/d’, provides a useful index of the tendency towards flexure- or shear-dominated behavior of the web post. Avoiding fracture in the beam-column connections of steel moment frames is critical to their seismic performance. Both Reduced Web Section (RWS) and Reduced Beam Section (RBS) methods apply the capacity design principle to shift the location of yielding into the beam and away from the beam-column connection. In the RWS approach, large openings are introduced into the web of the beam, so that the arrangement and configuration of the openings determine the mode of inelastic mechanism that develops within the beam. In this paper, experimental and numerical results are discussed for five RWS specimens that were subjected to reversed cyclic displacements. Also, the concept and potential inelastic modes of RWS beams are introduced, and beam shear equations corresponding to the assumed plastic mechanisms are derived. Of the five specimens, one had only two openings close to the beam-column connections, while the others had multiple openings distributed over the beam span. Most of the specimens exhibited stable hysteretic behavior up to approximately 6% story drift.