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.

This study investigates an innovative method of avoiding brittle fracture at the beam-column connection welds of steel moment frames in earthquakes. The Reduced Web Section (RWS) approach introduces large openings into the web to shift the location of inelasticity away from the connections. The configuration of the openings governs the mode and capacity of inelastic mechanism in the beam. In this paper, experimental results are reported for five RWS specimens that were subjected to quasi-static cyclic loading. Four specimens were designed to develop Mode-A mechanisms; three had a single unique opening at midspan, and one had two openings near the beam-column connections. The other specimen was designed to develop a Mode-B mechanism without having web post buckling (observed in the Phase 1 specimens [1]), which had a wide opening and two brass plates clamped to the web. The application of web openings was successful in achieving the intended inelastic mechanisms; inelastic deformation was due to yielding, buckling, and/or fracture of the webs around the opening(s) and plastic hinging of the T-sections above and below the opening(s). The three specimens with a single opening at midspan exhibited the most stable load-drift responses; the specimens displayed a loss of strength during the 3 or 4% drift cycles (due to local buckling and/or fracture of the webs) and subsequent transition from "full" to "S-shaped" hysteretic loops, but they regained full strength by the end of testing at story drifts up to 7%.

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Summary Reinforced concrete coupled wall systems that consist of multiple shear walls linked by coupling beams are known to be very effective for resisting lateral loads in high‐rise buildings. As to improving the seismic capacity of coupled wall systems, high‐performance fiber‐reinforced cement composites (HPFRCCs) have been recently considered. These materials are characterized by tension strain‐hardening behavior that can improve the ductility and toughness of structures subjected to reversed cyclic loading. In this study, nonlinear finite element analyses were conducted to investigate the effects of HPFRCCs on the seismic behavior of irregular tall buildings with coupled wall systems. The coupling beams were modeled using moment hinge elements, and the structural walls were modeled using fiber elements. Comparisons between analysis and test results of coupled wall specimens with and without HPFRCCs indicate that the modeling methods used well predict both the overall and local behaviors. The responses of a 56‐story irregular tall building with coupled walls are discussed with focus on the effects of HPFRCCs. It is noted that the use of HPFRCCs in coupling beams and structural walls of one‐fourth height from the base greatly affects the failure mode. For irregular tall buildings, nonlinear response history analysis indicates higher mode effects are critical.

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