Lateral Performance of Semi-Rigid Steel Frames with Precast Knee Bracing Systems: Testing and Finite Element Analysis

In this paper, the synergistic strengthening mechanism of a new type of prefabricated knee brace to semi-rigid steel frame lateral resistance was experimentally and numerically analyzed. Five full-scale specimens with a control steel frame and four knee-braced configurations were tested under pseudo-static cyclic loading in order to understand the stiffness evolution, failure mode, and energy dissipation characteristics of the specimens. Results show the following: (1) The innovative integrated knee braces increase initial lateral stiffness and yield capacity by 184–242% and 91–154% compared to conventional semi-rigid frames with acceptable ductility; (2) Three different failure modes coupled brace-joint yielding (Type I), brace dominated instability (Type II) and beam buckling brace connections (Type III) are identified; (3) Finite element simulations using ABAQUS with isotropic/kinetic hardening models show good agreement with experiments for their hysteretic responses confirming In particular the ultimate failure location is identified at the lateral screw holes of beam flanges located near brace supports where the local stress is greater than 1.8fy. The study further proposes a BIM-integrated design workflow. These results give a theoretical basis and some practical recommendations for the application of knee-braced semi-rigid systems in earthquake-resistant steel buildings.