Effective Steel Braced Frames for Tall Building Applications in High Seismic Regions

Steel braced frames are commonly used for building structures in seismic active regions. However, steel braced frame systems are limited to low- and medium rise structures because they are prone to concentration of inelastic demand resulting from adverse P-Δ effects and lack of vertical stiffness continuity. The article introduces a modified inverted-V buckling braced frame configuration in which one of two bracing members at every level is replaced with a conventional brace designed to remain elastic and form with the beam member an elastic secondary system providing the system with positive post-yielding storey shear stiffness annihilating P-Δ effects upon yielding of the BRB members and ensuring stable seismic response for tall building applications. The anticipated behaviour and design approach of the proposed E-BRBF system is first described. The stability of the system is then verified through nonlinear response history analysis for 20-, 30- and 40-storey buildings subjected to ground motions from shallow crustal, subduction in-slab, and subduction interface earthquakes. The analysis results are compared to those obtained with conventional BRBFs. The comparison shows that the proposed E-BRBF system can significantly enhance the seismic response of tall buildings, with reduced and more evenly distributed peak storey drift demand over the structure height.