Construction and Steel Structure

Biography

Biography: Bulent Akbas

Abstract

Current seismic design specification in the US (AISC 341-10) requires that braced-intersected beams in special concentrically braced frames be expected to remain elastic under the design earthquake ground motion. This design criteria yields in a large unbalanced force from the difference in yielding and buckling strengths in V-type or inverted V-type braces for the brace-intersected beams. As a result, brace-intersected beams always have heavy and deep sections in V-braced or inverted V-braced frames. As an alternative, structural engineers have been using the two–story X-braced frames, having inverted V-type braces in one story and V–type braces of the same sizes above it with an intention to reduce the beam size. Many practicing engineers believe that there is no need to consider unbalanced force in the brace-intersected beams in two-story X-braced frames assuming that unbalanced forces below and above the beam would be equal, but in opposite directions. Such design practice assuming no or little unbalanced force on the brace-intersected beam in X-braced frames appears to be encouraged by some design examples in AISC Seismic Design Manual. This paper will present a study to reveal actual mechanisms and seismic loading patterns on the braced-intersected beams in two-story X-braced frames and discusses the impacts of yielding beams on critical components, such as braces and connections.