Details Resembling the “Dog-Bone” in Seismic Resistant Concentrically Braced Frames

The present paper intends to illustrate some advantages of using “dog-bone” details in several seismic resistant steel structures equipped with concentrically braced frames. Configurations with “dog-bone” details near the base of bottom-story columns in concentrically braced frames are safer from the point of view of ensuring the general stability of the first-story columns (in the situations when plastic deformations occur in the bottom story columns). In addition, the maximum bending moment values, which can appear near the bottom of first-story columns during strong earthquakes, can be limited by using adequate “dog-bone” configurations. Configurations resembling the “dog-bone” near the ends of the upper story diagonals in concentrically braced frames ensure on one hand, the abidance of the slenderness demand for the braces and on the other hand, small values of the over-strength ratio evaluated with this reduced diagonal cross-section. At the same time the buckling behavior and slenderness of the braces are not significantly affected by the reduced cross-sections near the member ends and the slenderness demand of the braces will be satisfied. A favorable global plastic hinge mechanism can be imposed by design for concentrically braced frames with rigid member connections, by providing “dog-bone”-shaped configurations for additional potentially plastic zones located near the column ends of girders.