Shear Mechanism of Panel Zone Connecting Beam and Brace in Chevron-Bracing Frames

Abstract

Chevron-bracing frames provides adaptability to various architectural layouts, its practical application is currently constrained by the code-specified demand of resisting vertical unbalanced forces which leading to a very deep and heavy beams affecting the headroom. Recent research has revealed that acceptable strength and ductility can be achieved, even if this code-specified demand is violated. In this study, a chevron-bracing frame model based on an actual design project is established. A series of optimization analyses are carried out on the configurations of nodal domain in the chevron-bracing frame, and three series are discussed: vertical plate strengthened joints (PJR series), shear-weak joints (WJR series), and vertical plate and diagonal ribs strengthened joints at the same time (SJ series). From the demand of providing ductility through shear strain of joint panel zone, PJR3, WJR1 and SJ3 are recommended for each series of configurational types, respectively. For three recommended joints, the shear yielding of beam in the nodal domain and buckling of the compressive braces occur basically simultaneously, and the ductility of the structure is provided by both shear yielding of the nodal domains and buckling of the compressive braces. Because shear yielding in nodal domain provides ductility to the structure, the total length of the nodal domain should be greater than the height of the beam and vertical stiffening ribs should be provided strictly in accordance with the requirements of eccentrically braced frames. Meanwhile, the minimum unbalance force that the beam needs to resist is given.

Keywords: chevron-bracing frame, unbalanced force, panel zone, shear-weak joint, shear-strong joint