On the characteristics of new ductile knee bracing systems

In this paper, a new structural lateral bracing system called ‘Chevron Knee Bracing’ (CKB) is investigated. This new form of framing system is constructed through the knee and the diagonal brace elements. The knee part is a fuse-like component that dissipates energy by the formation of plastic flexural and/or shear hinges at its ends and mid-span, when the building is subjected to severe lateral loads. However, the diagonal brace component, on the other hand, provides the required level of lateral stiffness and remains in the elastic range without buckling at any time. In this investigation, first, by studying of the system in the elastic region, three new and practical parameters are established. Then, the best fitting optimal shape and angle of the knee and brace elements are projected, analytically. In the next step, by developing a nonlinear analytical knee element model, the actual behavior of this new CKB system is experienced in the nonlinear static and dynamic analysis, on two example structural systems, where the knee element happens to be in the moment and/or shear yielding mode. Using the results on nonlinear analysis of these test problems, the main properties of the CKB, such as the energy dissipation characteristics of the proposed systems, are properly inspected by establishment of an energy calculation algorithm. Finally, based on the presented optimal shape of the CKB in this paper, two step-by-step algorithms accompanied by appropriate main graphs and charts are suitably demonstrated and nonlinear behavior of the new model for flexural and shear yielding modes is well determined, which is followed in the next paper.