Seismic Response of Diagrid Systems: Ductility Concerns in Low- to Midrise Structures

Abstract

Diagrid structures recently have evolved as novel solutions for the design of tall buildings with unique geometrical layouts. The aesthetic value and flexibility in accommodating distinctive geometrical constraints make diagrids an attractive solution for many innovative structural designs. In diagrid structural systems, most often the diagonal bracings act as both primary gravity load resisting and lateral load–resisting elements. Another defining feature associated with this system is its reduced ductility, especially for shear-dominant systems with lower diagonal angles. Typically characterized by less structural redundancy and a nonductile postyield response, the design of diagrid structures in high seismic zones should be treated with caution. There could be a false sense that a structural system which is proven to be efficient for high-rise buildings could safely satisfy the requirements for low- to midrise structures. The increasing demand for free-form geometrical layouts could result in instinctive and incautious selection of these structural systems for low- to midrise buildings because of their effectiveness in high rise structures. However, under high levels of axial compression (typically associated with high seismicity), the diagonal members could be subjected to buckling, and the limited redundancy in the structural configuration significantly could affect the global postyield response of the structural system. Hence, this paper examined a case in which a diagrid structural system was used for the concept design of a multistory commercial structure in a high seismic zone, and the inefficacy associated with the seismic behavior of the system was addressed successfully by adopting two different methodologies, with buckling-resistant braces (BRBs) as the diagonal elements in the first approach and yielding connectors (YCs) as fuse elements in the second approach. Both solutions performed well in terms of improving the postyield response of the system. However, the use of yield connectors could be particularly effective in shear-dominant diagrid systems with lower diagonal angles due to the postyield hardening response in compression demonstrated by the connector elements.