Karydakis, Ionnides, and Vagias 2011
The authors presented the principles of the INSTED system for multi-story steel buildings in seismic areas. Vertical composite beams were used instead of the usual moment resisting frames and anti-diagonal bracings with or without eccentricity. In this paper, the system was investigated analytically and experimentally.
System Concept
The INSTED system was made up from two strong columns of square hollow section and joined together with horizontal beams in a relatively tight arrangement, a vertical vierendeel beam. The vertical strong columns remain elastic with expandable horizontal connections, where plastic hinges are formed and energy dissipation takes place. The horizontal connections can vary in beam section including I-beams, hollow sections, or solid rods and bars. The expandable section was located at the middle of the span in both cases.
The expandable connecting element was moved away from the columns by increasing the length of the replaceable beams that remain elastics, and the developed bending moment was smaller. On the other hand, more plasticity was required due to the bigger relative vertical displacement.
Experimental and Analytical Study, Results, and Discussion
Fifteen tests were performed with three groups of connecting elements: beams of similar section, bars and rods of similar section, and beams of variable connections. The variable sections were designed to maintain structural rigidity until failure during the progressive failure of the system.
In an analytical study, finite element models were used in order to simulate simple bi-linear results without including post-yielding behavior of the steel, final fracture or fatigue. The experimental results were very close to the analytical investigation.
Reference
Karydakis, P., Ionnides, G., and Vagias, I. (2011). “INSTED - Innovative Stiffness and Energy Dissipation System, Final Report,” Proceedings of the Eurosteel 2011, Budapest, Hungary, August 31-September 2.