Wang, Zhao, Gao, and Meng, 2020
A modular energy dissipation (MED) unit is proposed in place of a buckling restrained brace, acting as an energy dissipator within steel frame structures. The proposed MEDs consist of a series of energy dissipating units connected by screws to threaded couplers in series and contained within a restraining tube. The MEDs, along with nonmodular energy dissipation (NMED) units, are tested in a hydraulic servo universal testing machine under low cycle loading conditions, therefore revealing an axial deformation of the MEDs of up to 4%, without significant loss of strength, making them suitable for low cycle fatigue in structures due to their high energy dissipation and replaceability through screw connections.
System Concept
The proposed system within this paper is an MED, which is designed to be placed inside steel structures as a replaceable energy dissipating fuse. The proposed MED consists of several energy dissipation units connected in series through threaded couplers. The energy dissipation units are bamboo shaped steel units that can be produced under uniform specifications, and a number of repeated units in series can be used to increase energy dissipation capacity. The threaded couplers consist of locknuts and screws to hold the energy dissipation units in place and prevent rotation. The combination of the elements in series is to permit the fracture of the system to occur in the dog bone of the energy dissipating units, which are then replaceable through the screws in the threaded connections. The system is contained within a restraining tube in order to prevent excessive lateral movement of the system post failure.
The MED unit differs from the nonmodular energy dissipation (NMED) system in that the threaded connections between the modular energy dissipation units permit replaceability of the system, and the single module can be repeated in series for a greater energy dissipation capacity. Also, the modules can be factory produced, which makes production cheaper and more accessible. This also decreases the initial stress of the system by 30-40%. The goal of the MED system is to concentrate energy dissipation into numerous replaceable components in a steel system, namely a frame or a rocking column, and to create a system that can be easily manufactured for frequent use.
Experimental Study, Results, and Discussion
The experimental study consists of seven test specimens, five of which were MEDs and four of which were NMEDs. Among the five MEDs, design parameters for the modular system were adjusted to measure the increase in energy dissipation of higher numbers of modular units, and the effect of additional screws in the threaded connections, as well as the replaceability of the modular units by retaining the same connections for the different specimens. The specimens were loaded in a hydraulic servo universal testing machine using hydraulic clamps to secure them in place. The machine applied displacement informed low cycle lateral loads up to an axial deformation of 4% to the test specimens, followed by continuous cyclic loads at 3% axial deformation until failure, and an analysis of the results revealed the ability of the modular units to dissipate energy in the event of seismic loading.
It was found that all specimens exhibited a stable hysteretic response curve until failure without significant strength reduction, and that all specimens failed after the peak load was reached and the constant strain amplitude (CSA) loads were applied, though the MED specimens exhibited slip deformations at near zero axial loads. A solution is posed to add more screws, which increases the strength of the threaded connections but increases costs of manufacturing. Overall, MED specimens had similar performance curves to the NMEDs, but have an increased replaceability in the structures due to the threaded connections.
Reference
Wang, C.L., Zhao, J., Gao, Yuan., and Meng, S. (2020). “Experimental investigation of modular buckling-restrained energy dissipaters with detachable features,” Journal of Constructional Steel Research, 172. pp. 1-13.