Aghlara, Tahir and Adnan 2018
The authors analyzed the performance of a Pipe-Fuse Damper (PFD) designed to improve upon the seismic response of structures and the energy dissipation of fuses. Full scale specimens were prepared and tested cyclically and monotonically to determine how various parameters, including the number of pipes, diameter, length and thickness of the pipes, influenced the energy dissipating capabilities of the damper.
System Concept
In a PFD, a rigid inner and outer section are connected by a flexible fuse part. The outer part consists of a hollow square steel profile, two reinforced steel plates and an end steel plate. The two reinforced plates are fully welded to square profile from the outside to prevent its local buckling. Holes are drilled in opposite sides of the hollow square profile to allow the steel pipes to pass through. The end plate is added to connect the PFD to a brace having a similar plate, via bolts. The inner plate is composed of two channel profiles, a perforated steel plate and an end steel plate. Similar to the outer part, the perforation of the steel plate was added to enable the steel pipes to pass through. This steel plate also connects the two channel profiles to one another symmetrically, along with the end plate at one end, all of which is welded together to prevent deformation under axial loading. The flexible fuse part is comprised of threaded steel pipes that connect the inner and outer parts.
Experimental Study, Results, and Discussion
In order to test the four full scale dampers, the INSTRON machine was used. BlueHill and WaveMaker (device-controller software) were implemented for monotonic and quasi-static cyclic test, respectively. The specimens were subjected to the loading protocol outlined in the FEMA461 guideline. If the specimens did not fail after 20 cycles, a single cycle of 1.3-fold displacement amplitude was applied until failure.
All PFD specimens demonstrated allowable ductility and energy absorption characteristics, so much so that a sudden drop in strength and stiffness was not observed in the hysteresis loops within an appropriate displacement domain. The specimens also revealed that the samples having two pipes had a strength and stiffness two times stronger that the samples with only one pipe. The ultimate displacement in both tests indicates that within a range less than or equal to 50% of the monotonic ultimate displacement, the PFD can have a stable hysteretic behavior. Following the seventh cycle, there was a significant increase in the strength and stiffness, likely due to the change in the energy dissipating mechanism from flexural to tensile. All samples, sustained the 20 cycles at target displacement but an additional two cycles up to 17mm, implying the existence of a safety margin. The average stiffness and equivalent damping ratio of the PFDs were inversely correlated when the pipes had the same thickness, while the effective stiffness was proportional to the diameter. The effective stiffness was however, reduced by an increase in displacement. The number of pipes and their diameter and thickness were all directly proportional to the absorbed energy, but this absorbed energy was inversely proportional to the length of the pipe. Overall, the PFD would provide acceptable energy dissipation while maintaining a stable hysteretic behavior within the specific displacement domain without suddenly deteriorating the strength or stiffness.
Analytical Study
After experimental tests were completed, numerical analysis was conducted on the PFD to verify the results presented. The general finite program ANSYS, was utilized to non-linearly analyze the PFD. Varying the pipes diameter, length and thickness, 25 dampers were studied to determine the mechanical properties of the PFD. Utilizing data recorded in the experimental test to create conditions for the numerical analysis, it was concluded that the pipes properly dissipated energy, as they withstood more stress than the other elements of the damper. It was also revealed that strength and stiffness is directly correlated to the pipe’s thickness, while they are inversely proportional to the pipe length. While this analysis was administered on a PFD having only one pipe, it could be easily extended to a PFD with multiple pipes.
Reference
Aghlara, R., Tahir, M. M., and Adnan, A. B. (2018). “Experimental study of pipe-fuse damper for passive energy dissipation in structures.” Journal of Constructional Steel Research, 148, 351–360.