Aghlara and Tahir, 2018
Full scale bar-fuse damper (BFD) specimens consisting of a diagonal round steel member containing two bolted concentric square tubes with inner fuses are tested experimentally under cyclic loading conditions in order to determine their energy dissipation capacity under seismic applications. The experimental study determined that the BFD is effective in absorbing and dissipating energy in a brace system.
System Concept
The proposed BFD system consists of a steel member containing an embedded steel fuse. The round steel tube is to be used as a diagonal brace member within a steel frame, and is designed to carry no loads until the application of seismic energy results in the deformation of the fuse element. Two proposed system configurations include either a single diagonal brace containing a BFD, or two chevron braces each containing a BFD. Under seismic loading, the fuse element within the BFD deforms such that it absorbs and dissipates the applied lateral loads, therefore concentrating the energy dissipation of the system into one replaceable element. The benefits of this system are its replaceability, low cost, and low weight.
The embedded fuse consists of rigid inner and outer steel tubes with connection plates at either end to connect to the round steel bar. The two tubes are connected through flexible bolted connections containing steel bars and tightening nuts with some initial prestress. The steel bars are meant to undergo plastic deformation when subjected to lateral loads. Because the fuses are connected to the bar through bolted connections through the slotted connection plates, the fuses are replaceable when they reach inelastic deformation. This means that the fuses absorb the seismic energy to prevent structural damage to other elements of the frame, and can be replaced afterwards to install a new fuse.
Experimental Study, Results, and Discussion
Three full scale specimens of the fuse element of the rigid square elements of the BFD system were fabricated with the intention of them being reusable due to the steel bars sustaining the entirety of the plastic deformation due to applied loads. There were 18 total test specimens including the variable steel bars inside the three BFDs. The steel bars within the bolted connections were being tested in this experiment with variable diameter, length, and quantities within the system. The purpose of the experimental study was to determine the applicability of the BFD system under seismic loading and to test the different parameters of the system and the effect of these parameters on the energy dissipation capacity of the fuse.
The test specimens were loaded within an INSTRON8801 test machine using BlueHill and WaveMaker software to simulate monotonic and cyclic loading. The BFDs were placed vertically within the testing apparatus with a load cell on the top and an actuator to apply loads on the bottom end. The inner part of the BFD was attached to the load cell on top, and the outer part of the BFD was connected to the actuator on the bottom. Monotonic tests were performed in order to determine its mechanical characteristics using a downward vertical force until failure. Displacement-controlled cyclic loading was applied using the actuator, and the displacement was monitored through the testing software. Two cycles were conducted at each displacement of the system until the estimated maximum displacement, and subsequent individual cycles at 1.3 times the estimated maximum displacement were conducted until failure.
The experimental study determined that the BFD fuse system was able to dissipate seismic energy through plastic deformation of the steel fuse bars within the system. The energy dissipation capacity of the system was dependent mostly on the configuration of the nuts around the steel bars, which was most effective with two nuts on either end of the bars. The steel bars were able to withstand 20 loading cycles with a maximum displacement of 600mm, therefore achieving a 35%-65% damping ratio. Coupled with its low cost and weight, the replaceable fuse elements proposed in the BFD demonstrate reliable seismic energy dissipation to reduce structural damage to remaining components of a building.
Reference
Aghlara, R. and Tahir, M., (2018). “A passive metallic damper with replaceable steel bar components for earthquake protection of structures,” Engineering Structures, 159. pp. 185-197.