Bruneau and Vargas 2009
The authors examine the design and performance of a BRB analytically for the purpose of developing simple design procedures for fuse-type energy-dissipating systems. A 3-story sample structure designed with BRBs is then validated experimentally. The system is subjected synthetic ground motions.
System Concept
The purpose of any fuse system is to concentrate damage in specific structural elements, sparing the remainder of the structure. In this case, BRBs are meant to take all of the damage and be easily replaced, by being connected to the frame with easily removable gusset plates. The BRB consists of a rectangular plate that expands at the ends. The plate is surrounded by tube steel filled with mortar. The tube steel and mortar prevent the plate from buckling. It must yield in either tension or compression. This yielding and subsequent material entry into the inelastic zone dissipates energy. Self-centering occurs after the removal of the load as the BRB is brought back towards its original position through internal forces.
Experimental Study, Results and Discussion
Two BRBs were tested within a load frame and scaled to 1/3 for geometric quantities, and 1/18 for mass quantities. Ground motion was applied until the shake table had reached its maximum capacity. Uniaxial static tests were also performed on the BRBs so that their behavior could be compared to the dynamic behavior of the BRBs.
It was determined that the surrounding frame behaved elastically throughout the testing while the BRB dissipated seismic energy. Strain gauges were able to measure the deformation of each component. Another important feature of the study was the removability and reliability of the BRB with another BRB. It was found that having a removable eccentric gusset plate to connect the BRB to the frame allowed for easy replacement of the BRB after testing.
Analytical Study
The analytical study at hand served the purpose of laying out design procedures for structural fuse systems, using BRBs as an example, and verifying the validity of the approach using the experimental study. The process involves defining the allowable drift, determining the elastic period limit, determining a stiffness limit between the required stiffness and frame stiffness, and calculating the required base shear. After these input levels have been set, the metallic fuses are designed for the required base shear, and the actual parameters of the system of designed, the fundamental period of the system is determined, and the seismic response is evaluated through a time-history analysis. This method was found to be satisfactory when compared with the experimental results of the sample BRB.
Reference
Bruneau, M. and Vargas, R. (2009). “Experimental Response of Buildings Designed with Metallic Structural Fuses II,” Journal of Structural Engineering, 135.4, pp. 394-403.