Bo and Xingwen 2008
This paper introduced the TBD system and its installation configuration. Equivalent damping ratio and a simplified procedure for design and analysis of building incorporating TBD systems were proposed. The authors then introduce an expression for prediction of equivalent linear viscous damping ratio provided by the improved TBD systems installed in a building. Finally, validity of the design method was verified by a nonlinear RHA.
System Concept
The purpose of this system is for energy dissipation devices to consume the input energy to the system, so that damage to the main structure is reduced or eliminated. Viscous liquid dampers are one of many energy dissipation devices, and have been used for this purpose in both new and existing buildings. This system suffers from lowered efficiency of energy dissipation due to the low axial displacement when compared to story drift. This problem can be solved by using larger size dampers or amplifying the displacement and velocity in the damper. Larger dampers result in high cost for building rehabilitation, thus increasing the displacement and velocity of the damper is preferred. The TBD system can thus be useful as it creates device displacement larger than the structural drift.
The TBD is directly connected to the beam in a classic configuration. The displacement amplification factor may be smaller than expected due to the flexibility of the beam. In order to overcome this issue, the damper and brace elements were connected directly to the beam-column joints, in the configuration for upper damper and lower damper. So the RHA was conducted on buildings installed with improved upper TBD, lower TBD, and buildings with diagonal brace dampers to compare the efficiency of vibration control for different configurations of energy dissipation devices.
Design Procedure
In the calculation of equivalent damping ratio for structures with lower and upper configuration of TBD system, the magnification factor was derived based on the assumption of small deformations and an axially rigid brace. Based on the Chinese design response spectrum, the effective damping ratio was determined. Then this ratio was used to limit the roof displacement of the damped structure to a specified value.
After outlining design steps, an illustrative example was presented to design and analyze a building with improved TBD systems. The response quantity of interest of the damped structure obtained by the proposed method and the mean results obtained by nonlinear RHA of the designed structure under the artificial ground motions were compared to verify the validity of the proposed method. Finally, nonlinear RHAs of buildings installed with improved upper TBD, lower TBD, and the diagonal brace dampers were conducted in order to compare the efficiency of vibration control for different configurations of energy dissipation devices.
As a result, improved upper TBDs were found to more effectively reduce the floor displacements and story shears demands than improved lower TBDs and diagonal brace dampers.
Reference
Bo, L. and Xingwen L. (2008). “Seismic Design of Structure with Improved Toggle-Brace-Damper System,” Proceedings of the 14th World Conference on Earthquake Engineering, Beijing, China, October 12-17.