A quasi-tuned-mass-damper design concept for mitigating the dynamic displacement demand of tall piers

Abstract

For bridges with tall piers, how to control the excessive displacement at the top during base excitation is a difficult problem. Related research has involved additional components and very high-cost requirements. A quasi-tuned-mass-damper (quasi-TMD) concept is proposed in current paper controlling dynamic displacement demand at the top of tall piers. The term ‘quasi’ here refers to the fact that the mechanics of this proposed concept is similar to TMDs, but it is realized in a different way. In this quasi-TMD system, the tall piers are considered as the primary structures and the girders are regarded as an additional mass block. Bearings between super- and sub-structures are utilized offering the required stiffness and damping. Since girders provide significantly greater mass ratio, new characters and problems may be encountered and should be solved compared with traditional TMDs. One of the most significant advantages of this quasi-TMD system is that none of additional components are required. While a more detailed design procedure should be conducted for bearings selecting optimal parameters. The equations of motion of tall piers with ground excitations are derived and solved in the frequency domain. A detailed analysis and optimization process are then presented. The case analysis of a typical tall pier bridge illustrates the efficiency of the proposed quasi-TMD in suppressing the response of tall piers excited by seismic motions. Since no additional sub-structure is needed and it is easy to design and implement, it is believed that the quasi-TMD proposed in this paper will attract widespread attention and interest.