Heiti verkefnis : 

Seismic vibration control of bridges with nonlinear tuned mass dampers.

Verkefnastjóri : 

Rajesh Rupakhety

Stutt lýsing á verkefninu:

Lifeline structures like bridges need to be robust against natural hazards such as earthquakes and strong winds. Tuned vibration absorbers (TVAsa) have great potential in reducing dynamic vibration of bridges. Different types of TVAs, their design methods, optimization procedures, arrangement in the structure, and overall efficiency in reducing vibrations due to various environmental loads have been investigated in the literature. Most studies have concluded that single and multiple tuned mass steamers are effective in controlling seismic and wind response of pedestrian, highway, and railway bridges. In most studies, TVAs installed on bridges are assumed to be elastic.  In practice, such devices are expected to yield under certain conditions. It is therefore realistic to model their inelastic behavior. In fact, non-linear yielding behavior can be used to reduce displacement demand on the structure. However, optimal design of non-linear TVAs has not been adequately addressed in the literature, especially in relation to the design being excitation dependent, and the robustness of the device in preventing detuning effects. The main objective of the present study is to investigate design of non-linear TVs (n-TVAs)and their efficiency in reducing seismic response or bridges. Mathematical models of typical highway bridges will be prepared using the finite element method. Response simulation using nonlinear time history analysis will be carried out using strong ground motion recorded in Iceland. Probability density of response parameters for uncontrolled bridges, linear optimum TVAs and nonlinear TVAs will be compiled to investigate if nonlinear TVAs can be used as efficient and robust as linear TVs without using viscous dashpots used in the laughter. The results have practical importance because properly designed TVAs can provide a good alternative to base isolation systems, which typically tend to increase displacement demands.

Tilgangur og markmið:

The main purpose of this project is to investigate optimal design of nonlinear TVAs for seismic vibration control of bridges. Optimization of linear TVAs is well established in the literature. A linear TVA, when exposed to severe excitation can yield, resulting in softening and consequent detuning. Detuned devices are less efficient in vibration absorption and might even be hazardous for the overall safety of the structure. In most studies, non-linear behaviour of TVAs are studied by using devices designed to be optimal in the elastic regime. This project aims to change this design paradigm by introducing inleastic behaviour in the design stage. A potential approach to identify an equivalent elastic representation of the actually inelastic device. This can be achieved by consideration of equivalent (secant) stiffness and energy dissipated for a given level of ductility demand. In this sense, the design becomes excitation dependent to some extent. In this sense, the design process is iterative. The project will explore this design paradigm, and test the convergence of such iterations for earthquake ground motions of different intensity and frequency content. Another objective of this project is to compare the effectiveness of such devices against uncontrolled bridges and those controlled with conventional linear TVAs. Investigation of probabilities of exceednance of bridge response and its reduction by the proposed device will also be carried out. Another important aspect is to investigate the stroke of such devices, and potential measures for reducing it, as it can pose practical constraints in installing TVAs in bridges. Design optimization method for inelastic TVAs, investigation of their efficiency in reducing seismic response, and performance comparison with conventional TVAs are the expected results of this project.