Civil Engineering Association

Determining the Effective System Damping of Highway Bridges

In this study, a damping-enhanced strengthening (DES) strategy was introduced to retrofit bridge structures for multiple performance objectives. The main objectives of this study are (1) to numerically demonstrate the effectiveness of the anchoring mechanism of a constrained damping layer in the proposed DES system, and (2) to evaluate the performances of a highway bridge retrofitted with a DES retrofit technique of viscoelastic (VE) damping and carbon-fiber-reinforced-polymer (CFRP) strengthening components that are nearly independent under weak earthquakes but strongly coupled under strong earthquakes. The effects of various constrained surface damping layers on the responses of simply-supported beams and cantilevered columns were first investigated analytically. An emphasis was then placed on the development of a finite element modeling technique to simulate the effect of a distributed VE damping layer on the responses of columns. Finally, the DES strategy was applied to retrofit the Old St. Francis River Bridge columns. Both operational and safety performance objectives of the bridge were evaluated with pushover analyses under earthquakes of various magnitudes. An anchored constrained damping layer was found several times more effective than a conventional constrained layer, particularly when covering 20-80% of the column height. To meet the two performance objectives, the Old St. Francis River Bridge columns must be wrapped with three plies of CFRP sheets and one VE layer. The new retrofit strategy is well suited in the context of next-generation performance-based seismic design and retrofit of highway bridges and other structures.