A MULTI-FUNCTION UNSEATING PREVENTION DEVICE FOR ISOLATED BRIDGES

摘要

A multi-function unseating prevention device is investigated to provide energy dissipation and to regulate the structural system properties other than the traditional function of unseating prevention devices for isolated bridges. The isolators in bridge structures are effective in mitigating the induced seismic force by a shift of natural period. However, the deck displacement becomes excessively large when subjected to an extreme earthquake. Such a large displacement may increase the hazard of deck unseating. Also it is difficult to design an expansion joint accommodating with such a large displacement. In the past studies, supplementary dampers have been shown to be useful on reducing seismic responses of isolated bridges. Considering that the space is generally limited for installing supplementary devices in bridges, a viscous damper is inserted into an unseating prevention device to dissipate energy during earthquakes. The multi-function unseating prevention device consists of a linear viscous damper and an elastic spring connected in parallel or in series. Typical continuous highway elevated bridges equipped with multi-function unseating prevention devices are analyzed. Parametric study is performed by using nonlinear structural dynamic analysis including the hysteretic behavior of the columns and isolators to examine the effectiveness of the multi-function unseating prevention devices under near-field earthquakes. It is found from the numerical simulation that the interaction of the energy dissipation between the columns, the isolators and the unseating prevention devices is important to modify the deck displacement. The damper dissipates energy effectively while the spring modifies the structural properties of two adjoining bridges.