The fixed bearings of high-speed railway continuous bridges were vulnerable during earthquakes, since they transferred most of the seismic force between the superstructure and the piers. A type of ...

Effects of friction-based fixed bearings on the seismic vulnerability of a high-speed railway continuous bridge:

The Illinois Department of Transportation has adopted an economical and pragmatic methodology for designing earthquake-resistant highway bridges in the Midwestern United States. These so-called quasi-isolated bridges employ low-cost non-seismically designed bearing components as sacrificial structural fuses. During seismic events, fusing actions of these components and subsequent sliding of superstructures on substructures are intended to achieve response characteristics similar to those of conventionally isolated bridges that employ specially designed isolators. This study explores seismic structure-abutment-foundation interaction for quasi-isolated bridges in Illinois, employing a detailed yet efficient non-linear finite-element model for seat-type bridge abutments. The abutment model incorporates many structural components and geotechnical mechanisms that are critical to seismic response of the structure-abutment-foundation (SAF) system. Through non-linear static analyses performed on a complete bridge...

Seismic analysis incorporating detailed structure–abutment–foundation interaction for quasi-isolated highway bridges

Effects of changes in seismic design criteria in the transverse and vertical response of Chilean highway bridges

As all bridges get deteriorated over time, structural health monitoring of these structures has become very important for the damage identification and maintenance work. Evaluating a bridge’s health condition requires the testing of a variety of physical quantities including bridge dynamic responses and the evaluation of the functions of varied bridge subsystems. In this study, both the acceleration of the deck and the dynamic rotational angle of the bearings in a long-span steel girder bridge were measured when the bridge system was excited by passing-by vehicles. The nonstationary dynamical phenomena including vibration mode interactions and coupling are observed in response spectrogram. To elaborate the phenomena, the linear vibration mode properties of the bridge are characterized by finite element analysis and are correlated with the specific modes in test. A theoretical model is presented showing the mechanism of the mode coupling and instability originated from the friction effects in bearing. This study offers some insights into the correlation between complex bridge vibrations and the bearing effects, which lays a foundation for the in situ health monitoring of bridge bearing by using dynamical testing.

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Characterization of Nonstationary Mode Interaction of Bridge by Considering Deterioration of Bearing

In recent years, Illinois bridge engineers developed an innovative “quasi-isolation” seismic bridge design methodology. The objectives of this study are to assess the seismic performance of prototy...

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Seismic Performance Assessment of Quasi-Isolated Highway Bridges with Seat-Type Abutments

Steel fixed bearings are commonplace structural elements for transmitting loads from superstructures to substructures, and they have typically occupied a role of elastic force transfer elements within the overall scheme of an earthquake resisting system (ERS). Recent revisions to design and guide specifications have acknowledged the possibility of bearings acting as fuses, but there is little research available to characterize bearing behavior for such design roles or the associated bridge response to be expected when bearings have fused. One design approach, adopted by the Illinois DOT (IDOT), applies capacity design principles and permits the bearings and superstructure to slide on the substructure. The intent of this design approach is to capture some of the beneficial aspects of conventional isolated systems, such as period elongation, reduction of force demands, and protection of substructures from large inelastic displacement demands, without incurring the additional design provisions and fabrication costs to satisfy the requirements for seismic isolation systems. To achieve this quasi-isolated bridge response, steel fixed bearings are used as fusing elements, where the steel pintles or anchor rods rupture, and the fixed bearing plates become free to slide on the supporting pier cap. A properly proportioned bearing will fuse prior to superstructure/substructure elements experiencing inelastic demands. The University of Illinois has been collaborating with IDOT to investigate the behavior of quasi-isolated bridge systems and to calibrate and refine IDOT’s ERS design and construction methodology. The research is composed of experimental testing to characterize fundamental bearing behavior, coupled with nonlinear global bridge modeling to evaluate limit state progression and estimate maximum displacement demands of the superstructure relative to the substructure. The cyclic response of full-scale steel low-profile fixed bearings demonstrates predictable sliding behavior, but based on current design procedures, these bearings are often overdesigned for use as fuses in quasi-isolated bridges. Consequently, a bridge, which in other respects may exhibit satisfactory quasi-isolated response, might also incur significant damage to the substructure unit where fixed bearings are provided. A parametric study of global bridge response demonstrates that the anchorage of fixed bearings to substructures could be reduced to limit the damage to the supporting substructure unit while incurring only a nominal increase in superstructure displacement demands.

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J. R. Revell

Papers

Experimental behavior of steel fixed bearings and implications for seismic bridge response