Self-Centering Buckling Restrained Braces for Curved Bridges

Buckling restrained braces (BRBs) can be used as structural fuses by dissipating the lateral forces applied to a structure while the main structural components remain undamaged. Research on BRBs started in Japan in the 1970’s; they were used in buildings in Japan especially after the 1995 Kobe earthquake (Reina and Normile, 1997) and in the United States (US) after the Northridge earthquake (Clark et al., 1999). Almost all applications have been limited to seismic rehabilitation of existing buildings and construction of new buildings. Recently, researchers proposed implementing BRBs as structural fuses in steel bridges (Kanaji et al. 2003; Cardeni et al. 2004; El-Bahey and Bruneau 2010, 2011). In all previous research, BRBs were used in the transverse direction in order to retrofit bridges against seismic excitations; however, Celik and Bruneau (2009) introduced the idea of using BRBs in two directions for steel bridges. The nonlinear response of an existing multi-span concrete deck on steel girder type curved bridge has recently been studied by the principal investigator (PI). The bridge was modeled using non-linear beam elements. Bearings were modeled as non-linear link elements with stiffness based on maximum allowable load. Soil-Structure Interaction (SSI) was taken into consideration by modeling soil springs at pile-caps and abutments. The structure has two expansion joints, at bent 5 and bent 10, and is connected to the grade separator at abutments 1 and 15. Rocker and expansion type pot bearings are used to support the girders on bents and abutments. Expansion pot bearings are allowed to move in the longitudinal direction. Girders are connected together with cross-frames through bolted connections making the structure rigid. Nonlinear analysis including SSI effects showed that pounding at the abutments and the expansion joints occurred under large earthquakes. The effect of pounding on the girders in the longitudinal direction for the Loma Prieta earthquake record at abutment 15. The normalized girder longitudinal displacement and pounding force are shown; the maximum girder displacement follows the pounding force. Pounding of the girders with the abutment creates large forces thus increasing girder displacements. The maximum displacements of the girders away from the abutment after pounding for eight actual historical earthquake records. The maximum displacement of the girders in many cases is of the order of 200 mm which is significant; the resulting pounding force could damage the girders, abutment wall and shear keys. The bridge response was also obtained for the Kobe earthquake which was scaled to the Peak Ground Acceleration (PGA) expected at the bridge site which equals 0.575 g. Similar to the response at abutment 15 the axial force in the restrainer bars at the expansion joint of Bent 10 exceeded the yield force. Subsequently the bridge was analyzed without restrainer bars assuming that these had failed. The relative distance between the girders at the expansion joint with respect to time. The 200 mm gap was closed several times during the earthquake event causing pounding between the girders and causing the gap to increase up to 580 mm which is significant and could damage the pot bearings which have a 600 mm diameter. Buckling Restrained Braces (BRBs) have a very stable hysteretic behavior as a result, they dissipate significant earthquake input energy and are widely accepted in new design and retrofit for moderate to high seismic regions. The use of BRBs was investigated as a retrofit for this bridge and was found to be effective. A possible seismic retrofit implementation scheme at the abutment with three BRBs in the longitudinal direction (one per girder) and two in the transverse direction. Similarly, a possible seismic retrofit implementation scheme at the expansion joint with two BRBs in the longitudinal direction. The BRBs were designed using conventional sizes and capacities, and were found to reduce the effects of pounding significantly.

Language

  • English

Project

  • Status: Completed
  • Funding: $100000
  • Contract Numbers:

    DTRT13-G-UTC38

  • Sponsor Organizations:

    Research and Innovative Technology Administration

    Department of Transportation
    1200 New Jersey Avneue, SE
    Washington, DC  United States  20590
  • Project Managers:

    Kline, Robin

  • Performing Organizations:

    University of Utah, Salt Lake City

    City & Metropolitan Planning
    201 South Presidents Circle
    Salt Lake City, UT  United States  84112
  • Principal Investigators:

    Pantelides, Chris

  • Start Date: 20150731
  • Expected Completion Date: 20180731
  • Actual Completion Date: 20180613
  • Source Data: MPC-491

Subject/Index Terms

Filing Info

  • Accession Number: 01609821
  • Record Type: Research project
  • Source Agency: Mountain-Plains Consortium
  • Contract Numbers: DTRT13-G-UTC38
  • Files: UTC, RiP
  • Created Date: Sep 1 2016 2:26PM