This article describes the design and construction of the new Four Bears Bridge, which maintains access across Lake Sakakawea for the Ford Berthold Indian Reservation in North Dakota. Since Lake Sakakawea is very wide and is located in a northern climate, massive ice floes can occur. The bridge design team therefore undertook a substantial investigation of ice forces and their effects on deep foundations. A Monte Carlo probability analysis was used to establish design parameters for an ice-loading event with a 500-year return period. Historic data was used to determine ice thickness and the elevations where ice would most likely impact the structure. Ice loads based on the AASHTO Load and Resistance Factor Design code were used in the load combinations required by the project's standard specifications. Ice strength is dependent on the ice temperature and the grain size of the ice crystals. Based on simulations of ice-crushing strengths for Lake Sakakawea and the LRFD code requirements, an ice-crushing strength of 100 psi was used for the new bridge design. The ice-crushing strength and ice-thickness were also considered in the design of the piers, piles and pile caps. Ice loading was also considered during the period of construction. Because the structure could be exposed to an ice loading event during construction, a reduced design ice load was used to protect the bridges during the winter period.


  • English

Media Info

  • Features: Figures; Photos; References;
  • Pagination: p. 24-28
  • Serial:
    • Concrete International
    • Volume: 27
    • Issue Number: 2
    • Publisher: American Concrete Institute (ACI)
    • ISSN: 0162-4075

Subject/Index Terms

Filing Info

  • Accession Number: 00986642
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Feb 14 2005 12:00AM