Metropolitan Dade County, Florida, is now in the process of building a new rapid transit system of about 50 miles. The first-stage construction of this new system scheduled for completion in 1984, consists of 22.5 miles, and includes 21.5 miles of aerial guideways. The aerial structures to be used for the guideways are prestressed concrete double-tee girders, which is a first in the use of such a structure in a U.S. transit system. In view of large capital investment involved, and the fact that a double-tee has not been used on any rapid rail transit system, the Urban Mass Transportation Administration agreed to fund full-scale tests. These tests were to serve three purposes: (1) to prove the adequacy of all design methods; (2) to check some of the construction and reinforcement details; and (3) to verify the dynamic performance of the girders. Demonstration tests were carried out on three full-size 80 feet long by 5 feet deep by 12 feet wide precast prestressed double-tee girders proposed for the aerial guideways. Two of the three girders cast in Miami were shipped by rail to P.C.A. Laboratories in Skokie, Illinois for extensive static and dynamic testing, with the third girder kept in Miami to monitor camber and loss of prestress. Static test results of uncracked and deliberately precracked girders showed that service torsional rotations, which were in close agreement with a theoretical mixed torsion analysis, were small enough to ensure rider comfort. Fatigue resistance of the girders was fully established by two separate test spectra involving 5 and 6 million cycles of loading representing the cumulative damage of sixty years of operational life. No deterioration whatsoever was observed in terms of flexural and torsional stiffness, crack propagation, or strand stresses. Post-cracking behavior of the girders showed adequate strength and ductility with an ultimate capacity of 1.6 times the required factored severe derailment loading including 100% impact. This test report concludes that the excellent behavior of the girders from serviceability and strength considerations, substantiated all the design analyses and details used.

  • Corporate Authors:

    Dade County, Florida

    Office of Transportation Administration
    Miami, FL  United States 

    Urban Mass Transportation Administration

    400 7th Street, SW
    Washington, DC  United States  20590
  • Authors:
    • Hsu, TTC
  • Publication Date: 1979-10-10

Media Info

  • Pagination: 164 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00326449
  • Record Type: Publication
  • Source Agency: National Technical Information Service
  • Report/Paper Numbers: UMTA-FL-06-0017-80-1Final Rpt.
  • Files: NTIS, TRIS, USDOT
  • Created Date: Feb 6 1982 12:00AM