BRIDGE RESONANT EXCITATION WITH PORTABLE VIBRATION GENERATORS

THIS EXPERIMENTAL FIELD STUDY WAS UNDERTAKEN TO DETERMINE THE RESONANT VIBRATION RESPONSE CHARACTERISTICS OF FOUR TYPICAL HIGHWAY BRIDGES IN TENNESSEE. TWO IDENTICAL VARIABLE-FREQUENCY HARMONIC FORCE GENERATORS WERE INSTALLED NEAR THE MID-SPAN OF EACH BRIDGE IN TURN, AND EACH WAS EXCITED AT ITS VARIOUS RESONANT FREQUENCIES. ONE VIBRATION GENERATOR WAS LOCATED IN EACH LANE. THE OUTPUTS OF EACH WERE VARIED IN PHASE AND FREQUENCY TO EXPLORE NORMAL AND TORSIONAL RESPONSE MODES. THE RESPONSES WERE SENSED BY ACCELEROMETERS, STRAIN GAGES, AND DEFLECTION GAGES AT STRATEGIC POINTS ON THE STRUCTURES. THE FOUR BRIDGE TYPES INCLUDED A REINFORCED CONCRETE T-BEAM SIMPLE SPAN, A PRESTRESSED CONCRETE I-BEAM AND SLAB SIMPLE SPAN, A 3-SPAN CONTINUOUS ROLLED STEEL BEAM AND SLAB BRIDGE, AND A 4-SPAN CONTINUOUS ROLLED STEEL BEAM AND SLAB BRIDGE. THE MEASURED LONGITUDINAL VIBRATION MODE SHAPES AND FREQUENCIES COMPARED FABORABLY WITH PREDICTED RESPONSES. ALL BRIDGES WERE READILY EXCITED IN THE FIRST NORMAL MODE AND THE FIRST AND SECOND LATERAL MODES. TORSIONAL RESPONSES WERE OBTAINED ONLY IN THE STEEL BEAM CONTINOUS-SPAN BRIDGES. THE VIBRATION GENERATORS YEILDED MORE PRECISE DAMPING CHARACTERISTICS AND NEUTRAL AXIS LOCATIONS THAN DID PREVIOUS LOADINGS WITH MOVING VEHICLES. RESONANT VIBRATIONS WERE FOUND CAPABLE OF AGGRAVATING STRUCTURAL WEAKNESSES IN SOME OF THE BRIDGES. CERTAIN HIGHER-FREQUENCY RESONANT RESPONSES WERE DECIDEDLY UNCOMFORTABLE TO PEDESTRIANS ON THE BRIDGES. /FHWA/

  • Corporate Authors:

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590
  • Authors:
    • Varney, R F
  • Publication Date: 1971-9

Media Info

  • Pagination: 45 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00208116
  • Record Type: Publication
  • Source Agency: Federal Highway Administration
  • Report/Paper Numbers: FHWA-RD-71- 5 Final Rpt.
  • Files: TRIS, USDOT
  • Created Date: Jul 16 1974 12:00AM