VIBRATION MEASUREMENTS ON SIMPLE-SPAN BRIDGES

RESULTS ARE PRESENTED OF FIELD MEASUREMENTS OF DYNAMIC DEFLECTIONS OF SIMPLE-SPAN BRIDGES DUE TO THE PASSAGE OF A HEAVY VEHICLE. DATA ARE PRESENTED FOR FIVE BRIDGES OF TYPICAL DESIGN. NO STRAIN MEASUREMENTS ARE PRESENTED, AND THE DISCUSSION IS LIMITED TO A CONSIDERATION OF MIDSPAN DEFLECTIONS. TYPICAL DYNAMIC DEFLECTION RECORDS ARE SHOWN FOR THE FIVE BRIDGES TESTED. THE MAXIMUM OBSERVED AMPLITUDES OF VIBRATION FOR THE TEST BRIDGES VARY FROM 18 TO 40 PERCENT OF THE MAXIMUM STATIC DEFLECTION. THESE AMPLITUDES ARE CONSIDERABLY GREATER THAN WOULD BE PRODUCED BY A THEORETICAL SMOOTHLY RUNNING LOAD. THE FREQUENCIES OF THE OBSERVED VIBRATION WHILE THE LOAD IS ON THE SPAN IS GENERALLY NOT THE NATURAL FREQUENCY OF THE STRUCTURE BUT IS APPARANTLY RELATED TO THE NATURAL FREQUENCY OF THE VEHICLE ON ITS SUSPENSION SYSTEM. EXPERIMENTS WITH A VEHICLE IN WHICH THE SPRINGS HAD BEEN BLOCKED OUT OF ACTION INDICATE THAT CONSIDERABLY LARGER VIBRATIONS OCCUR IN THIS CASE THAN IN THE CASE OF A COMPLETELY SPRUNG VEHICLE. IT IS CONCLUDED THAT ONE OF THE MOST-IMPORTANT FACTORS WHICH INFLUENCE THE VIBRATION OF BRIDGES IS THE DYNAMIC CHARACTERISTICS OF THE VEHICLE ITSELF. ANOTHER IMPORTANT FACTOR IS THE CONDITION OF THE ROADWAY SURFACE ON THE APPROACHES, WHICH MAY CAUSE A VIBRATION OF THE VEHICLE MASS ON ITS SUSPENSION SYSTEM AS IT ENTERS THE SPAN. ALSO REPORTED ARE EXPERIMENTS WITH A VERTICAL ACCELEROMETER WHICH MAY BE USED TO MEASURE VIBRATIONS WITHOUT REFERENCE TO A FIXED POINT. THE USE OF AN ACCELEROMETER IS SHOWN TO BE A SATISFACTORY METHOD FOR MEASURING THE FREE VIBRATION OF A BRIDGE. /AUTHOR/

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  • Accession Number: 00208831
  • Record Type: Publication
  • Files: TRIS, TRB
  • Created Date: Dec 9 1994 12:00AM