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https://nap.nationalacademies.org/catalog/27432/critical-issues-in-transportation-for-2024-and-beyond

VIBRATION AND DEFLECTION OF STEEL BRIDGES

THE OBJECTIVE OF THIS PAPER IS TO SHOW THE EFFECTS OF THE SLENDERNESS AND FLEXIBILITY OF MULTISTRINGER STEEL HIGHWAY BRIDGES ON THEIR STRENGTH AND SERVICEABILITY. SLENDERNESS AFFECTS THE AMOUNT OF STEEL REQUIRED FOR BRIDGE STRINGERS AND HAS AN ASSOCIATED SECONDARY INFLUENCE ON THE DEAD WEIGHT OF THE BRIDGE. FLEXIBILITY AFFECTS RESPONSES TO STATIC (SLOWLY MOVING) LOADINGS AND TO DYNAMIC LOADINGS. THE EFFECTS OF FLEXIBILITY AND THEIR RELATIONSHIP TO BRIDGE PERFORMANCE IN TERMS OF DECK DURABILITY AND HUMAN RESPONSE, AS WELL AS THE INFLUENCE OF RELAXED FLEXIBILITY CRITERIA HAVE BEEN REVIEWED IN THIS PAPER. A FIRST CONCLUSION IS THAT A MORE FLEXIBLE BRIDGE IS STRONGER IN RESISTANCE TO YIELDING OF A STRINGER. THIS RESULTS FROM A MARKED IMPROVEMENT OF STATIC LOAD DISTRIBUTION WHICH IS ONLY PARTIALLY COUNTERACTED BY AN INCREASE OF THE IMPACT FACTOR. DURABILITY OF CONCRETE BRIDGE DECKS DOES NOT APPEAR TO BE AFFECTED BY STRINGER FLEXIBILITY. OBSERVED CRACKING IN DETERIORATED DECKS CANNOT BE RELATED TO LIVE LOAD STRESSES. HUMAN RESPONSE TO ACCELERATION, LIKE THAT TO SOUND, VARIES WITH THE LOGARITHM OF THE AMPLITUDE. THEREFORE, SUBSTANTIAL VARIATIONS IN FLEXIBILITY PRODUCE ONLY MODEST EFFECTS ON HUMAN RESPONSE TO BRIDGE MOTIONS. THE CURRENT DEFLECTION CRITERION, A LIMITING RATIO OF SPAN TO DEFLECTION DUE TO LIVE LOAD PLUS IMPACT, DOES NOT ASSURE HUMAN COMFORT BECAUSE IT DOES NOT CONTROL THE DYNAMIC COMPONENT OF ACCELERATION. THERE IS NO EVIDENCE OF BRIDGE MOTIONS PRODUCING DISCOMFORT OF OCCUPANTS OF MOVING VEHICLES, SO THERE APPEARS TO BE NO NEED FOR LIMITS ON DEFLECTIONS OR ACCELERATIONS OF BRIDGE WHICH DO NOT CARRY PEDESTRIAN TRAFFIC UNDER NORMAL CONDITIONS. EXAMPLE DESIGNS PRESENTED HERE FOR VERY SLENDER, VERY FLEXIBLE BRIDGES DO NOT EXHIBIT UNDESIRABLE SIDE EFFECTS OTHER THAN THE MILDLY INCREASED DYNAMIC COMPONENTS OF DEFLECTION FROM INCREASED FLEXIBILITY AND INCREASED AMOUNTS OF STEEL WITH INCREASED SLENDERNESS. ECONOMIC REQUIREMENTS ARE LIKELY TO PREVENT USE OF SLENDERNESS BEYOND THE RANGE CONSIDERED HERE. BRIDGES DESIGNED FOR PEDESTRIAN TRAFFIC OR STATIONARY VEHICLES SHOULD BE LIMITED IN MOTION BY A SERVICEABILITY CRITERION ASSURING HUMAN COMFORT. THE LEVEL OF LIMITATION IS STILL IN DOUBT, BECAUSE A TOLERABLE MOTION IS A QUESTION OF PSYCHOLOGY. THE MODEL USED TO PREDICT BRIDGE MOTIONS FOR DESIGN IS AS IMPORTANT AS THE DIRECT LIMITATION PLACED ON THE PREDICTED MOTIONS. A RATHER SIMPLE, YET ACCURATE, FORMULATION IS PRESENTED. BECAUSE RELIABLE EVIDENCE ON HUMAN REACTION TO BRIDGE MOTIONS IS SO SEVERELY LIMITED, IT IS SUGGESTED THAT THE RECOMMENDED ACCELERATION CRITERION RECEIVE EMPIRICAL CONFIRMATION PRIOR TO ANY ADOPTION. /AUTHOR/

  • Supplemental Notes:
    • Vol 9, No 1, PP 20-31, 10 FIG, 1 TAB, 36 REF
  • Authors:
    • Wright, R N
    • Walker, W H
  • Publication Date: 1972-1

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  • Accession Number: 00209624
  • Record Type: Publication
  • Files: TRIS
  • Created Date: May 16 1972 12:00AM