VIBRATION AND DAMPING OF ALUMINUM OVERHEAD SIGN STRUCTURES

THE WIND-INDUCED VIBRATION CHARACTERISTICS OF A 78-FT SPAN ALUMINUM OVERHEAD SIGN STRUCTURE AND THE DAMPING REQUIREMENTS TO PREVENT SIGNIFICANT VIBRATION WERE INVESTIGATED. STRESSES IN CHORD MEMBERS INTRODUCED WHEN SECTIONS OF THE TRUSS WERE BOLTED TOGETHER AND STRESSES IN MEMBERS AT TYPICAL JOINTS DURING VIBRATION WERE ALSO EVALUATED. STRESSES AS HIGH AS 12,900 PSI WERE DETERMINED IN A CHORD MEMBER NEAR A SPLICING FLANGE WHEN THE BOLTS WERE TIGHTENED. AVERAGE STRESSES FROM STRAIN GAGE READINGS TAKEN NEAR ALL FOUR SPLICING FLANGES AND IN MEMBERS NEAR TWO JOINTS WHEN THE STRUCTURE WAS FORCE-VIBRATED WERE GENERALLY SLIGHTLY LESS THAN THE AVERAGE VALUES CALCULATED ASSUMING PIN JOINTS IN THE TRUSS AND SIMPLE SUPPORTS. PEAK STRESSES IN THE MEMBERS WERE AS MUCH AS DOUBLE THE AVERAGE STRESSES. SINGLE AMPLITUDES AT MIDSPAN OF THE STRUCTURE AS HIGH AS PLUS OR MINUS 0.44 IN. WERE MEASURED DURING WIND-INDUCED VIBRATION. THE GREATEST RESPONSE OCCURRED WHEN THE COMPONENT OF VELOCITY OF WIND NORMAL TO THE TRUSS WAS BETWEEN ABOUT 7 AND 12 MPH. THE CALCULATED VELOCITY REQUIRED FOR VORTICES SHED FROM THE CHORD MEMBERS TO BE IN RESONANCE WITH THE NATURAL FREQUENCY OF THE TRUSS WAS 9 MPH. A SINGLE STOCKBRIDGE-TYPE VIBRATION DAMPER, ATTACHED TO THE TEST STRUCTURE AT MIDSPAN, PREVENTED VIBRATION IN THE WIND. THREE DIFFERENT DAMPER SIZES WERE TRIED: 15, 31, AND 35 LB. ALL WERE EFFECTIVE IN PREVENTING VIBRATION. LABORATORY TESTS OF THE THREE MODELS OF DAMPERS ESTABLISHED THE EFFICIENCY OF THE DAMPERS (POWER DISSIPATED) FOR FREQUENCIES FROM ABOUT 4 TO 11 CPS, THE RANGE OF FREQUENCIES EXPECTED IN OVERHEAD SIGN STRUCTURES. THESE DATA AND INFORMATION ON THE POWER SUPPLIED BY THE WIND TO THESE STRUCTURES PROVIDE MEANS FOR THE CHOICE OF DAMPERS FOR OTHER SIMILAR STRUCTURES. /AUTHOR/

• Record URL:
  http://onlinepubs.trb.org/Onlinepubs/hrr/1969/259/259-006.pdf
• Supplemental Notes:
  • Paper sponsored by Committee on Guardrails, Median Barriers, and Sign, Signal and Lighting Supports and presented at the 48th Annual Meeting. Distribution, posting, or copying of this PDF is strictly prohibited without written permission of the Transportation Research Board of the National Academy of Sciences. Unless otherwise indicated, all materials in this PDF are copyrighted by the National Academy of Sciences. Copyright © National Academy of Sciences. All rights reserved.
• Authors:
  • Lengel, J S
  • Sharp, M L
• Publication Date: 1969

Media Info

• Media Type: Digital/other
• Features: Figures; References; Tables;
• Pagination: pp 51-60
• Monograph Title: Development of safer roadside structures and protective systems
• Serial:
  • Highway Research Record
  • Issue Number: 259
  • Publisher: Highway Research Board

Subject/Index Terms

• TRT Terms: Aerodynamic force; Aluminum; Bolted joints; Bolts; Dampers; Damping (Physics); Design; Flanges; Joints; Laboratory tests; Overhead traffic signs; Splicing; Strain gages; Stresses; Velocity; Vibration; Wind
• Uncontrolled Terms: Wind load
• Old TRIS Terms: Wind velocity
• Subject Areas: Design; Highways;

Filing Info

• Accession Number: 00203418
• Record Type: Publication
• Files: TRIS, TRB
• Created Date: Aug 4 1994 12:00AM