PHASE I OF AN EVALUATION OF BRIDGE VIBRATION AS RELATED TO BRIDGE DECK PERFORMANCE

A SERIES OF FIELD TESTS WAS CONDUCTED ON 11 TYPICAL HIGHWAY BRIDGES IN TENNESSEE TO DETERMINE THE INFLUENCE OF BRIDGE VIBRATION ON BRIDGE DECK PERFORMANCE. THE THEORETICAL FREQUENCIES AND STATIC DEFLECTIONS DUE TO THE CONTROL LOAD WERE COMPUTED FOR EACH BRIDGE. A WILD THEODOLITE WAS USED TO VISUALLY OBSERVE THE AMOUNT OF DEFLECTION CAUSED BY THE CONTROL LOAD. THE CONTROL LOAD WAS A SCALES TRUCK WITH A GROSS LOAD OF ABOUT 36,000 POUNDS. THE TRUCK WAS DRIVEN OVER THE BRIDGE AT CRAWL SPEED, 20 MPH AND 40 MPH. A COMPUTER PROGRAM WAS DEVELOPED FOR THE STATIC DEFLECTION CALCULATIONS AND THE COMPUTATION OF THE NATURAL FREQUENCIES OF VIBRATION AND ASSOCIATED MODAL SHAPES FOR ANY BRIDGE. THE PROGRAM USES A FINITE DIFFERENCE TECHNIQUE TO FORMULATE THE CHARACTERISTIC EQUATIONS. ONE BRIDGE WAS INSTRUMENTED WITH FOIL STRAIN GAGES AT FIVE LOCATIONS TO CHECK THE GAGING TECHNIQUE AND DETERMINE THE STRAINS CREATED IN THE BRIDGE DUE TO NORMAL TRAFFIC. TRANSVERSE CRACKING WAS MORE EVIDENT ON THE BRIDGES SUBJECTED TO HIGHER VOLUMES OF TRAFFIC. THE CONTINUOUS SPAN STEEL BRIDGES DISPLAYED THE MOST CRACKING THAT COULD BE ASSOCIATED WITH TRAFFIC INDUCED VIBRATIONS. VARIABLES WHICH DETERMINE THE INFLUENCE OF BRIDGE VIBRATION ON BRIDGE DECK PERFORMANCE ARE CONSTRUCTION METHODS, SELECTION AND HANDLING OF MATERIALS AND MIX DESIGN. BRIDGES WITH HIGHER FREQUENCIES GENERALLY HAD THE LEAST AMOUNT OF CRACKING. THE HIGHER FUNDAMENTAL FREQUENCIES ARE ASSOCIATED WITH CONCRETE AND PRESTRESSED BRIDGES.