Dynamic response evaluation of fiber-reinforced composite bridge decks and bridges

Abstract

Fiber Reinforced Polymer (FRP) composite bridge decks are gaining attention of bridge owners because of their light self weight, corrosion resistance and ease of installation. The lighter weight and lower stiffness of the FRP decks combined with the lower level of damping (than concrete) can lead to excessive deck vibrations and may substantially increase the dynamic amplification of induced stress and deflections. Also, a global NDE technique using dynamic characterization is necessary to ensure the long term performance of FRP bridges. Therefore, an extensive study on FRP decks and FRP bridges is carried out both at laboratory and in the field to evaluate their dynamic characteristics including natural frequencies, mode shapes, acceleration values, dynamic load allowance (DLA) factors, and damping ratios. Test results of FRP deck modules revealed low moment transfer across the modules of the FRP deck. FRP deck stiffened with steel stringers was tested using forced vibration technique and a standard test procedure was developed including custom LabVIEW programs for automation of the test procedure. The developed procedure was used to conduct forced vibration testing on a small FRP bridge (Wickwire Run). Effect of temperature is found to have significant influence on the dynamics of FRP bridges. Further research is needed to study the effect of temperature on FRP bridge dynamics before applying vibration based damage detection techniques on FRP bridges. Controlled truck load tests are also conducted on three FRP bridges namely Katy Truss Bridge, Market Street Bridge, and Laurel Lick Bridge in the state of West Virginia. The dynamic response parameters evaluated for the three bridges include DLA factors, natural frequencies, damping ratios and deck accelerations caused by moving test trucks. It was found that the DLA factors for Katy Truss and Market Street bridges are within the AASHTO 1998 LRFD Specifications, but the deck accelerations were found to be high for both these bridges. DLA factors for Laurel Lick Bridge were found to be as high as 93% (0.93) against the design value of 33% (0.33). Test results showed low damping in the FRP bridges and a technique to improve damping in FRP decks is suggested and tested in the laboratory.