Alternative acceleration-based serviceability criterion for fiber reinforced polymer deck -on -steel girder bridges
The objective of this work is to develop an alternative serviceability criterion for honeycomb FRP deck-on-steel girder bridges. The existing AASHTO LRFD interim 2005 static deflection criteria are not applicable to honeycomb FRP decks due to their inherent characteristics, such as low mass and stiffness, and the discrete deck-to-girder connections which do not provide full composite action. The proposed alternative serviceability criterion is based on the bridge vertical acceleration response to traffic and limited to human tolerance to vibrations, or 50 in/s2, according to Oehler (1970). ^ The first step in the development of this serviceability criterion is the creation of a simplified three-dimensional finite element modeling technique for the complex geometry of the honeycomb FRP deck. The modeling technique includes the use of the eccentric beam model from the commercial finite element (FE) program ANSYS for the steel girders, the steel guardrails, and the pier supports. ^ The second step in the development of this serviceability criterion is a parametric study, used to examine the acceleration response of a matrix of FRP deck-on-steel girder bridge configurations to moving traffic loads. The developed FE modeling technique is used in the parametric study. The obtained acceleration responses are properly filtered to capture the first bending and first torsional modal frequencies of the bridges. The resulting filtered peak accelerations are directly compared to 50 in/s 2. ^ The last step in the development of this serviceability criterion includes recommendations for future design of honeycomb FRP deck-on-steel girder bridges. Empirical formulations for predicting the first bending and the first torsional modal frequencies of honeycomb FRP deck-on-steel-girder bridges are also proposed. The results of the parametric study show that the peak acceleration between girders varies quadratically with the girder spacing and deck thickness ratio. From this relationship, a maximum ratio equal to 11.33 is recommended. The results of the parametric study also show that the peak accelerations between girders and at overhang vary linearly with the product of the bridge first bending and first torsional modal frequencies. From this relationship, maximum products equal to 168 Hz2 and 176 Hz2, are recommended for bridges with and without overhangs, respectively.^
Judy Liu, Purdue University, Elisa Sotelino, Purdue University.