Analytical study of steel-FRP bridges vibration subjected to moving mass

Given the key importance of the bridges in transportation system lifelines and due to their high initial cost, there is a constant need for the study and monitoring of such structures. The FRP composites, due to their special characteristics including high specific modulus, high specific strength, corrosion resistance, low mass density, and modular construction, can be a good alternative for common bridge deck systems. Too much effort is devoted to implement FRP materials as a whole or in part in bridge construction. There have been several different methods of using FRP materials in bridges, including FRP stay-in-place forms for concrete decks and whole FRP bridge decks. Bridges constantly bear moving mass loads while due to technological progress the moving speeds are approaching higher and higher thresholds, so in this study, effects of moving mass on the dynamic response of steel-FRP and steel-concrete bridges are studied and compared. The deck and moving mass inertia substantially affect the dynamic response of the bridge system. To compare the effect of moving mass on both bridge types, at first, the multi layered beam method (MLB) for determining the FRP beam characteristics is reviewed and its applicability on determining the mechanical properties of laminated beams is investigated through comparison of this method results with numerical and experimental data. It is shown that by using the MLB method very good estimates of the mechanical properties of FRP composite can be achieved. Consequently, the problem of moving mass and its governing differential equations is reviewed and the numerical procedure for solving the set of governing PDEs of the moving mass problem is verified against experimental data. Comparing the theoretical results with the experimental data reveals that the presented methodology correctly estimates the dynamic response of beams subjected to moving masses. After setting up the theoretical framework for the moving mass problem on steel-FRP bridges, the effect of moving mass loading on the dynamic response of steel-FRP and steel-concrete bridge systems is investigated. The results indicate that the mass per length and the stiffness of the deck significantly affect the response of the bridge subjected to moving mass. These effects are captured through two different main parameters which characterize the dynamic behavior of beams subjected to moving masses. The first parameter is the Critical Influential Speed (CIS) at which the maximum deflection of deck at certain location happens. The calculated CIS through the aforementioned methodology indicate that the CIS for steel-FRP system is significantly higher than steel-concrete system. The second important parameter which is determined is the Dynamic Amplification Factor (DAF) which is defined as the ratio of maximum dynamics deflection at the midspan of the beam to its static value. The corresponding results of the DAF indicate that the steel-FRP bridges are less influenced by the moving masses than steel-concrete bridges of the same stiffness. It is shown that the values of DAF are lower in the case of steel-FRP bridge. It can be concluded that this will result in lower vibration amplitudes, which will contribute to higher fatigue life of the bridge system. Regarding these results, this system can be advised in the cases of high and ordinary speed transportation.