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MODAL ANALYSIS OF VERTICALLY CURVED CONCRETE FLY-OVER BRIDGES
Abstract:
The effectiveness and sensitivity of vertically curved concrete flyover bridge (VCCFB) profile is presented. Modal analysis was conducted on three VCCFB models; one for a profile achieved using horizontal beams, profile achieved using slightly curved beams and a profile achieved using combination of straight and curved beams. Twelve vibration mode shapes were recorded with corresponding natural frequencies for each model. In each mode, a model with a profile using straight beams were found to have higher natural frequencies with major differences in modes 2, 6 and 8 corresponding to 2.26, 3.01 and 2.87% differences from the model with curved beams respectively. Also, major differences were recorded in modes 2, 3 and 5 corresponding to 6.31, 5.51 and 4.24% differences in natural frequencies from model with combine beams when using CSiBridge (2015) software. Three vehicles were simulated each passing the bridge for a period of 10 seconds per lane at the same speed of 10, 20, 30, 40, 50km/h and at varying vehicular speeds of 45, 50, 60km/h and 60, 65,70km/h respectively. The response spectrum from time history analysis conducted for the three (3) vehicles moving on each of the model were plotted. The vertical component of acceleration was compared with the Irwin (1979) base curve for human perceptibility threshold. The profile achieved using a combination of straight and curved beams were found to induce less vibration compared to profiles achieved using straight and slightly curved beams. These result thus indicate that profiles of VCCFB achieved using combination of straight and slightly curved beams at the cusp induced less vibration compared to profiles achieved with straight or slightly curved beams. As such the use of combine geometry precast beams should be encouraged in achieving vertical profiles for this class of bridges.
MODAL ANALYSIS OF VERTICALLY CURVED CONCRETE FLY-OVER BRIDGES
