Modal Analysis Of Vertically Curved Concrete Flyover Bridges

The effectiveness and sensitivity of vertically curved concrete flyover bridge (VCCFB) profileis presented. Modal analysis was conducted on three VCCFB models; one for a profileachieved using horizontal beams, profile achieved using slightly curved beams and a profileachieved using combination of straight and curved beams. Twelve vibration mode shapeswere recorded with corresponding natural frequencies for each model. In each mode, amodel with a profile using straight beams were found to have higher natural frequencieswith major differencesin modes 2, 6 and 8 corresponding to 2.26, 3.01 and 2.87% differencesfrom the model with curved beams respectively. Also, major differences were recorded inmodes 2, 3 and 5 corresponding to 6.31, 5.51 and 4.24% differences in natural frequenciesfrom model with combine beams when using CSiBridge (2015) software. Three vehicles weresimulated each passing the bridge for a period of 10 seconds per lane at the same speed of10, 20, 30, 40, 50km/h and at varying vehicular speeds of 45, 50, 60km/h and 60, 65,70km/hrespectively. 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 accelerationwas compared with the Irwin (1979) base curve for human perceptibility threshold. Theprofile achieved using a combination of straight and curved beams were found to induce lessvibration compared to profiles achieved using straight and slightly curved beams. Theseresult thus indicate that profiles of VCCFB achieved using combination of straight andslightly curved beams at the cusp induced less vibration compared to profiles achieved withstraight or slightly curved beams. As such the use of combine geometry precast beams shouldbe encouraged in achieving vertical profiles for this class of bridges.

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