Authors:
I.A. Ja’e; I. Abubakar;
Abstract:
By there gemeotry, vertically curved reinforced concrete flyover bridges (VCRCFBs) are expected to provide parabolic profiles for smooth passage of traffic. Conventional use of straight precast beams in producing such profiles has consistently resulted in polygonal profiles with persistent expansion joint problems, causing
discomfort to users and reducing public confidence. Geometrical influence of three profiles on the dynamic characteristics of this type of bridges as well as bridge-vehicle response at varying vehicular speed with respect to human perception to vibration have been presented. Modal analysis was conducted on three VCRCFB
models using CSiBridge (2015); a profile achieved using horizontal beams, a profile using slightly curved beams and a profile using a combination of straight and curved beams. 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 and 50 km/h and at varying vehicular speeds of 45, 50, 60 km/h and 60, 65,70 km/h, respectively. Response spectrum from time history analysis conducted for the three (3) vehicles moving on each of the models was plotted. Vertical
component of acceleration at corresponding frequencies was compared with Irwin (1979) base curve for human perceptibility threshold. Profile with combination of straight and curved beams was found to induce less vibration compared to profile with straight and that with slightly curved beams. The results indicate that profiles of VCRCFBs with combination of straight and slightly curved beams at the cusp induced less vibration compared to profiles with straight or slightly curved beams. As such, the use of combined geometry precast beams should be encouraged in achieving vertical profiles for this class of bridges.
Keywords:
Vertically curved reinforced concrete flyover bridge (VCRCFB), VCRCFB profiles, Human perceptibility to vibration, Modal analysis, Time history analysis, Response spectrum analysis