Wind and vehicle induced forces on flat plates—Part 2: vehicle induced force

The current UK standard for the determination of loading on temporary road signs is generally perceived by the industry to be unrealistic, in that no account is taken of vehicle induced forces. To enable a rational revision of the standard to take place full scale data have been collected on the vehicle induced force acting on a representative range of 750 mm road signs, 1500 mm road signs and a pedestrian barrier. Preliminary measurements showed that wind and vehicle effects could be treated separately (to first order) because vehicle induced forces are related to the instantaneous pressure field generated by the vehicle motion rather than due to air movement. The results have been expressed as non-dimensional coefficients of force based on sign area and nominal vehicle speed. Sign shape appears to have no significant effect on the magnitude of the vehicle induced force coefficient. Nominal sign size (750 or 1500 mm) appears to have some effect on the overall force coefficient, with larger signs experiencing a longer period of exposure, at a slightly lower magnitude, to vehicle induced forces. In all cases where signs are positioned perpendicular to the vehicle motion the peak force is identified as being in the opposite direction to the vehicle motion as the front of the vehicle passes the sign. The results presented form part of a wider study, which included the wind and vehicle induced effects on flat plates in the atmospheric boundary layer.