Velocity Ratio of Wind-Driven Rain and Its Application on a Transmission Tower Subjected to Wind and Rain Loads

Wind-driven rain (WDR) refers to raindrops that have a horizontal velocity in the wind field. The WDR intensity on building envelopes as well as other issues such as wind-rain-induced vibration of stay cable has been extensively developed, whereas the mechanism and the effect of rain load acting on the structures are still not very clear. Based on the equations of motion of falling raindrops, the relationship between the raindrop horizontal velocity and corresponding wind speed is investigated under the effect of mean wind with or without turbulence. Further on, the simulation methods, referred to as the equation approach and program approach, are proposed to obtain the rain speed time history, based on which the formula for calculating rain load is established. Finally, the dynamic response analysis of a transmission tower subjected to wind and rain loads is carried out, and the results show that (1)when the rain intensity is up to 200mm/h, the maximum displacement percentage induced by rain load relative to wind load has already reached 7%; and (2)when the rainfall intensity is assumed to be 709.2mm/h, which is the heaviest rainfall ever recorded in China, the maximum displacement percentage at the tower tip is 15.4%, indicating that the effect of rain load on a transmission tower should not be ignored.