More Changes in TIA-222-H
In a recent newsletter we highlighted 3 big changes in the latest telecom standard which reduce loads and associated costs. In this article, we identify just the opposite—3 big changes in TIA-222-H which result in increased loading.
Rooftop Wind Speed-Up Factor (Ks)
Depending on building height and surrounding structures, some roof-mounted towers are subject to an increase in wind pressure of up to 30%. The new factor accounts for wind speed-up and turbulence above tall buildings.
Wind Direction Probability Factor (Kd)
This factor is not new to the telecom standard. It appears in previous versions and ASCE 7. The factor is related to the shape of the structure and its susceptibility to maximum stress caused by different wind directions. Consider the effect of wind on a standard monopole with antennas placed in three sectors. Such a monopole is likely to experience the highest stress when the wind direction aligns with one of the sectors. The stress will be lower when the wind direction is somewhere between sectors. The directionality factor accounts for the probability that the wind will approach the tower from the worst-case direction.
What’s new in TIA-222-H is a new requirement for tubular pole structures supporting antennas enclosed within a cylindrical shroud or which do not support appurtenances. Such structures are susceptible to peak stresses irrespective of wind direction and must be designed for the highest wind direction probability factor, Kd = 1. Monopoles with cylindrical shrouds are quite common, making this change noteworthy.
Exposure D Requirements
The previous version of the telecom standard allowed for shoreline areas in hurricane-prone regions to be classified as Exposure C, even for sites directly exposed to open water. This allowance was based on an incorrect belief that the roughness of the ocean surface during a hurricane reduces wind pressure. Recent studies have shown that Exposure D is more appropriate. Since the publication of ASCE 7-10, this information has been available. The requirement finally made its way into the telecom standard in TIA-222-H.
The list above is far from exhaustive but represents the main changes in wind loading requirements which can increase overall loading on a telecom structure.
Other changes we have yet to tackle include new analysis requirements for mounts, baseplates, connections, and ports, as well as new seismic requirements.
Contact Trevor Hawkes, P.E. (trevor@vectorse.com) with any inquiries.