Cantilever poles are used throughout the telecommunication industry to support ancillaries such as antennas and dishes. Frequently, the introduction of a proposed ancillary can exceed the capacity of the existing cantilever system, requiring new design requirements, new installations, and consequently, more money. There is a common misconception surrounding how to increase the capacity of a cantilever system.
There are two ways in which cantilever systems are significantly loaded, they can either be shear-dominant or moment-dominant (shown below):
If the system is shear-dominant from the forces presented (i.e. the weight load is greater than the wind load), and the connections consist of two sets of two U-bolts, the bolts will be loaded in shear. For this condition, the greater number of bolts, the more secure the connection. However, in a moment-dominant system, the wind force has a greater effect on the system than the weight load, inducing a moment on the connections. In a moment-dominant system, the distance between the two sets of bolts (or “lever arm”) is the main influence.
If the moment induced on the system is anticipated to exceed the capacity of the existing bolt arrangement, placing a third bolt connection into the system between the existing bolt sets actually reduces the capacity of a moment-holding connection. This is because the lever arm length is reduced in the connection: from the distance between the upper and lower bolt sets, to the upper and central bolt sets.
To conclude, for a shear-dominant cantilever system, a third set of bolts is an appropriate solution. However, for a moment-dominant cantilever system, a better solution is to increase the distance between the existing bolt connections, increasing the capacity of the cantilever system.
KAEG are at the forefront of providing cost-effective strengthening solutions to over-stressed telecommunication structures to ensure continuous safe operations.
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