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RE: Design Criteria for Falling Ice

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The fundamental equations are the same as in ASCE 7-05, Section C 5.4.5. The delta t will be the most difficult to figure. If you protect the structure with grating, the delta T will be relatively long and reduce the dynamic load because of the deformation of the ice and the deformation of the grating. If you use a solid structure and expect no deformation, the delta t will go up and increase the dynamic loads.

Ice shedding (and damage) for laticed towers has been a problem for quite some time. Adjacent roofs are often armored with pavers. Wave guide bridges for microwave towers have been protected with grating.

Heated radomes have been used. Flexible radomes have been used. Ice acretion resistant paints have been used. Heat wraps like Delta Therm have been used.

A 225' transmitter is pretty small. Broadcast towers are much taller. 1500' is not uncommon. And if you do not protect the adjacent structures, they can be taken out of service.

Regards,
Harold Sprague





From: "Josh Comfort" <jcomfort(--nospam--at)ggbse.com>
Reply-To: <seaint(--nospam--at)seaint.org>
To: seaint(--nospam--at)seaint.org
Subject: Design Criteria for Falling Ice
Date: Mon, 6 Mar 2006 11:11:41 -0800

Does anyone have recommendations for designing a structure to withstand
forces from falling ice?

I'm working on a repair/retrofit for a building that is located very close
to a 225' tall transmitter tower where some falling ice recently caused a
failure and partial collapse of the roof framing.  I am unaware of any
design standards for falling ice and was curious if anyone out there has any
experience with this type of problem.

Thanks.

Josh Comfort, P.E.


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