Ice Missles
Ice Missles
(OP)
I have an ice shield I have to design that is to be placed over some elex=ctrical equipment next to a 340 foot lattice tower. Does anyone know the mass of the chunk of ice that is required to be used to compute the impact force to the shield?
I am checking in TIA 222-G. IBC and ASCE7 do not cover that from what I can see.
I am checking in TIA 222-G. IBC and ASCE7 do not cover that from what I can see.
Mike McCann
MMC Engineering






RE: Ice Missles
Mike McCann
MMC Engineering
RE: Ice Missles
According to this article, chunks as long as 4 feet fell from the cables of this bridge.
http://www.theglobeandmail.com/news/british-columb...
RE: Ice Missles
RE: Ice Missles
RE: Ice Missles
Mike McCann
MMC Engineering
RE: Ice Missles
Mike McCann
MMC Engineering
RE: Ice Missles
Mike McCann
MMC Engineering
RE: Ice Missles
RE: Ice Missles
Mike McCann
MMC Engineering
RE: Ice Missles
The upper layer (roof/canopy structure) was designed to be more flexible than the lower layer. There was a reasonable gap between the layers (approx. 12") We found via testing that the upper layer would dissipate much of the energy and in many cases would retain much of the smaller and/or medium sized test chunks. In the event of a larger sized chunk, the upper layer would break, however, much of the energy was dissipated and the lower layer would easily retain the larger sized chunk. More expensive construction but if you have a small area to protect, it might be work considering.
I have also seen a large wire mesh net (supported via steel poles)installed above a large surface parking lot that is located directly beneath a tall tower to protect the vehicles from ice damage.
RE: Ice Missles
RE: Ice Missles
10-story apartment building with a low-sloped mansard roof of standing-seam metal construction. The seams were about six feet apart, and each section was about 10 feet long. During "Ice Storm Elvis" in Memphis in 1994, the ice layered up to over 4" thick. It was solid ice. It rained and sleeted for three days. When the precipitation started, it was 15°F outside, but the temperature warmed to 28°F to 30°F and stayed there during the whole three days.
Then came the sun and a 40°F day. Those chunks slid off and crushed the cars they hit. If I'm calculating right, they were maybe 1200 lb each. Nightmare.
Best to you,
Goober Dave
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RE: Ice Missles
http://www.youtube.com/watch?v=pfBp2QYOIbc
RE: Ice Missles
Terminal velocity of a pointy icicle would be a lot higher than 120 mph, unless it tumbled. A skydiver can get over 200 mph if falling headfirst rather than belly-down.
RE: Ice Missles
If you have a pointy projectile, all bets are off... (How low can you go? ... into the ground?)
Mike McCann
MMC Engineering
RE: Ice Missles
For those who are activists, please don't let the architects aim the roof at the parking stripes like the Google Earth capture below. This is the apartment building where I lived. I lived on the top floor, right across the hall from the swimming pool. It was a tiny apartment, 400 sf, but my mailbox said "Penthouse 6"
All of us tenants got small dents in our cars every winter from small ice chunks. I started parking across the street at a hospital when icy weather was in the offing. 1994 was immense, though, and caught me by surprise. Entire county was without power for several days, and it was five weeks before some folks got lights back on.
Best to you,
Goober Dave
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RE: Ice Missles
I like the idea of the double protection (fine particle solid cover plus heavy mass penetrant trap, but wounder about the order of the two.
Armor plating for tanks now uses a series of thinner plate to break up the entry projectile and then spaces between the plates to allow each penetrating remnant to shatter apart and spread out. The next thin plate then spreads that load out even more, etc.
So, for the same mass of steel against the same mass and velocity of the ice comet (icicle spear seems to easiest way to calculate mass ?) a grating system slightly angled could be "disguised" as an "architecture walkway feature" (a sunscreen even) while allowing a given amount of dollar of steel and structure to cover a wider area of parking lot and sidewalk.
So, I'd imagine a grating of 1 inch deep, 3/4 inch, or 1/2 deep parallel bars + cross round bars - kind of like the walking gratings you see over sidewalk openings - at angle 25 to 35 degrees to 45 degrees (45 probably too steep) so almost every size of icicle would hit a steel bar or cross rod. Then, under the grating, I'd suspend a lightweight net like a bird or insect gauze so the wind and rain could get through. or be sloped to allow the rain to run off into drains.
The problem with a net or gauze under the grating is cleaning leaves and debris - trapping those creates squirrel, mouse, rat, or elephant nests - depending on the size of your local rodent.