Stabilization: The climbing angle
When you tension a crib against a vehicle on its side, whether it is with Ground Pads, RESQ-jack, Warthogs, Airshore struts, the CRUTCH, or even homemade cribbing, you must place the brace at a proper angle. One easy way to tell if your brace is set correctly (at the approximate 70 degree angle), is to pretend that it is a ground ladder and that you have to climb up it. If you can visualize the climbing angle and it looks proper to you, then your diagonal brace is probably at the proper angle. Too low a "climbing" angle or too steep, and you probably have not used the buttress to itís best application. Once set in place, tensioning it completes the set up.
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06-13-1999, 03:26 PM #1rmooreFirehouse.com Guest
Stabilization: The climbing angle
06-15-1999, 03:34 AM #2RescueLogicFirehouse.com Guest
If you look at the reasoning behind the angle of a ladder, they dont want you putting a load on the rails, to prevent the ladder from bending in half at the center horizontaly, not so the ladder won't be prevented from failing verticaly from compression. Todays lightweight truss construction uses reinforcing units placed at a 45 degree angle for strength, both in tension and compression. Look at roof lines around the country. Usually the only time you see a steeply pitched roof is in heavy snow areas, not for strength but to better shed the snow and keep the weight reduced.
Also, by incresing the angle you also increase the footprint of the stabilized vehicle. The greater ther footprint (within reason) the more stability you will acheive. i.e. ladder trucks don't put their outriggers down next to the truck. they extend the outriggers down and away from the truck to increase the footprint. Also, are there many ladder trucks that have outriggers that come down at an angle as steep as 70 degrees. Not any that I have seen.
Now with all that said. Our units are set up to be used at or near a 45 degree angle however, they can be set up at any angle you are comfortable with. Our units are not limited by short extended lengths or ability to store in a short configuration from 46" to over 96".
Any questions or if you feel I am wrong in my inerpritaion of Pythagarims theory let me know: RescuLogic@aol.com
06-16-1999, 05:45 PM #3Ed DFirehouse.com Guest
I have to agree, the whole reason for the buttress is to widen the stance of the vehicle, to better stabilize it. 45-60 degrees would probably be the best, depending upon the situation.
06-22-1999, 01:06 AM #4smbffFirehouse.com Guest
Buttress supporting is a load bearing member that "butts" or pushes against the load. A good example is the old cathedrals, high roofs with no trusses. The compression of the roof was offset by the "buttresses" outside the building. Ladder trucks have a cantilevered support system and they need a "wide" footprint because of the loads that are away from the truck. A 100' aerial has a footprint of 9 feet(18'total width). That isn't very wide when you extend the 100'ladder horizontal. So, when you place the base of the "tensioned buttress" support only a couple of feet away from the vehicle, you have a substantial 'footprint'. This will occur when you have an angle of 60-75 degrees from horizontal.
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