Tuesday, February 5, 2002 7:01 AM
After watching such large footers from Xcellerator and Wicked Twister be constructed, I am slightly confused.
Obviously, they dig a very large hole and prepare concrete. But, do they pound pylons deep into the soil or use a different technique? Just wonderng.
Tuesday, February 5, 2002 8:10 AM
While I don't know for sure, I may be able to help deduce an answer. Watching Wicked Twister and Millennium Force go up, they typically only used spread (pad) footings. It also appears that pad footings are being used on Xcellerator as well. When an engineer or architect designs a footing, they have to know two things...the bearing capacity of the soil and the weight of the structure. The soil's bearing capacity is based on how many pounds per square inch it can take, and you calculate a pad footing by it's area in square inches therefore you take the weight of the structure and divide it by the soil bearing capacity which gives you the required area of the footing.
Sometimes, the soil bearing capacity is so poor, they'd have to pour very large footings to support the coaster. Generally, they'd switch to a pile footing, which is exactly what you described. Pounding several steel H sections into the ground to specified depths, then connecting them all at the top with concrete. This method relies on the friction between the steel and the soil it's pounded into or resting on the end of the pile if the bedrock is close enough. I beleve parts of mantis use a pile footing. Really, it's a factor of soil bearing conditions and cost-effectiveness.
Tuesday, February 5, 2002 8:11 AM
Not having examined the pictures I can't say for sure, but...
WT is built on a beach, which has a low bearing capacity. They are probably using piles or piers. What you call a "footer" is actually a pile cap which ties the piles together and gives a place to attach the structural steel.
Tuesday, February 5, 2002 10:29 AM
There are no piles on the beach for WT, that I can assure you of.
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Tuesday, February 5, 2002 10:41 AM
When you think about it, coasters are very light structures and spread footings are the cheapest solution for a light structure. Also, natural sand has a relatively good bearing capacity compared to landfill or other man-made soil. Pile footings are used most often in skyscrapers because they are extremely heavy and may even be built on landfill (i.e. Boston) Since coasters are light and sand is pretty good soil to bear on (i'm assuming Xcellerator is also being built on sand or something slightly more substantial), it's a pretty good bet that there are no piles for Xcellerator either.
Tuesday, February 5, 2002 11:22 AM
Coaster footers are designed primarily for overturning (wind loads & turning trains) rather than heavy vertical loads. Spread footers work well for this, as do grade beams. The style of the footers is more a function of the soil conditions a the site than of the particular coaster design. Footers for woodies do tend to be different from steel coasters though since there are many more columns on a wood coaster with less load on each.
Tuesday, February 12, 2002 4:41 PM
Interesting.....I just always assumed that every large coaster had footers sunk down and attached to piles.
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*** This post was edited by john peck on 2/12/2002. ***