Slab on grade design

[Higgy13]

Hey guys!
Novice here, fresh out of school. Was hoping someone could give me a few tips to get started on my first design project.

I've been tasked with designing a slab on grade as a foundation for a steel structure.

The structure is a 12 ft diameter historic steel sheave from a lift bridge.
Haven't yet received the details on the weight, but I believe it is about 27 in thickness.

Soil conditions unknown at this time. The location is in a cold weather great lakes climate on the shore of Lake Superior.
Given these conditions, how much of a concern is frost heave and what should be incorporated into the design to mitigate any potential frost issues? Insulation? Type/size/depth of coarse aggregate base?

Also the most challenging part for me is figuring out how to attach the structure.
There are talks of installing the sheave on an angle (30 to 45 degrees), laying it flat, or have it standing like a wheel.

If they decide to lay it flat, I figured a uniform depth reinforced concrete slab would work, with possibly 4 concrete pedestals with steel bearing connection plates to elevate the sheave about 6 inches off the slab.

For a 45 degree I was thinking steel plates bolted to the concrete, connected to H piles that would be cut at 45 degree angles at the top and welded to the structure.

Not sure of a approach to stand it up straight, but obviously tipping would be a huge concern.

Another large concern is that the 12 ft diameter sheave will have to be loaded onto the structure with a crane operating off a barge, so construct ability needs to be considered. Some of the guys were questioning being able to connect it at a 45 degree angle.

Any ideas or pointers you guys can throw at me would be greatly appreciated.

Like I said, first design assignment. Not asking you to design the slab for me at any rate, but some guidance would be very helpful.

 

[rowingengineer]

Just to clarify is this a slab or footing?

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

 

[Higgy13]

It's a footing or shallow foundation for an object that is to be displayed on the lawn of this property.
I'm open to ideas of changing it from square slab shape if there are better alternative.

The object being supported is a circular disk shape with at diameter of 12 ft. It weighs 14 tons(28,000 lbs). They want this object displayed on the lawn of the property. Need to figure out how to mount this object at 15 degree angle and support it with a shallow foundation.

I figured that to get the required angle I could support the elevated end with either 2 concrete pedestals or 2 HP steel members acting as short columns. The top of the columns would be cut at 15 degrees angles and welded to the object. A column supporting a load at an inclined plane seems like it would create some interesting shear effects at the welded connection and additional moment in the columns, but haven't gotten into calculations yet.

My idea was that the other end, at the bottom of the slope, the object could rest on a bearing plate that would transfer the load directly to the footing.

Two basic issues I'm having are:
1) Since the object being supported sloped at 15 degree angle, how does the load distribute between the 3 supports? On the horizontal plane, object would be resting on bearing plate at (0,0), and the two column supports would be at approx. (9,-3) and (9,3). The wheel being supported is symmetric with center of gravity in the middle.
2) Since there would be 3 supports transferring the load to the footing, the footing would be eccentrically loaded. How do I analyze this? Or is there a way I can size and arrange the footing to mitigate this issue?

Last thing is, soil conditions here are sandy soils.

Thanks for any help you can provide.

 

[ornerynorsk]

Duluth? Could 3 cast piers work better?

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[RHTPE]

My suggestion:

Bury a mat foundation below grade. Extend 3 concrete posts up to support the sheave. You have enough mass in the sheave such that a real connection between it and the posts really isn't necessary, other than a grout bed to provide full contact between the two.

The difference in materials will be aesthetically more appealing (IMO) than using steel columns as you're really trying to show off the sheave. Any offset required to put the center of mass of the sheave directly over the center of the mat footing will be easy to hide. This leaves the sheave as the focal point of the assembly.


Ralph
Structures Consulting
Northeast USA

 

[sdz]

Since you're a novice, fresh out of school, ask your supervisor for guidance.

 

[dicksewerrat]

When is this going to be viewable? And where? I may have to visit Duluth this summer. I shop there.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[BigH]

Dick - good shopping? I usually shop in Bangkok . . .

 

[dicksewerrat]

Not the greatest but when you live in the woods, even Kmart looks good.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[BigH]

I currently live in the jungle and a mom and pop shop (North American Style) is great - actually about 1 hour away is a few Walmart Wannabes and a few McDonalds and KFCs. Still, we have monkeys getting into our garbage, snakes crawling about the yard, etc.