INCINERATOR STACK

[LOUIE24]

I need some suggestions regarding the structural integrity of an incinerator stack. This stack I am referring to is 9,000 lbs and 45 feet high with a 48 inch diameter. We have three guy wires that are hand tight with three turns of the turnbuckle. The stack is moving at high winds 12" off of center. The stack is comprised of 9-60" flanged 10 gauge stainless steel. The bottom of the stack where it is flanged to the incinerator is moving and causing bolts to loosen and even snap.

The following are possibilities that we need to look into as to why this stack is such an issue.

1. Wind load to surface area on chimney at 9,000 lb. What moment is being created.

2. If the incinerator starts to rock, will it amplify the movement on chimney.

3. Will it be recommended to have more tension on guy wires .

4. Will the chimney require a lower support structure to brace movement.

Any and all suggestions are welcomed. I am trying to help out a friend.

Thanks,
Louie24

 

[msquared48]

Sounds like the guy wires are too loose, too small, or improperly positioned. Could also be a foundation failure problem with too small of a footing. Lots of possibilities.

The wind force causint overturning is about 70% of the projected area with the resultant located about midheight of the stack if the stack is uniform in width.

Your friend needs to engage a local structural engineer, and soon for reasons of safety. This thing is telling you that it wants to fail.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[JStephen]

With slender stacks, you can get wind-induced vibration that will be at 90 degrees to the wind direction. If that's the issue, there are some different approaches.

 

[LOUIE24]

Well this stack is a direct replacement of a similar stack in size (length width and height). The only difference is the weight. The original stack was 15,000 lbs. This new stack is 9,000 lbs. The position of the guy wires are all the same and we even added another for added precaution. I think the wires are too loose but another issue might be the cause which is galling (see attached link).

 

[charliealphabravo]

A couple of thoughts...

1. Guyed towers are often designed so that the base is pinned...in other words the base is not designed to resist moment and fixing the base can cause the development of unanticipated stresses in the tower and the base connection.

2. The capacity and stability of guyed towers is highly dependent on having the appropriate tension in the guys. Overtightening them can have effects that are not intuitive including precipitation of collapse. Excessive slack has obvious consequences. Guyed towers are designed for a certain amount of sway and deflection and the guys should not be overtightened in a well meaning attempt to stiffen or immobilize the structure.

 

[charliealphabravo]

If your new stack is so much lighter than the original with the same diameter, then it is also likely less rigid and this will increase the rotation at the base under lateral loads. This could account for the broken fasteners.

I agree that a structural engineer should look at it to make sure the guy tension, angle, and configuration is properly matched to the tower, as well as the base configuration.

 

[LOUIE24]

Thank you all for your advice. As to the Code of Ethics I will consult a Structural Engineer who is more competent in the subject matter like any good Engineer should do.

 

[paddingtongreen]

If you measure the sag in the guys, you can estimate the force in them. Do the guys go to the ground or to the top of the incinerator? Do the guys go to the top of the stack? my guess would be about two thirds of the way up. Did anyone note how much the old stack deflected. Often, people only look because some thing is new or repaired so they have nothing to compare it with.

Whoever decided to downgrade the stack should have provided a required tension in the guys.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[dik]

How would one go about measuring the tension in a guy? Hydraulic load cell, turn of nut after loading? or some other means?

Just curious and just looking for a quick practical method.

Dik

 

[msquared48]

"How would one go about measuring the tension in a guy?"

With a gal.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[paddingtongreen]

"How would one go about measuring the tension in a guy? Hydraulic load cell, turn of nut after loading? or some other means?"


From the sag and the material properties and dimensions. By looking up along the guy, and aiming at something of known dimension, one can get a good estimate of the displacement perpendicular to the theoretical line of the guy, then convert that to vertical sag, and thence calculate the tension.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[dik]

Thanks paddington... I caught that from your earlier post, but, I would have thought that would not have provided an accurate tension and I was wondering if there was a simple more 'accurate' method.

Dik