Chimney design 1

[John188]

I am designing a frame section so that the load at the opening of the chimney shell is transferred to the frame section. But, on analysis i find that most of the load are being transferred from the frame and the shell section(16mm steel) which is supposed to take the load shows unusual results. What might be the reason behind it? Is it because of some modelling errors?
I have attached my SAP2000 v22 file and a picture related to my model.
Thanks

 

[phamENG]

I don't have SAP2000 so I can't check your model, but if load isn't going where you think it should you may have some errors in your assumptions. If the shell is stiffer than your frame, the shell will take load from the frame.

The picture you mentioned didn't post, so I'm not sure what it looks like. Generically speaking, though, separate your shell and your frame. Apply a notional 1K load to the shell where it connects to the frame, and then do the same to the frame. Which one deflects less? If it shouldn't be that way, then look for modeling errors - boundary condition mistakes, etc.

Again, I don't have SAP2000 and my only experience with it was to do a small project for a Masters course several years ago. So I can't speak directly to the program or its capabilities. These are just some generic suggestions.

 

[John188]

This is the picture of the model.

 

[saplanti]

Is this self-supporting chimney and the opening rectangular?

If it is, the opening needs to be reinforced for external and internal loads in all direction. It may be required reinforcement along the height of opening at several levels, and the reinforcement need to be all around but stops at opening.

In your scenario, the chimney and frame look like separate structures and connected with plates.
I guess you are connecting the HRSG duct to the chimney. I hope the frame you shown is not the duct frame. Otherwise you will have lots of problems with thermal expansion within the system if the system externally insulated.

You need to use an expansion joint in between the duct frame and the reinforcement face frame which is in the height of the opening and supported by the chimney.

In case my guess above is not right, please explain what you are doing with frame and how the opening is supported for your application.

 

[John188]

The shell structure shown over there is a steel plate to support the upper structure. At the opening as the shell needs to be cut so to provide support the frame structrue is provided at the opening to prevent extra stress on the steel plate. The shell and frame structure shown over there is mainly to support the liner which is placed at the top.

 

[saplanti]

It seems that the chimney has two rectangular (opening) connections opposing each others, perhaps there is a level difference ( difficult to see levels adequately from the view). Assume they are at the same level for the sake of discussion.

As it is the frame structures on both sides will provide support to the chimney in all direction as the frame and chimney shell connected by the plates, chimney and frames are bolted on foundation.

My understanding in the duct side insulation is inside with liner plates. Is it the same for chimney? Is there any liner in the chimney or Is there any other gas containment lines in the chimney section for two seperate HRSG? In case they do not exist and the chimney insulated outside there will be a thermal load on the chimney side if we ignore the thermal expansion on HRSG frames or these frame thermal expansion is zero. The thermal load will be effecting the connections between steel frames and chimney shell.

Do you consider a suction pressure (partial vacuum) in the chimney shell for the design?
Do you think the the chimney openings are sufficiently reinforced with your arrangement under partial vacuum and perhaps external wind pressure if exposed?

Please note that I am not claiming anything, the design is yours. Mine is just to give you question to improve (in case you are not satisfied with your design, your post tells me you are not) your design.

Hope it helps.

 

[JLNJ]

It could be a lot of different things. You haven't given us too much to go on here.

For the frame to pick up the vertical load, the cross beam at the top has to deflect. As it tries to deflect, what's left of the stack either side of the opening (still a stiff element) takes up the load instead of loading the beam.

It looks to me like the stack sidewall would need to buckle before the beam sees much load.