Cooling tower analysis and design

[nishantnjoshi]

Hello everyone,

I just graduated with M.S. in Civil Engineering. Can anybody explain or forward links if any regarding analysis and design of cooling tower on roof top?

I want to understand how can wind load be mitigated?

I am designing a 4' steel frame which will be resting on existing beam. The frame will support the cooling tower.

Thank you in advance for your time and help.

-Nishant Joshi

 

[structSU10]

The frame should be made stable for wind load (and seismic), and the beams / roof diaphragm designed for the wind load due to the chiller. This can be accomplished in a number of ways, and depends on the height and size of the frame required what may be best. ASCE 7 also has a nice 1.9 factor for roof top equipment wind loads that increase the force you need to resist.

 

[nishantnjoshi]

I have attached a copy of screen shot. It is resting on the (W) 48" x (H) 20" R.C. beam. The height of the frame is 4'.

I want to know how will the wind force transferred to the beam?

Thank you!

 

[hokie66]

You would need to make the frame rigid, probably by all welded connections. Do the calculations to see if the frame is strong enough and also that the existing roof structure is adequate for the new loads, and then you need to provide adequate anchorage to the existing structure.

 

[structSU10]

Your long bay, along the z axis, looks like it should be a moment frame. I don't know if your kicker assembly is stiff enough, but maybe. You apply the wind to the chiller in each direction, with a 1.9 load factor on the wind pressure, then you have a shear at the top of the frame in each direction that you can apply to the model. You will also technically have an overturning moment from the chiller itself that you need to apply. Then analyze the frame for the appropriate load combinations, and check your existing roof for the loading.

 

[nishantnjoshi]

Thank you hokie66 and structSU10.

I do not know what is kicker assembly. Few questions:

1 - The lateral win pressure will generate shear on the frame?
2 - The overturning moment from chiller should be converted into forces and applied on the frame?

I am getting reactions on the frame which are higher than existing beam capacity in shear. Can I increase the shear capacity by increasing the beam depth, as retrofitting is not an option.

Thank you!

 

[structSU10]

I was referring to your framing in the X direction when I said kicker frame.

Draw your structure completely and understand the load path; the way the forces make their way to the roof should be self evident, and you should see how, and where, to apply the loads to the frame. It seems like you should speak with you supervisor about some of this if you are confused.

If the beam is existing, how can increasing the beam depth not be a retrofit? If you cannot retrofit the beam, move your frame to an area it can work, such as posting off existing columns, or to a beam that has capacity. If that is not an option, then the owner needs to understand that they need to reinforce the roof.

 

[nishantnjoshi]

My bad, when I said retrofitting, I meant adding CFRP around the beam.

Thank you so much for your help. I really appreciate it!