GC, Yes, the pipe support beam is positioned between 2 cooling towers. The beam is fastened to the top of the screen wall framing at each end. The pipe it is supporting runs parallel to the beam and about 45" below the beam. There are 3 hangers roughly 10' apart.
Besides the isolators on the...
Well, it looks like I will not be able to reinforce this beam to give it a natural frequency 2X to 2.5X the natural frequency of the fans.
And there is no way to brace the beam to anything. So, the only thing left is to isolate it from the vibrations of the fan.
UPDATE: I got the fan speeds today and found out that they are Variable on demand with VFD’s, 118 rpm up to 473 rpm.
Well this corresponds pretty closely to the weak axis beam frequency for Mode 1 = 2.20 Hz (132 rpm) and Mode 2 = 8.81 Hz (529 rpm). Unfortunately, the channel cap only raises...
The exception would be if there is a concentrated point load within the arching action triangle. For example, a bar joist could be bearing on the masonry wall above the window lintel.
canwesteng, Eq 3-1 is the same as Roark's 1b in your snip for the first mode. The point was equal loads at the quarter points (3 points) is what we have with the pipe hangers. This is closer to a uniform load than concentrating all of the hanger loads into one load at the midpoint. Plus, the...
"Would the amount of heat transferred to the beam due to welding have to be considered with respect to weakening the beam? or would this be inconsequential?" Yes, that's why you weld longitudinally instead of transversely. Yes, welding position is a big deal.
Thanks Bones for your posts. I think I will suggest a Piping Engineer. I would guess the supports are about 10 feet apart now. Spring Isolaters in the hangers might help the beam.
Would you believe the building is only 4 years old looking at the photo?
You are correct to run the welds longitudinally as shown. It appears that Anvil has specified a maximum load for their part and the welds. If their welds check out, you should be able to calculate the pipe loads based on the geometry of the pipes and hanger spacing.
I would agree with your...
I am waiting on the fan rpm values to see if they hit near any of the modes. I got 2.2 hz for the bare beam weak axis fundamental frequency and 3.8 hz with adding a C12x25 cap channel. Those numbers are based on using the pipe weight for the lateral vibration. Without the pipe weight, those...
Thanks for the comments. The building is only 4 years old!
The center-line of the beam is about 9" to 9.5" from the face of the cooling tower. The pipe is 45" clear and directly below the beam. It runs parallel with the beam and it is not braced. The end of the pipe turns 90 degrees up...
This equation does the fundamental mode or first mode. The second mode is 2^2 or 4 times that and the third mode is 3^2 or 9 times and so on.
So, you would include the pipe weight w/water in calculating the frequency in both directions. Correct?
The equation is based on a uniform load. It...
You may want to select a number of top or bottom chord panel points for full truss depth x-braced frames. It may be advantageous to locate these to coincide with the intersection of a compression web member and the bottom chord. These frames would probably be attached to the webs of your top...
I have an unbraced W18x65 beam spanning 35'-3". It is supporting 3 pipe hangers on the bottom flange. The hangers support an insulated 6" or 8" pipe. The top of the pipe hangs down about 45" below the beam and turns up and into a cooling tower. When you push on the top flange laterally near...
This would apply particularly for spreader beams. Is the allowable bending stress in Section 3-2.3 based on using the plastic section modulus or the elastic section modulus?
The text only refers to these two properties, Sx and Zx in terms of the unbraced length. In my case, there is a tube...
I appreciate everyone's comments above.
One the main points in my original post never got addressed concerning the design of the key which may or may not be a good idea to use.
Isn't it true that the active pressure wedge extends from the top elevation of the soil over the heel to the bottom...
Thanks 13,
We don't use passive against the wall since it has to be fill material that is placed above the footing.
I like to avoid keys when I can and use frictional resistance like Rod suggests.
Thanks Rod,
We always specify that footings for cantilever retaining walls must be placed in excavations with the toe being poured directly against virgin soil. We never allow footings to be formed. The top of the toe is always buried with at least 12" to 18" of soil on top to make sure the...
