Wind Loads
Wind Loads
(OP)
I am working on an optical sensor that will be mounted on a tower located out at sea. I have just been asked for a report/calculation on wind loading. I am not a civil engineer. I am not a PEng (PE). I have no access to a civil PEng to look over my shoulder. Failure could be catastrophic. I am hoping that there are qualified people at the customer's end who can review what I do.
I see that ASCI has a manual Minimum Design Loads for Buildings and Other Structures. How complicated is wind loading analysis? Should a mechie be able to the wind loading section and produce notes, calculations and a design that will satisfy a qualified civil engineer, or this is a job for a consulting engineer?
I see that ASCI has a manual Minimum Design Loads for Buildings and Other Structures. How complicated is wind loading analysis? Should a mechie be able to the wind loading section and produce notes, calculations and a design that will satisfy a qualified civil engineer, or this is a job for a consulting engineer?
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JHG






RE: Wind Loads
It is also based on ultimate loading vs. ASD loading, so appropriate load cases need to be applied (from a different part of the ASCE7-10)
I would recommend hiring a structural engineer
RE: Wind Loads
Some areas to be careful about -- if your tower is flexible (as defined by ASCE) you can get higher loads due to the Gust Effect Factor. Also, if your tower is latticed or sufficiently slender, you may get some odd vortice or aeolian vibration effects.
If either of these are the case, and you can't afford to just throw steel at the problem, you might still need a consultant.
RE: Wind Loads
RE: Wind Loads
If the stability of the whole tower with the added doohickey is in question, get the weight, general geometry, and projected area of he equipment to the tower designer and let them work on that end of it.
ASCE 7 is intended for stationary buildings on land in the USA, so it would be of limited use for that. Antennas, wind turbine towers, offshore platforms, ships, etc., would be covered by other standards (presumably) and you wouldn't use ASCE 7 for them.
RE: Wind Loads
I am responsible for the sensor only. I don't know how rigid the tower is. If our customer wants useful output, it will have to be rigid. I believe the winds are rated at 60m/s.
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JHG
RE: Wind Loads
I imagine out a sea during a hurricane velocity is even higher.
I remember years ago (1970's_before all the complications in ASCE-7, I used to design highway sign structures in the New York area for 110 mph, with just this simple equation as per NYC/NYS DOT procedures, no K factors, etc. None failed!
RE: Wind Loads
RE: Wind Loads
The mount flanges are mine. The floor and everything underneath is somebody else's. The customer will do the actual installation.
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JHG
RE: Wind Loads
Hire someone to do this for you. If for no other reason than the fact that whoever is designing the tower probably won't accept any wind load numbers you give them unless they are sealed.
RE: Wind Loads
qz = velocity pressure you're going to use
Kz = velocity pressure coefficient, which will depend on the height. If you're dealing with an ocean that's exposure D, and the higher the height, the higher the coefficient. If it was 50 ft, for example, Kz = 1.27. 100 ft, Kz = 1.43. Table T30.3-1 contains the values in the ASCE 7-10.
Kzt is usually one, and will be if there's no windspeed increase due to elevation change.
Kd = directionality facor, which I would take as 0.85 (grouped with signs).
V = you'll need to obtain the basic windspeed from either the drawings or the tower structural engineer of record.
If you want more information, you can find the equation and information in Chapter 26 in the ASCE7-10 (Or ASCE7-15). Included are simple conversions if you're dealing with metric, also.
Once you have all these and finally have your qz, I would apply that to the cross section of your sensor assembly and design the attachment for the resulting shear + moment.
If you want to do the engineering on this that's on you, just know you're assuming the liability for it.
RE: Wind Loads
Right now, it appears that the customer understands this stuff, and we don't. I have some estimates of wind load, and I am doing structural analysis. My bolts are getting bigger, and I am hardening some flanges. When I am done, we will submit drawings and calculations to the customer. We build instruments. They know how to mount stuff on elevated platforms at sea. They will have to decide if they want to approve this or not.
Most of my stuff gets mounted in aircraft, so I have experienced the attitude. This is a new set of problems and hardware.
Thanks.
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JHG
RE: Wind Loads
RE: Wind Loads
They are reviewing it.
Thanks for the help everyone.
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JHG