Lattice steel tower foundation design 1

[brettoshooter]

I have some questions for the forum, my local clay target gun club has acquired a lattice steel tower which we intend to locate at our club. The tower measures 1.9m x 1.9m and is 10.5m tall (6'2"x6'2"x35') and it is constructed of 100x100RHS verticals and 90x90RHS bracing (4"x4" and 3.5"x3.5&quot. The tower weighs 2000kg (4400lbs). On top of the tower will be an enclosed structure it measures 2.4m long x 1.9m wide and 2m tall (8'x6'x7'). The soil where the tower will be placed is a stable sand.My questions are:-
What size concrete footings are required for the height weight and wind loading? what size foundation bolts and how many? or are there any formulas available so i could calculate them myself. Thanks in advance, Bretto

 

[Laser28]

I note that your discipline is mechanical. How does it feel to have civils and electricals messing about in your field? Hire a structural engineer, who will take the liability for the design, and probably save you some money in the deal. You might be able to design something that works (cause it ain't rocket science) but a good structural engineer will OPTIMIZE the design, so that you get the CORRECT foundation.

Its bad enough that we undercut each other for work, but when we start to do work that we have no training or experience in, we are asking for trouble.

 

[ERV]

I agree with Laser28. The wind loading itself will prove to be very complex, along with other variables. The cost of local professional help will be small versus potential disaster or worse, loss of life.

 

[jheidt2543]

brettoshooter,

Perhaps you can find a local structural engineer that is also interested in trap shooting. You could gain a new member for your club and get a foundation designed correctly too. His services might equate to a life membership?

 

[squash1]

Here in a nutshell is why structural engineers (in the UK) have very little status - cos every Tom, Dick and Harry thinks that they can just nod something in or do a 'few sums' and carry out a structural design. (Sorry brettoshooter just having a moan!)
Must agree with previous replies - hire a structural engineer and don't take the risk! Mistakes in our game can lead to fatalities.

 

[oldrunner]

I'll be a little more charitable, as I have a good relationship with mechanical engineers as with we used to do a lot of heavy rigging together. Get a hold of the TIA/EIA-222 Standard (Purchase from Global Engineering Documents) and then also buy the latest edition of the "Wind Commentary to the Uniform Building Code" published by the Structural Engineers Association of Washington. Get the wind speeds from your local jurisdiction (should be free) and then hire a geotechnical to tell you what the allowable bearing pressure is for the sand as well as some sort of protection that the sand won't scour away from the foundation.

Follow the procedures in the Wind Commentary, but use the wind forces from the EIA/TIA code. If you've done basic statics and are pretty good with a spreadsheet, it's pretty simple. The connections can be checked using the examples in Shigley's Mechanical Engineering Design, but the anchor bolts in the concrete should be designed per the Uniform Building Code. The concrete foundation design should be designed per the Uniform Building Code (if you don't have this, it'll cost you). (This is to determine the proper strength and reinforcing) (Also check the sand for sulphates and chlorides to keep the rebar from eventually disinigrating)

The actual analysis of the tower can be done manually, but most structural designers have a program that they can input the data into.

I imagine that you already know how to check the axial loadings on a single angle. You'll find that on page 3-55 of the AISC manual, 9th edition.

Finally, have a competent structural designer review your design to insure that you haven't missed anything. I known that there is a lot of windage on the little building on top of the tower, so be careful.

 

[1dirtDr]

No Good deed goes what Oldrunner...???
Like what old civil Prof used to say... when designing critical structures, always hire a good structural engineer, have good insurance and keep your little 0.22 in the top drawer of your desk. 'cuz once you see your smiley mug in the front page of the daily news. Call the wife to say good by, pull the top drawer open, have a good prayer and then fire away..
I agree with fellas

just my $.02