defl = (5 x W x l^3)/(384 x E x I)
Yes. For a simply supported, distributed load only.
l is the length in inches
W = w x l or the total load in pounds while w is the load per
inch.
E is the modulas of elasticity for wood.
About 2,000,000 (Steel is 30,000,000)
Modulus of wood is listed as 1-2 E6 PSI. Check the exact number for
the wood you are using. Machinery Handbook should have the most
common.
I is the moment of inertia for the beam and is equal to
1/12 x height of the beam to the fourth power or I = 1/12 x h^4
I, for a rectangular beam, is 1/12 x bh^3. Your formula only
works for square beams. b is the width, h is the height. For I
beam
or other sections you must calculate I.
=====
Kevin Russert Walsh
Process & Equipment Development Engineer
Thanks for correcting me on that Kevin. It has been years since
I used those formulas. I glanced in the book and took the first
one I found :-)
Paul Lamar
Ok, so how does one calculate "I" for a steel I-beam? (A36).
I have a catalog listing depth, flange width and thickness, and web
thickness.
Problem: size a W beam 50' long, 75 pounds/inch distributed loading
(laterally supported all the way with 2' spacing).
I want to build a hangar/house like Tracy's but 50' x 50', but with
steel
structure.
BTW, what is the formula to dimension the vertical supports, knowing the
weight they'll have to carry?
Finn
You need to get another steel catalog. Many of them list I.
It depends on a lot of things like fillet radii and flange
taper.
What you need Finn is a Florida building code book. All that is spelled
out. There is dead load (weight of the structure) and live load
(the load you are going to put in the house expressed in pounds per square
foot).
In theory you don't know the dead load until you design the
house so you don't know the size of the beams until you know
how heavy they are :-) Chicken and egg. One must write a computer
program to iterate back and fourth until the error is small.
That's where the building codes comes in. They tell you what size
beams to use for how many stories you are going to put on your
house.
Paul Lamar
Uh... not quite Paul. The building codes in Florida don't spell out all the
details. They are very prescriptive in telling you what kind of loads must
be calculated, but not how to size the structural elements.
Finn, things in Florida were complicated enough before Hurricane Andrew
came and rearranged everything south of Miami (I was there... not something
I care to repeat), and now the Codes are just plain NASTY. This is not
something you want to undertake yourself (unless you are a licensed
Professional Engineer registered in Florida). The liability is huge and the
odds of passing an inspection are small. The banks won't lend you the money
without a PE designing it, and the insurance companies won't even talk to
you. Even the Architects defer to the Engineers when it comes to sizing the
structural elements. FWIW, I've got a current PE license in Florida, but
wouldn't dream of doing the designing such a thing myself because I've been
out of touch with it for about 6 years.
But, as best I can recall, the wind loads turn out to be the over-riding
factor in all of the structural load calcs. Deadweight and live loading are
seldom an issue (although yours may be... with the house over the hangar).
The wind loads in turn depend on the pitch of the roof, the height above the
ground, exposure, distance from shore, eave arrangement, whether it is a
gable or hip type roof, etc. Once you have the wind loads (uplift,
transverse, and overturning) calculated out, then you can set about
designing the structure to resist the loads.
But things are not totally bleak: If you can tell the truss manufacturers
what you want for dimensions, they will turn the crank in their computers
and provide you with a stamped, certified set of structural plans for their
product... included as part of the end product. Make sure not to cheat when
erecting the trusses however: I personally inspected several buildings that
blew apart because the contractor cheaped out and didn't install the
specified "wind bracing". They just screwed the sheet rock directly to the
bottom of the trusses and saved themselves $10 in 2x3s and $20 in labor.
Where you building? There are some canned plans for "stilt" homes that
could work very well: you enclose the hangar portion with "blow out" panels
that are designed to go at 80 mph or so, and the house sits on large
concrete piers that are buttressed to withstand the side loads. Then your
plan is to hop in the plane and LEAVE before the big winds hit. The house
stays intact above the flood waters, and once the runway is cleaned up you
return to retrieve your shop out of the mangroves/sawgrass/palmettos/pines.
Tom Kendall
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