Muddies??

How 'bout *dizzying* ?!

..001" per foot is not a whole helluva a lot!

What would you think the the max allowable deflection would be in a W beam
in a building application (floors, roofs, etc.)? Previously cited were
numbers like L/120, L/360, L/720.
For one foot, L/360 is .033" deflection, 33x greater than your .001"!

Is this pushing a failure point?
--
Mr. P.V.'d
formerly Droll Troll
wrote in message
oups.com...
Ned,

A standard section I-beam will have the same numerical value stress in
the tension and compression flange, when subjected to a given bending
moment. There is not much that can be done here. Therefore, if you
keep the compressive stress to the earlier stated limit of 0.6 Yp,
then you will get the same result (opposite sign) in the tensile
flange, Yp (36) x 0.6 = 21.6 ksi. There are slight exceptions to this
which, for home use, we shall ignore.

On custom built beams one can make the compression flange thicker, also
add gusset reinforcings, to allow it to withstand higher buckling
forces. This type of design is generally too expensive for my
clientele because of the design time required.
I stick to what I can pick out of the "Handbook of Steel
Construction" published by the "Canadian Institute of Steel
Construction", second edition, 1975. It still deals in lb, in, kips,
which I am more comfortable with in engineering applications.

As far as I know, the F.S. = 5 applies only to the crane, with the
following exeption: the hoisting cable is a consumable, and its life
expectancy may be increased by using a larger factor of safety on it.
Typically a F.S. = 7 or 8 is used on the hoisting cables. For really
severe duty cranes such as steel mill service (100% capacity loads, x
number of times a day) the factor of safety on the ropes may be even
much higher, including much larger sheave and cable drum diameters. All
this to increase the life time expectancy of the hoisting cable.

At the other extreme is the power house crane which may undergo a
full-capacity lift only half-a-dozen times or so during its life time.
Here the drum dia., sheave dia., cable size, are much closer to the
"average lift" capacity without encroaching on the F.S. = 5.

Under-hook appliances such as spreader beams, pallet hooks, coil hooks,
etc. require a F.S. = 3, based on the yield strength of the material.
The exception are vacuum cup lifting attachments where the rules say
that a F.S. = 2 is required. I don't subscribe to this rule; when I
design vacuum lift attachments I use my own ideas which are somewhat
more conservative. (Ref.: ANSI B30.20-1999. chapter 20.1)

What I AM unclear about is the factor of safety of any building into
which an overhead travelling crane is installed. Normally the building
structure is designed with a F.S. = 1.67. (That's why you can't turn
an ordinary building into a library!)

At Dominion Bridge Company, Limited, where I spent the formative part
of my career, the crane runways were always separately supported on
their own columns. These in turn were laced (shear-braced) with the
adjacent building columns, all moment connected to the concrete column
footings, making for very stiff and sway resistant building walls.
Visually this was a very elegant solution as it provided room for
offices and small storage between the columns.

I suppose a 1.67 F.S. for buildings, even with runways suspended from
the roof joists, is OK provided that you take all loading into
consideration during the design stage of said building, including
accelerations ot the load in the case of electric hoists with electric
traverse. It can get interesting when a client wants to attach a jib
crane to an existing building column!

Trust this muddies things not too badly!

Wolfgang