8 inch I-beam - how much will it hold?

_ fired this volley in news:lxg1bcz5v81e$.1eb3x34qv4byc$. snipped-for-privacy@40tude.net:

A 16-foot lam would cost a tad more -- well... a couple of tads .

LLoyd

Oops! Ned you are right. I grabbed the wrong beam condition. BTW I designed a sail boat trailer for a full keel sail boat using the deflections as the limiting condition for obvious reasons. Also a spiral staircase, a hydraulic engine hoist and a building addition, and a helicopter trailer modification. As well as the deflection calcs for a 30' non standard I beam with both distributed and concentrated loads. All had some safety factors added and all have been in use for some time with no failures to perform. With all that said, the table 4 on page 5-35 does have an easier to use formula for safe loads. Given that the ends of the I beam are restricted from rolling or departing from their location, I fail to see that using deflection, and keeping it small, doesn't yield a safe condition. This technique was used on the building addition, as well as the 30' non standard I beam with the concurrance of a P.E.

Stu Fields

Well, I certainly hope you don't build things that I have to use with your methods. I ran some calcs on standard 12" A36 steel I beams. Using the published yield strength (the point where it bends and takes a set)

of 36,000 psi, I can get deflections in the 1/240 range. This is the equivalent of NO factor of safety.

These calcs assume multiple beams that are cross braced and do not include any derating to account for mid space twisting

Is that titled "Approximate Safe Loads in Pounds on Steel Beams?" (I'm looking at the 5th edition, which I suspect is older than yours.) Note that this is an approximation, and uses a very conservative value for allowable stress. It'd be interesting to compare results from that table to the AISC code.

Here's an example: Take the OP's 8" beam (let's assume it's a W8x13) and set it up as a simply supported beam 5 feet long and apply a 12 ton point load at the middle. It'll deflect .090", which is less than

Make the beam even shorter and you'll get to a point where shear rather than bending stress is the limitation on loading.

Quite often deflection *is* the controlling factor. Presumably your PE evaluated the design and signed off on your deflection calculations as appropriate in that instance. He might not have agreed if the beam was unbraced or being used for overhead hoisting.

We have 4000 lb jib cranes with a 8"I beam as the boom. It was bolted to a mast and was supported at twelve feet. This beem had not measurable flex anywhere along its lenght.just make sure the load is lifted by tha bottom rail so not to roll

Which 8" I or WF (WideFlange) beam?