Calculating Flange Capacity of Beams 1

[srennekamp]

I am currently working on a problem that I really don't know how to solve. I need to calculate the flange capacity of an I-beam that is being used for an under-riding hoist system. The size of the beam is M8x6.5. Can anyone help me out. Thanks.

 

[SlideRuleEra]

Here is one of the old ways to get a rough idea:

Consider each side of the bottom flange to be short cantilever beams (For your M8x6.5 the length of each would be 1.14 inches long.)

Apply half of the total load (be sure to include an allowance for load testing requirements, moving load forces, impact, etc.) to each cantilever beam. To be conservative - apply it at the end of the assumed cantilever beam (1.14 inches). Assume that it is a point load.

Compute how long a distance (measured along the length of the M8x6.5) you would need to safely carry the point load. This distance is the "width" of your 1.14 inch long cantilever beam. The "thickess" is the flange thickness (0.189 inches).

If the computed "width" is shorter that the "wheelbase" of the under-riding hoist, you should be ok.

This is only a first order approximation - there are certainly are better ways to do this these days.

 

[jike]

From "Formulas for Stress and Strain" by Roark, the formula for flange bending is S = Km (6P/t^2) where Km = .509 if the concentrated load is positioned on the tip of the flange.

P will be the total lifted load plus impact and trolley and hoist weight, divided by the number of wheels you have on the trolley.

A simplified approach would be to assume a 45 degree load distribution. With the load on the tip of the flange, the effective width (for bending) would be equal to the full flange width of the beam. I believe this would give a Km coefficient of 0.5.

 

[ehcet]

Hi
The suggested method are old and outdated.
Get a copy of CMAA Single girder crane specification.
At the beginning you find 2 types of flange stress calculation.
One for the I beam and one for the parallel flange beam.
For the calculation you need the wheel diameter, the contact point on the flange, and the wheel conture.
The specs explains the calculation.
It is the latest and most modern and sure way. Developed
by DEMAG crane manufacturer after years of research, taken over by the European crane manufacturers comitte and
finally it is acknowledged by North America.

Good luck
Ernie

Doing calculations by the suggested methods you will be surprised how much heavyer beam you have to select.

 

[srennekamp]

Thanks for all your help guys.

 

[elpoblano]

I agree with ehcet, the Crane Manufacturer's Association of America standard 74 for under running cranes, has the best procedure to calculate the maximum lower flange wheel loading.

If your beam is new, then you can use the nominal flange thickness, otherwise you would have to measure the flange and take the smallest of the thicknesses measured.

 

[Lutfi]

I must agree 100% with elpobano. I wrote a basic program many years following their method. I will try to locate the program and update to an excel spread sheet.

Regards,

 

[elpoblano]

Srennekamp,

Thinking further in your problem, your beam is being used. To evaluate the max. wheel load, you need to ensure that the beam does not have undercuts or gauges made by the wheels onto the upper side of the lower flanges. These are noticeable in a visual inspection.

In my experience every time I encounter a gauge, I request a magnetic particle test of the gaugue itself. However, if the gauge reduces the nominal thickness of the flange by 30% or more, I order a beam replacement.

Yes there are ways to repair the flange, but around my location the price of repair vs. replace is about the same.

One way is to weld a reinforcement plate under the bottom flange, this is restricted to the clearance left by your hoisting device. Depending on the monorail use frequency , you may have to weld the plate continuously along the the flange. And that generates another problem, stress concentrations.