Combining Local Flange Bending with Longitudinal Bending

[black79ta]

Hello, I am designing an underhung crane that we will use on a bridge project. the runway beams will be attached to the floorbeams that run transverse to the roadway with Lindaptor Clamps. I am using CMAA 74, AISC dg 7, AISE rpt 13, and a few others along with osha. my question is combining the longitudinal bending stresses (fbx,fby,fb torsion) with the local flange bending generated by the lindaptor clamps clamping onto the runway beams. In the past I have used sqrt(sum of squares) in different applications. This approach seems like an average of the von Mises method, with shear almost dropping out. with von Mises, the +/- (fbx)*(fby) value adds or subracts depending on which side of the flange you are evaluating. Any thoughts? i am thinking the sum of squares method is acceptable.

i have attached a page from a Lindaptor data sheet that shows how these clamps can be used.

Thanks.

 

[ToadJones]

I suppose this is very similar to evaluating the local bottom flange bending due to the wheels on the under running crane end trucks or trolley.
CMAA 74 has a very detailed calculation for evaluating these effects. Be careful to watch your signs since normally these calcs are combining the tensile bending stress with the local bending stress from the wheel load. In your case you'll likely have compressive bending stress since your clamps are on the top flange.

Our friend Alex Tomanovich at STEELTOOLS.ORG has developed a pretty nice spreadsheet that will do most of your leg work. I have never checked his spreadsheet but it gives identical results to a spreadsheet I developed for the same purpose.

Go to

http://www.steeltools.org

and search "Monorail"

 

[hokie66]

Toad, what make you think the load is on the top flange? Sounds like bottom flange to me.

 

[ToadJones]

I am assuming he is hanging some crane girders from the underside bridge deck and then using an under running bride crane on the crane girders.
So, The crane girders have the clamps connecting their top flanges to the bottom flanges of the bridge deck girders. Then the bottom flanges of the crane girders support the wheel loads from the under hung crane/trolley.

Essentially there are loads on the top and bottom flanges on the crane girders.

 

[black79ta]

Yes, ToadJones that is correct. The loads on the top flange are not point loads, since the clamps are 2.1875" wide. however the loads are similar in that both inside surfaces of the flanges are loaded in transverse tensile whereas the outside surfaces are loaded in transverse compression. i am wondering if i need to apply Von Mises to the top and bottom of the top flange also.

 

[ToadJones]

Close enough to a point load for me!

Again, I don't think you need to go Von Mises on this (not that you can't or shouldn't).
The calc laid out in CMAA 74 covers all the stresses you are concerned with in pretty good detail.
It incorporates the major axis beam bending stress, shears, and the local bending effects from the wheel loads or clamps.
The difference I am noting is that the major axis beam bending stress on the top flange will be compressive, the top flange local bending will also be compressive on the top surface of the top flange. Normally the calc is for the bottom flange where the major axis beam bending stress is tensile so you'll have to watch your signs.

 

[black79ta]

I will take another look at the CMAA 74, but I am afraid that it will be to conservative since 2.1875" is a lot bigger than a wheel contact point!

 

[ToadJones]

Usually a wheel load contact point is only about 1/2" from the edge of the flange. You're clamps likely reach in further towards the web and this is a major factor in determining the stresses.

 

[black79ta]

I have had to go with 2 bogeys on each end truck (4 axles=8 wheels) to keep the local stresses down, my wheels only have a contact patch of 1/2" so the maximum "a" dimen would be 1/4" but i am using i/8" for clearances. the clamps actually bear on the edge of the flange the bearing strip is about 1/4" x 2 3/16"

 

[IFRs]

Are you sure these Linadapters are intended and designed for tension? From what I see on their web site, the pictures seem to be of assemblies in compression.

 

[black79ta]

Yes they are designed to take tension loads. (I am actually using KeySafe BY G20 clamps which are basically the same as Lindapter) Keysafe engr dept has told me these clamps have been used by several DOT's to hang monorails under bridges. They say to use the interaction equation for tension and shear (fa/Fa)^5/3 + (fv/Fv)^5/3 less than 1.0