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RMair
10th March 2011, 02:41 PM
In a current design I am working on, my ladder beam is outwith its shear capacity. The BM is well within its limit but SF is nearly double.

What can be done to reduce the shear force? What affect will knee bracing and pickups have? And how can the reduction be shown mathematically?? Does the knee brace create an addition support?

I hope someone can help...

phil181
10th March 2011, 03:58 PM
In a current design I am working on, my ladder beam is outwith its shear capacity. The BM is well within its limit but SF is nearly double.

What can be done to reduce the shear force? What affect will knee bracing and pickups have? And how can the reduction be shown mathematically?? Does the knee brace create an addition support?

I hope someone can help...

If you know that the bending moment it ok, but the shear force is out - then you should be able to calculate the rest yourself by moment distribution.

Don't forget you have to get rid of the horizontal reaction to the knee brace!

Hope this helps.

HatterScaff
11th March 2011, 07:09 AM
RMair
lets see your calculation so far

RMair
11th March 2011, 08:06 AM
thanks phil. unfortunately, i cannot change the position of my loading or the span so will need to use additional pickups. i'm assuming i treat the knee brace as an additional support with both a horizontal and vertical load. my problem now will be the axial loading on the uprights!!

biffo0911
11th March 2011, 11:05 AM
RMair,

If you position your pick-up braces directly below the load, they can support all of the load themselves (with the addition of supplementary couplers). As Phil says you will need to resolve the horizontal reaction too, keeping the brace as close to vertical as possible reduces this. The vertical axial load at the standards will be the same as before as the vertical component has not changed.
Another way to reduce the shear per ladder beam is to introduce double ladder beams, supported off double standards (if they are side by side).
The axial load in the standards can also be catered for by reducing the lift heights below the beams if this is possible.

SE1006
12th December 2011, 01:11 PM
In a current design I am working on, my ladder beam is outwith its shear capacity. The BM is well within its limit but SF is nearly double.

What can be done to reduce the shear force? What affect will knee bracing and pickups have? And how can the reduction be shown mathematically?? Does the knee brace create an addition support?

I hope someone can help...

RMair or anyone; could you please advise what the shear capacity is for steel ladder beams (and qualify source of info if possible)? I can't seem to find anywhere on the web, tried multiple suppliers but they only appear to have data sheets with various loading details with no shear capacity!

Thanks in advance

RMair
13th December 2011, 08:03 AM
Steel ladder beam compression chord laced at 1m c/c, tension chord 2m c/c

allowable BM - 13.5 kNm
allowable SF - 18 kN

I'll have a look for the data sheet...