Monorail support system problems

[Echan]

Hello,

Here is the situation. We have a monorail system (35ft span 5 Ton capacity) supported at both ends into the main building structure and by 8 anchor points welded to the main horizontal roof trusses. It has been in operation for 10 years plus and there is no sign of corrosion or cracking or yielding (paint is still like new).

Now here is the problem. A crane inspector had reservations about the 8 bracket anchor points. These are square tubing (2"x2" assuming 1/4" thickness and 7" long) welded between two 1/2" plates where the bottom is mounted to the main horizontal I-beam (w12x26) with 4 - 3/4" grade 5.2 bolts (Sp=85 Kpsi) and the top is welded to the roof trusses. We had multiple inspectors on site inspect our cranes and this is the first time that this was brought up. The square tubing seams to have been installed at an angle from that start with the bottom being flat with the I-Beam and the top being mounted at a small angle to the roof trusses.
Brackets looks like this:
____
\
|
|
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There is approximitly 1/2" difference between the top and bottom and seems have been pre-bent or bent during installation.

I have gone through stress calculations for the welds, bolts, beam and tensional stresses in the square tubing.
All ok.

My question is what is the best way to calculate the square tubings stress with the bend in it.

Thanks
Echan

 

[zvivik]

the bent you noticed,seems to me of no significant problem.
if you want to calculate, here is my suggestion:
the bent puts eccentric load which mean bending monent of [force]x[eccentricity] on the rectangular strut. calculate both the strut and the fillet weld to the plates for this moment.
zvi

 

[lilliput1]

Are you sure the brackets did not bend from the load because of horizontal force? If they did, it would show need for triangular gusset plate at each bracket on the same plane as the plane of the bent, to resist the horizontal force probably caused by acceleration force during start/stops.

 

[Reggie1968]

Well I think zvivik is correct about how to calculate the bending moment. But I must admit we design and build cranes and I have never seen it done that way. My crane inspectors would probably write it up also. Although that is at the discretion of the inspector. The best way I have found to hang the monorail beam is to use a toe clamp.