Using Metal Roof Diaphragm for Crane Lateral Loads

[Serhiy2]

Good day,

I'm designing a crane supporting structure made of steel and realizing that it takes a heavy frame structure to be within the lateral deflection limits recommended by crane design manual. I tried using the metal deck as diaphragm and load and deflection wise everything works out fine. I'm just having second thoughts on relying on the diaphragm for this kind of loads worrying about the fatigue/impact nature of the loading but on the other hand this type of diaphragm is used to resist/transfer seismic loads which are similar in behavior. Also, in Crane Supporting Structures Manual by CISC it does not recommend relying on roof diaphragm to transfer lateral crane loads. I'm curious to hear your opinion on using the metal deck roof diaphragm to transfer lateral crane loads to cross bracing located in the end walls. Thanks

 

[human909]

Doesn't sound like a good idea to me.

Around here we generally don't even use a metal roof for lateral loads from wind. How thick is the sheet in a 'metal deck' roof for you? Down we use roof sheeting and it is typically profile sheet that is 0.42mm thick. But we don't have snow loads.

 

[Serhiy2]

We typically use 1-1/2" 22 ga. (0.76mm) thick corrugated metal deck. Canam diaphragm design manual gives guidance on shear resistance calculations and, like I said, I can easily design the 22ga. deck with connections to carry my crane and wind loads while resulting in very minimal deflection.

 

[driftLimiter]

Be careful speccing that 22ga deck. It dents really easily. I haven't delt with this specific problem but if your crane manual suggests not to do it there is probably a good reason. In general bare-metal deck diaphragms are gaining popularity even for high seismic loads in my area.

 

[SteelPE]

What is the size of your crane?

I was always taught that for light cranes (5 tons or less) you can utilize the metal roof diaphragm. Larger cranes required roof bracing which consisted of either flat plate placed in-between the decking and roof members, or steel angles supported by the roof members. This is the direction that I have followed.

I don't recall if there is anything on paper to back this opinion up, but it's the way I was told to approach the design of crane buildings.

 

[Serhiy2]

There will be two additions to existing structure: one having the 10 ton crane and other having the 5 ton.