Fabrication Dwgs
Fabrication Dwgs
(OP)
I have a question about the loads that a fabricator usually uses to design connections when member loads are not indicated on the engineering dwgs....in this case the fabricator said that they use the loads recommended by AISC...
my question are:
on compression braces...would this mean that they assume full capacity of the brace in tension instead of the capacity of the brace in compression which would be a much smaller load..
on beams...what load would they assume for the bm in calculating the shear in the connection..again is it full capacity, fully braced?
thanks..
my question are:
on compression braces...would this mean that they assume full capacity of the brace in tension instead of the capacity of the brace in compression which would be a much smaller load..
on beams...what load would they assume for the bm in calculating the shear in the connection..again is it full capacity, fully braced?
thanks..






RE: Fabrication Dwgs
I recommend either calling out typical connections that you're comfortable with the capacities of or at a minimum, saying "Connections should develop the capacity of an AISC Table 10-1 Connections with 3/4 inch A325 SC Bolts" or something like that, so there's no misunderstanding.
As far as braces, luckily almost any connection will develop the capacity of a brace. But it is an interesting case. Once again, a note or detail will work wonders.
I'm guessing that from your question, it's too late to correct the project you're asking about.
RE: Fabrication Dwgs
RE: Fabrication Dwgs
But, in may cases general guidelines are given. A percentage of UDL for shear, often with a composite factor. Percentages of the moment or axial capacity of the member. The EOR must verify that this percentage is conservative enough to encompass the actual force. The fabricator can not verify any force information given. This method is typically very conservative and of little benefit to the overall project.
Refer to the Code of Standard Practice for industry guidelines on information required for connection design.
http://www.FerrellEngineering.com
RE: Fabrication Dwgs
RE: Fabrication Dwgs
Bolt bearing on the beam web, or bending on the coped section, often controls in the design of a bolted connection. The reaction resulting from the maximum bending capacity of the beam will often be impossible to achieve without adding reinforcing to the beam. A "standard" connection won't do it. This problem is exacerbated with shallow beams, beams with thin webs, and beams with short spans relative to their depth.
Almost any connection _type_ can be sized to develop the member's strength. Tensile rupture on the net section will sometimes make it impossible to reach the member's strength without reinforcing.
As for the original post, and the fabricator saying they use AISC recommendations, there are no AISC recommendations. The requirements have to come from the engineer of record. It sounds like this fabricator is saying what he thinks you want to hear. Rather than wondering what loads he's designing for, you need to be providing the loads.
RE: Fabrication Dwgs
As far as the braces, once again, the connection capacity can be reduced using tensile rupture or whatever. But in the range of most designs, two 3/4 inch bolts (or whatever the fabricator comes up with) will be sufficient.
My point was that fabricators, left on their own devices, will provide sufficient connections 90% or more of the time. But, we as design engineers, need to provide designs that work 100% of the time. And leaving all the connection work to fabricators is toom much risk in this regard.
RE: Fabrication Dwgs
..
in this type of environment, being conerned about the rupture capacity of one bold is not even in the mix...by intuition and experience you size the members..maybe some rough cal's..issue preliminary..then everybody runs with it..fabrication , construction etc..by the time you get around to doing some real design on it, some of it may be already fabricated, fdn's poured and maybe some erected....compare that with the trend of the codes today that are busey, busey coming up with more and extensive eguations and conditions on the premise that this may squeeze another 2 or 3% out of the weight of stl....somebody is not living in the real world..laughable , really..
anyway, thanks for all the input, I think I have enough info to influence the fabricator and quide him in a more reasable direction...
RE: Fabrication Dwgs
In our case, we have a lot of light W8's and W10 roof framing, mostly controlled by deflection. Sophisticated connection design is not required. But we don't want shoddy connections either.
RE: Fabrication Dwgs
Joints are often where problems occur so one must be careful.
RE: Fabrication Dwgs
I think many of your comments here must be with your typical light construction in mind.
On some of the large industrial projects I work on, "(2) 3/4" Bolts" in a brace might be what is required for the weight of the brace!