Question about Computer Modeling 1

[faromic]

I have a question about computer modeling. The extent to what I've used RISA, STAAD, and SAP is just modeling of an entire structure. I've always wondered though...can you design/check welds and bolted connections with these programs? How would I even do that? Or if I can do it, do I have to setup a seperate model for this?
Thanks

 

[canstruct]

Well it depends on your computer model infact. If you modelled all the joints as pinned, you have only axial forces in that joint, but if you modelled it as a moment connection with no release then you have to check that how much eccentricity that moment is causing on that particular weld or weld group. I think you have the chart to check that manually. Normally these programs do not give you the weld lengths as they can't assume you need WT, Angles or plates as a connection members also there is no assumptions in these programs for stiffener plates.

By the way, are u modelling 3D structure in SAP or other programs. These progrmas do not assume compression flange as braced, which might give you huge member sizes. You have to specify the braces yourself. Anyhow it is another issue of modelling.

 

[faromic]

Ok, that's what I usually do, take the resultants and design the connection. I was wondering if you can actually model a connection as part of the whole model with the plates, angles, or WT's and welds/bolts you desire and then the computer checks it for you. I guess it's easier to do it manually then setup the whole connection model anyways.
Thanks for the input. Did you say all programs don't assume a braced compression flange or SAP does and the others don't.

 

[canstruct]

Hi Faromic,

Actually i have the problem in my 3D Model that in addition to the fact i modelled steel deck it was not assuming beam top flange as braced. That is what we check the maximum moment capacity of the section, but the program ETABS (In fact SAP belongs to the same family) was giving capacity as the beam is restrained at end only. I contacted CSI and they inform me that only composite beams are assumed to be connected to top flangem, not simple steel deck (Even if we assumed puddle welding to top flange). The only way you can check is to laterally restrained at maximum unbraced lenght of the member by assigning member which acts as bracing, but it is a tedious process. And one more problem arises that some times these bracings have no force and the program gives an error message because it can't design those members. That is the experience i got. And CSI told me to fix it in new release. You might ask them for SAP too.
Hope this will help u.

 

[slickdeals]

Sometimes instead of using bracing members, I have selected the member and assigned "unbraced length" as a value that I think is appropriate, sometimes numbers like 0.01 depending on how much I think the top flange is braced. You can do it in the revise overwrites modules

 

[Lion06]

canstruct -
Check the defaults of the program. RAM has defaults will allow you to say that the deck braces the beams and other such things.

 

[canstruct]

But in ETABS as i talked with those guys they told that only composite beam makes compression flange as braced not the ordinary steel deck which is unfilled. Although we are welding it and making it braces.

 

[GalileoG]

RAM Connection for Staad works well. There is a price increase starting November 1st, so if you are interested, better order your copy before then.