Designing A Steel Shed (Bus Terminal)

[Sara Farooq]

I am designing a steel shed. I did manual calculations for the initial selection of sizes. But when I modeled it in ETABS all of them failed. For columns my initial section was W4x13 and it was failing in shear and D/C. I am attaching the file here.

The main issue is I don't know which checks should be applied in these members. And how should I control drift?

Bus terminal Shed.$ET

Bus terminal Shed.rar

[WR1]

at the outset, i want to suggest that you DONT actually need to send .ebk file which you did in zip. .$et file is enough for anyone to review and check.

 

The facility is in seismic zone 4

 

Make LL factor in p-delta = 1.0 (im leaving the question for you to research..why)

 

You have made the base fixed, take care in the design of baseplates. (Bi-axial moments....how would you design it)?

 

Coming back to your main question, When i ran the model, all of the members passed including the columns. (LOL). Is there something I am not getting?

 

Check in your model, the effective length factors for columns and beams. They might need to be adjusted.

 

I would assert that you should have made a simple 2d model of this and should have studied it properly before starting the 3d model. Its never too late, if you haven't done one yet. You can do it now. In 2 model, check how much are the reactions, column axial forces and drifts to have a FAIR idea about the structure you are dealing with.

 

For drift, search in this forum. I have made a lengthy topic about building drifts. Just do the struggle to search it. 

 

I am surprised to see no WIND load on the structure as it would be more critical for uplift of foundations and drift (If seismic is not governing). Is that the reason?

 

0.25inch thick shell to model the slab? I would recommend to make it as thin as possible (to the point just near where ETABS does not start giving errors...try 5mm may be). This is to exclude any out-of-plane effects of the shell.

[UmarMakhzumi]

W4x13 column looks thin and light. I can't open your model as don't have Etabs with myself but I wouldn't use any thing less than W12 or W14 for columns. Section should be bit heavy too as heavier sections help in connection design.

The checks you need to perform are member beam column utilization checks. Normally programs call such checks as unity checks and show unity ratio. There is a watch and learn video on Csi webpage that shows you how to select a section list and let Etabs select members that would satisfy drift requirements.

Rana has made some good points too.

[Badar (BAZ)]

There are major flaws in your structural system. There is no load path for transferring lateral loads from top to foundation. They way you have modeled it, you are relying on moment connections, which, I think is not practical, and also not applicable for open web joists.

 

Why have you selected open web joist for 15 ft span. You can use hot rolled section

 

You have not modelled bracing required to prevent local buckling of compression flanges of your flexural members. You can ensure buckling restraint by running beams in longer directions of the shed as well; Span between the beams will depend upon required unbraced length. You will also need to put cross bracing in the plane of roof deck, as well in the plane of column grid-lines (in both direction) , at-least in one bay, to improve global stability of the system.

 

You will need to check, among others, if the model is using correct values of unbraced length, moment gradient factor (Cb) and effective length factor. If you want to use open-web joist, then you need to ensure that Etabs knows that it is built up section.

 

I suggest you to select compact section for you flexural members, and ensure that slenderness ratio of elements of column-section are low enough to ensure inelastic behavior.

 

You should be using 2D model.

[Ayesha]

I don't have access to any softwares so I don't know about your framing. But, for Steel Design, don't model 2D unless you are completely familiar with the overall process. Generally, steel columns(I shapes) can be moment connected in the major axis and braced in the minor axis to provide a load path for lateral loads. You should see what you column orientation is. Unlike concrete, for steel design, you have be watch the load path. Engage a senior engineer in your office and get him to review what you are doing.