Civil Engineering Association

Warehouse (gable Frame) calculation notes and drawings

Size: 6.22 MB | Format: PDF | Quality: Original preprint | Year: 2010

Calculation notes of a gable-steel-frame, with construction drawings.
This is real building and drawings that all documents has been officially issued and approved.
I share it with you,

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Please do not share it with others, and it is for your personal use only.

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This post has been made by CivilEA Post-Generator ver 2.1.6[url=http://postgen.civilea.com/index.html][/url]

You can discus about any calculation notes on its topic, about faults, missed, ...

I just had a brief look I see for now 2 issues in the analysis model.
1. The variable section modeling technique
According to extruded view vs. drawings the beam and the column don't have eccentricity.
In sap (I see it's done in sap) you can change the insertion point to get that. I don't like this solution it can lead to wrong results.
Instead I would draw the frame lines along the section center line.
See Finite Element Design of Concrete Structures By Rombach first or second edition page 24-25
[Image: 96736962903935232874.jpg]

The bending moments in frame should increase after doing so. The shear at base (used for foundation design) should increase a little also.

I'll provide later a model, a comparison, between a frame like this one done with shells and with frames.

2. Bracings in roof plane 20mm diameter I guess.
In pdf at page 28 I can see that they have both compression and tension. I believe these are rods for tension only. If that's true we should be seeing there only tension.
The simplest way to get that in sap would be to assign releases for axial force to bracings in compression and leave only those in tension active, unreleased.
This means that from an X bracing only one will work /, while the other will be buckled.
so |X|X|X|X| becomes |/|/|\|\|
Possibly after doing so you'll see a double value for axial force. Also you'll see some increase in axial force in purlins.

I see an improvement the connection column-beam can be moved more to the middle.
I design for transport limitations of 3m width and 12m length for the steel part.
So you could move the connection away from the column closer to where bending moment is 0 in gravity loading.

Here's the model with shells in sap and ansys 14 workbench, I can't find the frame model.
The ansys 14 model was one of the first attempts to make a parametric model.

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Regarding sap insertion point.
This is similar to my modeling choice:

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And here's CSI Berkeley choice: (SAP2000 - 13 Cardinal Points)

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This one has flaws I can explain but it will take a while until then anyone interested can check with a plain cantilever column with vertical joint load at top, eccentrically loaded or with variable width aligned at one of the flanges.
Out of topic regarding the concrete shell-beam T section and some of my comments in Engineering problems:

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3. Issue I don't see a check for latteral-torsional buckling of the crane beam. Just strength and stiffness.
I don't see a buckling length evaluation for main column and beam.

^
Thank you for your comments, I think like this conversation will be useful for all. I hope all other members take part and discuss.

1- I agree with you, insertion point in SAP give wrong result, it is not reliable, but if you are in safe side you can rely to default sap modeling.

2- Bracing does not designed by software, as you said, they designed in tension only, due to ignoring bracing in compression, tension force extracted from software multiply by 2 and design manually, you can define element in SAP tension only, but it need nonlinear analysis. I usually use mentioned method (Design it manually).

3- Yes, it checked, but does not presented on calculation notes, in addition due to my expedience for light weight crane (in this case 5 ton) lateral-torsional buckling is not important.

In most of the gable-steel-frame, column & beam have outer edge straight and inner edge slopping. Most of structure design software have tapered section property available for analysis and/or design. But, tapered section have both edges slopping.

I think it is not possible to get such frame members even with series of small line members connected and even if available we need to combine those small member to check slenderness, Lateral torsional buckling or elastic buckling and modification of forces due to such effects.

If such members are modeled with finite elements using ANSYS or other software, it will be difficult to check safety of design of such members.

If there any software where we can model, analyze and design such members truly?

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