Oasys GSA

breadmonkey

Folks,

I badly need some sort of tutorials on GSA. There are some on their website but they're basically useless. If anyone knows of any vids or literature I'd greatly appreciate it.

Specifically, I'm trying to create a grillage model of a bridge deck so anything directly related to that would obviously be very helpful.

Thanks

PeterDebney

You can find a video directly related to the creation (and analysis) of grillage bridges on the website: http://www.oasys-software.com/support/events/webinars/gsa_bridge_analysis.shtml.

Other resources that maybe of use are Getting Started guide (http://www.oasys-software.com/faq/index.php?action=artikel&cat=9&id=118&artlang=en with the accompanying video at http://www.oasys-software.com/products/structural/gsa/viewlets.shtml), plus modelling tips and tricks: http://www.oasys-software.com/support/events/webinars/gsa_modelling.shtml

breadmonkey

Hi Peter,

Thanks for the reply. I didn't realise you were the commentator on the bridge video until I watched the tips and tricks one.

In the bridge video you mention that there is a seperate tutorial on the construction stage analysis but I have been unable to find it. Would you be able to link me to it?

Thanks

breadmonkey

I found the construction analysis webinar but it appears to open differently to the others and I can't view it. I can only use IE at the moment but I'll try some other browsers later. Are you aware of any difficulties viewing the file? I notice that it's not on your youtube channel either. Cheers.

P.S. The webinars are very helpful. I was not referring to them in my original post!

PeterDebney

There were some technical problems with the Construction Stages webinar recording (http://www.oasys-software.com/support/events/webinars/gsa_analysis_stages.shtml), so it has not been possible to convert it to a YouTube format.

Have you tried using a different browser? I am using IE9 and can see it OK

breadmonkey

Hi Peter,

I've tried IE8, Chrome, Firefox and had a friend try it out on Safari. Unfortunately I don't have access to a computer with Windows 7 so can't use IE9. I don't suppose it would be possible for you to send me a copy of the recording? It would *really* help me out and I'd appreciate it greatly.

Thanks

breadmonkey

Could you tell me if there is an equivalent of "TRIM" and "EXTEND" from autoCAD for GSA? I'd like to join up the lines below. Thanks

PeterDebney

While there is not explicitly an extend command, there are a number of tricks that you can use:

1. if the elements are orthogonal to the current grid, then you can use the Drag Nodes sculpt tool to move the ends into line
2. if the elements are perpendicular to each other then you can use the Flex command: select the nodes to move plus the end nodes of the target element, right click on a node that will remain stationary, choose the Flex command, and use the Linear option with the nodes spaced proportionally. This will pull them all into a straight line.

To trim the elements us the Connect 1D elements command. This will break the selected elements where they cross, causing them to share any new nodes. Delete any excess element pieces as necessary.

breadmonkey

Thanks again. I hope you don't mind answering these questions!

Every so often I get the error "an unexpected argument was encountered" and the model gets messed up. It happened to me just now after the following sequence of events:

1. I ran a bridge optimisation analysis and was messing around with the results.

2. I deleted the results to go back and modify the analysis.

3. When I clicked on "Beam effects" under "Influence effects", the error popped up.

Do you have any idea why this might be occuring?

PeterDebney

This is an occasional glitch. The cure it simply to close GSA and reopen the model.

breadmonkey

I'm a little confused over the output. Do I need to manually apply the various factors to get the different values for SLS and ULS. Surely some must have been applied by GSA no?

Also, what is the difference between the characteristic, combination and frequent values?

PeterDebney

GSA will analyse exactly what you tell it to, nothing more, nothing less. So if you input working loads (or SLS) then that is what will be processed.

Assuming that you ran a linear analysis, you can then use the Combinations section to multiple the analysis results by the appropriate factor and add them to other analysis results. For example, if A1 was the analysis of the dead load L1 and A2 live load, then the combination would be 1.4A1 + 1.6A2, or similar if you are using Eurocodes.

If your analyses are non-linear then you must not do this and you should instead include the multiplications and combinations within the analysis itself.

The bridge load optimization analysis is slightly different in that it will work out the appropriate factors to apply at any location, and give you the characteristic, combination and frequent load values in accordance with EC1. You can then combine these load cases or analysis results with others as is appropriate.

For more information see the help file (Program data > Cases and Tasks > Bridge Loading > Standard bridge Loading > Eurocode loading) and the Eurocode itself.

breadmonkey

Hello again,

I've just noticed something a little strange is happening. When I try to calculate the worst effect at the critical midpan element (A), the maximum moment actually occurs on an adjacent element (B).

If I then try to calculate the worst effect on the element (B), the worst moment occurs on element (A). Both elements represent Y beams and asociated slab in the middle of the deck, offset an equal distance from the central alignment. Is this just some quirk whereby the placement of the two tandem systems is a bit weird?

Any ideas what might be happening? If it's not fixable, I'm thinking I should just take all elements along both beams and envelope the results?

PeterDebney

Sounds strange, but it is difficult to say without seeing the model.

Can you email it to me?

PeterDebney

Sounds strange, but it is difficult to say without seeing the model.

Can you email it to me at oasys@arup.com?

PeterDebney

When you ask the bridge load optimisation to give you the loads for the worst bending moment at a point on an element, that is what you will get. It may not be the element with the maximum moment, but you will find the extreme moment for that particular location.

You will note that when the influence is set to element 709, the moment in 715 is less than when you have the influence point on 715. The fact that there are elements with a greater moment than the influence point is does not indicate that GSA has made a mistake, but it might indicate that other influence points are more significant.