topic Wood Armer Moments in Structural Bridge Design Forum

Wood Armer Moments

Anonymous — Fri, 03 Jan 2020 20:36:33 GMT

How do I obtain the Wood Armer moments (My and Mx) from a FE Grillage Model to design the slab deck.

Please find my FE grillage model attached.

Many thanks

Regards

Salman

Re: Wood Armer Moments

Anonymous — Sat, 04 Jan 2020 12:11:09 GMT

The error that I am getting is as shown below . How can I still get the Wood Armer moments from the model?

Doing it manually would be very tedious and enveloping the live load case would be unsafe.

regards

salman

Re: Wood Armer Moments

dave_geeves — Sat, 04 Jan 2020 17:01:20 GMT

Hi Salman,
The reason you are getting this error message is that the Wood Armer equations are really only applicable to moment field of an isotropic flat slab and the program is expecting that the reinforcement set definition is applied to all elements or grillage beams in that sub-model representing the flat slab only.

I have had a look at your model and it appears that sub-model A not only contains the flat slab element but the diaphragm beams and upstand beams also. To get the reinforcement moments for the flat slab only you will need to move the diaphragm and upstand beams into an additional new separate sub-model (in the same plane). This can be done by creating a new 2D sub model (Z=0) and then in the sum model Members form in sub-model A select all the beam members in the table and use the task "Move to sub model" to select the new sub-model.

You will probably be asked about the beam eccentricities being applied which you should answer yes. The model can be checked with the 3D Element viewer to ensure consistency.

If a reinforcement set is then defined just for sub model A this will apply only to the FE deck slab and the reinforcement moments should then be accessible.

It should be noted that as this model is for a composite steel beam deck the reinforcement determined from the reinforcement moments is for slab bending and twisting alone and does include any longitudinal membrane reinforcement required by the composite action of the composite moments. This will be established from the composite beam design checks.

I hope this helps and if it answers your query please mark this post as a solution so that others may benefit. Thanks

Kind regards

Dave Geeves

Re: Wood Armer Moments

Anonymous — Mon, 06 Jan 2020 23:31:51 GMT

Hi Dave,

Thank you very much. You are a Star, I really appreciated it.

However when I tried to view the reinforcement moment, SBD ran of out of memory. I have increased the memory in the memory management up to 500Mb both for the database memory and core memory but SBD still couldn't compile the reinforcement moment result.

For your information I have only selected two FE element (at one time) so that I can reduce the model size and the analysis running time. The analysis of model is carried out on my computer which has a lot free space.

Please find attached the Model attached

regards

Salman

Re: Wood Armer Moments

dave_geeves — Tue, 07 Jan 2020 11:59:57 GMT

Hi Salman,

I don't think I have come across this problem before.

I'm pretty sure that altering the memory requirement in the program (ie for database and real core requirement) as you have tried will not make any difference as these relate only to the structural analysis and the production of the basic results. The Wood Armer calculation is a post-processing operation of the basic results and the memory allocation here will generally be done dynamically by requesting virtual memory as it is required. The amount of dynamic virtual memory available is not controlled within the program but as a configuration of the operating system. I am not an expert in this field but I think that the virtual memory settings can be altered , but will be dependant on the amount of free disc space you have available locally.

If virtual memory is not changeable then I'm not sure what more to suggest. It may be possible if you split the submodel of the slab up into 2 or more submodels so that there are fewer elements in each. The calculations are done for all the elements in a particular reinforcement set - which of course is linked to a particular sub-model.

Let me know if any of these suggestions solves your problem.

Kind regards

Dave Geeves

Re: Wood Armer Moments

Anonymous — Tue, 07 Jan 2020 15:40:18 GMT

Hi Dave,

Thank you for your prompt reply.

I have tried increasing the virtual memory but it didn't help. I still got the out of memory error.

"It may be possible if you split the submodel of the slab up into 2 or more submodels so that there are fewer elements in each. The calculations are done for all the elements in a particular reinforcement set - which of course is linked to a particular sub-model."

Could you please further explain how can I split my model in order for it to work?

Thank you

Salman