Preliminary Girder Design

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dav3525
Preliminary Girder Design

I am designing girders using the "girder designer" option in Bridgelink v4.0.2 for a txdot related project.
The program recommends a compressive strength, f'c = 9.0 ksi for a 42 strand girder (girder with harped strands).

In an older version of pgsuper v2.9.2.1, using the same geometry and loadings (copied file) (loads and distribution factors are identical), the program recommends a compressive strength, f'c = 6.9 ksi for a 44 strand girder (girder with harped strands).

I then copied the design from the older version to the newer version, and the design works.

My question is: why does the program not recommend a 44 strand girder similar to the older version? Is there a setting that can be changed to where the program recommends girder designs that work?

I was also having an issue with Bridgelink v4.0.2 earlier today. I would select the "design girder" option and it would recommend a high concrete compressive strength. But the spec check report would recommend a much lower value. So i manually changed the compressive strength to match the spec check reports recommendations and the girder design worked.

Keep in mind txdot max compressive strength is 8.5 ksi as per bridge design manual.

Thanks,

Pickings
Several changes were made to

Several changes were made to the preliminary design algorithm from version 2.9 to version 4.x. The changes mostly improved design results, but in some cases made them worse as you have noticed. Version 5.0 has been released by WSDOT and a TxDOT version 5.0 is in the near future. 5.0 should give better design results for most cases.

TxDOT's engineers have entered design parameters into the PGSuper templates to optimize designs per their specifications. Settings are on the Design tab in the Girder Library. You can try, but I doubt that their are settings that will result in better designs over the wide range of girder types and strand configurations that PGSuper supports.

That said, it is called a preliminary designer on purpose. The algorithm does not always give, or should be expected to give, optimal results, so engineers are expected to scrutinize design results as you have done.

Regards,

Richard Pickings, P.E.
BridgeSight Inc.

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