How does STAAD determine beam deflections?

RE: How does STAAD determine beam deflections?

Sye — Mon, 14 Sep 2020 16:41:34 GMT

Yes -0.23 in is the deflection at node 1660. The literature I referred you to describes how stiffness analysis is carried out by STAAD.Pro. I am not sure how you can hand calculate and match the value of -0.23 inches because it is not just a simply supported beam in isolation but rather one that is connected to a slab which is a two way type element ( transferring load in both directions) and directly influences the displacement of the beam. Moreover the element matrices/global matrices also involve terms related to shear deformations which are not accounted for in hand calculations. If you want to do some verification on the software, there are a number of verification examples that you can find at

https://docs.bentley.com/LiveContent/web/STAAD.Pro%20Help-v11/en/GUID-8C62E6A3-4470-4E9E-92DB-4878EB27DF9D.html

RE: How does STAAD determine beam deflections?

Pascual Mauricio — Mon, 14 Sep 2020 15:43:44 GMT

By saying "displacement at the node at the start of the member", do you mean for this case the deflection is at node 1660?
If so, yes I understand that. What I don't understand is how STAAD is getting that deflection.

There are several beam segments along the line in red. I modeled beams between nodes with the plate mesh along the red line I show.

The literature on the stiffness analysis you shared didn't help on understanding how STAAD is getting the deflection of -0.230 in. Trying to do hand calcs to compare, I am not getting anything close.

RE: How does STAAD determine beam deflections?

Sye — Sat, 12 Sep 2020 01:39:19 GMT

The displacement you circled is the Global displacement in Y at the start of the beam. So basically this is the displacement at the node at the start of the member. For the beam and the slab to be considered as monolithic, please make sure that the beam is broken up into segments in line with the plate mesh.

Details on how the stiffness analysis is carried out by STAAD.Pro is available at

https://docs.bentley.com/LiveContent/web/STAAD.Pro%20Help-v11/en/GUID-3ED02290-F1A5-4EA7-8313-8A23C75A9F19.html