For the design of reinforced concrete slabs, an engineer needs design moments for the top and bottom reinforcement in two directions. STAAD.Pro currently gives the bending moments Mx, My and the twisting moment Mxy, and the Global Moments table expresses the moments in the global axes. However, it does not give design moments. The twisting moment still has to be combined with the bending moments by hand – for example with the Wood–Armer method – before the reinforcement can be designed.
This matters in practice. In slab corners, in skew slabs and anywhere the twisting moment is significant, reinforcement designed only for Mx and My is on the unsafe side. For a simply supported skew slab with a 30° skew, our check showed that designing only for the bending moments underestimates the bottom transverse reinforcement about four times and the top transverse reinforcement by about 80 %.
The Wood–Armer method is already implemented in the STAAD.Pro element design (parameter SRA), but only in the local axes of each element and only inside the design run. It is not available as a post-processing result. With an automatically generated mesh, the local axes of individual elements are not necessarily aligned, so these results cannot be used directly to lay out reinforcement in the real directions of the bars.
Proposal (one of the following):
Add design moments to the plate results: Mx,top, Mx,bottom, My,top, My,bottom calculated by the Wood–Armer method in the global axes (or in a user-defined reinforcement direction), available both as contour plots and as tables for each load case and combination, including envelopes.
Or – which would be more logical – turn the Global Moments output directly into design moments. Global moments without the twisting effect are not the final quantity the engineer needs, so in their current form they are an unfinished step. The raw components could remain available as an option for verification.
Why this is important
From the user's point of view the task is left unfinished: the program calculates all the components but stops one step before the result that is actually used for design.
Manual post-processing of hundreds of elements and many load combinations is time-consuming and a common source of errors – the twisting moment is easily overlooked, which leads to under-reinforced slabs.
Other programs already provide this to their users – for example, SCIA Engineer offers design (dimensioning) moments for 2D members directly in post-processing. Without this feature STAAD.Pro is at a competitive disadvantage for concrete slab design.
Implementing this would make STAAD.Pro more complete and safer for reinforced concrete slab design, and would save users a significant amount of manual work.
