Hi,
I am looking to understand how the design moments and shears are to be calculated when using triangular plates for concrete slab analysis.
For triangular plates the results are reported wrt the local plate axes. The 'Global moments' are also available from staad. However, how do the global moments relate to the twisting moments Mxy ? is this included ? or the global moments are purely the transformed local moment considering the skew angles of plates?
I have searched numerous discussions on web although no clear answer was found. In addition staad technical reference material also does not talk about deriving concrete design forces from the plate results. The Wood-Armer or Clarke-Neilson methods are not mentioned. These require the twisting moments Mxy to be added to the out-of-plane moments Mx or My in global directions. This only leaves an option of using quadrilateral elements with local axes aligned with the global rebar directions.
Although for more complicated structures it is not always possible to use quad elements and triangular plates are more preferable to generate quick and uniform meshing - especially the parametric meshing feature is useful. However, I am confused as to how the global orthogonal moments, shears and axial loads are determined when using trigular meshing in staad in relation to full consideration of twisting moments Mxy.
Please share your thoughts.
The Global Moments do include contribution from MXY. The following wiki contains more details on the topic
http://communities.bentley.com/products/structural/structural_analysis___design/w/structural_analysis_and_design__wiki/32092.global-moments-in-plates
So you can go ahead and use the Global Moments for reinforcement calculations. Direction should not be an issue with shear as long as your out of plane shear stresses SQY and SQX are within the allowable shear stress values.
Dear Sye,
Thanks for the response,as i too had the same query. I realize that using Wood-Armer equations for triangular plates to derive design internal forces is really pain staking.
Is there any other way in which STAAD.pro facilitates extraction of design internal forces for use as concrete slab/raft element (for reinforcement demand calculation) using triangular plate elements?
Hi Karthik,
Good to see someone else stumbled across the same issue. I didn't fully agree with the above suggestion from staad. I don't think the Global moments represent woood-armer moments for concrete design as they are simply the local moments transformed in the global axis directions. The twisting moments i.e. Mxy are not taken into account. What I have learned from my research is that you can not use triangular plates for concrete design in staad.pro or any other program without significant amount of post processing to obtain the design moments. My opinion is stick to rectangular or quad elements and everything is straightforward.