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# [CIVIL NX] What are Wood Armer moments? How to view ?

## Question

What are Wood Armer moments? How to view ?

Wood Armer method allows moment triads from plates (Mx, My, Mxy) to be transformed into simple bending moments in two directions (Wood Armer moments) for reinforcement design of plate elements.

This is important because the twisting moment Mxy can be significant. At any point in the slab, the normal moments in a direction, resulting due to design moments Mx, My, and Mxy, must not exceed the ultimate normal resisting moment in that direction. The ultimate normal resisting moment is typically provided by ultimate resisting moments Mux and Muα related to the reinforcement in the x- and α- directions. Mx, My and Mxy are bending and twisting moments, usually obtained from a finite element analysis program. α is angle of transverse steel, measured clockwise, from the Mx axis.

For those plates where, Wood Armer moments are to be found the reinforcement direction needs to be defined. Create plate elements either with Node/Element Create Element Plate or by using the Mesh option. Next is to define Domain. Invoke the ‘Define Domain’ dialogue box from Node/Element Tab. To assign the plates to a particular domain, follow the steps below :

Now, to add sub domain, one could either click on the Sub-Domain button form ‘Define Domain’ dialogue box or
click on ‘Define sub domain’ from Node/Element ribbon menu. The sub-domain is where details like the angle of reinforcement to
the global axis, angle between the reinforcements spanning in either direction and reference axis definition are specified.

Also if different parts of the same domain have different details, then these could be
provided using the subdomain.

On applying the necessary loads and boundary conditions, the Wood Armer moments could be checked graphically
as well as in form of table. For an irregular hypothetical slab as shown below, the Wood Armer moment result in
the direction of reinforcement (i.e., the design moment) will be more than those in local X and Y directions of the plate.

Along the red line shown in the image above, the Mxx value obtained for its dead load was 62kNm, while the
Wood Armer moment, considering the Mxx, Myy and Mxy, which would all be acting along the direction of reinforcement, i.e., at 20o angle to the global X direction is 74.2kNm. This is the moment for which
the slab needs to be designed.

The Wood Armer moments could be obtained at top and bottom of plates along both the reinforcement

directions. This option could be accessed by clicking on the ‘Wood Armer Moment’ button as highlighted in the image above.

The results could be viewed in tabular format from Results > Results Tables > Plate > Force (Unit Length)…
Once the table interface opens, click on Plate Force (UL:W-A Moment as in image below and select the required load cases as well as
output positions.

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