# D13.D.5 2DElements: Slabs, Walls, and Shells

In general, the calculation of reinforcement for two dimensional elements (i.e., slabs, walls, and shells) is performed two times: once according to conditions of strength and again according to limiting of width of cracks. In reinforcement calculations for strength conditions (i.e., the first limit state), design load values must be used. In reinforcement calculations for crack width limitation (i.e., the second limit state), characteristic (i.e., normative or service) load values are used. Using the multiple analysis capability of STAAD.Pro allows you to carry out both calculations in a single analysis and design run.

Symmetric or non symmetric reinforcement of elements is calculated according to either first or second limit states by using the `STA` parameter.

It is necessary to pay close attention to the arrangement of local axis of the element with respect to the direction of reinforcement for the calculation of reinforcement. This is controlled using the `CL` and `CRA` parameters, as shown in the following figure.

### Russian concrete design parameters CL and CRA

An example output of reinforcement calculations:

SLAB/WALL DESIGN RESULTS (by stresses in local axes for limitation of crack width) ----------------------------------------------------------------------------------------------------------------------------------- Element Asx Mx Nx Load. N. Asy My Ny Load N. sq.cm/m kNm/m kN/m (X) sq.cm/m kNm/m kN/m (Y) ----------------------------------------------------------------------------------------------------------------------------------- 60 TOP 0.00 *4.9 0.0 1 0.00 *4.5 0.0 1 BOT 3.53 *9.9 0.0 3 3.46 *8.9 0.0 3 61 TOP 0.00 *5.3 0.0 1 0.00 *4.7 0.0 1 BOT 3.87 *10.7 0.0 3 3.65 *9.4 0.0 3 62 TOP 0.00 *5.6 0.0 1 0.00 *4.8 0.0 1 BOT 4.10 *11.2 0.0 3 3.77 *9.6 0.0 3

where:

- Element – number of finite element, TOP – top zone of member, BOT – bottom zone of member (top zone of member is determined by positive direction of local axis Z see the following figure);
- Asx – intensity of reinforcing in the first direction (parallel to the local axis X), sq.cm/m;
- Mx – distributed bending moment in respect to the local axis Y, kNm/m;
- Nx – distributed longitudinal force directed parallel to the axis X, kNm/m;
- Load N.(X) – number of loading version, determining intensity of reinforcing in the first direction;
- Asy – intensity of reinforcing in the second direction (parallel to the local axis Y), sq.cm/m;
- My – distributed bending moment in respect to the local axis X kNm/m;
- Ny – distributed longitudinal force directed parallel to the local axis Y kN/m;
- Load N.(Y) – number of loading version, determining intensity of reinforcing in the second direction.