Calculations of RC walls (according to the American code ACI 318)

Wall design depends on whether or not a wall is exposed to seismic impact. Calculations are performed according to the guidelines of the ACI 318 code, based on the following assumptions.

• A wall is loaded and works only in its plane.
• A wall is designed to carry shear stresses from horizontal loads as well as compression/tension stresses resulting from loading with vertical forces and a bending moment acting in the wall plane.
• Currently, buckling of the wall perpendicular to the wall plane is not checked. It is assumed that the wall works in that direction as a short column.
• A wall is calculated for loads applied to the center of gravity of the wall section.

Detailed principles referring to individual steps of the structure design according to ACI 318 are as follows.

1. Shear

   Shear calculations are based on point 11.10 (regular walls) and 21.7.4 (walls subjected to seismic loads).

   Calculated reinforcement is arranged in the form of uniformly-distributed horizontal and vertical bars running throughout the entire length and height of a wall. Horizontal bars are anchored according to the requirements for tension bars (point 21.5.4).

2. Bending/compression and boundary elements

   Walls subjected to bending in the wall plane and compression are calculated according to the requirement of point 14.4 (regular walls) or 21.7.5 (seismic walls). Analysis is carried out according to chapter 10 (detailed analysis for the compression-bending interaction is conducted).

   Assumptions for calculations of a wall subjected to bending with compression are as follows.

   • The whole wall section is taken into account in compression/bending calculations.
   • Shear reinforcement is not taken into account in compression/bending calculations.
   • The total compression/bending reinforcement calculated is placed in boundary elements of a wall.

   It is always necessary to define the width of the boundary element, even if there are no visible boundary elements on edges of the wall. If there are no visible boundary elements, the width of a boundary element is interpreted as a dimension of a hidden zone in which compression/bending reinforcement is placed. By default, this value adopts the width equal to 0.2 of the wall length.

   If visible boundary elements are defined (a dimension of the boundary element perpendicular to the wall plane is greater that the wall thickness), the section is analyzed as an I-section or T-section. However, if a rectangular wall has been defined without visible boundary elements, then a section is interpreted as rectangular. The distance of the center of gravity of the reinforcement from the edge equals half the width of the boundary element.

   Reinforcement in walls subjected to seismic loads is enclosed within stirrups according to the principles for boundary elements (point 21.7.6). If special design of boundary elements is not required, then vertical bars are enclosed within stirrups.

   • If there is no compression as longitudinal bars in elements in bending, according to point 21.3.3.2
   • If there is compression, according to the principles for bars in boundary elements (point 21.7.6), exept that transversal reinforcement is distributed over the segment where the longitudinal reinforcement actually occurs (along the segment of the width D and not on the segment equal to the minimum width of the boundary element according to 21.7.6.4.a).

   In the case of walls not subject to seismic loads, transversal reinforcement of compression/bending members is calculated according to point 7.10.5.

3. Calculations of walls with openings

Note: Currently, user-defined openings are not taken into account in the calculations and design of walls. Constructional reinforcement of an opening according to point 14.3.7 of the code is generated.

Note: The RC Wall module does not support the Wall piers elements according to the ACI 318-11 code requirements.