We are designing a building to mu=2 and are working through the detailing of Clause 14.6 of AS3600:2018 (Limited Ductile Structural Walls). The building in question has more shear walls in the Y direction than the X direction, meaning the walls in the Y direction are not working that hard in the lateral cases.
We find ourselves in an interesting situation with the boundary elements where we have a lot of walls that are entirely in compression in the lateral case and requiring boundary elements for the full length of the wall driven more by the vertical load in the wall than the lateral load. An example wall from our calculations below:
Our reading about boundary elements suggests that they were added due to the wall losing compressive capacity after plastic tension strains occur under cyclic loading which makes sense for a high moment situation. Under the high axial/low moment case we have, the element never goes into tension and hence this shouldn’t be an issue.
AS3600:2018 clause 14.6.2.1 states that “The stress referred to in item (b) shall be calculated using the design action effects for the strength limit state, a linear-elastic strength model and the gross cross-section properties of the wall” implying that the initial calculation where the whole wall experiences compression (putting the NA outside the length of the wall) is the correct design situation.
How are others dealing with blade walls at mu=2? It seems unnecessary to be adding boundary elements to whole walls where it is governed by vertical axial compression, not large moments from lateral loads which never develop tension in the wall. Note that the walls have been designed to meet the requirements of 11.7.4 (b) so do not require ties for non-seismic cases, however 11.7.4 (a) also applies.
We find ourselves in an interesting situation with the boundary elements where we have a lot of walls that are entirely in compression in the lateral case and requiring boundary elements for the full length of the wall driven more by the vertical load in the wall than the lateral load. An example wall from our calculations below:
- Dimensions: 1750x194 wall (reduced thickness for afs rediwall permanent formwork system)
- Concrete Strength: 40MPa
- 0.15f’c Limit: 6.0MPa
- Force at end A: 3055kN/m in compression (15.7MPa)
- Force at end B: 579N/m in compression (3.0MPa)
- Governing Load Combination: 1.0G + 0.3Q + 1.0EQy -0.3EQx
Our reading about boundary elements suggests that they were added due to the wall losing compressive capacity after plastic tension strains occur under cyclic loading which makes sense for a high moment situation. Under the high axial/low moment case we have, the element never goes into tension and hence this shouldn’t be an issue.
AS3600:2018 clause 14.6.2.1 states that “The stress referred to in item (b) shall be calculated using the design action effects for the strength limit state, a linear-elastic strength model and the gross cross-section properties of the wall” implying that the initial calculation where the whole wall experiences compression (putting the NA outside the length of the wall) is the correct design situation.
How are others dealing with blade walls at mu=2? It seems unnecessary to be adding boundary elements to whole walls where it is governed by vertical axial compression, not large moments from lateral loads which never develop tension in the wall. Note that the walls have been designed to meet the requirements of 11.7.4 (b) so do not require ties for non-seismic cases, however 11.7.4 (a) also applies.
