Hello all,
We're having a discussion in our office about the use of non-orthogonal concrete shear walls. The structure is a 6-on-1 wood on PT podium slab. Concrete shear walls support the PT podium slab. We have some disagreement about how to treat the concrete walls in the corner of the slab shown in the attached sketch. We are modeling this as a rigid diaphragm in RISA Floor/RISA 3D. The structure is in a high seismic area (Design Category D).
The three arguments are as follows:
a) Ignore the non-orthogonal concrete walls for lateral analysis because they are difficult to analyze and we don't need them for lateral strength. Design the walls only for gravity. Detail with the same non-slip connections used for the concrete shear walls. Provide minimum vertical and horizontal reinforcement in the non-orthogonal walls.
b) Design the non-orthogonal concrete walls as shear walls. We are detailing the non-orthogonal walls with the same non-slip connections as the concrete shear walls so they will attract load no matter what we put in the program. The building doesn't know we told RISA this is actually just a gravity wall if we don't detail for that.
c) Design the non-orthogonal walls as gravity walls only. Detail a slip connection at the slab to allow for seismic deflection.
I am on the side of arguments (b) and (c). The other two (senior) engineers are arguing for (a). I was told by one of the older engineers that a slip connection for the top of concrete walls is prohibited by ASCE 7 because concrete walls are required to be braced, but I can't find the reference and the engineer couldn't produce it so I'm not sure if that is a real requirement or not. Anybody have any thoughts here? I'm decades behind the other engineers in experience but just turning it off in the program doesn't feel good to me.
We're having a discussion in our office about the use of non-orthogonal concrete shear walls. The structure is a 6-on-1 wood on PT podium slab. Concrete shear walls support the PT podium slab. We have some disagreement about how to treat the concrete walls in the corner of the slab shown in the attached sketch. We are modeling this as a rigid diaphragm in RISA Floor/RISA 3D. The structure is in a high seismic area (Design Category D).
The three arguments are as follows:
a) Ignore the non-orthogonal concrete walls for lateral analysis because they are difficult to analyze and we don't need them for lateral strength. Design the walls only for gravity. Detail with the same non-slip connections used for the concrete shear walls. Provide minimum vertical and horizontal reinforcement in the non-orthogonal walls.
b) Design the non-orthogonal concrete walls as shear walls. We are detailing the non-orthogonal walls with the same non-slip connections as the concrete shear walls so they will attract load no matter what we put in the program. The building doesn't know we told RISA this is actually just a gravity wall if we don't detail for that.
c) Design the non-orthogonal walls as gravity walls only. Detail a slip connection at the slab to allow for seismic deflection.
I am on the side of arguments (b) and (c). The other two (senior) engineers are arguing for (a). I was told by one of the older engineers that a slip connection for the top of concrete walls is prohibited by ASCE 7 because concrete walls are required to be braced, but I can't find the reference and the engineer couldn't produce it so I'm not sure if that is a real requirement or not. Anybody have any thoughts here? I'm decades behind the other engineers in experience but just turning it off in the program doesn't feel good to me.