Peer-to-Peer Standards Exchange

The structure you show in plan would be considered by most engineers to have horiozntal irregularity type 5.  It should be analyzed and deisnged for 100% of the forces in Direction X combined with 30% of the forces in Direction Y, and 100% of the forces in Direction Y combined with 30% of the forces in Direction X.

Great!  Agree on the applications of loads.

The follow-up question would be, is it required to be analyzed using 3D model per ASCE 7-16, 12.7.3?
12.7.3 states that for horizontal irregularity 1a, 1b, 4, and 5, a 3D model is required; the only exception is provided for a flexible diaphragm structure if it has horizontal irregularity 4 (out-of-plane offset).

The structure you show in plan would be considered by most engineers to have horiozntal irregularity type 5.  It should be analyzed and deisnged for 100% of the forces in Direction X combined with 30% of the forces in Direction Y, and 100% of the forces in Direction Y combined with 30% of the forces in Direction X.

In my opinion, a 3D model is not required because this building has a flexible diaphragm.  However, even if hand calculations and statics are used ot determine the forces on the walls, one has to consider the 3D behavior of the system.

Great!  Agree on the applications of loads.

The follow-up question would be, is it required to be analyzed using 3D model per ASCE 7-16, 12.7.3?
12.7.3 states that for horizontal irregularity 1a, 1b, 4, and 5, a 3D model is required; the only exception is provided for a flexible diaphragm structure if it has horizontal irregularity 4 (out-of-plane offset).

The structure you show in plan would be considered by most engineers to have horiozntal irregularity type 5.  It should be analyzed and deisnged for 100% of the forces in Direction X combined with 30% of the forces in Direction Y, and 100% of the forces in Direction Y combined with 30% of the forces in Direction X.

If hand calculations are done such that the stiffnesses of the shear walls are considered as well as the location and direction of those stiffnesses AND the center of force along with the eccentricities of the load (both actual and minimum) are taken into account, what else must one do to "consider the 3D behavior of the system"? IMO, if the roof diaphragm were considered as semi-rigid, i.e., the stiffness of the diaphragm considered, then I would totally agree with a 3D computer model to solve the problem. Otherwise, I don't see how one can do anything more to "consider the 3D behavior of the system". Not being critical for you have much more knowledge and experience in this area than I do. I'm sincerely curious.

Thank you,

In my opinion, a 3D model is not required because this building has a flexible diaphragm.  However, even if hand calculations and statics are used ot determine the forces on the walls, one has to consider the 3D behavior of the system.

Great!  Agree on the applications of loads.

The follow-up question would be, is it required to be analyzed using 3D model per ASCE 7-16, 12.7.3?
12.7.3 states that for horizontal irregularity 1a, 1b, 4, and 5, a 3D model is required; the only exception is provided for a flexible diaphragm structure if it has horizontal irregularity 4 (out-of-plane offset).

The structure you show in plan would be considered by most engineers to have horiozntal irregularity type 5.  It should be analyzed and deisnged for 100% of the forces in Direction X combined with 30% of the forces in Direction Y, and 100% of the forces in Direction Y combined with 30% of the forces in Direction X.

Great!  Agree on the applications of loads.

The follow-up question would be, is it required to be analyzed using 3D model per ASCE 7-16, 12.7.3?
12.7.3 states that for horizontal irregularity 1a, 1b, 4, and 5, a 3D model is required; the only exception is provided for a flexible diaphragm structure if it has horizontal irregularity 4 (out-of-plane offset).

The structure you show in plan would be considered by most engineers to have horiozntal irregularity type 5.  It should be analyzed and deisnged for 100% of the forces in Direction X combined with 30% of the forces in Direction Y, and 100% of the forces in Direction Y combined with 30% of the forces in Direction X.