Irregularity type 4 in light framed shear wall structure
Irregularity type 4 in light framed shear wall structure
(OP)
I am doing a SDS D seismic upgrade to a 3 story shotgun type building that is on the historic registry. Given this I have very little ability to move interior walls so that they align with the walls below. This results in the transverse non-bearing walls being offset by 1' to 3' with very few ending on a bearing line below.
I am designing new transfer beams under each wall to receive the end of wall reaction / hold down and transfer them to the exterior wall or centerline girder. The Girders will then carry the vertical reactions to the posts to ground. Per ASCE 7-10 section 12.3.3.3 these framing members and their connections will need to resist the seismic load effects including overstrength factor of 12.4.3.
My understanding is that the shear wall elements themselves will be designed per the normal loads of 12.4.2 and the over-turning vertical reactions will need to be increased by Ω0 and equations 5 & 7 in 12.4.3.2. Does this sound correct?
At locations where the end of these walls are in the exterior wall over the foundation do the hold downs need to also be design with overstrength? My thinking is that the beams and connections need to be at overstrength but the posts and wall hold downs do not because they do not have a horizontal discontinuity.
I am designing new transfer beams under each wall to receive the end of wall reaction / hold down and transfer them to the exterior wall or centerline girder. The Girders will then carry the vertical reactions to the posts to ground. Per ASCE 7-10 section 12.3.3.3 these framing members and their connections will need to resist the seismic load effects including overstrength factor of 12.4.3.
My understanding is that the shear wall elements themselves will be designed per the normal loads of 12.4.2 and the over-turning vertical reactions will need to be increased by Ω0 and equations 5 & 7 in 12.4.3.2. Does this sound correct?
At locations where the end of these walls are in the exterior wall over the foundation do the hold downs need to also be design with overstrength? My thinking is that the beams and connections need to be at overstrength but the posts and wall hold downs do not because they do not have a horizontal discontinuity.






RE: Irregularity type 4 in light framed shear wall structure
To answer your second question, if the shearwall itself is not continuous down to the foundation then you need to apply the overstrength factor below the floor supporting the wall.
RE: Irregularity type 4 in light framed shear wall structure
RE: Irregularity type 4 in light framed shear wall structure
You could argue that Figure C12.3-5 justifies your position. Personally, I see no difference behaviorally between figures C12.3-3/C12.3-4 and C12.3-5 and have a tough time justifying the application of overstrength to one but not the other. Also note that the first sentence of Section 12.3.3.3 says "Columns, beams, trusses or slabs supporting discontinuous walls or frames...shall be designed to resist the seismic load effects including overstength factor of Section 12.4.3." Logically if a member is designed for overstrength then its connections should be also, so I don't use the last sentence of 12.3.3.3. Just my 2¢.