sward1971
Structural
- Apr 13, 2006
- 2
I have several three-story & two-story wood-framed buildings with plywood shear walls. Where we have a beam supporting a discontinuous shear wall above, this is classified as a vertical irregularity Type 4 per ASCE 7-05 Table 12.3-2. According to ASCE 7-05 section 12.3.3.3 - Elements Supporting Discontinuous Walls or Frames, this beam shall be designed with the overstrength factor (Omega sub zero). In addition, "the connections of such discontinuous elements to the supporting members shall be adequate to transmit the forces for which the discontinuous elements were required to be designed."
I understand that the beam has to be designed with the overstrength factor, but here's my question: Aside from the beam, is the overstrength factor implemented throughout the rest of the design until reaching the foundation? In other words, do you have to design the beam-post connection, the post, and the post base connection using the beam reactions that have been increased by the overstrength factor? One could conservatively use the amplified loads throughout, but the connections can become quite expensive, especially for residential buildings. Therefore, it is more cost-effective not to use the increased load in the design unless it is warranted by the Code. The quote above is the only Code reference to using the 'amplified' loads for the connection design, but it refers to the wall-beam connection, i.e., the hold-down.
I have not yet found a definitive answer on any of these discussion threads and each engineer I talk to seems to have a different opinion on this all thanks to the ambiguity of the Code. Your help is appreciated.
Sincerely,
Stephen R. Ward, S.E.
I understand that the beam has to be designed with the overstrength factor, but here's my question: Aside from the beam, is the overstrength factor implemented throughout the rest of the design until reaching the foundation? In other words, do you have to design the beam-post connection, the post, and the post base connection using the beam reactions that have been increased by the overstrength factor? One could conservatively use the amplified loads throughout, but the connections can become quite expensive, especially for residential buildings. Therefore, it is more cost-effective not to use the increased load in the design unless it is warranted by the Code. The quote above is the only Code reference to using the 'amplified' loads for the connection design, but it refers to the wall-beam connection, i.e., the hold-down.
I have not yet found a definitive answer on any of these discussion threads and each engineer I talk to seems to have a different opinion on this all thanks to the ambiguity of the Code. Your help is appreciated.
Sincerely,
Stephen R. Ward, S.E.
