nuche1973
Structural
- Apr 29, 2008
- 300
Ladies and gents:
Attached to this post are two details of built up wood headers in a wood shear wall. The structure is a four story wood structure, located in a high seismic zone. These details are for the headers located in the exterior walls where the shear is transferred around the openings. We had to use this method because of low aspect ratios, there are numerous openings in the exterior wall. The maximum shear transferred is 700 lb/ft, at the lower floors. The shape of the structure is in a U, we have found that wind governs in one direction, where seismic governs in the other direction. The original header was to be (3) 2x12’s with spacers. However, the architect is looking for VE issues and is questioning all the exterior headers.
Header A is what the architect wants to use and swears that this is “common in the industry”.
Header B was suggested by a person in our firm as an option.
I have experience in metal stud structures but not wood; but for only single and double story buildings. Anything over three was steel frame with concrete deck and curtain wall framing. Hence, Header B makes more sense to me since it resembles a box beam.
My questions are:
1. Has anyone seen Header A? If yes, then how did you analyze the load path?
2. In a wood shear wall, where does the shear force load path occur? (I was told that all the forces occur on the exterior. Is this correct?)
3. How does one analysis Header B? (I was thinking: NDS – beam/column calc with shear converted to axial load, wind force as my out of plane bending, un-braced length of zero due to the top and bottom 2x6, divide the axial in half for each 2x8.)
Any insight/suggestions will be greatly appreciated. Thanks.
Attached to this post are two details of built up wood headers in a wood shear wall. The structure is a four story wood structure, located in a high seismic zone. These details are for the headers located in the exterior walls where the shear is transferred around the openings. We had to use this method because of low aspect ratios, there are numerous openings in the exterior wall. The maximum shear transferred is 700 lb/ft, at the lower floors. The shape of the structure is in a U, we have found that wind governs in one direction, where seismic governs in the other direction. The original header was to be (3) 2x12’s with spacers. However, the architect is looking for VE issues and is questioning all the exterior headers.
Header A is what the architect wants to use and swears that this is “common in the industry”.
Header B was suggested by a person in our firm as an option.
I have experience in metal stud structures but not wood; but for only single and double story buildings. Anything over three was steel frame with concrete deck and curtain wall framing. Hence, Header B makes more sense to me since it resembles a box beam.
My questions are:
1. Has anyone seen Header A? If yes, then how did you analyze the load path?
2. In a wood shear wall, where does the shear force load path occur? (I was told that all the forces occur on the exterior. Is this correct?)
3. How does one analysis Header B? (I was thinking: NDS – beam/column calc with shear converted to axial load, wind force as my out of plane bending, un-braced length of zero due to the top and bottom 2x6, divide the axial in half for each 2x8.)
Any insight/suggestions will be greatly appreciated. Thanks.
