Anchor bolts in retrofit double sill plate

[josta]

Got an issue with the local friendly plan check engineer: When retrofitting an existing 2x sill plate where a 3x sill is required I add another 2x member on top of it, tight-fitting between studs ("pressure blocks"). I also edge nail the shear panel to both the existing sill and the new 2x member, plus I face nail (or staple, to prevent splitting) the new member into the existing sill, so that they all perform as one piece; akin to but even stronger than 2-2x members allowed in lieu of a 3x edge stud.

I then show the retrofit anchor bolts to go through both the new and existing sill.

The plan check engineer does not feel that it would perform as one piece; he is concerned about any horizontal shear between the two members, even though the shear panel is edge-nailed equally to each of the two members at the nailing required for the load. In other words, if the load is 490 PLF and 3" o/c nailing is required, I use 3" o/c nailing into each of the two members.

My thinking is for that to not work, the edge nailing at the new and/or existing sill would have to fail.

I realize there is a now-closed thread on this subject, but the horizontal shear issue was not addressed there, nor was the anchor bolt issue addressed as below.

He is also insisting that if this was allowed, that we have two anchor bolts in each stud bay due to the new, shorter 2x member. I say this is not necessary because the purpose of having two anchor bolts per piece of sill is to prevent rotation of the sill about the vertical axis of the anchor bolts, and in this case since the two members are nailed tightly together it is not likely to occur.

I use this method with an addition where it is not possible or practical to make the addition "free-standing" with its own four walls and footing.

Any comments/suggestions? Thanks!

John

 

[josta]

I just found this handout from the City of Berkeley Building and Safety using this method. I showed it to the plan checker, who immediately accepted it since it created a "precedent" plus this handout was also peer-reviewed by CALBO, SEAOC, ICC chapters, and others.

http://www.cityofberkeley.info/uplo...CDWG PLAN A 121305_new_2-15-07(Darker)[1].pdf

John

 

[csd72]

josta,

I dont see how that second post relates to the first one.

I tend to agree with the plans examiner on this one. I have never been able to get in enough nails to make two timber members act composite in bending, particularly over such a short length.

Do the numbers and you will se what I mean.

 

[josta]

csd72, thanks for your response. I understand about making two timber members acting composite in bending such as in a beam but I don't see how that principle applies to a mudsill.

The second post from Berkeley shows the exact method of retrofitting that I use, "validation" I guess.

 

[RVSWA]

josta, I believe your solution addressed the necessary force transfer from the sheathing to the concrete.

 

[msquared48]

I agree with csd72 here, but for a different reason.

Part of the reason for the 3X member, or two continuous 2X members, is to limit the chance of horizontal splitting of the sill plate due to horizontal shear from the anchor bolt bearing. With blocking taking the place of a continuous top plate, the chance of splitting of the blocking is substantially increased due to the proximity of the bolts to the numerous ends of the blocking.

The better solution would be to shore the wall, and cut the studs off 1.5 " to accept a continuous new plate. Hard? Yes, but much better in the long run.

Mike McCann
MMC Engineering

 

[msquared48]

The alternate solution is to have sheathing on both sides of the wall that only require 2X edge members for nailing, assuming that the capacity to resist the required shear will be there.

Mike McCann
MMC Engineering