Multi Story Wood Apartment - Unbraced Load Bearing Walls During Construction

[fhsmith]

We have several apartment projects in our office, and due to the cost of wood skyrocketing, we are sharpening our pencils to trim off the fat in our design. During that process, we decided to look into the construction phase of the projects due to a horror story we heard from a colleague at another firm (5 stories built, first floor unsheathed due to tenant space, studs looked like bananas).

What we are finding is that a single 2x4 or 2x6 doesn't have a lot of load capacity when unbraced (see attached). We have used a CYA general note about what is shown in our drawings is the final state, and stability of the structure while it is under construction is the responsibility of the contractor. We have previously not had an issue with walls during the construction phase, but upon our calculations, we see a potential life safety concern for the contractor and feel like we should cover this situation more explicitly in our documents. However, we are also concerned that we will get push back from the contractor due to either added labor/material costs or sequencing concerns with other trades.

My questions are:
1) What are other engineers considering during the construction phase of multi-story load bearing wood buildings?
2) What type of notes or details are you using to cover the construction phase of multi-story load bearing wood buildings?
3) How have the notes or details been received by contractors in the field and are they pushing back?
4) When observing construction in the field, are the contractors following the notes or details?

 

[phamENG]

I haven't had an issue with this, but I haven't had any mixed use wood projects, either. The contractors are typically good about sheathing as they go. You could always determine how frequently the studs need to be braced for construction loading and say something like "Contractor shall sheath walls prior to erecting more than one level above unless solid, horizontal blocking has been installed at xft on center vertically with a minimum of 4' of full height sheathing at each end of blocking" or something of that nature (the sheathing at the ends is a load path for the brace force - remember that if you just brace the studs to each other, they could all buckle together the same way!). They may not like it, but that's tough. I bet they'd dislike getting pancaked under 5 floors of improperly supported wood floors a whole lot more.

 

[kipfoot]

and stability of the structure while it is under construction is the responsibility of the contractor.

I think that in a contractor's mind, this means 'the framing won't tip over while I nail it together." He's not thinking, "I wonder if the kL/r is sufficient for these interior bearing walls under dead load."

I've not done wood framing over three stories, but I could imagine that you'd need wood blocking for DL at lower interior bearing walls. That is, if you expect a stud to be braced with gypsum board, you can assume that the gypsum board will not be in place until after the roof is on.

 

[Brad805]

I would expect the vast majority of the problems will be the topping mass and the presence of large quantities of construction materials. If they don't want to sheath a floor I would add row(s) of temporary strapping that ends at a brace point somewhere. I would stipulate that they are responsible to hire someone to design that, and 99% of the time they will put the sheathing up. Personally, I do not see much reason to leave off the sheathing for the horror story described. If you sheath one side only, the other still leaves you access. That sounds like a contractor that does not appreciate how mass accumulates. Fighting with wood trades is par for the course. Wood suppliers are the worst for following directions. They never appreciate how their parts may fit with other trades. I had a project recently where we had something like 40 wood saddles and the wood trade wanted to change the beam sizes to save a nickle. Their drawings were rejected a few times and then they gave us what we asked for.