IRC Design

[IE22]

Hi All -

I have recently gone out on my own and am learning the joys of the IRC... I am getting requests for "Tall Wall" design as the building(s) in question has walls that are taller than the prescriptive methods of the IRC. I can wrap my head around the extent of my responsibility when it comes to vertical and out of plane checks on the individual pieces. Things start to get fuzzy for me when in comes to the global lateral design. Do I just need to be designing the shear walls in the offending line(s) as they are the "noncompliant portion" per IRC R301.3 or do I need to do a full lateral design including the diaphragm and its connections to the walls?

In my head I could come up with a building, with tall walls, that has less demand on a diaphragm than a building with short walls, but say high aspect ratios or long spans between shear walls. The latter would not require any engineering. So I could see an argument that full design of the diaphragm may be excessive. However the engineer in me is having hard time just looking away from some of the things I am seeing on the plans presented to me.

Thank you in advance!

 

[phamENG]

This is a tricky area. You have to figure out what you're comfortable with.

If they're asking you to design the tall wall, are they asking for just gravity and out of plane loads, or are they asking you to design it as a shear wall? If the latter, the whole house needs to be engineered shear walls. Braced walls are not 'capacity' driven like shear walls. They're just part of an overall system of stuff that has worked. I'm sure if you dig deep enough you can find some papers written about the analysis that has been done along with testing of assemblies to work something out, but it won't be worth it for you. You can't figure out how much load is going into that shear wall unless you know how the load is getting there.

If they just want you to do pieces, be careful. Who is doing the rest? Do you trust them? If you're the only engineer - or maybe even the only registered design professional - on the job, you could be hauled into court over any structural problem that comes up whether you put it on your drawings or not. They may not get anything out of you, but it could be painful and expensive. So make sure you're comfortable with the ability of whomever is designing everything else. I try to avoid these types of projects - you either want me to design it or you don't.

 

[IE22]

Thank you for the reply. So far I have been the only design professional. The homeowners get house plans drawn and then the Building Department tells them they have to get the walls over 10' tall designed. My approach thus far has been to tell the homeowners that as I get into things my scope may need to expand until I get to a place where I am comfortable with calling the rest prescriptive. I warn them that I may end up touching the entire house. I provide a memo stating what I checked and that the rest is assumed to be prescriptive and built per code. So far that approach has worked but the project in question has a chopped up enough diaphragm that I don't think I can get it to work. I wanted to make sure I wasn't over stepping my responsibility before I talk to the homeowner about some suggested changes.

I agree on trying to avoid these types of projects as I too feel that if anything happens I am likely to be drug into court even if it for portions of the building that I did not design.

 

[phamENG]

As the EOR, your design responsibility is the greatest of what you think it is, what your licensing board thinks it is, or what the AHJ thinks it is. So even if the AHJ doesn't care about that diaphragm and is willing to call it prescriptive, you don't have to. The homeowner can fire you...but I'd rather get fired for insisting on correcting what I considered to be an unsafe/inadequate design than cave and let it slide. If somebody else wants to shoulder that, I'll let them.

Good luck.

 

[IE22]

Agreed. Thank you!