Unreinforced CMU Foundations

[OldPaperMaker]

A few times each year I get asked to design modifications to a bldg, usually light frame walls with wood structural panels, that has a existing CMU foundation stem wall or bsmt wall that is unreinforced & ungrouted. Most of the time there is no bond beam at the top of the wall and no anchor bolts from the sill plate to the wall below.
I practice in the Puget Sound area of Washington (the State)and the structures are always in Seismic Design Category "D".
Table 12.2-1 in ASCE-7-05, Bearing Wall Systems, A-11 indicates that this system is "Not Permitted" (NP). I usually tell the client that they have to figure out how to reinforce the wall or replace it. Most of the time the client will try to find another engineer that will use the wall as is.
My question is: Am I correctly understanding the code requirements?

 

[Taro]

Many existing buildings do not conform to modern building codes. Whether they must be rehabilitated to bring them up to code often depends on the extent of the new work being performed and the policies of the jurisdiction. See IBC Chapter 34. The jurisdiction may also have dollar values or percentage of building values that may trigger an upgrade.

 

[JAE]

Agree - a lot of times you see something like a 20% of building's value as the remodel limit where the whole building would have to be brought up to code.

 

[OldPaperMaker]

Taro & JAE,
Thanks for the feedback. I understand section 3403.2 and the 5% increase in any structural element. The buildings that I am dealing with are usually homes that are 50 to 75 years old and the owners want to make extensive changes. Most of these buildings don't have any provisions for any lateral load paths. Basically, there is nothing to attach the anchor bolts for the sill plates and holdowns to.

 

[msquared48]

OldPaperMaker:

I, too am in the Puget Sound area and run into the same problem often.

Stick to your guns.

Mike McCann
McCann Engineering

 

[Taro]

I have done dozens of seismic rehabilitation projects in the Puget Sound area and throughout the western U.S. Many jurisdictions do not have well-defined policy regarding required upgrades and rely on the engineer's advice.

Seismic rehabilitation projects are usually voluntary. Politicians are often reluctant to enact mandatory seismic rehabilitation ordinances because of the economic impact and strong public opposition from owners. I believe Santa Monica, CA was one of the first jurisdictions to enact a mandatory URM rehabilitation ordinance almost 20 years ago but I have heard that there are still some buildings that have not been fixed.

My personal philosophy is to strongly recommend seismic rehabilitation if the remodel is extensive. The reasoning is that the owner is significantly increasing the service life of the building and therefore significantly increasing the probability that occupants will be endangered by an earthquake. But if rehabilitation is not mandatory and the owner is not willing, they will probably be able to find another engineer who will take the project.

 

[OldPaperMaker]

Thanks for the feedback from all of you on this subject. This seemed like a "no-brainer" to me but every now and then it makes sense to make sure that I am not being overly conservative with my assumptions.