Replies

1. 
   abbysdad | Nov 06, 2007 09:36pm | #1

   There are minimum codes and standards for such a thing. I'm not aware of any easy guides other than what you'd find from an organization like ASCE or ACI. retrofitting masonry structures for seismic concerns can be difficult. It's typically best to consider such things when the structure is built. But since that's not possible for you, check with your local agency or department for what they recommend or require.

   The trouble with brick in an earthquake is that you'll probably have to worry about both vertical and lateral movement. Depends on where you live and what standards you need to apply to the structure. Are you east coast, central or west coast?

   Also, what type of chimney design is it? Is it visible from the outside of the house or is it all internal? Many of the easy options I'm aware of are not that attractive.

   The quickest and best option I've seen involves laminating unidirectional fiber reinforced composite sheets to the exterior of the brick surface with a strong epoxy and then covering it with a fire protection/intumescent coating. This is similar to what DOT's use in retrofitting piers for highway supports in CA and PA. They also use it in foundation repairs.

   But it is not a typical DIY project. It's not even a typical contractor project. The benefit is a slim profile (only protrudes about 0.75 inch from the surface), excellent weather resistance, and support against both vertical and lateral movement and no drilling into the old brick (which means no cracks in the bricks/mortar that can fail during an earthquake!). The disadvantages are you've covered the brick, it needs a lot of staging to be done properly (winter or summer), the fumes are pretty nasty and it can be expensive.

   Hope this helps.

   Best Regards,

    Chris

    

1. 
   canon | Nov 06, 2007 09:44pm | #2

   Chris, Wow, that's an approach that I haven't heard about. I will check with the groups that you mentioned for advice. Thanks, Bob

2. 
   canon | Nov 06, 2007 10:05pm | #3

   Chris, You asked for some clarification on the project. I am in Mountain View, Ca, about 10 miles East of the San Andreas fault and about 10 miles West of the Hayward fault. Either one could go anytime as they are both "past due" for movement. The chimney is external and extends about 6 feet above the edge of the hip roof. During the 1989 Loma Prieta quake, most brick chimneys failed at the point where they lost contact with the roof. Some fell out into the yard and some fell onto the roof or through the roof and into the house. I am not trying to keep the chimney from falling, I just want to keep it from falling into the house. Your plan is intriguing and while we would loose the brick finish, we would wind up with a monolithic structure. Since the house is stucco, I guess that it could be covered to match the home's appearance. This sounds like a very specialized project that not just any contractor should attempt, so do you have suggestions as to the best places to look? Thanks so much for all your time. Bob

   Edited 11/6/2007 2:07 pm ET by canon

1. 
   abbysdad | Nov 06, 2007 10:25pm | #4

   Yeah, that chimney sounds like something I wouldn't want falling into my roof either.

   Check out: http://www.fyfeco.com/

   They should be able to help point you in a direction. I've worked with them before on other projects for larger scale issues and they are a good company.

   Masterbuilder and other companies have similar products. The contractor local to my area in Pittsburgh that does it is called "A Better Choice". They do the foundation repair and preservation work on the local Frank Lloyd Wright structures.

   You might call them for advice or how to find a dealer in your area. Here's their url: http://www.abetterchoiceinc.com/structure.html

   The product as it's sold for residential uses is called a Fiber, or Fibr, Strap. It's typically made from pre-preg fiber glass, carbon or kevlar fibers. The epoxy as it's applied is typically an isocyanuarate that puts off a lot of heat while curing.

   You'd probably have to find a PE or structures guy in the area to estimate the mass of your chimney and what would happen under typical earthquake conditions. I would insist on stamped and reviewed plans/drawings to make sure you didn't go through the effort for nothing. Then the contractor would be able to order the strapping to specs and apply it.

   Good luck.

   Chris

2. 
   popawheelie | Nov 06, 2007 10:32pm | #5

   I grew up in L. A.. In the Northridge earthquake of 94 a house up the street had a large chimney fall right through the middle of the house. They were Alright but the house was leveled.

   Chris has the right idea. You need to encapsulate the brick before you brace it. And the bracing needs to be strong enough to withstand some pretty heavy loads.

   I remember shortly there after they started re-enforcing the concrete columns that supported freeway overpasses. The concrete was strong and there was massive amounts of steel in them but if they were overloaded the concrete would just fragment off the steel. So they started welding steel plating over the columns to encapsulate them. You would still have to replace the column but you wouldn't have the complete catastrophic failure.

   Your chimney reminded me of them. You might have a pile of bricks inside the re-enforcement but it wouldn't fall through your Roof.

   My brother built a brick chimney after the codes changed. He had to have rebar all the way from the footing to the top of the chimney without any breaks. It was a pain to have these three story long rebars around when you were trying to build. He tied them together and looped them back down to themselves.

   Considering the cost of retrofitting it you might just consider demoing it and replacing it with a metal chimney. That's why nobody is building real chimneys anymore.

1. 
   abbysdad | Nov 06, 2007 10:50pm | #6

   Yeah, I was in CA during that earthquake. I have a great memory of my Dad sleeping through the aftershocks. I was scared and tried to wake him up. He said, "You know Son, I think we're having an earthquake." And then he rolled over.

   Back to the discussion...the beauty of the fiber composite option is that properly applied you put the whole masonry unit in compression so there is no crushing and the strapping stiffens the chimney or wall so that it doesn't oscillate as much or break during an event. It makes a monolithic and incredibly strong structure. That's why the technique has replaced the steel plating you mention at a lot of DOT's.

   But I agree with your point. All options should be on the table. If it cost less to demo and rebuild, I'd think about doing it. But not every chimney is a good candidate for that kind of work.

   I hope that in the future we have some easier options, like the simpsons strong walls and shear walls, for masonry units and brick work.

   Best Regards,

    Chris

   P.S. For the record, I'm a forensic and structural engineer at a company that does not sell or use the fiber composites I'm talking about.