13 Mar Secret #12: SEAU Recap – Residential Seismic Retrofit
A lot of older homes are in need of a seismic retrofit before the next earthquake hits. Here are some basics (adapted from the presentation by Barry H. Welliver, SE*) of what to know with a residential retrofit…
Building Code Basics
There are a lot of building codes and programs that provide important information for the seismic retrofits of residential buildings. Go check out topics pertaining to seismic retrofit using the following resources:
- Outline of mandated, triggered and voluntary requirements
- International Existing Building Code (IEBC)
- Seismic evaluation and retrofit of existing buildings
- ASCE/SEI 41-17
- Techniques for the seismic rehabilitation of existing buildings
- FEMA 547 – 2006 Edition
- Engineering guidelines for incremental seismic rehabilitation
- Fema 420 – December 2008 Edition
Another great resource is ‘The Utah Guide for the Seismic Improvement of Unreinforced Masonry Dwellings’. FEMA, SEAU, the Utah Seismic Safety Commission (USSC) and the Department of Public Safety put this resource together.
Client Relations
There is a stereotype that engineers have problems interacting with people. I don’t think that this is a fair stereotype, but I do think that sometimes it is hard to explain the complex analysis and design that is in our heads in a simple manner. However, the better that we are at expressing ourselves and our ideas, the better that we are as engineers.
In all honesty, your client will not know what they need to know. They will be naive and so the explanation that you provide needs to be effective. If they don’t understand the WHY behind the retrofit, they will not care WHAT the retrofit is. Sometimes they will understand that they need something but they won’t know WHAT they need to do.
You (the engineer) are the best resource that they have on the matter. But while you may be the best source of technical knowledge, it is important not to go too deep too quickly into the technical stuff. Focus on the bigger picture so they can understand what the concern is. Be sensitive to the anxieties that they may have moving forward with the retrofit.
Don’t be too prideful to recommend other consultants as well. There may be more information that they need in order to address the problem. They may need an architect, geotechnical engineer, or contractor to give them a better idea of the extent of their fix.
Unreinforced Masonry (URM)
A lot of older homes that require seismic retrofitting are unreinforced masonry structures (URM). Without any rebar in the masonry blocks, the only thing holding that together is a little bit of glue (aka grout) and the prayers of the homeowners.
The most costly repair of a URM structure is the foundations. Where foundation walls are made of rock, a concrete overlay will need to be added to the wall to reinforce it… Both sides if you are living in California. The fixes start from the foundation and go up to the walls.
Often times, the walls are also not attached to the roof structure which poses a problem when the walls want to move and the roof doesn’t move with it. I have seen pictures of homes where the walls have fallen outward, or worse they have fallen to the interior of the home. Ideally, the retrofit fix for connecting the roof framing to the top of the masonry walls will happen in conjunction with re-roofing. This makes it easier and more cost effective for the homeowner. The strengthening of the walls will take away of precious square footage in the house (added wall interior of the masonry wall), but safety of the homeowners is far more important.
We cannot fix everything when retrofitting a residential home due to budgetary constraints, but…
“Something is always better than nothing.”
– Barry H. Welliver, SE
‘Fix the Bricks’ Program
The average cost to repair a 2500 sq. ft. URM home with 2 chimneys is about $20,000. Fortunately for those local to Salt Lake City, Utah there is a program called ‘Fix the Bricks’ which will help pay up to 75% of the cost. The actual cost may vary from one home to the next but it is a substantial help to make the city a safer place. ‘Fix the Bricks’ is a hazard mitigation program designed to help homeowners with the costly seismic structural improvements to their URM homes.
Using grant money, they help homeowners to focus on the most critical elements of their home which include:
- Chimney bracing back to the structure, or filling them with concrete
- Fall protection of any other roof elements
- Wall bracing so that they don’t fall away or into the house
This program is doing a lot of great things in the community. It only takes one person or one organization to start passing along information that can help save lives. We as engineers have the responsibility to do the same in all aspects of our career. This is part of our ‘Code of Ethics’, which will be recapped another day.
Stay tuned for more SEAU recaps…
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*This information is adapted from Barry H. Welliver’s presentation entitled ‘Residential Seismic Retrofit’ given at the Structural Engineers Association of Utah (SEAU) Conference in Layton, Utah on February 21st, 2018. Barry H. Welliver, SE has been involved in structural engineering since 1973. After working at a few prominent firms, he established his own firm in California in 1979 called BHW engineers, LLC (www.barrywelliver.com). He currently resides in Utah where he runs his Utah office, while still maintaining his California office. Barry is very involved in the Structural Engineers Association of California and Utah (SEAOC and SEAU respectively). Barry is an advocate for seimic improvments in older existing building and is currently the chairman of the Utah Seismic Safety Commission (USSC).
I was not able to cover everything that was discussed, so I will may have to periodically come back and revisit these thoughts another day. In the meantime, the presentation can be found here: Residential Seismic Retrofit Presentation
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