by Howard Cook 1,231 views
The history and philosopy of the premier San Francisco Bay Area earthquake retrofit contractor with 16 years experience. Company founder Howard Cook was a FEMA Residential Earthquake Damage Inspector from 1989 to 1994 where he learned how earthquakes damage a house. He took the FEMA class on retroftting 5 separate times, teaches classes on earthquake retrofitting, cripple wall bracing, foundation bolting, and general earthquake safety for the Association of Bay Area Governments.
We will bolt a house, brace cripple walls, retrofit a soft story condition, provide complete earthquake retrofit engineering, and install seismic retrofits in Oakland, Berkeley,San Francisco, and all over the San Francisco Bay Area. We were featured in a PBS video on the Hayward Fault as well as the NewsHour with Jim Lehrer. Learn from us all you need to know about earthquake retrofitting and earthquake safety issures.
Homeowner's must be careful.
Lack of seismic retrofit building codes or special earthquake retrofit contractor licensing can cause you to pay thousands for an earthquake retrofit that will not work. How do you know if a house has been seismically retrofitted properly? This website will tell you everything you need to know about the right way to retrofit a house. We want to do all we can to provide you with the earthquakesafety you are seeking.
We will do everythig we can to protect your house from earthquakes. Owner Howard Cook teaches retrofit classes in the U.S. and Canada and helped develop a seismic retrofit building code see http://www.abag.ca.gov/bayarea/eqmaps/fixit/plansets.html Our 2 hour series of videos on retrofitting provide much needed educational videos on earthquake retrofitting in the San Francisco Bay Area. The videos show how and why converting cripple walls into shear walls will fully protect your house. In our pdf library at www,bayarearetrofit.com you will find an entire library of information relevant to residentuak seismic retrofitting. See our main website at www.bayarearetrofit.com for even more information.
by Howard Cook 1,164 views
Http://bayarearetrofit.com This PBS Channel 9 and NewsHour video reveals that a large earthquake in the Bay Area is overdue on the Hayward Fault. Earthquake retrofit contractor Howard Cook demonstrates how a seismic retrofit of a cripple wall into a shear wall can protect a house from earthquakes very economically. He points out that foundation bolting alone does not protect a home and also demonstrates and describes the three simple components that should be part of any effective retrofit. The video also explores soft story retrofits where homes have a living area above a garage.
Geologists and earthquake preparedness experts discuss the imminent threat posed by the Hayward Fault. They universally agree that seismic retrofitting in the Bay Area is the single most important thing we can do to prepare for a large earthquake.
by Howard Cook 569 views
http://bayarearetrofit.com/ Here Bay Area Retrofit describes your seismic retrofit proposal so that you can see the interrelation between the contract, the estimate, which breaks down the cost of the retrofit in terms of each installed piece of earthquake resisting hardware, and the drawing, which illustrates your retrofit design. The components on the drawing, such as foundation bolts, shear walls, transfer ties, and hold downs are all described in the contract with a cost break down in the estimate.
With this information you can in many ways decide how much retrofitting you want to do. Earthquake retrofits come in degrees of effectiveness and it is always better for your retrofit contractor to do some retrofit work, even if he can't do all the work dictated by the retrofit engineering formula found in video 9 http://www.youtube.com/watch?v=lWdr2Py22UY&list=PL0C5802141A
CD3CD5&index=9&feature=plpp_video rather than no work at all.
No matter what you do, if you are going to cut the cost of your retrofit, make sure and build complete shear walls. For example, you can't afford to convert 12 linear feet of your cripple walls into shear walls and can only do 8 linear feet. Make sure the shear walls are complete and that all of the retrofit components are there. Also, if you reduce the length of your shear walls, make sure the lengths are equal on all sides of the house. If the proposal from Bay Area Retrofit is not clear, please call us or email us off our website. We want to do all we can to provide you with earthquakesafety
by Howard Cook 3,392 views
The retrofitting principles discussed here only deal with the area under the floor. This is because most commonly observed earthquake damage is caused by inadequate lateral bracing under the floor. Under the house, there are generally almost no effective earthquake resisting elements such as bolts and plywood. The most critical part of the plywood shear wall construction is the attachment to the bolted mudsill. http://www.youtube.com/watch?v=z21rGNqxGp8&list=PL0C5802141A
Above the floor, interior finishes on the walls and partitions, though not designed to resist earthquakes, do in fact provide a lot of earthquake resistance and typically brace the house against serious damage. After a quake, wall and partition finishes may be cracked, doors and windows may be racked, and costly repairs may be required to restore livability to common standards, but damage above the floor is much less likely to result in a hazardous condition than would be found in a house damaged due to inadequate underfloor bracing. Effective underfloor bracing should keep your house from falling from its foundation. You should not expect that an underfloor retrofit will protect your house from earthquake damage above the floor.
Most homes need to be strengthened in three areas:
1. The cripple walls need to be braced with plywood.
2. The braced cripple walls need to be bolted to the foundation.
3. The floor of the house needs to be attached to the braced cripple walls.
All three of these components form a shear wall. If the shear wall is tall and narrow, you will also need hold downs to resist overturning. http://www.youtube.com/watch?v=s6HuzNvu8JM&list=PL0C5802141A
The plywood-braced cripple walls should be bolted to the foundation to keep them from sliding off of the foundation. It is not necessary to put plywood on the entire cripple wall. Knowing how much plywood and how many bolts to install involves the use of an engineering formula known as the base shear formula. http://www.youtube.com/watch?v=lWdr2Py22UY&list=PL0C5802141A
When evaluating bids from other companies like quakebusters and earthquake safety, you will find this information indispensable.
by Howard Cook 1,838 views
http://bayarearetrofit.com/ This video discusses the most important connection in any retrofit shear wall. There are four ways to make it, and practically every contractor uses the untested nailed blocking method, so you need to know what it is.
Different Ways to Build Retrofit Shear Walls
Retrofit plywood shear walls can be built in four different ways. The following shows those four ways starting with the least effective, and progressing to the most effective.
1. Nailed Blocking Method
This method nails 2x4 blocks between the studs into the mudsill. The plywood is then nailed to these blocks. This is the most common method used to attach the plywood to the mudsill. The
2x4 blocks are placed between the upright 2x4 studs and nailed onto the mudsill.
The plywood is then nailed into the 2x4 blocks at the bottom of the panel. The point of concern when using the nailed blocking method is that the blocks can split.
2. Stapled Blocking Method
This method is identical to the nailed blocking method except staples are used. The American Plywood Association recommends the use of staples. A report published by the American Plywood Association states: "Staples provide a method for developing high design shear values while still using 2 inch nominal framing. The small diameter of the staple legs is not as apt to cause splitting- of the framing as are large diameter nails
3. Reverse Blocking Method
Diagram 6 shows a shear wall made with reverse blocking. The reverse blocking method is quite effective in homes that have wide mudsills.
The 2x4 reverse block is nailed to the plywood before the plywood and 2x4 are installed on the cripple wall. Please note that the bolts and the shear transfer ties are not shown in the drawings below.
4. Flush Cut Method
With this method the mudsill is cut flush with the 2x4 upright studs with a special saw. The lower edge of the plywood is then nailed directly into the redwood mudsill as shown in Diagram 7. This method of building a retrofit shear wall is the method that most resembles the shear walls that have been tested in laboratories by the American Plywood Association.
"The flush cut and reverse blocking methods are the two methods that most closely resembles the tested shear wall configurations found in APA Research Report 154
Bay Area Retrofit does not ever use untested methods. One of four methods of converting your weak cripple walls will be used on your house and only one method has been thoroughly tested.. Make sure your earthquake retrofit contractor or seismic retrofit structural engineer uses this method when retrofitting your house.
by Howard Cook 2,495 views
http://www.bayarearetrofit.com/ Houses on level lots without cripple walls still need a seismic retrofit, even if they are bolted to the foundation. If your house was built after 1950 or so, and you know it is bolted according to earthquake provisions of the building code with a half inch bolt every six feet, (which was and still is the code) then go to http://www.youtube.com/watch?v=SEYfj3peLiU&list=PL0C5802141A
CD3CD5&index=11&feature=plpp_video to see how these bolted homes can benefit from a seismic retrofit.
However, many houses on flat lots do not have any foundation bolts; bolting did not become California State Law until the late 1950s. Up to then, some cities required house bolting, and some didn't. The way you find out is to crawl under your house, put your hand on top of the mudsill and see if you find any bolts. If they are spaced 6 feet apart then your house is bolted according to the current California Building Code. If not, you need a seismic retrofit that targets bolting the house to the foundation.
Houses on level lots without bolts are attached to the foundation with a type of retrofit bolting hardware peculiar to homes where the floor sits directly on top of the foundation. These homes usually only have 18 inches of crawl space under the floor so normal foundation bolts cannot be installed. This hardware has undergone rigorous testing and is certain to be effective in an earthquake and is the only retrofit hardware used by Bay Area Retrofit. Use of tested retrofit hardware is essential to a good retrofit. Another very important seismic retrofit components are called shear transfer ties, which are also thoroughly tested.
Some companies such as Quakebusters, EarthquakeSafety, and many others use a retrofit strategy called angle irons in lieu of the tested systems shown here. Angle irons are an untested system and are discussed in Video 13 http://www.youtube.com/watch?v=e3oo8FKzxFM&list=PL0C5802141A
by Howard Cook 789 views
Earthquake design, both for retrofitting and new construction, revolves some very simple engneering concepts that are easily understood by everyone. This video will give you the information you need to make sure your seismic retrofit contractor or engineer understands what these concepts are.
10 Overview of Residential Seismic Retrofit Methods and House Bolting according to Bay Area Retrofit
by Howard Cook 914 views
Review of videos 4-7, this video also has some brand new information on cripple wall retrofits in case you already think you know it all. This review includes a description of a cripple wall, how cripple walls collapse, why home foundation bolting alone does not provide earthquake safety, and why it is necessary to always build complete shear walls with a complete earthquake load path. Well built shear walls include house bolting, a special grade of plywood called structural 1 plywood, and shear transfer ties that connect the house to the shear walls. This is a summary of how Bay Area Retrofit installs seismic retrofits in East Bay and beyond.
by Howard Cook 734 views
Already bolted homes can suffer significant damage if not retrofitted. The building code requires newer houses be bolted 6 feet apart on all sides. When this happens the longer segments of foundation (usually on the left and right sides) have approximately twice as many bolts as on the short sides (usually on the front and back). Earthquake forces attack a house equally on all sides and each side must resist the same amount of force. Adding bolt hardware and shear transfers ties to the short sides now gives the house the ability to resist the same amount of force on all sides and the entire house is now twice as strong as it was before.
by Howard Cook 1,340 views
http://bayarearetrofit.com/ This video is based on research done on a life threatening structural conditionfound in hillside homes that caused many deaths Los Angeles in the Northridge earthquake. The City of Los Angeles has a special retrofit building code for these homes which the Bay Area is unaware of. http://bayarearetrofit.com/PDFs/L.A.%20Hillside%20Code.pd For this reason contractors and engineers can use plywood shear walls on hillside homes, even though actual earthquake damage and subsequent research has shown it does not work. Bay Area Retrofit is the only company in Northern California that knows how to retrofit these homes. The two most relevant documents related to hillside home retrofits are Voluntary Earthquake Hazard Reduction in Existing Hillside Buildings, which is the same as chapter 94 of the 1999 Los Angeles Building Code is available from the City of Los Angeles building department. The other document is titled Framing Earthquake Retrofitting Decisions: The case of Hillside Homes in Los Angeles available from UC Berkeley http://peer.berkeley.edu/publications/peer_reports/reports_2
000/0003.pdf written by Nels Roselund, a practicing structural engineer and two professors of engineering.
by Howard Cook 814 views
Seismic Retrofitofit engineers conclude that Angle Iron Struts are a terrible way to retrofit house. Business owner and engineer, Howard Cook, of San Francisco Bay Are business, Bay Area Retrofit discusses the specifics of why using angle iron struts are NOT the way to go to retrofit a house for earthquake protection.
by Howard Cook 1,027 views
See for yourself that the building department will approve earthquake retrofits that will never work and why you should do your own building inspections.
Business owner and engineer, Howard Cook, of the well-known San Francisco Bay Are business, Bay Area Retrofit discusses common, ineffective seismic retrofit strategies to avoid. Includes specifics with drawings and specifications by earthquake engineers. Why these strategies do not resist earthquakes.
by Howard Cook 272 views
Earthquake Safety through earthquake retrofitting and careful earthquake preparedness. Business owner and engineer, Howard Cook, of San Francisco Bay Are business, Bay Area Retrofit discusses how to protect your family, community by preparing for a large earthquake on the Hayward fault. Be prepared, by watching this video and taking steps to properly seismically retrofit your home.