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- To: <seaint(--nospam--at)seaint.org>
- Subject: Pictures needed of Seismic Damage to Residential Construction
- From: "Dennis Wish" <dennis.wish(--nospam--at)verizon.net>
- Date: Fri, 11 Apr 2008 23:10:51 -0700
I live in an area that is right on the west edge of the San Andreas Fault – the Coachella Valley (Palm Springs California area). As much as this area is a high risk for a major seismic event, the builders, framers, owners and developers are rather complacent about the potential damage. This stems from a number of reasons including:
1. The Lander’s Earthquake in the late 80’s occurred more than 70 miles from here and the damage from the moderate seismic event caused no real damage in Palm Springs to Indio area other than merchandise falling from the shelves of stores and some minor damage to adobe structures.
2. The last recorded moderate event reaching over 6.5 on the Richter occur in 1940 as the Imperial Earthquake. Again this too far from this area and at the time, the area was undeveloped so that whatever motion may have been detected would have had little recorded effects due to sparse nature of the development of the area.
The Desert Sun and Cal Tech have been warning the residents of the area that we are long overdue for a major earthquake, but it does not seem to faze those who were not in Los Angeles or Bay areas during the moderate events since the Sylmar Earthquake in the 70’s through the Northridge quake in ’94.
When I do a remodel and inspect some of the developments constructed in the 1950’s thru the 1970’s I’ve noticed that many of the interior (and some exterior bearing walls) are secured to the slab with PAF nails. Anchor bolts are few and far between. I have a number of times run across interior partitions that support ceilings only. There may be an attic and in some cases the high-roof beams are supported by nothing more than 4x4’s at the splice that are continuous through the interior non-bearing wall and simply resting on the mud sill.
Lately , I’ve run through much opposition by the owners and their contractors who do not want to do more than they have to – in other words they don’t want to reinvent the lateral design or even the anchorage of walls bearing at least the weights of massive ceilings. In the latest remodels I’ve written the owner who I signed directly with and received authorization to design HTT-22 connectors from the posts into an epoxy connection into a continuous foundation found below the slab. This will prevent the post from walking. In the latest remodel, the owner is invest over $250K in the remodel that included my removing all interior walls (with a few exceptions) to redesign an interior post and beam kitchen / Living room open plan with stepped up ceilings. All of my beams and columns are adequately secured to the foundations that I ended up having to add, but three interior walls are constructed to either bear the load of the ceiling on the double plate of the wall or have a 2x ledgered to the double 2x top plate and studs in the wall with ceiling joists flush framed to the ledgers and secured with LUS type connectors from the early 70’s.
The problem is that the walls are secured to the foundations below the slab with PAF fasteners rather than anchor bolts. This was one of the most common causes of damage that I noted in the Northridge earthquake while I was evaluating and doing repairs. The walls sheared the PAF nails and jumped out-of-plain often bringing down ceilings, landings, stair stringers etc. In my current job, I was able to exert some authority on the job to convince the owner to do the additional work pointing out that while his HOA may be responsible for the earthquake damage to the duplex, they could argue that since he remodeled either the remodel contributed to the damage or that he had the opportunity to correct the damage when the walls were opened and exposed. I am off the hook because I put it in writing that it was necessary and an inexpensive insurance considering his investment, but I often come to a brick wall when either the builder does not believe it because they think they went through a great earthquake when Landers hit 70 miles away or that they felt Northridge knock them off their feet from 150 miles away. The idea that they have not conception of the power that those who were living in the San Fernando Valley experienced from a moderate earthquake does not exist.
I thought if I could put together examples of the various types of damage that we encountered (my pictures were accidently lost in a clean out years ago) I could have something more concrete to share with clients to convince them to put their money where it cannot be seen but will protect their investment many times over.
If you have any Jpeg or other pictures of wood frame damage (especially interior walls or in conventional prescriptive construction) that can be e-mailed, I would greatly appreciate receiving them. I will post them but mostly I will create a PDF volume that the clients (anyone’s) can use to display the damage that we expect but have never experienced in this region – especially for the thousands who spend their winter’s here from the Midwest and East coast who have not experience with earthquakes.
Please let me know if you are willing to share your photos with me. Whatever I post I will list the photographer and source on in the PDF guide so others will know where it came from.
Thanks in advance.
Dennis S. Wish, PE
Dennis S. Wish, PE
California Professional Engineer
C-41250 Exp. 3/31/09
Structural Engineering Consultant
54625 Avenida Bermudas
La Quinta, CA 92253
760.564.0884 (Phone, Fax and Answering Machine)
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