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Re: Paso Robles and other earthquakes 1

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Richard,
 
I agree regarding the properties of stucco and drywall.  However, here are my reasons not to use stucco/drywall shear walls.
 
Nowadays, the homeowners (and their lawyers) want the damaged walls to be restored "exactly as they were."  They object to any attempt to repair the stucco (although, as we know, the crack repaired with construction adhesive is stronger than the surrounding intact stucco...).  So, it is much easier for everybody (including contractors) just to "shear" everything with plywood as it was recently discussed on this list.  In this case, there cannot be any objections to stucco and drywall repairs.
 
The important part of all of it is that the currently existing earthquake insurance is, eh, not quite what it seems to be.  At 15% deductible, the homeowner is pretty much on his own with repairs...  
________________
 
This earthquake was really weird, and IMO could damage even adequately designed/built structures. I saw a house that did the following: 
 
Jumped up as a whole (strange for a very large, but flimsy one-story structure, even without anchorage to footings);
The perimeter footings spread out along one axis;
The house came down, landing inside the perimeter footings (not quite missing them, though); 
About 30-to-50% of interior piers (obviously, not even nailed to baseplates and floor beams) were dislocated or missed during the fall.   
The soil around the house shifted about 1.5 inches and left fissures;
The stone chimney shifted 1.5" - as a whole. 
Other than that - the house was amazingly intact!
(The house was on sand, with water table about 12" below grade).
      
I did not see anything like that after Landers, Northridge, and Hector Mine earthquakes...
 
Steve Gordin SE
Irvine CA 
 
 
  
----- Original Message -----
Sent: Monday, December 29, 2003 2:28 PM
Subject: Re: Paso Robles and other earthquakes 1

Steve,
Thanks for the report even it you didn't say what their religion was.  ( sorry but I was beginning to think this list had changed to a philosophical discussion medium).
Seriously, I would not give up on stucco and drywall completely.  They are good products if designed and installed properly.  Was the stucco attached to "self furring" lath?  And was it nailed (through the drip screed where staples will not penetrate) to the sill plate?  Also, did the design take into account the torsional deformations at the plan irregularities and where the second floor terminated at a two level high ceiling section?   I have seen our building code changed in the past to increase demand and prohibit materials when what is needed is better design and structural observation (without having to get permission from the architect), all of which require that engineers not only learn what to do but also require higher fees to perform the detailing and observation necessary.
----- Original Message -----
Sent: Monday, December 29, 2003 11:52 AM
Subject: Paso Robles and other earthquakes 1

 
The original message was too long, so I divided it in two, and removed the attachment...
 
Part I: Happy Holidays!
 
I just came from the Paso Robles Area where I was inspecting damage after the recent earthquake.  Here are some observations from the site.
 
Several newer - and quite expensive - houses sustained substantial cosmetic and even some structural damage which I would not expect from such structures.  Generally it proved to me that drywall and stucco shear walls should not be used - especially in irregular houses - no matter how low the calculated forces/stresses are.  
 
I also observed distinctive soil damage that I did not see a lot during Northridge.  In one instance, a three-car garage, separated from the main house by a breezeway, visibly settled more than 1 inch (without any substantial damage/distortions inside it!).  The garage was obviously built on fill while the house proper had a sub-grade level with retaining walls.  Strangely, the house is about 15 years old, and never had settlement problems (no noteworthy old cracks in stucco).
 
The other case was even more amazing - a 3000 sq. ft one-story house on a flat lot on top of a hill (as many of them are in that beautiful country, imagine the view).  The house sustained very little - barely any - damage to the superstructure, in spite of heavy tile roof, brittle finishes, and irregular shape/composition.  But the slab it was built on cracked intensively - long linear cracks in, and under, ceramic floor tiles.  Some of the cracks have vertical offsets up to 1/2." 
 
There was some evidence of topsoil fissuring and distortion/shifting of the underground pipes; a large swimming pool had drained since the earthquake (in 7 days). 
 
It looks as if the apparent underlying rock-like shale was shifting along its weak planes...  Can it happen that way? And if so, why so little damage to the superstructure?    
 
To illustrate the force of that earthquake: a crew-cab F150 was parked in the garage (naturally, a 10-car garage).  The sectional door is now bent and would not open - apparently, because the truck was slammed against it from inside, and then was pushed back (~36" amplitude movement).  All that is verifiable by clearly visible tire marks on the garage floor.   
 
Also, it was nice to see the tower in the downtown Paso Robles already replaced with a wood-framed OCB-sheathed one.  BTW, a very neat job, and, obviously, much safer structure (attached)... I presume it is the one that collapsed and was in all news.
 
Other than that -
 
Happy, Healthy, Peaceful, and Prosperous New year to all. 
 
Steve Gordin, SE
Irvine CA