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RE: Terracotta Behaviour

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As I mentioned in my past post, Terrecotta has been used in the design of bearing wall systems here in the Los Angeles area. Those that are bearing wall are part of the state Hazardous Building programs that require them to be identified. Retrofit standards are left up to the local building officials, however, they are required to be retrofit within Los Angeles and most of Los Angeles County.
The design of URM bearing wall systems conforms to the Uniform Code for Building Conservation Appendix Chapter 1 - unless required otherwise by the local building official or if the building is listed on a historic registry.
The design of URM structures is much less restrictive than new construction - however their are to design proceedures that can be used upon the descretion of the engineer of record.
The Special Proceedure methodology is the least restrictive and assumes that failure will occur in the weakest element. Rather than strengthening the weakest link, all other elements are designed to the weak link failure. The thought is that these buildings exist and are used, in most part, for lower income housing and for affordable rent spaces. To try and bring them up to current code is expensive and would be detremental to ecconomy of the area's were most of these buildings occur. The allowable base shear used to design anchorage is generally around 0.10Wd or 10% of base shear rather than 30% based upon designing portions of a building.
 
The design intention is to try and maintain the structural integrety of the building sufficiently to allow people to escape. Once people are safely out, the building can be repaired or destroyed. It is purely a life safety issue, although there are no guarantees that the building won't cave in. Historically, retrofit buildings performed better than those which were not.
You might obtain a copy of the SEAOC Blue Book from seaosc(--nospam--at)aol.com . This is the document that the UCBC was dirived from. It explains your options should you wish to comply to a standard which is fairly well adopted along the US west coast.
 
One more thing: You might also contact Hilti Anchor about their veneer ties. They developed a pin that worked rather well with little patching required after installation.
 
Dennis S. Wish PE
 
-----Original Message-----
From: T [mailto:vicpeng(--nospam--at)vtcg.com]
Sent: Tuesday, August 11, 1998 2:18 PM
To: Seaoc
Subject: Re: Terracotta Behaviour

We are advising on the analysis parameters for a timber framed structure that has an existing terracotta (about 12" thick) wall.  One way is to consider the terracotta under guidelines for URM and check the recommended height to width ratios.  If we do that then the terracotta can theoretically be self-supporting except for support at foundation and roof level (single storey building). 
 
We understand that terracotta does not behave well under seismic events, in fact we have been told that it may even destruct "explosively".  We therefore considered the terracotta as a "veneer" and added the appropriate anchoring for veneers.  Here in Canada that means anchors at 2'-0" o.c. e.w.  That in turn means that we use a material seismic coefficient of R=1.5 by considering the terracotta as part of the structural restraint (i.e. therby reducing the deflection of the primary timber lateral support system to mitigate the impact on the terracotta) or R = 3.0 for the pure timber restraint system.
 
1)    Does anyone agree or disagree with either of these approaches?
2)    Does anyone have experience of the behaviour of terracotta during earthquakes?
 
Thank you.
 
Thor Tandy  P.Eng
Victoria  BC