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Seismic Retrofitting Of Older Homes Adapted from a presentation created by: Howard Cook, Bay Area Retrofit, Oakland CA Thor Matteson, Structural Engineer,

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Presentation on theme: "Seismic Retrofitting Of Older Homes Adapted from a presentation created by: Howard Cook, Bay Area Retrofit, Oakland CA Thor Matteson, Structural Engineer,"— Presentation transcript:

1 Seismic Retrofitting Of Older Homes Adapted from a presentation created by: Howard Cook, Bay Area Retrofit, Oakland CA Thor Matteson, Structural Engineer, Berkeley, CA Danielle Hutchings, Federal Emergency Management Agency (FEMA)

2 Wood-frame Construction: Whats The Risk? …after the last large earthquake in California there were few reports of structural damage to single-family homes. NOT TRUE! Times Colonist July 19

3 Magnitude 6.7 Considered Moderate $20 billion in residential damage most residential damage deemed preventable

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7 Construction view Forces on the house

8 House is supported on cripple walls Earthquake moves the foundation House rocks on the cripple walls House falls when cripple wall collapses

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12 Infinite variety of cripple wall configurations in homes built before building code standards introduced Design and retrofit installation is unique to each Retrofit engineering principles make it possible to retrofit a house no matter how its built

13 Earthquake forces pass through various structural components and their connections as they travel from the floor to the foundation

14 Ç Ç House fell 6 feet because somewhere the load path from floor to foundation failed Interior walls, plumbing and electrical systems suffered catastrophic damage An effective load path would have resulted in house remaining fully habitable

15 Plumbing, wiring, plaster… all severely damaged after 6 foot collapse

16 Establishes how much earthquake force the base of a house will be subjected to Properly retrofit house must be able to resist this force

17 Retrofit of 2,000 sq ft two-story house using the Base Shear Formula

18 The amount of plywood and hardware used in previous example is calculated by dividing its shear value into 8,000 Shear value of H10 shear transfer tie = 585 8,000 / 585 = 14

19 1.Bolt cripple walls to foundation 2.Secure cripple walls to the floor joists 3.Install plywood shear panels

20 Bolting is only of value where walls have been braced with plywood The number of bolts is calculated to have the same resistance capacity as the plywood

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22 Bearing plates increase strength of bolt-to-wood connection SEAOSC Research

23 Oversized bolt holes are found in most existing bolt installations. More than 1/16 of an inch larger than diameter of bolt is considered oversized.

24 Caused by over-sized holes Over-sized holes are common because they allow builders to adjust the position of the mudsill

25 Foundation plates replace bolts where drill-space is unavailable

26 Movement prevented by shear transfer ties

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28 There are three ways to attach a plywood panel to the mudsill: Directly to Flush Framing The Nailed Blocking Method The Flush Cut Method

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30 2x4 blocks installed between 2x4 studs on 2x6 mudsill

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33 Improper nailing often causes wood splitting Pneumatically driven staples can be driven closer and reduce splitting at time of driving and when loaded in shear

34 Updated plumbing, wiring and structural modifications

35 Old-fashioned, inconsistent and odd framing

36 Replacing rotted or pest-damaged wood

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38 Shear walls with finished-to-match panels between

39 Anchor plates and shear transfer ties house to foundation

40 For more information please contact Marney Mutch Tel: M Howard Cook Tel:


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