ML20151H197

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Evaluation of Earthquake Hazard & Risk in Puget Sound & Portland Areas, Presented at 880412-15 Meeting in Olympia, Wa
ML20151H197
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Site: Trojan File:Portland General Electric icon.png
Issue date: 04/12/1988
From: Phyllis Clark, Perbix R, Perbix T
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NUDOCS 8808010180
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( OUTLINE FOR THE WORKSHOP ON "EVALUATION OF EARTHQUAKE HAZARD AND RISK IN THE PUGET SOUND AND PORTIAND AREAS,"

April 12 - 15, 1988 Governor's House Hotel Olympia, Washington by Todd W. Perbix, P.E. , Ratti Perbix & Clark, P.S.

Seattle, Washington SESSION 11 Group I Building Practises The purpose of this discussion group is to explore current practises for the reduction of seismic hazards in buildings; emerging methods of hazard reduction; future needs; and barriers to the implementation of hazard reduction.

A. Current practise

'. Methods of seismic rehabilitation in the Puget Sound area are undergoing constant evolution. Many jurisdictions regularly deal with the concept of seismic rehabilitation while others rarely, if ever, insist on seismic improvement of older buildings. There are no code formats currently in general use which adequately address the issues of seismic rehabilitation; consequently, the practising engineer is left Aargely alone to assimilate the increasing volume of technical and empirical data produced by ICBO, ATC, NSF, USGS, FEMA and others.

While doing so, the engina.r must develop a design philosophy consistent with competing bureaucratic and economic demands of the owner, architect, and regulator. This design philosophy is most often unstatad, and even if presented, does not meet contemporary standards of new building design even for life safety.

In large part then, the development of seismic retrofit is anecdotal and relies on practises which have developed validity simply by their repeated use. Puget Sound has, for the last fifteen years, renovated pri=arily masonry and wood-f rame structures; therefore, the practises 1 developed in these buildings hold credence for other, more complex building types as well. Following are the methods most of ten employed:

1. Anchorage, both of walls and parapets.
2. Development of global lateral systems, usually of a very stiff type, regardless of a building's site / structure response.  ;

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( 3. Anchorage of building elements, such as masonry infill walls, equipment and fixtures.

4. Development of horizontal diaphragas.

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5. Maintenance and enhancement of vertical continuity.  !

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6. Development of detailing procedures to mitigate hazards inherent  !

in irregular building configurations and pounding. j t

There have, in addition, been movements in the past to add elements of j ductility to otherwise very stiff strue?.ures; this movement is now  !

j largely discredited,

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j. B. Emerging practises  !

] Eaergent practises are currently focused on two basic elementst the' E

, development of code formate consistent with the high variability of l

older buildings and the development of practises which are more .

( responsive to the economic demands of rehabilitation as well as the  !

structure's likely existing performance characteristics. Each of I
these requires a great deal more development, particularly the developcent of even the most general rehabilitation codes for seismic j

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strengthening and the laboratory testing of more satisfactory l' rehabilitation methods. Several of these emergent issues include

i' Code developments such as ATC-14 which particularize the problems 1

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) inherent in the many older building types. These codes are f general; however, they have systemetized issues by building type

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} rather than the making of presumption, as contemporary building

! codes do, of a particular standard for building construction by

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2. The development of the analytic and technical tools to assess i

site / structure response and to provide systems which improve a l j building's existing qualities r.ither than si= ply providi an  ;

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entirely different way of behaving during an earthquake.  !

} 3. Continued development of inelastic analysis touls which better {

i reflect an older structure's charactertatics. .

4. The development of a progressive response philosophy by t i techniques aimed at providing structures with initial strength l l and ductility using as auch as possible their current resources. I The issue is to develop a least-to-most important level of '

deterioration within a building system tied to a philosophy for j- life safety and the economic life of the building.

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( In this regard, methods for improving building dt.ctility need to t be addressed. . Older buildings ara decidedly lacking it,this area 't I

and such methods as column jacketing and the addition of frames ,

where appropriate need to be discussed. ,

i i Also, techniques and design philosophies for the' improvement of 5 damping characteristics within structures are being explored. [

5. Experiential data bases are being refined to assess the responses i t

of retrofit acthods. Whittier, in particular, allows comparison (

of retrofit methods with unrenovated construction. i I

6. Base isolation may become practical in a limited number of cases t where the historic character of a structure is conpronised by

! conventional methods.

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