the expression of seismic design - curee · architects have many sound reasons for laying out...

Consortium of Universities for Research in Earthquake Engineering1301 S. 46th Street, Richmond, CA 94804-4698 tel: 510-231-9557 fax: 510-231-5664

http://www.curee.orgCUREE

The Expression of Seismic Designadapted from the 2005 CUREE Calendar

illustrated essays by Robert Reitherman

© 2005 CUREE. All rights reserved.

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Before a building, utility system, or transportation structure is built, engineers spend agreat deal of time analyzing those structures to make sure they will perform reliablyunder seismic and other loads.

The public, however, never sees the analysis, only the completed construction, andfurthermore, they can obviously only see the visible portion of the structure. While abridge or an industrial facility may sometimes reveal its overall structural configurationand some of its detailing, most buildings usually conceal rather than reveal theirstructures, including the seismic features engineers worked so diligently to create.

Why Structural Features Are Concealed

The concealment rather than the expression of earthquake engineering, thoughunfortunate, is usually for good reasons. Although steel is noncombustible, it quicklyloses its strength when subjected to fire: When heated to a mere 650°C (1200°F), atemperature easily exceeded in a fire in a building, a steel member loses more than50% of its strength. Quite prudently, the fire resistance provisions of the buildingcode require in many occupancies that all of the steel columns and beams be completelycovered up with fire protective insulating material. Seismic detailing of reinforcingbars makes it easy to distinguish between the seismic moment-resisting frame orstructural wall and its non-seismic cousin while the building is being constructed.However, that carefully analyzed and designed reinforcing is quickly entombed inconcrete. One of the Star Trek movies included a futuristic reference to transparentaluminum, but transparent concrete would actually be a greater boon to the expressionof seismic design of structures. Look up now in the room where you are sitting andyou will probably see a ceiling rather than the underside of the floor or roof structureabove. The ubiquitous suspended ceiling can perform several functions that are

necessary from a lighting and acousticstandpoint as well as provide a uniformvisual surface behind which a chaoticcollection of ducts, conduit, bracing wiresand struts, and pipes are concealed, alongwith the structure above. Some of thewalls in a woodframe building may havebeen designed by an engineer to belateral-force-resisting, with the necessarystructural sheathing, nailing, and hold-

The Expression of Seismic Design

downs, and some of the walls in other building may be reinforced concrete and designedas shear walls. However, the occupant can’t see the difference between the structuralwall and the nonstructural one once the interior and exterior finishes are applied.

Should the Seismically Designed Structure Look Different?

Even in its configuration and overall appearance, many times the building, bridge, orother structure designed for a site in a highly seismic region often ends up lookingmuch like its non-seismic sibling. This is not by accident. The hotel chain that hasgrown to like an efficient floor plan and the architectural style of its elevations directsits architects to lay out the hotel on the West Coast and in the Midwest to be about thesame. Completely hidden inside the walls and floors of the Western building is thestructure that is quite different from that incorporated into the plans and elevations ofthe building in a low-seismic area. The modern suspension bridge that started todevelop around 1800 in Europe and the Eastern United States was created, prior to theadvent of seismic design, for one job only: to efficiently carry gravity loads. Seismicresistance is usually now built into a suspension bridge without changing the basicform of the 1800s that proved so successful and marked the type.

Architects have many sound reasons for laying out buildings as they do and addingparticular stylistic touches. As architect Christopher Arnold has pointed out, the onlystructures ever designed and built simply to resist earthquakes are the specimenssubjected to simulated earthquakes in the laboratory. Markets, schools, apartmentbuildings, airport terminals, and other kinds of buildings each present their own longlist of functional requirements and reasons for existence. Being able to resist theearthquake that may occur every few decades or centuries is not the primary designdeterminant. Perhaps it is not surprising how seldom seismic design is elevated toplay a major aesthetic role.

Occasionally, however, seismic design takes on visible, expressive form, and that isthe subject of this essay. Whether the revealing of seismic structure was broughtabout through design intent or as a byproduct of other design motives, it is a pleasureto encounter these relatively rare examples that visually document the existence ofearthquake engineering. When the design intent is not to expose and accentuate theseismic system, the usual reason for revealing these earthquake engineering featuresis cost. Just as the George Washington Bridge in New York ended up with its steelspace-frame towers exposed because the intended stone facing was too expensive,

by Robert ReithermanExecutive Director, CUREE

This storage facility for a library has a frame and wallstructure made of reinforced concrete, but as the steelstuds are added, with insulation and interior andexterior finish material, the structure is concealed.Structural Engineers: Rutherford & Chekene

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most X-braces, buttresses, and other “seismic signatures” are put on public view simplybecause that was the easiest and least expensive design solution. Nevertheless, thepotential exists for making the expression of seismic design a creative and intentionalprocess, rather than an accidental byproduct.

Earthquake Architecture

It has been noted that today “earthquake engineering”is a common phrase (at least ever since the foundingof the namesake Earthquake Engineering ResearchInstitute in 1949) while “earthquake architecture” hasan odd sound to it. (Reitherman, 1985) However,exploring “earthquake architecture” is exactly whatAndrew Charleson of Victoria University inWellington, New Zealand has been doing for severalyears. (Charleson and Taylor, 2000; Charleson,Taylor, and Preston, 2001; Charleson, Preston, andTaylor, 2001; Taylor, Preston, and Charleson, 2002;Charleson, 2004; Charleson and Taylor, 2004).Charleson has documented the fact that “earthquakeengineering design issues can be used to influence adesign aesthetic, or in other words to generateearthquake architecture” with respect to newconstruction. In the case of a retrofit, earthquake architecture provides examples of“deliberately expressing strengthening structure so as to make a new and positivearchitectural contribution to an existing building.” (Charleson, Preston, and Taylor,2002, p. 417)

“Structuralism” is a term used by architectural historians to describe some instancesof modern architecture that made a conscious effort to reveal and accentuate thestructure. While the structuralism branch on the family tree of modern architecturewas always relatively small, with structuralist works by engineers such as Fazlur Khanbeing in the minority, it became a withered as well as small branch with the coming ofpost-modernism from the 1970s to present. Though expressing seismic structure ismerely a subset of the expression of structure in general, “structuralism” as found inthe architectural history books almost always consists of examples of the expressionof gravity-load-resistance, not seismic design. An example of the almost completeabsence of seismic structuralism from modern architecture’s structuralism is the waysome texts have admonished the architect to make corner columns noticeably skinnierthan the others—because they have beams framing in from only one side on a givenaxis and thus receive less gravity load. However, when seismic overturning and

orthogonal effects that put extra loads on corner columns are understood, this kind of“structuralist” aesthetic guidance to make corner columns skinny seems more like“anti-structuralism” to an earthquake engineer. Indeed, a major engineering challengecan be to deal with the columns or walls that have to resist less gravity load, ratherthan more, because of uplift forces generated by overturning moments.

The term “Earthquake Architecture,” as compared to “structuralism,” thus moredefinitively expresses the theme of the way the building or other structure is designedto respond to earthquakes, rather than only to gravity. This expression of seismicdesign features could also be called the Seismic Style or Lateralism. Borrowing fromSpanish and Italian we get the term “Terremotoism,” or from Japanese “Jishen Style.”Perhaps architects and engineers could use such terms and seismic expression themesas a “marketing handle, a simple name or acronym with which a fashion will bepopularized” in making their work fashionable. (Reitherman, 1988) While the term“fashionable” seems pejorative, it is the rare architect or engineer who intentionallytries to produce creations that are unfashionable. One of the few architects involvedin earthquake engineering circles as far back as the 1950s and 1960s, the late GeorgeSimonds of the University of California at Berkeley, explained that while “form followsfunction” is a common phrase, “in architecture, form follows fashion.” If it werefashionable to express seismic design, thereby educating the public about earthquakeengineering and sometimes allowing more efficient structural solutions, how couldthat be a bad thing? Ambrose Bierce cleverly pointed out the power of fashion whenhe defined the term in his Devil’s Dictionary: “a despot whom the wise ridicule andobey.” (Bierce, 1911)

The word “architecture” is often used broadly to refer to the visual aspect of a structure’sdesign, as when someone says they like “the architectural look” of a bridge, but it canalso be treated more precisely. Engineering professor David Billington of PrincetonUniversity has articulated in words, engineering formulas, and illustrations what hehas termed “structural art, which is parallel to and fully independent of architecture.”(Billington, 1983, p. xiii) Billington illustrates the concept of structural art by leadingthe reader through an examination of the designs of structures by engineers such asThomas Telford, Gustave Eiffel, Robert Maillart, Pier Liugi Nervi, Felix Candela,Christian Menn, and others. Insistent on distinguishing structural art from architecture,Billington documents the aesthetic design role that can be played by the creativestructural engineer, whereas the public, as well as many critics and historians, usuallyassume that the engineer “gives us useful things but only the architect can make theminto art....” (Ibid, p. 15) In the works by engineers that Billington cites, the beauty isnot a decorative effect added to the structure but rather a beautiful result of the engineer’sability to integrate “the three leading ideals of structural art—efficiency, economy,

Design project for accentuating, ratherthan concealing a seismic retrofit.

source: Andrew Charleson

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and elegance” (Ibid, p. 5), which is reminiscent of the classic phrase of Vitruvius in DeArchitectura 2,000 years ago: firmness (firmitas), commodity (utilitas), and delight(venustas).

Billington cites examples of the leeway a creative engineer has to shape a structuresuch as a bridge to make it more beautiful. A beautiful bridge does not automaticallyresult from engineering efficiency or optimizing. “Optimizing” is a term often used inengineering analysis, but like the term “unique,” there is exactly one thing that can be“optimal.” Real world design problems, and certainly those involving seismic designand the associated large array of structural alternatives for handling the earthquakeproblem, do not have only one solution. The term “optimizing” is really only a validdescription for a compartmentalized analysis step, a step that can occur only after theengineering design process has eliminated a vast number of variables, especially thoseobjectives like aesthetics that cannot be quantified, however valuable they may be.

While the examples of the expression ofseismic design shown here haveobviously been selected with photogenicappeal in mind, that expression can beaccomplished in commonplace as well asheroic ways. Seismic design, like theinfluence of climate and local buildingmaterials, can be expressed in an ordinaryway that results in a cityscape of pleasingharmony. Architectural historian StephenTobriner of the University of Californiaat Berkeley has pointed out that theexpression of seismic design need not beachieved by creating “earthquakemonuments.” The exposed plate washers,

nuts, and bolts on the outside of retrofitted unreinforced masonry buildings, for example,become commonplace in the urban background of many older downtown areas whereseismic retrofits are carried out. Cable restrainer retrofits on California freewayoverpasses are so ubiquitous some motorists may think the brand new bridge, thatdoesn’t need this retrofit, is actually an old one that hasn’t yet been retrofitted.

Buttresses

Seismic buttresses, (both those that “fly” and those that don’t), have numerous non-seismic precedents in architectural history. Santa Sophia (532 AD) in Constantinoplereveals its massive transverse-axis buttressing wings that resist the dome’s lateral

(outward) forces in that direction. Its logicalbalancing of thrusts and counter-forces perhaps ispart of the reason the massive unreinforcedmasonry structure has survived so manyearthquakes with relatively minor damage. Gothicarchitecture on a large scale, especially theastonishingly innovative cathedrals that began torise from the ground in France more than 800 yearsago (e.g., Notre Dame de Paris, begun 1163),would be almost unrecognizable if their flyingbuttresses were removed. The flying buttresses,or piers detached from the wall and connected atan upper level to the main structure, were used inthese European buildings to resist the lateral forcesof thrust from the masonry arches and wind fromthe tall wood roof with its great “sail area,” not toresist earthquakes. Nonetheless, they are aremarkable innovation in structural design to resistlateral forces, and they create a powerfularchitectural statement inside (where the largewindows allow more light than in a Romanesquebuilding) and outside (where they give the buildinga stony exoskeletal look).

With this long and venerable lineage, it is no wonder thatbuttresses are one of the most prominent and often-expressed features of modern seismic design. If the siteallows, positioning walls on the exterior rather thancrowding the interior can be a major practical advantagein retrofit projects. Thus, when the seismic hazard levelof the site of the nuclear plant at Diablo Canyon onCalifornia’s coast changed due to investigation of a newlydiscovered offshore fault, one of the major structures therewas seismically retrofitted with external fin walls, orbuttresses. The basic structural action of such buttressescan be understood without a degree in civil engineering,because they function about the same way as bookendsto keep the books from leaning over too far and falling.A bookend has to have a flange or buttress extending outsome depth along its back to provide this resisting force.

Ubiquitous scene of large washers and nutsanchoring seismic retrofit joist anchors, in an

unreinforced masonry building.

Plan and section through one flyingbuttress of Chartres Cathedral.

illustration credit: Arnold andReitherman, 1982, p.186

Diablo Canyon,source: Arnold and Reitherman,

1982, p.198

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The non-engineer can also intuitively understand that if this buttress or bookend isn’tsufficiently heavy or anchored down, some sort of structural alchemy that transmutesthe purely horizontal force into a vertical one will make the side of the bookend nextto the books lift up and the bookend overturn. Engineers similarly must deal with theoverturning forces on buttresses and work with geotechnical engineers to ensure thatthe sheer mass of the foundation and the tributary load to it from the superstructure, orthe anchorage of the foundation into the soil, can resist any uplift induced from lateralseismic forces, or control such rocking to a prescribed amount.

Diagonal Bracing

Along with buttresses, diagonal bracing isprobably the other most commonlyexpressed aspect of a structure’s seismicdesign. Indeed, the diagonal brace isvirtually a symbol or caricature ofearthquake resistance. Some schoolchildren are unfortunately taught a “lesson”about earthquakes when they build a stickmodel of a frame (columns and beams withno diagonals) and shake it down, then buildthe same model with diagonals inserted andit doesn’t collapse. The simplistic lesson isthat diagonal braces are good, and theirabsence is bad. Frames with column-beamjoints that are rigidly connected together toresist rotation are of course one of the modern engineer’s standard types of earthquake-resistive systems, providing excellent ductility when properly designed.

A moment-resisting frame structure with seismic inadequacies can only occasionallybe retrofitted with a diagonal bracing scheme—unlike what the K-12 student hastypically “learned” from their models. Yes, the diagonals quickly introduce lateralstiffness and stabilize the structure admirably for light lateral loading, but for largeseismic loads the braced stiffening of the structure may make it respond moreaggressively to shaking; buckling of the diagonals is an issue to be resolved; and theends of the braces impart large forces, alternating between tension and compression,at the beam-column joints. Diagonal bracing is a legitimate part of the vocabulary ofexpressive seismic design, but it should not be its logo.

Even if the public perhaps has an exaggerated opinion of the braced frame as theearthquake resisting structural component, braced frames are one of the valued member

of the structural engineer’s seismic tool kit, and onewhich when revealed to view can convey its seismicrole to the public as readily as the buttress. Anyonewho has ever propped up a newly-planted tree with afew diagonal sticks (or wires, analogous to the tension-only diagonal bracing scheme), has an intuitive idea ofhow this system works. Too skinny a stick and itbuckles when the tree leans over, a basic problem facingthe structural engineer. If the ground is too soft, theend of the stick can sink deeper and the tree can leanover farther, a fact the real life geotechnical engineerconfronts.

A type of concentrically-braced frame developed inJapan in the 1980’s (Watanabe et al., 1988), usingenergy absorbing and buckling-preventing concrete-filled tubes surrounding a steel diagonal, a system calledbuckling-restrained braced frames—is a visually subtle seismic design feature whenexpressed. “The basic concept of the Unbonded Brace is the prevention of compressionbuckling of a central steel core by encasing it over its length in a steel tube filled withconcrete or mortar. A slip interface, or ‘unbonding’ layer, between the steel core andthe surrounding concrete is provided to ensure that compression and tension loads arecarried only by the steel core....inhibiting local buckling of the core as it yields in

compression.” (Brown, Aiken, andIafarzadeh, 2001). Other braced framesincorporate damper devices into thediagonals. Perhaps when this seismic designfeature is expressed it is for the members ofthe public who are at the “connoisseur-levelof seismic design appreciation,” akin to themuseum patron who not only appreciates therealistic draftsmanship of a Leonardopainting but also its simulation of the hazeeffect to provide atmospheric perspective.There is nothing wrong with trying to elevatethe taste of the public, so perhaps the nextphase of expression of diagonal bracing willbe subtlety in expressing connections andspecial technologies.

The seismic retrofit of the Bennett FederalBuilding in Salt Lake City took advantage of thenew technology of buckling-restrained bracedframes. Architects: GSBS; Engineers:Reaveley Engineers.

Alcoa Building, San Francisco:X-bracing to resist earthquakeforces is expressed as the dominatevisual feature of this building.

photo: Darryl Wong (CUREE)

Expression of (a) reinforced concrete bracedframe resisting seismic loads, and (b) seismicseparation of the building into two structures,each with a separate lateral-force-resistingsystem. (San Jose Convention Center, SanJose, CA.)

photo: Robert Reitherman

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Moment-resisting Frames

A typical building with a moment-resisting frame looks the same whether in therelatively low seismic region of New York or the more highly seismic setting ofAnchorage or Seattle, because the frame is concealed behind the exterior finish materialson the outside and inside. The grid seen on the outside is the architectural grid basedon the fenestration. An X-ray view of the steel or concrete columns and beams in themoment-resisting frame behind is rarely a one-to-one match with the opaque verticaland horizontal metal or concrete cladding stripes seen from the outside. In most high-rises, for example, many of the opaque vertical lines do not have columns behindthem: The columns are often spaced 10 or more meters (approximately 30 feet) apart,but the window units, and the partition walls of the offices or residences that extend tothe perimeter, follow a module of much closer spacing related to curtain wallconstruction and typical office dimensions.

When the grid of a moment-frame is left visible on a building elevation, it is sometimespossible to spot the differences between the seismic and the non-seismic variety. Gravityloads are the same in a city with little seismicity such as Paris as they are in Tokyowhere earthquakes are a major threat. However, the moment-resisting framesconstructed in those two cities, if exposed, look different because of seismic design,with the first thing one notices being the husky proportions of the members in thehighly seismic city. Even from a block away, the columns on the non-seismically-designed building may look noticeably slender.

More subtle but more indicative of thisstructural system’s process of resistingearthquake loads are the details used atthe beam-column joints because ofcapacity design considerations. Theconcrete frame being built in a seismicregion reveals a profusion of rebarresembling a bird cage, and thus thereinforcing is given that nickname. Theterm, however, was not first used bystructural engineers designing reinforcedconcrete joints—it was coined to refer tothe close spacing of bracing wires on earlybiplanes. (Taylor, ed., 1970, p. 71). The steel frame may employ haunches, showingthat the protection of that joint area from the forces induced by building or bridgesidesway is a prime goal of the design. Recently, one may occasionally see the “dogbone” or reduced beam section introduced to force inelastic behavior into the beam,

away from the beam-column connection. The non-engineer can similarly understandthat the rigid connection of the leg of a chair or table to its horizontal wooden rail or“beam” is critical to the furniture’s stability—more critical than excessive deflectionor even cracking in that horizontal member itself.

Expression of Seismic Design, or of the Effect of an Earthquake,on the Scale of an Entire City

While most cities look the way they do and have taken on a particular urban-scaleform for reasons completely unrelated to earthquakes, there are a few interestingexamples where an earthquake has left its visible mark on an entire city.

Following the devastating 1755 Lisbon Earthquake (and fire, and tsunami), King JosephI provided broad power to his chief minister, the Marquis de Pombal, who in turn gavecarte blanche to two designers for the reconstruction of Lisbon, Manuel de Maia andEugenio dos Santos. At the time, engineering, architecture, and planning had not yetspecialized off onto their own educational andprofessional tracks. All three disciplines werewielded by de Maia and dos Santos to rebuild themain portion of the city (Baixa district) using thethen-novel city planning device of a grid of broadstreets. On the hills where the fire and tsunamidamage had not reached and efficient commercewas not a priority (Alfama) there remains to thisday Lisbon’s medieval city plan—i.e., no city planat all, but an incremental accretion of windingstreets and irregularly placed buildings. TheAlfama is arguably picturesque, but definitely aless efficient layout than that of the maincommercial and port district that was rebuilt. Theunified architectural style of the buildings in therebuilt Baixa district was also relatively restrained and free of decoration, perhapsfrom seismic concerns or perhaps for stylistic reasons. While the grid layout withbroader streets increased fire safety, Lisbon as rebuilt after the 1755 earthquake is notprimarily an example of intentional application of seismic design principles on thescale of a city but rather of the imprint of an earthquake disaster and how the cityscapewas completely changed by it.

Architectural historian Stephen Tobriner has written about a similar re-construction ofan entire city, Noto, after an earthquake in Sicily in 1693. (Tobriner, 1983) Thereconstruction was complete, with all its buildings designed in the “modern” style of

Expression of the actions resisted by a steel moment-resisting frame that has been added to a concretestructure as a seismic retrofit.

(Oakland Airport, Oakland, California)photo by Robert Reitherman

Lisbon, Portugal

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the day, Baroque. The motive was not an engineering one to design more earthquakeresistance into the buildings; the motive was based on a desire to adopt the fashionablearchitectural style of the time and create a beautiful city.

After the 1906 San Francisco Earthquake, a new city plan produced by one of themost prominent architects and city planners in the country, Daniel Burnham, wasconsidered but not implemented. It would have rebuilt the city on a French beaux artsor “city beautiful” model, similar to the way Paris was revamped by Baron Hausmanwith a series of broad radiating boulevards cutting through the fabric of smaller pre-existing streets. Had the Burnham plan been implemented, it would also have beenvisible documentation of the occurrence of the earthquake disaster, whereas the citywas rebuilt along pre-existing lines (literally along pre-1906 property lines). The factthat Burnham’s plan was actually designed slightly prior to the earthquake emphasizesthat it was not a reflection of seismic concerns, but rather part of the architecturaltrends of the time.

The Hawke’s Bay Earthquake in NewZealand of 1931 has a role in the seismichistory of that country somewhat analogousto the 1755 Lisbon Earthquake in Portugal,the 1906 San Francisco Earthquake inCalifornia, and the 1923 Tokyo Earthquakein Japan—it is the largest earthquake disasterin the country’s history, and it was dominatedby fire loss. The largest and worst-hit cityin the Hawke’s Bay region was Napier(Nape’-i-er), which suffered not onlyunreinforced masonry building damage fromground shaking but also losses from the firethat spread when the city’s water pipelinesystem was damaged. While that sounds

reminiscent of the 1906 San Francisco Earthquake, it is actually the 1933 Long BeachEarthquake in California that is most analogous in terms of the path of reconstruction:The 1931 Hawke’s Bay Earthquake and 1933 Long Beach Earthquakes set theircountries on the road toward adoption of seismic building code regulations and publicprograms to reduce earthquake risks. Although unreinforced masonry buildingscollapsed in the 1906 earthquake, this damage-prone type of construction wascommonly used in San Francisco’s reconstruction, whereas it was shunned after the1931 and 1933 earthquakes. For example, there are approximately 2000 unreinforcedbuildings today in San Francisco, a collection of a seismically hazardous type of

construction that has required significant retrofit cost and disruption of use and led tothe deaths of several people in the 1989 Loma Prieta Earthquake. All but about 100buildings in this troublesome inventory were built after the 1906 earthquake. Half ofthat seismically problematic building stock was built in the first six years right afterthe earthquake. (Holmes et al., 1990, p. 2-2)

Consider, by contrast, the case in Napier, where the lesson was noted that “the masonrybuildings were severely damaged in almost all cases, although the new concrete onesgenerally survived. Many of the deaths were caused by heavy parapets, gable ends orornamental features falling through the verandah roofs or directly on to people as inpanic they rushed out through doorways on to the street.” (McGregor, 2002, p. 19).The city was re-built in the then-current Art Deco style for architectural reasons, but toimprove earthquake performance, it was rebuilt using reinforced concrete rather thanunreinforced masonry, and with buildings typically one or two stories in height. Thisurban reconstruction pattern “suited the need in Napier for a safe form of constructionto protect the town from future earthquakes. The new buildings had to be of reinforcedconcrete, free of the decorative attachments that had fallen off and killed and injuredso many people in the Earthquake.” (McGregor, 2003, p. 2) Reinforced concretebuildings had performed relatively well in the earthquake and fire while the unreinforcedmasonry ones had often collapsed or dropped large amounts of brickwork. Woodbuildings had withstood the shaking well but were vulnerable to, and the chief sourceof fuel for, the fire. And steel at that time was usually limited to the occasional beamor truss, because it was not available in New Zealand at reasonable cost. The Napiercase is thus different than the others cited: The face of the city was changed partly dueto architectural stylistic trends and economic factors of the day, but also due to explicitseismic design concerns. Aside from the low-rise, reinforced concrete, Art Decobuilding construction brought about by the earthquake, the Hawke’s Bay Earthquakeis notable for another effect on Napier: the way it changed the very landscape, i.e., theway it literally made new land. Along with the generation of the magnitude 7.8earthquake, there were two meters of uplift in the area, causing 3,000 hectares (7,500acres) of the harbor to suddenly drain and become dry land rather than part of the sea.Today, the entire airport of the city sits on this earthquake-made land.

“Catawampus” Designs

Rather than express how a structure resists earthquakes—how strong, and resilient itis—one rather unusual stylistic option is to express the disoriented geometry of adamaged building. The real structure must be a safe and sober design to meet theseismic safety demands of the building code, but in appearance the building could bemade to look unstable and squiffy. While this design approach may seem implausible,some examples are presented here that have actually been built. They express the

Aerial view of destruction of Napier, NewZealand. Reproduced by permission fromRobert McGregor, The Hawke’s BayEarthquake: New Zealand’s Greatest NaturalDisaster; photograph from the collection of theHawke’s Cultural Trust, Napier, New Zealand.

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concept of earthquake damage, notearthquake resistance. The precisemotives of post-modernist architectPeter Eisenman in designing his NCBuilding in Tokyo may be debated, butthe resulting visual impact to anyonewith the slightest awareness of thehighly seismic context of the city isobvious: It looks like a damage photoin an earthquake reconnaissance report.The architectural cognescenti maydiscern in its design deep deconstructivist meaning (if that is not a contradiction interms), or a philosophical basis for architectural design that is sometimes called “anti-humanism,” or the post-modern intent to displace the building from any traditionalvisual or functional context. To the ordinary passerby, however, as well as theearthquake engineer, the building is a clever cartoon of the post-earthquake state of abuilding. To use the “technical” term sometimes used by the late John Blume indescribing buildings that had been severely wracked by large displacements, it lookslike a building that has been “knocked catawampus.”

Technological Devices

In most cases, these technological devices are not literally “earthquake-resistant”devices, because they tend to work on the demand side of the equation, not the resistanceside. Devices that add damping subtract seismic response; isolation systems keep alarge amount of the ground motion from entering the structure and becoming load inthe first place; active control, while still primarily on the horizon rather than a commondesign feature in actual construction, seeks to counteract the motions that begin tooccur in a building by generating forces acting in the other direction, split second bysplit second.

There are significant challenges invisually expressing such devices. Themost common place to install seismicisolators is in the basement—which is notvery often an area readily exposed topublic view. It will be some time before“come on down to the basement and lookat my isolators” will replace “come on upand see my etchings.” Isolators oftenblend into the shadows and look like a

traditional bearing or support to the passerby, even when exposed on a building orbridge. Use of color is one obvious way to accent these features. Active controldevices are usually hidden away on the roof or in a special room the way mechanicalequipment is always concealed from view.

In the recent design of a building in Italy that must perform so well in an earthquakethat it can be used to direct post-earthquake emergency operations, the EmergencyManagement Centre in Foligno, Italy, the overall configuration of the structure as wellas the use of isolators was clearly expressed. (Mezzi, Parducci, and Verducci, 2004)This requires care in the structural and architectural detailing and effective use ofcontrasting colors.

The Taipei 101 (101 stories) highrise in Taiwan, 509 meters (1670 ft) in height, holdsseveral “tallest building” records, including the highest occupied floor. Its tuned massdamper system consists of a large (6 meter diameter) steel sphere weighing 660 metrictons (725 English-unit tons), suspended by steel cables in a five-story-high space at anupper level within the structure. Theslight swinging of the pendulum systemoffsets much of the wind-inducedmotion that would otherwise beexperienced by occupants. Far frombeing hidden from view, there areinterior windows around this atriumallowing this unique system to beviewed from restaurants, bars, andpublic viewing areas. For very highwinds, and for significant earthquakes,the swinging of the pendulum isrestrained at the bottom of the sphereby a large steel pin 60 cm (2 ft) indiameter that engages piston dampersin a surrounding restraint ring. Otheraspects of the Taipei 101 structural design include its mega-column and mega-framelayout, in which the superstructure is composed of large multi-story units, that are saidto form an architectural effect resembling a bamboo shaft. There are eight of thesemulti-story units, matching a lucky number in Chinese. Especially at the base, thelarge built-up steel columns slant outward as they go down, which has a beneficialeffect in resisting lateral forces.

Taipei 101, Taipei, Taiwan. Architect: C. Y. Lee andAssociates. Structural Design: Thornton-Tomasettiand Evergreen.

NC Building, Tokyo, Peter Eisenman, architect

Emergency Management Centre, Foligno, Italysource: Marco Mezzi, et al., 13WCEE,

paper no.: 1318, 2004

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Efficient Configurations

The use of a regular rather than an irregular configuration perhaps seems a mundaneapproach to shaping a structure’s design to increase its earthquake resistance.“Mundane,” however, means ordinary, and ordinary means that a design solution canbe applied on a mass production basis to broadly provide practical seismic designsolutions across society, as compared to one-of-a-kind specialty designs. While theworld would be a dull place without stand-out structures and works of architecturethat make an aesthetic point at extra expense, mundane seismic features are needed tocontrol earthquake risk to a reasonable level on a societal scale.

While the major buildings that wereexposed to the 1906 San FranciscoEarthquake had no benefit of quantitativeseismic load calculations, theirperformance was relatively good, partlybecause they were “usually symmetricaland regular in their configuration.” (Shah,Zsutty, and Padilla, 1977, p. 8-9). “It haslong been acknowledged that theconfiguration, and the simplicity anddirectness of the seismic resistance systemof a structure is just as important, if notmore important, than the actual lateraldesign forces.” (Holmes, 1976, p. 827)While the seismic design rationale for aregular distribution of strength, mass, andstiffness in plan and elevation iscompelling in its simplicity, this goal is anything but simple to achieve: “Much of theproblem would be solved if all structures were of regular shape, but economics of lotsizes and arrangements, various planning requirements for efficient use of space, andaesthetically pleasing proportions require the structural engineer to provide for safeconstruction of various shapes.” (Degenkolb, 1977, p. 111) Today’s seismic codesusually enumerate cases of irregularity, with quantitative thresholds to define them, sothat engineers will take appropriate countermeasures. (BSSC, 2001, chapter 5). Whilethe building of regular configuration may not seem to express seismic design, it is oneof the most efficient seismic design methods of integrating architecture and structure.

Several aspects of configuration are relevant. In plan, an architectural layout thatdisposes the location of lateral-force-resisting elements symmetrically about the centerof mass helps prevent torsion. More precisely, the stiffness as represented by the

resisting elements both elastically and during inelastic behavior should have a centerof rigidity co-located with the center of mass. Resistance along the perimeter is muchmore effective than resistance that is only located toward the center to control whateveramount of torsion may occur.

A fundamental architectural determinant is the linear amount of wall made availableto the engineer and the number and spacing of columns. Rarely does the engineermake this configuration decision. The “structural plan density” is the “footprint” areaof structural elements such as columns and walls at a given level, as a ratio of the grossarea. (Arnold and Reitherman, 1982, p. 61). Given a greater structural plan density,the structural engineer has a larger budget of space for designing sufficient strengthinto the walls and columns. As an approximation, the ratio of floor area (which is asurrogate for mass and seismic load) to plan area of resisting elements (a surrogate forresistance) can be a useful indicator. This approach has been used in Japan with respectto concrete buildings to relate damage in the 1968 Tokachi-Oki Earthquake to shearstresses. (Shiga, 1977) Applied to small wood buildings and called the Effective WallLength Method, this general approach was implemented in Japan’s Aseismic DesignMethod building code requirements of 1981. (Sakamoto and Ohashi, 1988). In Turkey,observed damage to brick masonry buildings was compared with reference to a similarratio of length of walls (which were of similar thickness) and floor area to find desirableratios. Percentage of openings in external walls was another measure. (Bayulke,1978, p. III-76.) More recently, Hassan and Sozen (1997) re-visited this approach andapplied it to a different kind of Turkish construction, low-rise concrete, and studied anumber of buildings to compute their ratios of floor areas to areas of structural materialsin the columns and walls and then compare performance in the 1992 ErzincanEarthquake. In New Zealand, an approximate relationship of floor area (load) andlength of wall (resistance) results in a calculation of required “bracing units” that acontractor can easily understand for small building design. (Deam and King, 1996).In the USA, the CUREE-Caltech Woodframe Project developed an “Area DemandRatio” that was again a ratio of floor area to area of structural elements. Its purposewas as an evaluation or screening tool rather than a substitute for more refinedquantitative analysis. (Cobeen, Russell, and Dolan, 2004, pp. 72 ff.)

Complex plans with re-entrant corners (L-shapes, T-shapes, and so on) introduceproblems that require either special care in tying the structure together at those interiorcorners or introducing seismic separation joints. Another way of geometricallydescribing this irregularity is in terms of its concavity in plan. (Arnold and Reitherman,p. 231 ff.)

An architectural configuration induced by a cornerlot that causes torsional response in a building.

source: Arnold and Reitherman, 1982, p. 74;reproduced by permission of John Wiley & Sons

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Because ground motions may attack a structure from various directions duringearthquakes, efficient earthquake resistance implies an omni-directional deploymentof resistance. The protection of cutwaters around the bridge piers that extend into ariver can be designed to aim along one axis, but earthquake resistance requires a “circlethe wagons” design philosophy. Absent any capability to predict strong directionalityof ground motion—a pattern that would have to align the same for all earthquakes ofinterest—the goal becomes building equal resistance into a structure along all axes.Except for the rare building or tower that is circular in plan with uniform walls orframing, this is rarely feasible to a complete degree.

In the vertical plane, the most common configuration irregularity is a story that isweak (less strong) or soft (less stiff), or both, as compared to the story above. Theusual case is a ground story that is taller or has fewer columns and walls because it isa more open space: the lobby of the hotel as compared to the floors of lodging above,the cafeteria and large rooms of a hospital as compared to the patient floors above, thestorefront on the street level as compared to the offices or residential units with morewalls above. Setbacks also introduce discontinuities in strength and stiffness.

Cables

A cable more than any other structural component, clearly expresses the forces withinit. Consider the fact that a stocky piece of structural material used for a diagonal in abraced frame or truss resists either tension or compression at a given moment, butunless the resulting deformations and deflections are grievously large, the observercan’t tell the difference. A building or bridge column may be in compression holdingup the structure against gravity one moment and act in tension due to seismically-induced overturning the next, but it requires strain gages to detect the difference in theshape of the member from its tensile or compressive loading. A cable, however, cannever do anything other than take tension. As they say when someone is acting in aself-defeating manner attempting something impossible, “you can’t push on a rope.”The cable clearly expresses to the casual passerby the type of load it resists.

Bridges are where cables are most often expressed in a dramatic way, in eithersuspension or cable-stayed variants of the basic cable system. However, most cablebridges in seismic regions rely on their cables primarily or exclusively for verticalsupport: The cables oriented in a vertical plane do not provide the necessary horizontalstabilizing transverse forces. Lateral bracing is provided by other elements, e.g., bythe extensive horizontal bracing of a suspension bridge deck that can be seen whenpassing beneath it on a boat, or by the moment-frame or braced-frame structure ofeach tower. Auguste Roebling was prominent among bridge designers and constructorsin the nineteenth century for his use of diagonal stays to stabilize his bridges againstthe lateral and vertical forces of wind and the vibrations they induced, but that designfeature did not sire a line of seismic designs in the twentieth, though the use of seismic(rather than gravity load) guy cables remains an intriguing design option.

The Ruck-A-Chucky Bridge is perhaps the mostbeautiful and structurally innovative bridge that wasnever built. The bridge was designed by lead engineerT.Y. Lin (1912-2003) to span a canyon of the AmericanRiver that was to be filled with water by the constructionof Auburn Dam in California. The bridge becameunnecessary when the project to build the dam wascancelled. (Zuk, 1989)

The bridge design was a single-span arc 1300-ft (396m) long of 1500-ft (457-m) radius in plan. It had thatshape because of the need for a curving U-turnconfiguration of the highway that would cross thecanyon. Had a straight bridge been used, it would haverequired massive excavation into the canyon wall at eachend; had central piers been used, they would have hadto extend 450 ft (137 m) down to the floor of the canyonand would have been subject to large hydrodynamic seismic forces. (Lin, Lu, andRedfield, 1979) The curving structural form of the deck became an integral part of theseismic resistant system, acting as an arch when loaded toward its concave side and asa catenary when ground motion loaded it the other way. Cable-stays splayed outwardaway from the vertical axis of the bridge at each deck-cable connection point as theyextended upward to anchorages in the canyon walls. Thus each cable’s tension forcehad a lateral component (lateral vis-à-vis the transverse axis of the bridge at a particulardeck-cable connection location). In the typical suspension or cable-stayed bridge, thecables all run longitudinally over the straight-line alignment of the deck. While thegeometry of the cable layout of the Ruck-A-Chucky Bridge was unique, the lateral-

Soft story configuration of the original Olive View Hospital main building damagedin the 1971 San Fernando Earthquake.

source: Mahin et al., 1976

Model of theRuck-A-Chucky Bridge.

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force-resisting role of the cables was vaguely akin to the way John Roebling usedsplayed stays on his Brooklyn Bridge to stabilize it under wind loading.

Especially when one considers that the bridge was designed in the mid 1970s, thedesign is notable for its extensive investigation of the seismic hazard of the site andthe seismic behavior of the bridge. Ground motion criteria were developed by ProfessorHaresh Shah of Stanford University, considering possible earthquake sources within200 miles (320 km) of the site. Those ground motion criteria defined the motions usedon the UC Berkeley shake table to simulate the bridge’s response in studies of a 1:200scale model by William Godden (Godden, 1977). The shake table experimentationconfirmed the analytical results from dynamic time history analysis for the “HangingArc”: “The bridge is exceedingly effective in resisting all horizontal components ofground motion. The response of the bridge to the vertical component of ground motionis also small....Under any conceivable earthquake motion...the bridge will remainvirtually undamaged.” (Lin, Kulka, Chow, and Firmage, 1979, p. 141) An engineerinvolved in the analysis of the bridge concluded that “Lateral motions under bothwind and earthquake forces will be hardly detectable.” (Zung, 1979, p. 2018) Theform that provided such a bold expression of the bridge’s structure at the same timeprovided an extremely efficient structural solution for resisting seismic, gravity, andwind loads.

The design team for the bridge is quite a who’s who of engineers. Others involved onthe Berkeley faculty besides Lin and Godden included Ray Clough, Ben Gerwick,Milos Polivka, Alexander Scordelis, Brady Williamson, Edward Wilson, and a then-teaching assistant who was later to become a renowned bridge designer in his ownright, Mark Ketchum. Professors involved from other universities, besides ProfessorShah (and a then-PhD student of Shah’s, Charles Kircher), included Allan Firmage ofBrigham Young University, Jack Cermak of Colorado State University (wind tunnelstudies), Ronald Heuer of University of Illinois, Robert Scanlan of Princeton, andconsulting engineer Michael Praszker of San Francisco. One of the most prominentarchitects of the second half of the twentieth century to contribute to structurallyexpressive designs, Myron Goldsmith of SOM, was the consulting architect. (Lin, Lu,and Redfield, p. 37).

Coupled Walls

Thomas Paulay was the first to analyze and experimentally verify the precise way inwhich coupled structural walls resist earthquakes. He began his research in his PhDthesis at the University of Canterbury, research that by chance was underway whenthe 1964 Alaska Earthquake demonstrated what he was predicting on the scale of twoidentical 14-story reinforced concrete buildings. The Mt. McKinley and 1200 L Street

Buildings in Anchorage had numerousconnecting beams between walls. This wasa geometry created by the fenestration—the structural response (and considerabledamage) was fated by the architecturalarrangement of windows. Paulaydiscovered the flaw in the use of traditionalstirrup reinforcing in these stocky linkbeams and introduced diagonalreinforcement, which enabled structuraldesigners to design coupled structural wallsas effective energy dissipators and improveoverall seismic performance. Oftentimesthe architect lays out an elevation thatdictates coupled shear walls, rather thanseismic design intent being the seminal factor, but in the design of the tower for a newreplacement bridge for the eastern portion of the San Francisco-Oakland Bay Bridge,these coupling beams were intentionally introduced for seismic reasons and became aprominent aspect of the design. The approximate number of levels where these beamelements could be placed to connect the four legs of the mast was based on aestheticpreference; given that decision, the required deformation capacity of these sacrificialelements then was carried out to maximize seismic performance.

Tsunami-resistant Design

There is one seismic hazard that is not directly posed by the ground itself, a hazardwhich is neither ground shaking nor ground failure, and that is the seismic sea wave,or tsunami. The usual rule of thumb is that the best defense for construction to betsunami-resistant is location: Do not locate the facility where tsunami inundation willoccur. The flooding can be damaging enough in its own right, but tsunamis can makethe water flow with significant velocity, and debris may also cause impact damage.However, siting all construction away from low elevation areas subject to the occasionaltsunami is not always feasible. Three basic design strategies exist, aside from theplanning approach of using a safer location. Elevation of the bulk of the structureabove the water line is one approach, raising a building up on stilts, though this cantend to create a soft story for resistance to ground shaking. A structure can be designedlike a lighthouse to stand its ground against flowing water. And protective walls canbe used to shield a site from the water. All three options are unusual and challenging.As pointed out by the huge loss of life in the December 26, 2004 Indian Ocean tsunami,the most effective countermeasures are efficient warning and evacuation.

Large-scale coupled wall seismic testing specimenused by Thomas Paulay and his students at theUniversity of Canterbury.

source: University of Canterbury

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“Lateral Thinking”

The term “lateral thinking” was coined by Edward De Bono in a book using thosewords in its title over thirty years ago (De Bono, 1967), a book that explored complexcognitive processes that De Bono illustrated in such simple terms as “You cannot diga hole in a different place by digging the same hole deeper.” A problem can be visualizedas a wall that one tries to penetrate by pushing on the first door that appears, an approachthat can be frustrating if that is the wrong door. De Bono developed techniques to leta mind probe laterally around barriers to seek out innovative approaches. As usedhere, for an earthquake engineering audience, lateral thinking has a meaning relatedto De Bono’s original idea but it has another aspect as well: thinking about a structureand how it responds in a lateral way to an earthquake’s motion, as compared to oureveryday experience of our own bodies and of observing objects and structures aroundus that respond vertically to gravity.

The seismic kind of lateral thinking is also akin to the puzzles presented by De Bonoin his books: They can quickly tire one’s brain: It takes persistent as well as creativethinking to look at a bridge, for example, and imagine how that structural systemwould act if rotated through 90 degrees to lie on its side, and furthermore, instead ofone-way loading, to visualize how it would resist back-and-forth lateral loading.

The Ruck-A-Chucky Bridge presented elsewhere herein connection with cable systems is a practical exampleof such thinking.

There is one ubiquitous seismic-load-resisting structuralcomponent that engineers are taught to conceive of as avertical-load-resisting-system on its side that is loadedhorizontally, namely the diaphragm. Texts andinstructors for many years have explained the role playedby the floor or roof of a building in resisting earthquakesas a “beam on its side,” and application of beam theoryto its analysis then follows logically for the students.

What happens when one imagines the other basicvertical-load-resisting components turned on their sidesand used as lateral-load-resisting components? Moment-resisting frames, shear walls,braced frames, arches, cables—all can be treated this way, and some of these exercisescan result in design concepts of practical merit. For example, how could one make alateral-force-resisting element out of an arch bridge of the elegant type designed byRobert Maillart or Christropher Menn in Switzerland?

Conclusion

The thesis discussed and illustrated here is simple: There are many opportunities forexpressing the way a structure has been designed to resist earthquakes. This expressioncan be an efficient and integral aspect of the design, not an afterthought add-on thattries to make a visual effect without having a structural purpose behind it. None butthe structural engineer is expected to develop a deep and quantitative knowledge aboutthe vocabulary of seismic design—to know exactly how the braces, buttresses, andother structural features work—but the general public can understand and appreciatethat vocabulary in a qualitative way when it is clearly expressed. An attempt has beenmade here to outline some generic ways that seismic design can be expressed, butthose categories and the specific examples presented are merely suggestive, notdefinitive. Who knows what exciting new forms will be invented that can combineseismic efficiency with aesthetics, designs that are pleasing to the earthquakeengineering expert, the architect, and the person on the street? The expression ofseismic design is relatively uncommon, but not because engineers and architects lacksufficient creative talent: It is simply that they seldom set their minds to it.

A “Robert Maillart bridge designon its side,” design conceptsketch of “lateral thinking.”

source: Robert Reitherman

CONSORTIUM of UNIVERSITIES for RESEARCH in EARTHQUAKE ENGINEERING

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Buttresses

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Because buttresses protrude from the building or structure, they inevitably become a prominent aspect ofthe construction’s appearance. Fins or walls are one form of buttress that can resist lateral forces; the strut-like flying buttress is an alternative form.

[left] Buttresses includedin original design ofNewman Center,Berkeley, California;Mario Ciampi, architect.

Reinforced concrete flying buttresses, although theyappear to be an original part of the architectural design,were added to St. Dominic's Church in San Francisco toseismically retrofit the building; Rutherford and Chekene,structural engineers. photos by Darryl Wong (CUREE)


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Diagonal Bracing

A vertical column clearly announces its role in holding up gravity loads; a horizontal beam publicizes thefact it carries gravity loads across the space it spans. A diagonal structural member obviously has adifferent role to play--resisting lateral forces. When exposed, the diagonal bracing of a braced frame is agraphic expression of seismic design.

Diagonal bracing on the exterior of University Hall, University of California,Berkeley, proved to be an efficient and non-disruptive seismic retrofit.

(Degenkolb Engineers)

The external location and red color of thisseismic retrofit braced frame have a boldarchitectural effect on the Sather ParkingGarage, University of California, Berkeley.

Models of an intentionally emphasized seismicretrofit design; (Andrew Charleson, 2002)

The carefully detailed pin joint controls loadsto the foundation and is a striking addition tothe streetscape. (Degenkolb Engineers)


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Moment-Resisting Frames

The way a moment-resisting frame resists lateral forces may not be as obvious to the non-engineer as isthe role of diagonal bracing, and the moment-resisting frame almost always plays a vertical-load-carryingrole as well. However, the earthquake-resisting purpose such a component will be called upon to fulfillcan be appreciated when detailing for ductility is expressed.

14

Prestressed concrete moment-resisting frame building, theStudent Association, University of Canterbury, Christchurch,New Zealand. This 1968 building was very innovative in its useof prestressed concrete for earthquake resistant purposes.(Lyall Holmes, Structural Engineer)

The beam stubs on this building at the University of Canterbury,Christchurch, New Zealand, were designed to accomodatereinforcing steel anchorage. Congestion at beam-column joints isa problem with ductile reinforced concrete moment-resisting frames.

Testing of a reinforced concrete moment-resistingframe with "stub" detailing of rebar anchorage,University of Canterbury, 1981. (Department of CivilEngineering, University of Canterbury)


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Expression of Earthquake Impact and Seismic Design at the Cityscape Scale

The vocabulary of seismic design that can be used to make a statement on the scale of an individualbuilding or bridge can also be applied at the scale of an entire city. The reconstruction of Napier, NewZealand, after its destruction in the 1931 Hawke’s Bay Earthquake is a striking example.

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One of the city's new reinforced concrete buildings being built after the 1931Hawke's Bay Earthquake. Reproduced by permission from "The New Napier:The Art Deco City in the 1930s," Robert McGregor, The Art Deco Trust, 1999,p.3; photograph from the collection of the Hawke's Bay Cultural Trust, Napier,New Zealand.

Scene of earthquake and fire destruction of Napier, New Zealand. Reproducedby permission from "The New Napier: The Art Deco City in the 1930s," RobertMcGregor, The Art Deco Trust, 1999, p.2; photograph from the collection of theHawke's Bay Cultural Trust, Napier, New Zealand.

An example, of the Art Deco style that became prominent in Napier during the reconstruction followingthe Hawke's Bay Earthquake. Reproduced by permission of Robert McGregor, Art Deco Trust, Napier,New Zealand.


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"Catawampus Design"

While most expressions of seismic design are statements of how a building or other structure resistsearthquake forces, another approach is just the opposite--to express or simulate damage. To use the"technical" term sometimes used by the late John Blume to describe extreme damage, this results in abuilding looking as if it has been "knocked catawampus."

NC Building, Tokyo, Peter Eisenman, architect. Whether or not the architect's motive was to makethe building look like an earthquake engineering reconnaissance report case study, its location inhighly seismic Tokyo evokes that impression. photos courtesy of Christopher Arnold.

This museum in Orlando, Florida, Wonderworks, is housed in a building thatwhimsically simulates the devestation of a hurricane. photo: Wonderworks Museum.

The aesthetics of damage, partial collapse and repair wereexplored in this design proposal for an office building. Thebuilding is also designed to a high level of performance underseismic loads.

Luke Allen, Victoria University, Wellington, New Zealand

(Charleson and Taylor, 2004)


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Expression of Load-Reducing Technological Devices

Devices such as isolators or dampers lessen seismic demand rather than literally providing earthquakeresistance. Such devices are another opportunity for expressing a key aspect of a structure’s seismicdesign.

The Taipei 101 Building, Taipei, Taiwan. (Construction scaffolding at left).

[left] Installation of buckling-restrained brace,Bennett Building, Salt Lake City.photo by Reaveley Engineers & Assoc., Inc.

[above] Details of the Emergency Management Centre, Foligno,Italy. Reduction of mass with height is a desirable configuration.Isolators just above grade level are prominently featured.(Engineering by Alberto Parducci and Guido Tommesani)

The massive suspended damper sphere in the Taipei 101highrise is not only expressed -- it is put on display in an upperlevel multi-story glass atrium with restaurants and shopsaround it. Artistic rendering by D. Wong (CUREE) based onMotioneering, Inc. design.


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Efficient Configurations

The configuration of a building can either be a seismic design asset or liability. Regular structuralproperties that follow from a symmetrical layout allow for more seismic resistance and increase thereliability of the analysis of how the structure will perform.

Innovative suggestions by structural engineer Eric Elsesser for employing theentire building's geometry as an energy dissipative mechanism.

(Elsesser, 2004)

Loma Linda Veterans Administration Hospital was explicitly configured to produce anefficient seismic system. Some of the shear walls are located on the exterior as theside walls of the mechanical equipment cores. Architect: SMP and BSD; engineer:Rutherford and Chekene.

Beams line up with reinforcedconcrete "bookend" external core

walls, VA Loma Linda Hospital.Rutherford and Chekene,

structural engineers; SMP andBSD, architects. Reproduced bypermission of the publisher from

Arnold and Reitherman, 1982.

[right] Typical structural framing plan,VA Loma Linda Hospital. The overallconfiguration was the result of aconsideration of several alternatives, eachhaving different periods of vibration,strength, and stiffness characteristics.(Holmes, 1976, p.837)


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Structural Plan Density

The area of the structural elements, such as the area of the structural footprint at the ground level, is arough measure of a building’s capacity. The floor area of a building is approximately proportional to itsmass and its inertial seismic load. Thus the ratio of the area of the structural elements to the gross floorarea, the structural plan density, is a relevant seismic design indicator. The ratio varies greatly, dependingon style, era, and structural system. Buildings that would otherwise be prone to collapse in earthquakesare sometimes saved by their high structural plan densities.

1.

5.

6.

9.

Building, City, Date

1. St. Peter's, Rome, 1506-1626

2. Temple of Khons, Karnak, 1198 B.C.

3. Parthenon, Athens, 447-432 B.C.

4. Santa Sophia, Istanbul, 532-537

5. Pantheon, Rome, 120-124

6. Sears Building, Chicago, 1974

7. Typical contemporary steel high rise, 1975

8. Monadnock Building, Chicago, 1889-1891

9. Chartres Cathedral, Chartres, 1194-1260

10. Taj Mahal, Agra, 1630-1653

Ground Level Structural

Plan Density

25%

50

20

20

20

2

0.2

15

15

50

2.

3. 4.

8.

7.

10.

Reproduced from: Christopher Arnold and Robert Reitherman, BuildingConfiguration and Seismic Design (New York: John Wiley & Sons, 1982),pp. 62-63), by permission of the publisher.

100

50

25

0 200FEET

75

50

25

0METERS


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Cables

The beautiful and fascinating geometry of the Ruck-A-Chucky Bridge conveys the lateral-force-resistingrole played by its cables. In addition, its curving deck behaves as an "arch on its side" in resistingearthquake forces.

[left] Shake table model of the Ruck-A-Chucky Bridge.Photo courtesy of William Godden (Godden, 1977)

Models of the Ruck-A-Chucky Bridge.source: Mark Ketchum

Planned cable layout of the Ruck-A-Chucky Bridge.

1. PEDESTALS NORTH OUTSIDE

2. PEDESTALS NORTH INSIDE

3. STAY CABLES NORTH OUTSIDE

4. STAY CABLE NORTH INSIDE

5. NORTH ABUTMENT

6. BRIDGE SPAN

7. SOUTH ABUMENT

8. STAY CABLES SOUTH OUTSIDE

9. STAY CABLE SOUTH INSIDE

10. PEDESTALS SOUTH OUTSIDE

11. PEDESTALS SOUTH INSIDE

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

source: T. Y. Lin, H. K. Lu, and C. Redfield, 1979, p.32.


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Coupled Walls

What is ductility to the engineer is damage to the owner: Controlling the location where ductile behavioroccurs is the same as designing damage into that area of the structure. With proper detailing, the coupledwall system provides a large amount of energy dissipation, prevents major damage to the walls, or piers,and localizes repairable damage in the shear links.

Shear Link Test Setup: [left] Overall View,[right] Test Setup Geometry

[left] Tower Cross Sectionand Elevations: (a) MainSpan Elevation; (b) SectionA-A; (c) Transverse TowerElevation; (d) LongitudinalTower Elevation

[right] Link Geometry andDetails (Type 1)

source: C.-M. Uang andF. Seible, UCSD, 2003.

Planned San Francisco-Oakland Bay Bridge East Main Spansource: C.-M. Uang and F. Seible, UCSD, 2003.

Photo credit: Powell Laboratory, University of California at San Diego.

[above] Ductile shear link fabricated from different types ofsteel to customize its inelastic behavior; small scalespecimen tested to verify the design of the Bay Bridgereplacement span. (University of Nevada, Reno)


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The Shape of Tsunami-Resistant Design

One means of reducing the impact of a tsunami on a building is to elevate most of the solid area above theexpected depth of the tsunami waves. However, this must be accomplished without introducing a softstory when the building responds to ground shaking. The other basic construction strategy is to make thestructure strong enough to resist the loading from the tsunami.

This tsunami-resistant structure in Nishiki, Japan, provides ready shelter for people inthe harbor area who have little time to respond to tsunamis that quickly arrive fromnearby offshore earthquakes. The outdoor stairway leads to a safe elevation. Thelighthouse shape is desirable for reducing the loading of the tsunami. The tsunami'simpact literally includes the impact of the mass of the water or debris that has velocityimparted to it by the tsunami; in addition, there is the hydrostatic effect of waterpressure present on one side of a wall that forces that element to suddenly act like aretaining wall. Foundations must also be protected from scour.

credit: Harry Yeh, Oregon State University

The original design for this multi-unit residential building on the San Mateo County coast in California,shown prior to complying with tsunami zonation requirements. The overall construction type iswoodframe, with the earthquake-force-resisting system relying on shear walls in all three stories.

The revised, tsunami-resistant design: Only break-away trellis-like panels are at ground level, which isusable only for under-building parking. To meet the local government's "flow-through" structural criteria,no X-bracing was allowed within the tsunami depth. The ground story lateral-force-resisting system isnow a collection of vertical cantilever reinforced concrete columns, with woodframe construction above.The regulations achieved an increase in tsunami protection; the trade-off was a reduction in usablebuilding space and the selection of a more costly and less desirable structural system to resist the otherearthquake hazard at this site, namely ground shaking.

Architect, Robert Allen WilliamsStructural engineer: Onder Kustu, Oak Engineering


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Ubiquitous and Mundane - But Effective on a Societal Scale

Ubiquitous and mundane seismic design features left exposed simply to be economical, not to make anaesthetic statement, may not be as dramatic as the structure that was intentionally designed to express itsseismic system. Nonetheless, the visibility of ordinary seismic features, such as retrofit joist anchors, orsteel jacket confinement added to freeway bridge columns, form an interesting background texture in acity and are essential to the implementation of seismic safety on the societal scale.

Seismic retrofit wrapped around anunreinforced masonry building, Berkeley,California. photo: Robert Reitherman

[left] Typical scene often viewable in a California garage--an anchor boltconnecting the sill plate to the foundation. This mundane feature,exposed simply because the interior finishes are usually not appliedin a garage, is a sign of earthquake resistant provisions in thelocal building code. photo: Robert Reitherman

Jacketed freeway column.source: EERC-NISEE

Typical unreinforced masonry wall connection to woodroof, resulting in a common sign of a seismic retrofit:the large washer anchorage on the exterior.

source: Holmes et al., 1990, p. 13-27.

FLOOR, ROOF TIES TO WALL.TYPICAL AT PERIMETER

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Arnold, Christopher and Robert Reitherman, 1982. Building Configuration andSeismic Design. New York: John Wiley & Sons.

Bayulke, Nejat, 1978. “Behavior of Brick Masonry Buildings DuringEarthquakes,” Seminar on Constructions in Seismic Zones. Rome: InternationalAssociation for Bridge and Structural Engineering.

Bierce, Andrew, 1911. Devil’s Dictionary. New York: Dover, 1958 (reprint);

Billington, David, 1983. The Tower and the Bridge. Princeton, New Jersey:Princeton University Press.

Brown, Parry, Ian Aiken, and Jeff Jafarzadeh, 2001. “Seismic Retrofit of theWallace F. Bennett Federal Building,” Modern Steel Construction, August, 2001.

BSSC (Building Seismic Safety Council), 2001. NEHRP Recommended Provisionsfor Seismic Regulations for New Buildings and Other Structures. FederalEmergency Management Agency (FEMA 368 publication, Part 1, Provisions, andpublication FEMA 369, Part 2, Commentary).

Cobeen, Kelly, James Russell, and J. Daniel Dolan, 2004. Recommendations forEarthquake Resistance in the Design and Construction of Woodframe Buildings.Part II, Topical Discussions. Richmond, CA: Consortium of Universities forResearch in Earthquake Engineering.

Charleson, Andrew W. and Mark Taylor, 2000. Towards an EarthquakeArchitecture, Proceedings 12th World Conference on Earthquake EngineeringJanuary 2000, NZ National Society for Earthquake Engineering, Paper 0858, 8p.

Charleson, Andrew, Mark Taylor, and Julieanna Preston, 2001. EnvisioningEarthquake Architecture in New Zealand, Proceedings of the Technical Conferenceof the New Zealand Society for Earthquake Engineering Annual Conference,Wairakei, March 2001, Paper 3.01.01, 7 pp.

Charleson, Andrew, Julieanna Preston, and Mark Taylor, 2002. “ArchitecturalExpression of Seismic Strengthening,” Spectra, vol. 17, no 3, 2002, pp. 417-426.

Charleson, Andrew W., 2004. Strengthening the Link Between EarthquakeEngineering and Architecture, Paper No. 4, Proceedings of the Conference of the NZSociety for Earthquake Engineering, 19-21 March 2004, 8 pp.

Charleson, Andrew and Mark Taylor, 2004. “Earthquake ArchitectureExplorations,” Proceedings of the 13th World Conference on EarthquakeEngineering. Vancouver, Canada, August 1-6, 2005. International Association ofEarthquake Engineering.

Deam, Bruce and Andrew King, 1996. “Pseudo-dynamic Seismic Testing ofStructural Timber Elements,” Proceedings of the International Wood EngineeringConference, vol. 1, pp. 53-59.

De Bono, Edward, 1967. The Use of Lateral Thinking. London: Jonathan Cape.Among De Bono’s works on topics related to this is the currently available title,Lateral Thinking: Creativity Step by Step. New York: Perennial, 1990; first editionby Harper & Row, 1970.

Degenkolb, Henry, 1977. “Seismic Design: Structural Concepts,” Summer SeismicInstitute for Architectural Faculty. Washington, DC: American Institute ofArchitects.

Elsesser, Eric, 2004. “Seismically Resistant Design--Past, Present, Future,”Proceedings of the 13th World Conference on Earthquake Engineering, August 1-6,Vancouver, Canada, paper No. 2034.

Godden, William, 1977. Seismic Model Studies of the Ruck-A-Chucky Bridge,prepared for T. Y. Lin International, San Francisco, July 25, 1977.

Hassan, Ahmed F. and Mete A. Sozen, 1997. “Seismic Vulnerability Assessment ofLow-Rise Buildings in Regions with Infrequent Earthquakes,” ACI StructuralJournal, vol. 94, no. 1, January-February 1997, pp. 31-39.

Holmes, William, 1976. “Design of the Veterans Administration Hospital at LomaLinda, California,” in Franklin Y. Cheng, editor, Proceedings of the InternationalSymposium on Earthquake Structural Engineering. University of Missouri-Rolla,vol. II.

Holmes, William et al., 1990. Seismic Retrofitting Alternatives for San Francisco’sUnreinforced Masonry Buildings, a study for the San Francisco City PlanningDepartment by Rutherford and Chekene.

Lin, T.Y., H. K. Lu, and Charles Redfield, 1979. “The Design of the Ruck-A-Chucky Bridge,” Concrete International, Design & Construction. July 1979, vol. 1,no. 7, pp. 31-37.

Cited References

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Lin, T. Y., F. Kulka, P. Chow, A. Firmage, 1979. “Design of Ruck-A-ChuckyBridge, American River, California, USA,” Proceedings of the 48th AnnualConvention, 1979, Structural Engineers Association of California.

Lu, Zung-An, 1979. “Dynamic Analysis of Cable-Hung Ruck-A-Chucky Bridge,”Journal of the Structural Division, American Society of Civil Engineers, vol. 105,no. ST 10, October, 1979.

Mahin, Stephen, et al., 1976. Response of the Olive View Hospital Main BuildingDuring the San Fernando Earthquake. UC Berkeley EERC Report No. 76-22.

McGregor, Robert, 1999. The New Napier: The Art Deco City in the 1930s.Napier, New Zealand: Art Deco Trust.

McGregor, Robert, 2002. The Hawke’s Bay Earthquake: New Zealand’s GreatestNatural Disaster. Napier, New Zealand: Art Deco Trust, second edition, 2002,p. 19.

McGregor, Robert, 2003. The Art Deco City: Napier, New Zealand. Napier,New Zealand: Art Deco Trust, fourth edition, p. 2.

Mezzi, Marco, Alberto Parducci, and Paolo Verducci, 2004. “Architectural andStructural Configuraions of Buildngs With Innovative Aseismic Systems,”Proceedings of the 13th World Conference on Earthquake Engineering,paper no. 1318.

Reitherman, Robert, 1985. “Earthquake Engineering and Earthquake Architecture,”Designing for Earthquakes in the Western Mountain States: A Workshop forArchitects and Related Building Professionals, short course proceedings, AmericanInstitute of Architects.

Reitherman, Robert, 1998. “Prospecting for the Future: Searching For Trends ThatWould Change Structural Engineering.” Proceedings of the 1998 SEAOCConvention. Sacramento, California: Structural Engineers Association ofCalifornia.

Sakamoto, Isao and Yosimitsu Ohashi, 1988. “Seismic Response and RequiredLateral Strength of Wooden Dwellings,” Proceedings of the 1988 InternationalConference on Timber Engineering. Seattle, Washington.

Shah, Haresh, Theodore Zsutty, and Luis Padilla, 1977. The Purpose and Effects ofEarthquake Codes. John A. Blume Earthquake Engineering Center,Stanford University.

Shiga, Toshio, 1977. “Earthquake Damage and the Amount of Walls in ReinforcedConcrete Buildings,” Proceedings of the Sixth World Conference on EarthquakeEngineering. Vol. 7, p. 51 ff. An earlier publication of this research in Japanese isin Shiga, T., A. Shibata, and T. Takahashi, “Earthquake Damage and Wall Index ofReinforced Concrete Buildings,” Proceedings, Tohoki District Symposium,Architectural Institute of Japan, No. 12, Dec. 1968, pp. 29-32.

Taylor, John William Ransom, ed., 1970. The Lore of Flight. Gothenburg, Sweden:Nordbok.

Taylor, Mark, Julieanna Preston, and Andrew Charleson, 2002. Moments ofResistance, Archadia Press, Sydney, 2002, 101 pp.

Tobriner, Stephen, 1983. Genesis of Noto: An Eighteenth Century Sicilian City.Berkeley: University of California Press.

Uang, C. M., and F. Seible, C. McDaniel, and C. C. Chou, 2003. “PerformanceEvaluation of Shear Links and Orthotropic Bridge Deck Panels for the SanFrancisco-Oakland Bay Bridge,” CD Proceedings, 5th International Conference:Seismic Bridge Design and Retrofit for Earthquake Resistance, American ConcreteInstitute, La Jolla, CA.

Watanabe, A., Y. Hitomi, E. Saeki, A. Wada, and M. Fujimoto, 1988. “Properties ofBrace Encased in Buckling-Restraining Concrete and Steel Tube,” Proceedings ofthe Ninth World Conference on Earthquake Engineering, Vol. IV, pp. 719-724,Tokyo and Kyoto, Japan.

Zuk, William, 1989. “Notable Unbuilt Bridges,” Steel Structures, Proceedings ofthe Sessions Devoted to Steel Structures at the Structures Congress ’89. New York:American Society of Civil Engineers, pp. 696-705.

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