cathedralchristlight_fall08

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Ping VillageMaple and cedar provide the

perfect backdrop for modern

Chinese fusion restaurant

Clear SpaceWood promotes creative

expression in Taubman Colleges

student resource lounge

Cathedral ofChrist the LightExemplary California cathedral

uses traditional building

materials in modern ways


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Korman Residence 11Modern remodel leverages techniques and treatmentsappropriate or a house tucked into a wooded Caliornia canyon

Ping Village 14Maple and cedar provide the perect backdrop or thismodern Chinese restaurants Asian-American usion concept

Clear Space 17Use o wood promotes a high degree o creative expression inTaubman Colleges Master o Urban Design + Master o UrbanPlanning student resource lounge

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Crats and Heritage

Cathedral o Christ the Light 28Exemplary Oakland, California cathedral utilizes

traditional building materials in modern ways

Wood Chips 6News and events on wood-related subjectsProvince to Raise Roo on Wood-Frame Constrction;Architectre Billings Index Contines in Negative Territory;Canadas Wood Prodcts Indstry to Lose $750M Againin 2008; 2009 Fresh Wood Stdent Competition Call or

Entries; Astralian Stdy Finds No Chemical Preservativesin 99% o Waste Wood Packaging; Certifed Wood and theImpact o LEED; Oklahoma, Florida and Indiana RecognizeGBIs Green Globes System; Code Concil CreatesSstainable Bilding Technology Committee; InternationalReal Estate Firm Acqires Original Developer o The GreenGlobes Site o Tools; Home Byers Increasingly Thinkingand Bying Green; Energy Conservation StrategiesMotivating Homeowners to Invest in Green DesignFeatres; Corporate Leaders and Consmers EmbraceProdcts From Responsibly Managed Forests; CertifedGreen Proessionals Now Top 1,000, says NAHB; KitchenCabinet Manactrers Association Gives Green Light toCabinet Indstry Sppliers

Ideas & Soltions 36Widely-used in the construction industry,

Visually-Graded Finger-Joined Lumberboasts straightness and dimensional stability,

among other things

Technical Abstract 40The Innovative use of Engineered Wood

Trusses for Concrete Bridge Deck Formwork:

William R. Bennett Bridge

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I N T E R N A T I O N A L

P R O F I L E

WWT Visitor Centreand Footbridge 22Local barn vernacular and strong linearityo a marshland context infuences thedesign o a U.K. visitor centre

cover)athedral of Christ the Light

kidmore, Owings and Merrill (SOM), San Francisco

hoto by John Blaustein


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Cathedral o Christ the Light

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Exemplary Oakland, California cathedral utilizes

traditional building materials in modern ways

P C. G, P.E., S.E. K Beebe, P.E.

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Cathedral photos by John Blaustein,

courtesy of The Cathedral of Christ the Light

and Skidmore, Owings and Merrill

To an engineer, locating a 110-t. high cathedralmade o delicate materials so close to an active aultline and expecting it to survive an earthquake likethe 1906 temblor that is the ultimate challenge,said Mark Sarkisian, S.E., Director o StructuralEngineering at Skidmore, Owings & Merrill (SOM),San Francisco. Yet, this is precisely what the newcathedral achieves. Set or a September 2008 opening,the 21,660-sq.t., 1500-seat, $80-million cathedralis an exemplary structure that utilizes traditionalbuilding materials in modern ways.

Exceeding a typical building design lie by 200-250 years, required special consideration structurally,as well as architecturally. Given the sites seismic-ity, the building was analyzed to resist a 1000-yearearthquake. Furthermore, the building needed to bearchitecturally worthy in 300 years. The outcome isa space rame structure with a glue-laminated tim-ber beam (glulam) and steel rod skeleton and glassskin. Using light as a central theme, the glass skinis composed o recently developed materials includ-

ing dichroic glass and ceramic ritted glass, whichemanate prismatic eects and add patterns o toneand line or additional color and texture. A serieso glulam louvers enhance the dynamic lighting byltering the eects o the glass as the sun movesthrough the sky.

Wood, rather than steel, orms the cathedralssupporting lattice because o its warmth and reer-ence to light, as well as its religious signicance,Craig Hartman, SOM. Furthermore, wood has aneconomic advantage over comparable building mate-

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The Cathedral of Christ the Light

in Oakland, CA, replaces the

Cathedral of St. Francis de Sales,

rendered unusable following the

1989 Loma Prieta earthquake.

Project leaders wanted the new

structure to have a design life of

300 years.


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rials. When I designed this building seven yearsago, we were just on the cusp o an unbelievableescalation in construction costs, especially in steel.And had this building been abricated in steel, whichwould have been the other choice, there is absolutelyno way we could have aorded it.

The foor plan o the building is in the shape o aVesica Pisces that creates a spherical elevation. TheVesica Pisces is a shape o religious signicance, twointersecting circles o the same radius, connected insuch a way that the center o each circle lies on the

circumerence o the other. Historically,this shape is an ancient sign among manyEastern and the Western cultures or

a gathering place and a symbol amongCatholics or the miracle o the loavesand shes.

Structural SystemThe cathedrals strength is achievedthrough the creation o glulam and steelrod space rames. The Vesica Pisces isconstructed with 26, 1034-in. wide by99-t. 9-in. long glulam ribs that vary indepth rom 30 in. at the base to 1912 in. atthe top. Between each rib are 32, 518-in.wide glulam louvers varying in depth

rom 2212 in. to 39 in. The louvers areinstalled at seven dierent anglesto optimize the light eects. Theroo o the cathedral is composedo a tension-ree glass oculus sup-ported by a steel compression ringwhich resists the horizontal thrusto the glulam ribs. Parallel to eachrib is a glulam mullion 1034 in.wide by 15 in. deep and 103 t.long. The mullions are installed 80degrees rom horizontal and areconnected to the wooden vaults othe Vesica Pisces by turned glulamstruts with tapered ends o lengthsvarying rom 2 t. to 15 t.

The space rames diagonalmembers are made with pre-ten-sioned high strength steel rodsinstalled such that in an earthquakethey will a lways be in tension. Thebuilding is subdivided into velevels where xed connections tiethe louvers to the ribs completingthe structural rame. To minimize

the seismic load on the cathedral, 34 seismicbase isolators were installed beneath the 12-t.concrete reliquary wall in a matrix to evenlydistribute the load. The specied isolators,double concave riction-pendulum base iso-lators, have a 4-t. diameter steel bearing andemploy a sliding system with an interacial mate-rial that slides across stainless steel. This isolationreduced the seismic motion by a actor o ve.

Given the cathedrals proximity to ault zones (4.7km rom Hayward and 25km rom San Andreas)

ExPlodEd axonomEtriC

roof SKyliGht

oCuluS CEilinG

wood louvrES

frittEd GlaSS

Glulam StruCturE

omEGa wall

alPha wall

rEliquary wall

Entry vEStiBulE


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and its nonconormance to a standardCaliornia Building Code lateral system,the City o Oakland hired a peer reviewcommittee, composed o three univer-sity proessors and one industry expert,to establish the required toughness andductility requirements.

Load TestingFirst, the committee determined that

the glulam timbers must remain elasticunder cyclic load conditions. Second,all o the ductility o the system wasrequired to come rom the pre-tensionedsteel rods. This required ductility testingo the tension members to demonstrate

that they could achieve 2.1 per cent elongation overthe entire length o the rod, not just at the threadedends. The rod manuacturer, Halen AnchoringSystems, tested all ve rod diameters. The initialtesting pointed out that the two largest rod diam-

eters did not meet this requirement as theelongation was limited to the threaded por-tion o the rod. Halen thereore re-tooledtheir machinery to upsize the threads on

these rods and achieved the required elongation. Theresulting stress strain curves o the testing were inputinto the SAP2000 computer model to dene non-linear behavior o the structure.

Third, the rods were required to be pretensioned tobetween 3 per cent and 10 per cent o their yield stressso that they were never loose and would be in tensionimmediately when loaded with seismic orces. Theglulam supplier/erector, Western Wood Structures(WWSI), Tualatin, OR, developed an ingenioustightening sequence to eliminate orce intererence

between rods. Without this sequence, tightening onerod would aect the orces already applied to all theother rods, tightening some and loosening others.

The tightening sequence was developed using atime step analysis on one-hal o the structure. Inthis analysis, a pretensioning orce was applied one ata time to each rod member until all were tightened.WWSI engineers determined i two opposing rodsat a joint were tightened simultaneously the loadsinduced into adjacent rods was minimized. WWSIalso developed the required tightening torques,


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which were calibrated to the desired pretension andambient rod temperatures. To veriy this analysisand tightening procedures in the eld, WWSI hiredVGO Testing and Inspection Engineers, Tigard, OR,to install 24 strain gauges on the rods to monitorthe orces in the rods during the tightening process.The strain gauge readings conrmed appropriatepretensioning orces were developed.

Fourth, the criteria specied a non-linear push-over analysis. This analysis required a progressive

ailure model which recalculated the stiness basedon the surviving structural elements to deter-mine structure viability along the way. The nalrequirement was a Time History Seismic Analysisessentially scaling the Loma Prieta earthquake to a1000 year event.

ConnectionsGiven the asymmetry o structure and the curvatureo the interior and exterior walls, very ew con-nections were the same. As a result, AutoCAD 3D

was utilized to model 220 uniqueconnections and resulted in over84 pages o shop drawings. Doubleker plates and hidden 1-in. steelpins were used to connect the ribsand mullions. These intricate con-nections were shop abricated orease o construction.

Another proactive step by thedesign team required WWSI tobuild a mock-up o the struc-tural system equivalent to twobays in width and one th thetotal structure height. The mock-

up, 22 t. high by 30 t. wide, revealedseveral issues that would have signi-icantly impacted the building. First,they learned that normal wood shrink-age would expose the steel ker plates.Thereore, the plates were trimmed in. to accommodate material changesand maintain the hidden nature o theconnections. Second, the moment con-

nections o the steel girts (glass support)to the mullions needed to be tested toveriy the rigidity o the connection.The design relied on a steel assemblyconnected with slip critical pre-ten-sioned bolts in order to minimize thedefection. This was necessary to pre-vent serviceability problems with thewindows such as a break in the windowseals. During this process, the connec-tion was tested and showed the need to


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strengthen the connection by installing stienersinside the rst 4 in. o the tube.

Specification of Glulam BeamsGiven the architectural signicance o the glulamtimbers, their appearance is crucial to the aestheticso the structure. SOM and WWSI collaborated todevelop a customized appearance specication thatprovided a more appropriate nish than the standardpremium appearance grade. WWSI worked with

the glulam manu-acturers to handselect the lumberused in the lamina-tions to minimizeknots and voids

on the aces o themembers. The ewremaining voidswere let unlled.F u r t h e r m o r e ,to minimize theappearance o glue-lines on the ace othe rib members,any nger jointson the ribs acingthe seating areawere located morethan 15 t. abovethe reliquary wallswhere they wouldbe less noticeableby the congregants.The louvers wereoriginally intendedto be covered withan acoustical mate-rial. In the end, itwas decided toleave them exposed

to view saving theproject nearly amillion dollars.

ConclusionIn the processo designing thecathedral, engi-neers at SOM wereable to achieveappropriate struc-

tural strength and toughness or this building usinga structural system not recognized by the buildingcodes. This was accomplished by careully dening

the ductility requirements o the structure, model-ing its non-linear behavior, testing the componentswhich were relied on or ductility and eld veriy-ing the installation o these components.

The design team at SOM worked closely with theglulam supplier to achieve appropriate nishes othe various glulam members. The use o a ull scalemock-up was instrumental in allowing the archi-tects and engineers to see how the structure wouldappear when completed. This allowed changes tobe made that had little or no economic impact butgreatly improved the structures appearance andperormance.

The design and erection o the Cathedral oChrist the Light demonstrated that modern glulamconstruction could be used to build a signicantbuilding intended to be structurally capable andarchitecturally worthy o lasting 300 years.

The Cathedral o Christ the Light is an extraor-dinary timber structure meeting demandingseismic and architectural design criterion that ismore economical and aesthetically pleasing thanconventional steel or a reinorced concrete momentrame building.

About the AuthorsKaryn Beebe, P.E., is an Engineered Wood Specialistwith APA. Beebe has written, lectured and consultedon residential and commercial wood-rame con-struction or the past 12 years. She can be reached [email protected].

Paul C. Gilham, P.E., S.E. has been designingengineered timber structures at Western WoodStructures, Inc. o Tualatin, Oregon or 26 years.Gilham has extensive experience in the design otimber bridges and building structures. Gilhamalso is involved in the inspection and rehabilitation

o existing timber structures. He can be reached [email protected].

D e s i g n a r c h i t e cT : SK I D M O R E , O W I N G S AN D M ER R I L L , SAN F R AN C I SC O , C A

ar c h i t ec t o f r ec o r D : KEN D AL L H EAT O N ASSO C I AT ES B ASED I N H O u ST O N , T X

c l i e n t / o w n e r : C AT H O L I C D I O C ESE O F O AKL AN D , O AKL AN D , C A

s t r u c t u r a l e n g i n e e r : SK I D M O R E O W I N G S AN D M ER R I L L , SAN F R AN C I SC O , C A

c o n t r a c t o r : W EB C O R B u I L D ER S , SAN M AT EO , C A

g l u l a m s u p p l i e r / e r e c t o r : W EST ER N W O O D ST R u C T u R ES , T u AL AT I N , O R

p h o t o g r a p h y: J O H N B L Au ST E I N

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