E NGINEERING A W A R D S O F E X C E L L E N C E

$100M OR GREATER NATIONAL WINNER Central Library Seattle

Photo by Lara Swimmer.

JUROR COMMENT he Seattle Central Library is ity loads. The trusses are supported by an elegant study in form fol- carefully positioned sloping columns that “Very inventive solutions lowing function. The project’s maximize counterbalancing opportuni- in structural steel to architects organized the ties, with platforms cantilevering as much meet complex structural library’s programmatic require- as 52’. The second system, the diamond- mentsT into five independent, yet con- shaped steel grid, forms the building’s challenges.” nected, “platforms” which were vertically exoskeleton. The steel grid provides the stacked, offset to maximize surrounding building’s lateral system, interconnects views, and enclosed in a steel-and-glass the platform trusses, serves as the inte- wrapper. This transparent package was rior architectural finish, and supports the delivered to the structural engineers with building’s glass curtain wall. a demanding set of rules: use no columns Specially designed slip connections in the corners, no vertical columns, and laterally join the steel grid to the platform as few columns as possible. In essence, trusses. The connections merge the two the project’s success depended on mak- structural systems while preventing the ing a 12-story, all-glass building — in transfer of gravity loads into the grid. UBC Seismic Zone 3 — appear to “float” This kept the grid slender, eliminated without support. the need for fireproofing of the grid MKA’s solution (working with Arup steel, and, most importantly, retained the during schematics) was two separate, desired aesthetics. Full-scale mockups layered structural systems. In the first of the connections were built and tested, system, multi-story-deep perimeter plat- and the connections were fully modeled form trusses carry the building’s grav- in 3-D.

Modern Steel Construction • May 2005 hoto courtesy P hoto courtesy Magnusson K lemencic As soci ates.

Structural Engineers Magnusson Klemencic Associates, Seattle Arup, Los Angeles, London, San Francisco, and New York offices (design development and schematics) Engineering Software SAP2000 Architects Office for Metropolitan Architecture (OMA), Rotterdam, the LMN Architects, Seattle Detailer BDS Steel Detailers, Mesa, AZ, AISC member, NISD member Action Steel Detailing, Inc., Mesa, AZ, AISC member, NISD member Detailing Software Xsteel Fabricator Canron Western Constructors, Inc., Portland, OR, AISC member General Contractor Hoffman Construction Company, Portland, OR

Photo by Michael Dickter, Magnusson Klemencic Associates.

May 2005 • Modern Steel Construction ates. soci lemencic As Magnusson K Graphic courtesy

The exoskeleton was designed so most directly from points of maximum built for significantly less than most recent that a common grid steel member size stress to the nearest support column main city libraries. Designed for function (W12×22) could be used throughout the ➜ Utilizing sloping gravity columns and aesthetics, the building also incor- structure. Diamond shape and size were in line with the plane of the seismic porates many sustainable elements. The optimized at 4’ per side and 7’ high based grid. Seattle Central Library applied for and on plate glass availability, most efficient Inside the 412,000-sq. ft building, a received “Silver” certification from the fabrication, and desire to eliminate the structural “ spiral” provides a contin- U.S. Green Building Council (USGBC), need for secondary mullions. The com- uous floor for the library’s nonfiction col- becoming one of the largest buildings to mon size also facilitated prefabrication of lection. The spiral required the creation receive a Leadership in Energy and Envi- the structural steel grid in “ladders” up to of a gradually sloping switchback ramp ronmental Design (LEED) certification. 85’ tall, greatly simplifying construction. system spanning four floors, accessible While the project’s design and engi- Three solutions were developed for to all ages and abilities, able to support neering achieved notable reductions in areas within the grid requiring reinforce- heavy bookracks, supported by minimal cost, they also helped lead to one signifi- ment: columns, and economically constructed. cant increase—library usership. Circula- ➜ “Strongbacking” the steel grid with Other unusual features include a nine- tion of materials is up 50%, the number an additional layer of grid in a shape story atrium through the center of the of library cards issued has increased reflecting the exact pattern and loca- building, a meeting level with tomato-red 500%, and attendance is 50% higher tion of stress demands curving walls, and a children’s area with than anticipated for the first year.  ➜ Sparingly inserting angled transverse playfully sloping columns. “intervention” columns to carry loads At $273 per sq. ft, the new library was

Modern Steel Construction • May 2005 E NGINEERING A W A R D S O F E X C E L L E N C E

$100M OR GREATER Adaptive Reuse of Soldier Field MERIT AWARD Chicago

ome to the Chicago Bears, Soldier Field is the oldest stadium in the National Foot- ball League. Because it had crumbling infrastructure, Houtdated facilities, and no club seating, the Bears decided to redevelop the sta- dium. However, with only 600’ between the existing colonnades, it fell more than 100’ short of accommodating today’s conventional football stadium. The architectural solution was an asymmetrical design with general admis- sion seats on one side of the stadium and stacked luxury suites atop two can- tilevered club decks on the other. That . configuration, a first in NFL stadiums, saved just enough space to fit a 61,500- seat stadium inside the colonnades. Completing the design and translat- omas etti Group ing it into a finished product within the required time frame raised the degree

Structural Engineer Thornton-Tomasetti Group, Chicago P hoto courtesy Thornton-T Engineering Software SAP2000 Ramsteel AutoCAD Owner Chicago Park District—Department of Planning & Development Architects Lohan Caprile Goettsch Architects, Chicago Wood + Zapata, New York Fabricator Hirschfeld Steel Company, Inc., Irving, TX, AISC member Erector Danny’s Construction Company, Inc., Gary, IN, AISC member, NEA mem- ber General Contractors Turner Construction Co., Chicago Barton Malow Co., Southfield, MI Kenny Construction Co., Wheeling, IL

Graphic courtesy Lohan Caprile Goettsch Architects and Wood + Zapata.

May 2005 • Modern Steel Construction of engineering difficulty considerably. Many of these breakthroughs were frame. Sixty-four accelerometers were The Soldier Field project schedule was made possible by the stadium’s 13,000- attached to the grandstand to monitor 20 months, with less than one month to ton structural steel frame, which provided its movement. When crowd movement demolish the existing grandstands. great design flexibility. However, the steel causes the structure to vibrate and the While the old stadium rested on 10,000 frame of the upper grandstand cantile- TMDs are tuned to vibrate at the same timber piles driven through landfill to an ver presented another challenge—main- frequency, the two structures move out average depth of 62’, supporting the new taining spectator comfort amidst syn- of phase, dissipating energy and vibra- stadium required 2,000 H piles driven 90’ chronous crowd movements of fans or tions. to 100’ down to bedrock. concertgoers. Because a bare steel and Finite-element modeling software Stadium seats are supported on pre- concrete structure has little natural damp- was used to model the structure and cast concrete risers. The risers span ing to diminish vibrations, a crowd mov- the crowd’s forcing function on it, and to between and are supported by main ing at the structure’s natural frequency determine the placement of the TMDs. structural steel rakers that are supported could create vibrations that were notice- To confirm the theoretical results of the at 40’ centers. The rakers supporting the able to spectators. A dynamic analysis modeling, a custom “Vibration Shaker” upper grandstand cantilever 60’ over the showed that while structural stability was was attached to various locations on the historic colonnades, one of the longest not an issue, vibration and acceleration grandstand. The shaker operated by such cantilevers supporting crowds. To in a packed stadium could reach inten- rotating two sets of weights in opposite keep this seating at a comfortable ele- sities uncomfortable to spectators in directions to induce a measurable vibra- vation and distance from the field, yet the grandstand. The typical solution of tion into the structure. This test confirmed avoid touching the existing west colon- adding more columns was impossible the frequencies at which resonance nade, a tapered, built-up plate girder because of the colonnades below the would occur and assisted in tuning the was designed that is approximately 7’ at cantilever. TMDs. With the TMDs operating in place, its maximum depth. To provide the needed vibration con- the accelerations remain within the limits The structure of the suites were tilted trol, the engineers incorporated 21 tuned for spectator comfort. 14° toward the field, bringing the upper mass dampers (TMDs), located at the tips Read more about Soldier Field in levels of seats closer to the field, thereby of the cantilever of the grandstand. The “Field Goals” in the July 2004 issue of providing better sightlines. Two massive TMDs, about 20 tons each, comprise a Modern Steel Construction, available video boards, 84’ long by 23’ high, attach concrete mass supported on air springs, online at www.modernsteel.com.  to cantilevered steel trusses extending tunable steel springs, and a tunable vis- 100’ in space over the end zones. cous damper connected to the structural

Modern Steel Construction • May 2005 E NGINEERING A W A R D S O F E X C E L L E N C E

$100M OR GREATER MERIT AWARD St. Luke’s Hospital Cardiac Center and Patient Tower Milwaukee

Photo by David Anderson. he Cardiac Center and Patient piers and 85’-tall, unbraced columns Tower, a 430,000 sq. ft, $187 were placed from the roof of the parking Structural Engineer million addition to St. Luke’s garage by a 65-ton drill rig. The rig drilled Graef, Anhalt, Schloemer & Medical Center in Milwaukee, the piers and placed the columns while Associates, Inc., Milwaukee has been dubbed “the hospi- traffic moved safely through the garage. Engineering Software talT on stilts.” With the first of eight floors Above grade, the majority of the new RAM Structural beginning seven stories up, it straddles a structure is supported by 32’-deep steel Visual Analysis multi-level parking garage and connects trusses which bridge the west portion of with the existing hospital. The project’s the parking structure, supporting the steel Owner major challenge was erecting the 12-story framing above. Due to the long required St. Luke’s Medical Center, Milwaukee steel superstructure over and through an reach of both tower cranes, the maxi- Architect existing parking garage that remained mum pick at longest reach was nine tons, Kahler Slater Architects, Milwaukee operational. thereby limiting the weight of any single By significantly widening the space truss piece. Detailer between columns and preventing column Construction of a nuclear medicine Pacific Drafting, Inc., Carson, CA, contact with the garage, the design sup- addition directly below the west half of AISC member, NISD member ports the hospital above and allows for the parking structure required the patient Detailing Software uninterrupted traffic flow in the garage tower to clear span 130’ over half the CDS Asteel below. Each column is encased by a parking structure. In order to best use the .5”-thick steel jacket. The column jacket space between trusses, the mechanical Fabricator serves a two-fold purpose: one, as a stay- level was placed on this first supported Merrill Iron & Steel, Inc., in-place form, and two, as protection from level. The four large mechanical units Schofield, WI, AISC member vehicular impact or explosion. A total of 33 used to serve this addition are 28’-tall, Erector columns support the new structure, 14 of which set the truss depth at 32’. A mez- AREA Erectors, Inc., Rockford, IL, which penetrate the parking structure and zanine floor was added to a portion of this NEA member are completely isolated from it, preventing level, requiring horizontal framing at the the transference of vehicular vibrations to truss’s mid-depth. A K-truss configuration General Contractor the patient tower above. was used to reduce the weight of indi- Oscar J. Boldt Construction Co., To perform the column work, drilled vidual chord and web members, allowing Waukesha, WI

May 2005 • Modern Steel Construction the members to comply within the tower used, significantly minimizing field fit-up as a number of sharply skewed connec- crane’s maximum load capacity. problems. tions. W14 members up to W14x730 were In the erection of the trusses, a series The seventh floor of the superstruc- used for chords (65 ksi) and webs (50 of 7’-deep temporary trusses were used to ture, which is supported off the top chord ksi). Members were oriented with flanges support the bottom chord off the new col- of the trusses, houses the cardiovascular parallel to the truss plane to reduce the umns and parking structure. The trusses operating rooms. This use requires maxi- weak axis unbraced compression length were first erected two in tandem to pro- mum isolation from vibration. Because to half the truss depth. This also allowed vide stability for the webs and top chords. the mechanical floor is directly below the use of both flanges for connections Once a truss was stable, the temporary the operating room floor, all mechanical to double gusset plates. Analysis of the truss was removed, re-fitted for adjacent ducts, pipes, conduits, and other compo- trusses considered continuity and redun- spans, and re-used. The trusses were pro- nents that could transmit vibration could dancy in the extent of a catastrophic load vided on four parallel column lines about not be hung directly from the steel sup- such as an explosion or fire in the park- 40’ apart. The top of the trusses formed porting the floor. A system of isolated HSS ing garage below. Resulting bar forces in a rectangular tabletop. This provided a columns supporting an additional frame- chords were up to 3,000 kips. Connec- stable working platform for erection of the work of beams supports this equipment tion plates were up to 2” thick, 8’ x 10’ in eight hospital floors above. independently. Vibration modeling done size and required over 300, 1”-diameter Above the truss system, the configu- before and testing done after completion A490X bolts. To fabricate the truss mem- ration of the patient rooms is rectangular of the structure indicated that vibration bers and gusset plates, software that inte- with a curved, concave exterior wall. The isolation efforts were successful.  grated shop drawing layout dimensions resulting column layout requires a sig- to automated fabricating machines was nificant number of transfer beams as well

Modern Steel Construction • May 2005