ROOF SHORING JUST HAD TO BE RIGHT 18 n ENR n October 26/November 2, 2020 enr.com ost contractors would jump at the chance to have a roof overhead during a major rebuild. But for the team turning earthquake-prone Seattle’s 411,000-sq-ft KeyArena into the 932,000-sq-ft Climate Pledge Arena, the city-owned fa- cility’s historic helmet has been a M44-million-lb design and construction headache. Keeping the roof in place “ended up being more com- plicated than anticipated,” says Ken Johnsen, construction executive for Oak View Group (OVG), the developer of the privately financed sports and entertainment venue. “More complicated” is an under- statement. The excavation for the mostly subgrade redevelopment, which has a larger footprint than COVER STORY SPORTS KeyArena, required undermining the CONSTRUCTION foundations of the 400-ft-square roof. The lid had be kept safely in place due to a city-imposed imperative to preserve the old arena’s landmarked looks. Extensive shoring was needed to keep the roof intact. The temporary support system, which also had to resist seismic loads and limit movement to ¼ in., ended up cost- ing $35 million and weighing 4,400 tons. To top that, the shoring was extremely challenging. “It’s one of those projects that screamed ‘Run away,’ ” says David Mortenson, chairman of the arena’s general con- tractor, Mortenson, which is operating under a CM-at- risk contract with a guaranteed maximum price of about $850 million. But “it’s going exceptionally well, given all we have to deal with,” he adds. Costs for the mind-boggling redevelopment—now at $1 billion—have increased by $250 million from OVG’s early budget. And the developer extended the planned opening by a year, to next fall. KICKSTAND Temporary pipe The toughest part is done. There assembly shores were no collisions or mishaps. The roof south buttress after 68-ft-deep is bearing on its permanent supports excavation, mostly and the shoring is all but removed. The for subgrade job, 55% complete, is on schedule. parking. Mortenson says the job would have been nearly impossible, taken longer and ARENA’S BUILDING TEAM IN QUAKE- cost even more without “extreme” planning, intense team PRONE SEATTLE USES 4D BIM TO collaboration, top-down construction and, especially, dig- MANAGE THE CONSTRUCTIBILITY ital tools. “We’re using 4D modeling to figure this out,” says Derek Cunz, a Mortenson senior vice president. NIGHTMARE ASSOCIATED WITH The contractor has been using 4D—which combines SUPPORTING AN ICONIC COVER a 3D model with a project schedule to simulate construc- DURING CONSTRUCTION tion—for more than 15 years. It began by experimenting BY NADINE M. POST with it on parts of the inscrutable Walt Disney Concert Hall, built in the early 2000s. PHOTO BY CHRIS MAST OF BLUE PIXEL BLUE OF MAST CHRIS BY PHOTO It’s no coincidence that Mortenson assembled its Dis- enr.com October 26/November 2, 2020 n ENR n 19 ney leadership team to fi gure out the equally mystify- UNDER THE contract award to a joint venture of Skanska USA and BIG TOP ing, though drastically different, arena project. After the steel AECOM Hunt. OVG and the joint venture soon One major constructibility puzzle was how to de- erector engaged parted company, amicably, because the project needed sign the shoring so it would not interfere with the new the central a dedicated single-source team, according to OVG. shoring tower, seating bowl structure and so that it could be cut out crews could begin Mortenson was engaged in December 2018, just after construction of the new structure. transferring loads before the offi cial start of construction. It didn’t take from Y-columns “The sequences of this job are so complex,” says to their shoring long to gear up. The contractor had spent six months Chris Rust, executive vice president of steel erector frames (left). Top- working for OVG, “trying to fi gure out the right cost down construc- Danny’s Construction Co. LLC. Danny’s is respon- tion of drilled and schedule,” says Mortenson. Then, it lost its bid for sible for shoring and jacking the roof, the installation shafts in limited the job due to its higher price and longer schedule. of permanent steel and the shoring removal. headroom around the perimeter This project is “pretty insane,” adds Adam Running, supports included Fossil-Fuel Free project executive for Malcolm/DBM JV, a joint venture erection of In the spring, there was another hurdle for the building trussed chevron of Malcolm Drilling Co. Inc. and Donald B. Murphy shoring frames at team, traceable to the sale of the naming rights, for an Inc. The JV is responsible for the 3-ft-dia drilled shafts, all the buttresses undisclosed sum, to Amazon, which selected the new perimeter foundation wall’s permanent shoring, tempo- (right) . name. At the same time, OVG, Amazon and the Na- rary and permanent foundations and dewatering. tional Hockey League (NHL) Seattle decided to create The arena saga started in 2017, when the city se- a fossil-fuel-free facility, powered only by electricity. lected OVG to redevelop the site. OVG, which is fi - They are also adding a “rain-to-rink” system for ice nancing the development, and the city signed a lease production and solar arrays, on and off site. agreement for 39 years, with two, eight-year renewable “The idea of creating a healthy arena for the planet options. Under the terms, the city will receive annual is in alignment with the ethos” of the developer, the rent of $2.8 million, with a baseline tax guaranty of NHL, the team and with Amazon, says Rob Johnson, $2.2 million, adjusted annually. OVG will receive a vice president of sustainability for the Climate Pledge rent abatement of $350,000 during the initial 10 years. Arena and the Seattle Kraken hockey team. The fi rst hiccup happened before a shovel hit the The arena is aiming to be the fi rst International ground, soon after a July 2018 construction Living Future Institute Zero-Carbon-certifi ed pro- MORTENSON OF COURTESY PHOTOS VIRTUAL BUILDING IN THE 4D MODEL COLOR KEY The arena redevelopment would have been Demolition nearly impossible without the help of 4D model- Activity Start ing, which combines a 3D model with the sched- Activity Complete ule. The team prebuilt the arena virtually in the model to work out in advance as many confl icts Excavation and clashes as possible. 4D is also helping to Shoring Complete resolve problems encountered in the fi eld. Permanent Steel Complete 6-04-2019 7-15-2019 20 n ENR n October 26/November 2, 2020 enr.com fessional sports venue, and a model for wall. They are currently putting it back. other arenas. “We ripped out all the The landmark lid bears on perimeter reinforced- [designed] natural gas infrastructure,” concrete supports, Y-columns and buttresses expressed says Jason F. McLennan, CEO of COVER STORY architecturally. The cap covered KeyArena’s sloping SPORTS McLennan Design, the arena’s sus- CONSTRUCTION sunken bowl with an event fl oor taken to 38 ft below tainability advisor, ILFI’s founder and grade in the 1995 expansion. the 2016 ENR Award of Excellence The new sports and entertainment venue, with four winner. levels below grade and two above, will contain 17,400 One hitch: The infrastructure, seats for hockey and host the Seattle Kraken. It will offer which had already been permitted, had 18,600 seats for basketball and will host the Women’s to be redesigned and repermitted. “We National Basketball Association team Seattle Storm. were building the plane while we were Climate Pledge Arena’s footprint is 720 ft x 580 ft and fl ying it,” says Johnson. the event fl oor will now be 60 ft below grade. The rede- The project is the second reincar- velopment includes the 740,000-sq-ft venue and a nation of the Seattle Center building, 192,000-sq-ft parking garage under the south entry plaza. fi rst built at grade with a clear-span pitched roof as the When fi nished, the arena will look virtually the exhibit hall for the 1962 Seattle World’s Fair. The INTERLACED same as the original, except for a new entrance pavilion building has been known as KeyArena since a 1995 Shoring frames attached to its hip on the south side. were located to expansion to create a mostly sunken seating bowl. both allow the “This is essentially a brand-new modern venue that Both the roof and the glass curtain wall became insertion of per- lives within this historic structure,” says Geoff Cheong, manent structure landmarks in 2017. Before the gut demolition of the and the removal lead designer for the job’s architect, Populous. 1995 interior, crews removed and stored the curtain of the frames. The combination of a mostly subgrade building and CONCRETE Y-COLUMNS CONCRETE RING BEAM N CHEVRON Y-COLUMN PIPE SHORING FRAME SHORING TOWER TOWER CRANE KICKSTAND CHEVRON TRUSS SHORING FRAME CONCRETE NEW PERMANENT STRUCTURE TRIPOD BUTTRESS SOURCE: THORNTON TOMASETTI 7-22-2019 8-25-2020 6-19-2021 SOURCE: MORTENSON enr.com October 26/November 2, 2020 n ENR n 21 ARENA SITE LOGISTICS PLAN TRUCK ROUTE a roof that was off limits for equipment and louvers SOUND WALL BARRIER MOVEABLE SITE FENCE complicated the mechanical system. “We couldn’t pen- TRUCK ROUTE Gates #6 Gates #5 etrate the roof or put anything on it,” says Jeff JERSEY BARRIER W W Sawarynski, a principal with the project’s consulting POLICE AS NEEDED engineer, ME Engineers.