JP Cullen’s remarkable resourcefulness and commitment to safety has earned the company well-deserved recognition by SEAA, who selected the Milwaukee Bucks Arena as Class IV Project of the Year. There were just 290 days between setting the first piece of steel and the topping off celebration, which marked the conclusion of an extraordinary accomplishment by the JP Cullen team.
The Milwaukee Bucks Arena was erected using approximately 8,000 tons of structural steel. The steel construction consisted of typical structural column and beam steel framing for the surrounding bowl structure, including six levels plus a roof. The roof over the arena floor consisted of nine long-span roof trusses approximately 33 feet deep.
Tight schedule, tight quarters
Workers were confronted with an aggressive schedule as the owners were looking to open the new arena in time for the 2018-2019 season.
Since the project began in early November, crane operation was subject to the whims of wintry Wisconsin weather, including snow, ice, freezing temperatures, and high winds. If the anemometer on the crane measured wind speeds exceeding 30 miles per hour, lifting of the roof trusses had to be stopped until it fell below the threshold. The inability to control Mother Nature made it even more imperative to carefully orchestrate operations and support the timely achievement of project milestones.
Since most of the structure was steel framed, steel fabrication and delivery was the critical path for all other follow-on activities and creating a reliable schedule to supply the material needed for onsite erection operation was crucial. Over the course of the project, more than 130 ironworkers logged 80,000+ manhours, and the project required 75 or more ironworkers onsite at one time along with more than 100 workers from other trades onsite each day. While an arena may seem like a spacious worksite, the task of erecting massive roof trusses along with all the crews, material, and multiple cranes and boom lifts sharing the space made the arena bowl feel more like a tin of sardines. The constrained space impacted the laydown and work area for the crews and demanded meticulous planning to avoid endangering tradespeople.
The 730,000-square-foot arena required a colossal amount of steel ― roughly 13,000 structural steel pieces with a total weight just over 8,000 tons. The longest truss spanned 313 feet and weighed 102 tons. Truss assembly racks and shoring towers were used for the erection of the trusses. The JP Cullen team set 358 steel columns, each weighing in at 10,700 lbs. and measuring 36 feet tall. Overall, the project included 7,673 main structural steel pieces and 6,000 miscellaneous structural steel pieces. Sequencing the work with the fabricator and having detailed safety plans were essential to the success of the project. JP Cullen’s team worked closely with Merrill Steel to clearly communicate the plan for organizing steel delivery and ensuring on-time delivery. Having the steel components sequenced and then delivered in order of erection greatly streamlined the process for ironworkers.
A detailed erection plan
JP Cullen developed detailed erection plans for the bowl structure as well as the trusses. The bowl structure erection started on the west side, working along the north and south sides and coming together on the east utilizing two erection crews simultaneously. Inside the arena, each individual truss was assembled into two “half” trusses and built concurrently on an engineered truss rack fabricated specifically for the project. JP Cullen developed a specific erection sequence for the roof trusses identifying required temporary bracing, tie-in pieces that needed to be erected before releasing the crane from each truss half, and tie-in pieces that needed be erected to stabilize the truss prior to the ironworker crews leaving for the day. JP Cullen’s BIM team developed models to determine exact crane locations for each truss pick as well as a pre-assembled pedestrian bridge pick, and for disassembly of the cranes. A specialized disassembly procedure had to be engineered by the crane manufacturer outlining the exact sequence for lowering the crane lattice boom underneath the already erected roof trusses due to the limited space available between roof trusses to lower the boom flat for disassembly. “This entire procedure was modeled utilizing BIM to ensure we could maximize the boom length while still being able to disassemble the crane after the roof trusses had been erected,” recalls Mentink.
At the main entrance on the arena’s east side, the design included splayed columns that were structural steel. The erector was tasked with determining how to temporarily brace these while eliminating the need for cable bracing as much as possible. To address this challenge, a combination of decking diaphragm and anchor bolts designed to specific sequencing was employed. The team decided to shorten the columns to a single floor level, making sure that the anchor bolts alone could support columns up to 30 feet high, and the decking diaphragm was in place and fastened down before adding the remaining portion of the column. This eliminated the need for any cable bracing which would have been in the way of other trade crews.
JP Cullen began work with Mortenson and Merrill Steel eight months before steel erection. According to project manager Adam Mentink, “As soon as we were awarded the contract, we sat down with the fabricator, construction manager, and erection engineer to put together the sequencing and direction of flow. The structure of the arena was all structural steel, so it was critical to develop a plan right away.”
Prior to the installation of the façade, the roof trusses that connect opposite sides of the bowl structure had to be in place. As the schedule did not allow for this, JP Cullen worked with the design team and construction manager to develop a temporary erection plan that allowed for façade installation to start sooner than the original permanent design allowed. Sequencing had to be very detailed to ensure the structural stability of the stadium before systematically moving the truss-loaded crane, a challenge the team met using 3D lift planning.
Although the weight of the load required a 300 ton crane, JP Cullen ultimately chose a larger crane (440 ton) with more extensive boom configurations that would accommodate the reach needed. To present the extensively detailed plan to field personnel in a more easily digestible format, the sequencing was broken into smaller daily packets with checklists and signoffs on specific procedures before proceeding.
Field and management collaboration pays off
With the scope of work taking place and the number of people present in the confined site, it was also critical for JP Cullen to have a detailed safety plan in place from the beginning. Mortensen, the construction manager, along with Cullen, wanted to protect workers from the hazard of falling tools and requested the development of a drop prevention plan. Mentink believed that involving both management and field workers would benefit the development of a maximally effective plan to ensure safety. When asked for their input, the connecting crews expressed concerns about the conventional approach of using tool tethers to mitigate drop hazards. Based on practical experience, they felt strongly that the use of tethers created the potential risk of snagging on a beam during erection and putting workers at risk, even in a 100% tie-off environment. That collaboration resulted in the decision to forego tethers for connectors only and use no-access zones to minimize the risk of injury from dropped tools.
The no-access zones were implemented to prevent entry by persons who were unqualified or unfamiliar with the steel operations, and steel erection crewmembers were allowed to enter only at controlled access points. Rather than relying only on a barricade, spotters were positioned at points of entry to ensure that access was controlled.
At several key points, thoughtful modifications of standard procedures allowed the JP Cullen team to make the steel erection process easier, safer and more efficient. Project management put the conventional playbook aside in favor of worker safety once more when the big roof trusses were in place and safely accessing the work area became an issue. As a rule, personnel are advised not to climb out of a boom lift, but in this case, workers felt that this may be necessary and may be the safest way. “When facing challenges, we always ask ourselves if there is a better piece of equipment for the task,” noted Mentink. “In this case, there just wasn’t a better alternative. We needed a customized approach. So, we chose to create a special boom lift procedure with specific, detailed criteria for exceptions that would allow workers to leave the lift, and then devised a way to communicate to the entire team each time this approved exception was in operation. We suspended flags from the boom lift to signal to the rest of the field crew that an approved exception was in place for each excursion from the lift. We wanted to be sure that our culture of safety was never compromised, and that worker safety was always a top priority.”
Extensive planning, sequencing, and coordination were all critical to the ultimate success of this demanding project. Despite a variety of challenging factors, a well-coordinated plan and precise execution of the plan allowed the JP Cullen ironworker crew to complete the job safely, three weeks ahead of schedule (allowing following trades to start early), and on budget.
The new Milwaukee Bucks Arena is an important project in the revitalization of downtown Milwaukee and the centerpiece of an all new entertainment district including a training center, parking structure, and entertainment plaza. The completed arena structure holds 17,500 seats, 34 suites, three clubs, and 170 theater boxes, and is designed to enhance the entire fan experience of game attendees.
