The Miami Valley Hospital cardiac center, currently nearing completion in Dayton, Ohio, is a 500,000-sf, 12-story addition that will provide state-of-the-art diagnostic and treatment services to the region. When it opens in a few months, the $137 million facility arguably will become the first major hospital project in the U.S. to have made extensive use of prefabricated components in its design and construction.
位于俄亥俄州代顿的迈阿密谷医院心脏中心(Miami Valley Hospital cardiaccenter)目前已接近完工，它是一座占地50万平方英尺、12层的新建建筑，将为该地区提供最先进的诊断和治疗服务。几个月后，这座造价1.37亿美元的医院将成为美国第一个在设计和施工中大量使用预制组件的大型医院项目。
At Miami Valley, prefabrication yielded higher quality construction, a safer work environment, and a faster construction schedule. This project raises the prospect that if prefabrication can be used successfully in a complex hospital project, it may also be a sound methodology for constructing affordable multifamily housing, college and K-12 classroom buildings, university residence halls, medical offices buildings, laboratories, hotels, senior living facilities, and other building types with numerous repetitive components.
At Miami Valley, five key component types were constructed and assembled off site:
• Patient room toilets, casework, and headwalls
• Integrated MEP racks above corridors
• Modular workstations for staff
• Unitized curtain wall sections
• A temporary pedestrian footbridge
The design firm, NBBJ, and construction manager, Skanska USA Building, are enthusiastic about applying what they’ve learned about prefab in Dayton to future projects.
RULES OF ENGAGEMENT FOR PREFAB CONSTRUCTION
Modular prefabrication makes sense when the project has a sufficient number of repetitive elements—for example, 178 patient rooms, as in the Miami Valley project. According to Building Team members on that job, once that baseline is set, several best practices should kick in:
1. Prefab must serve the design, not vice versa.
2. Engage key subcontractors and suppliers early in the design process.
3. Use BIM—without it, it’s almost impossible do prefab right.
4. Build a mockup, and test it on occupants and end-users.
5. Employ just-in-time delivery of modules to keep the job site free of clutter.
6. Make sure your modules can be delivered on conventional flatbed trucks or the equivalent. A miscalculation here could prove embarrassingly expensive.
Setting the stage for prefab
Three years ago, when the Miami Valley project was in preliminary design, NBBJ and Skanska independently were looking at how to ramp up use of prefab elements in building construction. NBBJ principals had just attended a seminar by James Timberlake, FAIA, founding partner of the Philadelphia architecture firm KieranTimberlake, examining how manufacturing approaches might transform building construction. The author of refabricating Architecture lit a fire under NBBJ staffers.
Around the same time, interest in prefab was percolating at Skanska. The construction management firm already had a couple of prefab-intensive hospital projects under way in the United Kingdom, and Skanska managers here were eager to try it on this side of the pond.
At an early process design charrette with the owner, Tim Fishking, AIA, NBBJ’s principal-in-charge, says he and Marty Corrado, Skanska’s project executive on the job, had one of those moments when the proverbial light bulb went on over their heads and prefab seemed to make sense for the project.
However, for Bob Eling, director of strategic construction for Premier Health Partners, the owners of Miami Valley Hospital, prefab represented a radical departure from established construction practices. Only after a tour of Skanska’s prefab hospital projects in London in the fall of 2008 was he reassured that prefab could work in Dayton.
然而，对于迈阿密谷医院(Miami Valley Hospital)所有者Premier Health Partners的战略建设主管鲍勃•埃林(Bob Eling)来说，预制装配式住宅代表着对既定建筑惯例的彻底背离。2008年秋，在参观了Skanska位于伦敦的预制装配式医院项目后，他才打消了在代顿使用预制装配式医院的疑虑。
When he took the case for prefab to his management, Eling was pleased to find them open to the idea. “They wanted to know the usual: ‘Are we going to get the job done, and how much will it cost?’” he recalls. His main selling point: trust. “We had worked with Skanska on another job, and we had faith in them
THINKING ‘PREFAB’ LEADS TO HIGH-FLYING BRIDGE SOLUTION
Three buildings had to be demolished to make room for the new addition, which created the need for a temporary bridge to maintain pedestrian circulation between buildings during construction. A conventional bridge would have cost $2.1 million and taken several months to build. Instead, the Building Team came up with a unique solution: have an airport jetway vendor build it. JBT AeroTech built the bridge in five sections using an off-the-shelf design. Workers on site poured the foundations, set the sections in place, and connected them in just three days, with no disruption to pedestrian traffic. The cost: $980,000.
“We wanted to use part of the bridge for a connection between one building and the parking garage,” said Premier Health Partners’ Bob Eling. But the permanent footbridge had to have glass on both sides, and the jetway had glass on only one side. Retrofitting it would have been more expensive than building one from scratch.
我们想用桥的一部分来连接一座建筑和停车场，Premier Health Partners的Bob Eling说。但是永久性的人行桥两边都要装玻璃，而高速公路只有一边装玻璃。改造它要比从头开始建造更贵。
Putting prefab in perspective
NBBJ’s Fishking is quick to point out that prefabrication did not rule the design process. The chief programmatic concerns were to provide high-quality construction and a facility that met the needs of staff and patients. “When we got to a certain point of understanding the function, operation, and aesthetics, we started to look at prefabrication,” he says. “We didn’t develop the components to try to jam them into a prefab box.”
“Prefab must serve the design,” says NBBJ senior associate Ryan Hullinger, the lead designer on the project. Once the design parameters were established, however, it became clear that there would be a number of opportunities for using prefabrication.
As it turned out, the actual design of the modules became largely a function of the means by which they would be transported from the manufacturing plant to the job site. In order to avoid the cost and hassle of securing special permits for oversize loads, it was determined that all components had to fit on a standard flatbed truck. The designers also had to take into account the weight and bulk of the components, so that onsite workers could readily hoist the units and put them in place.
These physical factors led to a decision that may look obvious in retrospect but took some clever thinking at the time: split the bladelike walls dividing patient rooms into three parts—a toilet unit, a headboard, and a casework unit—and use factory-built MEP racks as well.
Manufacturing the components
Once the decision to use prefabricated components was made, NBBJ went searching for suitable off-the-shelf bathroom modules—to no avail. “We couldn’t find anything that met our standard for quality,” says NBBJ’s Hullinger. They had no better luck finding modular MEP racks. The Building Team quickly realized that there was only one way these elements could be made: Skanska and its subcontractors would have to manufacture them themselves.
Skanska rented an old furniture warehouse less than three miles from the hospital as the fabrication plant. Before ramping up the assembly line, workers constructed a bathroom mockup at the warehouse. Nurses and other hospital professionals critiqued the design; as a result of their input, certain fixtures were repositioned to make patient care and maintenance easier.
All components were custom-assembled and constructed using conventional building materials. Tradespersons assembled the patient room “blades”—the room-dividing walls and bathrooms for 178 patient rooms—and the overhead MEP racks. All metal studs, ductwork, conduits, and pipes were ordered to length, reducing waste material almost to nothing. The 8×22-foot MEP racks were built to fit within 16-foot-wide corridors that spanned five patient-room floors.
Exactly how the blades and overhead racks would be lifted and placed in the building was something that the contractor determined after the modular components were built. “We had to figure out how we were going to rig these components and fly them into the building,” Corrado says. “We took them to a truck stop to have them weighed so we would know how much weight we were hanging off of the steel.”
With little room at the construction site to store components, workers employed just-in-time delivery of the modules from the warehouse to the hospital. Crews built a custom dolly to position the blades after they were lifted into the building. Notches were sunk into patient floors exactly where the bathroom modules were placed—an instance where precision was critical.
Another key area for prefabrication was the curtain wall. “Unitizing the curtain wall is not new, but we took the next step by having closer coordination with the curtain wall subcontractor,” Fishking says. NBBJ adopted a design-assist relationship with the fabricator. “This is very different from design-bid-build,” says Hullinger. “Here, the fabricator was brought into the design process and their knowledge of construction techniques was readily available to us. The result was a better design.”
Modular curtain wall construction also greatly increased the speed to getting the building enclosed. “This is especially important on a site where you don’t have a lot of space to store materials,” says Fishking.
BIM AIDS ACCURACY, PRECISION, PROBLEM-SOLVING
In any building project that makes extensive use of prefabrication, modular elements have to be largely complete when put in place and must fit precisely into the structure—on-site alterations are a no-no. That’s why competence with BIM has to be pretty much a given for any Building Team using a lot of prefab components. Skanska and subcontractors TP Mechanical, Dalmatian Fire Protection, and Chapel Electric used Autodesk Navisworks to coordinate design and construction of the MEP systems.
在任何广泛使用预制构件的建筑项目中，模块化元素必须在到位时基本完成，并且必须精确地适应结构——现场更改是一个禁忌。这就是为什么BIM的能力对于任何使用大量预制构件的建筑团队来说都是必须的。Skanska和分包商TP Mechanical、Dalmatian Fire Protection和Chapel Electric使用Autodesk Navisworks来协调MEP系统的设计和施工。
According to NBBJ principal-in-charge Tim Fishking, AIA, using BIM not only improved accuracy and precision, it also “greatly enhanced” the team’s ability to solve the design problems associated with the components.
据NBBJ的负责人Tim Fishking, AIA所说，使用BIM不仅提高了准确性和精度，还“极大地增强了”团队解决与组件相关的设计问题的能力。
Results vindicate the prefab approach
As the project nears completion, the advantages of the prefab approach—particularly improved construction quality and greater precision—are becoming more and more apparent.
“In conventional construction, no matter how well your design is coordinated, that can slip during field construction,” says NBBJ’s Hullinger. With prefabrication, “You can develop elaborate, well-coordinated 3D models that show the location of every pipe, duct, and beam. Overhead racks look exactly like they were modeled. That’s remarkable.”
Having major subcontractors involved early was essential to making the prefab strategy pay off, says Premier Health’s Eling. Bids were sent out when construction drawings were just 50% complete. The subs’ input led to higher quality prefab components; the resulting accuracy of the models made installation of the MEP racks go smoothly. “We didn’t have to modify one beam pocket out of hundreds of beam pockets,” says Skanska’s Corrado says. “Same with our attachment points.”
The prefabrication process also was a boon to worker productivity. For example, a good day’s output for a plumber working above ceiling level would be about 200 feet of pipe per day. At the warehouse, output was tripled, averaging 600 feet of pipe a day—this for workers who were paid about $40 an hour, compared to $50 an hour for on-site workers.
In fact, the manufacturing process was so efficient that the work on the construction site could not at times keep pace, so Skanska had to rent additional space to store the blades and MEP units until the construction crews were ready for them.
Prefab also helped accelerate the construction schedule. “You can start your interior rough-in while you’re still doing structure and foundation,” Corrado says. “We were able to do interior rough-in components in February in Ohio in a temperature-controlled warehouse instead of outside on an upper floor with the wind blowing through at zero degrees.”
There were ergonomic benefits as well. Factory workers standing on a level floor with easily accessible tools and materials were at lower risk for muscle strain than if they had had to climb up and down ladders to construct MEP racks above their heads at the job site. There were no shop injuries on the job.
Eling sums up the advantages of prefab in three words: schedule, safety, and quality. Although there were also some cost savings associated with prefabrication—notably more than $1 million on the temporary footbridge—prefabrication didn’t provide a huge overall project cost savings on the $137 million project, Eling says. Prefabbed components touched only about 11% of total construction costs.
Down the line, however, hidden savings could emerge. “The MEP racks on the five patient floors are identical,” Eling notes. “All of the ductwork, dampers, sprinkler piping, medical gases, and offshoots to patient rooms were constructed identically and positioned the same way on each floor. In the future, maintenance personnel will know exactly where to go to work on them.” The MEP racks also were constructed with extra room to add infrastructure, as needed.
Looking toward the prefab of tomorrow
“Early on, we had many of our people that thought this process was too far-fetched to try on a big hospital project,” Corrado says. Doubts faded once the skeptics were able to tour the manufacturing facility and, later, when installation of prefab components in the building worked as intended, Corrado says.
Skanska management has taken note of the results at Miami Valley. Skanska project teams must now submit a prefabrication plan to their area managers for consideration on all U.S. projects, according to Corrado.
The Miami Valley project proved that prefabrication can work in a complex building setting. In the future, Building Teams would be well advised to investigate how prefabrication might be applied to any structure with repetitive features. The benefits are too compelling to ignore.
WHAT THIS BUILDING TEAM LEARNED ABOUT PREFAB (AND WHAT THEY SAY THEY’LL DO BETTER NEXT TIME)
The Miami Valley Hospital project was a prefabrication proving ground for NBBJ and Skanska. Based on what they learned, here’s what project managers from these companies say they would do differently on future projects:
1. Look for more off-the-shelf options.
At the start of the project in 2007, the designers could not find off-the-shelf bathroom modules that met their criteria, but that’s no longer the case, as manufacturers are responding with new and better products. “The market is moving fast, and vendors are trending toward products that we could be pretty excited about on future projects,” says Ryan Hullinger, NBBJ lead designer.
2. Strive for just-in-time production.
Now that Skanska has a good handle on how long it takes to construct prefab modules, scheduling can be better coordinated. “We would do more just-in-time production of the modules so that we could get a much smaller place for the prefab work, which would be cheaper,” says Marty Corrado, Skanska project executive.
3. Prefab modules can be more finished products.
With a better handle on prefab production schedules, modules could be fabricated with a higher degree of finishes. Research labs, exam rooms in medical buildings, kitchenettes, and other spaces could be prefabricated in a more completed state, the Building Team members feel.
4. Apply prefab to more complex components.
At Miami Valley, design of prefabricated MEP racks was kept fairly simple; only straight sections were constructed in the fabrication plant. In the future, Skanska’s Corrado says he would like to take on more complex prefabricated systems, such as intersecting corridor sections. Spaces that are laden with high-tech infrastructure may also be good prefab candidates. “In an operating room that we’re developing now, the ceiling is very technology intensive, so we’re looking at how components in that ceiling could be built offsite,” he says.
5. Consider using prefab in renovation projects.
Prefab may not be just for new construction, the Miami Valley team says. “One of the interesting areas of potential is renovation work,” says NBBJ’s Hullinger. “You have the opportunity to prefabricate components before demolition begins, so that as demolition is occurring on site, components are being built off site. As soon as demolition is completed, these pieces could be inserted. You would minimize disruptions in the building and gain a lot of efficiencies.”