[Source: enr.ecnext.com, June 9, 2010]
Contractors building one of the largest and tallest pediatric research hospitals, hemmed in on a tiny site in Chicago, say they are several months ahead of schedule in part due to the owner's requirement that designers and contractors collaborate using building information modeling, a digital tool that helps prevent errors. However, the use of BIM apparently still has some growing up to do. For the 1.25-million-sq-ft hospital that stands 457 ft tall on just 1.8 acres, the building team not only is tackling the challenges of urban, vertical hospital construction, it also is conducting research to determine if the time and cost of modeling the hospital, down to its mechanical hangers, is adding value to the project.
Armed with laser scanners and their resulting "point cloud" diagrams, construction managers are beginning to compare BIMs to what was built. Early results of the reality check are in, even as the fast-tracked project is just 50% complete.
The scans are expected to go a long way toward understanding what is and isn't creating value. No one knows for sure what the BIM effort cost, but one project executive, Bob Gallo, guesses it saved seven figures. "The expectation is the premium up front pays for itself [in the] long term," says the senior vice president of Power Construction Co., Schaumburg, Ill. The firm is in a 50-50 construction management-at-risk joint venture with Minneapolis-based M.A. Mortenson Co. to deliver the $1-billion Ann and Robert H. Lurie Children's Hospital of Chicago.
"The real question ... is, what's adding value to the project?" says Stuart Baur, project manager in the Los Angeles office of Zimmer Gunsul Frasca Architects LLP, the project's lead designer. "We could model loose-hung cable and J-hooks, but do we add value by doing that?"
The tiny site inspired a high-rise hospital. The emergency room, for example, is located on the second floor, requiring extra elevators and a special state permit. The bed tower starts on level 14 of the 23-story building. There, the L-shaped plan becomes two squares. Floors are roughly 50,000 to 60,000 sq ft.
The building, which topped out last fall and is on course to be delivered by June 2012, has a steel frame with a shear-wall concrete core, designed by structural engineer Magnusson Klemencic Associates, Seattle. Floor-to-floor height is about 17 ft up to the mechanical level 10, which has a 42-ft-high ceiling. Above that, the floor plate expands to provide a bilaterally symmetrical floor for the nursing staff. To allow this, the engineer devised a 90-ft-deep supertruss, from levels 16 to 22, creating a 180-ft-long 30-ft cantilever over an easement that runs along the building's east side. Truss loads bear on the first set of internal columns.
BIM There, Done That
Most of the building team already was well-versed in BIM, or 3D parametric modeling, but none had modeled a project quite this big. Due to its digital emphasis as well as legal issues, the project has morphed into a hybrid between collaborative, or integrated, delivery, design-build and conventional building.
The owner ruled out integrated project delivery with a multiparty contract, which is popular with some hospital developers. "I'm still not convinced you have as much of a competitive situation" with IPD, says Bruce Komiske, Children's chief of design and construction. Rather than parties sharing models, designers created their own models, and prospective contractors were brought on as consultants during the design phase. The CM bid out subcontracts competitively last year. Then, construction models were added to the design model without an implied right of reliance. But common to IPD, the building team was collocated.
Each firm forced BIM to grow up a little for Children's, where use of BIM was not negotiable. "There were a lot of challenges in the beginning, particularly on the technology side," says Komiske. The end result is a lot of models: There are currently more than 50 primary models and thousands of smaller models.
For all its 3D complexity, however, not everything at Children's is modeled, and there's a reason for that: Only elements one inch or greater in size are included-a rule established in the team's protocol manual. The idea is that something as small as ¾-in. pipe-effectively spaghetti to a constructor-can be worked out in the field without extra expense. "It's a lot about time versus value in today's current state," says Peter Rumpf, senior integrated construction coordinator for Mortenson. "But I don't think that it's too far off where we'll add that extra level of granularity." With BIM, he adds, more is usually better. "Whatever is not in the model is going to come back to haunt you. We want to get as much information in there as possible," he says.
Prior to construction, BIM provided a helping hand with coordination inside the building's most complex space: a 60,000-sq-ft, 42-ft-high mechanical room with three levels of ductwork and air-handing equipment. "I'd like to think that, without BIM, it would have been nearly impossible to build," says Jason Smith, chief engineer for mechanical contractor F.E. Moran, Northbrook, Ill. About 250 tons of sheet metal-prefabricated from 3D models-had been installed by last month, when crews took down the second tower crane.
Unused Potential
Despite the project's digital savvy, participants admit they are not using BIM to its full potential. Field crews still are building from 2D paper plans, which remain the official contract documents. Design and construction models still are segregated for liability reasons. The owner doubts it will achieve what some believe to be BIM's Holy Grail: using the data for facility management. "We teed it up to knock it out of the park, and yet we still have a ways to go in the industry," Rumpf says.
Enter the lasers, a tool helping to close the digital divide. Mortenson/Power is using them to audit contractors' work and, indirectly, to conduct BIM research. The CM has shot portions of three floors-about 20,000 sq ft-at a cost of under $10,000. Superimposing the point clouds on the BIMs, engineers are visually checking discrepancies between BIMs and reality. "[BIM] allows us to trim the fat," Rumpf says. The hard part is to accurately measure the savings. So far, the discrepancies have been minor .
During a kickoff meeting in 2006, ZGF, its subconsultants and the CM developed their own BIM protocol manual, a roughly 40-page document that remains largely unchanged today.
The team then tested the protocols by creating a digital model of a 10,000-sq-ft building. "It gave us the opportunity on a very small scale to test all the scope issues," says Baur. The manual's final draft was issued four months later, in fall 2006, before ZGF began design work.
Firms were asked to share their models. "It was very clear" that we all needed to work together relative to BIM, says Baur. Yet designers would not vouch for their models' accuracy because existing insurance products would not cover problems arising from digital sharing. "We simply couldn't warrant the contract documents were identical to the model, and that's an issue the industry needs to resolve," Baur says.
A design-intent model (DIM) emerged on the design side, followed by what has become the industry custom: a more detailed fabrication model for major systems, including ductwork and steel. The resulting models had to be sorted out by dozens of modeling engineers and coordinators. Five design models emerged-enclosure, structure, bed tower, diagnostic and treatment floors, and mechanical systems-and 48 fabrication models followed. When disagreements arise among the subs during clash-detection meetings, Mortenson/Power referees. "Its our job to decide whatever directive is given is in the owner's best interest," says Rumpf.
Aside from the liability concern, pushing 3D data from this project into the field has been a struggle. One reason is that, while used on this job for quality control, digital displays such as tablet PCs are still not large or flexible enough to replace the paper drawings. "We just haven't made that leap yet," says Smith, who adds that robotic total stations have complemented paper plans by helping installers reference location against the model in real time and without measuring tape.
Subcontractors note that, as is now common in the industry, BIM helped them work out clashes. It also helps installers make sure their aerial lifts go up with the proper nuts and bolts. "With BIM, you can develop these bills of materials, and the computer will tell you exactly what you need," says Smith.
Fine-Tuning
Though BIM simplified the complicated mechanical floor, it didn't help all that much with the cantilevered, 10-story bed tower. The frame had to be erected this past winter without falsework due to site constraints. The procedure-designed by Farmington Hills, Mich.-based Ruby+Associates under the direction of subcontractor Chicago Steel and fabricator Zalk Josephs, Stoughton, Wis.-involved hanging the truss on steel suspension cables, which temporarily were tied back into columns and floor beams.
Mortenson/Power originally had proposed building up from the 16th floor, then coming back down to finish the truss. Because the upper floors would obstruct part of the work below, some were concerned the project's tower cranes would have trouble accessing it.
Ruby proposed building the cantilever from the bottom up, but it had no built-in means of supporting it during construction. "That's where the cable system came in," says Ronald O. Goetze, Ruby's project engineer. A system of 48 tieback cables, ¾-in. to 11?8-in. in dia, were rigged from the cantilever beams, over column-hung pulleys and tied back into the main floor beams. The cables at their termination points were fitted with turnbuckles so that ironworkers could slowly relax the loading of the floors, set 2 in. to 3 in. higher than designed, after all the steel was in place, to avoid shock-loading. The rigging supported the cantilever like "a little crane," says Goetze, who adds the procedure took nine months to plan and about two months to execute.
Lower down, the building also tricks the eye. Transfer girders at levels 3 and 5 and a transfer truss at level 10 eliminated 18 of 80 columns at ground level due to at-grade obstructions, such as access drives. "If you talk about developing an office building, a lot of those buildings are really designed from the outside in," says Bob Anderson, an MKA principal. Hospitals, he adds, "really are designed from the inside out because the program and the function drives the building."
Role Model?
Children's is an example of how the construction industry struggles to embrace technology so that its players can work together better, experts say. Yet at the same time, the project shows how far the industry has come. "It has been a tremendous challenge, and I absolutely would do it again in a heartbeat," says Baur.
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