When a contractor is brought to a project late in the game, as is so often the case, little opportunity exists for crucial design input. The result is reduced productivity, cost overruns and extended construction schedules.
At Palomar Medical Center West (PMC West), a 755,000-square-foot hospital project now under construction in Escondido, Calif., integrating key specialty contractors from design and steel fabrication through construction optimized project results.
Early integration of the structural steel fabricator resulted in a more efficient design that reduced cost and accelerated the schedule. The steel structure was completed for $7.2 million under the original estimate of $52.8 million and the original 13 month schedule was reduced by six weeks. Steel erection was completed with no change orders and one quarter of the typical number of RFIs.
Located in Northern San Diego County, the new 360-bed hospital scheduled for completion in 2011 will replace the acute-care services at the existing Palomar Medical Center in Escondido. For Palomar West, sustainable health care was defined as a high-performing hospital in which nature coexists with and is enhanced by technology. Targeted for LEED® Gold certification, sustainability was a consideration in every aspect of design, from water and energy efficiency to envelope and structural design.
As for the hospital’s structural frame, its gravity system consists of a concrete-filled metal deck supported on steel beams, girders and columns. The lateral force resisting system is composed of special steel moment frames using the proprietary SidePlate® system from level one to roof, and concrete shear walls in the one-story partial basement.
Delivery of the structural system on PMC West demanded an interactive and collaborative team effort between the structural engineer, KPFF Consulting Engineers, Los Angeles; the construction managers Rudolph & Sletten, San Diego and DPR Construction, San Diego; the steel contractor, The Herrick Corporation, Stockton, Calif.; and the architect, CO Architects, Los Angeles. The process combined design considerations with concerns about means and methods. Biweekly face-to-face meetings and countless e-mails were used to discuss framing, sequencing and detailing options for different areas of the building during the design process. Electronic sketches derived from the Revit Building information modeling (BIM) system, as well as hand sketches, were continuously exchanged between team members during the design process.
By employing an alternative project delivery method, feedback and discussion of the design was interactive and took place during the design process — a stark contrast with conventional design-bid-build processes in which contractor feedback is post-design.
Integrated process at work
Due to its architectural and functional importance, the project’s most compelling feature is the D&T wing’s “wavy” roof. This undulating architectural feature supports both a green roof and the MEP systems that feed the operating and imaging rooms on level two. It also provides future remodeling flexibility by providing a column-free zone 105 feet wide by 303 feet long in the operating rooms area. The roof undulates from 22 feet to 32 feet above level two, necessitating an interstitial support at the operating rooms’ ceiling level to accommodate secondary MEP systems, overhead medical equipment and ceilings.
Changes to the roof’s preliminary structural design saved nearly $2 million in material and labor and sped construction. The preliminary design was comprised of 105-foot-long structural steel trusses at 34 feet on center with sub-trusses at 11 feet on center, spanning between the main trusses. Because the complexity of the two-way truss system would require extensive field labor, the team eliminated the sub-trusses’ diagonals, turning the roof into a one-way truss system with top and bottom purlins at 11 feet on center. This shifted many of the field hours to the steel fabrication shop, simplifying the tasks to be performed in the field and optimizing transportation to the site.
Truss depths varying from 12 feet to 22 feet posed a transportation challenge. Discussions related to the truss end connections, allowable truss splice locations and possible truss vertical and diagonal member connections led to the decision that the trusses would be bolted together in the field.
To achieve the undulation, instead of utilizing radiused members as initially planned, the beams were segmented, with the small difference between the straight segments and the desired curvature achieved through variation of the concrete thickness.
Framing supporting outboard restrooms in patient rooms was also carefully evaluated during meetings, as this complex condition repeats 360 times on the project. The patient tower has a long and relatively narrow footprint with patient rooms located along the longer edges. Triangular-shaped restrooms cantilever from the perimeter framing forming saw-toothed edges that enhance the architecture.
The use of an end plate connection for the cantilever and back span at every other restroom is self-supporting and self-aligning, which eliminated the need for temporary posts at each cantilever prior to welding. The intermediate restroom framing was shop welded to the edge beam and installed as one piece in the field. These innovative ideas eliminated 720 complete penetration joints and transferred hours from the field to the shop, streamlining erection and improving job safety.
Other beneficiaries of intense collaboration were the patient tower terraces and central feature element tower. Staggered terraces on three sides of the tower support trees and heavy planting. The central terrace features a glazed tower feature element cantilevering above the upper floor. Exposed rectangular hollow structural sections (HSS) support the screens and cantilever above the roof to frame the feature element.
The steel contractor’s understanding of the design, as well as the design team’s understanding of the erection sequence, was essential to meeting the structural and erection challenges posed by the terraces. In order to accommodate vertical deflections from heavy planting loads and thermal expansion, slotted connections were provided at alternating floors and joints between segments of the vertical HSS members, allowing for expansion and contraction. The expansion joints were created using a male-female pin connection just above the supporting connection to the building frame. The specific geometry of the pin connection was conceived by the steel contractor to allow for ease of erection.
Teamwork pays dividends
Coordination sessions with the design team, steel contractor and concrete contractor ensured opportunities and conflicts were addressed in the design. Encased structural steel replaced traditional reinforcement at the more congested footings. Sequence and schedule impacts were addressed each time a revised detail was considered.
Elevator guide rail supports and slab edge details often require redesign and rework during construction when design input is not solicited from the relevant trade contractors. Early collaboration between the design team exterior wall and mechanical contractors allowed the team to coordinate closure details along the perimeter and interior openings of the building. Similarly, collaboration with the steel and the elevator contractors enabled the team to properly locate the elevator guide rail support HSS. These two items were successfully installed without any significant field rework, which benefitted the schedule.
Transportation of steel members, rarely a significant consideration in design, was addressed by the team. The heavy moment frame beam-column trees posed transportation challenges due to their width and weight. The design team voluntarily switched to the 2007 California Building Code (CBC) prior to its enforcement to reduce the design’s seismic base shear and realize a reduction in the LFRS steel tonnage. This also eliminated a need for custom built-up frame columns, allowing standard rolled sections to be used exclusively on the job. The resulting smaller, lighter sections allowed for fewer permit loads to the jobsite. The steel tonnage savings from the code switch totaled 800 tons.
As for sustainability, the elimination of sub-trusses, the code switch and the use of rolled column sections had a significant effect on reducing overall steel tonnages. The code switch alone reduced CO2 emissions by 1,200 tons due to the reduced steel tonnage. It also reduced energy used in fabrication by changing built-up members to rolled sections and minimized the steel shipped from outside the country. Besides the savings in emissions from transportation, domestic structural steel manufactured using an electric arc furnace is comprised of 93.3 percent recycled scrap material, which more than halves CO2 emissions compared to manufacturing steel from raw iron ore.
Without early and frequent participation by specialty contractors, the PMC West would not have achieved these positive outcomes. The collaborative process reduced the cost of materials by $1.5 million and labor by $1.8 million. Risk mitigation efforts and a highly detailed scope package allowed $2.7 million reserved for potential changes to go back to the owner. RFIs were reduced by an estimated factor of four with no change orders and the structural framing system was delivered three weeks ahead of schedule.
M.N. Zeidan, M.A. Hershberg, A.D. Reynolds and J.R. Gavan are with KPFF Consulting Engineers, Los Angeles. R. Nazareno, T. Kuznik and B. Hazleton are with The Herrick Corporation, Stockton, Calif.