nov 16 | Civil Engineering Magazine

Church Building Design Features Sweeping Curves and Connection to Nature

By Robert Reid

A new, 72,000 sq ft church building for the Chicago areas Willow Creek Community Church will have an elliptical form in plan that will provide both sweeping curves to facilitate circulation within the building and large windows that will offer views of the tree-lined courtyards and other vegetated spaces surrounding the building. The glazing will also help fill many of the church's rooms with natural light.

Willow Creek Community Church is based in South Barrington, Illinois, and has seven other locations in and around the Chicago metropolitan area. A permanent home for the North Shore congregation in Glenview, Illinois, which currently meets in a rented facility, is under construction and is expected to be completed by year's end. Designed by Chicago-based Adrian Smith + Gordon Gill Architecture, the new North Shore building will feature a curving form inspired by the shape of a mustard seed, which has biblical significance, as well as floor-to-ceiling windows to "strategically bring the experience of the outdoors inside to the occupants," explains a description of the project on the Willow Creek website.

Forefront Structural Engineers, Inc., of Chicago, was responsible for the structural design of the mostly steel-framed church building. Haeger Engineering, based in Schaumburg, Illinois, was the project's civil engineer and land planner and in that capacity was responsible for the stormwater management systems at the site and for helping the church staff resolve zoning and permitting issues with the Village of Glenview. Glenn H. Johnson Construction Company, of Des Plaines, Illinois, was the general contractor.

The new North Shore building is being erected on a 14-acre site, much of which formed part of the U.S. Naval Air Station Glenview, which closed in 1995. The buildings on the site had been demolished by the time the North Shore church project began, but existing underground utilities had to be removed. Moreover, a road had to be demolished to make way for a modern replacement. The land itself had to be regraded to eliminate a slope from west to east, the difference in elevation totaling approximately 10 ft, so that runoff on the property could be directed toward two new stormwater management systems, says Todd A. Shaffer, P.E., a Haeger principal.

The regrading lowered some portions of land on the west side of the site and raised certain parts on the east side. It also involved the installation of new storm sewer pipes so that the overland flows could be directed to a new stormwater basin and a new underground storage vault, explains Shaffer. The basin, essentially an excavated pond on the southeastern portion of the site, has a storage capacity of 7 acre-ft, whereas the concrete-framed vault is located in the northeastern portion and can store roughly 0.7 acre-ft.

The church's stormwater management infrastructure is part of a shared system designed to also accommodate runoff from an adjacent new residential development to the south of the church's property, adds Shaffer. On the northern side of the site is a cemetery at a lower elevation, and a segmental block retaining wall roughly 1,100 linear ft long was constructed along the northern perimeter to help redirect stormwater flows toward the basin, Shaffer says.

The main entrance to the church building will be oriented to the south beneath a long cantilevering sun canopy. The basin will therefore be an attractive feature near the entrance and will include a fountain to aerate the water, "making a functional need into a very nice frontage for the church as well," notes Sara Beardsley, AIA, a senior architect for Adrian Smith + Gordon Gill.

The design of the church building was intended to be "very in tune with nature," Beardsley adds, "to bring the outdoor spaces and views to all the different parts of the church." To that end, the one-story structure will include two large interior courtyards flanking the east and west sides of the central auditorium, the church's sanctuary space. Large picture windows will overlook those courtyards from the auditorium, and there will be extensive glazing along the perimeters of the circulation corridors and other spaces within the church building. The glazing will provide views both into the courtyards and out toward the trees that will surround the building and parking areas. A long, sloping skylight above the entrance, along with a cafe, will be located at the southern end of the building, the slope designed to help shed water, Beardsley says.

The architects worked closely with the Village of Glenview on the location of the surrounding trees to provide visual screening, and lighting poles shorter than traditional ones will be used around the site to avoid "light trespass issues" that might affect the surrounding residents, notes Beardsley.

Founded on shallow spread footings of reinforced-concrete, the steel framing of the church structure will vary in height from roughly 14 ft in the side wings surrounding the auditorium to roughly 44 ft at the peak of the auditorium roof, at its southern edge. At that point the roof will slope down toward the north and drop straight down to the lower roof above the cafe, explains Josh Dortzbach, S.E., P.E., a Forefront principal. The building will measure roughly 310 ft in the east-west direction and approximately 340 ft in the north-south direction.

The steel system will feature moment-resisting frames located approximately 20 ft apart on center along the building perimeters, as well as steel mullions located 10 to 15 ft apart to support the glazed curtain walls. Concrete masonry unit (CMU) shear walls will be located at the front and back of the auditorium -that is, at the southern and northern ends - and these presented some challenges because of the change in roof elevation at that point between the auditorium and the cafe, notes Pavan Sarguru, a Forefront structural engineer.

"We were framing an entire level of the roof midspan into the wall, but we were also using it as a shear wall," Sarguru explains. "So we had to find a way to maintain the structure and strength of the CMU wall without cutting the entire middle of it with steel embedments."

Ultimately, the solution involved framing a steel member at the elevation of the cafe roof, turning it 90 degrees, and putting steel scuds in the web so that the CMU wall would frame into the side of the steel member. In this way the wall can be framed on the other side of the steel member in the flanges of the beam, Sarguru says.

A template for holes to accommodate the reinforcement of the CMU wall will be fabricated in the web of the wide-flange beam so that the mason can easily erect the reinforcing for the CMU wall, Dorczbach adds.

The auditorium framing will feature hollow structural steel columns approximately 18 in. in diameter and transfer trusses in the ceiling that will be up to 10 ft deep and span as much as 175 ft in the ease-west direction, says Dortzbach. The trusses will be formed primarily from W14 elements and in at least one location will feature a sloping chord to accommodate the mechanical systems and holes for catwalks, notes Sarguru.

The sunshade canopy on the building's southern facade will be framed in aluminum and steel and, supported on outriggers formed from hollow structural steel elements, will cantilever approximately 15 ft from the building perimeter. Thermal breaks will be used to minimize any potential thermal transmission through the long radial members of the canopy.

Because of the building's irregular shape, the structure had to be evaluated for wind forces from any direction, Dorrzbach notes, and the varying heights of the roof had to be designed for the potential of drifting snow.