|Rendering of new performing arts center in downtown Kansas City, MO. (Courtesy Kauffman Center)|
From the steel cables that hold up the spectacular glass lobby to the precast walls that form the majestic arch-like exterior, the Kauffman Center for the Performing Arts in downtown Kansas City, MO, is an extraordinary architectural and engineering masterpiece.
Fast approaching the third year of construction, the $326-million project is well on its way to meeting a planned opening before the 2010-2011 performance season. JE Dunn Construction, Kansas City, MO, is managing construction of this world-class facility and is overseeing the work of more than 200 workers on-site, including steel, concrete, mechanical, electrical, and excavation personnel.
The Kauffman Center's philanthropic organizers look on with growing excitement, pride and, likely, some relief as a decade-long vision draws closer to reality. They know it wasn't that long ago that the structure's plans were nearly shelved.
As a privately funded, nonprofit institution governed by an all-volunteer, seven-member board of directors, the Kauffman Center for the Performing Arts relies solely on gifts from the community. The estimated cost of the center as originally designed proved to be well over the accumulated donations.
Organizers looked to the engineering and construction team for help, who in turn looked deep into the Missouri bedrock to find the answer and put the project back on track.
The Kauffman Center is 284,470 square feet and sits on about 3 acres of land. When complete, it will include a 1,800-seat proscenium theatre, a 1,600-seat concert hall, a 1,000-space parking garage, and a glass-enclosed grand lobby.
Conventional foundation engineering calls for a structure this size and this heavy to use drilled piers to support the large design loads. Kleinfelder, the geotechnical and design consultant for the Kauffman Center, suggested the design-build team consider alternative foundation solutions.
For almost a decade, Kleinfelder has partnered with Kauffman Center organizers to provide geotechnical analysis and design information for the performing arts center and adjacent parking garage. During this time, Kleinfelder had developed a subsurface exploration plan that includes detailed information about the site development, foundation system, lateral earth pressures, floor-slab support, seismic classifications, and pavement design for the entire structure.
When the cost issue came up, Kleinfelder suggested that the design-build team consider a mixed foundation system – a combination of rock-bearing spread footings and drilled piers extending to a more massive limestone unit to develop higher capacity foundation loads. Based on that study of the subsurface conditions and the engineer's understanding of the structural design characteristics, the team was able to provide a more economical foundation system.
Like much of downtown Kansas City, the Kauffman Center site sits on sedimentary bedrock consisting of interbedded limestone and shale formations. Original foundation engineering plans considered drilled piers throughout the site. Due to high initial cost estimates, areas including the foundation system were investigated for potential cost savings. The site was already being excavated into the underlying limestone bedrock formation to develop design grades, so areas within the building having lighter structural loads could be built on foundations bearing on the upper portions of the limestone and shale formations.
Kleinfelder recommended the use of shallow spread footings in areas behind the stages where the loads are not as heavy, and then drilled piers in areas where column loads were higher. Column loads generally ranged from 1,000 to 2,000 kips in the theatre areas. The contractor suggested a peer review to evaluate the possibility. The peer review engineering team agreed with the recommendation, ultimately helping save thousands of dollars and giving the Kauffman Center project the boost it needed to break ground.
Mass excavation began in January 2007, followed by drilling piers, digging footings and finally placement of concrete for the beginning of the foundation system.
By September 2007, the orchestra pit in the proscenium theatre was dug out and footings for it were progressing. Foundations were also completed for the fly tower – the tall backstage area within the proscenium theatre where equipment such as sets, scrims, lighting, and riggings can be suspended and ready for use.
Dual-Capacity Rock Anchors
Another key element of the Kauffman Center foundation is a complex rock anchor shoring system that performs the dual task of retaining the exposed shale and limestone bedrock face as well as providing lateral support for the north wall of the parking garage and south wall of the Kauffman Center.
The south wall is 50 feet tall by 350 feet long by 4 feet wide and will anchor the structural cables from the performing arts center's grand lobby, a central glass-enclosed lobby that connects the two performance spaces and leads sloping green space above the garage.
The wall is supported by an 8-foot-wide, cast-in-place concrete foundation bearing on the exposed limestone bedrock formation with rock anchors installed to provide increased resistance to the uplift forces. While this wall was built adjacent to the excavated rock face for the planned parking garage and will be backfilled between the wall and rock face, the opposite side will remain exposed along the side of the garage.
Because of this, it was critical that the wall be anchored to resist the forces from the cables along the top and also the lateral forces from the backfill material placed adjacent to the wall. To reduce the lateral pressure applied to the wall, the area between the wall and rock face was backfilled using a flowable fly ash fill material.
Design engineers designed the shoring anchors to support 50 kips and the wall tie-back anchors to be buried 35 feet into the bedrock and support 84 kips.
As one construction team dug out the garage space, another installed the rock anchors with engineers watching closely. Two rows of the anchors extend through the wall to provide additional resistance and lateral stability for the wall.
Difficulties were encountered during installation due to the upper row of the tie-back anchors extending through the transition area of the upper limestone formation into the underlying shale formation. Following a series of test anchors, engineers decided to increase the diameter of the holes, flatten the angle of the anchors to maintain the bonded length in limestone bedrock, and reduce the bonded length of the anchors to achieve the required design capacities of the tie-back anchors. These tie-back anchors were critical to providing the lateral stability that was required for this massive wall.
Throughout, Kleinfelder performed special inspection with respect to the installation of the shoring system, evaluation of the bearing materials for the wall foundation, and observation and testing of the reinforcing steel and concrete for the proposed south wall.
By December 2007, 10,000 cubic yards of concrete and 2 million pounds of rebar had been placed, nearly completing the foundation work. Underground work began in the central plant, enabling foundations and finished floors to be installed. Elevated decks were placed that allowed early mechanical and electrical work in equipment pits to take place.
In early 2008, walls began emerging above street level. The fly tower of the proscenium theatre was topped out in August 2008. At 74 feet, this structure is currently the tallest feature of the building, but will soon be dwarfed by the structural steel frame. Construction of the anchor wall that supports the unique atrium glass structure has also been completed with the large embed plates installed that will eventually secure the structural cables from the building.