The next Bond

Patrick Cassity, P.E., Brian Kidwell, P.E., and Patrick M. Byrne, P.E. / November 18, 2009

The I-29/35 corridor leading into downtown Kansas City is already heavily used (an average of 102,000 vehicles each day) and forecasts show traffic volumes will continue to rise.

This congestion increases travel time, fuel costs and pollution, and is a contributing factor to the rising number of crashes along the corridor. Without increased capacity, these issues were likely to worsen. In addition, the existing Paseo Bridge is more than 50 years old and needs to be rehabilitated or replaced altogether if this structure is to remain in use over the next 60 to 75 years.

The kcICON Design-Build Project was initiated to address the issues along the corridor by improving capacity, safety and mobility and either replace or rehabilitate the Paseo Bridge to extend its useful service life. The selected design includes the design and construction of a new landmark cable-stayed bridge over the Missouri River and reconstruction of over four miles of I-29/35.

Design and construction services were procured under a design-build contract where proposers developed their own design and construction approach that maximized value to the owner for a fixed, non-negotiable price of $232 million. This fixed-price approach ensured that bids did not exceed the available funding. The project was awarded to Paseo Corridor Constructors, a joint venture of Clarkson Construction Co. (managing partner), Massman Construction Co. and Kiewit. Massman is primarily responsible for construction of the river bridge and Parsons is the lead designer for the overall project and the river bridge.

There were significant challenges associated with developing a design in this constrained urban corridor and balancing competing goals for the project. The Missouri Department of Transportation (MoDOT) required a landmark bridge design that produced dramatic day and night views of the bridge. In addition, the bridge must be durable enough to meet a 100-year service life requirement. However, a competing goal was to maximize capacity, mobility and safety improvements throughout the rest of the corridor.

Trying to score points

MoDOT utilizes a fixed-price, best-value approach to procuring design-build contracts. The design of the project is first developed by MoDOT in sufficient detail to obtain environmental clearances and most third-party approvals while at the same time ensuring enough flexibility for alternatives development and refinement during the design-build precontract and contract phase. The bid price of the project is fixed at the budget allocated by MoDOT, and a proposal scoring system is developed that reflects the project goals.

The overall project goals were as follows:

  • Deliver the I-29/35 corridor improvements within the total program budget;
  • Construct a landmark Missouri River bridge that can be reasonably maintained to provide more than a century of useful service;
  • Maximize safety, mobility, aesthetic and capacity improvements in the corridor;
  • Engage stakeholders and the community to successfully develop and deliver the project; and
  • Meet or beat the project completion date of Oct. 31, 2011.

In order to incentivize bidders to develop designs that responded to these goals, the proposal scoring system was based on a 100-point scale with the following categories:

  • Missouri River bridge aesthetics—20 points;
  • Missouri River bridge durability—10 points;
  • Project definition (scope/extent of improvements)— 30 points;
  • Method of handling traffic during construction— 15 points;
  • Public information—5 points;
  • Completion schedule—10 points; and
  • Disadvantaged business enterprise commitments and socially/economically disadvantaged work force utilization—10 points

In an effort to meet the goal of engaging stakeholders and the community to successfully deliver the project, MoDOT facilitated the organization of a Community Advisory Group (CAG) to provide input into the design development process. The CAG comprised staff and members of local municipalities, business organizations and community organizations.

MoDOT’s commitment to engaging stakeholders and the community stretched as far as allowing members of the CAG to have confidential meetings with the design-build teams and review their Missouri River bridge design and determine the final aesthetic score. This is the first time that the authors are aware of third-party stakeholders being given 20% of the say in selection of the design-build team.

Although this type of procurement process offers significant value to the owner, it places extreme demands on the design-build teams to develop a design that maximizes the technical score while meeting the fixed-price budget. It also challenges contractors to develop accurate conceptual-level cost estimates early on in the process to guide the decision making during design development.

Makings of an icon

The river bridge consists of a two-span cable-stayed structure with composite-steel-plate girder approach spans. The cable-stayed main span is 550 ft with a side span of 451.5 ft. The bridge deck cross section includes three 12-ft traffic lanes in each direction with a 12-ft northbound auxiliary lane.

The superstructure comprises a composite steel and concrete deck system made of precast concrete deck panels erected on, and made composite with, the floor beams and steel-edge girders. The superstructure is supported by 40 stays that radiate in a semifan arrangement from a single reinforced concrete diamond-shaped pylon.

The deck wearing surface is a fully replaceable 2-in.-thick microsilica concrete overlay. The wearing surface is designed to be a low-permeability protective barrier for the structural deck system that can be replaced once saturated with chlorides or as its condition warrants.

The structural deck system is a 9-in.-thick, 8,000-psi high-performance precast concrete deck spanning 16 ft 8 in. between floorbeams. The use of high-performance concrete allows the service life of the bridge to be extended to 100 years. Because the deck will be precast, it allows for a higher degree of quality control during production, since the panels will be cast in a factory-controlled environment.

The panels also will be post-tensioned longitudinally to provide additional strength and precompression to prevent cracking. The post-tensioning steel is protected by multiple barriers consisting of the overlay, structural concrete, duct and high-performance grout. The ducts will be polyethylene instead of metal to prevent corrosion.

The steel framing system is composed of two continuous longitudinal edge girders supported by two planes of cable stays. Transverse floorbeams are spaced at 16 ft 8 in.

The concrete pylon is composed of hollow box legs connected at the apex of the diamond and framed transversely by the strut below deck. The strut provides framing action to assist in resisting lateral loads applied to the pylon and to resist the outward force created at the knuckle of the pylon.

The inward inclination of the upper pylon legs and corresponding inward inclination of the stays creates a superstructure system that is very stiff torsionally and provides superior aerodynamic stability. The change in the direction of inclination of the legs at the knuckle allows the supporting foundation footprint to be minimized resulting in significant foundation and cofferdam cost savings as well as reduced impact to the river.

Dan Brown and Associates led the geotechnical design for the bridge foundations. The pylon foundation consists of a single rectangular footing, supported by a group of eight 11-ft-diam. drilled shafts socketed into bedrock. The river alluvial sediments are underlain by a shale bedrock formation that is well suited for drilled-shaft foundations.

Construction of the footing was facilitated by using a concrete seal extending from the mudline to the base of the footing. The drilled shafts were constructed with a permanent steel casing extending to the top of the shale bedrock, with a 10.5-ft-diam. socket extending approximately 20 ft into the shale formation.

This single large footing with multiple shafts provides a robust and reliable foundation that is not sensitive to scour and has strength that substantially exceeds any vessel impact or lateral load demand.

The permanent steel casing provides additional strength, ductility and confinement for the bending stresses in the drilled shafts, and it facilitates construction by providing a stable environment in which to construct the rock socket.

The approach bents include multicolumn piers with a single shaft under each column. Shaft diameters and lengths vary according to load demand at each column.

The design and installation plans were verified by constructing and testing a test shaft in the center of the main pylon to determine actual rock conditions at the pylon foundation. The shaft was proportioned to evaluate the design values of side shear and end bearing in the rock socket using the O-cell load test method. The test shaft rock socket was drilled using similar tools and installation techniques as was used on the production shafts, including downhole camera inspection so that the condition of the bottom of the socket can be observed. Structural integrity of the drilled shafts was verified by post-construction integrity testing using cross-hole sonic logging techniques.

Way of the gateway

Touchstone Architecture led the architectural design of the bridge and Illumination Arts provided aesthetic lighting design services.

The bridge is intended to provide a unique visual statement that complements the identity of the Kansas City community. The bridge design is cohesive from end to end. The lines of the approach spans and bents have been developed to become visually integrated into the design of the suspended spans.

In addition, the bridge is transformed at night with a unique lighting scheme. Aesthetics is not applied as an afterthought. Rather, the design team has worked diligently to create a bridge whose graceful lines and unique visual experiences flow naturally from the structural elegance of this solution.

The creation of a “gateway” experience for motorists traveling on this bridge is a fundamental part of creating an icon for the Kansas City community. In addition, the result is a unique experience for the motorist. As you approach the pylon, the cables envelop the roadway. The lines of the cables bring your attention skyward, and the pylon serves as a focal point and gateway through which every motorist enters and exits.

A common practice in modern bridge design is to conceal the connections. The design team has taken the opposite approach and fully exposed the cable connections to the bridge. As motorists travel on the bridge, they can see and understand how the cables support the bridge deck. These exposed anchors create visual rhythm on the elevation of the bridge and provide an additional layer of interest for observers of the bridge. In addition, these exposed anchors provide a system that is easy to observe, inspect and maintain, further enhancing the durability, safety and security of the bridge.

The lighting became an important part of the aesthetic solution to satisfy the community’s desire for dramatic nighttime as well as daytime views. The traditional necklace lighting responds to the historical aspects of the surrounding area. The pylon and stay lighting reveals the bridge structure in a pleasing and aesthetic way, creating a nighttime experience that is completely different from the daytime experience.

The horizontal line of the bridge across the water is enhanced by a kinetic lighting solution, which is an effect that creates a visual connection between the two sides of the river. The lighting system includes necklace lights consisting of light-emitting-diode panels mounted to the outer surface of the edge girder. These color-changing light-emitting panels are controlled by a highly flexible and sophisticated lighting control system that allows for the display of infinite number of lighting shows across the length of the bridge, from simple one-color panels to complex, color-changing events.

The colors and lighting events can be coordinated with seasonal changes and with special events taking place in the community. This active lighting system will serve as a major element of communication and will involve the bridge in the community at a social level.

The Christopher S. Bond Bridge will be an icon that will serve Kansas City visually and functionally for the next century.

The aesthetic design is born directly from the structural elegance of the design solution and not applied as an afterthought. The diamond-shaped pylon and semifan stay arrangement forms a gateway experience for motorists traveling on this bridge.

The bridge is an excellent example of how creative performance-based procurement techniques, carefully crafted technical scoring criteria and a highly responsive design-build solution can result in a project that far surpasses the expectations and imaginations of an owner and community.

About the Author

Cassity is a vice president with Parsons, Chicago. Kidwell is a project director with MoDOT, Lee’s Summit, Mo. Byrne is a construction engineer with Massman Construction Co., Kansas City, Mo.

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