The multi-year Fayetteville Outer Loop project will provide traffic relief for the city of more than 300,000, as well as residents, employees and visitors to Fort Bragg, Pope Airfield, and several major defense contractors. The project consisted of the construction of more than six miles of roadways, three interchanges, and 24 bridges, including two tri-level curved girder flyover bridges.
KCI worked with Lee Construction Company of the Carolinas and The Conti Group on two different sections of the project to provide construction engineering services on more than 100 individual tasks, including:
- Design of multiple falsework and formwork for bridge deck overhangs to support screed equipment
- Design of specialty equipment such as sand jacks and an overhang buggy
- Design of hanging platforms for construction access and formwork
- Design of shoring walls and tiebacks
- Design of safety lines
- Modification of footings and caps to alleviate construction tolerances
- Load rating bridges for anticipated crane loads
- Mass concrete analysis
- Shoring of excavations
- Temporary haul road bridge and permitting
- Load rating of bridges for construction loading
To assist the contractor in meeting their tight construction schedule, KCI first initiated design of items that were on the critical path. Our team also provided additional engineering services to the contractor on short notice for critical items that arose during construction.
The project had a lot of unique features—a number of curved girder bridges, integral bents, unique falsework and complicated construction—that needed a high technical level of engineering support.
James D. Fitz Morris, PEVice President, Practice Leader
Many tasks required out-of-the-box strategies to overcome site-specific challenges. The multiple integral bents supporting curved steel girders for the tri-level bridge over the freeway required an innovative solution to support the girders and concrete cap with multiple obstructions below and adjacent to the bridge. Structural engineers designed a unique support system with arms that were braced back to the integral bent column to fit within tight space requirements. Additionally, KCI provided innovative internal bracing details to secure the falsework to the column and a system of sand jacks and other support brackets that allowed easy lowering of the falsework system under loads in excess of 200,000 pounds per jack.
Due to a good working relationship with the clients, additional services issued to KCI included creating models for the girders in various stages of erection using a finite element program to determine the stability and safety factor from buckling, as well as developing step-by-step plans for staging, handling, and erecting the equipment. Horizontally curved girders complicated the analysis and handling during erection, so stresses were checked during all phases of the erection to ensure proper stability of the girders and their resistance to buckling. This stress check was vital to ensure the safety of construction personnel and verify that operations could be performed without causing damage or leaving permanent deformities.
Because of the weight and length of the steel girders, limited lifting capacity of the cranes, and the crane access locations to the beam locations, KCI designed structural steel towers to temporarily support the girders during erection to allow for installation in individual pieces that would be spliced. One such erection included the design of a temporary tower placed on an existing bridge. In addition, KCI performed an analysis of the capacity of the bridge to support a holding crane weighing more than a half-million pounds to secure the steel girders from buckling after it was erected.