Bridging Relocation challenges

Utilities deal with road and highway relocations everyday, but what does a utility do when it must design a 100-foot tall distribution pole to accommodate a relocation? That is the challenge the Missouri Department of Transportation (MODOT) presented when it asked Kansas City Power & Light (KCP&L) to relocate several distribution lines that traversed and paralleled Interstate 29/35.

The MODOT project included construction of a new cable-stayed, six-lane bridge alongside the existing bridge. Several distribution lines had to be moved to allow for construction of the new bridge and its approaches. MDOT used a construction approach known as build-as-you-go, which ultimately meant that deck information could not be finalized until the build was complete. When the calculations were finished, the contractor informed KCP&L that several of the relocated poles needed to be more than 100 feet tall.

Workers set a pole during the relocation of distribution lines.

KCP&L had limited experience designing poles larger than 60 feet; so it needed a manufacturer willing to team up on the new poles’ design. Once the contractor identified the affected poles, KCP&L solicited interest from several steel manufacturers. The extremely short lead-time made it necessary to consider other options. Although KCP&L had limited experience with laminated structures, it selected Laminated Wood Systems (LWS) to design and supply the poles.

The old structures were 69kV lattice tower structures retrofitted with 15 kV equipment. KCP&L decided to keep the original circuit path and install taller poles. This path included some large angle transitions and included spanning 12 sets of railroad tracks. KCP&L provided LWS with the entering and exiting angles, tension of the conductors and the soil classification in which they would install the poles. The team selected vertical construction to make the transitions easier and allow KCP&L to double dead-end at the structures and jumper around the poles. Building the line vertically presented several challenges:

    * How much sag should the conductors have, and how would that affect the design?
    * What was the appropriate clearance to the other structures, buildings, cars etc?
    * How far apart should they install the conductors to prevent galloping?

To overcome these issues, the three 120-foot vertical poles were pre-cambered, and each consisted of two poles built with a separation between them to allow for mounting the insulator hardware. The cross-arm design of the other two poles would facilitate the transitions from the smaller poles that led to and away from the new structures.

A drill rig makes holes for relocated power poles during construction of the Christopher “Kit” Bond Bridge in Kansas City.

It was necessary to use a 7 to 8 foot diameter auger to drill the holes so the laminated poles could be embedded 15 to 20 feet below ground. The railroad required corrugated steel caisson tubes in the upper half of the pole holes for the three structures installed on its property. Once the poles were set, the holes where filled with 4,000-pound test concrete and supported by several boom trucks until the concrete could cure. When the poles were ready, KCP&L strung new conductor and removed the old structures and lines.

Pole casings wait to be installed during the construction of the Christopher “Kit” Bond Bridge in Kansas City.

The Christopher “Kit” Bond Bridge, now a new Kansas City icon, would not have been possible without the dedication and innovation of KCP&L and LWS. By working closely with its customer, MDOT, and its supplier, LWS, Kansas City Power & Light timely relocated its poles, which helped MODOT complete the new bridge ahead of schedule.