Historic Undertakings

WHILE IT WAS DIVERSIFYING AND EXPANDING its operations, Sundt was also putting its name in history books with unusual and challenging projects, one of them in the tiny town of Lake Havasu City, Arizona.

Relocation of the London Bridge

Lake Havasu City would be virtually unknown today if it weren’t for an enterprising businessman named Robert McCulloch. In the early 1960s, the city’s site was a barren, WWII auxiliary airfield with no population to speak of. But McCulloch, who was both an industrialist and a developer, thought it was the ideal place to relocate his large chainsaw company while creating a new community in the desert.

About the same time that McCulloch was planning the development of Lake Havasu City, it was determined that the London Bridge in England was literally sinking into the River Thames. The bridge had been dedicated in 1831 and was in a state of disrepair. Because refurbishment was no longer practical, the City of London decided to auction the bridge to raise funds to build a replacement. The bridge, which had survived machine gun attacks from enemy warplanes during World War II, was to be removed.

When McCulloch learned that the London Bridge was for sale, he thought of somehow making it the centerpiece of his new development at Lake Havasu City. In 1968, he was successful in his bid to the City of London to buy the well-known landmark. News of the sale of the London Bridge and plans to re-erect it in the Arizona desert caused somewhat of a furor in England, especially since it came on the heels of the permanent relocation of the venerable cruise ship Queen Mary to Long Beach, Calif.

In 1969, M.M. Sundt’s Heavy Construction Division was already working in the Lake Havasu area on a project to improve Arizona State Route 95, so the company bid on the London Bridge job and was successful. A new concrete structure, clad in stones from the original London Bridge, would soon be built in the Arizona desert.

The five-span reinforced concrete bridge was built entirely on dry land, using a technique called soffit fill. Basically, soffit fill involves building up a pile of earth so that the mound is as high as the bottom of the bridge to be constructed. Crews form and place a concrete waste slab on top of the mound, and then the entire bridge is built on top of it. When the bridge is finished, the mound, including the waste slab, is removed.

Although there were 130,000 tons of granite in the original bridge, McCulloch only bought 10,000 tons of the outer facing blocks. Most of these blocks were cut down to form a skin, or cladding, for the new structure. The pier footing design and use of soffit fill were cost saving proposals Sundt made to McCulloch after the bid. When the bridge structure was completed, Sundt received a separate contract to apply the facing stone, which had been match-marked so they could be placed in their original relative locations on the bridge. The stones weighed between 1,000 to 8,000 pounds. In addition, Sundt was contracted to construct the one-mile-long channel that cuts across the peninsula to place a watercourse under the bridge.

The New London Bridge and an adjacent English Village were dedicated in 1971, with the Lord Mayor of London in attendance. The ceremony, which closely matched the decor and menu of the original 1831 dedication, attracted 50,000 spectators. Time has shown that McCulloch’s vision for the London Bridge attraction in Arizona was correct. Today, Lake Havasu City draws over one million visitors annually, and the London Bridge is considered by many to be one of the seven wonders of Arizona.

Kitt Peak Observatory

The Mayall Telescope is the largest optical telescope at Kitt Peak, a world-renowned facility located on a mountaintop southwest of Tucson. Sundt began building the Mayall Telescope structure in 1968 and completed the project in 1970. A number of unique challenges were encountered along the way, primarily due to the project’s remote location and difficult site access via a winding mountain road. Because of the altitude and unprotected location, the site was subjected to cold weather and high winds. These factors, coupled with a very tight site, made scheduling the arrival and storage of material and equipment a critical activity.

The outer structure of the observatory was constructed using 10 hexahedron (6-sided)
structural steel units, each 96 feet long, 33 feet wide, and weighing 35 tons. They were set in place vertically and
connected to form a 108-foot-diameter circle. The units were fabricated in Phoenix, but were too large to bring to the jobsite using major highways. Instead, they were transported, one at a time, over back roads and then through the Indian Reservation, to the construction site.

A ring beam was placed on the top of the hexahedrons to support a rail for the observatory trolley wheels, and then the dome was erected on top of the rail. The dome, which moves with the telescope, was designed to withstand winds of up to 120 miles per hour. It weighs nearly 500 tons and stands 187 feet above the ground at its highest point.

Slip Forming

Slip form construction is frequently referred to as “sliding form” construction. Fresh concrete is placed in the forms, and the forms, acting as moving dies, shape the concrete. The process is very similar to an extrusion process. Vertical slip forming is used to form walls. Horizontal slip forming is used for highway paving, culverts and curbs. Sundt has used both of these slip form applications on its projects.

Sundt first used vertical slip forming to construct underground missile silos at Vandenberg Air Force Base in California and Shilling Air Force Base in Kansas.

In 1960, Sundt slip formed nine cement storage silos for the Arizona Portland Cement Co. at Rillito, Ariz. Ten years later, two coke storage silos were slip formed for Great Lakes Carbon at Long Beach, Calif. Then in 1972, four coal storage silos were slip formed for Peabody Coal at Kayenta, Ariz. After that, the company slip formed other storage silos, underground silos and special-use structures at various locations.

In the ’70s and ’80s, Sundt built upon its experience with slip form silo construction to become a leading contractor in the niche market of slip formed reinforced concrete cores for high-rise buildings. The cores were designed to house the building’s elevator shafts, stairwells and other service areas. A structural steel frame was constructed around the core to complete the structure for the building. Slip formed building cores were often the most economical structural system for high rises due to the speed with which they could be constructed.


Landmark Slip Form Projects

During this period, Sundt constructed 16 slip formed core projects in Atlanta, Dallas, Denver, Kansas City, Phoenix and Tucson. Several of the projects had multiple cores. There were seven projects alone in Denver. Several of the cores were over 500 feet tall. The slip form for the IBM Tower in Atlanta, Georgia is approximately 725 feet tall, and at the time it was completed it was the tallest slip formed building core in the United States. Sundt’s most unusual slip form building project was part of the Hyatt Regency Hotel in Dallas. Completed in 1976, the Reunion Tower consisted of a 562-foot-tall primary core surrounded by three service cores. Atop the structure sits a restaurant with spectacular views of the entire city. Today Reunion Tower is a defining feature of the Dallas skyline.

Slip Form Presents High-Risk Challenges

Slip forming building cores is high-risk, high-margin work, which is a perfect fit for Sundt. But many of them presented special challenges for the project team. For example, the Columbia Place slip form in Denver started off with a large form that cast the low- and mid- and high-rise elevator shafts as a single effort. When crews reached the point where the shorter shafts stopped and the high-rise shafts were to continue upwards, the unneeded portion of the form was cut loose and left for a short time atop the concrete walls.

The plan was to dismantle and remove that section of the form over the upcoming weekend when slip forming wouldn’t be going on and the tower crane would be free. But before that could happen there was a fire on the disconnected section caused by sparks from a welder’s torch. Fortunately the fire was extinguished quickly, and there were no injuries or significant property damage. After that incident Sundt made sure that all future slip form designs included a fire line up to the core. It was a simple thing to do, but something nobody thought we needed until after the fire on Columbia Place.

There were challenges of a different sort on the IBM Tower,
the company’s tallest slip form project. The form was pretty much square, and that made it hard to keep straight as the core is jacked upwards. This one was really giving the project team fits staying within tolerance, until one night they figured out
that welding units that had been attached below the middle deck for use by the structural steel subcontractor (who was installing elevator beams) had made the form rigid. After those units were removed, the form was much easier to control.

Because slip forming wasn’t done very often, the process itself was somewhat of a learning experience. On the Denver slip forms that were in operation during the freezing winters, the three-story form had to be completely enclosed and insulated so that the concrete would stay warm enough to set up properly. All perimeter block-outs were sealed, and insulation was sprayed on the freshly formed concrete as soon as the form rose above it. Inside the core, the heat of hydration kept it so warm that workers wore tee shirts and regular work pants instead of winter clothing, while outside, the temperature was below freezing. During these cold weather slip forming operations, the crews embedded temperature monitors in the concrete as it was placed to make sure the proper cure temperature was maintained.

Horizontal Slip Forming Remains Popular Today

The “golden era” of slip formed building cores slowly faded away in the late 1980s when other structural systems became more economical to construct. Horizontal slip forming, however, remains very popular. Its biggest use is to construct airport runways, taxiways and aprons; major streets and highways; and for culverts and curbs. Slip forming requires special skills and equipment, and Sundt has always prided itself in being able to perform this critical type of construction.