December 2010 Vol. 65 No. 12
New Products
Adjustable Manhole Frames Avoid Costly Problems
Misaligned manhole frames in streets often cause driving hazards, failure of pavement around the frames, cause poor access to manholes, may be responsible for inflow and infiltration and can also result in other problems. Because manhole frames are not manufactured to be adjustable, efforts to make repairs is time consuming and often ineffective.
A Canadian company, Terminal City Iron Works, believes it has the answer to these problems.
“Our adjustable manhole frame and support ring eliminates problems associated with current adjustment methods,” said Bill Zielinski, Terminal City Iron Works general manager. “They can be manufactured to work with any existing frame and cover. They are simple and easy to use — achieving perfect adjustment takes only minutes. Installing an adjustable frame and support rings will result in long-term cost savings for maintenance.”
The products and process are covered by Canadian and United States patents. They have been presented at various public works venues in Canada and the U.S. and have been favorably received, said Zielinski.
The support rings and adjustable frames have been successfully used by several cities in British Columbia and Western Canada for the past five years, and they soon will be available in Eastern Canada and the United States.
Components
The support ring is made of ductile iron and is light, but very strong. With a frame in an adjusted position, the ring meets the highest H load requirements without concrete or grout support. The ring is designed to keep the adjustable frame stable and centered over the manhole opening. For maximum strength and sustainability, concrete — not grout — can be placed between the frame and grade rings to eliminate voids creating structural weakness or where moisture could accumulate and freeze causing frost damage which could weaken the structure.
The adjustable frame is manufactured of cast iron and in some cases ductile iron; weight depends on diameter, averaging between 175 and 225 pounds. High-strength, low alloy set screws with additional corrosion coating applied are used to make adjustments. With the set screws, one worker can easily adjust the frame for perfect alignment and a smooth surface in the roadway.
The city of Kelowna, BC, participated in initial development and testing of the products and has been the most extensive user of the adjustable frames and support rings.
Wayne Nadasde, construction supervisor of the city’s Design and Construction Services Department describes the installation process.
“First,” he said, “the standard concrete grade ring is placed over the manhole opening. The support ring then is placed on top of the grade ring and the adjustable frame on top of the support ring. Using a 5/16-inch Allen or socket wrench, set screws built into the frame are used to adjust the frame’s elevation to the required elevation and grade.”
Next, ½-inch aggregate 20-30 MPA (megapascal) concrete is placed around grade rings, the adjustable frame and between the frame and support ring.
“The entire process takes 15-20 minutes,” Nadasde said. “Old, conventional methods would take close to an hour and in most cases structural integrity would be questionable with a very high failure rate, resulting in costly maintenance for years after. The new adjustable frame and support ring are far superior. They provide workers with a product that is easy to work with and provides long-term structural strength.”
Setting frames properly
Manhole frames need to be set accurately with a road surface on longitudinal grade and with cross fall. Yet, Nadasde said, conventional manhole frame design and adjustment procedures that are typically used to make adjustments are not adequate to prevent failure.
“Manhole frames are heavy, cumbersome, and frustrating to adjust,” he continued. “Workers are required to lift the frame on and off the manhole opening several times while trying to find the right thickness of wood using rocks, wood shims, old pieces of broken asphalt or concrete, pieces of scrap metal from fabricating shops and all kinds of other materials. Even if grout is used, such materials can deteriorate or leave point loads on grade rings which ultimately damages and weakens the manhole chimney structure. Historically, adjusted frames in this manner are very unstable and get knocked off adjustment by road building and paving equipment. It’s hard to believe, but without improvements, our industry has been setting frames like this for more than 100 years.”
In addition, he said, current specifications for adjustments are insufficient and do not consider the importance and diversity of the task.
Using the new adjustable frame and support ring provides the means to achieve perfect elevation and grade, minimizing inflow and reducing damage from traffic.
“Their design,” he said, “anchors the frame in concrete, creating a solid fixture that keeps the frame from becoming loose and preventing structural failure of the manhole chimney. These benefits will save significant dollars during initial installation, in repair and maintenance, reduce worker injuries and protect the environment. The adjustable frame and support ring are reusable. Adjustments can be made again during future asphalt replacement projects.”
Based in Vancouver, BC, for more than 100 years, Terminal City Iron Works has provided the public works market with fire hydrants, valves, fittings, joint restraints and related products. Terminal City Iron Works, assisted by sister companies, will be responsible for distribution of the adjustable manhole frames and rings in the United States.
FOR MORE INFO:
Terminal City Iron Works, (888) 443-4493, http://terminalcity-acs.com
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