Framing Errors / Forensic Investigations
Concrete Encased FRP Underground Metering Station
A client contacted Clark Engineers to review the design and to provide any
required modifications to eight unique FRP metering stations. The metering
stations had both flat bottoms and two flat sides. It was determined that the
thickness required to control bending and stress in the flat section was greater
than manufacturing constraints would allow.
The client had planned on encasing the metering station in unreinforced concrete,
however this was found to be inadequate. Clark Engineers developed a design
using the reinforced concrete to provide the required stiffness.
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FRP stiffeners
were added to the flat sides with a grid of reinforcing steel running through them
and in front of them (Left photo). The right sketch shows the resulting
stiffener stress in the flat walls (Right photo).
By using reinforced concrete and tying it to the flat walls, the structural FRP
thicknesses were minimized, saving the client money and creating a design that
could be manufactured.
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35 failed FRP USTs
A major oil company contacted Clark Engineers to do a forensic investigation of
35 failed FRP underground storage tanks (UST) located in a South East Asian
country. The investigation included planning a geotechnical investigation at six
sites and documenting data during tank exhumation of all 35 tanks. Also the
design and manufacturing quality of the tanks were reviewed.
It was found that the tanks were:
- Not installed according to the manufacturers’ installation instructions
- There was a design flaw in the tanks that resulted in a lack of redundancy of factor of safety
- UST laminate samples taken from the tanks did not agree with the company reported design construction
- Many tanks did not have UV Labels (Underwriters Laboratories) as required for UL listed tanks.
All tanks were replaced.
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Tanks being removed. Note: back-fill was not pea gravel
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Indentation due to hard spot in back-fill (common throughout 6 installations)
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