Clark engineers

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.

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.

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.

Tanks being removed. Note: back-fill was not pea gravel
Indentation due to hard spot in back-fill (common throughout 6 installations)