Anchor Pull-Testing

[M40A]

We are testing post-installed anchors in concrete, utilizing a hollow-cylinder jack, pump and pressure gauge type assembly; similar to the configuration referenced in ASTM C 900 and/or ASTM D 4435.

We have calibrated the pressure gauge and standardized the system in accordance with Annex A1, ASTM C 900. We have performed this type of pull-test a number of times over the past decade+ and have encountered a new request.

By utilizing the standardization method in the above referenced annex, we established a linear correlation between an applied load and the pressure reading on the gauge in the pull-out system.

We have witnessed another pull-test apparatus where they are using a calibrated pressure gauge in the system and using the surface area of the hollow-cylinder and the pressure on gauge to calculate the applied load. They are using the internal surface area, of the hollow ram, as the contact area in conjunction with the pressure to calculate the applied load.

When we calculate the applied force, we use the correlation established between the calibrated load cell and the pressure reading on the gauge. If we want to determine the pressure exerted on the anchor, we divide the applied load by the surface area of the bolt.

My question: Because the hollow ram is exerting a force against the nut/washer assembly that is securing the anchor, would you include the surface area of the hollow ram in a caclulation for applied force / pressure?

 

[Ron]

The "lifting" force of the jack is determined by the amount of pressure that is developed in its cylinder x the surface area of the pressurized plunger of the ram. For a center-pull jack like you've described, the area of the ram plunger is annular in shape.

Beyond that exercise of determining the actual load exerted on the bolt, there is no reason to include the ram face area in any calculation. It has nothing to do with the bolt area or its failure.

If you have calibrated your jack pressure gauge reading against a load cell placed in line, the calibration curve will tell you the load (obviously!). If you are not calibrating against a load cell placed in line, then you must know the ram face area to compute the load exerted on the bolt. Such a method is not as reliable as the in-line calibration and should not be relied upon without further calibration. Calibration of the gauge pressure alone is only a secondary calibration.