ASTM C1812 Standard Practice for Design of Journal Bearing Supports to be Used in Fiber Reinforced Concrete Beam Tests

ASTM C1812 prescribes the design of journal-bearing type rollers to support each end of fiber-reinforced concrete beams tested using Test Method

C1399/C1399M or Test Method C1609/C1609M.

The roller design is intended to provide a consistent and relatively low value of effective coefficient of friction at the beam supports.

The bearing design incorporates metal-on-metal sliding surfaces lubricated with grease.

NOTE 1: During the progress of a test, a crack or cracks open on the underside of the beam between the loaded third points causing the underside of each portion of

the beam to move away from the center.

The design is intended to provide for unlimited rotation of the roller at the point of contact with the test beam in response to this motion.

NOTE 2: The design of the supporting rollers is a significant factor in determining the magnitude of the arching forces that cause error in flexural test results.

Improperly designed supporting rollers can influence the apparent flexural behavior of fiber-reinforced concrete beams.

The effective coefficient of friction can be determined using a method similar to that described by Bernard.4

ASTM C1812  / Significance and Use

The presence of friction in the supporting rollers used when testing a fiber-reinforced concrete beam will increase the apparent load resistance of the beam.

Roller supports designed in accordance with this practice will provide a relatively low and consistent value of friction at the supports.

Two types of rollers are used to support a beam.

One includes a cylindrical bearing that allows the roller assembly to rotate along an axis parallel to the longitudinal axis of the beam and thereby

accommodate any warping introduced during specimen fabrication.

The other roller does not include the cylindrical bearing.

The rollers are designed for use with 150 mm [6 in.] or 100 mm [4 in.] deep beams of square cross-section.

A method is provided for correcting the apparent load resistance measured using the roller with a known value of the effective coefficient of friction

of the roller supports to obtain an estimate of the load resistance in the absence of friction.

*** Before conducting ASTM C1812 , it is important to read the entire specification. Standards can be obtained from appropriate standard authorities.