ASTM C1812

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

Description:

Significance and Use

4.1 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.

4.2 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.

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

4.4 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.

Scope

1.1 This practice 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.2 Improperly designed supporting rollers can influence the apparent flexural behavior of fiber-reinforced concrete beams.3 The effective coefficient of friction can be determined using a method similar to that described by Bernard.4

1.2 The text of this standard refers to notes and footnotes that provide explanatory material. These notes and footnotes (excluding those in tables and figures) shall not be considered as requirements of the standard.

1.3 Units—The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system are not necessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be used independently of the other, and values from the two systems shall not be combined.