1、Designation: C1812/C1812M 151Standard Practice forDesign of Journal Bearing Supports to be Used in FiberReinforced Concrete Beam Tests1This standard is issued under the fixed designation C1812/C1812M; the number immediately following the designation indicates theyear of original adoption or, in the
2、case of revision, the year of last revision. A number in parentheses indicates the year of lastreapproval. A superscript epsilon () indicates an editorial change since the last revision or reapproval.1NOTEThe designation was corrected editorially in June 2016 to conform with the units statement (1.2
3、).1. Scope1.1 This practice prescribes the design of journal-bearingtype rollers to support each end of fiber-reinforced concretebeams tested using Test Method C1399/C1399M or TestMethod C1609/C1609M. The roller design is intended toprovide a consistent and relatively low value of effectivecoefficie
4、nt of friction at the beam supports. The bearing designincorporates metal-on-metal sliding surfaces lubricated withgrease.NOTE 1During the progress of a test, a crack or cracks open on theunderside of the beam between the loaded third points causing theunderside of each portion of the beam to move a
5、way from the center. Thedesign is intended to provide for unlimited rotation of the roller at thepoint of contact with the test beam in response to this motion.NOTE 2The design of the supporting rollers is a significant factor indetermining the magnitude of the arching forces that cause error inflex
6、ural test results.2Improperly designed supporting rollers can influencethe apparent flexural behavior of fiber-reinforced concrete beams.3Theeffective coefficient of friction can be determined using a method similarto that described by Bernard.41.2 UnitsThe values stated in either SI units or inch-p
7、ound units are to be regarded separately as standard. Thevalues stated in each system may not be exact equivalents;therefore, each system shall be used independently of the other.Combining values from the two systems may result in non-conformance with the standard.1.3 This standard does not purport
8、to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:5C125 Te
9、rminology Relating to Concrete and Concrete Ag-gregatesC1399/C1399M Test Method for Obtaining AverageResidual-Strength of Fiber-Reinforced ConcreteC1609/C1609M Test Method for Flexural Performance ofFiber-Reinforced Concrete (Using Beam With Third-PointLoading)D4950 Classification and Specification
10、for Automotive Ser-vice Greases2.2 SAE International Standard:6J 404 Chemical Composition of SAE Alloy Steels3. Terminology3.1 Definitions:3.1.1 For definitions of terms used in this practice, refer toTerminology C125.3.2 Definitions of Terms Specific to This Standard:3.2.1 effective coeffcient of f
11、riction, na dimensionlessratio of the horizontal force required to initiate rotation of theroller support applied at the contact point between the rollerand test beam divided by the normal force applied at the samepoint (see Fig. 1).3.2.2 roller, na journal bearing capable of continuousrotation with
12、out exhibiting a significant variation in resistanceto rotation.4. Significance and Use4.1 The presence of friction in the supporting rollers usedwhen testing a fiber-reinforced concrete beam will increase the1This practice is under the jurisdiction of ASTM Committee C09 on Concreteand ConcreteAggre
13、gates and is the direct responsibility of Subcommittee C09.42 onFiber-Reinforced Concrete.Current edition approved July 1, 2015. Published September 2015. DOI:10.1520/C1812_C1812M-15E01.2Zollo, R. F., 2013. “Analysis of SupportApparatus for Flexural Load-deflectionTesting: Minimizing Bias,” Journal
14、of Testing and Evaluation, ASTM International,Vol. 41, No. 1, pp. 1-6.3Wille, K. and Parra-Montesinos, G.J., 2012. “Effect of Beam Size, CastingMethod, and Support Conditions on Flexural Behavior of Ultra-High-PerformanceFiber-Reinforced Concrete,” ACI Journal of Materials, Vol. 109, No. 3, pp.379-3
15、88.4Bernard, E.S., 2014. “Influence of friction in supporting rollers on the apparentflexural performance of third-point loaded fibre reinforced concrete beams,”Advanced Civil Engineering Materials, ASTM International Vol. 2, No. 1, pp.158-176.5For referenced ASTM standards, visit the ASTM website,
16、www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.6Available from SAE International (SAE), 400 Commonwealth Dr., Warrendale,PA 15096, http:/aerospace.sae.org.Copyright
17、 ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1apparent load resistance of the beam. Roller supports designedin accordance with this practice will provide a relatively lowand consistent value of friction at the supports.4.2 Two types of rolle
18、rs are used to support a beam. Oneincludes a cylindrical bearing that allows the roller assembly torotate along an axis parallel to the longitudinal axis of the beamand thereby accommodate any warping introduced duringspecimen fabrication. The other roller does not include thecylindrical bearing.4.3
19、 The rollers are designed for use with 150 mm 6 in. or100 mm 4 in. deep beams of square cross-section.4.4 A method is provided for correcting the apparent loadresistance measured using the roller with a known value of theeffective coefficient of friction of the roller supports to obtainan estimate o
20、f the load resistance in the absence of friction.5. Apparatus5.1 GeometryA pair of rollers is required to support abeam during a test. The barrel of each roller, which is thatportion of the roller in contact with the beam, shall be free torotate about an axis perpendicular to the longitudinal axis o
21、fthe beam to accommodate movement of the initial supportpoint on the beam away from the center during a test. Frictionbetween sliding surfaces within each roller will generate asmall resistance to rotation of the barrel relative to themounting (see Fig. 1). A roller fabricated in accordance withthis
22、 practice will exhibit an effective coefficient of friction ofabout 0.10.4Journal bearing supports manufactured in confor-mance with this practice do not need to be tested to confirmthat the effective coefficient of friction meets requirements.5.1.1 One of the two rollers supporting the underside of
23、 thebeam shall be able to rotate about an axis parallel to thelongitudinal axis of the beam to accommodate a warped testbeam surface that could induce torsion in the beam duringtesting (see Note 3 and Fig. 2). The other roller shall be fixedagainst rotation about a longitudinal axis to prevent the b
24、eamfrom overturning during installation and testing (see Fig. 3).Rotation about a longitudinal axis shall be accommodated byinclusion of a cylindrical bearing surface under the rollermount with a center of rotation that coincides with the plane ofthe contacting surface between roller and bottom of t
25、he beam.The base of the cylindrical bearing surface shall include boltPL= frictional force applied to the roller by the beam.PV= vertical force applied to the roller by the beam.FIG. 1 Forces Acting on a Supporting Roller During a TestFIG. 2 General Arrangement Drawing of Supporting Roller with a Cy
26、lindrical Bearing BaseC1812/C1812M 1512holes to facilitate fixing the roller to the testing machine. Theroller that is fixed against rotation about a longitudinal axis(Fig. 3 and Fig. 6) shall incorporate a similar mounting so thatthe total height is the same as the roller assembly shown in Fig.2 an
27、d Fig. 5 and the beam is maintained level during a test. Thebarrel of each roller is fabricated from one piece of steel. Capssecure the roller barrel in place so that it may rotate but notdisplace during a test. The cylindrical seat of the roller that isfree to rotate about a longitudinal axis shall
28、 include a flangeand a recess as shown in Fig. 4 to prevent longitudinaltranslation during testing.NOTE 3The upper half of the cylindrical bearing surface is not fixedto the lower half, but is restrained by guides intended to prevent the upperpart of the bearing from sliding in the longitudinal dire
29、ction in response tothe forces imposed by the beam as it deflects at the bottom surface andeach half of the beam moves away from the center as the crack(s) widen.NOTE 4To check that a properly manufactured and lubricated journalbearing assembly is functional, the rotating roller within the assemblym
30、ust turn at least 360 without undue resistance when turned by hand.Such a check should be performed before each test is undertaken.5.2 Steel GradeThe rollers and their correspondingmountings shall be fabricated using SAE 4140 alloy steel orequivalent.5.3 Surface TreatmentThe sliding and rotating sur
31、faces ofthe roller, bushings, and cylindrical bearing within the supportmounting shall be machined to a high-grade machine finishwith a roughness average of 0.8 m 32 in. or better. Thedifference in radius between the contacting surface of the rollerbarrel and the corresponding contacting surface of
32、the bushingis limited to 0.10 mm 0.004 in.5.4 LubricationThe design includes grease ports for lu-bricating the sliding surfaces. Grease shall be applied to thesurfaces via the grease ports to limit friction and expel debristhat may collect at the junctions between the shaft of the rollerand the bush
33、ing caps. The user shall establish a schedule forgrease application to ensure proper operation of the rollerassemblies. The grease shall be National Lubricating GreaseInstitute (NLGI) Grade 2 lithium complex molybdenum disul-phide high-pressure grease as described in Specification D4950or equivalent
34、.5.5 Mounting of Rollers within Testing MachineThemounting shall include a 25 mm 1 in. thick steel plate withbolts located so as to secure the roller supports to the testmachine during testing. The designs shown in Figs. 2-6incorporate four bolt holes in the base of the bearing mountwith an overall
35、height of roller and mount equal to 100 mm4.0 in. These dimensions have been found to performsatisfactorily in service, but the exact dimensions of the basesare permitted to be altered to suit the dimensions of the testmachine to which they are fixed.5.6 DimensionsThe dimensions of the rollers shown
36、 inFigs. 5 and 6 are based on SI units. Equivalent dimensions ininches are listed in Table 1. Tolerances on dimensions are 60.1 mm 0.004 inches.6. Keywords6.1 fiber-reinforced concrete; flexural performance; friction;post-crack; residual strength; roller supportsFIG. 3 General Arrangement Drawing of
37、 Supporting Roller with a Fixed Bearing BaseC1812/C1812M 1513FIG. 4 Exploded View of Roller Assembly Showing Bushing Caps to Secure Roller Barrel and Flanges to Prevent Sliding in the Longitu-dinal DirectionC1812/C1812M 1514FIG. 5 Sectional View of Roller on Cylindrical Bearing Base with Dimensions
38、in mmFIG. 6 Sectional View of Roller on Fixed Bearing Base with Dimensions in mmC1812/C1812M 1515APPENDIX(Nonmandatory Information)X1. CORRECTION OF TEST RESULTS FOR FRICTION IN SUPPORTSX1.1 ScopeX1.1.1 This appendix provides recommendations for cor-rection of flexural strength results obtained in b
39、eam tests whenan effective coefficient of friction of known magnitude ispresent in the supporting rollers under a beam subject tothird-point loading.X1.1.2 The correction method may be applied to all valuesof load resistance obtained prior to and after cracking of theconcrete matrix in the beam test
40、.X1.2 CalculationX1.2.1 Apparent Load Resistance of BeamFig. X1.1 is aTABLE 1 List of Dimensions in SI Units and Equivalents inInchesDimension in millimetres Dimension in inches1 0.047 0.288 0.3212 0.5015 0.5918 0.7120 0.7921 0.8325 1.0034 1.3438 1.5040 1.5850 2.0065 2.5670 2.7675 3.0090 3.50120 4.7
41、2150 6.00FIG. X1.1 Free-Body Diagram for a Third-Point Loaded Beam with Off-Center Crack and an Effective Coefficient of Friction Equal to atEach Supporting RollerC1812/C1812M 1516free-body diagram of the cracked portion of a beam for whichthe effect of friction on the apparent load resistance can b
42、eevaluated. The ratio, , of the apparent load resistance, PF,ofa third-point loaded beam in the presence of friction within thesupporting rollers to the load resistance of the same beam in theabsence of friction, P0, is found as: 5PFP05LL 2 3 d!(X1.1)where:L = beam span, mm in., = effective coeffici
43、ent of friction of the roller support,dimensionless, andd = beam depth, mm in.For Test Methods C1399/C1399M and C1609/C1609M, d =L/3, thus the ratio for a third-point loaded beam is expressedas: 511 2 !(X1.2)X1.2.2 Correction of Apparent Load ResistanceThe valueof is equal to 1.11 for an effective c
44、oefficient of friction, , ina roller support under a third-point loaded beam equal to 0.10.To remove the error introduced by the presence of friction inthe rollers, the corrected load resistance of the beam is foundas:P05 PF (X1.3)X1.2.3 Application of Correction FactorIf a roller con-forming to the
45、 design prescribed in this practice is used tosupport each end of a third-point loaded beam, the effectivecoefficient of friction can be taken to equal 0.10 assuming therollers are regularly cleaned and maintained. The correction tothe load resistance of the beam indicated by Eq X1.3 is thenapplied
46、to all points of the recorded load-deflection record.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent ri
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