1、Designation: D7914/D7914M 14Standard Test Method forStrength of Fiber Reinforced Polymer (FRP) Bent Bars inBend Locations1This standard is issued under the fixed designation D7914/D7914M; the number immediately following the designation indicates theyear of original adoption or, in the case of revis
2、ion, 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.1. Scope1.1 This test method determines the quasi-static ultimatestrength of fiber reinforced polymer (FRP) compo
3、site bent barscommonly used as anchorages for stirrups in reinforced,prestressed, or post-tensioned concrete structures. This testmethod only applies to bars with a solid cross section.1.2 FRP bent bars are often used in reinforced concreteapplications to shorten the development length of the bar or
4、 toact as a tie or a stirrup to resist shear forces. Bent bars can beproduced with varying angles of bend in order to fit theirintended purpose.1.3 For this test method, the FRP bars are bent at a 90degree angle. In general, bars have a regular pattern of surfaceundulations, a coating of bonded part
5、icles, or both, thatpromote mechanical interlock between the bar and concrete.1.4 The strength values provided by this method are short-term, quasi-static tensile strengths that do not account forsustained static or cyclic loading. If bars are to be used underhigh levels of sustained or repeated loa
6、ding, additional materialcharacterization may be required.1.5 The characteristic values obtained from this test methodare intended to represent the quasi-static ultimate strength ofFRP bent bars with a tail length of twelve bar diameters.1.6 The values stated in either SI units or inch-pound unitsar
7、e to be regarded separately as standard. The values stated ineach system may not be exact equivalents; therefore, eachsystem shall be used independently of the other. Combiningvalues from the two systems may result in non-conformancewith the standard.1.6.1 Within the text, the inch-pound units are s
8、hown inbrackets.1.7 This standard does not purport 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
9、.2. Referenced Documents2.1 ASTM Standards:2A615/A615M Specification for Deformed and Plain Carbon-Steel Bars for Concrete ReinforcementC39/C39M Test Method for Compressive Strength of Cylin-drical Concrete SpecimensC143/C143M Test Method for Slump of Hydraulic-CementConcreteC192/C192M Practice for
10、Making and Curing Concrete TestSpecimens in the LaboratoryD792 Test Methods for Density and Specific Gravity (Rela-tive Density) of Plastics by DisplacementD883 Terminology Relating to PlasticsD3171 Test Methods for Constituent Content of CompositeMaterialsD3878 Terminology for Composite MaterialsD5
11、229/D5229M Test Method for MoistureAbsorption Prop-erties and Equilibrium Conditioning of Polymer MatrixComposite MaterialsD7205/D7205M Test Method for Tensile Properties of FiberReinforced Polymer Matrix Composite BarsE4 Practices for Force Verification of Testing MachinesE6 Terminology Relating to
12、 Methods of Mechanical TestingE122 Practice for Calculating Sample Size to Estimate, WithSpecified Precision, the Average for a Characteristic of aLot or ProcessE456 Terminology Relating to Quality and Statistics3. Terminology3.1 Terminology in D3878 defines terms relating to high-modulus fibers and
13、 their composites. Terminology in D883defines terms relating to plastics. Terminology in E6 definesterms relating to mechanical testing. Terminology in E456 andin Practice E122 define terms relating to statistics and theselection of sample sizes. In the event of a conflict between1This test method i
14、s under the jurisdiction of ASTM Committee D30 onComposite Materials and is the direct responsibility of Subcommittee D30.10 onComposites for Civil Structures.Current edition approved Aug. 1, 2014. Published December 2014. DOI:10.1520/D7914_D7914M-14.2For referenced ASTM standards, visit the ASTM we
15、bsite, 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.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United Sta
16、tes1terms, Terminology in D3878 shall have precedence over theother terminology standards.3.2 Definitions:3.2.1 bar, na linear element, with a substantially roundcross-section, often with surface undulations or a coating ofparticles that promote mechanical interlock with concrete.3.2.2 bend radius,
17、ninside radius of the bend.3.2.3 bend strength, nultimate tensile stress that can becarried by the FRP bent bar provided that failure occurs in thebend.3.2.4 bent bar, na bar with a section formed in such amanner as to deviate from its primary axis.3.2.5 equivalent bar diameter, nthe equivalent bar
18、diam-eter is determined according to Test Method D7205/D7205Mand is based upon the standard cross-sectional area of the FRPbar.3.2.6 quasi-static, adjloading where inertial effects (timeand inertial mass) are irrelevant.3.2.7 standard cross-sectional area, nthe cross-sectionalarea of a standard numb
19、ered steel concrete reinforcing bar asgiven in Specification A615/A615M, Table 1, and based upona circular cross section and determined over at least onerepresentative length.3.2.8 stirrup, na bar shape comprised of one or more bentbars used to resist shear forces in reinforced concrete.3.2.9 tail l
20、ength, nthe length provided beyond the bendportion of a bent bar.3.2.10 tensile strength, nultimate tensile strength of FRPbars in the direction parallel to the fibers.3.3 Symbols:3.3.1 Astandard cross-sectional area of a single leg of theFRP bent bar determined according to Test Method D7205/D7205M
21、,mm2in.23.3.2 CVsample coefficient of variation, in percent3.3.3 dbeffective bar diameter taken as the equivalent bardiameter determined according to Test Method D7205/D7205M and is based upon the standard cross-sectional area ofthe FRP bar, mm in.3.3.4 Ffuultimate tensile strength parallel to the f
22、ibersdetermined according to Test Method D7205/D7205M, MPapsi3.3.5 Ffbultimate bend strength of the FRP bent bar, MPapsi3.3.6 Lttail length of the FRP bent bar occurring after thebent portion of the bar, mm in.3.3.7 nnumber of specimens3.3.8 Pfbultimate force capacity of the FRP bent bar, Nlb3.3.9 r
23、repeatability limit, the value below which theabsolute difference between two individual test results obtainedunder repeatability conditions may be expected to occur with aprobability of approximately 0.95 (95 %)3.3.10 rtinside radius of the bent portion of an FRP bentbar, mm in.3.3.11 Sn-1sample st
24、andard deviation3.3.12 percentage of the guaranteed tensile strength ofthe straight portion of the bar that is retained in the bendlocation3.3.13 xImeasured or derived property3.3.14 xsample mean (average)4. Summary of Test Method4.1 One or more FRP bent bars, cast into two blocks ofconcrete, are lo
25、aded in tension until failure occurs at the bentportion of the bar.An actuation device is placed in between thetwo concrete blocks so that the blocks are forced apart,inducing tension on the FRP bent bar.4.2 Force is recorded throughout the test.4.3 The principal variables used in the tests are the
26、cross-sectional area, bend radius, and type of FRP bent bar.5. Significance and Use5.1 This test method is intended to determine the bendstrength developed at a standard twelve bar diameters ofembedment and the strength reduction factors of FRP bent barsthat are typically used as anchorages in concr
27、ete. From thistest, a variety of data are acquired that are needed for designpurposes. Material-related factors that influence the tensileresponse of bars and should therefore be reported include thefollowing: constituent materials, void content, volume percentreinforcement, methods of fabrication,
28、and fiber reinforcementarchitecture. Similarly, factors relevant to the measured tensileresponse of bars include specimen preparation, specimenconditioning, environment of testing, specimen alignment, andspeed of testing. Properties, in the test direction, that may beobtained from this test method i
29、nclude:5.1.1 Ultimate bend strength of the FRP bent bar and5.1.2 Percentage of the guaranteed tensile strength of thestraight portion of the bar that is retained in the bend location.5.2 The results may be used for material specifications,research and development, and structural design and analysis.
30、NOTE 1Two FRP bends are tested simultaneously in this test method,but in some cases only one bend may rupture. While resulting in a validfailure, notice should be taken that only one bend has been effectivelymeasured and that the final compiled test results using this method coulddiffer from those r
31、esulting from single FRP bend testing.6. Interferences6.1 The results from the procedures presented are limited tothe material and test factors listed in Section 5.6.2 Loading ProvisionsThe test is completed using ahydraulic jack that exerts equal and opposite forces onto twoconcrete blocks. The blo
32、ck containing the test section of theFRP bent bar must be free to translate so that force exerted onthe bent bars can be accurately measured. Bending of the bentbars during casting of the concrete or testing of the specimenmay cause premature failure outside of the bend. Every effortshall be made to
33、 minimize bending and uneven loading of thebent bars.D7914/D7914M 1426.3 Bend GeometryIn this test standard, the bend in theFRP bar comprises a 90 degree change of direction with aconstant radius of curvature through the bend. Bends other than90 degrees may produce different test results, and are no
34、tcovered by this standard.6.4 Measurement of Actual Cross-Sectional AreaThe ac-tual cross-sectional area of the bar is measured by immersinga prescribed length of the specimen in water to determine itsbuoyant weight. Bar configurations that trap air during immer-sion (aside from minor porosity) cann
35、ot be assessed using thismethod. This method may not be appropriate for bars that havelarge variations in cross-sectional area along the length of thebar.6.5 Variation Tolerance Between Actual and StandardCross-Sectional AreaAll specimens shall have an actualcross-sectional area that varies no more
36、than +20% and -0%from the bars standard cross-sectional area6.6 Specimen HandlingDuring the handling and prepara-tion of specimens, all deformation, heating, outdoor exposureto ultraviolet light, and other conditions possibly causingchanges to material properties of the specimen shall beavoided.7. A
37、pparatus7.1 Hydraulic CylinderThe hydraulic cylinder shall haveforce capacity in excess of the capacity of the specimen, and becapable of applying force at the required loading rate. Handoperated testing machines, electro-mechanical cylinders, ormotorized pumps having sufficient volume in one or mor
38、estrokes to complete a test may be used if they satisfy theloading provisions in 11.2.6.7.2 Force IndicatorThe testing apparatus force-sensingdevice (a load cell or similar) shall be capable of indicating thetotal force being carried by the specimen. This device shall beessentially free from inertia
39、-lag at the specified rate of testingand shall indicate the force with an accuracy over the loadrange(s) of interest of within 6 1% of the indicated value, asspecified by Practices E4.7.3 Environmental Test ChamberAn environmental cham-ber is required for conditioning and test environments otherthan
40、 ambient laboratory conditions. These chambers shall becapable of maintaining the required relative temperature towithin 63C 65F and the required relative humidity levelto within 65% RH. In addition, the chambers may have to becapable of maintaining environmental conditions such as fluidexposure or
41、relative humidity during the conditioning andtesting.7.4 The test set-up, shown in Fig. 1, consists of a hydraulicjack to distribute the applied force to the surface of theconcrete. A plywood bearing pad 200 mm square and at least6 mm deep 8 in. square and 0.25 in. deep in conjunction withsteel spre
42、ader plates 100 mm square and 6 mm deep 4 in.square and 0.25 in. deep, or similar provisions shall be used atthe end of the actuator to spread the force on the concreteblocks and minimize bending forces on the bent bars. Hydrau-lic cylinder shall be placed in the same plane as the FRP bars,and shall
43、 be centrally located between the legs (6 6mm 0.25in.). The block containing the test section of the bar shall beplaced on top of steel rollers to minimize the friction forcesbetween the block and testing bed. When moving thespecimens, special care shall be taken to avoid damaging ordisplacing the c
44、ast FRP bars.FIG. 1 Test SetupD7914/D7914M 1438. Sampling and Test Specimens8.1 SamplingAt least five specimens shall be tested pertest condition. For statistically significant data, the proceduresoutlined in Practice E122 should be consulted. The method ofsampling shall be reported.8.2 Geometry:8.2
45、.1 FRP bent bars shall be representative of the lot orbatch being tested. In general, specimens shall not be subjectedto any processing beyond manufacturing.8.2.2 The cross-sectional area of the FRP bent bar shall bebased upon the standard area of the bar. The use of the actualcross-sectional area a
46、s described in section 6.4 is allowed ifrequired, but shall be reported and used for all calculations.8.2.3 Bend angle of FRP bar shall be 90 6 5 degrees off ofstraight. Bend angle shall be measured and reported in section14.1.1.8.8.2.4 The configuration of a typical specimen is shown inFig. 1.8.2.5
47、 The free length of the FRP bars between the twoconcrete blocks shall not be less than 200 mm 8 in. with asuggested length of 400 mm 16 in.8.2.6 Concrete blocks are dimensioned as shown in Fig. 2.Steel stirrups are optional and may be required to preventsplitting of the concrete blocks prior to a va
48、lid FRP rupture inthe case of large diameter FRP bars. Use of stirrups shall bereported. The concrete blocks shall be arranged in such amatter that each corresponding face is parallel to the other toensure proper loading of the samples.NOTE 2In some cases, large diameter FRP bars may cause rupture o
49、fthe concrete blocks back face.An increased clear cover or horizontal steelstirrups may be used to prevent this rupture, but shall be reported.8.2.7 FRP bent bar dimensions are variable, but shall have atail length (Lt)of1261 bar diameters per bend to minimizeslippage and to help ensure a valid failure mode. To allow foreasier FRP bent bar production, two “C”-shaped bars arrangedand used in the same manner as the single FRP bar shown inFig. 2 may be used in place of a single FRP bar.8.2.8 A debonding tube is to be u
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