1、Designation: C 215 02Standard Test Method forFundamental Transverse, Longitudinal, andTorsional Resonant Frequencies of Concrete Specimens1This standard is issued under the fixed designation C 215; the number immediately following the designation indicates the year oforiginal adoption or, in the cas
2、e of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope *1.1 This test method covers measurement of the fundamen-tal transverse, longitudinal, and to
3、rsional resonant frequenciesof concrete prisms and cylinders for the purpose of calculatingdynamic Youngs modulus of elasticity, the dynamic modulusof rigidity (sometimes designated as “the modulus of elasticityin shear”), and dynamic Poissons ratio.1.2 Values in SI units are the standard.1.3 This s
4、tandard 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.2. Referenced Documents2.
5、1 ASTM Standards:C 31/C 31M Practice for Making and Curing Concrete TestSpecimens in the Field2C 42/C 42M Test Method for Obtaining and Testing DrilledCores and Sawed Beams of Concrete2C 125 Terminology Relating to Concrete and ConcreteAggregates2C 192/C 192M Practice for Making and Curing ConcreteT
6、est Specimens in the Laboratory2C 469 Test Method for Static Modulus Elasticity and Pois-sons Ratio of Concrete in Compression2C 670 Practice for Preparing Precision and Bias Statementsfor Test Methods for Construction Materials2E 1316 Terminology for Nondestructive Examinations33. Terminology3.1 De
7、finitionsRefer to Terminology C 125 and the sec-tion related to ultrasonic examination in Terminology E 1316for definitions of terms used in this test method.4. Summary of Test Method4.1 The fundamental resonant frequencies are determinedusing one of two alternative procedures: (1) the forced reso-n
8、ance method or (2) the impact resonance method. Regardlessof which testing procedure is selected, the same procedure is tobe used for all specimens of an associated series.4.2 In the forced resonance method, a supported specimen isforced to vibrate by an electro-mechanical driving unit. Thespecimen
9、response is monitored by a lightweight pickup uniton the specimen. The driving frequency is varied until themeasured specimen response reaches a maximum amplitude.The value of the frequency causing maximum response is theresonant frequency of the specimen. The fundamental frequen-cies for the three
10、different modes of vibration are obtained byproper location of the driver and the pickup unit.4.3 In the impact resonance method, a supported specimenis struck with a small impactor and the specimen response ismeasured by a lightweight accelerometer on the specimen. Theoutput of the accelerometer is
11、 recorded. The fundamentalfrequency of vibration is determined by using digital signalprocessing methods or counting zero crossings in the recordedwaveform. The fundamental frequencies for the three differentmodes of vibration are obtained by proper location of theimpact point and the accelerometer.
12、5. Significance and Use5.1 This test method is intended primarily for detectingsignificant changes in the dynamic modulus of elasticity oflaboratory or field test specimens that are undergoing exposureto weathering or other types of potentially deteriorating influ-ences.5.2 The value of the dynamic
13、modulus of elasticity obtainedby this test method will, in general, be greater than the staticmodulus of elasticity obtained by using Test Method C 469.The difference depends, in part, on the strength level of theconcrete.5.3 The conditions of manufacture, the moisture content,and other characterist
14、ics of the test specimens (see section onTest Specimens) materially influence the results obtained.1This test method is under the jurisdiction of ASTM Committee C09 onConcrete and Concrete Aggregates and is the direct responsibility of SubcommitteeC09.64 on Nondestructive and In-Place Testing.Curren
15、t edition approved Dec. 10, 2002. Published February 2003. Originallyapproved in 1947. Last previous edition approved in 1997 as C 215 97e1.2Annual Book of ASTM Standards, Vol 04.02.3Annual Book of ASTM Standards, Vol 03.03.1*A Summary of Changes section appears at the end of this standard.Copyright
16、 ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.4 Different computed values for the dynamic modulus ofelasticity may result from widely different resonant frequenciesof specimens of different sizes and shapes of the sameconcrete. Therefore,
17、it is not advisable to compare results fromspecimens of different sizes or shapes.6. Apparatus6.1 Forced Resonance Apparatus (Fig. 1):6.1.1 Driving CircuitThe driving circuit shall consist of avariable frequency audio oscillator, an amplifier, and a drivingunit. The oscillator shall be calibrated to
18、 read within 62%ofthe true frequency over the range of use (about 100 to 10 000Hz). The combined oscillator and amplifier shall be capable ofdelivering sufficient power output to induce vibrations in thetest specimen at frequencies other than the fundamental andshall be provided with a means for con
19、trolling the output. Thedriving unit for creating the vibration in the specimen shall becapable of handling the full power output of the oscillator andamplifier. The driving unit is used in contact with the testspecimen or separated from the specimen by an air gap. Whenthe test specimen is contact-d
20、riven, the vibrating parts of thedriving unit shall be small in mass compared with that of thespecimen. The oscillator and amplifier shall be capable ofproducing a voltage that does not vary more than 620 % overthe frequency range and, in combination with the driving unit,shall be free from spurious
21、 resonances that will be indicated inthe output.NOTE 1It is recommended that the calibration of the variable fre-quency audio oscillator be checked periodically against signals transmit-ted by the National Institute of Standards and Technology radio stationWWV, or against suitable electronic equipme
22、nt such as a frequencycounter, the calibration of which has been previously checked and foundto be adequate.6.1.2 Pickup CircuitThe pickup circuit shall consist of apickup unit, an amplifier, and an indicator. The pickup unitshall generate a voltage proportional to the displacement,velocity, or acce
23、leration of the test specimen, and the vibratingparts shall be small in mass compared with the mass of the testspecimen. The pickup unit shall be free from spurious reso-nances in the normal operating range. Either a piezoelectric ormagnetic pickup unit meeting these requirements is acceptable.The a
24、mplifier shall have a controllable output of sufficientmagnitude to actuate the indicator. The indicator shall consistof a voltmeter, milliammeter, or a real-time graphic displaysuch as an oscilloscope or a data acquisition system withmonitor (see Note 2).NOTE 2For routine testing of specimens whose
25、 fundamental fre-quency may be anticipated within reasonable limits, a meter-type indicatoris satisfactory and may be more convenient to use than an oscilloscope orcomputer monitor. It is, however, strongly recommended that wheneverfeasible a graphic display be provided for supplementary use or to r
26、eplacethe meter-type indicator. The use of a graphic display as an indicator maybe necessary when specimens are to be tested for which the fundamentalfrequency range is unpredictable. The graphic display is valuable also forchecking the equipment for drift and for use in the event that it should bed
27、esired to use the equipment for certain other purposes than thosespecifically contemplated by this test method.6.1.3 Specimen SupportThe support shall permit thespecimen to vibrate freely (Note 3). The location of the nodalpoints for the different modes of vibration are described inNotes 4, 5, and 6
28、. The support system shall be dimensioned sothat its resonant frequency falls outside the range of use (from100 to 10 000 Hz).NOTE 3This may be accomplished by placing the specimen on softrubber supports located near the nodal points or on a thick pad of spongerubber.6.2 Impact Resonance Apparatus (
29、Fig. 2):6.2.1 ImpactorThe impactor shall be made of metal orrigid plastic and the mass of the head shall be 0.11 6 0.02 kg.The striking end of the impactor shall have a spherical shapewith a diameter of 6 6 1 mm.6.2.2 SensorThe sensor shall be a piezoelectric acceler-ometer with a mass less than 30
30、g and having an operatingfrequency range from 100 to 10 000 Hz. The resonant fre-quency of the accelerometer shall be at least two times themaximum operating frequency.6.2.3 Frequency AnalyzerDetermine the frequency of thespecimen vibration by using either a digital waveform analyzeror a frequency c
31、ounter to analyze the signal measured by thesensor. The waveform analyzer shall have a sampling rate of atleast 20 kHz and shall record at least 1024 points of thewaveform. The frequency counter shall have an accuracy of61 % over the range of use.6.2.4 Specimen SupportSupport shall be provided asspe
32、cified in 6.1.3 for the forced resonance method.7. Test Specimens7.1 PreparationMake the cylindrical or prismatic testspecimens in accordance with Practice C 192/C 192M, Prac-tice C 31/C 31M, Test Method C 42/C 42M, or other specifiedprocedures.FIG. 1 Schematic of Apparatus for Forced Resonance Test
33、 FIG. 2 Schematic of Apparatus for Impact Resonance TestC2150227.2 Measurement of Mass and DimensionsDetermine themass and average length of the specimens within 60.5 %.Determine the average cross-sectional dimensions within61%.7.3 Limitations on Dimensional RatioSpecimens havingeither small or larg
34、e ratios of length to maximum transversedirection are frequently difficult to excite in the fundamentalmode of vibration. Best results are obtained when this ratio isbetween 3 and 5. For application of the formulas in this testmethod, the ratio must be at least 2.8. Determination of Resonant Frequen
35、ciesForcedResonance Method8.1 Transverse Frequency:8.1.1 Support the specimen so that it is able to vibrate freelyin the transverse mode (Note 4). Position the specimen anddriver so that the driving force is perpendicular to the surfaceof the specimen. Locate the driving unit at the approximatemiddl
36、e of the specimen. Place the pickup unit on the specimenso that the direction of pickup sensitivity coincides with thevibration direction, that is, the transverse direction (see Fig.3a). Position the pickup near one end of the specimen. It ispermissible to position the driver on the vertical face so
37、 that thespecimen vibrates perpendicular to the direction shown in Fig.3a.8.1.2 Force the test specimen to vibrate at varying frequen-cies. At the same time, observe the indication of the amplifiedoutput of the pickup. Record the fundamental transversefrequency of the specimen, which is the frequenc
38、y at which theindicator shows the maximum reading and observation ofnodal points indicates fundamental transverse vibration (Note4). Adjust the amplifiers in the driving and pickup circuits toprovide a satisfactory indication. To avoid distortion, maintainthe driving force as low as is feasible for
39、good response atresonance.NOTE 4For fundamental transverse vibration, the nodal points arelocated 0.224 of the length of the specimen from each end (approximatelythe quarter points). Vibrations are a maximum at the ends, approximatelyFIG. 3 Locations of Driver (or Impact) and Needle Pickup (or Accel
40、erometer)C215023three fifths of the maximum at the center, and zero at the nodal points;therefore, movement of the pickup along the length of the specimen willinform the operator whether the vibrations observed in the indicator arefrom the specimen vibrating in its fundamental transverse mode. Anosc
41、illoscope may also be used to determine whether the specimen isvibrating in its fundamental transverse mode. The driver signal isconnected to the horizontal sweep and the pickup signal is connected tothe vertical sweep of the oscilloscope. When the pickup is located at theend of the specimen, which
42、is vibrating in its fundamental transversemode, the oscilloscope will display an inclined elliptical pattern. When thepickup is placed at a node, the oscilloscope displays a horizontal line.When the pickup is placed at the center of the specimen, the display willbe an elliptical pattern but inclined
43、 in the opposite direction to when thepickup was placed at the end of the specimen. The oscilloscope can alsobe used to verify that the driving frequency is the fundamental resonantfrequency. Resonance can occur when the driving frequency is a fractionof the fundamental frequency. In this case, howe
44、ver, the oscilloscopepattern will not be an ellipse.8.2 Longitudinal Frequency:8.2.1 Support the specimen so that it is able to vibrate freelyin the longitudinal mode (Note 5). Position the specimen anddriver so that the driving force is perpendicular to andapproximately at the center of one end sur
45、face of the specimen.Place the pickup unit on the specimen so that the direction ofpickup sensitivity coincides with the vibration direction, that is,the longitudinal axis of the specimen (see Fig. 3b).8.2.2 Force the test specimen to vibrate at varying frequen-cies. At the same time, observe the in
46、dication of the amplifiedoutput of the pickup. Record the fundamental longitudinalfrequency of the specimen, which is the frequency at which theindicator shows the maximum reading and observation of thenodal point indicates fundamental longitudinal vibration (Note5).NOTE 5For the fundamental longitu
47、dinal mode, there is one node atthe center of length of the specimen. Vibrations are a maximum at theends.8.3 Torsional Frequency:8.3.1 Support the specimen so that it is able to vibrate freelyin the torsional mode (Note 6). Position the specimen anddriver so that the driving force is perpendicular
48、to the surfaceof the specimen. For prismatic specimens, locate the drivingunit near the upper or lower edge of the specimen at a distancefrom the end that is between 0.10 and 0.12 of the length of thespecimen (see Fig. 3c). For cylindrical specimens, locate thedriving unit above or below the mid-lin
49、e of the cylinder. Placethe pickup unit on the surface of the specimen at a position onthe opposite end that coincides with the node point forfundamental transverse vibration (see Fig. 3a). Position thepickup so that the direction of pickup sensitivity coincides withthe vibration direction, that is, perpendicular to the longitudinalaxis of the specimen.8.3.2 Force the test specimen to vibrate at varying frequen-cies. At the same time, observe the indication of the amplifiedoutput of the pickup. Record the fundamental torsional fre-quency of the specimen, which is th
