BS 1881-209-1990 Testing concrete - Recommendations for the measurement of dynamic modulus of elasticity《混凝土试验 第209部分 动态弹性模量测定的推荐方法》.pdf

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1、BRITISH STANDARD BS 1881-209: 1990 Testing concrete Part 209: Recommendations for the measurement of dynamic modulus of elasticity UDC 666.972:691.32:620.1BS1881-209:1990 This British Standard, having been prepared under the direction of the Cement, Gypsum, Aggregates and Quarry Products Standards P

2、olicy Committee, was published under the authority of the Board of BSI and comes into effect on 30 April 1990 BSI 12-1998 The following BSI references relate to the work on this standard: Committee reference CAB/4 Draft for comment 88/10608 ISBN 0 580 17925 7 Committees responsible for this British

3、Standard The preparation of this British Standard was entrusted by the Cement Gypsum, Aggregates and Quarry Products Standards Policy Committee (CAB/-) to Technical Committee CAB/4, upon which the following bodies were represented: Association of Lightweight Aggregate Manufacturers Association of Me

4、tropolitan Authorities Association of Quality Pulverised Fuel Ash Suppliers British Aggregate Construction Materials Industries British Cement Association British Civil Engineering Test Equipment Manufacturers Association British Precast Concrete Federation British Ready Mixed Concrete Association B

5、uilding Employers Confederation Cement Admixtures Association Cementitious Slag Makers Association Concrete Society County Surveyors Society Department of the Environment (Building Research Establishment) Department of the Environment (Property Services Agency) Department of Transport Department of

6、Transport (Transport and Road Research Laboratory) Electricity Supply Industry in England and Wales Federation of Civil Engineering Contractors Institute of Concrete Technology Institution of Civil Engineers Institution of Highways and Transportation Institution of Structural Engineers Institution o

7、f Water and Environmental Management (IWEM) Royal Institution of Chartered Surveyors Sand and Gravel Association Society of Chemical Industry The following bodies were also represented in the drafting of the standard, through sub-committees and panels: British Nuclear Fuels Limited United Kingdom At

8、omic Energy Authority Amendments issued since publication Amd. No. Date CommentsBS1881-209:1990 BSI 12-1998 i Contents Page Committee responsible Inside front cover Foreword ii 1 Scope 1 2 Definitions 1 3 Applications 1 4 Principle 1 5 Summary of the test method 1 6 Apparatus 1 7 Methods of testing

9、laboratory made specimens 2 8 Calculations 3 9 Report 3 Figure 1 Test configuration for determination of dynamic modulus of elasticity 4 Publications referred to Inside back coverBS1881-209:1990 ii BSI 12-1998 Foreword This Part of BS 1881 has been prepared under the direction of the Cement, Gypsum,

10、 Aggregates and Quarry Products Standards Policy Committee. It supersedes clause 4 of BS 1881-5:1970, which has been deleted. All aspects of testing concrete are being included as Parts of BS 1881, from sampling fresh concrete to assessing concrete in structures. Part 201 gives general guidance on t

11、he choice of non-destructive test methods and should be consulted for advice on methods which can be used to complement this method of measuring the dynamic modulus of elasticity. Testing of concrete by the measurement of dynamic modulus of elasticity is a laboratory technique and involves applying

12、an alternating force of variable frequency to the end of a prismatic sample and recording the resonant frequency. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a Bri

13、tish Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 4, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments

14、 incorporated. This will be indicated in the amendment table on theinside front cover.BS1881-209:1990 BSI 12-1998 1 1 Scope This Part of BS 1881 gives recommendations for the determination of dynamic modulus of elasticity of plain concrete in the laboratory using resonance of vibration in the longit

15、udinal mode. NOTEThe titles of the publications referred to in this standard are listed on the inside back cover. 2 Definitions For the purposes of this Part of BS1881 the definitions given in BS3683-4 and BS6100-6 apply, together with the following. 2.1 resonance condition in which the frequency of

16、 a vibration applied to a body is equal to one of the natural frequencies of vibration of that body NOTEThis concurrence of frequencies maximizes the amplitude of vibration in the body. 2.2 longitudinal mode of vibration mode in which compression waves travel through a prismatic specimen in the dire

17、ction parallel to its length NOTE 1The waves are partially reflected by the end faces of the specimen and thus travel to and fro within it. NOTE 2Other modes exist such as transverse and torsional. 2.3 fundamental frequency lowest resonant frequency at which a body will vibrate in a particular mode

18、2.4 dynamic modulus of elasticity of concrete (E D ) ratio of the stress to that part of the strain corresponding to elastic deformation only NOTEThe modulus obtained refers to the initial tangent to the non-linear stress/strain relationship for concrete, which does not obey Hookes Law. It is normal

19、ly appreciably larger than the statically measured value obtained by the method described in BS1881-121. 3 Applications Measurement of dynamic modulus is most commonly used for comparative testing of concretes in the laboratory and for assessing degradation in durability tests, e.g. in freezing and

20、thawing tests. 4 Principle An elastic or partially elastic body will vibrate if struck a blow. Each body possesses many modes of vibration and in geometrical bodies well defined modes may be identified. This method is concerned only with identifying the fundamental longitudinal mode of vibration in

21、concrete prisms. The frequency at which this vibration occurs depends largely on the dynamic modulus of elasticity, density, and length of the specimen. 5 Summary of the test method A variable frequency oscillator imparts an alternating force to the specimen and the response is sensed by an accelero

22、meter or vibration pick-up. The amplitude of vibrations is monitored by an indicator and when a resonant frequency is reached, the indicator shows the amplitude to be at a well defined maximum. If this resonant frequency is the fundamental frequency it is related to the modulus of elasticity of the

23、concrete through the equation in clause 8. 6 Apparatus 6.1 Variable frequency oscillator, providing a variable narrow-band sinusoidal output from500Hz to 20 kHz with power adjustable from zero to at least 2 W. The frequency of the oscillator output should be indicated within an accuracy of 0.5 %. Th

24、e output of a good quality oscillator tuned to a given frequency should not contain more than 2 % of its amplitude in the second and third harmonics of the frequency and should have a stability within 5% of the operating voltage. 6.2 Exciter, of which the part in contact with the specimen should hav

25、e a mass of not more than 0.2% of the mass of the specimen. 6.3 Pick-up, of which any part in contact with the specimen should have a mass of not more than 0.2% of the mass of the specimen. The vibration pick-up should have no resonances at frequencies below20kHz. 6.4 Amplitude indicator, consisting

26、 of a voltmeter or cathode ray oscilloscope incorporating appropriate amplification facilities.BS1881-209:1990 2 BSI 12-1998 6.5 Support, consisting of a pair of horizontal steel bars between which the specimen can be clamped. The width of the contact area of the clamping bars should not exceed one

27、twentieth of the length of the specimen. The bars can be positioned by threaded vertical rods attached to a rigid baseboard which also carries the exciter and pick-up mounting posts as shown in Figure 1. The baseboard stands on soft elastomeric pads on a rigid workbench to reduce the effects of extr

28、aneous vibrations transmitted through the laboratory floor. Alternatively, the specimen may lie on a block of foam rubber provided that the exciter and pick-up centrelines are normal to the specimens end faces. 6.6 Balance, of appropriate capacity to weigh the specimen to the accuracy required by 7.

29、2. 6.7 Vernier calliper, complying with BS887, capable of measuring the lateral dimensions of the specimen to the accuracy required by 7.2. 7 Methods of testing laboratory made specimens 7.1 Preparation The laboratory made specimens should be prisms of circular or square section with a length not le

30、ss than three nor more than five times the maximum transverse dimension. Specimens should preferably be beams made in accordance with BS 1881-109 and then cured in accordance with BS 1881-111. 7.2 Preliminary measurements Immediately before testing, the length and density of each specimen should be

31、obtained from the following procedures. a) Length. Calculate the mean length, L, (in mm) from at least four symmetrically placed measurements read to an accuracy of 1mm. b) Density. Weigh the specimen in air and record its mass, M A , (in kg) to an accuracy of 0.25 %. Determine the volume, V, (in m

32、3 ) of the specimen either from its dimensions or by water displacement as follows. 1) Dimensions. For a beam, calculate the mean width, a, and depth, b, (inmm) from at least six measurements of each dimension spaced equally along its length read to an accuracy of 0.25mm. Then V = L b a 10 9 For a c

33、ylindrical specimen, calculate the mean diameter, d, (inmm) from at least six measurements spaced equally along its length read to an accuracy of 0.25 mm. Then 2) Water displacement. Weigh the specimen in water and record its apparent loss in mass, M L , (inkg) to an accuracy of 0.25%. Then V = M L

34、/r w where Method 2 should not be used for unsaturated specimens. Calculate the density, r, (in kg/m 3 ) of the specimen from the equationr = M A /V. 7.3 Measurement of resonant frequency Specimens should be tested in a condition appropriate to the purpose of the investigation. Where specimens have

35、been stored in water they should be tested immediately on removal from the water, whilst they are still saturated. Surface water and grit should be wiped off the specimen. The specimen should be clamped or balanced at its centre on the fixed support. Contact should be made between the vibrating part

36、 of the exciter and the centre of one end face of the specimen by means of a weak adhesive or by gentle spring loading. Contact should be made between a piezo-electric vibration pick-up and the opposite end of the specimen in a similar way, as indicated in Figure 1. Alternatively, an electromagnetic

37、 non-contacting pick-up can be used in accordance with the manufacturers recommendations. Ensure that the axes of the transducers are in the centre of and normal to the end faces of the specimen. The exciter should be driven by the variable frequency oscillator and the oscillations received from the

38、 pick-up should be fed to the amplitude indicator to show the changes in amplitude received. The frequency of excitation should be varied until a resonance is obtained and the frequency noted. Resonance will be recognized when the amplitude indicator shows a peak response. As the frequency is furthe

39、r varied, the indicator may show the existence of several resonant frequencies, some of these relating to modes of vibration other than longitudinal. r w is the density of water which may be taken as 1 kg/m 3at ambient temperature. V L p d 2 4 - 109 =BS1881-209:1990 BSI 12-1998 3 The identification

40、of the fundamental frequency in the longitudinal mode requires care. Generally the required frequency produces the greatest response on the indicator for given settings of the output and gain controls. As a check, with the specimen set up as shown in Figure 1, resonance should also be obtainable at

41、a frequency three times that of the fundamental frequency. If difficulties are still encountered, an approximate value for the dynamic modulus of elasticity of the concrete may be obtained from a pulse transit time measurement (see BS 1881- 203). This value may then be substituted into the equation

42、in clause8 to yield an approximate value for the desired resonant frequency. The search for the exact frequency may then be confined to a narrow range about the value so calculated. Instrument manufacturers literature sometimes provides very useful instructions for identifying the fundamental freque

43、ncy. Once identified, this value should be recorded. 8 Calculations The dynamic modulus of elasticity of concrete, E D , (in GN/m 2 ) for each specimen should be calculated to the nearest 0.5 GN/m 2from the formula E D= 4n 2L 2r 10 15 where NOTEThis formula applies to all uniform specimens of consta

44、nt cross section. 9 Report 9.1 General The report should affirm that the dynamic modulus of elasticity of concrete was determined in accordance with the recommendations given in BS1881-209:1990. 9.2 Information to be included in the test report 9.2.1 Obligatory information. The following information

45、 should be included in the test report: a) date of test; b) description and nominal size of the specimen with any identifying mark; c) age of the specimen when tested; d) conditions in which the specimen had been stored between manufacture and testing; e) the calculated dynamic modulus of elasticity

46、 of the concrete. 9.2.2 Additional information. When requested, the following information should also be included in the test report: a) the fundamental frequency; b) the measured dimensions of the specimen; c) the density of the specimen at the time of testing. L is the length of the specimen (inmm

47、); n is the fundamental frequency in the longitudinal mode of vibration of the specimen (inHz); ris the density of the specimen (in kg/m 3 ).BS1881-209:1990 4 BSI 12-1998 Figure 1 Test configuration for determination of dynamic modulus of elasticityBS1881-209:1990 BSI 12-1998 Publications referred t

48、o BS 887, Specification for precision vernier callipers. BS 1881, Testing concrete. BS 1881-109, Method for making test beams from fresh concrete. BS 1881-111, Method of normal curing of test specimens (20 C method). BS 1881-121, Method for determination of static modulus of elasticity in compressio

49、n. BS 1881-201, Guide to the use of non-destructive methods of test for hardened concrete 1) . BS 1881-203, Recommendations for measurement of velocity of ultrasonic pulses in concrete. BS 3683, Glossary of terms used in non-destructive testing. BS 3683-4, Ultrasonic flaw detection. BS 6100, Glossary of building and civil engineering terms. BS 6100-6 Concrete and plaster. 1) Referred to in the foreword only.BSI 389 Chiswick High Road London W4 4AL | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |