1、1288-k2000 Glass in building - Determination of the bending strength of I glass - Part 1: Fundamentals of testing glass The European Standard EN 12881:2000 has the status of a British Standard ICs 81.040.20 NO COPYING WTHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW BS EN 128 - present to
2、the responsible European committee any enquiries on the interpretation, or proposals for change, and keep the UK interess informed; - monitor related international and European developments and promulgate them in the UK A list of organizations represented on this subcommittee can be obtained on requ
3、est to its secretary. Cross-references The British Stan - Part 3: Test with specimen supported at two points (four point bending); - Part 4: Testing of channel shaped glass; - Part 5: Coaxial double ring test on flat specimens with small test surface areas. According to the CENICENELEC Internal Regu
4、lations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and the
5、United Kingdom. 8 BSI 08-2000 Page 4 EN 1288-1 12000 1 Scope This European Standard specifies the determination of the bending strength of monolithic glass for use in buildings. The testing of insulating units or laminated glass is excluded from this standard. This standard describes: - consideratio
6、ns to be taken into account when testing glass; - explanations of the reasons for designing different test methods; - limitations of the test methods; and gives pointers to safety requirements for the personnel operating the test equipment. EN 1288-2, EN 1288-3, EN9+2288-4 and EN 1288-5 specify test
7、 methods in detail. The test methods specified in this standard are intended to provide large numbers of bending strength values that can be used as the basis for statistical evaluation of glass strength. 2 Normative references This European Standard incorporates by dated or undated reference, provi
8、sions from other publications. These normative references are cited at the appropriate places in the text and the publications are listed hereafter. For dated references, subsequent amendments to or revisions of any of these publications apply to this European Standard only when incorporated in it b
9、y amendment or revision. For undated references, the latest edition of the publication referred to applies. EN 1288-2 Glass in building - Determination of the bending strength of glass - Part2: Coaxial double ring test on flat specimens with large test surface areas. EN 1288-3 Glass in building - De
10、termination of the bending strength of glass - Part3: Test with specimen supported at two points (four point bending). EN 1288-4 Glass in building - Determination of the bending strength of glass - Part 4: Testing of channel shaped glass. EN 1288-5 Glass in building - Determination of the bending st
11、rength of glass - Part 5: Coaxial double ring test on flat specimens with small test surface areas. EN 572-1 Glass in building - Basic soda lime silicate glass products - Part 1: Definitions and general physical and mechanical properties. 8 BSI 08-2000 EN 572-2 EN 572-3 EN 572-4 EN 572-5 EN 572-6 EN
12、 572-7 EN 1748-1 EN 1748-2 EN 1863-1 Page 5 EN 1288-1 12000 Glass in building - Basic soda lime silicate glass products - Part 2: Float glass. Glass in building - Basic soda lime silicate glass products - Part 3: Polished wired glass. Glass in building - Basic soda lime silicate glass products - Par
13、t 4: Drawn sheet glass. Glass in building - Basic soda lime silicate glass products - Pari 5: Patterned glass. Glass in building - Basic soda lime silicate glass products - Part 6: Wired patterned glass. Glass in building - Basic soda lime silicate glass products - Part 7: Wired or unwired channel s
14、haped glass. Glass in building - Special basic products - Part 1: Borosilicate glasses. Glass in building - Special basic products - Part 2: Glass ceramics. Glass in building - Heat strengthened soda lime silicate glass - Part 1 : Definition and description. EN 12150-1 Glass in building - Thermally
15、toughened soda lime silicate safety glass - Part 1: Definition and description. EN 12337-1 Glass in building - Chemically strengthened soda lime silicate glass - Part 1: Definition and description. EN IS0 12543-1 Glass in building - Laminated glass and laminated safety glass - Part 1 : Definitions a
16、nd description of component parts. prEN 13024-1 Glass in building - Thermally toughened borosilicate safety glass - Part I : Definition and description. 3 Definitions For the purposes of this European Standard, the following definitions apply. 3.1 flat glass: any glass product conforming to EN 572-2
17、, EN 572-3, EN 572-4, EN 572-5, EN 572-6, EN 1748-1, EN 1748-2, or any transformed glass made from these products without deliberately inducing profile or curvature 3.2 bending stress: the tensile bending stress induced in the surface of a specimen NOTE: For testing purposes, the bending stress shou
18、ld be uniform over a specified part of the surface. Q BSI 08-2000 STD-BSI BS EN L288-L-ENGL 2000 Lb24bb9 OBb70b5 OLT Page 6 EN 1288-1 12000 3.3 calculated by applying a factor to take into account non-uniformity of the stress field effective bending stress: a weighted average of the tensile bending
19、stresses, 3.4 breakage of the specimen bending strength: the bending stress or effective bending stress which leads to 3.5 equivalent bending strength: the apparent bending strength of patterned glass, for which the irregularities in the thickness do not allow precise calculation of the bending stre
20、ss 3.6 section modulus of a channel shaped glass (EN 572-7) profile bending strength: the quotient of the maximum bending moment and the 3.7 stress intensity factor: a measure of the stress at a crack tip 3.8 and prEN 13024-1 prestressed glass: any glass product conforming to EN 1863, EN 12150, EN 1
21、2337, Symbols Applied load Specimen thickness Length of side of square test sample Constant for calculation of bending stress in EN 1288-3 Constants for calculation of bending stress in EN 1288-5 Maximum bending moment Gas pressure applied within loading ring in EN 1288-2 Profile bending strength (o
22、f channel shaped glass) = hnb$z Radius of loading ring Radius of supporting ring Radius of circular specimen Average specimen radius (for evaluation) Central deflection of specimen Section modulus (of channel shaped glass) Poisson number of specimen NOTE: For soda lime silicate glass (see EN 572-1)
23、a value of 0,23 is used. O BSI 08-2000 STD-BSI BS EN L2BB-L-ENGL 2000 Lb24bb9 0867066 T56 m Page 7 EN 1288-1 :ZOO0 ab Bending stress akff Effective bending stress ObB Bending strength ObqB Equivalent bending strength a b) rate and duration of loading (see 5.1.3); c) area of surface stressed in tensi
24、on (see 5.1.4); d) ambient medium, through stress corrosion cracking as well as healing of surface damage in the glass (see 5.1.5 and I of annex A); O BSI 08-2000 STD-BSI BS EN LEBB-L-ENGL 2000 W 1624669 O867067 992 9 Page 8 EN 1288-1 :2000 e) age, .e. time elapsing since the last mechanical surface
25、 treatment or modification to simulate damage (see 5.1.6); 9 temperature (see 5.1.7). The influence exerted by factors b) to 9 on bending strength has been taken into account in this standard. 5.1.2 Effect of surface condition For the purpose of bending strength tests according to this standard, gla
26、ss behaves as an almost ideally linear-elastic material that fails in a brittle manner. This brittleness means that contact with any hard object can lead to surface damage in the form of ultra-fine, partly submicroscopic cracks and chips. Surface damage of this kind, which is practically unavoidable
27、 during normal handling of glass, exerts a notch action which is a major factor in reducing mechanical strength, whereas the chemical composition of the glass has only a minor and in some cases entirely negligible, significance. Hence it follows that the bending strength determined by the methods re
28、ferred to in this standard is related largely to the surface condition of the specimen to be tested. This surface condition is characterized by the following main features. a) The surface condition imparted by a particular method of treatment, which produces a specific damage spectrum and thus resul
29、ts in a strength which is specific to the finished surface condition; b) Residual stress, e.g. in the form of thermal or chemical prestress intentionally imparted, as well as unintended residual stresses. 5.1.3 Effect of rate of loading For the interpretation of the bending strength values determine
30、d as described in this standard, the rate of loading is of special importance. Cracks propagate in glass over a wide range of values of tensile stress (see 2 of annex A). There is a lower limit to the stress intensity factor below which cracks do not propagate (see I of annex A). There is then some
31、subcritical crack propagation at higher levels of stress intensity factor, which is influenced by humidity, temperature and chemical agents. Above a critical stress intensity factor crack propagation is very rapid and leads to (almost) instantaneous failure. The consequence of the subcritical crack
32、propagation is, for example, that the rate of load increase and/or the duration of static loading influences the bending strength. For prestressed glass, this time dependence does not manifest itself until the tensile stress induced ir the surface exceeds the compressive stress permanently present t
33、here (see 3 of annex A). 5.1.4 Effect of test surface area The decrease in bending strength of glass with increasing size of the test area exposed to high stress is also of importance (see 4 of annex A). This area effect is accounted for by the statistical distribution of surface defects varying in
34、effectiveness; the larger the test area, Q BSI 082000 STD.BSI BS EN 1288-1-ENGL 2000 W Lh24bb9 0667066 829 Page 9 EN 1288-1 12000 the greater is the probability of its containing a large surface defect. Consequently, the influence of the area effect increases with decreasing incidence of defects in
35、the surface, so that this influence is more pronounced in the case of undamaged, e.g. fire-finished glass surfaces (see 5 of annex A). Differences are likely between the mean values of the bending strength as measured in accordance with EN 1288-2 (maximally stressed area: 240 O00 md), or by using de
36、vices R45 and R30 in accordance with EN 1288-5 (maximally stressed areas: 254 md and 11 3 mm2), due to the size of the stressed area. Depending on surface damage, the results obtained from testing smaller surface areas may be significantly higher than those obtained from testing larger surface areas
37、, as shown in Table 1. Table i : Approximate effects of test surface area on the mean measured bending strength I Test Method I Device I Relative bending strength 1 nn o/- I Since glass for use in buildings is often in large sizes, the test methods specified in EN 1288-2 and EN 1288-3 give values wh
38、ich are more appropriate as the basis for designing flat glass for use in buildings. The test method specified in EN 1288-5 can be useful as a method of evaluating the comparative bending strength of flat glass. 5.1.5 Effect of ambient medium The surrounding medium in which the glass is tested has a
39、n influence on the strength of the glass, particularly if the moisture level is very low. When glass is used in buildings, the relative humidity typically ranges from 30 % to I00 %. Within this range, the effect on the bending strength, as tested according to this standard, is not great. However, te
40、sts on glass for use in buildings shall be undertaken in test conditions with relative humidity levels in the range of 40 YO to 70 YO, in order to eliminate this effect when comparing bending strength resu Its. 5.1.6 Effect of aging If the glass surface is modified (by abrasion, etching, edge workin
41、g, etc.) before the testing, it is necessary to allow the fresh damage to heal before the test is undertaken. The continual surface modification by moisture affects the damage in a way that can reduce any weakening effect (see I of annex A). In practice, glass is highly unlikely to be stressed direc
42、tly after it has been treated, so it shall be conditioned for at least 24 h before testing. 5.1.7 Effect of temperature The bending strength of glass is affected by changes in temperature. Within the normal range of temperatures experienced by glass in buildings, this effect is not very ;“significan
43、t, but, to avoid possible complications in the comparison of bending strength values, testing shall be undertaken in a restricted range of temperatures. 8 BSI 08-2000 STD=BSI BS EN 1288-1-ENGL 2000 D 1624669 08b70b9 765 Page 10 EN 1288-1 :2000 5.2 Bending stress and bending strength 5.2.1 General Th
44、e test methods described in EN 1288-2, EN 1288-3, EN 1288-4 and EN 1288-5 are designed to induce a uniform bending stress over an area (the test area) of the specimen. However, the tests are statically indeterminate, that is, the stresses induced by the applied loads depend on the nature of the mate
45、rial tested as well as the load distribution. 5.2.2 Effective stress Where the stress varies significantly over the test area, as is the case in EN 1288-3 (see 6.2.2), it can be represented by a weighted average stress, called the effective bending stress, ukff. The weighting is obtained by statisti
46、cally evaluating the probability of fracture at any point in the stressed area. 5.2.3 Equivalent bending strength Variations in homogeneity or thickness of the specimen affect the stress distribution. Hence, the bending strength, ObB, is never entirely an accurate value and, in some instances, it is
47、 better termed the equivalent bending strength, okqe. For some of the glass types tested (for example float glass), such variations are very small and the bending strength determined by the tests is sufficiently close to the actual bending strength for the difference to be unimportant. In the case o
48、f patterned glass, however, only the equivalent bending strength can be determined. 5.2.4 Profile bending strength When channel shaped glass is tested according to EN 1288-4, most of the specimens fail from fractures originating at the corner of the profile, where the web and flange meet, and not at
49、 the extreme of the flange or surface of the web. This is due to secondary stresses generated by the spreading of the flanges when the channel section is bent. In this test the bending strength is better expressed as the profile bending strength, the stresses along the medians and the diagonals differ slightly, within a range of about 5 %. The curves in Figure 3 of EN 1288-2 and the values in Table 3 of EN 1288-2 have been determined from measurements. Deviations of individual measured values from the curves or table values are at most 5 %. 0 BSI 08-2000 STD-
