BS EN 408:2006 pdf download
BS EN 408:2006 pdf download.Timber structures ——Structural timber and glued laminated timber— Determination of some physical and mechanical properties.
12 Determination of shear modulus — Variable span method
12.1 General
This method involves the determinatIon of the apparent modulus of elasticity Eee for each test piece over a number of spans with the same cross section at the centre.
12.2 Test piece
The test piece shall have a minimum length of 21 times the depth of the section.
12.3 Procedure
The test piece shall be loaded in centre point bending over at least four different spans with the same cross section at the centre of each. The spans shall be chosen so as to have approximately equal increments of – between them, within the range 0,0025 to 0.035.
The test piece shall be s4mpfy supported.
NOTE Small steel plates of length not greater than one-half of the depth of the test piece may be iiserted between the piece and the loacng heads or supports to minimize local indentation.
Lateral restraint shall be provided as necessary to prevent buckling. This restraint shall permit the piece to deflect without sgnihcant frictional resistance
Load shall be applied at a constant rate. The rate of movement of the loading head shall be not greater than 5 x ‘2I6hmm/s
The symbols are as given in clause 4.
The maxerium load applied shafl riot exceed the proportional limit load or cause damage to the piece.
The loading equipment used shall be capable of measuring the load to an accuracy of I % of the load applied to the test piece or. for loads less than 10% of the applied maximum load, with an accuracy of 0,1 % of the maximum applied load.
Deformations shall be measured at the centre of the spans.
Deformation shal be determined with an accuracy of I % or. for deformations less than 2 mm. with an accuracy of 0.02 mm.
12.4 ExpressIon of results
12.4.1 General
The apparent modulus of elasticity and shear modulus for each piece and each test span shall be calculated as described in 12,42 and 12.4.3 respectively.
12.4.2 Apparent modulus of elastIcity
The apparent modulus of elasticity E. is gwen by the equation
13 Determination of bending strength
13.1 Test piece
The test piece shall normally have a minimum length of 19 times the depth of the cross section. Where this is not possd4e. the span of the beam shall be reported.
13.2 Procedure
The test piece shall be symmetrically loaded in bending at two points over a span of 18 times the depth as shown in figure 3. lIthe test piece and equipment does not permit these conditions to be achieved exactly, the distance between the inner load points and the supports shall be changed by an amount not greater than 1.5 times the depth of the test piece, and the span and test piece length may be changed by an amount not greater than three times the depth of the test piece, while maintaining the symmetry of the test.
The test piece shall be simply supported.
NOTE 1 Smal steel plates 01 length not greater than one•hall o the depth ol the test piece may be mserted between the piece and the loadeg heads or supports to minimize local indentation.
Lateral restraint shall be provided as necessary to prevent buckling. This restraint shall permit the piece to deflect without significant frictional resistance.
The loading equipment used shall be capable of measuring the load to an accuracy of 1 % of the load applied to the test piece.
Load shalt be applied at a constant loading-head movement so adjusted that maximum load is reached within (300
• 120)5.
NOTE 2 ThIs rate should be determined horn the results ol preliminary tests The objective Is that the tine to reach F,. br each piece is 300 a..
The time to failure for each test piece shall be recorded and its average reported. Any single peace diverging more than 120 s Iron, the target of 300 s shall be reported.
13.3 Expression of results
The bending strength l,, is given by the equation 1= a (2 Ve
The symbols are as given in clause 4.
The bending strength shall be calculated to an accuracy oil %.
The mode of fracture and the growth characteristics at the fracture section of each test piece shaM be recorded.
14 Determination of modulus of elasticity in tension parallel to the grain
14.1 Test piece
The test piece shall be of full structural cross section, and of sufficient length to provide a test length clear of the testing machine grips of at least nine times the larger cross-sectional dimension.
14,2 Procedure
The test piece shall be loaded using gripping devices which will permit as far as possdle the application ol a tensile load without inducing bencng. The gripping devices arid loading conditions actually used shall be reported.
Load shall be applied at a constant rate. The rate of strain In the piece shall be not greater than 0,00005 per.s.