LY/T 3146-2019Test methods for end-joints in structural wood products (English PDF)

4.1 General

The test methods of this standard shall include the strength and structural evaluation of the longitudinal timber interface for the structure, divided into offline testing methods and online testing methods.

law. Off-line testing methods include axial tensile testing methods, flexural testing methods, and pressure-reduced dipping peel test methods; online testing methods Methods include guaranteed load detection methods.

The test methods of this standard allow special pretreatment of test specimens or test specimens under moisture imbalance.

4.2 Axial tensile test method

4.2.1 Equipment requirements

4.2.1.1 Clamping device

Transmit tensile load from the drive chuck to the fixed clamping end with a distance of at least 600 mm between the clamps; for miter joints, remove the miter joints Outside the length, make the distance between the clamps at least 600mm. Do not apply any bending impulse on the cross section of the test piece, and avoid causing the test piece in the chuck.

Internal failure or stress concentration failure. The device can be connected to the test piece by a flat plate, or it can be clamped by other means. The clamping device is shown in Figure 1.

As shown.

Explanation.

t-- length of the clamping part of the fixture, unit is millimeter (mm);

L-- Distance between fixtures, in millimeters (mm).

Figure 1 Schematic diagram of axial tensile test

4.2.1.2 Loading device

The loading should be carried out at a uniform speed, and the loading fixture can be moved to meet the load accuracy. According to the test requirements, adjust the Distance. The maximum load is displayed and corrected to ensure accuracy.

4.2.2 Test specimen

The length of the test piece shall not be less than 600 2t mm. The test piece should be selected according to the actual test purpose.

4.2.3 Test steps

a) Measure and record the thickness and width of the test piece at the longitudinal joints, to the nearest 0.1 mm.

b) The moisture content of the test piece shall be measured and recorded in accordance with GB/T 1931-2009 for the left and right parts of the test piece.

c) The test specimen shall be tested at a constant loading speed and reach the breaking load within 1 to 10 minutes.

d) The longitudinal joint of the test piece should be in the middle of the span between the two ends of the fixture, so that the longitudinal axis of the test piece and the direction of the applied load are consistent.

e) The test record shall include the maximum load reached during the test, and if necessary, describe the characteristics of the specimen failure and the wood breakage rate.

4.3 Bend test method

4.3.1 Equipment requirements

4.3.1.1 Test specimen support loading fixture

The width of the support block should be greater than the thickness of the test piece, and the length should be greater than 1/2 of the thickness of the test piece, usually not more than.200 mm, as shown in Figure 2. Should note

Note that when the width to thickness ratio of the cross section of the test piece is greater than or equal to 3, lateral support should be added to prevent lateral deformation, and it should not hinder the test piece.

Deformation in the direction of the load.

Explanation.

l-- span, unit is millimeter (mm);

h--thickness of the test piece in millimeters (mm);

L--Longitudinal test piece length, unit is millimeter (mm);

b--The width of the longitudinal test piece, in millimeters (mm).

Figure 2 Schematic diagram of bending test

4.3.1.2 Loading device

The loading device shall meet the specified accuracy. The distance between the centre lines of the two equivalent loads shall be greater than 51 mm.

4.3.2 Test specimen

The minimum length of the specimen is not less than the test span, and the ratio of the span to the width of the cross-section of the specimen during the test is between 17. 1 and 21. 1. Outside the support point the length of the test piece shall be less than 10 times the width of the test piece and greater than 2 times the width of the test piece. The size of the test piece is subject to actual measurement.

4.3.3 Test steps

a) Before testing, the cross-sectional size and length of the test specimen shall be accurately measured to the nearest 0.1 mm.

b) The moisture content of the test piece shall be measured and recorded in accordance with GB/T 1931-2009 for the left and right parts of the test piece.

c) The test piece is placed on the support, and the longitudinal joint of the test piece is placed between the loading points as much as possible. The curved tensile surface is randomly selected. According to test the purpose is to allow the applied load to be perpendicular to the width direction or thickness direction of the test piece, but for the test direction and loading direction at the longitudinal joint interface, Instructions.

d) The test shall be carried out at a constant loading speed and the breaking load shall be reached within 1 to 10 minutes.

e) The test record shall include the maximum load reached during the test, and if necessary, describe the characteristics of the specimen failure and the wood breakage rate.

4.4 Test method of pressure and pressure dipping and peeling

4.4.1 Equipment requirements

The requirements for the equipment are as follows.

a) The pressure and pressure reducing equipment shall have a space for water to completely impregnate the test specimen, and the pressure to withstand the safety shall be at least 520 kPa. Pressure vessel A vacuum pump or similar device should be provided to ensure a pressure of 520 kPa in the pressurized device.

b) The constant temperature dryer should ensure that it can fully accommodate the test piece, and can control the lateral air velocity at 2m/s-3m/s, and maintain the temperature (70 ± 3) °C.

4.4.2 Test specimen

The intercepted test piece shall include a complete finger joint or miter joint structure, the length is not greater than 154mm, and the finger joint or miter joint part is under cut Take the middle position of the test piece. The second cross-section was performed from the middle position of the intercepted test piece, resulting in two smooth end faces and a vertical longitudinal axis of the structural material.

Small test piece. Each small test piece should keep the glued part at least 6mm away from the finger joint or the miter end. As shown in Figure 3.

Explanation.

s-- the distance from the center cross-section to the joint or miter end, in millimeters (mm);

L-- length of the test piece in millimeters (mm).

Figure 3 Schematic diagram of specimen preparation

4.4.3 Test steps

a) Immerse the test piece in water at 18 °C -30 °C;

b) For the test piece immersed in water, evacuate to 68 kPa ~ 85 kPa for 30 minutes, release the vacuum pressure and pressurize it to 520 ± 34kPa, holding pressure for 2 h.

c) After repeating the above steps a) -b) 2 times, take out the test piece from the water, put it in a constant temperature dryer (70 ± 3) °C, and Under the condition that the temperature is not more than 15% and the air flow speed is 2m/s-3m/s, the test piece is dried to the range of 95% -100% of the mass before the test.

d) During the drying process, a distance of at least 50 mm should be maintained between the test pieces, and the bonding gap of the cross section of the structural material should be parallel to the air.

Flow direction; after drying, the peeling length of the cross section of the test piece shall be measured, recorded and the peeling rate shall be calculated in accordance with the provisions in 4.4.4.

e) Choose whether to repeat the above steps according to the test purpose. The percentage of peel after each iteration should be determined after the test is completed and recording. The test record shall include the immersion time, pressure time, drying time, pressure value and number of tests during the test and calculate the peel rate.

4.4.4 Measurements and calculations

Immediately after the test is completed, the peeling position of the test piece, that is, the peeling of the adhesive layer, should be checked, and the length of the peeling gap (3mm to Except for the following), peeling of the side glue layer and peeling of the node interface are not counted. For areas that are uncertain whether to peel or not, use a feeler gauge to the nearest 0.10mm for testing, care should be taken to control the pressure intensity of the feeler gauge to ensure measurement accuracy.

Calculate the peel rate of the test piece, the calculation formula is as follows.

4.5 Guaranteed load detection method

4.5.1 Equipment requirements

The requirements for the equipment are as follows.

a) Ability to transfer loads such that loads from the axial tensile or flexural test are applied to the test piece.

b) Ability to apply a preset load to the test piece.

c) The load value can be measured during the load application and when the preset load value is reached.

d) The pressure can be maintained when the preset load value is reached.

e) The specimen can be removed when it fails to reach the preset load.

4.5.2 Test specimen

For the axial tensile guaranteed load test, the test specimen requirements are the same as 4.2.2; for the flexural guaranteed load test, the test specimen requirements are the same as 4.3.2. Specimen the moisture content is the moisture content in the production process and cannot be adjusted.

4.5.3 Test steps

a) For the axial tensile guaranteed load test, the longitudinal joint of the test piece should be in the middle of the span between the two ends of the fixture, so that the longitudinal axis of the test piece the direction of the applied load is the same; for the bending guaranteed load test, the test piece is placed on the support, and the longitudinal joint of the test piece is placed as much as possible.

Between loading points.

b) In the same batch of production, the loading speed of the load to the longitudinal joint should be consistent, and the guaranteed load value should be reached within 3 seconds. according to the test purpose and quality control target should choose the appropriate guaranteed load value. It is recommended to choose a guaranteed load that is higher than the load to which the product is subjected.