EN 302-8-2017 pdf download.Adhesives for load-bearing timber structures – Test methods – Part 8: Static load test of multiple bond line specimens in compression shear.
This EN 302-8 specifies a method of determining the ability of adhesive bonds to resist static load. It is applicable to adhesives used in load bearing timber structures.
It is suitable for the following applications:
a) for assessing the compliance of adhesives according to EN 301, EN 15425 and EN 16254;
b) for assessing the suitability and quality of adhesives for load-bearing timber structures;
c) for assessing the effect on the bond strength resulting from constant load at different climate cond i ti OflS.
This method Is Intended primarily to obtain performance data for the classification of adhesives for load bearing timber structures according to their suitability for use in defined climatic environments.
This method is not intended to provide data for structural design, and does not necessarily represent the performance of the bonded member in service.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
EN 30 1:2013, Adhesives, phenolic and aminoplastic,. for load-bearing timber structures — Classification and performance requirements
EN 15425:20 17, Adhesives — One component polyurethane (PURJ for load-bearing timber structures — Classification and performance requirements
EN 16254:2013+A1:2016, Adhesives — Emulsion polymerized isocyanate (EPI) for load-bearing timber structures — Classification and performance requirements
3 Principle
Bonded test pieces are subjected to a constant compression shear load under a series of three different climates. Number of failures and the amount of deformation is measured after the end of the last climate cycle.
If longer rods are used, distance blocks need to be placed on top and/or under the specimen. The distance blocks shall be prepared in such a way that the two contact surfaces, between the distance block and the jig and between the distance block and the specimen, are parallel. Dimension of distance blocks: at least 48 mm x 51 mm x 10mm.
NOTE Blocks produced from several pieces of plywood bonded together have been found suitable
The spring shall have the following characteristics:
— outside diameter (unloaded): 105 mm;
— end fix: both ends fixed and grounded;
— free length: 320 mm;
— compression at maximum load: 45 mm to 50 mm.
NOTE A spring rate of 81 N/mm has shown to be suitable.
4.2 Equipment for climate control
The used equipment shall be capable of maintaining (50 ± 2) °C, (70 ± 2) °C or (90 ± 2) °C with a relative humidity of (10 ± 5) % in order to reach one of the climate conditions 1 a), 1 b) or 1 c) in Table 1, and the two climates (20 ± 2) °C and (85 ± 5) % relative humidity and (50 ± 2) °C and (75 ± 5) % relative humidity.
4.3 Testing machine
A testing machine capable to apply a compression load is required.
5 Test specimens
5.1 Selection of wood
Untreated beech wood (Fagus sylvatica L) with a density of (700 ± 50) kg/rn3 at 12 % moisture content shall be used. The material shall be straight-grained and free from knots, machining defects (such as chipped grain, dubbed ends, feed roll polish, coarse knife marks and feed roll compression) and any drying defects such as case hardening, collapse, splits or checks. The angle of the annual rings to the surface to be bonded shall be between 300 and 600.
After gluing, the specimens shall be conditioned for a minimum of 14 days in climate [20/651 before the preparation of the test specimens.
5.3 Preparation of test specimens
After curing, each laminated assembly shall be trimmed along the sides to leave a width of (50,8 ± 0,1) mm (according to Figure 5). The outer lamellas of the specimen shall then be cut with a width of (3,2 ± 0,1) mm. The cuts shall divide each centre piece symmetrically, resulting in an overlapping glue line of (12,7 ± 0,1) mm. The cuts shall separate the wood layer and the adhesive layer, but they shall not go beyond the adhesive layer.
From each of the three laminations, two test specimens with a length (133,5 ± 0,1) mm are made, each containing four centre pieces. Each of the six specimen will then contain a total of 12 glue lines (nominal dimension 50,8 mm x 12,7 mm) for axial compression loading, providing a series of 6 pairs of load bearing glue lines. Each pair of load bearing glue lines has a total nominal glue line area of 1 290 mm2. The two outer lamellas are then trimmed, in order to make the terminal surfaces parallel to each other and with an angle of 90 O in relation to the loading direction.
Prior to testing, use a straightedge and a razor blade to cut marks perpendicular to every adhesive glue line for measuring possible slippage (according to Figure 6).EN 302-8-2017 pdf download.
EN 302-8-2017 pdf download
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