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Integrity check of structural softwood glue lines: correspondence between delamination and block shear tests

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Abstract

In factory production control (FPC) of glued-laminated timber the integrity of glue lines according to product standards has to be checked by carrying out either delamination or block shear tests. The chosen test method should provide reliable and reproducible results, and from a practical point of view should be as cheap and easy to perform as possible. An extensive experimental study aiming at systematically comparing the outcomes of delamination and shear tests on structural softwood glue lines using different wood species and adhesives was carried out. In the delamination tests, the length of open glue lines was assessed after subjecting the test specimens to vacuum- and pressure-soaking and to subsequent drying. In the block shear tests, the shear strength and wood failure percentage were determined. Only if the benchmark values in the product standards were met or exceeded, the respective specimen passed the test and the glue lines were regarded as sound. As a main overall result it turned out that the outcomes of both test methods generally agree well, but will not necessarily lead to the same pass/fail conclusion in any case. Therefore, for FPC the choice of their application should be defined more specifically.

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Abbreviations

ASTM:

American Society for Testing and Materials

CEN:

European Committee for Standardization

DIB:

Percentage of intact glue line length after the delamination test (aggregated result of delamination tests, averaged over methods A and B)

EN:

European standard

EPI:

Emulsion Polymer Isocyanate

FPC:

Factory production control

Glulam:

Glued-laminated timber

MC:

Moisture content

MUF:

Melamine-Urea–Formaldehyde

PUR:

Polyurethane

PRF:

Phenol-Resorcinol-Formaldehyde

RH:

Relative humidity (of air)

SC:

Service class

SFV:

Shear strength (aggregated result of block shear tests, averaged over 3 pre-conditioning treatments)

SWF:

Wood failure percentage (aggregated result of block shear tests, averaged over 3 pre-conditioning treatments)

UF:

Urea–Formaldehyde

WFP:

Wood failure percentage (in block shear tests)

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Acknowledgments

This study was supported by the Swiss Federal Office for the Environment FOEN (Fonds zur Förderung der Wald- und Holzforschung, Project number 2009.16). Five members of the Swiss Glulam Association SFH (www.glulam.ch) supplied the test material. The assistance of the Empa technicians Daniel Heer and Michael Strässle taking care of preparation of tests specimens and performing shear tests, respectively, is gratefully acknowledged.

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Authors and Affiliations

  1. Structural Engineering Research Laboratory, Empa-Swiss Federal Laboratories for Materials Science and Technology, Ueberlandstrasse 129, 8600, Dübendorf, Switzerland

    René Steiger

  2. Applied Wood Materials, Empa-Swiss Federal Laboratories for Materials Science and Technology, Ueberlandstrasse 129, 8600, Dübendorf, Switzerland

    Martin Arnold & Walter Risi

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  1. René Steiger
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  2. Martin Arnold
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  3. Walter Risi
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Correspondence to René Steiger.

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Steiger, R., Arnold, M. & Risi, W. Integrity check of structural softwood glue lines: correspondence between delamination and block shear tests. Eur. J. Wood Prod. 72, 735–748 (2014). https://doi.org/10.1007/s00107-014-0838-0

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  • DOI: https://doi.org/10.1007/s00107-014-0838-0

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