Fire tests on finger-jointed timber boards

Transcription

1 Research Collection Report Fire tests on finger-jointed timber boards Author(s): Klippel, Michael; Frangi, Andrea Publication Date: Permanent Link: Rights / License: In Copyright - Non-Commercial Use Permitted This page was generated automatically upon download from the ETH Zurich Research Collection. For more information please consult the Terms of use. ETH Library

2 i b k Institut für Baustatik und Konstruktion, ETH Zürich Fire tests on finger-jointed timber boards Michael Klippel Andrea Frangi IBK Bericht Nr. 354, Juni 2014

3 KEYWORDS: Fire resistance, timber construction, adhesive, finger joint, residual strength, fire safety Dieses Werk ist urheberrechtlich geschützt. Die dadurch begründeten Rechte, insbesondere die der Übersetzung, des Nachdrucks, des Vortrags, der Entnahme von Abbildungen und Tabellen, der Funksendung, der Mikroverfilmung oder der Vervielfältigung auf anderen Wegen und der Speicherung in Datenverarbeitungsanlagen, bleiben, auch bei nur auszugsweiser Verwertung, vorbehalten. Eine Vervielfältigung dieses Werkes oder von Teilen dieses Werkes ist auch im Einzelfall nur in den Grenzen der gesetzlichen Bestimmungen des Urheberrechtsgesetzes in der jeweils geltenden Fassung zulässig. Sie ist grundsätzlich vergütungspflichtig. Zuwiderhandlungen unterliegen den Strafbestimmungen des Urheberrechts. Michael Klippel, Andrea Frangi: Fire tests on finger-jointed timber boards Bericht IBK Nr. 354, Juni Institut für Baustatik und Konstruktion der ETH Zürich, Zürich Gedruckt auf säurefreiem Papier Printed in Switzerland Sie finden das Verzeichnis der IBK-Publikationen auf unserer Homepage unter: The catalogue of IBK publications is available on our homepage at: Die meisten Berichte von Nr. 270 bis Nr. 333 sind auch noch in gedruckter Form unter Angabe der ISBN-Nr. erhältlich bei: Most reports from No. 270 to No. 333 can still be purchased in printed form by indicating the ISBN number from: AVA Verlagsauslieferung AG Centralweg 16 CH-8910 Affoltern am Albis Tel Fax Berichte ab Nr. 334 sind nur noch in elektronischer Form verfügbar. Sie finden die entsprechenden Dateien in der e-collection der ETH Bibliothek unter oder über die Links auf unserer Homepage. Reports from No. 334 onwards are only available in electronic form. The respective files can be found in the e-collection of the ETH Library at or through the links on our homepage.

4 IBK Report No. 354 Fire tests on finger-jointed timber boards Michael Klippel Andrea Frangi Institute of Structural Engineering Swiss Federal Institute of Technology Zürich June 2014

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6 i Foreword The combustibility of wood is one of the main reasons why most building codes strongly limit the use of timber as a building material, in particular by limiting the number of storeys of timber buildings. Fire safety is the main precondition for the use of wood for multi-storey timber buildings and therefore an important criterion for the choice of material for buildings. Significant advances in research and numerical simulations have increased the theoretical knowledge of the fire behaviour of timber members. However, the influence of adhesives on the fire behaviour of glued structural timber elements has not yet been studied and important experimental basic data is still missing. The present report shows the results of a comprehensive series of fire tests with finger joints glued with different types of adhesives. The experimental investigations were conducted in the frame of the research project entitled Fire safety of bonded structural timber element and sponsored by the Commission of Technology and Innovation CTI. The adhesive manufacturers Purbond AG, Casco AG, Dynea AG, Jowat AG and Türmerleim AG supported this campaign and provided their products so that all types of adhesives nowadays used in structural timber members were tested in this campaign. The overall objective of the research project is the improvement of the reliability and safety of glued structural timber elements under consideration of the influence of the adhesive used. The project fits into the overall research strategy of the institute on the fundamental knowledge of the structural behaviour of timber structures. The fire tests presented in this report form one important step to evaluate the fire performance of finger joints glued with different types of adhesives of glued-laminated timber beams. The specimens were assembled in different timber companies in Switzerland, such as Roth Burgdorf AG/ Burgdorf, Nussbaumer Holz AG/ Baar and Schilliger Holz AG/ Küssnacht. The fire tests were performed in the fire lab of the Swiss Federal Laboratories for Materials Science and Technology (Empa). The results significantly enlarge the experimental background on the fire behaviour of finger joints and provide reliable data for the evaluation of existing design models. Further, the fire tests allow the development of a calculation model for the fire design of glued-laminated timber members, taking into account the influence of the adhesive. I would like to thank Michael Klippel who has prepared and carefully conducted all fire tests and has also processed and evaluated the large amount of data and edited this report. I would like to also thank the team of the IBK testing and research lab (Patrik Morf, Christoph Gisler, Thomas Jaggi and Dominik Werne) as well as of the fire lab of the Swiss Federal Laboratories for Materials Science and Technology Empa (Erich Hugi, Angelo Demont, Marcel Steiner) for the support. Further, I would like to gratefully acknowledge the support by the Swiss Commission for Technology and Innovation (CTI) and all industrial partners involved in this project. Zurich, June 2014 Andrea Frangi

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8 iii Abstract This testing report summarises the experimental investigations on finger-jointed timber specimens, glued with different types of adhesives, loaded in tension and exposed to standard ISO-fire. The tests were performed as part of the project entitled Fire safety of bonded structural timber elements in the frame of a CTI-project (Commission for Technology and Innovation). The extensive testing programme on finger-jointed timber specimens was performed in cooperation with industry partners at the Swiss Federal Institute of Technology Zurich (ETH Zurich). The main aim of this research project is to clarify if the currently used design model for the fire resistance of bonded structural timber elements, such as glued-laminated timber, should consider the behaviour of adhesives at elevated temperatures. In this experimental study, different adhesives available on the market from adhesive manufacturer from Europe (such as Casco AG, Dynea AG, Jowat AG, Türmerleim AG, Purbond AG) were tested. Adhesives being used for structural applications as well as adhesives not certified according to current European testing standards for the use in structural applications were tested. The fire performance of 12 different adhesives - of type 1C PUR, MUF, PRF, EPI, PVAc, UF - were tested in a finger-jointed connection for cross-sections with a width of 80, 140 and 200 mm. In total, 49 fire tests were performed under ISO-fire exposure at the Swiss Federal Laboratories for Materials Testing and Research (EMPA) in Duebendorf/ Switzerland. Two tests were conducted with specimens equipped with thermocouples to determine the temperature distribution along the cross-section width. In the other tests, different parameters and their influence on the fire resistance were varied, such as the adhesive in the finger joint, the width of the specimen, the load level and the type of fire exposure on the testing lamella. The tests were performed in two test series in March and April, 2011 as well as in July and August, The second test series was extended by five additional tests with higher graded timber in August The main result from the first test series can be concluded as follows: The adhesives tested (2 x PUR, 1 x MUF) fulfil current approval criteria according to EN 301 (2013c) and EN (2008) for the use in load-bearing timber components in Europe. The adhesives fulfil at least the A7 test at 70 C according to EN (2013a). Taking into account the failure pattern, no significant difference was observed between these adhesives. It could be shown that the higher loss of strength for some adhesives tested at elevated temperature does not necessarily lead to the same loss of strength in fire, since defects like knots may be dominant - depending on the strength class (grading). The main result from the second test series can be concluded as follows: No substantial difference was obtained for finger-jointed specimens glued with PRF and other structural adhesives. The PUR adhesive fulfilling the ASTM D7247 (2007) standard test at temperatures higher than 200 C did not reach a higher fire resistance than PUR adhesives which do not fulfil this standard. It was found that adhesives, which are used in structural timber members such as glued-laminated timber beams, need sufficient strength at lower temperatures than 200 C.

9 iv This is especially explained by the steep temperature gradient typical for timber members such as glued-laminated timber. In addition to the fire tests, about 120 tensile tests on finger-jointed lamellas were performed at normal temperature. These lamellas were produced with the same types of adhesives as studied in the fire tests. The results of the whole investigation are summarised in this test report.

10 v Zusammenfassung Der vorliegende Versuchsbericht fasst die experimentellen Untersuchungen an keilgezinkten Holzlamellen zusammen. Die keilgezinkten Holzlamellen wurden mit verschiedenen Klebstoffen geklebt und unter einer reinen Zugbelastung bei ISO-Normbrand geprüft. Die Versuche wurden im Rahmen eines KTI-Projektes (Kommission für Technologie und Innovation) mit dem Titel Brandsicherheit von verklebten tragenden Holzbauteilen durchgeführt. Das umfangreiche Testprogramm zur Prüfung keilgezinkter Holzlamellen wurde in Zusammenarbeit mit Industriepartnern an der Eidgenössischen Technischen Hochschule Zürich (ETH Zürich) durchgeführt. Im Rahmen dieses Projektes wurde untersucht, ob die derzeit verwendeten Modelle zur Brandbemessung (z.b. die Methode mit reduziertem Querschnitt nach EN (2004)) von verklebten tragenden Holzbauelementen, wie Brettschichtholz, das temperaturabhängige Klebstoffverhalten berücksichtigen sollen. In dieser experimentellen Studie wurden verschiedene handelsübliche Klebstoffe von unterschiedlichen Klebstoffherstellern aus Europa (Casco AG, Dynea AG, Jowat AG, Türmerleim AG, Purbond AG) untersucht. Es wurden Klebstoffe untersucht, die im strukturellen Holzleimbau eingesetzt werden und nach aktuellen europäischen Teststandards zugelassen sind. Zudem wurden Klebstoffe untersucht, die nicht im tragenden Holzleimbau eingesetzt werden und aus diesem Grund nicht hierfür zertifiziert sind. Das Verhalten im Brandfall von 12 verschiedenen Klebstoffen - vom Typ 1C PUR, MUF, PRF, EPI, PVAc, UF - wurde in einer keilgezinkten Holzlamelle für Querschnitte mit einer Breite von 80, 140 und 200 mm getestet. Insgesamt wurden 49 Brandversuche unter ISO Normbrandbedingung an der Eidgenössischen Materialprüfungs- und Forschungsanstalt (EMPA) in Dübendorf / Schweiz durchgeführt. In zwei Versuchen wurde die Holzlamelle mit Thermoelementen ausgestattet, um die Temperaturverteilung entlang des Querschnitts zu bestimmen. In den übrigen Versuchen wurden verschiedene Parameter variiert, um deren Einfluss auf den Feuerwiderstand zu untersuchen. Diese Parameter waren im Wesentlichen der Klebstoff in der Keilzinkung, die Breite des Prüfkörpers, die Laststufe und die Art der Brandbeanspruchung des Prüfkörpers (ein- und zwei-dimensionale Brandbeanspruchung). Die Tests wurden in zwei Testreihen im März und April 2011 sowie im Juli und August 2012 durchgeführt. Die zweite Testreihe wurde von fünf zusätzlichen Versuchen mit Holz höherer Festigkeitsklasse im August 2013 erweitert. Die erste Versuchsreihe kann wie folgt zusammengefasst werden: Die getesteten Klebstoffe (2 x PUR, 1 x MUF) erfüllen die aktuellen Zulassungskriterien gemäß EN 301 (2013c) und EN (2008) für den Einsatz in tragenden Holzbauteilen in Europa. Die Klebstoffe erfüllen dabei mindestens die A7 Prüfung bei 70 C nach EN (2013a). Unter Berücksichtigung der beobachteten Bruchbilder ließen sich keine signifikanten Unterschiede zwischen den geprüften Klebstoffen feststellen. Es zeigte sich, dass der stärker ausgeprägte Festigkeitsverlust für einige Klebstoffe bei Versuchen bei konstanten hohen Temperaturen nicht automatisch zu der gleichen Reduktion im Brandfall führt, da ein frühzeitiges Versagen im Brandfall durch Schwachstellen wie Äste eintreten kann.

11 vi Das wichtigste Ergebnis der zweiten Versuchsreihe kann wie folgt zusammengefasst werden: Es wurde kein substantieller Unterschied festgestellt zwischen keilgezinkten Holzlamellen, die mit PRF verklebt wurden und anderen strukturellen Klebstoffen. Der PUR Klebstoff, der den Teststandard ASTM D7247 (2007) bei Temperaturen von mehr als 200 C erfüllt, erreichte keinen höheren Feuerwiderstand als PUR Klebstoffe, die diesen Teststandard nicht erfüllen. Es wurde festgestellt, dass Klebstoffe, die in tragenden Holzbauteilen wie Brettschichtholz verwendet werden, eine ausreichende Festigkeit bei niedrigeren Temperaturen als 200 C erreichen müssen, um eine ausreichende Festigkeit des Holzbauteils sicherzustellen. Dies ist insbesondere auf den steilen Temperaturgradienten zurückzuführen, der typisch für Holzbauteile wie Brettschichtholz ist. Neben den Brandversuchen wurden etwa 120 Zugversuche bei Normaltemperatur durchgeführt. Hierbei wurde die Zugfestigkeit von keilgezinkten Holzlamellen bei Normaltemperatur als Referenz bestimmt, wobei die gleichen Klebstoffe zur Verklebung verwendet wurden wie im Brandfall. Die Ergebnisse der gesamten Untersuchungen sind in diesem Versuchsbericht zusammengefasst.

12 Contents List of Tables ix List of Figures xi 1 Introduction Motivation and goal of this investigation Experimental overview Organisation of this report Fire tests Test specimens and materials Test program and test parameters Test set-up Test results Charring rate and temperatures Deformations Strain measures Fire resistance and failure type Tests at normal temperature Test specimen and material Test set-up Test results Conclusion 55 A Performance of finger-jointed region 57 A.1 Fire test series A.2 Fire test series

13 viii CONTENTS B Crack patterns 73 B.1 Fire test series B.2 Fire test series B.3 Tests at normal temperature series B.4 Tests at normal temperature series C Deformation measurements 111 C.1 Fire test series 1 and series Nomenclature 115 Bibliography 117

14 List of Tables 1.1 Overview of different adhesives tested in fire tests Configuration of the standard test Adhesives tested in both series of fire tests Properties of the specimens tested in fire test series Properties of the specimens tested in fire test series Overview of test program of fire tests - series Overview of test program of fire tests - series Information about the tensile testing machine Overview of results of the fire tests - series Overview of results of the fire tests - series Information about the tensile testing machine used for the tests at normal temperature Compilation of test results for test series 1 at normal temperature Results from the ultrasonic and eigenfrequency measurements in test series 1 at normal temperature Compilation of test results for test series 2 at normal temperature Compilation of test results obtained from lamellas with higher graded timber for test series 2 at normal temperature Measured MOE in the finger-jointed region for test series 1 at normal temperature Measured MOE in the finger-jointed region for test series 2 at normal temperature. 53 ix

15 x LIST OF TABLES

16 List of Figures 2.4 Manually gluing and pressing process of the protective lamellas as well as the standard assembly and dimensions (mm) of the specimen in the fire tests (c). The specimen was exposed to fire on four sides Assembly of the thermocouples in the cross-section of the testing board Assembly of the different specimens tested in the fire tests Load level during five different fire tests performed Test set-up for the fire tests Details of tensile testing machine Transversal section of the test set-up (dimensions given in (mm)) Longitudinal section of the test set-up (dimensions given in (mm)) Dimensions of the tensile testing frame (dimensions given in (mm)) Assembly of the cover found to be most preferable Assembly of the LVDTs on the testing board outside the furnace Bonding of the strain gauges on the timber surface next to the finger joint in four fire tests of series Position of the strain gauges on the testing lamella in four fire tests of series Temperature versus time of fire exposure measured in the tests P2.T1 and P2.T Deformation as a function of the time of fire exposure Strain and Temperature over time for specimen Strain and Temperature over time for specimen Strain and Temperature over time for specimen Strain and Temperature over time for specimen : Temperature profile after 30 and 60 minutes of one-dimensional fire exposure (Measurement and Simulation), : Typical crack pattern with timber failure in the middle of the cross-section and failure along the fingers in the highly heat influenced outer region of the cross-section Fire resistance as a function of the cross-section width depending of the failure type (see Fig. 2.28) for fire test series 1 and series 2. The specimens were loaded with a constant tensile load parallel to the grain direction of 0.3 F u xi

17 xii LIST OF FIGURES 2.31 Residual cross-section of specimen 5.1 at different locations along the specimens length Test specimen heat influenced on three sides Specimen dimension for tests at normal temperature Set-up of the tests at normal temperature using an universal testing machine (SCHENCK) and an optical camera Comparison of dynamic Young s Modulus (MOE) determined with ultrasonic (E dyn,us,u ) and eigenfrequency (E dyn,f,u ) measurements Tensile strength at normal temperature for adhesives tested in series 2 (width 140 mm) and shown in Table 3.4 (box quartile of distribution; whiskers at most 1.5 x interquartile range; points outliers) : Tensile strength for the specimens tested at normal temperature as a function of the density of the specimens; : Tensile strength for the specimens tested at normal temperature as a function of the stiffness of the specimens Assembly of the LEDs on the timber surface during the tensile tests at normal temperature. Fig. 3.6 and 3.6 show the assembly in series 1 and Fig. 3.6(c) the assembly in series

18 Chapter 1 Introduction 1.1 Motivation and goal of this investigation Adhesives are commonly used to produce engineered wood products such as glued-laminated timber beams or cross-laminated timber panels. The load-bearing capacity of these structural timber elements is influenced by the adhesive used. As a consequence, adhesives have to meet requirements regarding strength and durability to ensure the functionality of structural timber elements during the whole lifetime. Also during fire, the performance requirements have to be fulfilled for a certain time period. For the safe use of glued structural timber elements in fire, important basic data is still missing. Uncertainties with regard to the fire behaviour of glued structural timber elements lead nowadays to difficulties in design and application for engineers and authorities. In 2009, a research project was initiated entitled Fire safety of bonded structural timber element at ETH Zurich. This research project investigates the influence of adhesives in glued structural timber elements. The effect of fire on the finger joint strength should be quantified and the effect of the adhesive strength reduction on the fire resistance of glued-laminated timber beams should be determined. The fire tests presented in this report form one important step to evaluate the fire performance of finger joints glued with different types of adhesives as used in glued-laminated timber beams. The fire tests were performed in the fire lab of the Swiss Federal Laboratories for Materials Science and Technology (Empa). The fire tests give the basis to derive an experimentally established model for the fire design of glued-laminated timber members and clarifies if the behaviour of adhesives at elevated temperature should be considered in the fire design of such members. 1.2 Experimental overview The fire tests were performed on finger-jointed timber lamellas. In addition, fire tests were performed with unjointed timber boards (solid wood) as a reference. Two series of fire tests were performed. The first series of fire tests was performed in March and April 2011 and the

19 2 Chapter 1. Introduction second series in July and August The second test series was extended with additional tests on higher graded timber in August In total, 49 fire tests were performed. The results of the fire tests are presented in chapter 2. In addition, further tests at normal temperature (20 C) were conducted (see chapter 3). The following parameters were investigated in the fire tests: Adhesive in the finger joint Width of the specimens Stress level during the fire test Type of fire exposure (one- and two-dimensional) Type of test (constant load until failure or constant load and increase after a certain time of fire exposure) Table 1.1 shows an overview of the different adhesives tested in the fire tests. Adhesives certified for the use in structural members in Europe as well as in North America were tested. Furthermore, adhesives not-certified for the use in structural applications were tested. The standard test was performed with a 1C PUR adhesive and 140 mm wide specimens. The stress level at the beginning of the fire test was chosen to 10 N/mm 2, which is approximately 30% of the mean tensile strength determined at normal temperature (see chapter 3). This stress level is typical for the design at normal temperature according to EN (2005) and for the fire design according to EN (2004). The standard specimen consisted of one testing lamella, which was protected on the top and bottom sides by a so-called protective lamella. This was done in order to expose the specimen to fire only on two sides. The standard test was performed using the standard fire-curve according to EN (2012a) and a constant tensile load parallel to the grain. Tab. 1.1: Overview of different adhesives tested in fire tests. Adhesive in finger joint No. of adhesives No. of fire tests One-component polyurethane 1 C PUR 5 (4) a 30 b Melamine-urea-formaldehyde resin MUF 3 (2) a 6 Phenol-resorcinol-formaldehyde resin PRF 1 (1) a 2 Emulsion-polymer-isocyanate EPI 1 (1) a 2 Urea-formaldehyde resin UF 1 2 Poly(vinyl acetate) PVAc 1 3 Unjointed (solid wood) (8) a 49 a In brackets: Number of adhesives certified for the use in structural members. b Including two unloaded fire tests (temperature measurements).

20 1.2. Experimental overview 3 Table 1.2 shows the configuration of a standard test. In order to test the finger-jointed region of the lamella, in most tests insulation material (stonewool) of 50 mm thickness was placed on both sides of the specimen (the assembly is shown later in chapter 2, Fig. 2.4). By placing the insulation material, the effective and direct fire exposed area could be reduced to a length of approximately 200 mm. Tab. 1.2: Configuration of the standard test. Parameter Configuration Adhesive 1C PUR (P2) Width of lamella 140 mm Stress level at start ca. 10 N/mm 2 (corresponds to ca. 0.3 F u,20 C) Fire exposure 2-sided (testing lamella protected on its top and bottom side) Test type Constant load until failure of the lamella The adhesives type and abbreviations in both fire test series are shown in Table 1.3. The table also gives an overview of the standards to which the adhesives are certified to. It should be noted that the studied adhesives fulfil at least the A7 test at 70 C according to EN (2013a). Tab. 1.3: Adhesives tested in both series of fire tests. Type Adhesive Remarks 1st series 2nd series MUF M1 - certified according to pren 301 (2013c) 1C PUR P4 - certified according to EN (2008) 1C PUR P2 1 P2 certified according to EN (2008) 1C PUR - 2 P3 certified according to ASTM D 7247 (2007) 1C PUR - 3 P7 c not-certified, used in furniture industry EPI - 4 EPI certified according to pren (2013b) PRF a - 5 PRF certified according to pren 301 (2013c) PVAc b - 6 PVAc c not-certified, used in furniture industry MUF - 7 M2 certified according to pren 301 (2013c) UF - 8 UF c certified according to pren 301 (2013c), type 2 1C PUR - 9 P6 certified according to EN (2008) MUF - 10 M3 c not-certified a System Aerodux 185 b Approved according to EN 204 (2001) D3 quality, Watt 91, EN (2006) c Not certified adhesives for the use in structural timber elements

21 4 Chapter 1. Introduction 1.3 Organisation of this report In chapter 2 of this report, a detailed description of the fire tests including the results of the tests is presented. Chapter 3 describes the reference tests performed at normal temperature. The appendix of this report shows further information about the performance of the finger-jointed region (appendix A), the crack patterns observed in the fire tests as well as in the tests at normal temperature (appendix B) and results from the deformation measurements in the fire tests (appendix C).

22 Chapter 2 Fire tests 2.1 Test specimens and materials The specimens designed for the fire tests should describe the structural behaviour of finger joints in a fire situation relevant for glued-laminated timber beams. At normal temperature, failure of such engineered wood products is usually initiated due to the failure of a finger joint, failure of a knot or other defects of the naturally grown timber. In order to decrease the scatter of the test results, the highest visually graded timber strength (C30) according to EN 338 (2009b) was selected and taken from the production line of glued-laminated timber beams (spruce) in a timber industry company in Switzerland (company Roth in Burgdorf). Additionally, five tests were performed using machined graded timber lamellas (L36 and L40) according to EN (2009a). Lamellas with visually a low number of knot defects were chosen. Further, the ends of the original boards had been cut at preselected areas to ensure that no knots appeared in the finger-jointed region of the lamella. In order to obtain a reference value for the tensile strength, specimens without finger joints were also produced. In the first test series, the finger-jointed specimens glued with adhesive P2 were produced completely by the machine at the company Nussbaumer/ Baar in Switzerland. The bonding with the adhesives P4 and M1 was made in two steps at the company Roth/ Burgdorf. First, the adhesive was manually applied on the fingers using a special brush, see Fig Next, the boards were subsequently connected by a machine with a prescribed pressure. In the second test series, all finger-jointed specimens (except for adhesive P6) were produced by first manually application of the adhesive with the brush and then pressed by the machine. In case of adhesive P6 (specimens 9.1 and 9.3), the specimens were completely produced by the machine [application as shown in Fig. 2.1(c) and pressing] or a brush as seen in Fig. 2.1 was used for the application of the adhesive (specimens 9.4, 9.5 and 9.80). All finger-jointed lamellas were prepared under the strict supervision of the manufacturers of the adhesives.

23 6 Chapter 2. Fire tests (c) Fig. 2.1: Application of the adhesive: Manually with a special brush (see and ) and with the machine (c). In the case of a manual adhesive application, the application was selectively checked. For this purpose, a hand saw was used to cut off the fingers and then checked whether a complete penetration of the adhesive in the fingers was achieved. Fig. 2.2: Check of the manually adhesives application: Cutting the fingers of the joint and inspection of the fingers. Before testing, the lamellas were preconditioned in a climate chamber (20 C/65% RH) to 12±1% moisture content. In both test series, the average density of the test specimens was approximately 450 kg/m 3. The material properties of the test specimens of both timber and adhesives were in accordance to the tests used in Frangi et al. (2012). Also the same geometry of the finger joint was used (see dimension of finger joint in Fig. 3.1). All specimens consisted of a testing board, which was finger-jointed in the middle, and lamellas glued together with this testing board on its top and bottom. These lamellas were added in order to protect the testing board against the fire exposure from its top and bottom during the test. Hereby, a one-dimensional fire exposure from the side was achieved, which makes the evaluation of the results more reliable. In order to specifically determine the fire resistance of the finger joint, the test specimen was mounted with insulation on the side (see Fig. 2.3). This was done in most of the tests with 50 mm thick stonewool from the company Flumroc located in Switzerland placed on both sides of the specimen. The insulation material did not influence the fire exposure in the finger-

24 2.1. Test specimens and materials 7 jointed region. This was confirmed by measuring the same development of the timber surface temperature with and without insulation. The insulation material was mechanically fastened with a thin layer of gypsum and two nails to make sure that it stays in place during the whole fire test. Hence, the effective testing length, which was exposed to fire and loaded in tension, was reduced to about 200 mm with the finger joint in the middle. However, in some tests, the specimen did still not fail in the finger-jointed region but in the unprotected solid wood region next to the insulation. Because of this reason, it was decided during test series 2 to totally protect the specimen on the side except for the 200 mm wide finger-jointed region (see Fig. 2.3(c), lower picture). Table 2.3 and 2.4 show in which tests the insulation was used. (c) Fig. 2.3: Placing the insulation material (thickness t = 50 mm) with gypsum, nails ; Different set-ups of the insulation (c). The assembly of a typical test specimen is shown in Fig. 2.4(c). To ensure that in the finger-jointed region of the testing board no load is carried by the protective lamellas, a special assembly was designed. The protective lamellas on top and bottom of the specimen consist of two pieces (in Fig. 2.4(c) piece 1 and piece 2) in longitudinal direction. Further, the adhesive between the testing board and its protective lamellas was only applied in some regions (see dashed line in Fig. 2.4(c)). No adhesive was applied in the finger-jointed region between the testing board and the protective lamellas. In these two bondlines, a standard one-component polyurethane adhesive was used to ensure that during the fire tests the protective lamellas stayed in place and did not fall off. The protective lamellas themselves were glued to each other with a standard one-component polyurethane adhesive as well. The protective lamellas were manually glued together with the finger-jointed lamella, as seen in Fig. 2.4 and 2.4. Before the protective lamellas were glued, pictures of the finger-jointed region had been taken from both sides of the boards. The pictures are illustrated in appendix A.

25 8 Chapter 2. Fire tests cut piece 1 Protective lamellas 40 piece Testing board Finger-joint in [mm] Adhesive in the bondline between protective lamellas and testing board (c) Fig. 2.4: Manually gluing and pressing process of the protective lamellas as well as the standard assembly and dimensions (mm) of the specimen in the fire tests (c). The specimen was exposed to fire on four sides. The testing boards length was chosen to be about 3.50 m given by the testing frame dimensions. The depth of all lamellas was 40 mm, which is a typical dimension used for lamellas of glulam beams. The lamellas widths varied from 80 to 200 mm. Small sections were selected because they are more influenced by fire exposure. The main part of the tests was performed with 140 mm wide specimens. Among others, the test specimens dimension and assembling was chosen in order to investigate the influence of finger joints itself and especially of different adhesives used in finger joints on the fire resistance. achieve failure at different times of fire exposure in order to investigate the adhesives behaviour for different temperature profiles in the cross-section. investigate the difference of time to failure for timber lamellas with different locations in a glued-laminated timber beam. This was achieved by two configurations of the protective lamellas at the bottom side of the testing board (see Fig. 2.7).

26 2.1. Test specimens and materials 9 find a correlation between tensile tests on finger-jointed timber boards tested at elevated temperatures by Frangi et al. (2012) and these fire tests (this belongs to adhesive P2, P3, P4 and M1). apply a pure tensile load on the testing board. The applied tensile load in the fire tests corresponded to about 30% of the mean ultimate tensile resistance obtained in tests at normal temperature (see chapter 3) and the tests by Frangi et al. (2012). This load level can be typically expected for the design at normal temperature at serviceability limit state according to EN (2005) and for fire design at ultimate limit state according to EN (2004), respectively. Stiffness and strength of both timber and adhesive vary with temperature. EN (2004) gives in annex B effective temperature-dependent strength and stiffness reduction factors for timber. However, no reduction factors for different types of adhesives exist. To analyse the temperature development during the fire test in the cross-section, two fire tests were conducted with specimens containing thermocouples placed along the cross-section width (see Fig. 2.6). With these thermocouples, the temperature was measured in the cross-section at certain points while the specimen was exposed to standard ISO-fire according to ISO 834 (1999). Together with the tensile tests exposed to ISO-fire, it is possible to obtain the temperature-dependent strength in the finger-jointed region. For placing the thermocouples as accurate as possible along the cross-section width, holes (diameter d = 4 mm) were drilled in 45 angle with the help of a prismatic positioning device out of metal. The wires of the thermocouples were placed in small channels milled in the wood in order to protect them from fire exposure. Fig. 2.5 shows the operation of milling and drilling as well as the placing of the thermocouples. (c) Fig. 2.5: : Milling machine to mill the channels for the thermocouples, : Positioning device to drill the holes, (c): Placing the thermocouples. For the fire test series 1, the moisture content and the density of the specimen was determined. The moisture content of the specimens was measured with a typical instrument based on electrical resistance measurements of type COMBO 100 (control accuracy: 0.1%) from the company Kruger + Co. AG. Table 2.1 shows the properties for each specimen.

27 10 Chapter 2. Fire tests Tab. 2.1: Properties of the specimens tested in fire test series 1. Specimen Moisture Density name content ρ [%] [kg/m 3 ] P2.T P2.T P P P P P P P P M M P P P P2.S P2.S V V P P Note: The density refers to the moisture content measured and given in this table.

28 Test specimens and materials Top face: Cut Cut Finger-joint TC 25 TC 35 in [mm] TC 5 TC 15 TC 34 TC 24 TC 4 TC 14 TC 33 TC 23 TC 3 TC 13 TC 32 TC 22 TC 2 TC 12 TC 31 TC 21 TC 1 TC Finger-joint (Picture of top face) Side face: TC TC TC TC Thermocouple with copperdiscs Thermocouple inside testing board Wire Cut Finger-joint (side face specimen) Fig. 2.6: Assembly of the thermocouples in the cross-section of the testing board. For test series 2, the dynamic modulus of elasticity Edyn,US,u was additionally determined by the help of an ultrasonic measurement device. The device sends ultrasonic waves in lengthwise direction through the specimen and measures the duration. The ultrasonic impulse is generated by piezoelectric crystals, which are initiated to vibrate by voltage. For infinite and anisotropic bodies, the differential equation of the elastic movement can be used to determine mechanical vibrations in such bodies (Steiger 1996). Having small lateral dimensions of the specimen in relation to the wavelengths, the lateral contraction can be neglected. Hence, the dynamic modulus of elasticity Edyn,US,u for anisotropic materials can be determined using equation (2.1). 2 Edyn,US,u = ρ veff (2.1) where Edyn,US,u u ρ veff is is is is the the the the dynamic modulus of elasticity based on ultrasonic measurements measured moisture content of the lamella density of the lamella measured effective wave velocity To calculate the modulus of elasticity for a specimens moisture content of 12%, equation 2.2 can be used according to pren 384 (2013d). Edyn,US,u=12% = Edyn,US,u ( (u 12)) (2.2)

29 12 Chapter 2. Fire tests The ultrasonic measurements were performed with a CBS-CBT/Silvatest-Duo device. This device was especially developed to determine stiffness properties of wood. The modulus of elasticity was determined only for the specimens tested in the fire test series 2. The results are shown in Table 2.2. Further information about the concept to measure the modulus of elasticity can be taken from Görlacher (1984, 1990).

30 2.1. Test specimens and materials 13 Tab. 2.2: Properties of the specimens tested in fire test series 2. Specimen Moisture Density MOE name content ρ v eff E dyn,us,u E dyn,us,u=12% [%] [kg/m 3 ] [m/s] [N/mm 2 ] V V Note: The density refers to the moisture content measured and given in this table.

31 14 Chapter 2. Fire tests 2.2 Test program and test parameters In the fire tests, the influence of adhesive used in the finger joint, the width of the cross-section, the loading level and the type of fire exposure on the fire resistance of a single finger-jointed timber lamella were investigated. In the following paragraphs, the different parameters and their variations are described. Commercially available adhesives from different producers in Europe were studied with regard to their thermal stability. Adhesives used in structural timber members in Europe must fulfil the requirements according to EN 301 (2013c), EN (2008) and pren (2013b). Different adhesive systems that fulfil current approval criteria according to these standards were tested as follows (given is the full name and the abbreviation in the present study): Emulsion-polymer-isocyanate (EPI): EPI One-component polyurethane (1C PUR): P2, P3, P4, P6 Melamine-urea-formaldehyde resin (MUF): M1, M2 Phenol-resorcinol-formaldehyde resin (PRF): PRF These adhesives fulfil at least the requirements at a maximum temperature of 70 C according to EN (2013a). In addition to the certified adhesives for use in structural components, non-certified adhesives were tested: Urea-formaldehyde resin (UF): UF Melamine-urea-formaldehyde resin (MUF): M3 Poly(vinyl acetate) (PVAc): PVAc One-component polyurethane (1C PUR): P7 In the first test series, two different one-component polyurethane (1C PUR) adhesives (Notation: P2 and P4) and one melamine-urea-formaldehyde adhesive (M1) were studied. The other adhesives mentioned above were studied in test series 2. The adhesives are named in accordance to the work by Frangi et al. (2012). An overview of the adhesives and their certification is shown in Table 1.3. The testing board as well as the protective lamellas had in all tests a depth of 40 mm. The tested standard specimen consisted of 140 mm wide lamellas and had a total depth of 280 mm including the depth of one testing board and six protective lamellas (see Fig. 2.7). In addition, specimens with a width of 80 mm and a depth of 200 mm (including one testing board and four protective lamellas) and specimens with a width of 200 mm and a depth of 360 mm (including one testing board and eight protective lamellas) were tested. The most common way of evaluating the strength of finger joints is probably through the flatwise bending of finger-jointed laminations, as in practice a bending test is much easier to perform than a tensile test (i.e. due to an easier load application). However, since in a glulam

32 2.2. Test program and test parameters 15 One-dimensional fire exposure on the finger-jointed lamella Two-dimensional exposure Key: Testing lamella Protective lamellas Fig. 2.7: Assembly of the different specimens tested in the fire tests. beam the beam depth is much greater than the thickness of the single laminations, the outer lamination is subjected to almost pure tension or pure compression. Thus, in most fire tests of the present study a constant tensile stress parallel to the grain direction was applied with a value of 10 N/mm 2. This is about 30% of the mean load-bearing capacity F u of tensile tests performed at normal temperature. The applied load level throughout the whole test can be taken from Fig. 2.8, number 1. Further, tests were performed with 20% and 45% of the average determined load-bearing capacity at normal temperature to study the influence of the applied load level (see Fig. 2.8, number 2 and 3). In addition, the residual load-bearing capacity of a specimen after 30 min of fire exposure initially loaded with 0.3 F u was determined in one test by increasing the load (see Fig. 2.8, number 4). The failure load F i determined in this test was then applied to a specimen in another test as the starting load (see Fig. 2.8, number 5). F i Load level F u 0.3 F u 0.2 F u Start fire test 30 Time [min] F u : Mean value of tensile strength at normal temperature Fig. 2.8: Load level during five different fire tests performed.

33 16 Chapter 2. Fire tests The total depth of the protective lamellas was chosen so that within the testing time a onedimensional heat flux could take place with the specimen exposed to fire from two sides. In addition, two tests were performed with testing boards that had the same protection on top but only one 40 mm thick lamella at the bottom (see Fig. 2.7). This assembly leads to a twodimensional heat exposure on the finger joint (from three sides). With these tests, the failure mechanism of a glulam beam was simulated, in which failure in the second bottom lamella causes failure of the whole beam. The test specimen glued with adhesive P2 in the finger joints and a width of 140 mm and 3 x 40 mm protective lamellas was defined as the standard specimen. This standard specimen was subjected to a constant loading of 30% of the load bearing-capacity at normal temperature and then exposed to ISO-fire until failure occurred (standard test). The parameters described above were varied in the other tests with respect to the standard test. Table 2.3 and Table 2.4 give an overview of the 49 fire tests performed in the experimental program of test series 1 and series 2, respectively. In addition, the tables show in which tests insulation was applied on the specimens side.

34 2.2. Test program and test parameters 17 Tab. 2.3: Overview of test program of fire tests - series 1. Specimen Type Width Applied name adhesive [mm] load b Insulation Parameters tested P2.T1 P P2.T2 P P2.1 P F u - P2.2 P F u X P2.8 P F u X P2.10 P F u - P4.1 P F u X P4.2 P F u - P4.3 P F u X M1.1 M F u X M1.2 M F u X P2.80 P F u X P2.200 P F u X Temperature measured Standard test (1) a Adhesive P4 Adhesive M1 Width P2.4 P F u X Load level (2) a P2.6 P F u X Load level (3) a Determination residual P2.7 P F u X strength after 30 min P2.3 P F u X P2.S1 P F u X P2.S2 P F u X fire exposure (4) a P2.7-failure load applied (5) a Two-dimensional heat exposure V F u - Solid wood V F u X a Load level according to Fig b Load level at start of the fire test (see Fig. 2.8). Solid wood, determination residual strength after 40 min fire exposure

35 18 Chapter 2. Fire tests Tab. 2.4: Overview of test program of fire tests - series 2. Specimen Type Width Applied Insulation Strain gauge Parameters tested name adhesive [mm] load b 1.2 P F u X compare manual and machine application 1.3 c P F u X - Timber strength grade L P F u X X 2.3 P F u X P F u X P F u X EPI F u X EPI F u X PRF F u X X 5.2 PRF F u X PVAc F u X X certified a, PUR non-certified a, PUR certified a, EPI certified a, PRF 6.2 PVAc F u X - non-certified a, PVAc 6.3 PVAc F u X M F u X M F u X UF F u X UF F u X P F u X P F u X c P F u X c P F u X M F u X X 10.2 M F u X - certified a, MUF non-certified a, UF certified a, PUR non-certified a, MUF V F u X - Solid wood V F u X - Solid wood 2.80 P F u X - Width, adhesive P c P F u X - Width, adhesive P d P F u X - Width, adhesive P2 a Certified according to current European standards (see Table 1.3). b This is the load level at start of the fire test (see Fig. 2.8). c Timber strength grade L40. d Timber strength grade L36.

36 2.3. Test set-up Test set-up All fire tests were performed at the Swiss Federal Laboratories for Materials Science and Technology (Empa) in Dubendorf. The tests were carried out on the small horizontal furnace with inner dimensions of 1.0 m x 0.8 m. A special testing frame was developed to apply a defined tensile load and placed around the furnace. A cover closed the furnace at its top (see Fig. 2.9). The loading of the specimens in the standard fire tests was in accordance to EN (2012a). The testing frame placed on top of the furnace consisted of steel profiles type HEB 300. In the first fire test series, the whole frame had dimensions of 3320 mm x 1660 mm. In the second series of fire test, the frame was slightly modified in order to decrease the self-weight. However, the basic concept of load application was in both test series the same. Key: 1 Horizontal furnace 2 Test frame 3 Test specimen 4 Cover 5 Hydraulic cylinder Fig. 2.9: Test set-up for the fire tests. Details of the tensile testing machine are shown in Fig and given in Table 2.5. The dimensions of the whole set-up are given in Fig to Fig

37 20 Chapter 2. Fire tests Tab. 2.5: Information about the tensile testing machine. Cylinder to apply a clamping force (see no. 1 in Fig. 2.10) Company ENERPAC Type Hollow piston cylinder Model number RCH-202 Number of piston 2 x 2 Max force [kn] 215 Stroke length [mm] 49 Effective piston area [cm 2 ] 30.7 Oil volume [cm 3 ] 150 Cylinder to apply a tensile load (see no. 2 in Fig. 2.10) Company ENERPAC Type Short stroke cylinder Model number RCS-502 Number of pistons 2 Max force [kn] 435 Stroke length [mm] 60 Effective piston area [cm 2 ] 62.1 Oil volume [cm 3 ] 373 LVDT (see no. 3 in Fig. 2.10) Company RDP Electronics Type LVDT Model description LDC 1000C Measurement range [mm] ±25.0 Accuracy of measurement [mm] ±0.025 Load cell (see no. 4 in Fig. 2.10) Company ERPATEC AG Type Interface Model description 1221 LS Max force [kn] 250 Accuracy of measurement ±0.5%

38 Test set-up Left side Right side Key: Hollow piston cylinder Short stroke cylinder LVDT 4 5 Load cell Additional steel plates Fig. 2.10: Details of tensile testing machine Insulation (different layers) 40 Cement based plate Screw-on bracket Opening Insulation Area on fire 800 Fig. 2.11: Transversal section of the test set-up (dimensions given in (mm)). 300 HEB Test specimen HEB 300

39 22 Chapter 2. Fire tests Cement based plate Screw-on bracket Insulation (different layers) 280 Test specimen Insulation Area on fire Finger joint Fig. 2.12: Longitudinal section of the test set-up (dimensions given in (mm)).

40 2.3. Test set-up HEB HEB Test specimen HEB steel plates (each 30mm depth) x M24 HEB Stiffener 15mm Fig. 2.13: Dimensions of the tensile testing frame (dimensions given in (mm)). 23

41 24 Chapter 2. Fire tests During both fire test series, the cover was continously modified and the assembly had to be improved with regard to the fire resistance. However, this process had no influence on the results of the fire tests. The final set-up, which can also be found to be the optimal set-up of the cover, is depicted in Fig The cover had a structural clearance of 1000 x 800 x 537 mm3. The cover consisted of a cement-based particle board with a thickness of 28 mm by the company CETRIS, CZ according to EN (2007). In the direction to the fire room, first, a 50 mm depth stonewool was glued with a thin gypsum layer on the cement-based board. This stonewool was inspected very thoroughly after each fire test and was replaced if it was found to be not sufficient in terms of protection anymore. The stonewool was protected by a layer of fire protection plates (Promatecht H, depth t = 20 mm) from the company Promat located in Switzerland and, in addition, by 25 mm depth ceramic plates Superwool 607 HT provided by the company Morgan ThermalCeramics from England. All plates were attached to the cement-based boards with the help of pre-drilled bolts. The cement-based boards were connected to each other with anchors and screws Key: 1 Ceramic based plate 2 Promatect H-plate 3 Stonewool 4 Cement based particle board Fig. 2.14: Assembly of the cover found to be most preferable. During the fire tests, the applied load and the deformation of the test specimens were measured. Thereby, the deformation was measured both by adding LVDTs on the specimen itself outside the furnace and by recording the deformation of the jacks. The distance between the LVDTs before loading was about 1320 mm (see Fig. 2.15). The LVDTs were from type D5/300AG with a range of ±5 mm and from the company Precisor Messtechnik in Munich/ Germany. Further, in two tests the temperature at selected locations in the timber cross-section was recorded with thermocouples of chromel-alumel, type K (both welded thermocouples and thermocouples with cooper discs were used). The thermocouples came from the company R. Wick AG located in Cham/ Switzerland. Temperature and pressure in the furnace were also measured. The pressure in the furnace has no significant impact on the fire load-bearing performance of the specimen and was set to a value of -10 Pa. With this negative pressure, smoke emissions can be limited (i.e. at the openings of the cover). The furnace temperature was regulated with six stationary NiCrNi sheathed thermocouples according to the ISO-curve (ISO 834, 1999) through an automated computer system. The arrangement of the six stationary thermocouples in the furnace is shown in Fig

42 Test set-up 1320mm Cover LVDT LVDT Testing board Finger joint Fig. 2.15: Assembly of the LVDTs on the testing board outside the furnace. T41 T42 T43 T44 T45 T46 Burner 800mm 1000mm Fig. 2.16: Assembly of the six stationary thermocouples in the furnace.

43 26 Chapter 2. Fire tests Fig. 2.17: View of the specimen at the opening of the cover in : a test with temperature measurement; : a test with loading. In Fig. 2.17, the opening of the cover can be seen for a test with temperature measurements in the specimen: 2.17 as previously described and for a test with loading In series 2 of the fire tests, strain gauges were placed on the surface of the specimen close to the finger joint in four tests. The bonding procedure is shown in Fig Strain gauges from type PFL LT with a gauge length of 10 mm from the company Tokyo Sokki Kenkyujo Co., Ltd from Japan were used. The strain gauges were bonded on the timber surface using a SICOMET 50 adhesive, which is a fast curing instant adhesive based on Ethyl-2-cyanoacrylate with a low viscosity. Before bonding, the timber surface was first preconditioned with sand paper and alcohol-based liquid. After bonding, small weights on top of the gauges ensured that the strain gauge kept in place while hardening of the adhesive. The position of the strain gauges can be taken from Fig The strain gauge was glued at about 6 cm distance from the finger joint on the timber surface of the testing lamella. The Information strain gauges Information glue Preparation of the surface using sandpaper Cleaning of surface Bonding of strain gauges Fig. 2.18: Bonding of the strain gauges on the timber surface next to the finger joint in four fire tests of series 2.

44 2.3. Test set-up 27 distance from the edge of the specimen was also about 6 cm. The strain gauge was glued in the direction parallel to the grain orientation. Each testing board was equipped with two strain gauges, one gauge on each side opposite to each other in the same plane. In addition to the strain gauges glued on the testing lamella, strain gauges were also glued on both protective lamellas. These strain gauges were unloaded during the fire test and, therefore, only influenced by heat. The protective lamellas protected the strain gauges during the tests from direct fire exposure. The temperature was measured next to the strain gauge by a thermocouple. Thus, the timber strain can be determined depending upon the temperature. With the help of the unloaded strain gauge placed on the protective lamellas, it was possible to obtain a corrected strain taking the difference of the strain measured on the loaded testing lamella and the strain determined on the unloaded protective lamellas. Both strain gauges should be influenced by the same temperature. (c) Fig. 2.19: Position of the strain gauges on the testing lamella in four fire tests of series 2. (c) Fig. 2.20: Strain gauges and thermocouple on the protective lamellas. The set-up was suitable for the purpose to investigate the fire behaviour of finger-jointed timber boards. Fig shows the whole process of performing one fire test. First, the testing frame had to be partly disassembled in order to put the specimen in the testing frame. Next, the LVDTs were installed to measure the deformation of the specimen as shown in Fig and After that, the cover was placed to close the furnace and the fire test was started. After

45 28 Chapter 2. Fire tests failure when the load could not held constant anymore, the cover was removed from the furnace and the testing lamella was cut on both sides in order to take the specimen out of the hall with the help of the crane. Last, the burning specimen was extinguished with water. This procedure usually took less than two minutes. Finally, the failure mode was checked. (c) (d) (e) (f) Fig. 2.21: Process of performing one fire test: : Disassembling of the testing frame, : Putting the specimen in the testing frame, placing all LVDTs and closing the furnace with the cover, (c): After failure, remove the cover from the furnace, (d): Cut the testing lamella, (e): Take the specimen out of the hall with the help of the crane, (f): Extinguish the specimen with water and check the failure mode.

46 2.4. Test results Test results Table 2.6 and 2.7 gives an overview of the results of the fire tests. In addition to the onedimensional charring rate measured by hand after the test, the time of fire resistance is summarised for each fire test. The fire resistance is the time from start of the fire test until the applied load could not held constant anymore. In the following sections, the results are presented and the influence of the different parameters studied is described in detail. Tab. 2.6: Overview of results of the fire tests - series 1. Specimen Width Applied Failure Load at One-dim. Type of Fire name load load failure charring rate failure a resistance [mm] [-] [-] [kn] [mm/min] [min] P2.T P2.T P F u Along fingers 47.0 P F u Along fingers 53.0 P F u Along fingers 52.5 P F u Mixed-type 52.0 P F u Mixed-type 48.0 P F u Solid wood 48.0 P F u Of fingers 41.0 M F u Solid wood 45.0 M F u Along fingers 58.0 P F u Along fingers 24.5 P F u Along fingers 66.5 P F u Along fingers 59.5 P F u Along fingers 35.5 P F u 0.6 F u Of fingers 31.5 P F u Mixed-type 16.5 P2.S F u Along fingers 36.0 P2.S F u Along fingers 42.0 V F u 56.5 n/a V F u 0.63 F u a Failure type according to Fig. 2.28

47 30 Chapter 2. Fire tests Tab. 2.7: Overview of results of the fire tests - series 2. Specimen Type Width Load at One-dim. Type of Fire name adhesive failure charring rate failure a resistance [mm] [kn] [mm/min] [min] 1.2 P Along fingers P Along fingers P Along fingers P Along fingers P Along fingers P Along fingers P Along fingers P Along fingers EPI Along fingers EPI Along fingers PRF Solid Wood PRF Of fingers PVAc Along fingers PVAc Along fingers PVAc Along fingers M Mixed-type M Of fingers UF Along fingers UF Along fingers P Along fingers P Along fingers P Along fingers P Of fingers P Along fingers M Along fingers M Along fingers 57.0 V V Note: The load level was kept constant in all tests at 0.3 F u. a Failure type according to Fig. 2.28

48 2.4. Test results Charring rate and temperatures The specimens in the tests P2.T1 and P2.T2 (according to Table 2.3) were equipped with thermocouples along the width of the cross-section in the finger-jointed region. The temperature was measured in the lamination in three cross-sections at different depths (top surface and middepth) and distances from the surface exposed to fire (30 mm, 50 mm, and 70 mm corresponding to mid-width) - see Fig Fig shows the temperature development measured by the thermocouples at the fingerjointed region. It is remarkable that the temperature in 50 mm distance from the edge reached 100 C in both tests after approximately 50 min of fire exposure. In the middle of the cross-section (TC 3 and TC 13), temperatures greater than 100 C were reached after 60 min of fire exposure. The comparatively low temperatures in the cross-section result from the char-layer which is formed on the fire-exposed surfaces. The char-layer grows in thickness as the fire progresses and reduces the cross-sectional dimensions of the timber member. The char-layer protects the remaining unburned residual cross-section against heat. The protection by the char-layer and especially the relatively low conductivity of timber lead to a steep temperature gradient in the cross-section with comparatively low temperatures in the inner cross-section. In Table 2.6 and 2.7 the charring rate for all tests with two sides of fire exposure is summarised. The charring rate measured by hand ranges from 0.59 mm/min to 0.8 mm/min. The mean charring rate of all fire tests was calculated to 0.70 mm/min. This value is slightly larger than the one-dimensional charring rate β 0 of 0.65 mm/min given in EN (2004) Deformations Fig shows the deformation measured in selective tests of the part of the testing board, which was exposed to fire. The assembly of the LVDTs is shown in Fig The start of the curves coincides with the start of the fire test. In Fig. 2.23, the comparison of tests with the same adhesive (P2) for different widths of the cross-section is shown, whereas Fig shows the comparison with the same width of the cross-section (140 mm) and different types of adhesive tested in series 1. As revealed by both diagrams, with increasing time of fire exposure the deformation rises due to the decreasing stiffness of the specimen with increasing temperature in the cross-section. It can be seen that no significant difference in the stiffness was observed depending on the adhesive in the finger joint. However, the deformation of the specimen (with adhesive M1) which failed after 58 minutes tends to increase slower in comparison with the other deformations of specimens with a width of 140 mm. Further, the deformation of the 200 mm wide specimen P2.200 increased much slower than others. For this specimen, the deformation at failure was lower and almost no increase of the slope before failure could be observed as in all other fire tests. The deformations measured in the fire tests of series 1 and 2 are given in detail in appendix C. It has to be noted that the measurement of the deformation was not recorded in all fire tests.

49 32 Chapter 2. Fire tests Temperature [ C] TC 1 TC TC 2 TC 4 TC Furnace TC 11 TC TC 12 TC TC Distance to fire exposed edge: 30mm Distance from fire exposed edge: 30mm x x mm 50mm mm mm 70mm Time [min] Temperature [ C] TC 11 TC TC 12 TC TC 13 TC 1 TC TC 2 TC 4 TC Furnace Distance to fire exposed edge: 30mm Time [min] Test P2.T Distance from fire exposed edge: 30mm 400 x x mm mm mm 0 40 Temperature [ C] Test P2.T Test P2.T Temperature [ C] Test P2.T (c) Time [min] 50mm mm Time [min] (d) Fig. 2.22: Temperature versus time of fire exposure measured in the tests P2.T1 ( and ) and P2.T2 ((c) and (d)); location of the thermocouples TC can be taken from Fig. 2.6.

50 2.4. Test results 33 Deformation [mm] 4 3 Cross-section width: Deformation [mm] 4 3 Adhesive: P2 P4 M Time [min] Time [min] Fig. 2.23: Deformation as a function of the time of fire exposure; : Comparison of tests with the same adhesive (P2) and different width of the cross-section, : Comparison with the same width of the cross-section (140 mm) and different types of adhesive Strain measures In four tests of the fire test series 2, strain gauges were glued on the timber surface on both sides of the specimen in the same plain. The assembly of the strain gauges is described in section 2.3. In addition to the strain, the temperature in the same plain was measured. The results of the measurements are shown in Fig to With this data, it could be possible to determine the temperature-dependent stiffness. Further, the local stiffness measured with the strain gauges can be compared with the global stiffness obtained by means of ultrasonic measurements.

51 34 Chapter 2. Fire tests Strain [-] Temperature [ C] Specimen Strain top - loaded Strain top - unloaded Strain bottom - loaded Strain bottom - unloaded Temperature (bottom) 2 40 Temperature (top) Time [min] Fig. 2.24: Strain and Temperature over time for specimen 2.2 Strain [-] Temperature [ C] Specimen Strain top - loaded Strain top - unloaded Strain bottom - loaded Strain bottom - unloaded Temperature (bottom) Temperature (top) Fig. 2.25: Strain and Temperature over time for specimen Time [min]

52 Test results Strain [-] Temperature [ C] Specimen Strain top - loaded Strain top - unloaded Strain bottom - loaded Strain bottom - unloaded Temperature (bottom) 1 20 Temperature (top) Time [min] Fig. 2.26: Strain and Temperature over time for specimen 6.1 Strain [-] Temperature [ C] Specimen Strain top - loaded Strain top - unloaded Strain bottom - loaded Strain bottom - unloaded Temperature (bottom) 2 Temperature (top) Fig. 2.27: Strain and Temperature over time for specimen Time [min]

53 36 Chapter 2. Fire tests Fire resistance and failure type The fire resistance was dependent on the type of failure. basically observed in the fire tests: Four different failure types were Failure in the finger joint along the fingers (Fig. 2.28) Failure in the finger joint of the fingers (Fig. 2.28) Mixed-type failure (Fig. 2.28(c)) Failure in solid wood region (Fig. 2.28(d)) (c) (d) Fig. 2.28: Failure types observed during the tensile tests: : Failure in the finger joint along the fingers, : Failure in the finger joint of the fingers, (c): Mixed-type failure, (d): Failure in solid wood region (here: due to a knot defect). In case of a mixed-type failure, it was not possible to determine the cause of the failure during the fire tests. The specimen assembly was chosen to investigate failure in the finger joint, which did occur in most of the tests. For this type of failure, it was further distinguished between failure along the fingers and failure of the fingers due to exceeding the tensile strength of the wood fibres. A typical observed crack pattern in the fire tests is shown in Fig In the comparable cold inner part of the region, failure of the fingers due to exceeding the tensile strength of the wood fibres occurred. In the outer and warmer region, failure along the fingers was observed. In the inner part, the temperature is also after one hour of fire exposure still below 100 C, see Fig In this region of the cross-section, the adhesive has still sufficient strength and the timber tensile strength governs the load-carrying capacity. Fig shows the fire resistance as a function of the cross-section width depending on the failure types for test series 1. In addition, the adhesive (P2, P4 and M1) in the finger joint is given. The fire resistance varied in series 1 between about 40 min and 60 min of fire exposure for the specimens with a width of 140 mm. The specimens illustrated in Fig were loaded with a constant tensile load parallel to the grain direction of 0.3 F u. For adhesive M1, in one test failure in the finger joint along the fingers was observed after 58 min of fire exposure. In the second test performed with adhesive M1, failure occurred after 45 min in the solid wood region because of a knot defect. The comparison of these two test results shows that the timber strength has clearly an influence on the fire resistance of finger-jointed timber boards. Weak

54 Test results Temperature [ C] 1000 Measurement Simulation (FEM) MIN 60 MIN x Failure of fingers ( cold inner part) x mm Cross-section width [mm] Failure along fingers ( warm outer part) Failure along fingers ( warm outer part) Fig. 2.29: : Temperature profile after 30 and 60 minutes of one-dimensional fire exposure (Measurement and Simulation), : Typical crack pattern with timber failure in the middle of the cross-section and failure along the fingers in the highly heat influenced outer region of the cross-section. sections in the solid wood region such as knots might lead to failure of the board before the finger joint reaches its maximum fire resistance. However, in order to judge the fire resistance of the finger joint with different types of adhesive, also the tests in which failure occurred in the solid wood region should be considered. In fact, in these tests the finger joint reached at least the fire resistance of the solid wood region. Further, in the tests with adhesive P4 no pure failure in the finger joint along the fingers was observed. Whereas in the test with specimen P4.2 a knot in the solid wood region caused failure, in the other two tests with adhesive P4 failure in the finger joint (failure of the fingers) with a large amount of failure of the wood fibres and a mixed-type failure were observed. The crack pattern of each specimen tested is shown in appendix B. In the tests on 140 mm wide specimens glued with adhesive P2 in series 1, one mixed-type failure occurred and three times failure in the finger joint along the fingers was observed. It is remarkable to note, that these four tests reached a fire resistance very similar to each other in a five minutes time frame. In series 2 of the fire tests, two tests with adhesive P2 were performed (see Fig. 2.30). The adhesive of specimen 1.2 was manually applied with a brush (as described in section 2.1) whereas the specimens glued with adhesive P2 in series 1 were completely produced by the machine (application of adhesive and pressing). However, it is very important to note that this specimen glued with adhesive P2 using the brush also reached similar fire resistance as the specimens of series 1 with the same adhesive. Hence, with the manually application of the adhesive finger joints with sufficient strength were produced.

55 38 Chapter 2. Fire tests This fact can also be concluded on the basis of the tests at normal temperature as described in chapter 3. Cross-section width [mm] Serie 1, Load level: 0.3 F u Cross-section width [mm] Serie 2, Load level: 0.3 F u 200 Failure in finger joint: Failure along fingers Failure of fingers Mixed type failure Failure in solid wood region P2 200 PUR (P2) PUR (P3) PUR (P6) EPI PRF MUF (M2) Non-structural adhesives PUR (P7) PVAc UF MUF (M3) Solid wood (V) 140 P4 P4 P2 P4 M1 P2 P2 P2 M1 140 b c d b d d 140mm 80 P2 80 a) Failure along fingers (all tests without further explanation) b) Failure of fingers c) Mixed type failure d) Failure in solid wood region 80mm Fire resistance [min] Fire resistance [min] Fig. 2.30: Fire resistance as a function of the cross-section width depending of the failure type (see Fig. 2.28) for fire test series 1 and series 2. The specimens were loaded with a constant tensile load parallel to the grain direction of 0.3 F u. In Fig. 2.30, the fire resistance as a function of the cross-section width depending on the adhesive is shown for test series 2. In addition, the failure types observed in the tests are given. In most of the tests, failure along the fingers was observed in the tests with finger-jointed specimens. In those tests, either a failure along the fingers was observed for the whole crack pattern or a failure type as shown in Fig was observed with failure of the fingers in the cold inner part of the cross-section. In both test series, two tests were performed with 200 mm wide specimens and finger joints glued with adhesive P2. The fire resistance in both tests was considerable different. Specimen (series 2) reached a fire resistance of 86.5 min, whereas specimen P2.200 (series 1) reached a fire resistance of only 66.5 min. The fire resistance of specimen P2.200 is only 16.5 min more than the mean fire resistance of 140 mm wide specimens. One possible reason for this small increase of fire resistance might be the size effect appearing in brittle timber members subjected to tension. However, additional reference tests at normal temperature showed indeed sufficient strength, but a noticeable amount of failure along the fingers was observed, which could be explained by problems during the production. The fire resistance of specimen was in the expected range. Based on these observations, it can be concluded that if failure in the finger joint was observed along the fingers, the specimens usually had a greater fire resistance than when failure of the fingers (wood fibres) occurred. Hence, the influence of the finger joint on the load-bearing

56 Test results capacity may depend on the timber strength. It is expected that for lower graded timber classes the finger joint glued with the studied adhesives has little influence on the load-bearing capacity in fire. This is because for lower graded timber, failure in the solid wood region can be expected to occur more often than in high graded timber due to defects (knots, deviation of the grain, etc.). As previously already mentioned, the specimens were partly protected on their sides during the fire test to cause failure in the finger-jointed region. Although the rest of the specimen was almost fully covered with insulation, failure occurred for some tests also in the non-protected area left and right hand side of the insulation and not in the finger-jointed region. Such failure was obtained for specimen 5.1, which was glued with PRF. Fig shows the residual cross-section measured by hand for different sections along the specimens length. It can be seen that the residual cross-section is slightly different along the length; the charring-rate after 56.5 minutes was not the same for the different sections exposed to fire. In the finger-jointed region, the residual cross-section width was about 56 mm. However, failure occurred in the solid wood region with a residual cross-section of about 67 mm. Failure 67mm 56mm Finger joint 75mm Fig. 2.31: Residual cross-section of specimen 5.1 at different locations along the specimens length. To investigate the difference of the fire resistance for timber lamellas with different locations in a glued-laminated timber beam, two tests were performed with only one lamella glued on the bottom of the testing board in test series 1. This assembly leads to an influence of fire exposure on the testing boards from three sides. Fig shows the specimen before the fire test. The tests (P2.S1 and P2.S2 according to Tab. 2.6) reached a fire resistance of 36 and 42 minutes, respectively. The lower fire resistance in test P2.S1 may be due to the fact that during the fire test the protective lamella glued on the bottom separated some millimetres from the testing board leading to an increased fire exposure of the testing board. The separation was possible since in the finger-jointed region no adhesive was used in the bondlines between the testing board and the protective lamella (see Fig. 2.4). No separation was observed in the second test. In comparison to the standard tests, in which heat influence to the finger joint was achieved only from two sides, the fire resistance was about 10 to 15 minutes lower. Fig shows a failure pattern of a finger joint exposed to heat/fire on three sides, where the bottom side was initially protected by a 40 mm thick timber lamella. It is important to note that the bottom lamella was not totally converted into charcoal when failure of the finger

57 40 Chapter 2. Fire tests failure along the fingers wood failure Fig. 2.32: : Test specimen (P2.S2) with finger joint (1), testing board (2), protective lamellas (3) before the fire test equipped with insulation material (4) on its side; : finger joint of test P2.S2 after the fire test, which was influenced by heat/fire from three sides. joint occurred so that the bottom of the testing board was partly not directly exposed to fire. However, an influence of heat can clearly be observed. It can be seen from the failure pattern (Fig. 2.32) that in the inner region of the lamella with comparatively low temperatures, failure of timber fibres occurred (indicated by wood failure). Failure along the fingers mostly occurred closer to the fire exposed sides, where higher temperatures were observed. This is in accordance to tests at elevated temperatures by Frangi et al. (2012), in which very often failure along the fingers occurred at high temperatures.

58 Chapter 3 Tests at normal temperature 3.1 Test specimen and material For the fire test series 1, tensile tests were performed at normal temperature with specimens glued with adhesive P2, P4 and M1. The results of the tests can be taken from a previous investigation by Frangi et al. (2012). However, additional tests were performed with specimens glued within the test series 1 and tested at normal temperature with the same procedure as in the previous investigation. Also tests at normal temperature with specimens from test series 2 were performed in the same way. In order to obtain failure in the finger-jointed region, the cross-section was reduced in this region. Fig. 3.1 shows the dimensions of the specimen tested at normal temperature Finger joint detail: 90 Ø [mm] Fig. 3.1: Specimen dimension for tests at normal temperature. 3.2 Test set-up In some tests at normal temperature, the local deformation in the finger-jointed region was measured by means of an optical camera. During the test, the LEDs glued on the timber surface send light impulses with a defined frequency (5 Hz). The relative displacement of the LEDs was recorded with the optical camera. Fig. 3.2 shows the set-up used for the tests at normal temperature with the optical camera and the tensile testing machine (SCHENCK). Table 3.1 gives the information about the tensile testing machine and the cylinders to apply the support pressure.

59 42 Chapter 3. Tests at normal temperature Key: Optical camera Specimen with LEDs Hollow piston cylinders Universal testing machine (SCHENCK) Fig. 3.2: Set-up of the tests at normal temperature using an universal testing machine (SCHENCK) and an optical camera. With the help of the optical camera and the LEDs glued on the timber surface, it is possible to estimate the modulus of elasticity (MOE). Therefore, the strain over the board axis is determined on the basis of the LEDs relative displacement. The assessment of the MOE was made based on a linear regression model of the stress-strain estimates according to EN 408 (2012b); i.e. with strains between 10% and 40% of the maximum tensile capacity. However, EN 408 (2012b) requires R for the determination of the MOE over the length of five times the width. Since in the present study, in particular the stiffness next to the finger joint was of interest, the required length was significantly smaller than according to EN 408 (2012b). 3.3 Test results Table 3.2 and 3.4 show the compilation of the test results for both test series 1 and 2 conducted at normal temperature. More information on the tensile strength at normal temperature for test series 1 can be taken from Frangi et al. (2012). The moisture content of the specimens were measured with a typical instrument based on electrical resistance measurements of typ COMBO 100 (control accuracy: 0.1%) from the company Kruger + Co. AG. It is important to note that for the 200 mm wide specimens P2.200 of test series 1, a sufficient tensile strength at normal temperature was reached. However, a considerable amount of failure along the fingers occurred, especially in comparison to the tests with 140 mm wide specimens (see appendix B). Given the fact that the 200 mm wide specimen P2.200 reached a lower fire resistance in the fire test than expected, it cannot be excluded that something went wrong during the production of the 200 mm wide specimens of this batch. For these specimens, the adhesive was applied with the machine and thus no reliable explanation is possible to give.

60 3.3. Test results 43 Tab. 3.1: Information about the tensile testing machine used for the tests at normal temperature. Universal testing machine (SCHENCK) (see no. 4 in Fig. 3.2) Company SCHENCK Hydropuls cylinder Max stroke length [mm] ±125 Max force (static) [kn] ±1600 Load cell Control accuracy [%] 0.02 LVDT Measurement range [mm] ±125 Company Type Cylinder to apply the support pressure (see no. 3 in Fig. 3.2) Model number Enerpac Hollow piston cylinder RCH-202 Number of pistons 2 Max force [kn] 215 Stroke length [mm] 49 Effective piston area [cm 2 ] 30.7 Oil volume [cm 3 ] 150 Note: Pressure for tests with 140 and 200 mm wide specimen was 350 and 460 bar, respectively.

61 44 Chapter 3. Tests at normal temperature The results of test series 2 on C30-lamellas are summarised in Fig It can be seen that for all adhesives a similar mean tensile strength was obtained. This shows that the process of manufacturing the finger joints was appropriate. The application of the adhesive by hand did not lead to a decrease of the tensile strength considering the results by Frangi et al. (2012). In test series 1, the dynamic MOE was measured by means of ultrasonic measurements as described in section 2.1. In addition, the MOE was determined on the basis of eigenfrequency measurements. For the determination of the eigenfrequency, the boards are put on two foam mats and set into oscillation with a plastic hammer. The frequency of the oscillated board was recorded with a microphone. Subsequently, a FFT Analyser (Fast Fourier Transformation) was used to derive the eigenfrequency of the boards. With the eigenfrequency f, the board length l and the density ρ the dynamic MOE was determined with equation 3.1. Subsequently, this dynamic MOE was moisture corrected as already shown for the ultrasonic measurements according to EN 384 (2013d) on page 11. Table 3.3 shows the dynamic MOE determined based on the ultrasonic and frequency measurements. E dyn,f,u = 4 l 2 f 2 ρ (3.1) where E dyn,f,u=12% = E dyn,f,u ( (u 12)) (3.2) E dyn,f,u u l ρ f is the dynamic modulus of elasticity based on eigenfrequency measurements is the measured moisture content of the lamella is the length of the lamella is the density of the lamella is the measured eigenfrequency Fig. 3.3 shows a comparison of the dynamic MOE determined with ultrasonic (E dyn,us,u ) and eigenfrequency (E dyn,f,u ) measurements. It can be seen that the eigenfrequency measurements gave, in general, slightly higher results for the dynamic MOE than the ultrasonic measurements. Fig. 3.5 shows the tensile strength measured for specimens tested at normal temperature as a function of the density of the specimens. The tensile strength f t was calculated based on the cross-sectional area according to the following equation: f t = F u A with F u : failure load; A: cross-sectional area in the finger-jointed region. The cross-sectional area was measured for each specimen with 1 mm measuring accuracy. In Fig. 3.5, a slight increase in the tensile strength by increasing density of the specimens tested at normal temperature was observed. The same effect was also obtained by Frangi et al. (2012). Further, Fig 3.5 shows that no difference between certified and non-certified adhesive was observed, by comparing grey and black coloured results. (3.3)

62 3.3. Test results 45 Tab. 3.2: Compilation of test results for test series 1 at normal temperature. Specimen Moisture Density Tensile Remarks name content strength [%] [kg/m 3 ] [N/mm 2 ] P Mixed-type, 50% finger joint P Finger joint P Shear failure P Mixed-type, 45% finger joint P Finger joint P Mixed-type, 30% finger joint P Finger joint P Mixed-type, 40% finger joint P Shear failure P Shear failure M Finger joint M Finger joint (90%) M Finger joint M Mixed-type, 30% finger joint M Finger-joint P a Mixed-type, 40% finger joint P a Mixed-type, 20% finger joint P a Finger joint P a Finger joint a Specimen width w = 200 mm; all other specimens w = 140 mm Note: The density refers to the moisture content measured and given in this table. Further test results at normal temperature for the same types of adhesives can be taken from Frangi et al. (2012).

63 46 Chapter 3. Tests at normal temperature Tab. 3.3: Results from the ultrasonic and eigenfrequency measurements in test series 1 at normal temperature. Specimen MOE MOE name E dyn,us,u E dyn,us,u=12% E dyn,f,u E dyn,f,u=12% [N/mm 2 ] [N/mm 2 ] P P P P P P P P P P M M M M M P a P a P a P a a Specimen width w = 200 mm; all other specimens w = 140 mm

64 3.3. Test results E dyn,f,u=12% [10 3 N/mm 2 ] Test series E dyn,us,u=12% [10 3 N/mm 2 ] Fig. 3.3: Comparison of dynamic Young s Modulus (MOE) determined with ultrasonic (E dyn,us,u ) and eigenfrequency (E dyn,f,u ) measurements Tensile strength [N/mm ] n=6 n=6 n=7 n=8 n=7 n=5 n=5 n=6 n=6 P3 P7 EPI PRF PVAc M2 UF P6 M3 Adhesive name Fig. 3.4: Tensile strength at normal temperature for adhesives tested in series 2 (width 140 mm) and shown in Table 3.4 (box quartile of distribution; whiskers at most 1.5 x interquartile range; points outliers).

65 48 Chapter 3. Tests at normal temperature Tab. 3.4: Compilation of test results for test series 2 at normal temperature. Specimen Moisture Density Tensile Specimen Moisture Density Tensile name content strength name content strength [%] [kg/m 3 ] [N/mm 2 ] [%] [kg/m 3 ] [N/mm 2 ] P3 2a M2 7a b b c c d d e e f P7 3a UF 8a b b c c d d e e f EPI 4a P6 9a b b c c d d e e f f g PRF 5a M3 10a b b c c d d e e f f g h PVAc 6a P2 1_200a a b _200b a c _200c a d e f g a Specimen width w = 200 mm; all other specimens w = 140 mm Note: The density refers to the moisture content measured and given in this table.

66 3.3. Test results 49 Tab. 3.5: Compilation of test results obtained from lamellas with higher graded timber for test series 2 at normal temperature. Specimen Moisture Density Tensile MOE name content strength E dyn,f,u E dyn,f,u=12% [%] [kg/m 3 ] [N/mm 2 ] [N/mm 2 ] [N/mm 2 ] 9.L40.a L40.b L40.c L40.d L40.e L40.f L40.g L40.h L40.i L40.j L40.k L40.l L40.m L40.n L40.o L40.p L40.q L40.r P2.L40.a P2.L40.b P2.L40.c P2.L40.d P2.L40.e P2.L40.f L36.a a L36.b a L36.c a L36.d a L36.e a L36.f a L36.g a a Specimen width w = 200 mm; all other specimens w = 140 mm Note: The density refers to the moisture content measured and given in this table.

67 50 Chapter 3. Tests at normal temperature 60 Tensile strength [N/mm2 ] P3 P7 EPI PRF PVAc M2 UF P6 M3 P2 P4 M1 Test series 1 and 2 60 Tensile strength [N/mm2 ] P2 P4 P6 M1 Test series 1 and Density [kg/m 3 ] E dyn,f,u=12% [10 N/mm ] Fig. 3.5: : Tensile strength for the specimens tested at normal temperature as a function of the density of the specimens; : Tensile strength for the specimens tested at normal temperature as a function of the stiffness of the specimens. No clear dependency was observed between the tensile strength and the dynamic modulus of elasticity, as shown in Fig In the tests at normal temperature, the deformation in the finger-jointed region was measured with an optical camera. The assembly of the LEDs on the timber surface can be taken from Fig Two different configurations for the LEDs were chosen: In test series 1, a very detailed configuration was used to determine the local MOE in the finger-jointed region (Fig. 3.6). In test series 2, the amount of LEDs was reduced as shown in Fig. 3.6(c). The optical camera was selectively used in both test series. Table 3.6 and 3.7 show the results of the measured local MOE in the finger-jointed region at normal temperature. The MOE is derived on the basis of the LED s deformation as described above and is given in both tables for the area between the positions indicated and shown in Fig. 3.6 and 3.6(c).

68 Test results [mm] (c) Fig. 3.6: Assembly of the LEDs on the timber surface during the tensile tests at normal temperature. Fig. 3.6 and 3.6 show the assembly in series 1 and Fig. 3.6(c) the assembly in series 2.

69 Tab. 3.6: Measured MOE in the finger-jointed region for test series 1 at normal temperature. Adhesive Specimen MOE [N/mm 2 ] name Position a M1 M M1 M M1 M M1 M P2 P P2 P P2 P P2 P P4 P P4 P a The position is given as the area between two LEDs named according to Fig Chapter 3. Tests at normal temperature

70 3.3. Test results 53 Tab. 3.7: Measured MOE in the finger-jointed region for test series 2 at normal temperature. Adhesive Specimen MOE [N/mm 2 ] name Position a Mean P3 2a b e P7 3d e f EPI 4b c e PRF 5a b c PVAc 6a c e M2 7b d e UF 8b c e P6 9a c d M3 10a d f a The position is given as the area between two LEDs named according to Fig. 3.6(c).

71 54 Chapter 3. Tests at normal temperature

72 Chapter 4 Conclusion The behaviour of finger-jointed timber boards was studied with an extensive testing program. In total, 49 fire tests under ISO-fire exposure and about 120 tests at normal temperature are summarised in this report. Particular attention was given to the analysis of different parameters on the load-bearing capacity in fire, such as the influence of the adhesive, the influence of the width, the influence of the load level and the influence of the type of fire exposure. The following main conclusions regarding the different parameters studied can be drawn: Taking into account the different failure modes, no significant difference was observed between the studied adhesives in the fire tests. This is in contradiction to tests performed at elevated temperature by Frangi et al. (2012) with the same type of adhesives (P2, P3, P4, M1) and also to fire tests performed by König et al. (2008). The increase in fire resistance with increasing width was approximately linear in the performed fire tests on 80, 140 and 200 mm wide specimens glued with structural adhesives. A reduction of the load level from 30% to 20% of the average load-bearing capacity measured at normal temperature led to an increase of the fire resistance of 8.5 minutes. The increase of the load level to 45% of the average load-bearing capacity resulted in a decrease of the fire resistance of about 15.5 minutes. The increase in fire resistance with load was linear in the performed fire tests. Finger-jointed lamellas that were protected until failure on its top and bottom and only fire exposed on two sides reached a fire resistance of 10 to 15 minutes larger than lamellas influenced by heat from three sides. Finger joints, glued with adhesives which are not-certified for the use in structural timber members in Europe, reached in case of PVAc and the PUR adhesive P7 a fire resistance of about 25 to 30 minutes. This is, on average, 20 minutes lower than the fire resistance reached by finger joint connections glued with certified (structural) adhesives. Further, one UF and one MUF adhesive (M3), which are both not certified according to European testing standards, reached a fire resistance similar to the fire resistance of certified adhesives.

73 56 Chapter 4. Conclusion Finger joints glued with PRF failed in the solid wood region or in the finger-jointed region as failure of the fingers (exceeding the tensile strength of the wood fibres). The fire resistance was similar to timber members glued with some PUR and MUF adhesives. This is in contradiction to tests performed by König et al. (2008). Specimens glued with the PUR adhesive P3 [this adhesive was developed for the North American market and is certified according to ASTM D7247 (2007)]did not reach a higher fire resistance than specimens glued with the PUR adhesive P2. Adhesive P2 does not pass the test according to ASTM D7247. It can be concluded that adhesives need sufficient strength at temperatures considerably lower than 200 C for the application in gluedlaminated timber. The test specimens were designed with the purpose to achieve failure in the finger joint. However, failure in the solid wood region limited the fire resistance in some tests. The charring leads to a reduction of the timber cross-section and was still governing the load-bearing capacity for the finger-jointed specimens with the structural adhesives tested in this experimental analysis. As shown in the fire tests, the larger strength reduction of some adhesives in tests performed at elevated temperatures does not necessarily lead to a greater reduction of the mechanical resistance (load-bearing capacity) of structural components in fire, since defects like knots or other may be dominant - depending on the strength class (grading). In commercially graded glued-laminated beams these defects may be the dominating cause of failure, whereas high quality lamellas will cause more finger joint failures.

74 Appendix A Performance of finger-jointed region In the following, pictures of both sides of the specimens finger-jointed region are presented for the fire test series 1 and 2. The pictures were taken from the testing boards just before the protective lamellas were glued on their top and bottom. A.1 Fire test series 1 Fig. A.1: Test specimen P2.1

75 58 Chapter A. Performance of finger-jointed region Fig. A.2: Test specimen P2.2 Fig. A.3: Test specimen P2.3 Fig. A.4: Test specimen P2.4

76 A.1. Fire test series 1 59 Fig. A.5: Test specimen P2.6 Fig. A.6: Test specimen P2.7 Fig. A.7: Test specimen P2.8

77 60 Chapter A. Performance of finger-jointed region Fig. A.8: Test specimen P2.10 Fig. A.9: Test specimen M1.1 Fig. A.10: Test specimen M1.2

78 A.1. Fire test series 1 61 Fig. A.11: Test specimen P4.1 Fig. A.12: Test specimen P4.2 Fig. A.13: Test specimen P4.3

79 62 Chapter A. Performance of finger-jointed region Fig. A.14: Test specimen P2.S1 Fig. A.15: Test specimen P2.S2 Fig. A.16: Test specimen V1

80 A.1. Fire test series 1 63 Fig. A.17: Test specimen V2 Fig. A.18: Test specimen P2.80 Fig. A.19: Test specimen P2.200

81 64 Chapter A. Performance of finger-jointed region A.2 Fire test series 2 Fig. A.20: Test specimen 1.2 Fig. A.21: Test specimen 1.3 Fig. A.22: Test specimen 1.200

82 A.2. Fire test series 2 65 Fig. A.23: Test specimen Fig. A.24: Test specimen 2.2 Fig. A.25: Test specimen 2.3

83 66 Chapter A. Performance of finger-jointed region Fig. A.26: Test specimen 3.2 Fig. A.27: Test specimen 4.1 Fig. A.28: Test specimen 4.2

84 A.2. Fire test series 2 67 Fig. A.29: Test specimen 5.1 Fig. A.30: Test specimen 5.2 Fig. A.31: Test specimen 6.1

85 68 Chapter A. Performance of finger-jointed region Fig. A.32: Test specimen 6.2 Fig. A.33: Test specimen 6.3 Fig. A.34: Test specimen 7.1

86 A.2. Fire test series 2 69 Fig. A.35: Test specimen 7.2 Fig. A.36: Test specimen 8.1 Fig. A.37: Test specimen 8.2

87 70 Chapter A. Performance of finger-jointed region Fig. A.38: Test specimen 9.1 Fig. A.39: Test specimen 9.4 Fig. A.40: Test specimen 9.5

88 A.2. Fire test series 2 71 Fig. A.41: Test specimen 9.80 Fig. A.42: Test specimen 10.1 Fig. A.43: Test specimen 10.2

89 72 Chapter A. Performance of finger-jointed region Fig. A.44: Test specimen V3 Fig. A.45: Test specimen V4

90 Appendix B Crack patterns B.1 Fire test series 1 Fig. B.1: Test specimen M1.1 Fig. B.2: Test specimen M1.2

91 74 Chapter B. Crack patterns Fig. B.3: Test specimen P2.1 Fig. B.4: Test specimen P2.2 Fig. B.5: Test specimen P2.4

92 B.1. Fire test series 1 75 Fig. B.6: Test specimen P2.3 Fig. B.7: Test specimen P2.10

93 76 Chapter B. Crack patterns Fig. B.8: Test specimen P2.6 Fig. B.9: Test specimen P2.7 Fig. B.10: Test specimen P2.8

94 B.1. Fire test series 1 77 Fig. B.11: Test specimen P2.80 Fig. B.12: Test specimen P2.200 Fig. B.13: Test specimen P2.S1

95 78 Chapter B. Crack patterns Fig. B.14: Test specimen P2.S2 Fig. B.15: Test specimen P4.1 Fig. B.16: Test specimen P4.2

96 B.1. Fire test series 1 79 Fig. B.17: Test specimen P4.3 Fig. B.18: Test specimen V1 Fig. B.19: Test specimen V2

97 80 Chapter B. Crack patterns B.2 Fire test series 2 Fig. B.20: Test specimen 1.2 Fig. B.21: Test specimen 1.3 Fig. B.22: Test specimen 1.200

98 B.2. Fire test series 2 81 Fig. B.23: Test specimen 2.2 Fig. B.24: Test specimen 2.3 Fig. B.25: Test specimen

99 82 Chapter B. Crack patterns Fig. B.26: Test specimen 3.1 Fig. B.27: Test specimen 3.2 Fig. B.28: Test specimen 4.1

100 B.2. Fire test series 2 83 Fig. B.29: Test specimen 4.2 Fig. B.30: Test specimen 5.1 Fig. B.31: Test specimen 5.2

101 84 Chapter B. Crack patterns Fig. B.32: Test specimen 6.1 Fig. B.33: Test specimen 6.2 Fig. B.34: Test specimen 6.3

102 B.2. Fire test series 2 85 Fig. B.35: Test specimen 7.1 Fig. B.36: Test specimen 7.2 Fig. B.37: Test specimen 8.1

103 86 Chapter B. Crack patterns Fig. B.38: Test specimen 8.2 Fig. B.39: Test specimen 9.1 Fig. B.40: Test specimen 9.3

104 B.2. Fire test series 2 87 Fig. B.41: Test specimen 9.4 Fig. B.42: Test specimen 9.5 Fig. B.43: Test specimen 10.1

105 88 Chapter B. Crack patterns Fig. B.44: Test specimen 10.2 Fig. B.45: Test specimen V3 Fig. B.46: Test specimen V4

106 B.3. Tests at normal temperature series 1 89 Fig. B.47: Test specimen 9.80 B.3 Tests at normal temperature series 1 Fig. B.48: Test specimen M1.11 and M1.12 Fig. B.49: Test specimen M1.13 and M1.14

107 90 Chapter B. Crack patterns Fig. B.50: Test specimen M1.15 and P2.11 Fig. B.51: Test specimen P2.12 and P2.13 Fig. B.52: Test specimen P2.14 and P2.15

108 B.3. Tests at normal temperature series 1 91 Fig. B.53: Test specimen P4.11 and P4.12 Fig. B.54: Test specimen P4.13 and P4.14 Fig. B.55: Test specimen P4.15

109 92 Chapter B. Crack patterns Fig. B.56: Test specimen P and P Fig. B.57: Test specimen P and Fig. B.58: Test specimen P and

110 B.4. Tests at normal temperature series 2 93 B.4 Tests at normal temperature series 2 Fig. B.59: Test specimen 2a and 2b Fig. B.60: Test specimen 2c and 2d Fig. B.61: Test specimen 2e and 2f

111 94 Chapter B. Crack patterns Fig. B.62: Test specimen 3a and 3b Fig. B.63: Test specimen 3c and 3d Fig. B.64: Test specimen 3e and 3f

112 B.4. Tests at normal temperature series 2 95 Fig. B.65: Test specimen 4a and 4b Fig. B.66: Test specimen 4c and 4d Fig. B.67: Test specimen 4e and 4f

113 96 Chapter B. Crack patterns Fig. B.68: Test specimen 4g Fig. B.69: Test specimen 5a and 5b Fig. B.70: Test specimen 5c and 5d

114 B.4. Tests at normal temperature series 2 97 Fig. B.71: Test specimen 5e and Fig. B.72: Test specimen 5f and 5g Fig. B.73: Test specimen 5h

115 98 Chapter B. Crack patterns Fig. B.74: Test specimen 6a and 6b Fig. B.75: Test specimen 6c and 6d Fig. B.76: Test specimen 6e and 6f

116 B.4. Tests at normal temperature series 2 99 Fig. B.77: Test specimen 6g Fig. B.78: Test specimen 7a and 7b Fig. B.79: Test specimen 7c and 7d

117 100 Chapter B. Crack patterns Fig. B.80: Test specimen 7e Fig. B.81: Test specimen 8a and 8b Fig. B.82: Test specimen 8c and 8e

118 B.4. Tests at normal temperature series Fig. B.83: Test specimen 8d and Fig. B.84: Test specimen 9a and 9b Fig. B.85: Test specimen 9c and 9d

119 102 Chapter B. Crack patterns Fig. B.86: Test specimen 9e and 9f Fig. B.87: Test specimen 10a and 10b Fig. B.88: Test specimen 10c and 10d

120 B.4. Tests at normal temperature series Fig. B.89: Test specimen 10e and Fig. B.90: Test specimen 10f Fig. B.91: Test specimen 1_200a and 1_200b

121 104 Chapter B. Crack patterns Fig. B.92: Test specimen 1_200c

122 B.4. Tests at normal temperature series Higher graded finger-jointed timber (L40 and L36) Fig. B.93: Test specimen 9.L40.a and Fig. B.94: Test specimen 9.L40.b and 9.L40.c Fig. B.95: Test specimen 9.L40.d and 9.L40.e

123 106 Chapter B. Crack patterns Fig. B.96: Test specimen 9.L40.f and 9.L40.g Fig. B.97: Test specimen 9.L40.h and 9.L40.i Fig. B.98: Test specimen 9.L40.j and 9.L40.k

124 B.4. Tests at normal temperature series Fig. B.99: Test specimen 9.L40.l and 9.L40.m Fig. B.100: Test specimen 9.L40.n and Fig. B.101: Test specimen 9.L40.o and 9.L40.p

125 108 Chapter B. Crack patterns Fig. B.102: Test specimen 9.L40.q and 9.L40.r Fig. B.103: Test specimen P2.L40.a and P2.L40.b Fig. B.104: Test specimen P2.L40.c and P2.L40.d

126 B.4. Tests at normal temperature series Fig. B.105: Test specimen P2.L40.e and P2.L40.f Fig. B.106: Test specimen L36.a and L36.b Fig. B.107: Test specimen L36.c and L36.d