Racking Behaviour of Stabilising Walls and the Anchorage Systems for Beam and Post System in Timber

Transcription

1 TECHNICAL REPORT Racking Behaviour of Stabilising Walls and the Anchorage Systems for Beam and Post System in Timber Test Report Gabriela Tlustochowicz

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3 Racking Behaviour of Stabilising Walls and the Anchorage Systems for Beam and Post System in Timber Test Report Gabriela Tlustochowicz Luleå University of Technology Department of Civil, Mining and Environmental Engineering Division of Structural engineering

4 ISSN: ISBN Luleå 21

5 Summary This report presents the laboratory racking load tests on special composite stabilising wall elements as parts of a beam-and-post system called trä8 developed by the Swedish glulam manufacturer Moelven Töreboda. The wall elements comprise of glued laminated timber as framing members and Kerto-Q laminated veneer lumber as double-sided sheathing. The tests were performed on full-scale specimens. Two series of tests were carried out with three specimens each, where the series represented samples with two different anchorage systems, one using a special anchorage device including glued-in rods anchored to the foundation via a steel I-beam and the other using nail plates. The racking load was applied in both directions (by pushing and pulling, respectively) to enable tensile testing of the anchorage device at each bottom end of the wall element. The objectives of the testing were to evaluate the efficiency of the wall elements including the anchorage devices, and the detailed racking behaviour of the wall used as stabilising walls, both with respect to the ultimate and serviceability limit states. Thus, the stiffness, displacements and the shear capacity of the wall elements were evaluated together with their failure modes. Especially, the behaviour of the anchorage connections subjected to tensile uplifting forces was studied. The test results indicate a strong potential for using these composite stabilising wall elements for stabilising purposes in multi-storey timber buildings, and they also indicate good performance of both tested anchorage types. Future studies on the stabilising wall system would include further development and optimization of the anchorage connections, both with respect to the load capacity and the ductility of the joint. Key words: glulam, LVL, Kerto-Q, beam and post system, glued-in rods, nail plates

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7 Acknowledgements The work presented in this report was carried out at COMPLAB at Luleå University of Technology during the period April-September 29. The financial support, the manufacturing and delivery of the samples from the company Moelven Töreboda AB is greatly appreciated. Also the financial support through collaboration with Ulf Arne Girhammar within the project Multi-story timber buildings (The Europen Union's Structural Found - Regional Fund) is greatly appreciated. I would like to thank my supervisors Helena Johnsson and Ulf Arne Girhammar for support and advice, Thomas Johansson from Moelven Töreboda AB for technical advice, and research engineers Lars Åström, Georg Danielsson and Roger Lindfors for their great help in performing the experiment June, 21 Gabriela Tłustochowicz

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9 TABLE OF CONTENTS Summary... 3 Acknowledgements General Scope Limitations Other assumptions loads (theoretical calculations) TESTS Samples wall elements Material properties Samples anchorages Type 1 - Glued-in rods Type 2 Nail plates Test set-up General description Instrumentation Loading Anchorage to the steel rig RESULTS Glued-in rods Sample Sample Sample Summary of the results for glued-in rods Nailed connection General observations Summary of the results for nail plates Total summary ANALYSIS OF DISPLACEMENTS GLOBAL analysis Corrected horizontal displacements of the stabilising element Rotation Horizontal translation Displacements at the anchorage joints Out-of-plane displacements FINAL REMARKS Production of the walls Assessment of samples with glued-in rods Failure modes Assessment of samples with nail joints Conclusions and discussion References Appendix A - Density and moisture content results Appendix B Instrumentation of the samples with anchorage type Appendix C Instrumentation of the samples with anchorage type Appendix D Theoretical calculations Appendix E Horizontal displacements, series Appendix F Horizontal displacements, series Appendix G Displacements at the anchorage joints for glued-in rods

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11 1. INTRODUCTION 1.1 General A beam and post system in timber for multi-storey buildings is currently under development in Sweden. Moelven Töreboda leads the process of the development of the system as a product under the commercial Swedish name trä8. In the process of design and development of the system Luleå University of Technology participates through a PhD project being part of the competence platform Lean Wood Engineering. The components included in the system are beams, columns, floor cassettes, roof elements and stabilising wall elements. These components create the main bearing structure that should be complemented with curtain walls of some type. The PhD project focuses on the stabilising structure of the system trä8 based on prefabricated composite stabilising wall panels and issues related to their performance. The lateral load resistance of the wall panel itself and the performance of the proposed anchorage systems are of interest. 1.2 Scope The scope of this report is to present results of the laboratory tests of the stabilising walls with their anchorage devices being the main elements of the stabilising system for trä8. The tests aimed to: - evaluate the overall behaviour of the stabilising element under horizontal static loading, - evaluate the use of glued-in rods as connectors in a stabilising system, - compare the capacity and behaviour of a connection with glued-in rods and a nailed connection (stiffness, load bearing capacity, failure mode). Experimental work has been conducted at Luleå University of Technology during April to September Limitations The laboratory tests were performed on elements which had all the cross-sectional dimensions in 1:1 scale. The ideal situation would be to test a continuous wall with four-storey height, since they are intended to be used in real projects in this manner. However, this was not possible with respect to the limitations of the laboratory facilities. Tested elements were thus 6 m long, which corresponds to the approximate height of a two-storey building. The tested anchorage systems were limited to two types with respect to the costs of the experiment. The first system utilizing glued-in rods was developed by Moelven Töreboda. The system utilizes a technology with steel rods glued in the timber members. The second system is a commonly used connection with nail plates. Such a solution was used in the pilot project built in Töreboda in 28 (Tlustochowicz, 28). 3

12 1.4 Other assumptions experimental case To obtain a realistic design of the anchorage joints, an actual building was used as an example. The calculations of the wind load acting on the assumed model building were performed according to the Swedish building design code (BKR 99) for the most unfavourable wind load that can occur in Sweden. (a) Figure 1.1: (a) Illustration of the model building used for calculations (b) Plan (b) The anchorage joints with nail plates were designed according to the recommendations in the Swedish building design code (BKR, 1998). Since connections with glued-in rods are not included in the Swedish code, the calculations were made according to the instructions found in (Blass et al. 1995). The calculations of loads and load-bearing capacities of the anchorage joints are presented in Appendix D. 4

13 2. TESTS Two series of three stabilising walls were tested subjected to static racking load, imitating wind influence. The specimens were manufactured by Moelven Töreboda in Töreboda, Sweden, transported to the laboratory facilities of Complab at Luleå University of Technology and thereafter stored in a non-heated hall for a period of about 2 months. The procedure of manufacturing and delivery will be similar in the future, when ready-toassemble elements will be delivered to the building-site. The tests were numbered in a sequence from 1 to 6. Since more than one loading of each sample was performed (intentionally two), the second assignation of the test was a letter indicating the number of loading. In some cases, the first attempts of loading were neglected due to certain problems with the performance of the test rig. Table 1: Test configurations Test assignation Sample/series Anchorage Loading mode 1D 1 Glued-in rods Pull 1F 1 Glued-in rods Push 2B 2 Glued-in rods Push 2C 2 Glued-in rods Pull 3A 3 Glued-in rods Push 3B 3 Glued-in rods Pull 4B 4 Nail plates Push 4C 4 Nail plates Pull 5A 5 Nail plates Push 5B 5 Nail plates Pull 6A 6 Nail plates Push 6B 6 Nail plates Pull 2.1 Samples wall elements A glulam A 16 Kerto-Q Section A - A Figure 2.1: Sketch of the stabilising element (in this case with anchorage with glued-in rods) 5

14 The stabilising elements are prefabricated insulated wall panels with the outer dimensions 6.m x 2.4m x.214m. The main skeleton is made of glulam members of class (according to Swedish designation, BKR (1998)), equivalent to GL28c in Eurocode 5 (Dec 23). The outer members of the skeleton have the dimensions 36mm x 16mm, and are 6m long. The middle inner post is 225mm wide, 16mm deep, and also 6m long. Between these vertical members, at the bottom, top and in the middle shorter members are placed (225x16x728 mm). The plane view and cross-section are presented in Figure 1.1. The spaces between members are to be filled with mineral wool (in the test specimens, the wool was not applied), so the element has a structural and a functional role (insulation). Members of the skeleton are connected only by means of sheathing on both sides made of 27mm thick LVL boards glued with the use of Resorcinol Casco bas 1719 (Phenol-Resorcinol adhesive type), and screwed with screws Heco TFT Protect 4 6.x8. The screws connect the sheathing to the skeleton, but also apply pressure during bonding and provide additional safety in case of failure of the glue (see Figure 2.2). The weight of the sample excluding anchorage devices is 98 kg. Figure 2.2: Production of specimens at factory of Moelven Töreboda AB The LVL used for sheathing of the stabilising wall is a product of Finnforest Finland known as Kerto-Q. The specific property of this material is that approximately 2% of the veneers are glued crosswise, which improves the lateral bending strength and stiffness of the material Material properties Stiffness parameters The material properties of engineered wood product used for producing stabilising walls according to the manufacturers (LVL Finnforest Finland) and according to literature (Thelandersson, Larsen, 23) are given in Table 2. 6

15 Elastic modulus [N/mm 2 ] Shear modulus [N/mm 2 ] Table 2: Properties of used materials (nominal characteristic values) Glulam 1 Kerto-Q, thickness mm 2 E L =14 E T =5 E R =8 E L =159 E T =2967 E R =244.6 G LR =8 G LT =5 G RT =6 G LR =147.5 G LT =5 G RT =48.9 Poisson's ratio n LR =.2 n LT =.2 n RT =.45 n LR =.2 n LT =.2 n RT =.68 Density and moisture content After each test, material samples were taken from the test samples (glulam and LVL). All the bottom corners with joints were cut off from the wall and from the close neighbourhood of them small samples for material properties measurements were cut off as well. From each side of wall element 3 glulam cubes were cut out with dimensions 4 x 4 x 4 mm 3 and three Kerto-Q samples with dimensions 4 x 4 x 27 mm 3 (the last dimension is determined by the thickness of the board). The samples were stored in moisture proof bags until the end of all tests, and the moisture content measurement was performed simultaneously for all samples. The moisture content and density were determined according to recommendations of ISO 313 and ISO 3131 respectively. The moisture content (w) was calculated according to the following formula (ISO 313): m1 m2 w = 1 [%] m2 Where: - m 1 is the mass of the test piece before drying [g], - m 2 is the mass of the test piece after drying [g]. The density of the samples (ρ) was calculated according to the following formula [ref]: mw kg ρ w = 3 V w m Where: - m w is the mass of the test piece at moisture content w [kg, g], - V w is the volume of the test piece at moisture content w [m 3, cm 3 ]. The resulting mean values of moisture content for both materials are presented in Table 3. The detailed data from measurements are available in Appendix A. Table 3: The average values of measured moisture content Material Moisture content W test [%] Glulam LVL Kerto-Q The stiffness parameters of glulam were assumed according to recommendations by Thelandersson and Larsen (23). 2 The stiffness parameters of Kerto-Q according to manufacturer s data (Kerto brochure - product specification, 26). 7

16 The mean and characteristic values of the determined density of tested specimens are presented in the Table 4. The detailed results of measurements can be found in Appendix A. For Kerto-Q LVL also the manufacturer s values of the characteristic and mean density are presented in the table. Table 4: The average values of measured and defined density values Experimental data Manufacturer s data Material Mean value δ test,m Charact. value δ test,k Mean value 3 δ mean Charact. value 3 δ k Glulam LVL, Kerto-Q, 27mm Since the number of specimens for testing material properties of each material was n=18, the coefficient k pn =1.95 (95% confidence level) for the calculations of the characteristic values of densities. The statistical analysis of densities is presented in the Table 5. Table 5: The statistical data for density measurements Glulam average value [kg/m 3 ] standard deviation 34,83 [kg/m 3 ] variation coefficient 7.3 [%] characteristic value [kg/m 3 ] Kerto-Q average value [kg/m 3 ] standard deviation 2.66 [kg/m 3 ] variation coefficient 4.2 [%] characteristic value [kg/m 3 ] No tests of material properties were performed on the steel parts of the anchorage joints. 2.2 Samples anchorages In the experiments two different types of anchorage system were included: - Type 1 is a system based on the glued in rods, - Type 2 involves nail plates. In both cases, the anchorage is placed at the bottom corners of the wall element, which with respect to the considerable length of the wall element, can theoretically be treated as a pinned connection. 3 The stiffness parameters of Kerto-Q according to manufacturer s data (Kerto brochure - product specification, 26). 8

17 2.2.1 Type 1 - Glued-in rods The connection consists of six metric threaded rods M24, 8.8 glued-in to a depth of 3 mm (see Figure 3). The holes drilled in the glulam had 1 mm larger diameter than the diameter of the rods and length of 31 mm. The adhesive used for bonding-in rods was type Casco PU Bond CR 421 (polyurethane). During production, the adhesive mixed with hardener is injected into the hole; thereafter the rod is screwed in pressing out the adhesive and distributing it along the rod. The procedure should assure relatively even distribution of the adhesive in the hole despite of the horizontal position of the assembly. B xM24, 8.8 Lg=3 mm 3 HEB 18 WITH 1mm STIFFENERS A B 1 A B - B A - A Figure 2.3: Anchorage type 1- glued-in rods The process of gluing-in rods awakes doubts concerning the quality of the joints. Therefore, the manufacturer performs one pull-out test for each ten glued-in rods. To enable mounting of the rods to the foundation, an intermediate steel HEB 18 profile was applied. The rods glued into glulam as well as rods casted in the concrete plate are fastened in the holes in the flanges of the steel profile. To minimize deformations of the flanges of the steel profile, 1mm thick stiffening plates were welded on both ends of the profile Type 2 Nail plates The anchorage with nail plates were used in the experiment for comparison purposes and also as a standard solution used in timber engineering generally. Such a solution was used also in the pilot house built in the beam and post system (Tlustochowicz, 28). Anchorage system type 2 is constructed of two nail plates on both sides of the wall elements that are welded to a 3 mm thick horizontal plate which is fastened in the concrete (Peikko catalogue). The plates are located centrally in relation to the vertical member of the skeleton. Each nail connection consists of 82 annular ringed shank nails with diameter, d=4 mm and with nail penetration depth, p=6 mm. 9

18 PL 5x12x61 S nails 6-4, Ø a5 a Peikko JPL 3x3 B - B A - A Figure 2.4: Anchorage type 2 nailed connection For the experiment purposes the whole joint was prepared in the factory, plates welded together and nailed to the wall element. In the future, most probably the horizontal plate anchored in the concrete/ground plate with the nail plates welded to it will be prepared on the building site. The wall element then could be placed in between plates and nailed on site, as was done during construction of the pilot project in Töreboda (see Figure 2.5). Figure 2.5: Assembly of the wall element during construction of the pilot project (Tlustochowicz, 28) 2.3 Test set-up General description The experiment was performed in a horizontal set-up due to the height limitations of the laboratory facilities. The wall element was connected to the steel frame simulating the ground plate, which in turn was fixed to a coordinate floor. Initially, the steel frame was only screwed to the mounting points in the floor by means of steel rods. During the first attempts of loading that anchorage proved insufficient because of large deformations of the frame. Therefore, to strengthen the position of the steel frame, it was welded to the floor. The load was applied by an Intron hydraulic Cylinder (Static load capacity 27 kn, Measuring equipment HBM Spider 8, Stearing Control module Dartec 95) by means of a load distribution beam screwed to the top edge of the specimen. At two thirds height of the wall, a roller support was applied, constructed of two outer layers and a thin plywood matrix 1

19 with round holes keeping steel balls in place and assuring freedom of movements in all directions. The steel frame itself was designed by an employee of Complab at LTU and manufactured by an external manufacturer. A 27 kn INSTRON HYDRAULIC JACK ROLLER SUPPORT SQUARE STRUCTURAL STEEL TUBE 15x15x1 A - A STEEL LOAD DISTRIBUTION BEAM 3x3 COACH SCREWS PER SIDE A 1 2 [3] 3 [6] 4 8 PLAN VIEW STEEL FRAME ANCHORED TO COORDINATE FLOOR MEASUREMENT POINTS Figure 2.6: Plan view of the experiment Figure 2.7: Overview of the test set-up Consequences for further analysis: In the evaluation of the experimental results it should be taken into account that the self weight of the wall element, which is normally placed in an upright position, was in this case not counteracting the turn-over of the wall when subjected to racking static load. Also the placement of the hydraulic jack in the same position for both directions of loading (push and pull) caused that in these two loading cases there were different rotation points of the sample. 11

20 It is not without significance that the same sample was used for two loading cases, which could influence the second performed test Instrumentation The specimens were instrumented with 17 (when testing anchorage type 1) and 18 (when testing anchorage type 2) Linear Voltage Displacement Transducers (LVDT), with measurement lengths 1-1 mm. To assure a smooth surface for the measuring device in all measurement points either Plexiglas plates or steel/aluminium plates or profiles were glued to the specimen (see Figure 2.8). The channels, transducer designations and their specifications, as well as the illustrations of instrumentation are included in Appendices B (for samples type 1) and C (for samples type 2). (a) Figure 2.8: Instrumentation of: (a) upper corner of the sample, (b) point along the length In each top corner of the specimen three transducers were placed to measure displacements in the longitudinal and lateral directions, as well as out-of-plane displacement (Figure 2.8). The anchorage joints were instrumented as presented in the Figure 2.9. (b) (a) Figure 2.9: Instrumentation of the anchorage points (a) Type 1 (b) Type 2 (b) 12

21 2.3.3 Loading The experiment was carried out through loading each sample twice, in two different directions. Due to the element s weight and the character of the anchorage (set-up of the test), rotation of the elements would be problematic. Therefore loading of each element was performed in one position only, with load applied at the same point but in different directions. Firstly, the wall was pushed (see Figure 2.1a) until the right anchorage connection failed, after unloading the wall it was loaded in the opposite direction pulled until obtaining failure in the left anchorage point (Figure 2.1b). LOAD LOAD (a) (b) Figure 2.1: Illustration of the loading modes: (a) push test, (b) pull test The loading device in the experiment was a servo-hydraulic testing machine with the static load capacity of 27 kn. The device was placed horizontally at a suitable height so the load is applied in the middle of the wall thickness (Figure 2.11). The loading speed was in the range of.1 m/sec. The total testing time was between 1 and 44 minutes, depending on the failure load. Figure 2.11: Placement of the hydraulic jack The hydraulic jack ended with a threaded rod that enabled connecting it to the load distributing beam. The rod (ø2 mm) was screwed to a 2 mm thick steel plate that was welded to the load distributing beam (Figure 2.12). 13

22 27 kn INSTRON HYDRAULIC JACK M THREADED ROD 2x3 COACH SCREWS φ16 A A M THREADED ROD 2x3 COACH SCREWS φ16 A - A Figure 2.12: The loading point, drawing and photograph Such a connection does not allow for full freedom of movements, meaning that it can not be treated theoretically as a hinge, but at the same time the stiffness and strength of the connection is presumably much lower than the rest of the structure, so it allows almost full freedom of movement Anchorage to the steel rig For glued-in rods (anchorage type 1), the bottom of the steel profile was screwed to the steel rig as it would be screwed to the rods casted in the foundation in a real assembly. The intermediate measure was a square structural steel tube (15x15x1 mm), Figure For anchorage type 2, the bottom plate was welded to a similar square tube as it would be welded to the plate casted in the concrete. The steel tubes were in turn screwed to the steel frame with two screws, Figure B 6 x M GLUED-IN 6 x M B STEEL FRAME HEB 18 WITH 1mm STIFFENERS SQUARE STRUCTURAL STEEL TUBE 15 x 15 x 1 B - B Figure 2.13: Connection with the steel frame for anchorage type 1, drawing and photograph 14

23 The biggest problem with the square tubes was that their dimensions and in consequence also strength and stiffness were too low in comparison to the strength of the joints (glued and nailed), so during loading unwanted deformations were generated in the steel supporting structure. B B STEEL FRAME SQUARE STRUCTURAL STEEL TUBE 15 x 15 x 1 B - B Figure 2.14: Connection with the steel frame for anchorage type 2, drawing and photograph 15

24 3. RESULTS For each test the total horizontal displacements measured on both sides of the stabilising element are presented. The unintentional displacements caused by rotation and horizontal translation of the stabilising elements due to the compliancy of the test rig are subtracted from the total displacements and presented in separate diagrams. Additionally, the summarizing diagrams of displacements caused by rotation and translation are presented at the end of the section. 3.1 Glued-in rods Generally, it can be observed that for a connection with glued-in rods, the expected failure mode would be brittle and quite sudden. One of the connections with glued in rods (in test 3A) was not destroyed, the loading capacity of the jack was reached. In the remaining tests the dominating failure mode was shear failure in timber. For each test the total measured loaddisplacement curves are presented, illustrating displacements of six points on both edges of the specimens Sample 1 (a) (b) Figure 3.1: (a) Failure in test 1D, (b) Failure in test 1F Test 1D (L): All six screws were pulled out from the holes. On the visible threaded parts of the screws no adhesive was visible; no destruction of the timber could be observed either (Figure 3.1a). Test 1F (R): Three glued-in rods at the bottom were pulled out without any sign of timber or adhesive on them, similarly as in 1D. For the top layer, the joints failed in the timber, which can indicate better functioning of the adhesive/adhesion. The middle screw demonstrated that the connection can achieve very high strength, which in this case exceeded the strength of the upper flange of the steel profile, causing its bending (Figure 3.1b). The failure of this middle screw took place when all other screws in the joint had failed. The failure modes are visible on the load-displacement curves, where in test 1D the failed definitely at once and in test 1F the jumps on the curves are caused by successive failures of glued-in rods and plastic deformation of upper flange of the steel profile. 16

25 7 1B 1C 6 5 1A 4 load [mm] horizontal displacement [mm] Figure 3.2: Load-displacement curves for tests 1A-1C In Figure 3.2 the load-displacement curves for the first three (trial) loadings are presented (for the top right corner of the stabilising element). During the first tests large unplanned displacements occurred, caused by insufficient anchorage or strength of the steel rig. The experimental set-up was therefore successively improved to eliminate these influences, for instance additional welding of the steel frame to the floor was required Sample 2 (a) (b) Figure 3.3: Failure after unloading (a) 2C, (b) 2B Test 2B (R): Five of the rods were pulled out successively and without any sign of timber or adhesive on it (Figure 3.3b). Only one screw, the bottom most outer one, failed partially in timber. This failure resulted in the jumps on the load-displacement curve. Test 2C (L): The final failure mode was not registered on any photograph. The connection failed stepwise, the rods were not pulled out simultaneously, which is visible on the loaddisplacement curve (Figure 3.5, Appendix E). 17

26 3.1.3 Sample 3 (a) (b) Figure 3.4: (a) Sample after test 3A (b) Failure in test 3B Test 3A (R): The right anchorage connection did not fail during testing. The capacity of the loading cylinder was reached (at level of 213 kn, as a result of experiment set-up), but the connection did not brake. In Figure 3.4a connection T3-R is presented with visibly deformed lower flange of the steel profile. Test 3B (L): Four out of six rods were pulled out with a shear block. In the remaining two, the failure took place in the adhesive-wood layer, adhesive was visible on the threads of these screws Summary of the results for glued-in rods The obtained loads and displacements for joints with glued-in rods are summarized in Table 6. The measured load is the load applied to the specimen at its top right corner, where minus and plus are related to the direction of the applied load which is also indicated in the table by means of arrows. The failure load is the pull-out load at the pulled anchorage joint, calculated from maximum applied load, specimen s geometry and experimental set-up. The presented maximum horizontal displacement of the specimen is the displacement measured at maximum load. Statistical analysis of pull-out strength: N GIR, test = kN S GIR = kN V GIR = 27.8% The characteristic value of the pull-out (tensile) strengths for both types of anchorages based on the experimental data can be calculated with the use of the following formula: x k k pn N ( k V ) = x 1 pn, where = 2.33[ ], coefficient for 95% confidence level, and n=6 (number of tests) GIR, k = kn 18

27 Test Table 6: Summary of the results for anchorage type 1 (glued-in rods) Direction of loading Ultimate horizontal load [kn] Tensile load in anchorage device [kn] Max horiz. displ. at failure [mm] T1D T1F T2B T2C T3A T3B Mean values: Standard deviation (S GIR ): Variation coefficient (V GIR ): 27.8% 27.8% 54.% The load-displacement curves for all tests in series 1 representing the maximum horizontal displacements as average absolute values form top corners LVDTs ( and ) are presented in Figures 3.5 and 3.6. Figure 3.5 shows the means of total measured displacements and curves on Figure 3.6 represent the corrected data. The shapes of the curves in Figure 3.6 are the result of different load-displacements characteristics representing horizontal translation and rotation of the stabilising element that were subtracted from the total values A 3B 15 1F 2B 2C LOAD 1 1D horizontal displacement [mm] Figure 3.5: Load-displacement curves for samples in series 1 These characteristics are presented in section 4 and the complete load-displacements curves for all tests in series 1 and all transducers measuring horizontal displacements can be found in Appendix E. 19

28 25 2 3B 3A 15 1F 1 1D 2B 2C horizontal displacement [mm] Figure 3.6: Corrected load-displacement curves for samples in series 1 The experimental mean and characteristic (calculated according to Dimensionering genom provning *) failure loads represented as pull-out loads of the glued-in rods are compared with the theoretical load capacities in Table 7. The calculations of theoretical strengths can be found in Appendix D. Table 7: Comparison of experimental pull-out loads with theoretical values. Experimental Theoretical pull-out strength [kn] pull-out load [kn] According to Carling et al According to STEP 1/C14 mean result charact. *) charact. design charact. design Stiffness The stiffness of the stabilising wall was estimated as a load to displacement ratio for the 4% of the maximum applied load. The displacements used for these calculations are the average displacements from both top corners of tested elements. The results and the statistical analysis are summarized in Table 8. 2

29 Test Table 8: Stiffness analysis for samples with glued-in rods Ultimate horizontal load [kn] 4% of ultimate load [kn] Average displacement / [mm] Stiffness [kn/mm] T1D T1F T2B T2C T3A T3B Mean value [kn/mm]: 7.88 Standard deviation (S) [kn/mm]: Variation coefficient (V) [kn/mm]: % The characteristic stiffness of stabilising element when anchored with glued-in rods, calculated from the experimental data, equals 3.49 kn/mm. 3.2 Nailed connection General observations During testing the joints on the right-hand side (pushing load) of the sample were loaded until maximum load was reached (on the load-displacement curve). For all three nailed joints on the left-hand side, the failure mode was exactly the same, which was plug shear failure in the LVL sheathing and withdrawal from the inner glulam columns. Figure 3.7: Failures in tests 4B and 5B A proposal to improve the behaviour of this type of connection is to increase the spacing between the nails (even though the recommended by Swedish design code spacing was used) to avoid plug shear failure. 21

30 B 5A 4C 5B 12 6B 6A 1 8 LOAD horizontal displacement [mm] Figure 3.8: Load-displacement curves for samples in series 2 The load-displacement curves for all tests in series 3 representing the maximum horizontal displacements as average absolute values from placed at top corners displacements transducers ( and ) are presented in Figures 3.8 and 3.9. Figure 3.8 shows the average of the total measured displacements and curves in Figure 3.6 represent the corrected data. The unusual shapes of curves in Figure 3.9 are the result of different load-displacements characteristics representing horizontal translation and rotation of the stabilising element that were subtracted from the total values A 1 8 4B 4C 6B 5B 6 6A horizontal displacement [mm] Figure 3.9: Corrected load-displacements curves for samples in series 2 Since the stiffness of the steel rig was not satisfactory, the displacements from the steel rig had to be subtracted from the measured values. The analysis of the displacements follows in 22

31 section 4 and the complete load-displacements curves for all tests in series 2 and all transducers measuring horizontal displacements can be found in Appendix F. It can be observed that the stiffness in all cases has decreased in the second loading of the same sample Summary of the results for nail plates The summary of the obtained loads and displacements for joints with nail plates are summarized in Table 9. The measured load is the load applied to the specimen at its top right corner, where minus and plus are related to the direction of the applied load which is indicated in the table by means of arrows. The failure load is the pull-out load at the pulled anchorage joint, calculated from maximum applied load and the geometry of the specimen. The presented maximum horizontal displacement of the specimen is the displacement measured at the maximum load. Statistical analysis of pull-out strength: N, test = 49. S NP = 29. 2kN V NP = 7.3% NP 27 kn The characteristic value of the pull-out strengths for both types of anchorages based on the experimental data can be calculated with the use of the following formula: x k k pn N ( k V ) = x 1 pn, where = 2.33[ ], coefficient for 95% confidence level, and n=6 (number of tests) NP, k = Test kn Direction of loading Table 9: General summary of results for series 2 No of nails in connection in tension Ultimate horizontal load [kn] Tensile load in anchorage device [kn] Max horiz. displ. at failure [mm] T4B T4C T5A T5B T6A T6B Mean values: Standard deviation (S NP ): Variation coefficient (V NP ): 7.1% 7.1% 29.8% 23

32 The experimental failure loads represented as pull-out loads for nail plates are compared with the theoretical load capacities in Table 1. It is visible from the presented data that the number of nails in the connection was not uniform. Moreover the calculations of load bearing capacity were made in a simplified way. Table 1 presents all the results of theoretical calculations, which indicate that the failure in the designed connections should occur due to shear plug failure which in fact happened. The characteristic value of failure load for nail plates was not calculated due to the different numbers of nails in connections. Obtained failure loads are visibly higher than the theoretical capacities of the joints. The theoretical calculations of nail connections, including group effect and shear plug failure (that occurred in all tests) can be found in Appendix D. Table 1: Comparison of theoretical results Load-bearing capacity (BKR) Load-bearing capacity (BKR) Group effect Shear plug failure Number of nails n BKR =178 n EC5 =18 n eff =18 n =18(min) F v,k [kn] F v,d [kn] Stiffness The stiffness of the stabilising wall was estimated as a load to displacement ratio for the 4% of the maximum applied load. The results and the statistical analysis are summarized in Table 11. Since for all three specimens the visible tendency observed was a decrease in stiffness during second loading, therefore only data form first loading was considered for stiffness calculations, despite the fact that three measurements are not a representative sample. Test Table 11: Stiffness analysis for samples with nail plates Ultimate horizontal load [kn] 4% of ultimate load [kn] Average displacement / [mm] Stiffness [kn/mm] T4B T4C T5A T5B T6A T6B Mean value [kn/mm]: Standard deviation (S) [kn/mm]: Variation coefficient (V) [kn/mm]: % The characteristic values of stiffness calculated for first loadings with factor k pn taken as 3.19 ( 95% confidence level for 3 samples) equals 4.67 kn/mm. 24

33 3.3 Total summary 25 3A B 4B 2C 1F 5A 4C 6B 6A 5B 3B 1 T1 LOAD T1 1D horizontal displacement [mm] Figure 3.1: Original load-displacement curves, all tests Comment There was a certain inconsistency in the performed measurements. For the horizontal displacements of the stabilising walls that were measured along the edges of the wall the measurement points were placed on the glulam members of the wall s skeleton, whereas other measurement points (e.g. for measuring longitudinal and out of plane displacements at the top corners, displacements at the anchorage points) were placed on the sheathing board. The relative slip/displacement between the glulam skeleton and the sheathing was not measured. However, since the sheathing board is glued and screwed to the glulam skeleton, it can be assumed that there are no relative displacements between these elements. Figures 3.11 and 3.12 demonstrate the shapes of deformed walls during different loading modes for samples type 1 and type 2 respectively. The figures were created based on deformation values obtained from tests 3A/3B and 6A/6B just to illustrate the phenomena. Values used for figures represent the displacement at maximum load and were scaled up 5 times for a better visual effect. The sketches represent only the principle directions and form of displacements and the angles at corners are not correctly represented. 25

34 TEST 3A TEST 3B Figure 3.11: Deformed shapes of sample type 1 under (a) pushing and (b) pulling load TEST 6A TEST 6B Figure 3.12: Deformed shapes of sample type 2 under (a) pushing and (b) pulling load 26

35 4. ANALYSIS OF DISPLACEMENTS 4.1 GLOBAL analysis The horizontal displacements are composed of bending and shear deformations of the stabilising wall panel itself (Figure 4.1 a-b) and the deformations in the anchoring devices causing tilting of the element (Figure 4.1 c), cf. (. Due to the flexibility of the test rig, local deformations in the steel tube and in the steel plates of the test rig, some unintentional rotation and translation took place related to the test rig (Figure 4.1 d-e). δ shear (a) δ bend (b) δ tilt (c) (d) (e) δ rot Figure 4.1: Components of wall displacement To obtain the values of displacements that occured only due to shear and bending of the stabilising wall and the deformations in the anchorage joints, the analysis of displacements was performed and the total measured displacements were corrected. Below, the summarizing diagrams and comments are presented for horizontal displacements and rotation of the samples. δ slip 4.2 Corrected horizontal displacements of the stabilising element Rotation Displacements (rotation of specimens) resulting from the deformations of the steel rig are presented in Figures 4.2 and 4.3. Positive values of the displacements indicate uplift in the measured corner; negative displacements indicate that the measured corner was pressed in under the initial level of anchorage. The diagrams are generated directly from displacements measured to control the rotation of the stabilising wall. The designations and illustrations of relevant displacements transducers are visible on the figures. 27

36 Glued-in rods 25 3A-3 2 3A-7 3B-3 3B-7 1F-7 2C-7 2C B-3 1D-7 1F-3 LOAD 2B-7 5 1D vertical displacement [mm] Figure 4.2: Load vs. vertical displacements at the bottom corners of samples due to rotation, series 1 Nail plates 18 5B-2 5A- 4C A-2 4C- 5B- 14 6B B- 6A- 4D A-2 LOAD 6 4 4B vertical displacement [mm] Figure 4.3: Load vs. vertical displacements at the bottom corners of samples due to rotation, series Horizontal translation Glued-in rods The horizontal translation of samples in series 1 was controlled by LVDT 5 and the curves in Figure 4.4 are generated directly from its measurements. 28

37 25 3A-5 2 3B-5 1F-5 2B C-5 LOAD 1 1D horizontal displacement [mm] Figure 4.4: Load vs. horizontal translation of the stabilising element, series 1 Nail plates The horizontal translation of samples from the second series (with nail plates) was calculated as the difference of the absolute values of the displacements measured at the bottom of the sample on both sides (Figure 4.5). δ transl = abs abs( δ 14 ) abs( δ ))[ mm] ( L A positive value of translation indicates right direction of displacement, and negative value left B 4C 4B 14 5A 12 6B 1 8 LOAD 6A horizontal displacement [mm] Figure 4.5: Load vs. horizontal translation of stabilising elements, series 2 (test 4-6) 29

38 4.3 Displacements at the anchorage joints Glued-in rods Since the stands of displacements transducers, 2, 3 and 7 (Figure 4.6) were placed on the floor, the vertical displacements at the anchorage joints can be calculated as differences displacements between points located on the Kerto board (sheathing) just above the steel profile ( and 2) and displacements induced in the steel rig (3 and 7). Thus, the formulas for vertical displacements at right and left joints are as follows: δ δ R L = δ = δ 2 δ δ 3 7 [mm] [mm] Compression side 25 Tension side 3A-R 2 3A-L B-L 3B-R 15 1F-L 1F-R 1 1D-R 1D-L 5 2C-L 2B-R 2C-R 2B-L vertical displacement [mm] Nail plates Figure 4.6: Load vs. displacements at the anchorage joints of stabilising elements, series 2 (test 4-6) Similarly as for the previous case, the stands of displacements transducers, 2, 7 and 8 (Figure 4.7) were placed on the floor, the vertical displacements at the anchorage joints can be calculated as differences displacements between points located on the specimen s body ( and 2) and displacements induced in the steel rig (7 and 8). Thus, the formulas for vertical displacements at right and left joints are as follows: δ δ R L = δ = δ 2 δ δ 7 18 [mm] [mm] 3

39 Compression side 18 Tension side 5B-R 4C-R 5A-L 16 4B-R 4C-L 5A-R 5B-L 14 6B-R 12 6B-L 4B-L 1 8 6A-R 6A-L vertical displacement [mm] Figure 4.7: Load vs. displacements at the anchorage joints of stabilising elements, series 2 (test 4-6) 4.4 Out-of-plane displacements During the experiment the out-of-plane displacements were measured at the top corners of the stabilising element to control if buckling occurred. No such tendencies were observed. Figure 4.8: Displacement transducer for measuring the out-of-plane displacement of the left top corner of SE Table 12 presents the out-of-plane displacements at the maximal loads. Negative value indicates movement upwards, and positive movement downwards. 31

40 Table 12: Out-of-plane displacements at ultimate loads Test Right corner L3 Left corner L6 [mm] [mm] 1D F B C A B B C A B A B At failure load the out-of-plane displacements varied between.11 and 3.2 mm for samples with glued-in rods, and between.22 and 4.1 mm for samples with nail plates. The larger out-of-plane displacements for samples with nailed connections are caused by larger deformations at these joints at failure. In case of samples with glued-in rods, despite of failures of the anchorage joints, the anchored rods remained inside the elements. 32

41 5. FINAL REMARKS 5.1 Production of the walls Figure 2.2 suggests that the technology of production of the stabilising walls has a large improvement potential. One could expect the quality of these elements to be high, but errors were probably dependent on the following factors: - manual production (human factor), - lack of connections between members of the inner skeleton, 5.2 Assessment of samples with glued-in rods One of the general conclusions that can be drawn from the experiment and the further (post experiment) examination of the samples is that the gluing process requires improvements Failure modes The dominating (in almost 1%) failure mode was pull out of the screws with a certain amount of wooden fibres, ranging from a very thin layer and finishing with larger shear blocks of wood. (a) (b) (c) Figure 5.1: Observations of failures (a) plug of glue at the bottom of the hole,(b) visible space between edge of the hole and the screw (c) well glued-in rod One of the effects that could have influenced the joints is drying of the wood. Drying most probably caused an increase of the hole, which resulted in weakening the joint without loading. In Figure 5.1b it can be observed that there is a space between the adhesive layer and the surrounding wood. This kind of effect is most probably difficult to avoid Bonding areas An examination of the rods showed that the area of the effective adhesive bond in the connections is quite low, see Table

42 Table 13: Screws removed from the connections (the rods are shown in the same position as they were located in the anchorage joint) up up T1-L down up T1-R down up down down T2-L T2-R up up down down T3-L T3-R 34

43 5.2.3 Relation between the real bonding area and failure loads One possible suggestion for improving the gluing process, since the analysis of the samples showed insufficiency of adhesive in the space between wood and rod, is to calculate the required amount of the adhesive that needs to be injected in the hole before inserting rod. A quantitative assessment of the joints was made with respect to obtained loads and visually estimated amount of adhesive. The results are presented in Table 14 and they do not indicate a direct proportionality between the area of adhesive and the failure loads. A detailed quantitative analysis would be required, directly related to the stress distribution in the adhesive joint and its length. Table 14: Quantitative comparison of joint areas with failure loads Test assignation Connection Ultimate horizontal load [kn] Tensile load in anchorage device [kn] Area of adhesive T1D T1-L % T1F T1-R % T2A T2-R % T2C T2-L % T3A T3-R % T3B T3-L % Recommendations for future production If the manufacturing method with oversized hole is used, some requirements are recommended to obtain high quality connections. The amount of adhesive that is applied into the bottom of the hole should be well defined and respected. Also the length of the hole should be adjusted to the amount of adhesive. The rod should be inserted under quite large pressure with simultaneous rotation of the rod to assure uniform spreading of the adhesive. Generally, it is recommended to use some equipment, since the force needed for larger rods can be large and not possible to apply manually. Moreover, the interior of the hole should be well cleaned from sawdust and the adhesive s viscosity should be adjusted to allow even distribution of the adhesive up to the entrance of the hole. 5.3 Assessment of samples with nail joints The joints with nail plates were generally produced without agreement with the instructions and production drawings, which causes some difficulties in comparing the experimental results with theoretical calculations. Nail plates were cut out from a larger arch of a standard plate with holes and because of that the connections were not identical. They were also unsymmetrical (Figure 5.2) and with different number of holes and nails (Figure 5.3). Regarding the number of nails the instructions were not followed either and all the holes present in the plates were used for nailing, even cut holes on the edges of some plates. 35

44 Figure 5.2: Examples of unsymmetrical connections Figure 5.3: Connection with 5 rows of nails instead of 6 According to the instruction (Figure 5.3) the number of nails in each joint should be 89, in reality the number of nails varied between 9 and 18 nails (Table 15). Table 15: Number of nails in connections (type 2) Connection Test Total number of nails Designed number of nails Ultimate horizontal load [kn] Tensile load in anchorage device [kn] T4-L 4C T4-R 4B T5-L 5B T5-R 5A T6-L 6B T6-R 6A For such large samples, the influence of the differences in the joints is not decisive; however the fact of existing differences will definitely make the analysis of results more difficult and indirect. In the design stage of experiment, the shear plug failure was not taken into consideration. The theoretical calculations can be found in Appendix D. 36

45 6. Conclusions and discussion The general observation from the experiments is that in the cases of specimens anchored with connections with glued-in rods the large strength (load capacity) of the joint caused the stabilising element to deform under the load. In the case of samples anchored with nail plates, the relatively weaker (in relation to the wall) joint responded immediately and the major part of deformation occurred in the anchorage joint (with other words: rotation of the element took place rather than deformation). Anchorage with glued-in rods The anchorage connections with glued-in steel rods are strong and stiff connections. However, there are some unfavourable features of these connections. First of all, the failure of pulled joints is brittle and sudden. Secondly, the production of the joint awakes doubts and is difficult to control. Additionally, the presence of the steel profiles in the connections adds an element which behaviour should be controlled and also will demand weather and fire protection in real applications. The application of connection with glued-in rods is limited by the building standards to climate class 1 and 2, and design recommendations are currently not presented in any design code. Anchorage with nail plates The connections with nail plates can be successfully used for anchoring the stabilising walls for a beam and post system in timber. The connections have a relatively large freedom of design and the desired performance can be obtained, e.g. the failure mode can be modelled by for example changing the number of nails and the distances between them. The connections develop a ductile behaviour when failing and these are well-known low-cost solutions. The disadvantage is the large number of nails that will need to be mounted during assembly, but on the other hand the solution is cheap and can be realized on the building site (does not require special environmental conditions). 37

46 References Blass, H. J., Aune, P., Choo, B. S., Görlacher, R., Griffiths, D. R., Hilson, B. O., Racher, P. and Steck, G. (1995). STEP 1 Basis of design, material properties, structural components and joints. Centrum Hout, Almere, The Netherlands. Boverkets Konstruktionsregler (BKR), BFS 1993:58 med ändringar t.o.m. BFS 1998:39, (1998) Boverket, Karlskrona. COMITÉ EUROPÉEN DE NORMALISATION CEN ( Dec 23). Final draft pren Eurocode 5 Design of timber structures, Part 1-1: General -Common rules and rules for buildings. Dimensionering genom provning (1994) Handbok, Boverket, Karlskrona. ISO (E). Wood determination of moisture content for physical and mechanical tests. International Organization for Standardization, Switzerland. ISO (E). Wood determination of density for physical and mechanical tests. International Organization for Standardization, Switzerland. Kerto brochure - product specification (26/1) [Online]. Finnforest Finland. Available: [Accessed ]. Källsner, B. and Girhammar, U. A. (28). Horizontal stabilising of light frame timber structures. Plastic design of wood-framed shear walls. SP Technical Research Institute of Sweden, 28:47. (in Swedish) Peikko Produktkatalog 29/21, Available: [Accessed ] Thelandersson, S. & Larsen, H. J. (eds.) (23). Timber Engineering, The Atrium, Southern Gate, Chichester: John Wiley&Sons Ltd. Tlustochowicz, G. (28). Stommontaget av ett demonstrationshus byggt i pelar-balk system i limträ. Technical report 28:2, Luleå, Division of Structural Engineering. Vessby, J. (28). Shear walls for multi-storey timber buildings. Licenciate thesis, School of Technology and Design Växjö University 38

47 Appendix A - Density and moisture content results Specimen Initial Density Final Volume Material weight during testing weight w [%] [g] [cm3] - [kg/m3] [g] - T4-L A Glulam % T4-L B Glulam % T4-L C Glulam % T4-L D Kerto-Q 27mm % T4-L E Kerto-Q 27mm % T4-L F Kerto-Q 27mm % T4-R A Glulam % T4-R B Glulam % T4-R C Glulam % T4-R D Kerto-Q 27mm % T4-R E Kerto-Q 27mm % T4-R F Kerto-Q 27mm % T5-L A Glulam % T5-L B Glulam % T5-L C Glulam % T5-L D Kerto-Q 27mm % T5-L E Kerto-Q 27mm % T5-L F Kerto-Q 27mm % T5-R A Glulam % T5-R B Glulam % T5-R C Glulam % T5-R D Kerto-Q 27mm % T5-R E Kerto-Q 27mm % T5-R F Kerto-Q 27mm % T6-L A Glulam % T6-L B Glulam % T6-L C Glulam % T6-L D Kerto-Q 27mm % T6-L E Kerto-Q 27mm % T6-L F Kerto-Q 27mm % T6-R A Glulam % T6-R B Glulam % T6-R C Glulam % T6-R D Kerto-Q 27mm % T6-R E Kerto-Q 27mm % T6-R F Kerto-Q 27mm % 39

48 4

49 Appendix B Instrumentation of the samples with anchorage type 1 Detalj A 1 2 [3] [6] Detalj B Channel LVDT Specification 1 - Applied load 2 - Applied displacement 3,6 T1,T1 Lateral displacement at the top corners of the wall 4,7 L2T1,L5T1 Longitudinal displacements at the top corners of the wall 5,8 L3T1, L6T1 Displacements out of plane at top corners of the wall 9,1 T5, T5 Lateral displacement at the mid-height 11,13 L9T1, 1T1 Lateral displacement at the anchorage points 12,14 T25, 2T25 Longitudinal displacements at the anchorage points 16,18 4T1, T1 Lateral displacement at the approximate height of bonded-in anchorage bolts 15,19 3T1, 7T1 Control longitudinal displacement at the anchorage surface 17 5T1 Control lateral displacement at the anchorage surface Detail A Detail B 41

50 42

51 Appendix C Instrumentation of the samples with anchorage type 2 Detalj A 1 2 [3] [6] Detalj B Channel LVDT Specification 1 - Applied load 2 - Applied displacement 3,6 T1,T1 Lateral displacement at the top corners of the wall 4,7 L2T1,L5T1 Longitudinal displacements at the top corners of the wall 5,8 L3T1, L6T1 Displacements out of plane at top corners of the wall 9,1 T5, T5 Lateral displacement at the mid-height 11,13 L9T1, 1T1 Lateral displacement at the anchorage points 12,14 T25, 2T25 Longitudinal displacements at the bottom point of the wall 15,17 3T1, 5T1 Relative longitudinal displacement between nailing plates and wall element 16,18 4T1, T1 Lateral displacement at the height of 3 cm 19,2 7T25, 8T25 Control lateral displacement at the anchorage surface (bottom of the horizontal plate) Detail A Detail B 43