Seismic Behaviour of Cross-Laminated Timber Buildings

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UNIVERSITÀ DEGLI STUDI DI TRIESTE

XXV CICLO DEL DOTTORATO DI RICERCA IN CORSO DI DOTTORATO IN INGEGNERIA CIVILE E

AMBIENTALE

Seismic Behaviour of Cross-Laminated Timber Buildings

SSD: ICAR/09 - Tecnica delle Costruzioni

DOTTORANDO Igor Gavric

COORDINATORE Prof. Claudio Amadio

SUPERVISORE DI TESI Prof. Massimo Fragiacomo

CO-SUPERVISORE DI TESI Prof. Ario Ceccotti

ANNO ACCADEMICO 2011 / 2012

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ABSTRACT

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Cross-laminated timber, also known as X-Lam or CLT, is well established in Europe as a construction material. Recently, implementation of X-Lam products and systems has begun in countries such as Canada, United States, Australia and New Zealand. So far, no relevant design codes for X-Lam construction were published in Europe, therefore an extensive research on the field of cross-laminated timber is being performed by research groups in Europe and overseas. Experimental test results are required for development of design methods and for verification of design models accuracy.

This thesis focuses on the continuation of SOFIE research project which started in 2005, conducted by IVALSA Trees and Timber Research Institute (San Michele all' Adige, Trentino, Italy). The aim of this project is the development of multi-storey timber building systems using prefabricated cross-laminated panels. As several parts of Italy are earthquake- prone areas, seismic resistance of such building system has to be ensured. Thus, within the scope of the SOFIE project, an extensive experimental research on seismic resistance of X- Lam building system has been performed. The project started with performance of racking tests on wall panels with different layouts of connections and openings and pseudo-dynamic tests on a full scale one-storey building, continued with shaking table tests on a 3-storey building and on a 7-storey building, the latter one conducted at E-Defense facility in Miki, Japan. Experimental tests provided excellent outcomes, as the buildings were able to survive a series of strong recorded earthquakes, such as Kobe earthquake (1995), virtually undamaged, while at the same time demonstrating significant energy dissipation.

In the scope of this thesis, an extended experimental programme on typical X-Lam connections was performed at IVALSA Research Institute. In addition, cyclic tests were carried out on full-scale single and coupled cross-lam wall panels with different configurations and mechanical connectors subjected to lateral force. The outcomes of these tests were used for evaluation of mechanical properties, ductility ratio, energy dissipation, and impairment of strength, which are all needed in seismic design and are currently not provided

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ii by codes of practice such as the Eurocode 8. In addition, analytical models to predict stiffness and strength at different building levels such as connections, wall systems and entire buildings were developed. Further, capacity design method for X-Lam buildings was introduced and was verified with extensive database of experimental results. In the capacity design, overstrength factors are needed, thus these factors were evaluated based on experimental tests on X-Lam subassemblies.

Experimental results served also for calibration of advanced component FE models for non-linear static and dynamic numerical analyses of X-Lam walls and buildings, developed at the University of Trieste. Numerical analysis of X-Lam wall systems using the FE model was carried out in order to extend the results of the experimental tests to different configurations of technical interest. Outcomes of the parametric study provided better understanding of the seismic behaviour and energy dissipation capacities of X-Lam wall systems.

It was concluded that the numerical and analytical models, presented in this thesis, are a sound basis for determining the seismic response of cross-laminated timber buildings.

However, future research is required to further verify and improve these prediction models.

Keywords: Cross-laminated timber panels, Experimental cyclic tests, Joints with mechanical fasteners, Seismic behaviour of X-Lam panels, Finite Element analyses

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SOMMARIO

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Il legno lamellare a strati incrociati, conosciuto anche come X-Lam o CLT, è ormai ben affermato in Europa come materiale da costruzione. Recentemente, questo materiale è stato introdotto anche in paesi extraeuropei come il Canada, gli Stati Uniti d‘America, l‘Australia e la Nuova Zelanda. Tuttavia, finora questo materiale non è stato incluso nelle norme di calcolo europee quali gli Eurocodici. Pertanto, una vasta ricerca sul campo delle costruzioni a pannelli in X-Lam è in corso di esecuzione da parte di gruppi di ricerca Europei e d‘oltreoceano. Risultati di prove sperimentali sono necessari per lo sviluppo di metodi di progettazione e per la verifica della precisione dei modelli di calcolo proposti.

Questa tesi si concentra sul proseguimento del progetto di ricerca SOFIE, che è iniziato nel 2005 ad opera del CNR-IVALSA - Consiglio Nazionale delle Ricerche - Istituto per la Valorizzazione del Legno e delle Specie Arboree (San Michele all 'Adige, Trentino, Italia).

Lo scopo di questo progetto è lo sviluppo di edifici multipiano in legno con l'utilizzo di pannelli prefabbricati a strati incrociati. Poichè molte zone del territorio Italiano sono ad alta sismicità, la resistenza al sisma di tale sistema di costruzione è un requisito essenziale che deve essere garantito. Per questa ragione, nell‘ambito del progetto SOFIE è stata eseguita una vasta ricerca sperimentale sulla resistenza sismica di edifici a pannelli in X-Lam . La ricerca è iniziata con l'esecuzione prove di carico laterale su pannelli a parete con diverse configurazioni delle connessioni e delle aperture, ed è continuata con delle prove pseudo- dinamiche su un edificio a un piano in scala reale. Successivamente si è passati alle prove sismiche su tavola vibrante di un edificio di 3 piani e di un edificio di 7 piani, queste ultime condotte presso il laboratorio della E-Defense a Miki, in Giappone. Le prove sperimentali hanno fornito risultati eccellenti, in quanto gli edifici sono stati tutti in grado di sopravvivere a una serie di forti terremoti quali quello di Kobe (1995) rimanendo praticamente intatti, e allo stesso tempo dimostrando significativa dissipazione di energia.

In questa tesi, un vasto programma di prove sperimentalei è stato eseguito presso l‘Istituto di ricerca IVALSA sui sistemi di connessione tipici delle strutture in X-Lam. Inoltre, sono state eseguite prove cicliche su pareti in cross-lam singole e accoppiate in scala reale con

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iv diverse configurazioni e connettori meccanici sottoposte a carichi laterali. I risultati di queste prove sono stati utilizzati per valutare le proprietà meccaniche, duttilità, dissipazione di energia, e degrado della resistenza dei pannelli, proprietà necessarie alla progettazione sismica e attualmente non fornite dalle normative di calcolo quali l'Eurocodice 8. Inoltre, modelli di analisi per la previsione della rigidezza e della resistenza sono stati sviluppati a livelli diversi quali ad esempio le connessioni, le pareti, e l‘intero edificio. La progettazione per capacità, o ―Capacity base design‖, è stata introdotta e verificata sulla base di un vasto database di risultati sperimentali. Inoltre, i fattori di sovraresistenza che sono necessari per la progettazione di capacità sono stati determinati sulla base di prove sperimentali eseguite sulle connessioni per i pannelli X-Lam.

I risultati sperimentali sono serviti anche per la calibrazione di un modello avanzato ad elementi finiti per componenti per le analisi numeriche statiche e dinamiche non lineari di pareti ed edifici in X-Lam sviluppato presso l'Università degli Studi di Trieste. Analisi numeriche sono state eseguite con lo scopo di estendere i risultati delle prove sperimentali a diverse configurazioni di interesse tecnico. I risultati dello studio parametrico hanno fornito una migliore comprensione del comportamento sismico e della capacità di dissipazione energetica di sistemi a pareti in X-Lam.

I modelli numerici e analitici presentati in questa tesi rappresentano una solida base per la determinazione della risposta sismica di edifici lignei a pannelli in legno lamellare incrociato.

Ulteriore ricerca è necessaria per verificare e migliorare i modelli di previsione.

Parole chiave: Pannelli in legno lamellare incrociato, Prove sperimentali cicliche, Giunti con connettori meccanici, Comportamento sismico di pareti in X-Lam, Analisi agli elementi finiti

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ACKNOWLEDGMENTS

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This thesis would not be possible without the financial support of several organizations. PhD research grant form University of Trieste and CNR-IVALSA Trees and Timber Institute is greatly appreciated. Final part of my studies was financially supported with a research grant from University of Sassari.

First, I would like to express my sincere gratitude to my both PhD supervisors for giving me possibility to be part of this very interesting research project. Participation in national and international conferences, presenting the outcomes of our research work and spending productive work periods in Canada and New Zealand are greatly acknowledged.

My main supervisor, Prof. Massimo Fragiacomo, guided me through my PhD research period with great dedication and enthusiasm. His insight, advice and ideas have been extremely valuable to the outcomes of this research project. Encouragement, availability, patience and help from his side are deeply appreciated. Massimo, thank you for being such a great advisor. Further deep gratitude is extended to my co-supervisor, Prof. Ario Ceccotti, who guided me during my research period at CNR-IVALSA Trees and Timber Institute. Prof.

Ceccotti provided me with very valuable advice and suggestions for my experimental research work and shared with me his ideas and his rich experiences. He allowed me to be part of his research group, which helped me gain precious experiences and knowledge.

‗Professore‘, thank you for everything you have done for me. Thanks are also expressed to the staff of CNR-IVALSA for their help with preparations and running all my experimental tests.

I would also like to express my sincere thanks to Dr. Bruno Dujič for his guidance, support and advice during my graduate studies, and his encouragement for continuation of my research work in the timber engineering field.

Further acknowledgement is extended to Dr. Marjan Popovski from FPInnovations, Vancouver, for hosting me during my research visit period. His hospitality, kindness and professional guidance during my four months stay are deeply appreciated.

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vi I am also grateful to COST organization who granted me STSM (Short term scientific mission) research grant for a research visit to University of Canterbury in New Zealand.

Gratitude is extended to Prof. Richard Harris, chairman of COST FP1004 action, who provided his support before and during the grant application process. Special thanks go to Prof. Geoff Chase and Dr. Geoff Rodgers from the Mechanical Engineering Department of the University of Canterbury for their hospitality during my research visit and to Prof. Andy Buchannan form Civil Engineering Department for his valuable advice.

I would also like to acknowledge the invitation of Dr. Simon Aicher from MPA Otto Graf Institute, University of Stuttgart, for collaboration in their research project in scope of my Doctor Europaeus research period.

Also many thanks to all my fellow PhD students, especially to Giovanni Rinaldin and Agnese Menis, who assisted me many times and gave me support in different ways.

My very deepest gratitude to my nearest: my parents and my brother, who showed me true values of life and supported me all the time during my studies, and to my friends, who were always there for me when I needed them. Finally, I would like to thank my dearest Tatiana, for all her love, patience, understanding, constant encouragement and precious presence in my life.

Igor Gavrić

Trieste, March 2013

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LIST OF FIGURES

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Figure 2.1 Cross-laminated timber panel (ETA-06/0138, 2006) ... 6 Figure 2.2 Examples of different cross-sections of X-Lam panels (ETA-06/0138 2006) ... 8 Figure 2.3 Manufacturing process of X-Lam panels (FPInnovations, 2013) ... 11 Figure 2.4 Typical three-storey X-Lam building showing various connections between

the X-Lam panels ... 17 Figure 2.5 Typical wall-to-foundation X-Lam connections: (a) Connection with an

exposed metal plate; (b) Connection with a concealed connector; (c) Connection with a wooden profile (FPInnovations, 2013) ... 19 Figure 2.6 Typical parallel wall-to-wall X-Lam connections: (a) Connection with an

internal spline; (b) Connection with a surface spline; (c) Connection with a half-lapped joint; (d) Tube connection system (FPInnovations, 2013) ... 21 Figure 2.7 Typical perpendicular wall-to-wall X-Lam connections: (a) Connection

with self-tapping screws; (b) Connection with a wooden profile; (c) Connection with a metal bracket; (d) Connection with a concealed metal plate (FPInnovations, 2013) ... 22 Figure 2.8 Typical wall-to-floor X-Lam connections: (a) Connection with self-tapping

screws; (b) Connection with a metal bracket; (c) Connection with concealed metal plates (FPInnovations, 2013) ... 23 Figure 2.9 Typical wall-to-floor X-Lam connections in balloon construction

(FPInnovations, 2013) ... 24 Figure 2.10 Typical wall-to-roof X-Lam connections (FPInnovations, 2013) ... 25 Figure 2.11 Sihga Idefix innovative conncetion system (Sihga) ... 26 Figure 2.12 Residential and non-residential X-Lam projects: (a) 10-storey Forté in

Melbourne; (b) 9-storey Stadthaus in London; (c) Open Academy in Norwich (KLH) ... 28 Figure 2.13 Structural configurations of four possible options: (a) 12-storey building

with core only; (b) 20-storey building with core and interior shear walls; (c)

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xii 20-storey building with core and perimeter moment frames; (d) 30-storey building with core, perimeter moment frames and interior walls (Green, 2012) ... 30 Figure 3.1 (a) WHT Hold-down connector; (b) BMF 90x116x48x3 angle bracket; (c)

BMF 100x100x90x3 angle bracket ... 42 Figure 3.2 (a) Annular ringed nail Φ 4x60 mm, type Anker; (b) An example of a self-

drilling HBS screw ... 43 Figure 3.3 Test setup for wall-foundation hold-down connection loaded in tension (Test

1, left); test setup for wall-foundation angle bracket connection loaded in tension (Test 5, right); measures are in mm. ... 43 Figure 3.4 Test setup for wall-foundation hold-down connection loaded in shear (Test

3, left); test setup for wall-foundation angle bracket connection loaded in shear (Test 7, right); measures are in mm. ... 44 Figure 3.5 Test setup for wall-floor hold-down connection loaded in tension (Test 2,

left); test setup for wall-floor angle bracket connection loaded in tension (Test 6, right); measures are in mm. ... 45 Figure 3.6 Test setup for wall-floor hold-down connection loaded in shear (Test 4,

left); test setup for wall-floor angle-bracket connection loaded in shear (Test 8, right); measures are in mm. ... 45 Figure 3.7 Test setups for in-plane shear tests of screwed connections between

adjacent wall- and floor panels (Test setups 9, 19 and 19); measures are in mm. ... 46 Figure 3.8 Test setups for in-plane tests of screwed connections between adjacent wall-

and floor panels loaded in axial direction (Test setups 11, 12 and 20);

measures are in mm. ... 47 Figure 3.9 Test setups for orthogonal wall-wall panel screwed connection (Test 13)

and orthogonal wall-floor panel screwed connection (Test 16) loaded in the direction of the longer side of the panel edge; measures are in mm. ... 48 Figure 3.10 Test setups for orthogonal wall-wall panel screwed connection (Test 14)

and orthogonal wall-floor panel screwed connection (Test 17) loaded in the direction of the shorter side of the panel edge; measures are in mm. ... 49

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Figure 3.11 Test setups of wall-wall (Test 15) and wall-floor (Test 18) screwed connections loaded in withdrawal direction; measures are in mm. ... 49 Figure 3.12 Typical hysteresis loops and monotonic curves: (a) Test 1; (b) Test 3 ... 50 Figure 3.13 Wall-foundation hold-down connection loaded in tension (Test 1, (a));

Wall-foundation hold-down connection loaded in shear (Test 3, (b)) ... 51 Figure 3.14 Typical hysteresis loops and monotonic curves: (a) Test 2; (b) Test 4 ... 51 Figure 3.15 Wall-floor hold-down connection loaded in tension (Test 2, (a)); Wall-floor

hold-down connection loaded in shear (Test 4, (b)) ... 52 Figure 3.16 Typical hysteresis loops and monotonic curves: (a) Test 5; (b) Test 7 ... 54 Figure 3.17 Wall-foundation angle bracket connection loaded in tension (Test 5, (a));

Wall-foundation angle bracket connection loaded in shear (Test 7, (b), (c)) ... 55 Figure 3.18 Typical hysteresis loops and monotonic curves: (a) Test 6; (b) Test 8 ... 56 Figure 3.19 Wall-floor angle bracket connection loaded in tension (Test 6, (a)); Wall-

floor angle bracket connection loaded in shear (Test 8, (b)) ... 56 Figure 3.20 Typical hysteresis loops and monotonic curves: (a) Test 9; (b) Test 10 ... 58 Figure 3.21 Half-lap screwed in-plane wall-wall panel connection loaded in shear (Test

9, (a)); LVL Spline screwed in-plane wall-wall panel connection loaded in shear (Test 10, (b)) ... 58 Figure 3.22 Typical hysteresis loops and monotonic curves: (a) Test 11; (b) Test 12 ... 60 Figure 3.23 Half-lap screwed in-plane wall-wall panel connection loaded in axial

direction (Test 11, (a)); LVL Spline screwed in-plane wall-wall panel connection loaded in axial direction (Test 12, (b)) ... 61 Figure 3.24 Typical hysteresis loops and monotonic curves: (a) Test 19; (b) Test 20 ... 62 Figure 3.25 Half-lap screwed in-plane floor-floor panel connection loaded in shear

(Test 19, (a)); Half-lap screwed in-plane floor-floor panel connection loaded in axial direction (Test 20, (b)) ... 62 Figure 3.26 Typical hysteresis loops and monotonic curves: (a) Test 13; (b) Test 14 ... 64 Figure 3.27 Orthogonal wall-wall panel screwed connection loaded in the direction of

the longer side of the panel edge (Test 13, (a)); Orthogonal wall-wall panel screwed connection loaded in the direction of the shorter side of the panel edge (Test 14, (b)) ... 64

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xiv Figure 3.28 Typical hysteresis loops and monotonic curves: (a) Test 16; (b) Test 17 ... 65 Figure 3.29 Orthogonal wall-floor panel screwed connection loaded in the direction of

the longer side of the panel edge (Test 16, (a)); Orthogonal wall-wall panel screwed connection loaded in the direction of the shorter side of the panel edge (Test 17, (b)) ... 66 Figure 3.30 Typical hysteresis loops and monotonic curves: (a) Test 15; (b) Test 18 ... 68 Figure 3.31 Orthogonal wall-wall panel screwed connection loaded in withdrawal

direction (Test 15, (a)); Orthogonal wall-floor panel screwed connection loaded in withdrawal direction (Test 18, (b)) ... 68 Figure 3.32 Set-up for withdrawal tests with screws positioned perpendicular to the

plane of the X-Lam panel (1.1-1.4); Set-up for edge withdrawal tests with screws in the X-Lam panel (A-C), (Uibel & Blaß, 2007) ... 72 Figure 3.33 Comparison between test results of X-Lam metal connectors and calculated

characteristic load carrying capacities ... 76 Figure 3.34 Comparison between test results of X-Lam screwed connections positioned

perpendicular to the plane and calculated load-carrying capacities ... 77 Figure 3.35 Comparison between test results of X-Lam screwed connections positioned

in the narrow side of the panels and calculated characteristic load-carrying capacities ... 79 Figure 3.36 Undesired (brittle) failures modes of X-Lam connections: yielding of steel

part of angle bracket with nails withdrawal (a), failure of steel part of hold- down (b), and pull-through of the bolt in the steel part of angle bracket (c) ... 86 Figure 3.37 Piecewise linear relationship of screws and angle bracket springs (left, (a))

and hold-down springs (right, (b)), Rinaldin (2011) ... 90 Figure 3.38 Strength domain (left, (a)) and friction force at constant axial load (right,

(b)), Rinaldin (2011) ... 92 Figure 3.39 (a) Calibration of angle bracket springs in shear direction (Test 7); (b)

calibration of hold-down springs in axial direction (Test 1) ... 93 Figure 4.1 Test setup with measurement instruments ... 102 Figure 4.2 Wall panel test configurations – single wall (a) and coupled wall panel with

LVL strip joint (b) (measures in mm) ... 103

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Figure 4.3 Experimental setup of full-scale X-Lam wall panels subjected to horizontal load - single wall (a) and coupled wall with LVL spline vertical joint (b) ... 104 Figure 4.4 (a) Failure of wall panel 1.1 (sliding behaviour); (b) buckling of the hold-

down due to exceeded horizontal displacements; (c) shear failure of the angle bracket ... 106 Figure 4.5 (a) Wall panel 1.2 before testing; (b) rocking behaviour of the panel in the

initial phase of loading; (c) failure of the wall panel due to a combination of rocking and sliding ... 107 Figure 4.6 (a) Wall panel 2.3 with the so called ‘coupled wall behaviour’; (b)

transducers placed in the central part of the panel to measure the vertical displacements; (c) shear failure of self-threaded screws used to connect adjacent wall panels within the vertical joint ... 108 Figure 4.7 Time history of dissipated energy during the cycling loading of single wall

panels and coupled wall panels ... 109 Figure 4.8 (a) Comparison of force-displacement backbone curves; (b) comparison of

dissipated energy of wall tests 3.1, 3.5 and 3.6 ... 111 Figure 4.9 X-Lam wall panel subjected to vertical and horizontal load (Hi = hold-

down, Ai = angle bracket) ... 113 Figure 4.10 Non-linear static constitutive relationships in axial direction for hold-

downs (a) and angle brackets (b) ... 114 Figure 4.11 Displacement of wall panel due to rocking (left) and bending (right). ... 115 Figure 4.12 Displacement of wall panel due to shear deformation (a) and slip (b) ... 117 Figure 4.13 Hysteresis curves of top horizontal displacement and analytical predictions

for wall panel 1.1 (a) and wall panel 1.2 (b) ... 118 Figure 4.14 Hysteresis curves of bottom vertical displacement (uplift) and analytical

predictions for wall panel 1.1 (a) and wall panel 1.2 (b) ... 119 Figure 4.15 Hysteresis curves of bottom horizontal displacement and analytical

predictions for wall panel 1.1 (a) and wall panel 1.2 (b) ... 119 Figure 4.16 Mesh and springs used to model the Panel 1.2. (a) and an example of

deformed shape predicted in the numerical analysis (b) ... 123

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xvi Figure 4.17 Numerical-experimental comparison on cyclic behaviour of X-Lam panel

1.1 (a) and panel 1.2 (b) ... 124 Figure 4.18 Numerical-experimental comparison on cyclic behaviour of X-Lam panel

2.1 (a) and 3.1 (b) ... 125 Figure 4.19 Numerical-experimental comparison of time-history of the total dissipated

energy during the cyclic tests on X-Lam panel 1.2 (a) and 2.1 (b) ... 126 Figure I.1 (a) Floor panels, used from the 7-storey SOFIE building; (b) wall panels,

used from CNR-IVALSA wall tests ... 141 Figure II.1 (a) Steel frame with steel foundation beam; (b) drilling a threaded hole for

bolted anchorage of metal connectors (hold-downs, angle brackets) ... 219 Figure II.2 (a) Rollers in vertical direction for imposing vertical loads, and rollers in

horizontal direction for prevention of out-of-plane rotations of wall panels;

(b) hydraulic actuator for imposing controlled lateral displacements of wall panels ... 220 Figure II.3 (a) Adjacent wall panels tightened with straps, prepared to be attached

with screws; (b) half lap joint for connecting two wall panels ... 221 Figure II.4 (a) wall panel with a steel bar attached on the top; (b) wall panel placed

and attached onto the steel frame ... 221 Figure II.5 (a) Measurement instruments installed on the wall panel; (b) shear failure

of screws in the vertical LVL spline joint between two adjacent wall panels ... 222 Figure II.6 (a) Signs of embedment of nails into the panel at the position of an angle

bracket; (b) signs of embedment of nails into the panel at the position of a hold-down ... 223 Figure II.7 Input displacements for cyclic testing of X-Lam walls (EN12512, 2001) ... 223 Figure II.8 Wall test configuration 1.1 with specifications (measures in cm) ... 224 Figure II.9 Wall test 1.1: (a) dissipated energy vs. time; (b) dissipated energy of each

half-cycle vs. time; (c) equivalent viscous damping (positive side); (d) equivalent viscous damping (negative side); (e) strength degradation (positive side); (f) strength degradation (negative side) ... 225 Figure II.10 Wall test 1.1: (a) dissipated energy vs. time; (b) dissipated energy of each

half-cycle vs. time; (c) equivalent viscous damping (positive side); (d)

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equivalent viscous damping (negative side); (e) strength degradation (positive side); (f) strength degradation (negative side) ... 226 Figure II.11 Wall test configuration 1.2 with specifications (measures in cm) ... 227 Figure II.12 Wall test 1.2: (a) dissipated energy vs. time; (b) dissipated energy of each

half-cycle vs. time; (c) equivalent viscous damping (positive side); (d) equivalent viscous damping (negative side); (e) strength degradation (positive side); (f) strength degradation (negative side) ... 229 Figure II.14 Wall test configuration 1.3 with specifications (measures in cm) ... 230 Figure II.15 Wall test 1.3: (a) dissipated energy vs. time; (b) dissipated energy of each

half-cycle vs. time; (c) equivalent viscous damping (positive side); (d) equivalent viscous damping (negative side); (e) strength degradation (positive side); (f) strength degradation (negative side) ... 235 Figure II.20 Wall test configuration 2.1 with specifications (measures in cm) ... 236

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xviii Figure II.21 Wall test 2.1: (a) dissipated energy vs. time; (b) dissipated energy of each

half-cycle vs. time; (c) equivalent viscous damping (positive side); (d) equivalent viscous damping (negative side); (e) strength degradation (positive side); (f) strength degradation (negative side) ... 246

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Figure II.31 Wall test 2.4: (a) dissipated energy vs. time; (b) dissipated energy of each half-cycle vs. time; (c) equivalent viscous damping (positive side); (d) equivalent viscous damping (negative side); (e) strength degradation (positive side); (f) strength degradation (negative side) ... 247 Figure II.32 Wall test configuration 3.1 with specifications (measures in cm) ... 248 Figure II.33 Wall test 3.1: (a) dissipated energy vs. time; (b) dissipated energy of each

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xx Figure II.41 Wall test configuration 3.4 with specifications (measures in cm) ... 257 Figure II.42 Wall test 3.4: (a) dissipated energy vs. time; (b) dissipated energy of each

half-cycle vs. time; (c) equivalent viscous damping (positive side); (d)

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equivalent viscous damping (negative side); (e) strength degradation (positive side); (f) strength degradation (negative side) ... 267 Figure II.52 Wall test 4.1: (a) dissipated energy vs. time; (b) dissipated energy of each

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LIST OF TABLES

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Table 3.1 Test matrix for hold-down connections ... 34 Table 3.2 Test matrix for steel angle bracket connections ... 35 Table 3.3 Test matrix for parallel wall-wall connection details ... 36 Table 3.4 Test matrix for perpendicular wall-wall connection details ... 37 Table 3.5 Test matrix for wall-floor connection details ... 38 Table 3.6 Test matrix for floor-floor connection details ... 39 Table 3.7 X-Lam connection test configurations based on typical connections in the

3-story SOFIE building ... 40 Table 3.8 Mechanical properties of hold-down connections according to EN12512

(2001) ... 53 Table 3.9 Mechanical properties of angle bracket connections according to

EN12512, 2001 ... 57 Table 3.10 Mechanical properties of in-plane panel-panel connections loaded in

shear according to EN12512 (2001) ... 59 Table 3.11 Mechanical properties of in-plane panel-panel connections loaded in

axial direction according to EN12512 (2001) ... 63 Table 3.12 Mechanical properties of orthogonal panel-panel connections loaded in

shear according to EN12512 (2001) ... 67 Table 3.13 Mechanical properties of orthogonal panel-panel connections loaded in

withdrawal direction according to EN12512 (2001) ... 69 Table 3.14 Density of X-Lam test specimens ... 74 Table 3.15 Overstrength factors (γRd) of typical hold-down and angle bracket X-

Lam connections ... 81 Table 3.16 Overstrength factors (γRd) of typical in-plane screwed panel-panel X-

Lam connections ... 82 Table 3.17 Overstrength factors (γRd) of typical orthogonal screwed panel-panel X-

Lam connections ... 83

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Table 3.18 Basic definition of non-linear springs (Rinaldin, 2011) ... 89 Table 3.19 Calibration of mean values obtained from experimental results on X-

Lam connections ... 94 Table 4.1 Wall test configurations ... 101 Table 4.2 Measurement instruments and number of channels ... 102 Table 4.3 Mechanical properties of tested X-Lam wall panels according to

EN12512 (2001) ... 105 Table 4.4 Mechanical properties according to EN12512 (2001) and statistical

analysis of selected X-Lam wall panel tests ... 110 Table 4.5 Percentage of axial and shear forces in hold-downs and angle brackets

corresponding to the peak resistance for Wall 1 configuration and different number of connectors using the analytical method ... 120 Table 4.6 Maximum horizontal (lateral) resistance for wall 1.2 with different

number of connectors and different vertical loads ... 121 Table II.1 Mechanical properties of wall test 1.1 ... 224 Table II.2 Mechanical properties of wall test 1.2 ... 227 Table II.3 Mechanical properties of wall test 1.3 ... 230 Table II.4 Mechanical properties of wall test 1.4 ... 233 Table II.5 Mechanical properties of wall test 2.1 ... 236 Table II.6 Mechanical properties of wall test 2.2 ... 239 Table II.7 Mechanical properties of wall test 2.3 ... 242 Table II.8 Mechanical properties of wall test 2.4 ... 245 Table II.9 Mechanical properties of wall test 3.1 ... 248 Table II.10 Mechanical properties of wall test 3.2 ... 251 Table II.11 Mechanical properties of wall test 3.3 ... 254 Table II.12 Mechanical properties of wall test 3.4 ... 257 Table II.13 Mechanical properties of wall test 3.5 ... 260 Table II.14 Mechanical properties of wall test 3.6 ... 263 Table II.15 Mechanical properties of wall test 4.1 ... 266 Table II.16 Mechanical properties of wall test 4.2 ... 269

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LIST OF PUBLICATIONS

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Gavric I., Ceccotti A., Fragiacomo M. (2011a). Experimental cyclic tests on cross-laminated timber panels and typical connections. Proceedings of the 14th ANIDIS Conference, Bari, Italy.

Gavric I., Ceccotti A., Fragiacomo M. (2011b). Experimental cyclic tests on cross-laminated timber panels and typical connections. Proceedings of the 9th Grazer Holzbau- Fachtagung Conference, Graz, Austria.

Gavric I., Fragiacomo M., Ceccotti A. (2012a). Earthquake resistance of multi-storey timber buildings made of cross-laminated timber panels. Proceedings of the COST Action FP1004 Conference: Enhance mechanical properties of timber, engineered wood products and timber structures, Zagreb, Croatia.

Gavric I., Fragiacomo M. and Ceccotti A. (2012b). Strength and deformation characteristics of typical X-LAM connections. 12th World Conference on Timber Engineering, Auckland, New Zealand.

Gavric I., Rinaldin G., Fragiacomo M., Ceccotti A., Amadio C. (2012c). Experimental- numerical analyses of the seismic behaviour of cross-laminated wall systems. 15th World Conference on Earthquake Engineering, Lisbon, Portugal.

Negri M., Gavric I., Marra M., Fellin M., Cuccui I. and Ceccotti A. (2012). Using low quality timber for X-Lam: raw material characterisation and structural performances of walls under semi-dynamic solicitations. 12th World Conference on Timber Engineering, Auckland, New Zealand.

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NOTATIONS

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b Width of an X-Lam panel COV Coefficient of variation D Ductility ratio

d Fastener diameter

D₃₀ Ductility ratio at 30 mm displacement d_el Displacement at yielding force

d_kf Stiffness degradation parameter D_max Maximum displacement

D_u Ultimate displacement D_ult Ultimate displacement

d Additional displacement at reloading

Edis Dissipated energy

Edis(A) Dissipated energy at the beginning of unloading path EIeff Elastic flexural stiffness of an X-Lam panel

F0.05 Characteristic strength capacity (5^th percentile of a strength distribution) F0.95 95^th percentile of a strength distribution

F30 Force at 30 mm displacement

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xxvi F_A,a Contribution of an angle bracket in axial direction to the lateral resistance of an X-

Lam panel

F_A,s Contribution of an angle bracket in shear direction to the lateral resistance of an X- Lam panel

F_d Design strength capacity F_f Static friction force

F_H,a Contribution of a hold-down in axial direction to the lateral resistance of an X-Lam panel

fh,k Characteristic embedment strength

FH,s Contribution of a hold-down in shear direction to the lateral resistance of an X-Lam panel

Fmax Maximum load FN Axial force

FRd,b Design strength of a brittle connection FRd,d Design strength of a dissipative connection Fu Ultimate load

FV Shear force F_y Yielding load

ΔF1-3 Strength degradation between 1^st and 3^rd loading cycle GAx,eff Shear stiffness of an X-Lam panel

h Height of an X-Lam panel H Horizontal load

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xxvii

H_i Horizontal load in the step i of the loading H_min Minimum horizontal load

ΔHi Increment of the horizontal load k_A,a,i Axial stiffness of an angle bracket k_A,s,i Shear stiffness of an angle bracket k_d Dynamic friction coefficient k_deg Degraded stiffness

kel Elastic stiffness

kf Static friction coefficient kH,a,i Axial stiffness of a hold-down kH,s,i Shear stiffness of a hold-downs kp1 1^st inelastic stiffness

kp2 2^nd inelastic stiffness kpl Plastic stiffness

Ksc Unloading stiffness of branches #4 and #50 of connection spring models lef Effective point-side penetration length

M Moment

MO Overturning moment M_S Stabilizing moment N Axial (normal) force n_A Number of angle brackets

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xxviii n_H Number of hold-downs

qv Vertical load

Rax,s,k Characteristic withdrawal capacity

RC Reloading ratio of the connection spring models RN Axial strength

RV Shear strength

SC Unloading ratio of the connection spring models T Shear force

ux Horizontal displacement

Δux,i Increment of horizontal displacement uy Vertical displacement

Δu_y,i Increment of vertical displacement vmax Maximum displacement

v_u Ultimate displacement v_y Yielding displacement

x_A,i Distance of a hold-down from the lower corner of an X-Lam panel x_H,i Distance of a hold-down from the lower corner of an X-Lam panel xmean Mean value

 Exponential degradation parameter in calibration of a connection strength degradation

 Exponential degradation parameter in calibration of a connection strength degradation

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xxix

 Linear parameter in calibration of a connection strength degradation

M Strength partial factor

Rd Ovestrength ratio

b Top displacement of an X-Lam wall due to the panel bending

r Top displacement of an X-Lam wall due to the panel rocking

sh Top displacement of an X-Lam wall due to the panel shear deformation

_sl Top displacement of an X-Lam wall due to the panel horizontal slip

_tot Total top displacement of an X-Lam wall

 Angle between the screw axis and the X-Lam grain direction κ Shape reduction factor

νeq(1st) Equivalent viscous damping ratio at the 1^st loading cycles νeq(3rd) Equivalent viscous damping ratio at the 3^rd loading cycles ρk Characteristic density of cross-laminated timber panels ρ0.05 Characteristic density of cross-laminated timber panels

ρ_layer,k Characteristic density of the relevant layer of cross-laminated timber panels ρ_max Maximum density of cross-laminated timber panels

ρmean Mean density of cross-laminated timber panels ρ_min Minimum density of cross-laminated timber panels

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1

CHAPTER 1: INTRODUCTION

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CHAPTER 1

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INTRODUCTION

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1.1 Research background and motivation

Wood as a building material possesses some inherent characteristics that make timber structures particularly suited for the use in regions with a high seismic risk, both due to material properties, such as lightness and load bearing capacity (good weight-to-strength- ratio), and to system properties, like ductility and energy dissipation. Recently, there have been new developments with prefabricated timber elements, which aim to address modern building requirements for cost, constructability and structural performance.

Massive cross-laminated timber panels (X-Lam), which can be used as wall panels, floor panels or roof panels in timber buildings, are becoming stronger and economically valid alternative to traditional masonry or concrete buildings in Europe, and recently also overseas.

Especially in seismic-prone countries, X-lam buildings are gaining more and more popularity.

However, due to relatively short time since this wood engineered product has been launched to the market, the knowledge about cross-lam as a structural material is still limited.

In recent years, several research projects around Europe and in North America have been launched, with an aim to better understand the potential of cross-lam technology as a seismic resistant construction system. A large research project, called SOFIE (‗Sistema Costruttivo Fiemme‘), started to investigate, among other issues such as fire resistance, building physics and durability, the seismic behavior of multi-story X-Lam buildings. This project was born as a collaboration between the IVALSA Trees and Timber Research institute of the National Research Council (San Michele all' Adige, Italy) and the Autonomous Province of Trento (Italy). Within this project, an extensive experimental program was carried out which, in the preliminary stage, included racking tests of wall panels and sub-assemblies and pseudo-

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2 dynamic tests on a one-storey building. The results from the reversed cyclic tests on CLT wall panels showed that the connection layout and design has a strong influence on the overall behaviour of the wall.

The second phase of the project was conducted in cooperation with the National Research Institute for Earth Science and Disaster Prevention (NIED), Shizuoka University, Building Research Institute (BRI) and Centre for Better Living in Japan. A series of seismic dynamic tests were carried out in the laboratories of the NIED in Tsukuba in July 2006 on a full-scale three-storey SOFIE building. The building has survived practically undamaged a series of 15 large earthquakes, including the great Hanshin-Awaji earthquake in Kobe from 1995 at its maximum intensity showing only minimal damage which was repairable with only a couple of easy interventions.

It follows the phase started in October 2007, with full scale shake table tests on seven- story SOFIE building on the seismic testing facility E-Defense in Miki, the biggest shaking table in the world. The tests provided excellent outcomes, as the building was able to survive strong recorded earthquakes, with minimal structural damage, while at the same time demonstrating significant energy dissipation. The building survived multiple ―destructive‖

earthquakes in a row without significant repairs, and that even the quake producing a near- collapse state was not able to permanently deform the building. However, relatively high floor accelerations were recorded. These accelerations were due to the dynamic response of the high stiffness solid timber walls with relatively low weight. Thus, SOFIE buildings built with X-Lam technology proved to have a self-centering ability and showed advantageous and exceptional seismic performance.

Further research is still needed in order to better define the seismic behavior of typical X- Lam connections, as they govern the behaviour of X-Lam wall systems and entire X-Lam buildings (1-D models). In addition, behavior of single wall panels or series of adjacent wall panels (2-D models) has to be investigated in order to understand advantages and disadvantages of these two systems in terms of seismic performance in X-Lam buildings.

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3

1.2 Objectives and scope

The focus of this Ph.D. Thesis is on a continuation of the SOFIE research project on seismic behaviour and seismic design of cross-laminated timber buildings and subassemblies, such as X-Lam wall panels and typical X-Lam connections. The research work will include experimental investigation on such subassemblies, development of analytical models and performance of numerical analyses, which will be supported with experimental and analytical results. To achieve these objectives, several milestones must be reached. These are listed below:

a) Experimental tests:

 Performance of experimental cyclic tests on cross-laminated wall panels and typical connections used in cross-laminated timber construction systems. Evaluation of mechanical properties and analysis of the behaviour under cyclic loading.

 Evaluation and analysis of energy dissipation properties and damping capacity of cross-laminated timber panels and typical X-Lam connections. Investigation of influence of various parameters on seismic performance, including geometry of panels, configuration of connections, type of fasteners, vertical loads and loading protocol.

 Comparison study of CNR-IVALSA experimental test programme on X-Lam wall panels and other experimental studies.

b) Analytical models:

 Development of analytical models of X-Lam connections behaviour: analytical predictions of strength and stiffness, capacity based design principles on a connection level. Comparison with existig building codes.

 Assessment of the overstrength factor based on the experimental results and on the analytical prediction of the design strength of connection. The overstrength factor of each connection is needed for capacity design of cross-laminated timber structures.

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4

 Development of capacity based design method for X-Lam wall systems based on connection properties. Verification of the newly developed method against the experimental X-Lam wall results. Additional parametric study will be performed.

 Derivaton of analytical kinematic models of non-linear X-Lam wall behaviour (single walls, coupled walls) based on connection mechanical properties.

c) Numerical analyses:

 Implementation of experimental results of X-Lam connection tests into the finite element (FE) numerical model with non-linear springs, representing the hysteretic behavior of cross-lam connections, as a way to model the cyclic behavior of cross-lam buildings.

 Such hysteretic models will be fitted with a software, developed at the University of Trieste by another PhD candidate, for auto-calibration of parameters used in Abaqus FE numerical model.

 Numerical analyses using Abaqus with models of the wall tests (single walls, coupled walls). Comparison of numerical model with the experimental results of X-Lam wall tests.

1.3 Thesis structure

A brief summary of each chapter of the thesis is given in this section. In each chapter, the first section overviews general information about the chapter topic and presents previous research done in this field. In subsequent sections, experimental, analytical and numerical investigations are described, with special emphasis on comparison of the results among different types of analyses.

Chapter 2 provides an overview of general information about cross-laminated timber technology. First, description of cross-lam panels and their application in construction is introduced. Then, typical X-Lam connection systems are presented and their significance in cross-lam technology is described. A state-of-the-art of cross-lam timber application is highlighted at the end of this chapter.

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5

Chapter 3 provides an extensive experimental study on typical X-Lam connections.

Details of test configurations and loading procedures are given. The test results in terms of mechanical properties under cyclic loading are reported. Comparison of test results with existing analytical models is presented and design models on the connection level (1-D models) are introduced. Numerical calibration of FE component spring hysteretic models is described.

In Chapter 4, behaviour of cross-lam wall systems under cyclic loads is examined.

Experimental investigation of single walls and adjacent wall panels (coupled walls) in terms of cyclic behaviour under lateral loading is discussed. Test setups, loading protocols, connection details and material specifications are provided. An analytical model was developed to describe the lateral force-displacement response of cross-lam wall systems. This analytical model was verified with numerical finite element models and experimental results.

Numerical analysis of X-Lam wall systems using the FE model was carried out in order to extend the results of the experimental tests to different configuration of technical interest. The outcomes of the study provided better understanding of the seismic behaviour and energy dissipation capacities of X-Lam wall systems.

The most essential findings from this research project are summarized in Chapter 5, giving the reader an overview of the most important aspects to be considered in understanding of seismic behaviour of cross-laminated timber buildings. Lastly, recommendations for further research are outlined.

In appendices, process of experimental cyclic tests on typical X-Lam connections and X- Lam wall panels is described, including step by step description of experimental testing programme conducted at CNR-IVALSA Research Institute.

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6

2

CHAPTER 2: GENERAL ABOUT X-LAM TECHNOLOGY

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CHAPTER 2

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GENERAL ABOUT X-LAM TECHNOLOGY

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Cross laminated timber (X-Lam or CLT) is an engineered wood product fabricated by adhering and compressing wood layers called lamellas in perpendicular grain orientations to form a solid panel. Wood layers are glued together on their wide faces and, usually, on the narrow faces as well. X-Lam technology was invented and developed in central Europe in the early 1990‘s and since then it has been gaining increased popularity in residential and non- residential applications. The number of buildings constructed using X-Lam panels as the main structural system has seen exponential growth in the last decade, and market share for X-Lam construction is expected to continue to escalate in the future. The European experience showed that X-Lam construction can be competitive, particularly in mid-rise and high-rise buildings due to its easy handling during construction and a high level of prefabrication.

Recently, X-Lam was introduced also overseas, in North America, Australia and in New Zealand. A number of production plants have been established or they are proposed to be built in aforementioned countries.

Figure 2.1 Cross-laminated timber panel (ETA-06/0138, 2006)

Seismic Behaviour of Cross-Laminated Timber Buildings

UNIVERSITÀ DEGLI STUDI DI TRIESTE

XXV CICLO DEL DOTTORATO DI RICERCA IN CORSO DI DOTTORATO IN INGEGNERIA CIVILE E

AMBIENTALE

Seismic Behaviour of Cross-Laminated Timber Buildings

SSD: ICAR/09 - Tecnica delle Costruzioni

DOTTORANDO Igor Gavric

COORDINATORE Prof. Claudio Amadio

SUPERVISORE DI TESI Prof. Massimo Fragiacomo

CO-SUPERVISORE DI TESI Prof. Ario Ceccotti

ANNO ACCADEMICO 2011 / 2012

ABSTRACT

SOMMARIO

ACKNOWLEDGMENTS

TABLE OF CONTENTS

LIST OF FIGURES

LIST OF TABLES

LIST OF PUBLICATIONS

NOTATIONS

1

CHAPTER 1

INTRODUCTION

1.1 Research background and motivation

1.2 Objectives and scope

1.3 Thesis structure

2

CHAPTER 2

GENERAL ABOUT X-LAM TECHNOLOGY