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An experimental study of the stiffness and strength of cross-laminated timber wall-to-floor connections under compression perpendicular to the grain

https://research.thinkwood.com/en/permalink/catalogue3197
Year of Publication
2022
Topic
Connections
Material
CLT (Cross-Laminated Timber)
Application
Floors
Walls
Author
Schweigler, Michael
Akter, Shaheda T.
Sabaa, Stephen
Bader, Thomas K.
Organization
Linnaeus University
Publisher
Elsevier
Year of Publication
2022
Format
Journal Article
Material
CLT (Cross-Laminated Timber)
Application
Floors
Walls
Topic
Connections
Keywords
Compression Perpendicular To Grain
Stress Dispersion
Nominal Stiffness
Nominal Strength
Digital Image Correlation
Research Status
Complete
Series
Engineering Structures
Summary
In platform-type multi-story cross-laminated timber (CLT) buildings, gravity loads from upper floors, and vertical reaction forces from horizontal actions, like wind loads, cause substantial compressive forces in the CLT-floor elements. The combination of these high forces with a comparable low compression stiffness and strength perpendicular to the grain of timber, makes the compression perpendicular to the grain (CPG) verification of CLT an important design criterion. In this experimental study, CPG of CLT was investigated by means of typical wall-to-floor connections in CLT platform-type structures. CLT-wall elements were used for load application to transmit forces through the CLT-floor element by CPG. Compared to load application by steel elements, as it commonly is done in experiments, lower stiffness but similar strength were found for CLT walls. The study of different connection types showed the highest stiffness and strength for connections assembled with screws, followed by pure wood-to-wood contact, while connections with acoustic layers between the floor and wall elements showed the lowest stiffness and strength. In addition, these connections were tested for center and edge load position on the CLT-floor element. The strength for center and edge position compared to full surface loaded specimens increased linearly with the activated material volume, as determined by earlier proposed stress dispersion models. The stress dispersion effect was visualized by surface strain measurements using digital image correlation technique. Also, the stiffness increased with the activated material volume. Stress dispersion in the CLT-floor allowed to explain the increase in stiffness and strength with decreasing CLT-wall thickness. Strength values at different strain levels, and stiffness and strength increase factors suitable for the engineering design of CLT structures are provided.
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An innovative timber-steel hybrid beam consisting of glulam mechanically reinforced by means of steel rod: Analytical and preliminary numerical investigations

https://research.thinkwood.com/en/permalink/catalogue3135
Year of Publication
2021
Topic
Mechanical Properties
Material
Glulam (Glue-Laminated Timber)
Application
Beams
Author
Wang, Tianxiang
Wang, Yue
Crocetti, Roberto
Franco, Luca
Schweigler, Michael
Wålinder, Magnus
Organization
KTH royal institute of technology
Univiersità IUAV di Venezia
Linnaeus University
Publisher
Elsevier
Year of Publication
2021
Format
Journal Article
Material
Glulam (Glue-Laminated Timber)
Application
Beams
Topic
Mechanical Properties
Keywords
Hybrid Structure
Mechanical Connection
Shear Key
Timber-Steel Hybrid Beam
Analytical Model
Numerical Analysis
Retrofitting Techniques
Research Status
Complete
Series
Journal of Building Engineering
Summary
There is an increasing interest in large-dimensional timber structural elements within the construction sector in order to fulfil the combined demand of sustainability, open spaces and architectural flexibility. Current timber technology allows for efficient production of long-size beams, but many problems are related to their overall high costs due to difficulties in transportation, manufacturing on site and handling during the mounting phase. Hence, the aim of this work is to propose and study an innovative timber-steel hybrid structural element composed of shorter pieces of beams connected and reinforced by means of a system consisting of steel shear keys and steel rods. The small timber elements and steel devices can be prefabricated with low costs and easily assembled into large elements at the construction sites. The proposed system can also be used for retrofitting of existing timber members when it is necessary to increase their strength, stiffness and ductility. The structural behavior of the proposed system was therefore studied both as a connection and as a retrofitting technique, which were analyzed via two types of hybrid beams, one with a splice at mid-span and one without, separately. A simple glulam beam with the same geometrical characteristics of the two hybrid structures was also investigated for the comparison of the structural behavior. The analytical results show that the hybrid beams with and without splice have both obtained significant increasement in the stiffness, strength and ductility. The numerical analyses are limited in the elastic stage due to the elastic mechanical properties assigned to the structural components. The numerical results show good agreement with the analytical ones for each type of beam in terms of the stiffness in the elastic stage. Finally, the influence of the parameters such as the distance between shear keys, slip modulus of shear keys and diameter of rod, on the structural behavior of hybrid beams is discussed in this paper.
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Design of Connections in Timber Structures

https://research.thinkwood.com/en/permalink/catalogue1937
Year of Publication
2018
Topic
Connections
Design and Systems
Material
CLT (Cross-Laminated Timber)
Author
Bader, Thomas
Blaß, Hans Joachim
Bocquet, Jean-François
Branco, Jorge
Brandner, Reinhard
Manuel Cabrero, José
de Proft, Kurt
Descamps, Thierry
Dietsch, Philipp
Franke, Bettina
Franke, Steffen
Görlacher, Rainer
Jockwer, Robert
Jorissen, André
Kleiber, Marion
Lemaître, Romain
Munch-Andersen, Jørgen
Pazlar, Tomaž
Ranasinghe, Keerthi
Ringhofer, Andreas
Sandhaas, Carmen
Schweigler, Michael
Stepinac, Mislav
Tuhkanen, Eero
Verbist, Maxime
Yurrita, Miguel
Editor
Sandhaas, Carmen
Munch-Andersen, Jørgen
Dietsch, Philipp
Publisher
COST (European Cooperation in Science and Technology)
Year of Publication
2018
Format
Book/Guide
Material
CLT (Cross-Laminated Timber)
Topic
Connections
Design and Systems
Keywords
Eurocode 5
Fasteners
Screws
Dowel Type Fastener
Glued-In Rods
Numerical Modeling
Europe
Load Distribution
Research Status
Complete
Summary
This state-of-the-art report has been prepared within COST Action FP1402 Basis of structural timber design from research to standards, Working Group 3 Connections. The Action was established to create an expert network that is able to develop and establish the specific information needed for standardization committee decisions. Its main objective is to overcome the gap between broadly available scientific results and the specific information needed by standardization committees. This necessitates an expert network that links practice with research, i.e. technological developments with scientific background. COST presents the ideal basis to foster this type of joint effort. Chapter 8 Connections presents an integral part of Eurocode 5 and is in need of revision. This state-of-the-art report shall provide code writers with background information necessary for the development of the so-called Second Generation of the Eurocodes, now aimed to be produced in 2022.
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Dowel Deformations in Multi-Dowel LVL-Connections Under Moment Loading

https://research.thinkwood.com/en/permalink/catalogue583
Year of Publication
2015
Topic
Connections
Mechanical Properties
Material
LVL (Laminated Veneer Lumber)
Author
Bader, Thomas
Schweigler, Michael
Hochreiner, Georg
Serrano, Erik
Enquist, Bertil
Dorn, Michael
Publisher
Taylor&Francis Online
Year of Publication
2015
Format
Journal Article
Material
LVL (Laminated Veneer Lumber)
Topic
Connections
Mechanical Properties
Keywords
Ductility
Bending Moment
Steel Dowels
Double-Shear
Steel-to-Timber
Four Point Bending Test
Research Status
Complete
Series
Wood Material Science & Engineering
Summary
The aim of the experimental study presented herein is the assessment and quantification of the behavior of individual dowels in multi-dowel connections loaded by a bending moment. For this purpose, doubleshear, steel-to-timber connections with nine steel dowels arranged in different patterns and with different dowel diameters were tested in 4-point bending. In order to achieve a ductile behavior with up to 7° relative rotation, the connections were partly reinforced with self-tapping screws. The reinforcement did not influence the global load-deformation behavior, neither for dowel diameters of 12 mm nor for 20 mm, as long as cracking was not decisive. The deformation of the individual dowels was studied by means of a non-contact deformation measurement system. Thus, the crushing deformation, i.e. the deformation at the steel plate, and the bending deformation of the dowels could be quantified. In case of 12 mm dowels, the bending deformation was larger than the crushing deformation, while it was smaller in case of 20 mm dowels. Moreover, dowels loaded parallel to the grain showed larger bending deformations than dowels loaded perpendicular to the grain. This indicates that the loading of the individual dowels in the connection differs, depending on their location.
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Load Distribution in Multi-Dowel Timber Connections Under Moment Loading - Integrative Evaluation of Multiscale Experiments

https://research.thinkwood.com/en/permalink/catalogue1499
Year of Publication
2016
Topic
Connections
Mechanical Properties
Material
LVL (Laminated Veneer Lumber)
Author
Bader, Thomas
Schweigler, Michael
Hochreiner, Georg
Eberhardsteiner, Josef
Year of Publication
2016
Format
Conference Paper
Material
LVL (Laminated Veneer Lumber)
Topic
Connections
Mechanical Properties
Keywords
Load Distribution
Steel Dowels
Steel Plates
Conference
World Conference on Timber Engineering
Research Status
Complete
Notes
August 22-25, 2016, Vienna, Austria p. 244-252
Summary
The load distribution in multi-dowel timber connections under bending moments was investigated by means of an integrative evaluation of a hierarchically organized test program, which encompassed component tests as well as single-dowel and multi-dowel connection tests. It was demonstrated that the anisotropic material behaviour of Laminated Veneer Lumber, and consequently of wood in general, leads to a non-uniform load distribution among the dowels, even for multi-dowel connections with a circular arrangement of dowels. Model predictions from this study highlight inefficiencies of the simplified calculation approach, based on the polar moment of inertia, i.e., based on isotropic theory. Loads of dowels loaded parallel to the grain were found to be underestimated by up to 50%. Through the hierarchically organized experimental campaign with full-field deformation measurement techniques, load distribution effects could be related to the orthotropic material behaviour of wood expressed in terms of load-to-grain angle dependent slip curves of single-dowel connections.
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A Numerical Study of the Stiffness and Strength of Cross-Laminated Timber Wall-to-Floor Connections under Compression Perpendicular to the Grain

https://research.thinkwood.com/en/permalink/catalogue2839
Year of Publication
2021
Topic
Connections
Mechanical Properties
Material
CLT (Cross-Laminated Timber)
Application
Walls
Floors
Author
Akter, Shaheda
Schweigler, Michael
Serrano, Erik
Bader, Thomas
Organization
Linnaeus University
Lund University
Editor
Brandner, Reinhard
Publisher
MDPI
Year of Publication
2021
Format
Journal Article
Material
CLT (Cross-Laminated Timber)
Application
Walls
Floors
Topic
Connections
Mechanical Properties
Keywords
Parametric Study
Perpendicular to the Grain
Elasto-Plastic Behaviour
Numerical Modeling
Research Status
Complete
Series
Buildings
Summary
The use of cross-laminated timber (CLT) in multi-story buildings is increasing due to the potential of wood to reduce green house gas emissions and the high load-bearing capacity of CLT. Compression perpendicular to the grain (CPG) in CLT is an important design aspect, especially in multi-storied platform-type CLT buildings, where CPG stress develops in CLT floors due to loads from the roof or from upper floors. Here, CPG of CLT wall-to-floor connections are studied by means of finite element modeling with elasto-plastic material behavior based on a previously validated Quadratic multi-surface (QMS) failure criterion. Model predictions were first compared with experiments on CLT connections, before the model was used in a parameter study, to investigate the influence of wall and floor thicknesses, the annual ring pattern of the boards and the number of layers in the CLT elements. The finite element model agreed well with experimental findings. Connection stiffness was overestimated, while the strength was only slightly underestimated. The parameter study revealed that the wall thickness effect on the stiffness and strength of the connection was strongest for the practically most relevant wall thicknesses between 80 and about 160 mm. It also showed that an increasing floor thickness leads to higher stiffness and strength, due to the load dispersion effect. The increase was found to be stronger for smaller wall thicknesses. The influence of the annual ring orientation, or the pith location, was assessed as well and showed that boards cut closer to the pith yielded lower stiffness and strength. The findings of the parameter study were fitted with regression equations. Finally, a dimensionless ratio of the wall-to-floor thickness was used for deriving regression equations for stiffness and strength, as well as for load and stiffness increase factors, which could be used for the engineering design of CLT connections.
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6 records – page 1 of 1.