The use of Cross-Laminated Timber products has increased in recent years with a range of structural applications including CLT tall buildings and folded structures. As CLT is used in more innovative structural applications the need for specific methods of design and analysis are apparent. A review of the literature demonstrates that despite the increasing popularity of CLT in construction there are limited methods for the design and analysis of CLT panels and structures that fully utilise its unique properties. Manufacturer data relating to the CLT material properties varies how the cross directional laminas are considered. Finally it was found that there is limited published knowledge regarding CLT material properties for panels loaded non-tangentially to the direction of the timber grain. A method for predicting failure loads and modes has been presented and compared with experimental test data. A Strut and Tie model is proposed for the analysis of CLT panels, a methodology originally developed to design of reinforced concrete deep beams. The Strut and Tie approach considers panel geometry, loads, supports, different properties in tension and compression and was adapted to consider anisotropic behaviour. The procedure, advantages and limitations have been presented and a model developed for an application in CLT. The use of this model is considered for the analysis of simple CLT panel loadings. The behaviour of CLT at different timber grain angles demonstrate a complex composite behaviour influencing the strut and tie capacities. The definition of node sizes was also found to be critical to the definitions of the struts and ties and hence the capacity of the sections. Comparison of experimental tests to the model demonstrates some application to using a Strut and Tie in CLT panels. It identifies where additional investigation is required to improve, develop and validate the model into a method that may be used for full-scale CLT panels and structures in design practice and consider a variety of geometries and loading arrangements.
Since the development of Cross Laminated Timber (CLT), there has been a surge in interest in massive timber buildings. Furthermore, recent conceptual and feasibility designs of massive timber towers of 30 or more stories indicate that performance of mass timber structural elements can compete with other building materials in the commercial industry (MGB Architecture and Design et al.). However, in order for massive timber to penetrate the commercial market even further, a solution is needed for long-span massive timber floor systems. Unfortunately, CLT falls short in this area and is unable to span long distances. The hollow massive timber (HMT) panel presented in this thesis offers one potential long-span solution.
At the institute of structural engineering at the ETH Zurich multiple of investigations are conducted to analyse the material properties of Norway spruce timber boards. The investigations are part of the research project “Influence of varying material properties on the load bearing capacity of glued laminated timber (glulam)”. The majority of the investigations are non-destructively.
The investigations are taking place on 400 timber boards. On all specimens the moisture content, the density, the Eigenfrequency and the longitudinal ultrasonic runtime was investigated. Further all knots with a diameter larger then 10mm are measured. Thereby the position and the size of all the knots are documented. Subsequently on 200 selected boards non-destructive tensile test are performed to analyse the local young modulus. Herewith it was particularly focused on the investigation of the stiffness of areas having knots or knot clusters and areas without knots. The strains are measured with an optical coordinatemeasurement device. In the last part of the experimental investigation the deformation and failure behaviour of significant knot clusters is analysed. The strains are measured with digital image correlation.
Focus of the entire experimental analysis was the investigation of the young modulus and the quantifications of its variability within timber members and between timber members. Within this study a database was produced to evaluate existing test methods for the estimation of the young modulus. Further, the results can be used as a basis for further investigations on the variability of structural timber.
The goal of this project is to contribute to the development of design values for cross-laminated timber (CLT) diaphragms in the seismic load-resisting system for buildings. Monotonic and cyclic tests to determine strength and stiffness characteristics of 2.44 m (8 ft) long shear connections with common self-tapping screws were performed. Understanding and quantifying the behavior of these shear connections will aid in developing design provisions in the National Design Specification for Wood Construction and the International Building Code so structural engineers can use CLT more confidently in lateral force-resisting systems and extend the heights of wood buildings. Experimental strength-to-design strength ratios were in the range of 2.1 to 8.7. In the ASCE 41 acceptance criteria analysis, the m-factors for the Life Safety performance level in cyclic tests ranged from 1.6 to 1.8 for surface spline connections and from 0.9 to 1.7 for cyclic half-lap connections. The half-lap connections, where screws were installed in withdrawal, shear, shear, and withdrawal, performed exceptionally well with both high, linear-elastic, initial stiffness, and ductile, post-peak behavior.
Timber-Concrete Composite (TCC) systems are comprised of a timber element connected to a concrete slab through a mechanical shear connection. When TCC are used as flexural elements, the concrete and timber are located in compression and tension zones, respectively. A large number of precedents for T-beam configurations exist; however, the growing availability of flat plate engineered wood products (EWPs) in North America in combination with a concrete topping has offered designers and engineers greater versatility in terms of architectural expression and structural and building physics performance. The focus of this investigation was to experimentally determine the properties for a range of proprietary, open source, and novel TCC systems in several Canadian EWPs. Strength and stiffness properties were determined for 45 different TCC configurations based on over 300 small-scale shear tests. Nine connector configurations were selected for implementation in full-scale bending and vibration tests. Eighteen floor panels were tested for elastic stiffness under a quasi-static loading protocol and measurements of the dynamic properties were obtained prior to loading to failure. The tests confirmed that both hand calculations according to the -method and more detailed FEM models can predict the basic stiffness and dynamic properties of TCC floors within a reasonable degree of accuracy; floor capacities were more difficult to predict, however, failure did usually not occur until loading reached 10 times serviceability requirements. The research demonstrated that all selected connector configurations produced efficient timber-concrete-composite systems.
Cross Laminated Timber (CLT) technology has been growing in the EU and Canada since the early 1990's and utilizes the mechanical properties of structural grade lumber to create a strong panel product for use in floor, ceiling and wall systems. The hypothesis of this project was that CLT panels made from non-structural lumber from lightweight species could also meet the performance criteria of the CLT product Standard. The objective of this project was to compare bond integrity in an optimized hybrid poplar CLT panel with standard CLT performance criteria Standard bond integrity tests were performed on CLT samples constructed using two adhesive types and three clamping pressure levels in order to find combinations that may pass the CLT product standard requirements. A lightweight structural CLT product made from hybrid poplar could be used as a model for other low density CLT products made from other less utilized resources.
This paper examines CLT-steel hybrid systems at three, six, and nine storey heights to
increase seismic force resistance compared to a plain wood system. CLT panels are used as
infill in a steel moment frame combining the ductility of a steel moment frame system with a
stiffness and light weight of CLT panels. This system allows for the combination of high
strength and ductility of steel with high stiffness and light weight of timber. This thesis
examines the seismic response of this type of hybrid seismic force resisting system (SFRS) in
regions with moderate to high seismic hazard indices. A detailed non-linear model of a 2D
infilled frame system and compared to the behavior of a similar plain steel frame at each
Parametric analysis was performed determining the effect of the panels and the connection
configuration, steel frame design, and panel configuration in a multi-bay system. Static
pushover loading was applied alongside semi-static cyclic loading to allow a basis of
comparison to future experimental tests. Dynamic analysis using ten ground motions linearly
scaled to the uniform hazard spectra for Vancouver, Canada with a return period of 2% in 50
years as, 10% in 50 years, and 50% in 50 years to examine the effect of infill panels on the
interstorey drift of the three, six, and nine storey. The ultimate and yield strength and drift
capacity are determined and used to determine the overstrength and ductility factors as
described in the National Building Code of Canada 2010.