The current research investigated the delamination process of adhesively bonded hardwood (European beech) elements subject to changing climatic conditions. For the study of the long-term fracture mechanical behavior of gluedlaminated components under varying moisture content, the role of moisture development, time- and moisture-dependent responses are absolutely crucial. For this purpose, a 3D orthotropic hygro-elastic, plastic, visco-elastic, mechano-sorptive wood constitutive model with moisture-dependent material constants was presented in this work. Such a comprehensive material model is capable to capture the true historydependent stress states and deformations which are essential to achieve reliable design of timber structures. Besides the solid wood substrates, the adhesive material also influences the interface performance considerably. Hence, to gain further insight into the stresses and deformations generated in the bond-line, a general hygro-elastic, plastic, visco-elastic creep material model for adhesive was introduced as well. The associated numerical algorithms developed on the basis of additive decomposition of the total strain were formulated and implemented within the Abaqus Finite Element (FE) package. Functionality and performance of the proposed approach were evaluated by performing multiple verification simulations of wood components, under different combinations of mechanical loading and moisture variation. Moreover, the generality and efficiency of the presented approach was further demonstrated by conducting an application example of a hybrid wood element.
FPInnovations carried out a survey with consultants and researchers on the use of analytical models and software packages related to the analysis and design of mass timber buildings. The responses confirmed that a lack of suitable models and related information for material properties of timber connections was creating an impediment to the design and construction of this type of buildings. Furthermore, there is currently a lack of computer models and expertise for carrying out performance-based design for wood buildings, in particular seismic and/or fire performance design.
In this study, a sophisticated constitutive model for wood-based composite material under stress and temperature was developed. This constitutive model was programmed into a user-subroutine which can be added to most general-purpose finite element software. The developed model was validated with test results of a laminated veneer lumber (LVL) beam and glulam bolted connection under force and/or fire.
Glued laminated timber (glulam) is manufactured by gluing and stacking timber lamellas,
which are sawn and finger-jointed parallel to the wood grain direction. This results in a
sustainable and competitive construction material in terms of dimensional versatility and
load-carrying capacity. With the proliferation of glued timber constructions, there is an
increasing concern about safety problems related to adhesive bonding. Delaminations are
caused by manufacturing errors and in service climate variations simultaneously combined
with long-sustained loads (snow, wind and gravel filling on flat roofs). Several recent
building collapses were related to bonding failure, which should be prevented in the future
with a timely defect detection. As an outlook, the feasibility of air-coupled ultrasound tomography was demonstrated with numerical tests and preliminary experiments on glulam. The FDTD wave propagation model was excited by the difference of the time-reversed sound fields transmitted through a test and a reference (defect-free) glulam cross-section. Both datasets were obtained with the same SLT setup. Wave convergences then provided a map of bonding defects along the height and width of the inspected glulam cross-sections. Further
research is envisaged in this direction
New Zealand Society for Earthquake Engineering Conference
April 13-15, 2012, Christchurch, New Zealand
The Nelson Marlborough Institute of Technology Arts and Media building was completed in 2011 and consists of three seismically separate complexes. This research focussed on the Arts building as it showcases the use of coupled post-tensioned timber shear walls. These are part of the innovative Expan system. Full-scale, in-situ dynamic testing of the novel building was combined with finite element modelling and updating to obtain an understanding of the structural dynamic performance within the linear range. Ambient testing was performed at three stages during construction and was combined with forced vibration testing for the final stage. This forms part of a larger instrumentation program developed to investigate the wind and seismic response and long term deformations of the building. A finite element model of the building was formulated and updated using experimental modal characteristics. It was shown that the addition of non-structural elements, such as cladding and the staircase, increased the natural frequency of the first mode and the second mode by 19% and 24%, respectively. The addition of the concrete floor topping as a structural diaphragm significantly increased the natural frequency of the first mode but not the second mode, with an increase of 123% and 18%, respectively. The elastic damping of the NMIT building at low-level vibrations was identified as being between 1.6% and 2.4%
We model the dynamic behavior of laminated curved beams on the assumption that the different layers of such structures are perfectly bonded at the interface and can show different flexural rotations from one another. We formulate a mechanical theory and a finite element model accounting for bending, shear, warping and extensional deformation modes, as well as radial, tangential and rotary inertias. The main novelty of the proposed theory consists of a generalization of layer-wise displacement approaches available in literature to the dynamics of beams with finite curvature. The work includes some numerical results related to the free vibration of laminated arches and showing different support conditions and aspect ratios to establish comparisons with different theories in the literature. We observe that an accurate mechanical modeling of curved laminated beams is crucial for correct estimation of the eigenfrequencies and eigenmodes of such structures within a 1D framework.
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
This thesis is part of a large research project on the development of a software
for the modelling of CLT structures, including analysis, calculation, design and
verification of connections and panels. It was born as collaboration between Padua
University and Barcelona"s CIMNE (International Centre for Numerical Methods in
Engineering). The research project started with the thesis “Una procedura numerica per
il progetto di edifici in Xlam” by Massimiliano Zecchetto, which develops a software,
using MATLAB interface, only for 2D linear elastic analysis. Follows the phase started
in March 2015, consisting in extending the 2D software to a 3D one, with the severity
caused by modelling in three dimensions. This phase is developed as a common project
and described in this thesis and in “Pre-process for numerical analysis of Cross
Laminated Timber Structures” by Alessandra Ferrandino.
The final aim of the software is to enable the modelling of an X-Lam structure in
the most efficient and reliable way, taking into account its peculiarities. Modelling of
CLT buildings lies into properly model the connections between panels. Through the
connections modelling, the final aim is to enable the check of preliminarily designed
connections or to find them iteratively, starting from hypothetical or random
This common project develops the pre-process and analysis phases of the 3D
software that allows the automatic modelling of connections between X-Lam panels. To achieve the goal, a new problem type for GiD interface and a new application for
KRATOS framework have been performed. The problem type enables the user to model
a CLT structure, starting from the creation of the geometry and the assignation of
numeric entities (beam, shell, etc.) to geometric ones, having defined the material, and
assigning loads and boundary conditions. The user does not need to create manually the
connections, as conversely needs for all commercial FEM software currently available;
he just set the connection properties to the different sides of the panels. The creation of
the connections is made automatically, keeping into account different typologies of
connections and assembling of Cross-Lam panels. The problem type is special for XLam structures, meaning that all features are intentionally studied for this kind of
structures and the software architecture is planned for future developments of the postprocess phase.
It can be concluded that sound bases for the pre-process and analysis phases of
the software have been laid. However, future research is required to develop the postprocess and verification phases of the research project.
Initially, timber was considered only as an easily accessible and processable material in nature; however, its excellent properties have since become better understood. During the discovery of new building materials and thanks to new technological development processes, industrial processing technologies and gradually drastically decreasing forest areas, wood has become an increasingly neglected material. Load-bearing structures are made mostly of reinforced concrete or steel elements. However, ecological changes, the obvious problems associated with environmental pollution and climate change, are drawing increasing attention to the importance of environmental awareness. These factors are attracting increased attention to wood as a building material. The increased demand for timber as a building material offers the possibility of improving its mechanical and physical properties, and so new wood-based composite materials or new joints of timber structures are being developed to ensure a better load capacity and stiffness of the structure. Therefore, this article deals with the improvement of the frame connection of the timber frame column and a diaphragm beam using mechanical fasteners. In common practice, bolts or a combination of bolts and pins are used for this type of connection. The subject of the research and its motivation was to replace these commonly used fasteners with more modern ones to shorten and simplify the assembly time and to improve the load capacity and rigidity of this type of frame connection.