Skip header and navigation

5 records – page 1 of 1.

Effect of cast-in-place concrete application on moisture distribution in timber-concrete composite floors with notched connections, investigated via finite element simulations

https://research.thinkwood.com/en/permalink/catalogue2902
Year of Publication
2021
Topic
Moisture
Material
Timber-Concrete Composite
Application
Floors
Author
Lukacevic, Markus
Autengruber, Maximilian
Raimer, Thomas
Eberhardsteiner, Josef
Füssl, Josef
Organization
TU Wien
Publisher
Elsevier
Year of Publication
2021
Format
Journal Article
Material
Timber-Concrete Composite
Application
Floors
Topic
Moisture
Keywords
Notches
Moisture Uptake
Sealing
Research Status
Complete
Series
Journal of Building Engineering
Summary
Timber-concrete composite (TCC) structures are an efficient way to combine the advantages of cross-laminated timber (CLT) and concrete plates. By cutting notches into the timber part and applying the concrete on top, efficient shear connections can be formed, eliminating the need for additional use of any type of fasteners. However, fresh concrete releases moisture after application, which is absorbed by the highly hygroscopic wood and can lead to a critical reduction in mechanical properties or to problematic situations due to a difference in expansion behavior. Therefore, a separating foil is usually applied between the two materials, which represents an additional time and cost effort and can also negatively influence the connection properties or make the use of notch-only connections impossible. Thus, we investigate numerically what effects the exclusion of such a foil has on the moisture distribution in the CLT plate. Further, the moisture propagation after a fictitious installation on site is analyzed by applying realistic indoor climates to the open wood surface on the bottom of the CLT plate for a period of two years. In addition, the numerical model allows us to study the effect of local sealings of the most critical wooden part, the end-grain surfaces in the notch region. We were able to confirm that, especially in the unsealed case, locally high moisture contents can occur in the critical region next to the notch, where the highest shear stresses are also to be expected. However, by fully sealing the end-grain surfaces in these regions, the moisture levels and thus the risk of failure could be reduced efficiently. The use of such detailed moisture simulations, where moisture uptake due to bleeding of fresh concrete has been calibrated based on experiments, allows the long-term moisture behavior of such critical situations to be studied and effective solutions to be developed.
Online Access
Free
Resource Link
Less detail

Experimental Study on Glued Laminated Timber Beams with Well-Known Knot Morphology

https://research.thinkwood.com/en/permalink/catalogue1373
Year of Publication
2018
Topic
Mechanical Properties
Material
Glulam (Glue-Laminated Timber)
Application
Beams
Author
Kandler, Georg
Lukacevic, Markus
Füssl, Josef
Publisher
Springer Berlin Heidelberg
Year of Publication
2018
Format
Journal Article
Material
Glulam (Glue-Laminated Timber)
Application
Beams
Topic
Mechanical Properties
Keywords
Four Point Bending Test
Cracks
Knots
Research Status
Complete
Series
European Journal of Wood and Wood Products
Summary
Nowadays, the impact of knots on the failure behaviour of glued laminated timber (GLT) beams is considered by subjecting the single lamellas to a strength grading process, where, i.a., tracheid effect-based laser scanning is used to obtain information about knot properties. This approach single-handedly defines the beam’s final strength properties according to current standards. At the same time, advanced production processes of such beams would allow an easy tracking of a scanned board’s location, but, at this point, previously obtained detailed information is already disregarded. Therefore, the scanning data is used to virtually reconstruct knot geometries and group them into sections within GLT beams. For this study, a sample of 50 GLT beams of five different configuration types was produced and tested under static four-point-bending until failure. As for each assembled lamella the orientation and position within the corresponding GLT beam is known, several parameters derived from the reconstructed knots can be correlated to effective GLT properties. Furthermore, the crack patterns of the tested beams are manually recorded and used to obtain measures of cracks. A detailed analysis of the generated data and their statistical evaluation show that, in the future, dedicated mechanical models for such timber elements must be developed to realistically predict their strength properties. A potential approach, using fluctuating section-wise effective material properties, is proposed.
Online Access
Free
Resource Link
Less detail

Finite-Element-Based Prediction of Moisture-Induced Crack Patterns for Cross Sections of Solid Wood and Glued Laminated Timber Exposed to a Realistic Climate Condition

https://research.thinkwood.com/en/permalink/catalogue2764
Year of Publication
2021
Topic
Moisture
Serviceability
Material
Glulam (Glue-Laminated Timber)
Author
Autengruber, Maximilian
Lukacevic, Markus
Gröstlinger, Christof
Füssl, Josef
Publisher
ScienceDirect
Year of Publication
2021
Format
Journal Article
Material
Glulam (Glue-Laminated Timber)
Topic
Moisture
Serviceability
Keywords
Eurocode 5
Finite Element Simulation
Finite Element Method (FEM)
Failure
Cracks
Load Bearing Capacity
Research Status
Complete
Series
Construction and Building Materials
Summary
Moisture may significantly influence the dimensions and behavior of wooden elements and, thus, it is important to consider within both serviceability as well as ultimate limit state designs. Dimensional changes, also called swelling (during wetting) and shrinkage (during drying), are non-uniform due to the direction-dependent expansion coefficients of wood and usually lead to eigenstresses. If these exceed certain strength values, cracking may occur, which reduces the resistance to external loads, especially to shear stresses. The current standard Eurocode 5 takes these circumstances very simplified into account, by so-called service classes, defined based on the surrounding climate and average moisture levels over the course of a year. Accordingly, reduction factors for strength values and cross section widths are assigned. For a better understanding of the climate-induced changes in wooden beams, we exposed 18 different beams with varying cross sections to a representative climate of Linz, Austria, within the framework of a finite element simulation and investigated the resulting moisture fields and crack patterns. For this purpose, expansions and linear-elastic stresses were simulated by using the thermal and moisture fields obtained in the first simulation step and expansion coefficients. Using a multisurface failure criterion, two critical points in time were determined for each cross section, at which advanced crack simulations were carried out using the extended finite element method. The resulting crack lengths showed that the Eurocode 5 assumption of a linear relationship between crack-free and total width could be verified for both drying and wetting cases. In future, the obtained crack patterns might also be used to investigate the actual reduction of load-bearing capacities of such cross sections, since the position of a crack and, for example, the maximum shear stress may not coincide. For the first time in this work, a consistent concept is presented to estimate the resulting crack formation in a wooden element from any moisture load based on a mechanical well-founded simulation concept. For this reason, this work is intended to lay a basis for a more accurate consideration of climate-related loads on wooden elements up to timber constructions.
Online Access
Free
Resource Link
Less detail

From the Knot Morphology of Individual Timber Boards to the Mechanical Properties of Glued Laminated Timber

https://research.thinkwood.com/en/permalink/catalogue1610
Year of Publication
2016
Topic
Mechanical Properties
Material
Glulam (Glue-Laminated Timber)
Author
Kandler, Georg
Lukacevic, Markus
Füssl, Josef
Year of Publication
2016
Format
Conference Paper
Material
Glulam (Glue-Laminated Timber)
Topic
Mechanical Properties
Keywords
Knots
Simulation
Conference
World Conference on Timber Engineering
Research Status
Complete
Notes
August 22-25, 2016, Vienna, Austria p. 2195-2204
Summary
Knots and the resulting fibre deviations around them have significant impact on the mechanical properties of timber boards. Subsequently, the effective mechanical properties of timber products, such as glued laminated timber (GLT), are strongly influenced by those timber board properties. This motivated the development of an algorithm for reconstructing the knot morphology within individual timber boards, which is presented and discussed in this work. Furthermore, the link to the effective mechanical behaviour of GLT by using stochastic simulation techniques is explored, allowing the estimation of effective mechanical properties of GLT based on the morphology of individual timber boards.
Online Access
Free
Resource Link
Less detail

Modeling approach to estimate the bending strength and failure mechanisms of glued laminated timber beams

https://research.thinkwood.com/en/permalink/catalogue2939
Year of Publication
2022
Topic
Mechanical Properties
Material
Glulam (Glue-Laminated Timber)
Application
Beams
Author
Vida, Christoffer
Lukacevic, Markus
Eberhardsteiner, Josef
Füssl, Josef
Organization
TU Wien
Publisher
Elsevier
Year of Publication
2022
Format
Journal Article
Material
Glulam (Glue-Laminated Timber)
Application
Beams
Topic
Mechanical Properties
Keywords
Extended Finite Element Method
Bending Strength
Size Effect
Laminating Effect
Failure Mechanism
Research Status
Complete
Series
Engineering Structures
Summary
The numerical simulation of four-point bending tests on glued laminated timber (GLT) beams requires an adequate description of the material behavior and of relevant failure mechanisms. The wooden lamellas, building up the GLT element, include knots, as a result of the natural tree growth process, which significantly affect the mechanical behavior. The variability of the morphology and arrangement of these knots lead to a large fluctuation, especially of strength properties, along the wooden lamellas. This leads to complex and, in general, quite brittle structural failure mechanisms of the GLT element. Such failure mechanisms can numerically be described with discrete cracks, using the framework of the extended finite element method (XFEM) for cracks without predefined positions or cohesive surfaces for cracks with predefined positions. In this work, a modeling approach to reliably estimate the bending strength and failure mechanisms of GLT beams subjected to four-point bending tests is proposed. Herein, the approach is validated by simulating replications of experimentally tested GLT beams of two beam sizes and strength classes, where each knot group is considered as a section with reduced individual stiffness and strength in exactly the same position as in the real beam. The results show that the application of quasi-brittle material failure may still result in a brittle global failure of GLT beams. The present study exemplarily shows how valuable insight into progressive failure processes can be gained by allowing the formation of continuous crack patterns. Moreover, a refined consideration of the knot geometries with such sophisticated realizations of discrete cracks may be able to simulate the actual failure mechanisms even more precisely.
Online Access
Free
Resource Link
Less detail