Material model for wood

Wood is highly anisotropic and shows ductile behaviour in compression and brittle behaviour in tension and shear where both failure modes can occur simultaneously. A 3D material model for wood based on the concepts of continuum damage mechanics was developed. A material subroutine containing the developed model was implemented into a standard FE framework. Eight stress-based failure criteria were derived in order to formulate piecewise defined failure surfaces. The damage development of wood was controlled by nine damage variables. Embedment tests using three different wood species (spruce, beech, azobé) were carried out whose results were compared to modelling outcomes. The failure modes could be identified and the general shape of the load-displacement curves agreed with the experimental outcomes up to a numerical limit

Mechanical behaviour of timber joints with slotted-in steel plates

Timber joints are a key part of timber structures. Their reliable performance is a prerequisite to successful timber construction. The structural loadbearing behaviour of timber joints is mechanically complex and difficult to predict. Although numerical tools are currently available, these do not consider all anisotropic aspects of timber. However, to predict performance of a timber joint with useful accuracy a 3D material model need to be taken into account in the calculation of the global load-slip behaviour. The research reported in this thesis describes a newly developed 3D material model based on the concepts of continuum damage mechanics. Furthermore, it describes experiments on hardwood timber joints using dowels with different steel grades. Finally, it compares the calculated mechanical behaviour (based on the developed 3D model) with the experimental results. Betrouwbare houtverbindingen zijn essentieel voor houtconstructies. Het mechanisch gedrag van een houtverbinding onder verschillende belastingen is echter complex en laat zich moeilijk voorspellen. De huidige rekenmodellen nemen de anisotropische aspecten van hout niet volledig in beschouwing. Om de sterkte van een houtverbinding te voorspellen is het echter noodzakelijk een 3D materiaalmodel toe te passen in de berekening van het kracht-verplaatsingsgedrag. In dit proefschrift wordt een 3D materiaalmodel voor toepassing op houtverbindingen beschreven. Daarnaast worden de experimenten beschreven die zijn gedaan op loofhout verbindingen met stalen stiften met verschillende materiaalkwaliteit. Het voorspelde mechanische gedrag (gebaseerd op het ontwikkelde 3D model) wordt vervolgens vergeleken met de resultaten van de experimenten.Structural EngineeringCivil Engineering and Geoscience

A proposal for a standard procedure to establish the seismic behaviour factor Q of timber buildings

A simplified method for the determination of the seismic behaviour factor q of timber buildings is presented. The proposed approach is a hybrid approach with element testing such as cyclic testing of wall elements combined with numerical modelling using the test results as input parameters for complete building models. The method combines non-linear-in-the-time-domain dynamic modelling of 2D or, better, 3D building models. The models are spring - lumped mass models. The mechanical behaviour of the buildings is determined by the springs; all other components are rigid. The springs are calibrated on reversed cyclic testing data of large-scale elements such as shear walls. With this method, computationally efficient and stable models can be developed which can cover many different geometrical setups or mass distributions. Subjecting these building models to different earthquakes and increasing the seismic intensity until near-collapse, behaviour factors q for the simulated construction typologies can be derived

Dreidimensionales nichtlinear-elastisches materialmodell für holz unter berücksichtigung der schädigung

Ein holistisches konstitutives Modell für das Material Holz wurde entwickelt, das das dreidimensionale Verhalten mit duktilen Versagensmechanismen bei Druckbelastung und sprödem Versagen bei Zug- und Schubbelastung sowie die großen Festigkeitsunterschiede in den einzelnen Materialrichtungen abbilden kann. Das Modell basiert auf Ansätzen der Schädigungsmechanik, die die Spannungs-Dehnungsbezie- hungen nach dem Erreichen der Elastizitätsgrenze mit nichtlinearelastischen Algorithmen beschreiben. Das Material Holz wurde als orthotropes Kontinuum modelliert mit einzelnen Schädigungsparametern für die definierten Versagensarten. Die Versagenskriterien, die die Elastizitätsgrenzen bestimmen, formen keinen einfachen Versagenskörper im Spannungsraum, sondern sind stückweise definiert; der 6D Versagenskörper setzt sich also aus unterschiedlichen Körpern zusammen. Die Schädigungsparameter können in der Auswertung angezeigt werden. Somit kann eine zunehmende Faserstauchung bei Druckbelastung in Faserrichtung ebenso identifiziert werden wie bspw. eine Risszunahme im zugbeanspruchten Bereich. Das Modell wurde als Subroutine in ein bestehendes FE-Programm eingebaut und zur Modellierung von Lochleibungsversuchen und zweischnittigen Verbindungen mit Stabdübeln unter Verwendung unterschiedlicher Holzarten eingesetzt. Die Modellierungsergebnisse zeigen deutlich eine zunehmende Schwächung der Querrichtungen durch lokales Entfestigungsverhalten bei zunehmenden Verformungen, während das globale Lochleibungs- oder Verbindungsverhalten duktil bleibt. Das Modell ist in der Lage, beobachtete Versagensmechanismen abzubilden. Ein großes Problem bleibt die Verfügbarkeit von benötigten Materialparametern für die Steifigkeit und Festigkeit sowie die Entfestigung. Dies gilt besonders für selten untersuchte Holzarten wie tropisches Hartholz, die jedoch sehr wohl in der Praxis verwendet werden.Structural EngineeringArchitectur

Il Progetto Sofie. Prestazioni sismiche di edifici in x-lam

In this paper the seismic performance of wooden buildings made of Cross-laminated-timber (CLT) is illustrated as a part of an extensive research project undertaken in Trentino (Italy) to promote the use of CLT for residential and non residential buildings. Strength, deformability and capability of dissipating energy are addressed. Design action reduction factor is also evaluated according to Seismic Eurocode format. Finally the amazing capability of shape keeping and self centering of such buildings under the design quake is highlighted

Seismic Behaviour of Multistory Cross-laminated Timber Buildings

In this paper the seismic performance of wooden buildings made of Cross-laminated-timber (XLAM) is illustrated as a part of an extensive research project undertaken in Trentino (Italy) to promote the use of XLAM for residential and non residential buildings. Strength, deformability and capability of dissipating energy are addressed. Design action reduction factor is also evaluated according to Seismic Eurocode format. Finally the amazing capability of shape keeping and self centering of such buildings under the design quake is highlighted

Material model for wood

Wood is highly anisotropic and shows ductile behaviour in compression and brittle behaviour in tension and shear where both failure modes can occur simultaneously. A 3D material model for wood based on the concepts of continuum damage mechanics was developed. A material subroutine containing the developed model was implemented into a standard FE framework. Eight stress-based failure criteria were derived in order to formulate piecewise defined failure surfaces. The damage development of wood was controlled by nine damage variables. Embedment tests using three different wood species (spruce, beech, azobé) were carried out whose results were compared to modelling outcomes. The failure modes could be identified and the general shape of the load-displacement curves agreed with the experimental outcomes up to a numerical limit.Structural EngineeringCivil Engineering and Geoscience