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Title [sv]
Hardwood_joint: Innovative joints in hardwoods
Title [en]
Hardwood_joint: Innovative joints in hardwoods
Abstract [sv]
Volymen i de befintliga lövträbestånden i Europas skogar ökar vilket gör dem till en betydande, men samtidigt underutnyttjad, resurs med stor potential för ökat nyttjande. Lövträ lämpar sig väl för användning i ingenjörsmässiga lastbärande konstruktionselement. Dessvärre saknas effektiva mekaniska förbandlösningar för att sammanfoga sådana element vilket innebär ett hinder för en effektiv och ekonomisk användning av lövträ i bärande träkonstruktioner. För att övervinna detta hinder utvecklas ekonomiska, tillförlitliga och innovativa förband för lövträelement och dimensioneringsregler utarbetas. Numeriska modeller som är specifika för lövträskruvar utvecklas baserat på resultat från omfattande experimentella testserier av elementära parametrar som hålkanttryck och utdragskapacitet hos olika typer av mekaniska infästningar men också utifrån friktionsegenskaper i skjuvplan i förbandsområdet. Det senare optimeras genom att avsiktligt utforma skjuvplanets ytor för att maximera den kraft som kan överföras med friktion. Modellerna kan användas för att förutsäga lastfördelning mellan infästningselement med hänsyn tagen till stokastiska effekter och den så kallade rep-effekten i mekaniska förbindare med glatta ytor vilket hittills inte utnyttjas i dimensioneringssammanhang. Infästningar i icke-förborrade hål i lövträelement undersöks för att ta fram regler för utförandet, såsom minsta avstånd mellan infästningar eller kantavstånd. Slutligen härleds uttryck för olika typer av spröda brott som exempelvis block-skruv brott vid axiellt belastade skruvar eller brott i stålinfästningar som är utsatt en kombination av moment, normal- och tvärkraft.
Abstract [en]
The existing hardwood stocks in Europe’s forests are increasing, making them a significantly underutilised potential. Hardwood lends itself to high volume use in engineered structures. However, efficient mechanical joints for hardwood structures are widely missing which prevents the effective and economical use of structural hardwoods. To overcome this barrier, economic, reliable and innovative joint technologies for hardwood members are developed and design rules are derived. Numerical models specific to hardwood joints are developed based on extensive testing of elementary parameters like embedment and withdrawal behaviour of different dowel-type fasteners in hardwood or the friction in shear planes. The latter are optimised by intentionally shaping the shear plane surfaces to maximise friction. The models are able to predict load distribution between fasteners and take into account stochastic effects as well as rope effects in smooth fasteners not exploited to date. Fasteners in non-predrilled holes in hardwood members are investigated and missing execution rules such as minimum fastener spacing or distances determined. Long- term effects on the axial load-carrying capacity and stiffness of axially loaded screws are quantified, enabling new types of truss joints. Novel member failure modes as block shear failure around axially loaded screws or fastener failure modes as MNV interaction failure in steel fasteners are studied and design rules derived.
Publications (3 of 3) Show all publications
Lemaitre, R., Bocquet, J.-F., Schweigler, M. & Bader, T. K. (2019). Beam-on-Foundation Modelling as an Alternative Design Method for Timber Joints with Dowel-Type Fasteners: Part 2: Modelling Techniques for Multiple Fastener Connections. In: INTER: International Network on Timber Engineering Research: Proceedings, Meeting 52, 26-29 August 2019, Tacoma, USA. Paper presented at 6th meeting of INTER (International Network on Timber Engineering Research), Tacoma, USA, August 26-29, 2019. Karlsruhe, Germany: Timber Scientific Publishing, KIT Holzbau und Baukonstruktionen, Article ID 52-7-9.
Open this publication in new window or tab >>Beam-on-Foundation Modelling as an Alternative Design Method for Timber Joints with Dowel-Type Fasteners: Part 2: Modelling Techniques for Multiple Fastener Connections
2019 (English)In: INTER: International Network on Timber Engineering Research: Proceedings, Meeting 52, 26-29 August 2019, Tacoma, USA, Karlsruhe, Germany: Timber Scientific Publishing, KIT Holzbau und Baukonstruktionen , 2019, article id 52-7-9Conference paper, Published paper (Refereed)
Abstract [en]

In many design codes for timber structures (e.g. Eurocode 5 and SIA 265), the stiffness of a connection is given by empirical equations for a single dowel-type fastener per shear plane. The global stiffness of the connection is then given by multiplication with the number of dowels and shear planes. In the codes cited above, the empirical equations to estimate stiffness only depend on two parameters, namely the dowel diameter and the wood density. The main difference between different codes and stiffness of different types of fasteners is the choice of the exponent on these two parameters. Development and background of empirical equations for stiffness in different codes were recently reported in Jockwer and Jorissen (2018), who analysed about one thousand double shear timber-to-timber connection tests to evaluate the influence of further parameters on stiffness, such as number of fasteners in a row, number of rows of fasteners and dowel slenderness. From this huge database, they have been able to estimate another empirical stiffness equation, that includes dowel slenderness as an additional parameter. Effects of the latter have even been reported in Lemaître et al. (2018), by using a phenomenological numerical model instead ofexperiments. Sandhaas and van de Kuilen (2017) reported that using the slip modulus Kser, calculated according to Eurocode 5 for stiffness prediction of multiple fastener joints, considerably overestimates the experimentally observed stiffness and they proposed to introduce an effective number of dowels in their design, which was also recommended in Jockwer and Jorissen (2018).

This paper continues the work presented in Lemaître et al. (2018) on strength and stiffness estimations of single-fastener connections using a beam-on-foundation (BOF) modelling. In Lemaître et al (2018), the beam-on-foundation model calculations were compared to design equations of Eurocode 5, i.e. the load-carrying capacity and slip modulus. By these comparisons, the validity of the method for the design of single-fastener connections was highlighted. Moreover, effects that are not explicitly covered in the empirical design equations, namely the influence of the dowel slenderness and the nonlinear dowel diameter on the slip modulus were demonstrated.

In the present paper, the same comparisons are made for multiple dowelled connections. Moreover, load distribution between dowels in this type of connection, which was shown to be non-uniform by Blass (1995), is studied by means of the BOF model. Different approaches to estimate the load distribution have been proposed by Cramer (1968), Lantos (1969) and Wilkinson (1986).

Place, publisher, year, edition, pages
Karlsruhe, Germany: Timber Scientific Publishing, KIT Holzbau und Baukonstruktionen, 2019
Keywords
Dowelled timber connections, Numerical modelling, Beam-on-foundation
National Category
Building Technologies
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-89340 (URN)
Conference
6th meeting of INTER (International Network on Timber Engineering Research), Tacoma, USA, August 26-29, 2019
Available from: 2019-09-29 Created: 2019-09-29 Last updated: 2019-10-01Bibliographically approved
Schweigler, M., Bader, T. K., Bocquet, J.-F., Lemaitre, R. & Sandhaas, C. (2019). Embedment test analysis and data in the context of phenomenological modeling for dowelled timber joint design. In: INTER: International Network on Timber Engineering Research: Proceedings, Meeting 52, 26-29 August 2019, Tacoma, USA. Paper presented at 6th meeting of INTER (International Network on Timber Engineering Research), Tacoma, USA, August 26-29, 2019. Karlsruhe, Germany: Timber Scientific Publishing, KIT Holzbau und Baukonstruktionen, Article ID 52-7-8.
Open this publication in new window or tab >>Embedment test analysis and data in the context of phenomenological modeling for dowelled timber joint design
Show others...
2019 (English)In: INTER: International Network on Timber Engineering Research: Proceedings, Meeting 52, 26-29 August 2019, Tacoma, USA, Karlsruhe, Germany: Timber Scientific Publishing, KIT Holzbau und Baukonstruktionen , 2019, article id 52-7-8Conference paper, Published paper (Refereed)
Abstract [en]

Numerical models, like the phenomenological Beam-On-Foundation (BOF) approach, have proven to be an efficient alternative to the analytical European Yield Model (EYM) for the design of dowelled timber joints according to EN 1995-1-1 (2004) (EC 5) (see e.g. Lemaître et al. (2018), Bader et al. (2016)). In contrast to the EYM, BOF-models allow not only for prediction of the load-carrying capacity, but also for prediction of the load-displacement behavior of single-dowel connections, and thus of their stiffness. This makes BOF-models predestined for the design of joints in advanced modern timber structures, which for reason of their complexity rely on a reliable prediction of the jointload-deformation behavior.

BOF-models are used since the early thirties of the last century (Hager, 1930). Models of different complexity were used from simplified (i) rigid-ideal plastic models, which allow only for strength prediction (cf. Johansen (1949)); to (ii) bi-linear elastic approaches, being able to predict stiffness and strength (Sawata and Yasumura (2003), Cachim and Franssen (2009)), and (iii) nonlinear elastic models, which are optimized for numerical simulations (Lemaître et al., 2018). BOF-models might be even used for earthquake design by application of plastic, or even hysteresis models (Izzi et al. (2018), Girhammar et al. (2017)). Developers and users of such phenomenological models face the challenge to find reliable input data on the load-deformation behavior of steel dowels embedded in wood or wood-based products.

Lack of input data for numerical models, like BOF, is one of the main reasons which hinders application of such models in engineering practice and in research. Since the EYM of EC 5 uses only the embedment strength (fh,EC5) but no stiffness, as input, the related European standard for embedment testing, EN 383 (2007), focuses mainly on the embedment strength determination. However, numerical modeling requires information on the entire load-displacement curve from embedment tests.The aim of this contribution is to

  1. present methods to analyze and parameterize experimental load-displacement curves for BOF-models, with embedment parameters suitable for this purpose;
  2. provide a database of embedment parameters for different wood spieces and wood products, and try to find correlations between parameters;
  3. give recommendations for embedment testing, with the aim to exploit data in numerical models.
Place, publisher, year, edition, pages
Karlsruhe, Germany: Timber Scientific Publishing, KIT Holzbau und Baukonstruktionen, 2019
Keywords
Dowelled timber joints, Embedment tests, Load-displacement curves, Numerical analysis, Database
National Category
Building Technologies
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-89339 (URN)
Conference
6th meeting of INTER (International Network on Timber Engineering Research), Tacoma, USA, August 26-29, 2019
Available from: 2019-09-29 Created: 2019-09-29 Last updated: 2019-10-01Bibliographically approved
Schweigler, M. & Bader, T. K. (2019). Numerical modeling of dowel-type connections in soft- and hardwoods including the rope effect. In: CompWood 2019 - International Conference on Computational Methods in Wood Mechanics - from Material Properties to Timber Structures: . Paper presented at CompWood 2019 - International Conference on Computational Methods in Wood Mechanics - from Material Properties to Timber Structures, 17-19 June, 2019, Växjö (pp. 10-10). Växjö, Sweden: Lnu Press
Open this publication in new window or tab >>Numerical modeling of dowel-type connections in soft- and hardwoods including the rope effect
2019 (English)In: CompWood 2019 - International Conference on Computational Methods in Wood Mechanics - from Material Properties to Timber Structures, Växjö, Sweden: Lnu Press , 2019, p. 10-10Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

In laterally loaded dowel-type connections, forces are not only transferred perpendicular to the fastener axis via contact forces (so-called embedment forces) and shear forces in the fastener, but also by means of forces evoked by displacement along the fastener axis and frictional forces within shear planes. The latter load transfer, the so-called rope effect, is often neglected or simplified in numerical models for laterally loaded connections, but considerably increases strength in case of large bending deformations of the fastener. In partially threaded screws, the rope effect is a result of the withdrawal behavior of the threaded part in combination with the axial resistance of the head of the fasteners. The tensile force along the axis of the fastener causes compression between connected members and frictional forces within the shear planes of the connection, which increase the load bearing capacity [1]. Consideration of the rope effect in numerical models is decisive for valid and suitable prediction of the load-deformation behavior and discussed in this presentation.

Place, publisher, year, edition, pages
Växjö, Sweden: Lnu Press, 2019
National Category
Building Technologies
Research subject
Technology (byts ev till Engineering), Civil engineering
Identifiers
urn:nbn:se:lnu:diva-89768 (URN)978-91-88898-64-7 (ISBN)
Conference
CompWood 2019 - International Conference on Computational Methods in Wood Mechanics - from Material Properties to Timber Structures, 17-19 June, 2019, Växjö
Available from: 2019-10-22 Created: 2019-10-22 Last updated: 2019-11-12Bibliographically approved
Principal InvestigatorBader, Thomas K.
Co-InvestigatorSchweigler, Michael
Coordinating organisation
Linnaeus University
Funder
Period
2019-02-01 - 2022-01-31
Keywords [sv]
Byggteknik
National Category
Building Technologies
Identifiers
DiVA, id: project:1935Project, id: 2018-04980

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