Performance evaluation of traditional timber joints under cyclic loading and their influence on the seismic response of timber frame structures

Published Date
Construction and Building Materials
30 November 2016, Vol.127:321–334, doi:10.1016/j.conbuildmat.2016.09.122

• Author 

• Elisa Poletti ^a,,
• Graça Vasconcelos ^a
• Jorge M. Branco ^a
• Aikaterini M. Koukouviki ^b

• aISISE, Department of Civil Engineering, University of Minho, Campus de Azurém, 4800-058 Guimarães, Portugal
• bCivil Engineer

Received 29 January 2016. Revised 20 August 2016. Accepted 28 September 2016. Available online 7 October 2016. 

Highlights

• •
  Joints govern the behaviour of a timber structures.
• •
  Joints constitute the dissipative mechanism of timber structures for seismic events.
• •
  The quality of the joint (presence of gaps) greatly alters the response of a joint.
• •
  Strengthened joints present significantly higher stiffness and dissipative capacity.

Abstract

Timber joints represent the governing part of a timber structure, particularly when assessing its seismic response. In order to better assess the seismic capacity of traditional timber frame structures, particularly timber-framed shear walls, pull-out and in-plane cyclic tests were carried out on their joints (half-lap joints). The aim is to better understand the influence of the joints on the walls and their influence on failure mechanisms and capacity.

Their seismic characterisation was obtained via the analysis of the hysteretic behaviour and dissipative capacity of both unreinforced and retrofitted joints (using self-tapping screws, steel plates and GFRP sheets).

Results show that all strengthening techniques were able to improve the dissipative and load-bearing capacity, but care should be taken into not over-stiffening the joints, as it would lead to an overly rigid structure.

Keywords

Half-lap joint

Seismic retrofitting

Self-tapping screws

GFRP

NSM

Steel plates

Dissipative capacity

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• ⁎ 
  Corresponding author.

© 2016 Elsevier Ltd. All rights reserved.

For further details log on website :
http://www.sciencedirect.com/science/article/pii/S0950061816315720

Improved performance of reinforced rounded dovetail joints

Published Date
Construction and Building Materials
15 August 2016, Vol.118:262–267, doi:10.1016/j.conbuildmat.2016.05.038

Author 

• Thomas Tannert 

• Wood Science and Civil Engineering, The University of British Columbia, 2424 Main Mall, Vancouver BC V6T1Z4, Canada

Received 12 February 2016. Revised 2 May 2016. Accepted 3 May 2016. Available online 14 May 2016. 

Highlights

• •
  Rounded Dovetail Joints (RDJ) are a viable option to connect timber members.
• •
  Structural performance of hand- and machine routed joints is similar.
• •
  Design equation for RDJ yields conservative predictions.
• •
  RDJ performance can be improved through reinforcements.

Abstract

The paper presents experimental investigations on different methods to increase the stiffness of Rounded Dovetail Joints (RDJs). Departing from a reference geometry, the specific methods were (i) oversizing the dovetail tenon part for a tighter fit; (ii) reinforcement with self-tapping screws; (iii) reinforcement with an adhesive layer; and (iv) a combination of adhesive layer and self-tapping screws. The specimens from the reinforced test series were compared to regular RDJ specimens and to beam to joist connections by means of self-tapping screws only. It was demonstrated that all methods significantly increased the joint stiffness of RDJs. Furthermore, the research showed that there is no difference in structural performance between hand-routed joints and CNC-routed joints, and that a previously suggested design equation for RDJs yields conservative predictions when compared to the experimentally obtained 5th percentile values.

Keywords

Timber joints

Reinforcements

Failure modes

Capacity

Stiffness

Statistics

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© 2016 Elsevier Ltd. All rights reserved.

For further details log on website :
http://www.sciencedirect.com/science/article/pii/S0950061816307607

Dynamic mechanical analysis and creep-recovery behavior of agglomerated cork

Author

• D. Paiva
• F. D. Magalhães

Original

First Online: 

09 March 2017

DOI: 10.1007/s00107-017-1158-y

Cite this article as: 

Paiva, D. & Magalhães, F.D. Eur. J. Wood Prod. (2017). doi:10.1007/s00107-017-1158-y

Abstract

The mechanical behavior of agglomerated cork, made of cork granules bound with polyurethane moisture-cured adhesive is investigated and compared to natural cork in the small strain regime (strain <5%). Dynamic mechanical analysis (DMA) of the agglomerated material revealed two distinct thermal transitions, one at −45 °C, related to the glass transition of polyurethane, and one at 3 °C, associated with melting of suberin, a natural polyester that is the main component of cork’s cell walls. Natural cork showed the latter transition to occur at a higher temperature range, between 10 and 25 °C, probably due to a different crystalline arrangement being formed upon cooling the cork granules under pressure in the mold. The storage modulus of agglomerated cork was found to be similar to that of natural cork. Creep and recovery experiments were well described by Burgers model and Weibull distribution function, respectively. Agglomerated cork showed higher instantaneous creep strain and viscous flow than natural cork, probably due to relative displacement and slippage of the granules being allowed by the binder. In all cork materials, not all the instantaneous creep strain was instantaneously recovered. A fraction underwent delayed recovery and another turned into permanent strain. This behavior was associated with the deformation of corrugations in the cork cell walls. Cyclic creep-recovery tests showed for all cork materials recoveries above 90%, except for the first cycle.

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