Recently completed research projects in timber engineering at the National University of Ireland, Galway have shown that the structural performance of glued, laminated, C16 grade, Irish-grown Sitka spruce can be significantly enhanced by including modest percentages of bonded-in composite rod materials strategically positioned in the section.
The lead investigator and primary supervisor of the research initiatives was Dr Gary Raftery BE, PhD, MIEI, who was an instrumental figure in the development of the timber-testing resources at NUI Galway. He worked as an academic staff member at the university for three years and was awarded his PhD degree from NUI Galway in 2010.
Dr Raftery recently moved to the University of Auckland and is now lecturing in timber engineering and leading forest products research in the Department of Civil and Environmental Engineering at the University of Auckland, New Zealand. The University of Auckland is in the top 1% of universities worldwide.
At present, with increased focus on sustainability, timber is a construction material that is receiving considerable international attention for further research and development because it is a natural renewable resource, it is recyclable and it is relatively inexpensive. A primary motivation factor for the research that Dr Raftery was leading was that the use of home-grown timber in the construction sector is associated with considerably lower embodied energy than imported timber – and therefore, increased focus should be placed on the development of engineered wood products manufactured using Irish timber.
The material also acts as a carbon store and therefore, the promotion and extension of its use in the construction industry is of critical importance to withstand the effects of climate change.
POSTGRADUATE RESEARCH PROJECTS
[caption id="attachment_5541" align="alignright" width="640"] Dr Gary Raftery[/caption]
Two recent postgraduate research projects continued the research from the multiple-award-winning project that Dr Raftery directed and which was undertaken by NUI Galway Bachelor of Engineering students Damien Kearns and Joe Lucid (2010); winners of the Ryan Hanley Award (best project in the College of Engineering and Informatics, NUI Galway) and of the National Student Wood Awards (engineering category), where the use of bonded-in GFRP (glass fibre reinforced polymer) rod reinforcement for the strengthening of home-grown laminated spruce was examined.
Fibre-reinforced polymer materials are characterised by an excellent strength to weight ratio when compared to other construction materials and portray superior durability over conventional construction materials. They therefore comprise a class of attractive materials that can offer many benefits to timber as a reinforcement for both strengthening and rehabilitation applications.
One postgraduate research project extended the investigation into the use of GFRP rods materials for the flexural reinforcement of the glued laminated timber beams. Experimental testing was undertaken for both single (tension) and double (tension and compression) reinforcement configurations and the geometry of the grooves in which the reinforcement is positioned was optimised.
A considerable number of repetitions were tested in order to assess the effects of variability in the timber stock. A nonlinear numerical model which can accurately predict the mechanical response of the hybrid elements was developed and is a useful tool that can be used to further examine the beam response subject to variations in geometric arrangements and loading environments.
The use of basalt rod reinforcement was examined in the second project. Basalt is a commonly occurring rock type and the reinforcement of structural timber elements with a product manufactured from another natural material would be strongly favoured from an environmental aspect.
The use of rod reinforcement, in comparison to plate reinforcement, adhesively bonded into routed out grooves in the glued laminated timber elements has the advantage that the reinforcement is concealed which maintains the aesthetic characteristics of the timber. The use of bonded-in rods can also be easily and effectively integrated into the glued laminated timber manufacturing procedure and adds no additional depth to the member that is being reinforced.
[caption id="attachment_5547" align="alignright" width="1024"] The research focused on the Sitka spruce[/caption]
Mechanical protection is provided to the reinforcement material and the possibility of premature delamination is significantly reduced because of the greater bond area associated with the arrangement. Furthermore, strengthened beams using bonded in rods possess better protection from fire, because of the charring effect that would occur with the timber around the reinforcing material.
Both projects resulted in numerous promising results. The research showed that when the reinforcement was internally positioned in higher stressed zones, considerable improvements were achieved in the flexural stiffness of the hybrid elements in comparison to unreinforced sections with substantial enhancements in the ultimate moment capacity.
Furthermore, ductility was associated with the reinforced beams in comparison to the brittle tensile failure modes which were experienced by the unreinforced beams. The groove geometry in which the reinforcement is positioned was optimised which improved the mechanical performance of the hybrid system.
The internally placed rod reinforcement was also seen to bridge over weak local defects inherent with timber and improve the performance of the wood adjacent to the reinforcement. Such hybrid reinforced laminated products can facilitate the use of lower grade faster home-grown wood competing with the mechanical performance of imported glued laminated timber from Scandinavia.
According to Dr Raftery, the development of such products would result in reduced transportation costs with lower on-site installation costs during the construction phase of a given project, because of the lower weight that would be associated with the hybrid elements.