NUI Galway – UL Alliance First Annual ENGINEERING AND - ARAN ...

GFRP Rods for Strengthening and Repair of Structural Timber Elements
Conor Whelan*, Dr. Gary Raftery, Dr. Annette Harte
Civil Engineering, NUI Galway
*Corresponding author: conorwhelan@gmail.com
Abstract
This project investigates the use of near surface
mounted pultruded glass fibre reinforced polymer
(GFRP) rods in relation to two applications. Firstly, the
performance enhancement of reinforced low-grade
glued laminated timber beams is being examined. The
production of glued laminated timber beams overcomes
many of the natural deficiencies that are found in
timber, especially the low-grade timber that is produced
in Ireland. Secondly, the use of bonded-in FRP rod
materials to repair and strengthen existing structural
timber elements is being looked at. Additionally a 3-D
non-linear finite element model is to be developed using
the finite element package, Ansys. It is envisaged that
the use of reinforced glued laminated timber will
increase in the construction industry, and with the
underutilised timber resources Ireland has it could
highlight a potential area for a growth in the
production of glulam and reinforced glulam products.
1. Introduction
Timber’s structural weaknesses stem from its nature as
a natural anisotropic material. The fact that it is a
natural renewable material however is also one of its
greatest strengths. The transition is being made to
greener, more environmentally friendly, materials not
only because it is good for the environment, but because
it is becoming more and more cost effective. Ireland has
increased its roundwood production by 540% from
1979 to 2003[1]. The majority of this timber fed the
Celtic tiger construction industry and now we are left
with an underutilised resource that is low grade Sitka
spruce. Our climate makes the growth of Sitka spruce
quite rapid and as a result we get less dense lower grade
timber. The variability of strength in timber is primarily
due to deficiencies such as warping, bowing, knots and
splits. In the past 100 years, the method of glued
laminated timber has developed to reduce and in many
cases overcome the shortcomings of timber as a
structural material. Glued laminated timber (Glulam) is
a combination of individual boards or laminates bonded
together with an adhesive to form a stronger grade
beam with reduced strength variability and
imperfections. In comparison to a similar sized
monolithic beam a glulam beam has the advantage of
imperfections being contained to single laminates rather
than running throughout the beam. This restriction of
deficiencies results in a product with a much lower
variability in strength and stiffness.
2. Objectives
The objective of this report is to investigate the use of
near surface mounted GFRP rods as reinforcement in
148
glued laminated beams made with low grade Irish
grown Sitka spruce. Through different reinforcement
configurations and methods of reinforcement we hope
to develop the most efficient reinforcing arrangement.
A finite element analysis will also be undertaken. It is
envisaged that the simulated behavior of this model will
concur with our experimental data. Testing this model
will allow us to carry out parametric analysis and could
assist practicing engineers in design scenarios involving
laminated timber structures and FRP rod reinforcement.
Another objective of this project is to examine the use
of near surface mounted FRP rod materials to repair and
strengthen existing structural elements. This application
is of particular interest considering out of 41,743 timber
bridges that are in use across the United States 47% are
considered as structurally deficient in the national
bridge inventory. The cost to replace all of these beams
would not be economically viable but retrofitting and
strengthening with FRP rods could offer a potential
solution [2].
3. Testing Programme
A beam test programme was undertaken which
involved initially testing all glued laminated timber
beams in stiffness in their unreinforced state. All beams
comprised five laminations of C16 grade spruce bonded
together using a phenol resorcinol formaldehyde
adhesive. The beams measured 3610mm in length
(3420mm span) and 190mm in depth. Unreinforced,
artificially fractured, artificially fractured and repaired,
single reinforced on the tension face and double
reinforcement configurations were examined for
flexural stiffness performance, ultimate moment
capacity and strain profile distribution. A number of
different groove arrangements were examined during
the testing.
4. Conclusion
The development of structural timber members with
less strength variability and increased load capacity
would give an aesthetically pleasing and sustainable
alternative to concrete and steel. The method of NSM
GFRP retrofitting and repair could extend the service
lives of existing timber structures providing an
alternative to total bridge replacement.
5. References
[1] Radford. (2002). Composite repair of timber structures,
Journal of Construction and Building Materials, 417-425.
[2] O’Carroll, J. 2003, COFORD connects publication no.4.
Council for Forest Research and Development, Ireland