World Journal Of Engineering
Design and Testing of Road Side Guardrail Using Composite Materials
A. S. DEBAIKY
Associate Professor, Department of Civil Engineering,
Benha University, Egypt
debaiky@hotmail.com
ABSTRACT
This paper presents innovative new product
made using thermoplastic composite is proposed
to replace the traditional metallic highway guard
fence. The most commonly used highway fence
used nowadays is the W-shaped steel one, which
is used all over the world. This product has
several drawbacks such as corrosion, heavy
weight, and relatively low level of energyabsorption. The proposed fence made using
glass/polypropylene composite is a very
promising replacement as it negates the
drawbacks mentioned for the metallic version.
KEYWORDS
Highway fence, composite, FRP, thermoplastic.
1. INTRODUCTION
The composite guard fence is immune to
corrosion from de-icing salts, which is a chronic
problem. Steel fences have to be galvanized in
order to fight the corrosion problem, adding
more cost to the product. Galvanic corrosion
between the steel fence and the unprotected steel
bolts used to fix the guard fences to the wooden
supports will also be eliminated when composite
guard fences are used.
The composite guard fence provides several
advantages over steel regarding environmental
impact. The composite guard fence requires very
little energy for manufacturing. The production
procedure is simple and requires no hazardous
chemicals. In addition, the material is fully
recyclable and produces no volatile emissions.
During service life, composites in general
require very little maintenance unlike metallic or
timber products.
Thermoplastic fence is currently being fabricated
using vacuum bag molding at 3.5 mm thickness.
2. DETAILS OF THE EXPERIMENTAL
PROGRAM
Two specimens were tested in three-points
bending as shown in Figure 1 until failure. The
loaded span was 1.9 m, identical to that used in
the field (spacing between supporting wood
blocks).
The failure was initiated by tensile rupture of the
material at the tension side of the guard fence,
clear breaking voice was heard prior to the
failure. It is clear that the material reached its
nominal ultimate strain at failure (1.5% or 15000
micro-strain). This means that no premature
failure due to web buckling or warping of the
element took place. The load-strain diagram is
linear only during the first 10-15% of the
maximum load then it tends to follow a parabolic
shape with higher strains with non-linear
behavior. This is probably due to inter-laminar
shear failure within the material thickness.
Figure 1: Specimen under load before failure.
450
900
Load [lbs]
1350
1800
The comparison with traditional steel guard with
respect to strength & ductility is simpler than
was initially thought. The ultimate strengths of
the mild steel and the glass composite are about
370 and 189 MPa, respectively. This makes the
failure load of steel guard about twice that of
composite guard (for the same section
properties). Since The profile of the traditional
steel guard was obtained by highway research
engineers after years of tests and trials, the
choice was to adopt the same profile for the
composite guard. The thickness of the composite
guard was then chosen to be 3.5 mm to obtain
the same failure moment of the traditional 2.0
mm thick steel guard.
0
Microstrain
0
5000
10000
15000
20000
On another note, the composite guard offers
much higher deformation compared to steel
guard due its very low elasticity modulus (~10
GPa versus 200 GPa). This means 20 times the
deflection value. Numerically, the steel guard
will suffer only 4.0mm deflection (instead of the
obtained 80mm in composite). This reduction
means much less energy absorption in the case
of vehicle impact. This is the topic of another
research paper.
Figure 2: Load-strain relationship at mid-span on
tension side.
For a continuous fence, the failure load is
expected to be around 3,000 lb (13.35 kN).
3. NUMERICAL MODELING
Finite Element method was used to simulate the
behavior of the composite guard fence, and to
evaluate its efficiency. The modeling was made
assuming a central load simulation maximum
flexure effect of car impact. Figures 3 shows
stress distribution along the length of the panel
under the maximum load.
4. CONCLUSIONS
1. Innovative highway guard fence made of
thermo-plastic glass fibre/Polypropelene is a
promising alternative to traditional steel
guard.
2. The new product is immune to corrosion,
light weight, 100% recyclable, and
environmental friendly.
3. (failure)
stable and almost linear behavior in 3-points
Max comp. stresses
bending test is obtained. Deflection and
stress levels at critical location are consistent
with theoretical values.
4. The composite guard fence is much more
flexible than the traditional steel counterpart,
enabling higher energy absorption that is
much desired in highway fence elements.
5. Improved product shall be obtained by using
continuous thermo-pressing technique rather
Figure 3: Maximum stresses distribution
than the current vacuum bag method. The
latter does not fully ensure full bond between
the different layers of the material.
4. COMPARISON WITH STEEL FENCE
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