ABC of FRP
An Aspect of Bolted Connections of Fibre Reinforced Polymer Structures: Pin Bearing Strength
Research Poster Competition | 2012
5. TEST RESULTS
1. INTRODUCTION
Increased demand for Fibre Reinforced Polymer (FRP) materials in
construction has resulted in the need for reliable and rigorous design
procedures. Presented are test results of experiments conducted on
pultruded FRP (PFRP) material to characterize pin bearing strengths
needed for design of bolted connections.
Pin
Diameter,
d/t
d
Fibre
Orientation
(degrees)
0
M10
The basic building blocks of a PFRP structural joint are plate-to-plate
connections and for the simplest form, having a single-bolt connection,
failure can occur in several distinct mechanisms as illustrated in
Figure 1.
1.02
45
90
0
M20
2.05
45
90
Characteristic Bearing Strength
(N/mm2)
Table 1: Pin Bearing Strengths from Test Matrix
Pin type
Plain
Threaded
170
173
154
151
146
160
149
111
112
113
98
104
Maximum load value was taken as the failure load. Characteristic values were
calculated from this load using the statistical method in Eurocode 0: Annex D7
(BS EN 1990:2002). Coefficients of variation for given 12 batches (of 10
specimens) in Table 1 are less than 10%.
Shear-out
Cleavage
Characteristic Pin Bearing Strength Values for
Web Material of a PFRP Wide Flange Beam Section
Fibre Orientation (Degrees)
Nettension
Bearing
Fig. 1: Modes of Failure in Single Bolt Tension Tests
2. AIMS and OBJECTIVES
•
•
•
Develop test methodology for determination of pin‐bearing strength
Complete series of plate‐to‐plate tests for bolted connections of PFRP
Critically evaluate test results to revise or modify current design provisions.
90
M20 Threaded
M20 Plain
45
M10 Threaded
M10 Plain
0
3. PIN BEARING STRENGTH FOR BEARING FAILURE MODE
0
Bearing resistance per bolt given by Equation (1) is used to determine the
strength of the connection. Bearing failure is the single ‘benign’ failure mode
depicted in Figure 1.
Rbr=td
br
Fθ
25
50
75
100
125
150
175
Pin Bearing Strength (N/mm2)
Typical Load-Stroke Plots for M10
Plain and Threaded Pin Bearing Tests
(1)
18
16
Where:
Fθbr is specific pin bearing strength for given fibre orientation (θ);
t is material thickness;
d is pin diameter.
Load (kN)
14
12
10
8
Plain 0
Plain 45
Plain 90
Threaded 0
Threaded 45
Threaded 90
6
Key factors affecting bearing strength: fibre orientation and architecture; pin
diameter; clearance hole size; connection geometry; bolt torque; environmental
conditions.
4
2
0
4. EXPERIMENTAL PROGRAM
0
0.5
1
1.5
2
Stroke (mm)
Material : Pultex® SuperStructural Wide Flange 1525 profile (254 x 254 x 9.5 mm)
• Warwick University Test Method (WUTM) for pin bearing strength
• 250kN DARTEC Hydraulic Test Machine
• 10 specimens per batch @ room temperature (~21°C)
Test Matrix : • Threaded and Plain Pins of M10 and M20 sizes
• Three Fibre Orientations: 0°, 45° and 90°
WUTM
Compression
Die Set
Constant Stroke 0.01 mm/s
A316
Stainless Steel
Pins:
Ø 10 and 20
mm
Anti-buckling
Specimen
Holder
Fig. 2: WUTM for Characterisation of Pin Bearing Strength
PhD Supervisor: Prof. J. T. Mottram
•
•
Specimens
nominally
80 x 80 x
9.53 mm
Clearance:
1.6mm +
maximum
allowable
tolerance
6. CONCLUDING REMARKS FROM TEST RESULTS
•
Reduction in plain pin bearing strength occurs as θ
increases and there is a significant difference with the two
pin sizes.
Except for 0° material and M20 pin the plain and threaded
strengths are similar.
600+ specimens will be tested, including pin diameters of
M12 and M16; accelerated aging as well as naturally
weathered specimens.
7. ACKNOWLEDGEMENTS
This research is a part of the project “Connections and Joints for
Buildings and Bridges of Fibre Reinforced Polymer” (EP/H042628)
and funded by ESPRC. Materials for testing were kindly provided by
Access Design and Engineering, Telford, UK. The support and
guidance of technician staff at the School of Engineering is also
gratefully acknowledged.
Navroop Singh Matharu
Method :
PhD Student | Civil Research Group | School of Engineering
e: n.s.matharu@warwick.ac.uk
Bearing strength increases with bolt torque and because the benefit from lateral
restraint cannot be relied upon, Equation (1) requires the pin-bearing value.