Aspects on the Behaviour of Bolted Joints School of Engineering

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Aspects on the Behaviour of Bolted Joints
for Pultruded Reinforced Polymer Profiles
J. Toby Mottram, Cyprien Lutz, and Guy C. Dunscombe
School of Engineering
Advanced Polymer Composites for Structural
Applications in Construction
ACIC 2004
PFRP Bolted Plate-to-Plate Joints
Design Approach SIMPLISTIC LEVEL
Ultimate joint strengths
S
Creative Pultrusions Inc. for
cleated beam connections
(SF = 4)
– Knock-down factors (for
hot/wet conditioning, etc.)
W/D = 3
E/D = 7
W/D = 7
E/D = 5
W/D = 10
E/D = 2
E
P
– Minimum joint dimensions
(for “bearing” failure; RT)
– Load tables (Fiberline
Composites (SF = 3 (?)) and
P
D
Pultrusion
direction
W
P is Pitch
S is Side distance
Net-tension
Shear-out
EXTREN 525 flat sheet 1/4 inch
Motivation - Bolted Joint Variables
1700+ concentric load joint tests
810 single and 900 multi-bolted (RT, hot, wet, and hot/wet)
11 test centres choose different variables to study
62% of total tests at Lancaster Univ. and Warwick Univ., UK
Variables in blue not studied previously:
• type of loading (e.g. stroke or load control, by-pass load).
• materials (bolts and PFRP).
• plate thicknesses and fibre orientations.
• joint geometries.
• bolt arrangements (washers, torque, and clearance holes).
• serviceability (SSL) loading (creep and cyclic).
• working environment (e.g. hot/wet, etc.).
Constant Load Tests - Method
PURPOSE -- To find out if resistance changes by how the load is applied
E
P
D
Bolt force
P
Concentric load
Tensile
load
S
3x3 joint, EXTREN Series 625 of 6.35 mm thickness, load in direction of pultrusion.
M10 bolts of steel grade 8.8, D = 10 mm (hole clearance 0.1 - 0.3 mm).
Two groups E/D = 6 and P/D = 4 constant; first S/D = 2 and second S/D = 4.
Torque finger tight (< 3 Nm).
Load rate at 0.3 kN/s to 80% of the 100% stroke control ultimate load. 10 mins
constant load, then load increased by 5% to 85 %, held constant for 10 mins,
repeat procedure until ultimate joint failure.
Load (kN)
Constant Load Tests - Results
90
80
70
60
50
Ultimate
failure
7-D12
1-D11
3-D10
40
30
20
10
0
-10
1-D7
1-D6
0
500
1000
1500
2000
Time (S)
Mode of failure is net tension at first bolt row - same in stroke control (0.01 mm/s).
S/D = 4, four specimens failed when load is 90% and two failed at 95% of 72 kN.
S/D = 2, three specimens failed at 90% and at 95% of 85 kN.
The 100% ultimate load is the minimum from three stroke controlled tests.
Stroke controlled resistance can be 10% higher than when load is kept constant for
only 10 minutes.
Bolt Torque and Load Transfer by Friction - Test Method
PURPOSE -- To determine coefficient of friction for load transfer by shear
0.2 mm clearance
> 2mm clearance hole
6.35 mm thick
Fixed side
Slip side
116 mm
360 mm
PFRP on PFRP
Slip side hole clearance is 4 mm for
inner 9.53 mm thick plate
M12 and M16 bolts and washer
diameters are 24 and 29 mm
Stroke rate is 1 mm/min
Bolt tension measured by load cell
Bolt Torque and Load Transfer by Friction - Results
20
18
Slip starts
16
14
Load (kN)
Increasing
10 kNmm
20 kNmm
30 kNmm
40 kNmm
50 kNmm
torque
12
10
8
6
4
Bolt
bearing
2
0
0
1
2
3
4
Stroke (mm)
Load-stroke curves for M12 bolting and increasing torque
Bolt Torque and Load Transfer by Friction - Results
20
Bolts were not
lubricated
M12
Slip Load (kN)
15
M16
M16 trendline
10
M12 trendline
Torque
applied to
M16 bolt
head, poor
method!
5
0
0
10
20
30
40
50
60
Bolt torque (kNmm)
Load-slip results with scatter bars and trendlines (intercept is 0, 0)
Bolt Torque and Load Transfer by Friction - Results
Approximate coefficient of friction for PFRP on PFRP is:
0.22 with the M12 bolting
0.14 with the less reliable M16 bolting.
In design can we rely on friction to transfer joint loading?
Testing does not account for bolt tension relaxation (20% in one
week).
Allowable bolt torque for the bolt tension not to exceed 75% of the
steel’s proof strength might lead to compressive crushing of
PFRP.
Preliminary calculations indicate that a joint design procedure
neglecting bolt bearing cannot be developed.
Conclusions
• Test series with PFRP plate-to-plate bolted joints have been
used to investigate two variables previously not studied.
• Under constant load the resistance of 3x3 multi-bolted joints
is found to be less than that determined by testing under
stroke control.
• The coefficient of friction for PFRP on PFRP has been found
to be about 0.2 (new tests with lubricated M16 bolts gives
0.27 - the lubrication increases the bolt tension per unit
torque).
• The low coefficient of friction of 0.14 with M16 bolting shows
by how much bolt tension can be changed by the method
used to apply the bolt torque.
• Preliminary work indicates that a joint design procedure
cannot be developed which relies on the entire joint force
being carried by friction.
Thank you for your attention
Any questions?
Email: [email protected]
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