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Epoxy at Warm Temperatures - 1 / 26
Tim StratfordLuke Bisby
The University of [email protected]
Epoxy BondedJoints at “Warm”
Temperatures
Steel in Fire ForumSheffield, 21/9/10
Epoxy at Warm Temperatures - 2 / 26
Overview
2 - Experimental work1 - Motivation
3 - Modelling
Epoxy at Warm Temperatures - 3 / 26
Ambient Cure Epoxy Adhesive
Glass Transition
Epoxy Adhesive
Epoxy at Warm Temperatures - 4 / 26
Motivation: FRP strengthening
Epoxy at Warm Temperatures - 5 / 26
Structural alterationsor
Increased permanent actions⇓
FRP carries permanent load
Motivation: FRP strengthening
Epoxy at Warm Temperatures - 6 / 26
ConcreteSociety
TechnicalReport 55
“Fire protection.Regulations may require theapplication of an over-coat layer, whichhas been tested on the fully-curedcomposite system”
“Unless a rigorous analysis is undertakenit is sensible to neglect the strengtheningfrom FRP in fire situations.”
Design guidance ⇒
But, if the FRP is needed during the fire:
Motivation: FRP strengthening… in Fire
CIRIAReport
C595
TR55
TR55
Epoxy at Warm Temperatures - 7 / 26
Motivation: FRP strengthening… in Fire
Blondtrock, Taerwe,Vandevelde (2001)
Unp
r ot e
cted
Gypsum boardprotection
Unprotectedplate
Intumescentprotection
Epoxy at Warm Temperatures - 8 / 26
Motivation: FRP strengthening… in Fire
Epoxy at Warm Temperatures - 9 / 26
Motivation: FRP strengthening… in Fire
Temperatures>> Tg in all tests
Epoxy at Warm Temperatures - 10 / 26
Motivation: FRP strengthening… in Fire
Assessment of FRP strengthening after fire• Beneath protection• FRP in adjacent compartment warmed by fire
Design of protection for FRP strengthening• Possible to keep T < Tg?• Improvements through insulation of existing structure?
(Bisby et al., 2005)
Epoxy at Warm Temperatures - 11 / 26
London UndergroundCovered Ways(Cast iron girders)
Motivation: FRP strengthening… in Fire
Epoxy at Warm Temperatures - 12 / 26
Motivation: FRP Strengthening…
Bridge design temperatures(BD37/01, Highways Agency)
… at Warm Temperatures (<100ºC)
Epoxy at Warm Temperatures - 13 / 26
What happens to adhesive joint at warm temperatures?
Current design method based on elastic analysis (CIRIA C595)
Strength ↓ Stiffness ↓ Deformation capacity ↑
Differential thermal expansion between CFRP and steel
Epoxy at Warm Temperatures - 14 / 26
Experiments: Overview
T1
T2
Epoxy at Warm Temperatures - 15 / 26
Experiments: Digital Image Correlation to determine Slip
Slip displacement of FRP plate relative to beam
Epoxy at Warm Temperatures - 16 / 26
Test ID Load (kN) Temperature T2 (ºC) Comment
1 190.0 Ambient Capacity of a strengthened beam (lateral torsional buckling)
7 140.4 Ambient Capacity of an unstrengthened beam (lateral torsional buckling)
2 150 65
Plate debonding failure
4a 170 74
4b 170 74
5a 180 60
5b 180 64
Experiments: Headline Results
Epoxy at Warm Temperatures - 17 / 26
Experiments: Measured Slip
Epoxy at Warm Temperatures - 18 / 26
Tg from ISO 6721
Experiments: Measured Slip
Epoxy at Warm Temperatures - 19 / 26
Modelling: Basis of Model
Temperature (ºC)
Nor
mal
ised
Stif
fnes
s
Elastic bond models(eg: CIRIA C595)
Epoxy constitutive responsethrough glass transition
Elasto-plastic bond model for epoxy at warm temperatures
Epoxy at Warm Temperatures - 20 / 26
Modelling: Basis of Model
Temperature (ºC)
Nor
mal
ised
Stif
fnes
s
Measured adhesiveproperties
Elasto-plasticadhesive idealisation
Epoxy at Warm Temperatures - 21 / 26
Modelling: Predicted Slips
0kN
50kN
100k
N15
0kN
180k
N
Epoxy at Warm Temperatures - 22 / 26
Modelling: Predicted Slips
No load
Full analysis No D.T.E.
ElasticG varies with T
ElasticG constant
Epoxy at Warm Temperatures - 23 / 26
Modelling: Slip Distribution
Camera fieldof view
Epoxy at Warm Temperatures - 24 / 26
Modelling: Shear Stress Distribution
Spread of plastic zone at elevated T ⇒ Runaway failure of adhesive
Epoxy at Warm Temperatures - 25 / 26
Modelling: Plate Force Distribution
Epoxy at Warm Temperatures - 26 / 26
Concluding Remarks
Strength ↓ Stiffness ↓
Deformation capacity ↑
Irrecoverable slip from ≈40ºC, significantly below theISO 6721 glass transition temperature (65ºC).
However, the implications are not obvious:
Creep?
Post-cure elevation of Tg?
Epoxy at Warm Temperatures - 27 / 26
For more information…Bisby, L. A., Green, M. F., Kodur, V. K. R. (2005). “Response to Fire of Concrete Structures that Incorporate FRP”, Progress in Structural Engineering and Materials, Vol. 7, No. 3, pp. 136-149
Blondtrock H., Taerwe L., Vandevelde P. (2001). “Fire Testing of Concrete Slabs Strengthened with Fibre Composite Laminates”, Proceedings of FRPRCS-5, Thomas Telford, London
Concrete Society (2004), “Design Guidance for Strengthening Concrete Structures using Fibre Composite Materials”, Technical Report 55, 2nd Edition, The Concrete Society, Camberley, UK
Cadei J.M.C., Stratford T.J., Hollaway L.C., Duckett W.H. (2004). “C595 - Strengthening metallic structures using externally bonded fibre-reinforced composites”, ISBN 0-86017-595-2, CIRIA, London
Highways Agency. (2001). “BD37/01: Loads for highways bridges.” Design Manual for Roads and Bridges, The Stationary Office Ltd., London, UK.
Stratford T.J., Gillie M., Chen J.F., Usmani A.S., (2009), “Bonded Fibre Reinforced Polymer Strengthening in a Real Fire”, Advances in Structural Engineering, 12(6), 867-878
Stratford T., Bisby L., (2010). “Temperature Effects in Adhesively Bonded FRP Strengthening Applied to Steel Beams: Experimental Observations”, Fifth International Conference on Composites in Construction 2010, Beijing
Stratford T., Bisby L., (2010). “Temperature Effects in Adhesively Bonded FRP Strengthening Applied to Steel Beams”, Structural Faults and Repair 2010, Edinburgh
Stratford T.J., Bisby L.A. “The effect of warm temperatures on externally bonded FRP strengthening.” Submitted to ASCE Journal of Composites in Construction
Relate directly to current work