epoxy bonded joints at “warm”...

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


Overview

2 - Experimental work1 - Motivation

3 - Modelling


Ambient Cure Epoxy Adhesive

Glass Transition

Epoxy Adhesive


Motivation: FRP strengthening


Structural alterationsor

Increased permanent actions⇓

FRP carries permanent load

Motivation: FRP strengthening


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



Blondtrock, Taerwe,Vandevelde (2001)

Unp

r ot e

cted

Gypsum boardprotection

Unprotectedplate

Intumescentprotection



Temperatures>> Tg in all tests



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)


London UndergroundCovered Ways(Cast iron girders)



Motivation: FRP Strengthening…

Bridge design temperatures(BD37/01, Highways Agency)

… at Warm Temperatures (<100ºC)


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


Experiments: Overview

T1

T2


Experiments: Digital Image Correlation to determine Slip

Slip displacement of FRP plate relative to beam


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


Experiments: Measured Slip


Tg from ISO 6721

Experiments: Measured Slip


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


Modelling: Basis of Model

Temperature (ºC)

Nor

mal

ised

Stif

fnes

s

Measured adhesiveproperties

Elasto-plasticadhesive idealisation


Modelling: Predicted Slips

0kN

50kN

100k

N15

0kN

180k

N


Modelling: Predicted Slips

No load

Full analysis No D.T.E.

ElasticG varies with T

ElasticG constant


Modelling: Slip Distribution

Camera fieldof view


Modelling: Shear Stress Distribution

Spread of plastic zone at elevated T ⇒ Runaway failure of adhesive


Modelling: Plate Force Distribution


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?


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

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