09 Strengthening 2009 Nov9

8/4/2019 09 Strengthening 2009 Nov9

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Flexure and Shear

using EB FRP Reinforcement

Tams NAGY-GYRGYLecturer, CE, Ph.D.


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fib

Initial load Mo = service moment acting during strengthening

Mo

is typically larger than the cracking moment Mcr

the calculation is based on a cracked section


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fib

1. full composite action of concrete and FRP is maintained

until the concrete reaches crushing in compression or the

FRP fails in tension (such failure modes may also be characterized as

2. composite action is lost prior to class 1 failure, e.g. due to

pee ng-o o e


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fib

Steel yielding followed by concrete crushing

Steel yielding followed by FRP fracture

Concrete crushing(high reinforcement ratios brittle and undesirable failure mode)


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fib

Debonding and bond failure modes


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fib

Bond behaviour of RC members strengthened with FRP

Most failures observed caused by peelingoff of the EBR element.These depends on the starting point:

in an uncrackedanchorage zone

caused atflexural cracks

caused atshear cracks

caused by the unevennessof the concrete surface


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fib

Bond behaviour of RC members strengthened with FRP

Also was observed FRP end shear failure (or concrete ripoff)


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fib


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fib

VRd = min (Vcd + Vwd + Vfd , VRd2 )

Vfd = 0.9 fd,e Efu fbw d (cot + cot ) sin

fd,e = design value of effective FRP strain=w

d = effective depth of cross section

f = FRP reinforcement ratio equal to 2tfsin / bw for continuously bonded shearreinforcement of thickness tf or (2tf/bw)(bf/sf) for FRP reinforcement in the form of

f

Efu = elastic modulus of FRP in the principal fibre orientation

= angle of diagonal crack with respect to the member axis, assumed equal to 45 = angle between principal fibre orientation and longitudinal axis of member


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fib

Vfd = 0.9 fd,e Efu fbw d (cot + cot ) sin

= k k = 0.8

fd,e = fk,e / f f= 1.3

, ,

fu

.

ffu

/

cme,f

E

f.

30032

170 Fully wrapped (or properly anchored) CFRP - FRP fracture controls:

Side or U-shaped CFRP jackets:

fu

.

ffu

/

cm

.

ffu

/

cme,f

E

f.;x

E

f.min

30032

3

56032

17010650

Fully wrapped AFRP (FRP fracture controls):fu

.

ffu

/

cme,f

E

f.

47032

0480

Note that in the equations () fcm is in MPa and Efu is in GPa.


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Taljsten

Where f= 0.6fu


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fib


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Comparison of the axial compressive stress as a function of the

axial strain for an unreinforced, reinforced with steel stirrups and

- , , .


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fib

(c

/

fck

)

(c / cc )


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fib

Circular column

Continuous confinement Confinement with gaps

f = fu


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Teng et. al.

Rectangular column

09 Strengthening 2009 Nov9

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