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Freyssinet anchorage

Freyssinet hydraulic jack stressing wires

Post-tensioning systems

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Glifford-Udall anchorage system

Lee-Mcall anchorage system

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Typical service loads are:

(1) Dead load of the member

(2) Any superimposed dead load like finishes etc.

(3) Live load

(4) Prestressing force after losses

Stresses shall be within permissible limits for the worst combination of the above loads

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Wire tendon

Strand tendon

Stress strain curves for reinforcing and prestressing steels

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Stress-strain curves for reinforcing and prestressing steels

Tensile strength and elongation characteristics of plain and indented wires

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Gross concrete section

is taken. No deduction for

hole due to the tendon

Analysis is being carried

out at the final stage or at

service loads. Hence, losses

are being accounted for.

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Analysis is being carried

out at the final stage or at

service loads. Since nothing

is said about losses it may be

assumed that the effectiveprestressing force is given.

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The applied load intensity is such that thebottom fibre stress at the mid-span = 0

Note that the position of P is fixed.

Note that this is opposite to what

happens in the case of a R.C.C.

beam

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50

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Suitable for a concentrated

external load

Suitable for a UDL

Suitable for two concentrated

external loads

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x

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Since the prestressing jack is

bearing against concrete, the

tensioning of the cable and the

prestressing of concrete occurs

siimaltaneously.

In this case during

prestressing the jacks

are NOT bearing against

the concrete. At transfer, all

the cables are released together

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Since dead load data is

not given, the loss due to

creep has been calculated

only for the permanent

stresses due to the prestress

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Friction is acting along the entire

length of the cable in one direction

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Design for flexure under service/working loads

Knowns: span, loading, support conditions, concrete grade and steel grade

Unknowns: Section modulus/size (b x D), cable profile, prestressing force, eccentricity

Note that we will be designing the sections either as Type I or as Type II members

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Initial stage

Final stage

Dead load moments will be acting on the section.

First subscript:

p: due to prestress

d: due to dead loadl : due to live load

Second subscript:

t: top fibre

b: bottom fibre

Third subscript:

c: compressiont: tension

1 2 3

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Subjectively Substituting numerical values

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Subjectively

Substituting numerical values

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Note that only numerical

values of the stresses have

to be substituted in these

equations and the signs have

to be ignored.

Note that only numerical

values of the stresses have

to be substituted in these

equations and the signs have

to be ignored.

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Note that only numericalvalues of the stresses have

to be substituted in these

equations and the signs have

to be ignored.

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612 940

600 600 510

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600 575

2

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