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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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