SEMI FINALS Flashcards
Most of the codes provide for the loss of stress due to relaxation of steel as a percentage of initial stress in steel.
Loss due to relaxation of stress in steel
Values varying from 0 to 90MPa for stress in wires varying from ____ to ___
0.5fpu to 0.8fpu
Characteristic strength of prestressing tendon
fpu
Is the loss of stress in steel under nearly constant strain at constant temperature
Relaxation
Depends upon the tendon form of alignment, which generally follows a curved profile along the length of the beam
Loss due to curvature effect
Depends upon the local deviations in the alignment of the cable
Loss of stress due to wobble effect
Is the result of accidental or unavoidable misalignment, since duck or sheaths cannot be perfectly located to follow a predetermined profile throughout the length of beam
Wobble or wave effect
The prestressing force at the jacking end
Po
Coefficient of friction between the cable and duct.
μ
Friction coefficient for wave effect
k
The IS Code recommend for the value of k per 100m for normal condition
0.15
The IS Code recommend for the value of k per 100m for thin walled ducts where heavy vibrations are encountered and in alter adverse conditions
1.5
In prestress, the combined effect of prestressing force and external load can be resolved into a
single force
The locus of the points of application of this force in any structure is termed as
Pressure Line
The load in pressure line is such that stress at the top fiber of support and bottom fiber of central span is
Zero
Refers to the evaluation of permissible prestress, stresses under service load, ultimate strength, and entire load, similar to axial load
Analysis of members under flexure
Based on allowable stresses at transfer
Permissible prestress
These are compared with allowable stresses under service conditions
Stresses under service loads
This is compared with the demand under factored loads
Ultimate Strength
The entire load versus ____ behavior
deformation
Assumption
Concrete is a ______ material
homogeneous elastic material
Assumption
Within the range of working stress, both concrete and stell behave elastically withstanding the small amount of creep, which occurs in both the materials under the
sustained loading
Assumption
A plane section before bending is assumed to remain plane even after bending, which implies a ______ across the depth of the member
linear strain distribution
Assumption
Prestress concrete is one in which there have been introduced internal stresses of such _______ that stresses resulting from given external loading is counter balanced to desired degree
magnitude and distribution
Assumption
Plane sections remain plane until failure, known as
Bernoulli’s hypothesis
Assumption
Perfect bond between concrete and prestressing steel for
bonded tendons
3 Principle of Mechanics
- Equilibrium of internal forces with external loads
- Compatibility of the strains in concrete
- Constitutive relationship
The compression in concrete (C) is ____ to the tension (T) in tendon.
equal
The couple of CT are equal to the moment due to ______
external loads
_______ of the strains in concrete and in steel for bonded tendons
Compatibility
The formulation involves the first assumption of plane remaining plane after
bending
For unbonded tendons, the compatibility is in terms of
deformation
______ relationships relating the stresses and the strains in the materials
Constitutive
Variation of internal forces in reinforced concrete
C₂ > C₁
Z₂ ≈ Z₁
Variation of internal forces in prestressed concrete
C₂ ≈ C₁
Z₂ > Z₁
Compression and tension at transfer due to self weight symbol
C₁
T₁
Compression and tension under service load symbol
C₂
T₂
Self weight symbol
W₁
Service load symbol
W₂
Lever arm at transfer symbol
Z₁
Lever arm under service load symbol
Z₂
