This Presentation was presented as a partial fulfillment of Prestressed Concrete Design Lab Course. Behavior & Design of Prestress on above topic is shortly discussed on the presentation. The part "Shear & Shear Design in Prestressed" Concrete was prepared by me. Other topics were prepared by other members of my group. Thanks to all my teachers & friends who helped us in different stages during preparation of the total presentation.

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2. Course No: CE-416
Course Name: PRESTRESS
CONCRETE DESIGN SESSIONAL
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4. Name Student ID
Md. Zahidul Islam 10.01.03.142
Shaikh Mahfuzur Rahman 10.01.03.143
Rifath Ara Rimi 10.01.03.145
MD. Jahirul Islam 10.01.03.146
MD. Rakibul Islam 10.01.03.148
Md. Neshar Ahmed 10.01.03.151
Raiyan Fardous Ratul 10.01.03.153
Md. Shahadat Hossain 10.01.03.154
Md. Ridwan-Ur-Rahman 09.02.03.109
Group : 4
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6. What Is Shear Force
Shear forces are unaligned
forces pushing one part of
a body in one
direction, and another part
the body in the opposite
direction. Shear force
acting on a substance in a
direction perpendicular to
the extension of the
substance.
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7. Shear Mechanism
In a simply supported
rectangular beam, self
weight & super imposed
loads act downward,
reaction acts upward.
Resultants of all these
vertical forces generates
vertical shear in a
member.
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8. Shear
Normal Concrete Vs Pre-stressed Concrete
• Comparatively smaller sectioned member needed for load carrying, so less self weight i.e.
less shear.
RCC BEAM
Prestressed Concrete Member
D1
D2
D1>D2 i.e. for same load carrying
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9. Shear
Normal Concrete Vs Pre-stressed Concrete
• Sagged tendon in most case provide additional
shear but opposite direction.
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10. Shear
Normal Concrete Vs Pre-stressed Concrete
• Prestressing prevents the occurrence of shrinkage
cracks which could conceivably destroy the shear
resistance.
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11. Modes of Failure
in Prestressed
Beam
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12. Flexure-Compression (FC):
Flexure compression failures are the result of having a beam
with higher shear strength than flexural strength. Failure
occurs at the point of maximum flexural stress where the
compressive strain exceeds its capacity.
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13. Flexure-Shear Failure
A flexure-shear failure, is the result of a crack which begins as a flexural crack,
but as shear increases, the crack begins to “turn over” and incline towards the
loading point. Failure finally occurs when the concrete separates and the two
planes of concrete slide past one another. This mode of failure is common in
beams which do not contain web reinforcement.
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14. Shear-Compression Failure
Shear compression failures, shown in Figure, typically occur in beams which contain
adequate web reinforcement. In this mode, the crack propagates through the section
until it begins to penetrate the compression zone. This crack causes a redistribution of
compressive forces in the compression zone onto a smaller area. When the compressive
strength is exceeded, a shear compression failure occurs. This type of failure is common
in deep beams, where arch action is prevalent. The compressive strut caused by arch
action prevents a diagonal tension crack from propagating into the compression zone.
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15. Web-shear Failure
Before a section cracks from flexure, it is possible to exceed the
tensile strength of the concrete at the point of maximum shear
stress. This mode is primarily observed in sections with thin webs.
Failure occurs at the location of peak shear stress, as shown in
Figure. While, the mechanics of this failure are identical to flexure-
shear, failure is brittle and occurs with little or no warning.
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16. Factors Influencing Shear Strength
• Axial Force: Shear failures are commonly due to tensile failure of the
concrete. Axial compression can delay the onset of critical tension in the
section, axial tension can hasten the failure. Compression, such as provided
by an axial force or prestressing tendons, provides an increase in shear
strength.
• Tensile Strength of Concrete: As the tensile strength of the concrete is
increased, there is a corresponding increase in the shear strength of the
section.
• Longitudinal Reinforcement Ratio: Low amount of steel may result in wider
flexural cracks, resulting in reduced dowel action and aggregate interlock.
• Shear Span-to-Depth Ratio: High values of require a larger compression zone,
raising the amount of shear which can be transferred by the uncracked
concrete shear transfer mechanism, thus increasing shear strength
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17. Shear Carrying of Concrete & Tendon
on Different Tendon Profile
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18. Some Important Notes about Shear in
Prestressed Concrete
• Prestressed beam never fail under direct shear or punching shear. They fail as
a result of tensile stress produced by shear.
• In some rare instance the transverse component of prestress increases the
shear in concrete.
• By following load balancing approach, it is theoretically possible to design a
beam with no shear in concrete under a given condition of loading.
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19. Development of Shear Cracking
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20. Steps of Shear Design
For a Simply Supported Beam Section with UDL loading
• Step -1: Calculate the moment of inertia of the
section.
• Step -2: Calculate Support reaction.
• Step -3: Calculate Moment at desire beam section
from x distance from support.
• Step -4: Calculate ‘a’ and then the eccentricity of
tendon at desire (x) distance from support i.e. ex
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21. For Flexural Shear Crack
• Calculate
• Calculate
• Calculate Flexural Cracking Moment
• Calculation of cracking flexural shear
• Calculation of Nominal flexural shear
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22. For Web Shear Crack
• Calculate
• Calculation of Nominal web shear
• Calculate ultimate load
• Calculate factored shear at a section x distance from support
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23. Shear Reinforcement Spacing
Smallest spacing among S1, S2, S3 should be
chosen as stirrup spacing.
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24. End of topic
Shear in
Prestressed
Concrete
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25. “BOND” in
Prestressed
Concrete
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26. Definition
Interlocking between two properties e.g. pre-
stressed tendon and concrete.
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27. Main Types of Internal Prestressed
Concrete
• Pre-Tension Concrete: Pre-stressing steel is tension
stressed prior to the placement of the concrete and
unloaded after concrete has harden to required
strength.
• Bonded post-tensioned concrete: Unstressed pre-
stressing steel is placed with in the concrete and then
tension stressed after concrete has harden to required
strength
• Un-bonded post-tensioned concrete: Differs from
bonded post-tensioning by providing the pre-stressing
steel permanent freedom of movement relative to the
concrete.
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28. Transfer of Prestressing Force:
Bond between concrete and prestressing steel.
Bearing at end anchorages.
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29. Existence of Bond
in Prestressed
concrete
1.Pre-Tension
Concrete
2.Bonded post-
tensioned
concrete
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30. “Bond ” effects in Prestressed
concrete
Bond exists on two different basis:
1. Pre-tensioning system
 Used as a means of transferring the prestressing force of tendon to the
concrete section.
2. Post-tensioning system
 In this, bond is necessary for two purposes,
-Protection against corrosion
-Increase in ultimate strength
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31. Bond effect in Pre-tensioned construction
1.It is furnished by two factors,
-Reduction in area of cross section of steel
-Adhesive property
2.The phenomenon of recovery of lateral contraction develops a wedge
action at the end of the cable by which prestressing force is transferred.
3.This property was discussed detail by Hoyer and is called “HOYER EFFECT”.
4.Transverse reinforcement has to be provided to resist tensile force.
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32. Bond mechanisms in the
prestressing concrete :
1) Adhesion between concrete and steel
2) Mechanical bond at the concrete and steel
interface
3) Friction in presence of transverse compression.
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33. Hoyer Effect
After stretching the tendon, the diameter
reduces from the original value due to
the Poisson’s effect. When the prestress
is transferred after the hardening of
concrete, the ends of the tendon sink in
concrete. The prestress at the ends of
the tendon is zero. The diameter of the
tendon regains its original value towards
the end over the transmission length.
The change of diameter from the original
value (at the end) to the reduced value
(after the transmission length), creates a
wedge effect in concrete. This helps in
the transfer of prestress from the tendon
to the concrete. This is known as the
“Hoyer effect”.
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34. Development length(Ld):
The development length (Ld) is the sum of the
transmission length (Lt) and the bond length (Lb).
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35. Transmission length:
 The bond needed to transmit the complete prestressing force is called
transmission length(Lt).
 The stress in the tendon is zero at the ends of the members. It increases
over the transmission length to the effective prestress (fpe) under service
loads and remains practically constant beyond it.
Fig : Variation of prestress in tendon along transmission length
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36. Factors that influence the transmission
length:
1) Type of tendon
 ¾ wire, strand or bar
2) Size of tendon
3) Stress in tendon
4) Surface deformations of the tendon
 ¾ Plain, indented, twisted or deformed
5) Strength of concrete at transfer
6) Pace of cutting of tendons
 ¾ Abrupt flame cutting or slow release of jack
7) Presence of confining reinforcement
8) Effect of creep
9) Compaction of concrete
10) Amount of concrete cover.
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37. The bond length:
Fig : Variation of prestress in tendon at
ultimate
The bond length (Lb) is the minimum length over which, the stress in the
tendons can increase from the effective prestress(fpe) to ultimate
prestress(fpu) at critical location.
The expression of the bond length is
derived as,
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38. The bond length depends on the
following factors:
1) Surface condition of the tendon
2) Size of tendon
3) Stress in tendon
4) Depth of concrete below tendon
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39. End zone reinforcement
The prestress and the Hoyer effect cause transverse tensile stress (σt). This is largest during
the transfer of prestress.
To resist the splitting of concrete, transverse reinforcement need to be provided at each end of a
member along the transmission length. This reinforcement is known as “End zone
reinforcement’’.
The minimum amount of end zone reinforcement is given as,
h = total depth of the section
M= moment at the horizontal plane at the level of
CGC due to the compressive stress block
above CGC
fs = allowable stress in end zone reinforcement
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40. Bond in Post-tensioned construction
 Effect of bond in post-tensioned construction has two distinct
purposes;
1.Protection against stress corrosion
-Moisture enters into duct
-Cause corrosion to high tension steel
-Rusting reduces effective area of steel
-This causes splitting of wires called stress corrosion
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41. 2.Increase in ultimate strength
● In bonded construction
-Crack at the critical section does not affect the strain in
steel
-Because of this, the compressive area is not reduced
considerably
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42. Process
– Concrete is casted around a curved
duct (usually corrugated), to allow room
for the Tendon to be inserted.
– After the concrete has hardened the
tendons are pulled in tension and then
wedged.
– The duct is then injected with grout
 There are 2 layers of bonding media in
post-tensioned construct
-Bond between the steel and the
sheath or duct
-Bond between the sheath and
the concrete
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43. End of this topic
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44. Bearing or Bearing plate
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45. Definition
A bearing plate is a specially-designed metal
plate used to spread the force of a load-
bearing wall or column out over a larger area
Fig: Bearing plates
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46. The end zone (or end block) of a post-tensioned member
is a flared region which is subjected to high stress from
the bearing plate next to the anchorage block. It needs
special design of transverse reinforcement. The design
considerations are bursting force and bearing stress.
Some Important things to know
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47. Behavior of the local zone
• The behavior of the local zone is influenced by the anchorage
device and the additional confining spiral reinforcement
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48. The transverse tensile stress is known as splitting tensile
stress. The resultant of the tensile stress in a transverse
direction is known as the bursting force(Fbst). Compared to
pre-tensioned members, the transverse tensile stress in
post-tensioned members is much higher.
Behavior of the local zone (Contd.)
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49. For calculating bursting force (Fbst) an individual
square end zone loaded bearing plate.
Calculating bursting force
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50. End Zone Reinforcement
• The amount of end zone reinforcement in each direction (Ast)
can be calculated from the following equation.
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52. • The bearing stress in the local zone
should be limited to the following
allowable bearing stress (fbr,all)
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53. Dispersion of bearing stress in concrete
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54. Manufacturing of an end block specimen
Fabrication of end zone reinforcement Anchorage block and guide
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55. Manufacturing of an end block
specimen (Contd.)
End zone reinforcement
with guide and duct
End block after casting
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56. End of this topic
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57. Camber & Deflection
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58. Camber
 Camber is the upward deflection in the beam after release of
the prestressing strands due to the eccentricity of the force in
the strands. The camber of the beam is usually the largest
contribution to hunch.
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59. Factors of camber
The ability to predict camber accurately is critical for the
design and constructions . However, this is a complex
task, since the camber is dependent on many variables,
some of which are interdependent and change over
time. Four of the most significant variables are the
properties of the concrete ,
1. creep of the concrete,
2. concrete temperature
3. the magnitude
4. location of the prestress
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60. Deflection
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61. Definition
 In general, Deflection is the degree to which a structural
element is displaced under a load.
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62. Types of Deflection
 Short-term deflection occurs immediately upon the
application of a load.
 Long-term deflection takes into account the long-term
shrinkage and creep movements.
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63. Causes of Deflection in PSC Beams
Due to external loads
Due to prestress force
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64. Tendon Profile
The deflection due to prestress depends on
the profile of the c.g.s. line
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65. Methods of Calculation
 Double Integration Method
 Moment Area Method
 Conjugate Beam Method
 Principle of Virtual Load
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66. Calculations of the Short-term Deflection
The usual loading which should be
investigated in calculating deflections are:
Prestress plus dead load
Prestress plus maximum service load
Prestress plus minimum service load
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69. ANY QUESTION
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