Prestressed Flashcards
A _________ structure is different from a
conventional reinforced concrete structure due to the
application of an initial load on the structure prior to its
use.
prestressed concrete
The _______ or ‘prestress’ is applied to enable the
structure to counteract the stresses arising during its
service period.
initial load
tensile strength of concrete is only about ___ to ____ of its compressive strength
8% to 14%
cracks tend to develop at _________ of loading in flexural members such as beams and slabs
early stages
to prevent cracks, _________ can be suitably applied in the perpendicular direction
compressive force
_________ enhance the bending, shear, and torsional capacities of the flexural members
Prestressing
In ____ and ______ tanks, the hoop tensile stresses can be effectively counteracted by circular prestressing
pipes, liquid storage
It was observed that the effect of prestress
reduced with ______
time
The ________ of the members
were limited.
load resisting capacities
Under ________, the members were
found to fail
sustained loads
Under sustained load, the strain in concrete
increases with increase in time. This is known
as ________
creep strain
The reduction in length due to creep and
shrinkage is also applicable to the _______, resulting in significant loss in the tensile
strain.
embedded
steel
The total loss in strain due to elastic shortening, creep and shrinkage was also close to _______
0.0007
Obtained a patent for the manufacture of Portland
cement
1824 Aspdin, J
Introduced steel wires in concrete to make flower pots,
pipes, arches and slabs.
1857 Monier, J
Introduced the concept of tightening steel tie
rods in artificial stone and concrete arches.
1886 Jackson, P.H.
Manufactured concrete slabs and small beams with embedded
tensioned steel
Doehring, C.E., (Germany)
Recognized losses due to
shrinkage and creep, and suggested retightening
the rods to recover lost prestress.
1908 Stainer, C.R
Developed a method of winding
and pretensioning high tensile steel wires around
concrete pipes.
1923 Emperger, F.
Hoop-stressed horizontal
reinforcement around walls of concrete tanks through the
use of turnbuckles.
1924 Hewett, W.H.
Used high strength unbonded steel rods. The rods
were tensioned and anchored after hardening of the concrete
1925 Dill, R.H
Used high tensile steel wires, with ultimate strength as high as 1725
MPa and yield stress over 1240 MPa. In 1939, he developed conical
wedges for end anchorages for post-tensioning and developed
double-acting jacks
1926 Eugene Freyssinet (France)
Developed ‘long line’ pre-tensioning
method.
1938 Hoyer, E
Developed an anchoring system for
post-tensioning, using flat wedges
1940 Magnel, G.
_______ is a single unit made of steel
Prestressing Wire
two, three, or seven wires are wound to form a ________
Prestressing strand
a group of strands or wires are wound to form a ________-
Prestressing tendon
A ground of tendons for a ______
prestressing cable
a ______ can be made up of a single steel bar
tendon
when there is adequate bond between the prestressing tendon and concrete, it is called ___________-
bonded tendon
__________ and _________ tendons are bonded tendons
Pre-tensioned, grouted post-tensioned
when there in no bond between the prestressing tendon and concrete, it is called _________
unbonded tendon
when _____ is not applied after post-tensioning, the tendon is an unbonded tendon
grout
Stages of loading
initial
Intermediate
Final
Span to depth ratio for non-prestressed slab
28:1
Span to depth ratio for prestressed slab
45:1
In the Philippines, the application of prestressed concrete
diversified over the years. Among bridges, the __________ in
Bukidnon, Philippines remains a classic example of prestressed
Atugan Bridge
Prestressing needs __________
skilled technology
Types of prestressing
Hydraulic
Mechanical
Electrical
Chemical
This classification is based on the location of the prestressing tendon with respect to the
concrete section.
External or internal prestressing
This is the most important classification and is based on the sequence of casting the
concrete and applying tension to the tendons.
Pre-tensioning or post-tensioning
This classification is based on the shape of the member prestressed.
Linear or circular prestressing
Based on the amount of prestressing force, three types of prestressing are defined.
Full, limited or partial prestressing
As the names suggest, the classification is based on the directions of prestressing a
member.
Uniaxial, biaxial or multi-axial prestressing
The _______ is transferred to the concrete from the tendons, due to the bond between them.
prestress
The various stages of the pre-tensioning operation are summarized as follows.
1)Anchoring of tendons against the end abutments
2) Placing of jacks
3) Applying tension to the tendons
4) Casting of concrete
5) Cutting of the tendons.
is suitable for precast members produced in bulk
Pre-tensioning
___________ is required for the pre-tensioning operation.
prestressing bed
There should be good bond between concrete and steel over the ____________
transmission length
_________ is suitable for heavy cast-in-place members.
Post-tensioning
the relative disadvantage of post-tensioning as compared to pre-tensioning is the requirement of ___________ and ___________
anchorage device, grouting equipment.
In post-tensioned members the ___________ transfer the prestress to the concrete.
anchoring devices
principles of anchoring the tendons.
1) Wedge action
2) Direct bearing
3) Looping the wires
The_________ based on wedge action consists of an anchorage block and
wedges. The strands are held by __________ of the wedges in the anchorage block.
anchoring device, frictional grip
_________ or _________ or ________ formed at the end of the wires directly bear
against a block.
rivet or bolt heads or button heads
The _______, Leoba system and also the Dwidag single-bar anchorage bo
system, work on this principle where the wires are looped around the concrete. The
wires are looped to make a bulb.
Baur-Leonhardt system
The _________ are used to connect strands or bars. They are located at the junction of
the members, for example at or near columns in post-tensioned slabs, on piers in posttensioned bridge decks.
couplers
_________ can be defined as the filling of duct, with a material that provides an anticorrosive alkaline environment to the prestressing steel and also a strong bond between
the tendon and the surrounding grout
Grouting
