Design of tension and compression members – Tanks, pipes and poles – Partial prestressing – Definition, methods of achieving partial prestressing, merits and demerits of partial prestressing.

1. UNIT V
MISCELLANEOUS STRUCTURES
Mr.P.SELVAKUMAR
Assistant Professor
Department of Civil Engineering
Knowledge Institute of Technology, Salem

2. Prestressed concrete tanks
• Prestressed concrete tanks are generally cylindrical
with diameters up to 100m and liquid depths up to
36m and capacities of about 50million litres.
Applications:
• It have been widely used for the storage of fluids, such
as water, oil, gas, sewage, granular materials like
cement, liquids, chemicals, slurries and more recently
cryogens.
• Recent applications include special forms of
Prestressed concrete tanks which are triaxially
prestressed and serve as contaminant vessels and
biological shields for nuclear reactors.

3. Shape of prestressed concrete tanks

4. Economic dimensional Proportions
• A majority of the prestressed concrete tanks built all over the
world are of circular shape.
• The economic proportion of diameter to height of the circular
cylindrical tanks was found to be 4:1.

5. Prestressed Concrete Poles
• During the last two decades, prestressed
concrete poles have bean gradually replacing
the traditional poles made of wood or steel or
RC.
• It is widely used in most countries for railway
power and signal lines, lighting poles, antenna
masts, telephone transmission, low and high
voltage, electric power transmission and
substation towers.

6. • Resistance to corrosion in humid and temperate
climates and to erosion in desert areas.
• Freeze-thaw resistance in cold regions.
• Easy handling due to less weight than other poles.
• Fire resistant, particularly to grass and bush fires near
the ground line.
• Easily installed in drilled holes in ground with or
without concrete fill.
• Lighter because of reduce C.S. when compared with
reinforced concrete poles.
Advantages

7. Shapes of P.S.C. Poles

8. Design considerations
• The poles are generally designed for the following critical load
conditions.
– Bending due to wind load on the cable and on the exposed face
– Combined bending and torsion due to eccentric snapping of
wires
– Maximum torsion due to skew snapping of wires
– Bending due to failure of all the wires on one side of the pole
– Handing and erection stresses.
• The flexural strength of the pole in the direction of the cable line
should not be less than one quarter of the strength in the
transverse dirction.

9. Prestressed concrete Sleepers
• During last 20years the concrete sleepers have been
increasingly used by the world railway system in high
speed and heavy traffic density tracks.
• To date, there are more than 100 million prestressed
concrete sleepers of mono-block type in service.
• The developments in sleepers extending over the last
three decades, has resulted in adoption of different
types.
– Two-block sleepers
– Longitudinal sleepers
– Beam-type sleepers

10. Types of P.S.C. Sleepers

11. Prestressed concrete bridges
• Prestressed concrete is ideally suited for the
construction of medium and long span bridges.
• Solid slabs are used for the span range of 10 to
20m, while T-beam slab decks are suitable for
spans in the range of 20 to 40m.
• Single or multi cell box girders are preferred for
larger spans of the order of 30 to 70m.
• Prestressed concrete has been widely used
throughout the world for simply supported,
continuous, balanced cantilever, suspension,
hammer-head and bridle-chord-type bridges in
the span range of 20 to 500m.

12. Pretensioned prestressed bridge decks
• It is generally comprise precast Pretensioned
units used in conjunction with cast in situ
concrete, resulting in composite bridge decks
which are ideally suited for small and medium
spans in the range of 20 to 30m.
• In UK, the precast prestressed I- and inverted T-
beams have been standardised by the cement
and concrete association.
• The design and development of the Y-beams,
which are superior to M-beams, are ideally suited
for medium spans of 15 to 30m.

13. • Cross Section of standard Y-Beams

14. • Section properties of standard Y-beams

15. • Typical C.S. of pre-tensioned prestressed concrete bridge
decks

16. Post tensioned prestressed bridge
decks
• Post-tensioned bridge decks are generally adopted for
longer spans exceeding 20m.
• Bridge decks with precast post tensioned girders of
either T-type or box type, in conjunction with a cast in
situ slab are commonly adopted for spans exceeding
30m.
• Post tensioning facilitates the use of curved cables,
which improve the shear resistance of the girders.
• Post-tensioning is ideally suited for prestressing long
span girders at the site of construction, without the
need for costly factory-type installations like pre-
tensioning beds.

17. • Typical C.S. of post-tensioned prestressed concrete bridge
decks

18. Advantages of P.S.C.Bridges
• High strength concrete and high tensile steel, besides
being economical, make for slender sections, which are
aesthetically superior.
• Prestressed concrete bridges can be designed as class-I
type structures without any tensile stresses under
service loads, thus resulting in a crack free structure.
• In comparison with steel bridges, prestressed concrete
bridges require very little maintenance.
• Prestressed concrete is ideally suited for composite
bridge construction.
• Post-tensioned prestressed concrete finds extensive
applications in long span continuous girder bridges of
variable cross sections.

19. Principles of design
• Design moments and shear forces
• Design of slab section and reinforcement
• Design of longitudinal girders
• Design of supplementary reinforcements
• Design of end block
• Design of cross girders

20. Thank You