A Study on the
Construction Process

Precast Concrete
In-situ cast Concrete
Shoring and Underpinning
Introduction

Precast concrete
In-situ cast concrete

Shoring
Underpinning
Precast Concrete
What is Precast Concrete?
•

Cast into specific shapes at another location

•

Developed in the late 1960s

•

First use: ...
Characteristics
•

Great accuracy and high quality

•

Additional features: reinforcing, moles, anchor bolts, etc

•

Char...
Manufacture
• Casting beds used
• High strength steel strands
pretensioned

• Transverese bulkhead
seperators inserted

• ...
Slabs
•

The most standardised precast elements

•

Includes solid flat slab, hollow core slab, double tee
slab, and singl...
Solid flat slab
Hollow core slabs
Double tee slabs
Single tee slabs
Beams
• Made in different sizes
• Rectangular beams, L shaped
beams, inverted T beams and
AASHTO beams
Wall panels
• Prestressed or conventional
reinforcement

• Used as load bearing walls
• Includes solid wall panels,
hollow...
Solid wall panels
Hollow core wall
panels
Tee wall panels
How are precast buildings put together?

Double tee slabs supported on frame of columns and
girders
Hollow core slabs supported on load bearing walls
Double tee slabs supported on load bearing walls,
columns and inverted tee beams
In-situ cast concrete
What is in-situ cast concrete?
•

Concrete that is cast into forms on the building site

•

Any shape that can be formed c...
Selecting an in-situ cast concrete framing system
•

Are the bays of the building square or nearly square?

•

How long ar...
In-situ Concrete mix
•

Appropriate concrete properties designed

•

Appropriate mix design developed

•

Mixing, transpor...
In-situ concrete placement
•

Should not be placed more rapidly than it can be spread

•

Deposit as near as possible to t...
Curing
•

Satisfactory moisture content and temperature required

•

Concrete in formwork is protected from drying out

•
...
Advantages
•

Easy transportation of wet concrete

•

Flexible when it comes to geometric shapes

•

Relatively easy to do...
Disadvantages
•

Produced in an unprotected environment

•

Additional time required for drying out process

•

Requires m...
Shoring
What is shoring?
•

Construction of a temporary structure to support an
unsafe structure
When do we need shoring?
•

When walls bulge out

•

When walls crack

•

When an adjacent structure needs to be pulled do...
Shoring during
construction
Raking shores
•

Rest upon the ground and
support the wall by being inclined
against it
Using raking shores
• Size of the raker decided on
anticipated thrust from the wall

• Center of the raker and wall
should...
Dead Shores
Flying Shores
Scaffold type shoring
• Scaffolding was first designed to
support loads imposed by
workers

• Often used as support for
fo...
Underpinning
What is
underpinning?
• Strengthening and stabilising
the foundation of an existing
building

• Installation of temporary ...
When do we need
underpinning?
• Construction of a new building
adjacent to the old one

• Settlement of an existing
buildi...
Temporary support with maintenance jacking
•

Light structures may be supported with timber or concrete mats

•

If settle...
Bracket pile
underpinning
• Steel bracket piles driven
adjacent to the structure

• Load is transferred from the
structure...
Minipiles
• Minipiles inserted through the
existing foundation

• Generally do not require
temporary support of the
buildi...
New foundation wall
and footing constructed
underneath the existing
foundation
•

•
•

The area is excavated
The new footi...
Support during
underpinning
•

•

Digging trenches at intervals
This leaves most of the
foundation supported by the soil
Support during
underpinning
•

•
•

Using needle beams
Beams are threaded through
holes cut in the wall
Entire wall can be...
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A study on the construction process (Precast concrete, In-situ cast concrete, Shoring, Underpinning)

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A study on the construction process (Precast concrete, In-situ cast concrete, Shoring, Underpinning)

  1. 1. A Study on the Construction Process Precast Concrete In-situ cast Concrete Shoring and Underpinning
  2. 2. Introduction Precast concrete In-situ cast concrete Shoring Underpinning
  3. 3. Precast Concrete
  4. 4. What is Precast Concrete? • Cast into specific shapes at another location • Developed in the late 1960s • First use: stair treads, coping, lintels, and window sills • Known for its high quality architectural products
  5. 5. Characteristics • Great accuracy and high quality • Additional features: reinforcing, moles, anchor bolts, etc • Characteristics controlled by different materials • Reinforcement: Conventional reinforcing or prestressed steel
  6. 6. Manufacture • Casting beds used • High strength steel strands pretensioned • Transverese bulkhead seperators inserted • Additional reinforcement added • Concrete poured and vibrated • Cured with live steam or radiant heat
  7. 7. Slabs • The most standardised precast elements • Includes solid flat slab, hollow core slab, double tee slab, and single tee slab
  8. 8. Solid flat slab
  9. 9. Hollow core slabs
  10. 10. Double tee slabs
  11. 11. Single tee slabs
  12. 12. Beams • Made in different sizes • Rectangular beams, L shaped beams, inverted T beams and AASHTO beams
  13. 13. Wall panels • Prestressed or conventional reinforcement • Used as load bearing walls • Includes solid wall panels, hollow core wall panels and tee wall panels
  14. 14. Solid wall panels
  15. 15. Hollow core wall panels
  16. 16. Tee wall panels
  17. 17. How are precast buildings put together? Double tee slabs supported on frame of columns and girders
  18. 18. Hollow core slabs supported on load bearing walls
  19. 19. Double tee slabs supported on load bearing walls, columns and inverted tee beams
  20. 20. In-situ cast concrete
  21. 21. What is in-situ cast concrete? • Concrete that is cast into forms on the building site • Any shape that can be formed can be cast • Certain types of concrete elements cannot be precast, and can only be cast in-situ
  22. 22. Selecting an in-situ cast concrete framing system • Are the bays of the building square or nearly square? • How long are the spans? • How heavy are the loads?
  23. 23. In-situ Concrete mix • Appropriate concrete properties designed • Appropriate mix design developed • Mixing, transporting and handling coordinated with placing and finishing
  24. 24. In-situ concrete placement • Should not be placed more rapidly than it can be spread • Deposit as near as possible to the final position • The concrete is placed in forms and consolidated
  25. 25. Curing • Satisfactory moisture content and temperature required • Concrete in formwork is protected from drying out • Curing compounds and treatments prevent loss of moisture • Large surface areas problematic during curing
  26. 26. Advantages • Easy transportation of wet concrete • Flexible when it comes to geometric shapes • Relatively easy to do late changes to structure • Structure becomes monolithic
  27. 27. Disadvantages • Produced in an unprotected environment • Additional time required for drying out process • Requires more temporary work • Complex process with many inputs and flows
  28. 28. Shoring
  29. 29. What is shoring? • Construction of a temporary structure to support an unsafe structure
  30. 30. When do we need shoring? • When walls bulge out • When walls crack • When an adjacent structure needs to be pulled down • When openings are to be newly made or enlarged in a wall • During construction
  31. 31. Shoring during construction
  32. 32. Raking shores • Rest upon the ground and support the wall by being inclined against it
  33. 33. Using raking shores • Size of the raker decided on anticipated thrust from the wall • Center of the raker and wall should not meet at floor level • Shoring may be spaced at 3 4.5m • Wedges should not be used on sole plates • For tall buildings, rider raker can be used
  34. 34. Dead Shores
  35. 35. Flying Shores
  36. 36. Scaffold type shoring • Scaffolding was first designed to support loads imposed by workers • Often used as support for formwork • Provides rapid utilisation for formwork support
  37. 37. Underpinning
  38. 38. What is underpinning? • Strengthening and stabilising the foundation of an existing building • Installation of temporary or permanent support • Provides additional depth or increase bearing capacity
  39. 39. When do we need underpinning? • Construction of a new building adjacent to the old one • Settlement of an existing building • Change in how a structure is used • Need to add a basement below an existing building
  40. 40. Temporary support with maintenance jacking • Light structures may be supported with timber or concrete mats • If settlement occurs, mechanical or hydraulic jacks keep the structure level
  41. 41. Bracket pile underpinning • Steel bracket piles driven adjacent to the structure • Load is transferred from the structure into the pile through a steel bracket • Backfilled with lean sand cement mix
  42. 42. Minipiles • Minipiles inserted through the existing foundation • Generally do not require temporary support of the building
  43. 43. New foundation wall and footing constructed underneath the existing foundation • • • The area is excavated The new footing is constructed The excavated area is backfilled
  44. 44. Support during underpinning • • Digging trenches at intervals This leaves most of the foundation supported by the soil
  45. 45. Support during underpinning • • • Using needle beams Beams are threaded through holes cut in the wall Entire wall can be exposed at once

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