Temporary Supporting Structures

Temporary Supporting Structures

Classifications

  • Formworks/shuttering
  • Scaffolding
  • Shoring
  • UnderpinningTemporary Supporting Structures

Form work-requirements

  • Strength
  • Rigidity
  • Less leakage
  • True to size
  • Smooth surface
  • Easy removal
  • Supports

Economy in formwork

  • Forms of regular sizes and shapes
  • Allow reuse
  • Design structural components to allow use of commercially available forms
  • Clean and oil forms after use
  • Pre-fabricate the forms on the ground

Materials For Formwork

  • Steel
  • Timber
  • Plywood

General Arrangements Of Formwork

Formworks are used for

  • Wall footings
  • Column footings
  • Columns
  • RCC beams
  • RCC beam and slab floor construction
  • Stairs

Forces Acting On Formwork

  • Dead load
  • Live load
  • Vertical loads
  • Lateral pressure
  • Lateral loads
  • Special equipment loads
  • Other loads

Formwork Vibration For Compaction Of Concrete

  • External/Shutter Vibrators
  • Clamped to forms, vibration is conveyed to concrete through the form
  • Useful, where reinforcement is congested
  • Forms need to be designed for strength
  • Formwork should be watertight
  • Operates at 3000 to 9000 rpm
  • Requires more power than internal vibrators to compensate the energy absorbed by the forms

Shoring

Used to support formwork

  • Wood post shores
  • Adjustable shores
  • Horizontal shores
  • Permanent shores

Stripping Of Forms

Depends upon:

  • Amount and nature of dead load
  • Character and quality of concrete
  • Shape, span and situation of structure
  • Temperature of the atmosphere
Sl noMemberPeriod of time
1.Walls, columns and vertical sides of beams1 to 2 days
2.Slab (props left under)3 days
3.Beam soffits (props left under)7 days
4.Removal of props to slabs:
(a) For slabs of span up to 4.5m7 days
(b) For slabs of span over 4.5m14 days
5.Removal of props to beams and arches:
(a) Spanning up to 6m14 days
(b) Spanning over 6m21 days

Failure of Formwork

  1. Improper or inadequate shoring
  2. Improper design of formwork
  3. Negligence
  4. Lack of control over placement of concrete
  5. Inadequate strength of form material
  6. Inadequate bracing of members
  7. Premature stripping
  8. Incompetence
  9. Failure to follow codes and standards

 

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