Temporary Supporting Structures
Classifications
- Formworks/shuttering
- Scaffolding
- Shoring
- Underpinning
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 no | Member | Period of time |
| 1. | Walls, columns and vertical sides of beams | 1 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 4.5m | 7 days | |
| (b) For slabs of span over 4.5m | 14 days | |
| 5. | Removal of props to beams and arches: | |
| (a) Spanning up to 6m | 14 days | |
| (b) Spanning over 6m | 21 days |
Failure of Formwork
- Improper or inadequate shoring
- Improper design of formwork
- Negligence
- Lack of control over placement of concrete
- Inadequate strength of form material
- Inadequate bracing of members
- Premature stripping
- Incompetence
- Failure to follow codes and standards