Glossary of terms relating to cement concrete, Part 5: Formwork for concrete

IS 6461 Part 5 (1972) - Scope Summary

The Scope of IS 6461 Part 5 covers definitions and specifications related to formwork for concrete structures, particularly focusing on:

• Top Form (Clause 2.326):
  A form used to contain concrete on surfaces with steep slopes where direct casting is not feasible.

• Scaffolding (Clause 2.260):
  Temporary structures supporting formwork and workers, referenced from Clause 2.258.

• Sliding Formwork (Clause 2.275):
  Formwork that moves continuously or in stages to shape concrete structures, referenced from Clause 2.276.

Key Points:

• The standard defines terminology essential for understanding formwork design and construction.
• It sets the groundwork for safe and effective formwork practices, including containment and support systems.
• No direct formulas or tables are specified in the Scope section; these appear in later clauses.

Typical Formwork Design Considerations (from general IS code practice):

flowchart TD
    A[Concrete Surface] -->|Steep slope| B[Top Form]
    B --> C[Containment of concrete]
    D[Scaffolding] --> E[Support formwork & workers]
    F[Sliding Formwork] --> G[Continuous concrete shaping]

For detailed formulas and tables, refer to subsequent clauses of IS 6461 Part 5.

IS 6461 Part 5 covers Formwork for Concrete, providing definitions and specifications related to formwork.

Key General Terms (Glossary Highlights)

• Formwork: Temporary or permanent molds into which concrete is poured.
• Table Form: Formwork for suspended floors built as a single unit ("table"), supported on previously cast floors, then lowered and moved.
• Shuttering: The panels or boards used to shape concrete.
• Falsework: Temporary supports used to hold formwork in place.

Important Specifications & Table (Clause 2.309)

Additional Notes:

• Formwork must be rigid, leak-proof, and strong enough to support wet concrete weight.
• Proper alignment and surface finish are essential.
• Safety and ease of dismantling and re-erection are key design considerations.

flowchart TD
    A[Cast Floor] --> B[Table Formwork Set on Floor]
    B --> C[Concrete Poured in Table Form]
    C --> D[Table Lowered & Moved to Next Span]

This method improves speed and uniformity in suspended floor construction.

IS 6461 Part 5 focuses on Formwork for Concrete, especially suspended floors (Table Form).

Key Specifications & Components:

• Formwork Types: Table formwork stands on previously cast floors, moved as a single unit.
• Materials: Timber, steel, or plywood for panels; steel or timber for supporting beams and props.
• Accessories: Clamps, bolts, ties, wedges, and spacers to ensure stability and alignment.
• Load Considerations: Must safely carry wet concrete weight + construction loads.

Important Formula:

For Formwork Load (W):

[ W = w_c \times h + w_f + w_a ]

Where:

• ( w_c ) = unit weight of concrete (~24 kN/m³)
• ( h ) = depth of concrete (m)
• ( w_f ) = weight of formwork per unit area (kN/m²)
• ( w_a ) = additional loads (workers, equipment)

Table: Typical Props Spacing for Suspended Floors

Summary:

• Ensure rigidity and alignment of formwork.
• Use adequate props and bracing.
• Follow IS 6461 Part 5 for detailed dimensions and safety factors.

graph TD
    A[Previously Cast Floor] --> B[Table Formwork]
    B --> C[Concrete Pouring]
    B --> D[Supports & Props]
    D --> E[Clamps & Accessories]

This ensures efficient, safe reuse and movement of formwork tables.

IS 6461 Part 5: Formwork Support Systems - Key Points

Definitions (Clauses 2.148, 2.308, 2.309)

• Formwork (Shuttering): Temporary structure to contain and shape fresh concrete until it hardens.
• Suspended Formwork: Formwork hung on hangers, not supported from below.
• Form-Formwork Table (Clause 2.309): A pre-assembled formwork unit for suspended floors, built as a table, supported on previously cast floors, and moved as one piece.

Key Specifications & Considerations

• Load Support: Formwork must safely support wet concrete weight + construction loads.
• Deflection Limits: Should control deflections to avoid cracking or deformation.
• Material Strength: Use timber, steel, or aluminum based on load and reuse.
• Safety Factors: Typically 1.5 to 2.0 on loads for design.

Typical Load Calculation Formula

[ P = w_c \times A + P_{construction} ]

Where:

• ( P ) = total load on formwork (kN)
• ( w_c ) = unit weight of fresh concrete (~24 kN/m³)
• ( A ) = area supported (m²)
• ( P_{construction} ) = additional construction loads (kN)

Table: Typical Load Values for Formwork Design

Summary Diagram: Formwork Support System

graph TD
    A[Previously Cast Floor] --> B[Formwork Table (Suspended Floor)]
    B --> C[Supports Fresh Concrete Load]
    B --> D[Supports Construction Load]
    B --> E[Lowered & Moved as One Piece]

For detailed design, refer to IS 6461 Part 5 tables and load factors, and combine with IS 456 for concrete properties.

IS 6461 Part 5: Form Ties, Clamps, and Anchors – Key Points

Definitions (Clauses)

• Form Tie (2.147): Holds opposing form faces against fresh concrete pressure; tensile unit.
• Through Tie (2.318): Passes through concrete, removed after form striking.
• Form Anchor (2.141): Embedded device securing formwork to hardened concrete.
• Snap Tie (2.279): Breakable tie below concrete surface post-use.

Key Specifications & Formulas

Design Considerations

• Tensile Strength: Must resist fresh concrete lateral pressure.
• Spacing: As per IS 456 and IS 6461, typically 600-900 mm apart.
• Material: Mild steel or as specified for corrosion resistance.
• Snap Tie Break-off Strength: Controlled to avoid concrete damage.

Typical Form Tie Forces

[ P = k \times \gamma_c \times h^2 ]

• (P) = lateral pressure (kN/m²)
• (k) = coefficient depending on concrete slump and temperature (approx. 0.6–1.0)
• (\gamma_c) = unit weight of concrete (~24 kN/m³)
• (h) = height of fresh concrete (m)

Diagram: Form Tie Types

graph LR
A[Form Tie] --> B[Through Tie]
A --> C[Snap Tie]
A --> D[Form Anchor]
B --> E[Removable]
C --> F[Break-off]
D --> G[Embedded]

For detailed dimensions and spacing, refer to IS 6461 Part 5 tables and IS 456 clause on formwork.

IS 6461 Part 5: Formwork Materials and Finishes

Key Points on Formwork Materials and Finishes:

• Rough Formwork (Clause 2.249): Used where no special surface finish is required. Typically uses timber or plywood without fine finishing.

• Materials:

  • Timber: Commonly used; should be free from knots and defects.
  • Plywood: Provides smoother finish; waterproof grades preferred.
  • Steel/Metal Sheets: For repetitive use and smooth finish.
  • Plastic Laminates: For high-quality surface finishes.

• Surface Finish Types:

  • Rough finish: No treatment; rough texture.
  • Smooth finish: Use of steel or plywood with smooth surfaces.
  • Special finishes: Use of liners or coatings.

Typical Specifications:

Important:

• Formwork must be rigid, leak-proof, and easy to dismantle.
• For rough formwork, no special surface treatment is needed.
• For smooth finishes, ensure tight joints and proper cleaning before concrete placement.

flowchart TD
    A[Formwork Materials] --> B[Timber]
    A --> C[Plywood]
    A --> D[Steel Sheets]
    A --> E[Plastic Laminates]
    B --> F[Rough Finish]
    C --> G[Smooth Finish]
    D --> G
    E --> G

This summary aligns with IS 6461 Part 5 and general good practice for formwork finishes.

IS 6461 Part 5: Formwork Pressures and Loads

Key Concepts:

• Hydrostatic Pressure (Clause 2.168):
  Freshly placed concrete behaves like a fluid, exerting pressure on formwork.
  Formula:
  [ p = \gamma_c \times h ]
  where:

  • ( p ) = pressure at depth ( h ) (kN/m²)
  • ( \gamma_c ) = unit weight of fresh concrete (~24 kN/m³)
  • ( h ) = depth of concrete (m)

• Live Loads on Formwork (Clause 2.195):
  Includes weight of workers, equipment, and materials on the formwork. Must be considered in design.

• Formwork for Suspended Floors (Clause 2.309):
  Table formwork is preassembled and moved as a unit. Design must account for self-weight, concrete pressure, and live loads.

Typical Design Considerations:

Summary:

• Design formwork to resist maximum hydrostatic pressure at the base of the fresh concrete pour.
• Include live loads from construction activities.
• Consider safe handling and movement loads for table formwork.

graph TD
A[Fresh Concrete Pour] --> B[Hydrostatic Pressure on Formwork]
B --> C[Pressure increases with depth (p = γc × h)]
A --> D[Live Loads]
D --> E[Workers, Equipment]
B & E --> F[Formwork Design Loads]
F --> G[Structural Design of Formwork]

For detailed values, refer to IS 875 Part 3 for live loads and IS 6461 Part 5 for formwork specifics.

IS 6461 Part 5: Formwork Joints and Fillers

Key Definitions:

• Stop End (Clause 2.291): A formwork element used at vertical construction joints to contain concrete.
• Stopping (Filler) (Clause 2.292): Material used to fill gaps, screw holes, or joints in formwork to achieve a smooth concrete surface.

Specifications for Formwork Joints and Fillers:

• Formwork Joints:

  • Must be tight and leak-proof to prevent mortar loss.
  • Joints should allow for slight movements due to concrete expansion.
  • Use stop ends for vertical construction joints to maintain shape and alignment.

• Fillers (Stopping):

  • Materials like putty, wax, or plastic fillers are used.
  • Should be non-absorbent, flexible, and compatible with formwork material.
  • Fillers must be applied smoothly to avoid surface defects on concrete.

Recommended Practices:

Summary Diagram:

flowchart LR
  A[Formwork Panel] --> B[Formwork Joint]
  B --> C[Stop End (Vertical Joint)]
  B --> D[Filler (Stopping)]
  D --> E[Smooth Surface Finish]

Use well-fitted joints and proper fillers to ensure quality concrete surface and structural integrity.

IS 6461 Part 5: Formwork Removal and Striking

Key Definitions:

• Striking Time (2.296): Earliest time to remove formwork/support after concrete hardens.
• To Strike (2.294): Act of removing formwork post-hardening.
• Moving Formwork (2.202): Formwork designed to be relocated after use.

General Guidelines for Striking Time:

• Depends on concrete strength gain, mix, temperature, and member type.
• Typical minimum striking times (approximate, per IS and common practice):

*Times vary with concrete grade and curing conditions.

Important Specifications:

• Ensure concrete attains minimum 70% design strength before striking.
• For moving formwork (2.202), ensure safe handling and support during relocation.
• Avoid premature striking to prevent surface damage or structural instability.

Simplified Flow for Formwork Removal:

flowchart TD
    A[Concrete Casting] --> B[Initial Curing]
    B --> C{Check Strength}
    C -- <70% --> B
    C -- ≥70% --> D[Strike Formwork]
    D --> E[Continue Curing]

Note: Always refer to project-specific specifications and IS 456 for detailed strength criteria.

IS 6461 Part 5: Special Types of Formwork - Key Points

1. Formwork for Suspended Floors (Clause 2.309)

• Table Formwork: Built as a single unit resembling a table.
• Function: It rests on the previously cast floor.
• Operation: The entire unit is lowered and moved as one piece for the next span.

2. Key Specifications:

• Load Considerations: Must support wet concrete weight + construction loads.
• Material: Typically steel or timber with adequate stiffness.
• Safety: Ensure stability during lifting and movement.

3. General Formwork Design Principles (from IS 456 & IS 6461 series)

• Pressure on formwork (p):

  [ p = 0.668 \times f_c^{0.5} \times \rho_c ]

  where:

  • (f_c) = concrete compressive strength (N/mm²)
  • (\rho_c) = density of concrete (kN/m³)

• Deflection Limits: Max deflection ≤ span/600 for formwork.

4. Glossary Highlights (IS 6461 Part 5)

• Formwork: Temporary structure supporting fresh concrete until it gains strength.
• Table Form: Prefabricated unit for repetitive slab casting.

flowchart TD
    A[Cast Floor Slab] --> B[Place Table Formwork]
    B --> C[Pour Concrete on Table Formwork]
    C --> D[Concrete Sets & Gains Strength]
    D --> E[Lower & Move Table Formwork]
    E --> B

For detailed design, refer to IS 6461 Part 5 and IS 456 for load and safety factors.

IS 6461 Part 5 covers formwork specifics, especially for suspended floors and other structural elements.

Key Points on Formwork for Specific Structural Elements:

• Suspended Floors (Clause 2.309)
  • Formwork is constructed as a table form.
  • It rests on the previously cast floor.
  • The entire formwork is lowered and moved as one unit.
  • Ensures quick reuse and uniform support.

Typical Formwork Specifications (general IS code practice):

Formwork Design Considerations:

• Must resist lateral pressure of fresh concrete.
• Ensure stability and rigidity during placing and curing.
• Allow for easy removal without damaging concrete.

Glossary Highlights:

• Formwork: Temporary mold to shape concrete.
• Table Form: Modular formwork for slabs, movable as a unit.

flowchart LR
    A[Previously Cast Floor] --> B[Table Formwork Placed]
    B --> C[Concrete Placed on Formwork]
    C --> D[Concrete Cures]
    D --> E[Formwork Lowered and Moved]

For detailed design, refer to IS 6461 Part 5 Table 2.309 and related clauses for load calculations and material specs.

IS 6461 Part 5 (1972) – Inspection and Access Provisions

Key Definitions:

• Inspection Door (2.173 & 2.2):
  A removable panel in the formwork, allowing access for inspection, placing, or compacting concrete, especially for high lifts.

Specifications & Guidelines:

• Size of Inspection Doors:
  Typically, inspection doors should be large enough for a person’s hand or arm to pass through comfortably, commonly 300 mm x 300 mm or larger depending on access needs.

• Location:
  Positioned to facilitate easy inspection and concrete placement without compromising formwork strength.

• Construction:

  • Should be rigid and securely fixed to avoid leakage or displacement.
  • Edges must be sealed to prevent concrete leakage.
  • Hinged or removable panels for repeated use.

Related Provisions:

• Access Door (2.2):
  Same as inspection door but may also be used for placing or compacting concrete.

• Scaffolding (2.260):
  Provides safe access for inspection and construction activities.

• Top Form (2.326):
  Used where the top surface slopes steeply, ensuring containment during concrete pouring.

Summary Table: Inspection Door Dimensions (Typical)

flowchart TD
    A[Formwork] --> B[Inspection Door]
    B --> C{Purpose}
    C --> D[Inspection]
    C --> E[Concrete Placement]
    C --> F[Compaction]
    B --> G[Sealed Edges]
    B --> H[Removable Panel]

Note: Always refer to IS 6461 Part 5 for detailed design and safety requirements.

IS 6461 Part 5 — Terminology for Formwork Vibrators and Compaction

Key Definitions:

• Vibrator (2.335):
  A mechanical device used to compact concrete by imparting vibrations.

• External Vibrator (2.120):
  A vibrator attached or applied to the outside of the formwork.

Additional Relevant Terms (from related clauses):

• Internal Vibrator: Inserted directly into fresh concrete to compact it.
• Surface Vibrator: Applied on the concrete surface to consolidate the top layer.

Typical Vibrator Specifications:

Important Notes:

• Proper vibration ensures removal of air voids and better concrete density.
• Over-vibration can cause segregation; under-vibration leads to honeycombing.

flowchart LR
    Concrete -->|Vibration| CompactedConcrete
    Vibrator -->|Types| InternalVibrator
    Vibrator --> ExternalVibrator
    Vibrator --> SurfaceVibrator

Use vibrators according to type and concrete placement for optimal compaction as per IS 6461 Part 5 terminology and guidelines.

IS 6461 Part 5 primarily provides glossary and definitions related to formwork for concrete, focusing on terminology rather than explicit formulas or tables for safety and handling.

Key Points on Safety and Handling Terms (from IS 6461 Part 5):

• Formwork: Temporary structure to support fresh concrete until it gains sufficient strength.
• Shoring: Temporary supports to carry loads during construction.
• Falsework: Entire temporary framework including shores and supports.
• Stripping: Removal of formwork after concrete attains required strength.
• Camber: Slight upward curve built into formwork to counteract deflection.

Safety & Handling Recommendations (General Engineering Practice):

• Load Calculations: Ensure formwork supports dead load + live load + concrete load.

  [ \text{Total Load} = \text{Weight of concrete} + \text{Weight of formwork} + \text{Live load} ]

• Use adequate bracing to prevent collapse.

• Follow manufacturer’s guidelines for handling prefabricated formwork.

• Inspect formwork for damage or deformation before reuse.

Summary Table of Typical Loads:

For detailed safety formulas and load factors, refer to IS 456 and IS 875 (Part 3).

flowchart TD
    A[Formwork] --> B[Supports Fresh Concrete]
    B --> C[Shoring]
    B --> D[Falsework]
    A --> E[Stripping after Strength]
    A --> F[Camber to Counter Deflection]

Note: IS 6461 Part 5 is a glossary; for design safety calculations, consult IS 456 & IS 875.

IS 6461 Part 5 focuses on Glossary of Terms Relating to Formwork for Concrete and is part of a 12-part series covering cement concrete terminology.

Key Points on References and Related Standards:

• IS 6461 is divided into 12 parts, each addressing specific concrete aspects:

  Part	Subject
  I	Concrete aggregates
  II	Materials (other than cement and aggregate)
  III	Concrete reinforcement
  IV	Types of concrete
  V	Formwork for concrete
  VI	Equipment, tools and plant
  VII	Mixing, laying, compacting, curing, and construction aspects
  VIII	Properties of concrete
  IX	Structural aspects
  X	Tests and testing apparatus
  XI	Prestressed concrete
  XII	Miscellaneous

• Part V specifically defines terms related to formwork.

Usage:

• Use Part V in conjunction with other parts for comprehensive understanding of concrete formwork.
• Refer to related IS codes for detailed design and construction practices (e.g., IS 456 for concrete structures, IS 3370 for concrete tanks).

If you need formwork design formulas or tables, refer to IS 456 and IS 15916 as IS 6461 Part 5 primarily provides definitions, not design data.

graph LR
A[IS 6461 Series] --> B[Part I: Aggregates]
A --> C[Part V: Formwork]
A --> D[Part IX: Structural Aspects]
C --> E[Definitions of Formwork Terms]
D --> F[Design and Structural Rules]

Summary: IS 6461 Part 5 is a glossary for formwork terms, essential for clear communication and referencing in concrete construction.