Glossary of terms relating to cement concrete, Part 5: Formwork for concrete
1972 Edition

The scope of IS 6461 Part 5 (1972) encompasses definitions and terminology pertinent to concrete formwork systems. It addresses components such as top forms designed for steep surfaces where direct casting isn't feasible, scaffolding as temporary support for formwork and personnel, and sliding formwork which involves continuous or staged movement during concrete shaping. This section lays the foundation for understanding formwork design and construction without delving into specific formulas or tables, which are covered in subsequent parts.

This segment outlines fundamental terms associated with formwork for concrete. Definitions include formwork as temporary or permanent molds for concrete, table form which refers to preassembled units for suspended floors that are repositioned after casting, shuttering as panels shaping concrete, and falsework being the temporary supports holding the formwork. Specifications emphasize the necessity for formwork to be strong, leak-proof, and accurately aligned, with consideration for safety and ease of reuse.

The focus here is on the various types of formwork, particularly table formwork for suspended slabs, and their constituent materials such as timber, steel, and plywood. It details accessories including clamps, bolts, ties, wedges, and spacers which ensure stability and proper alignment. Load calculation formulas are presented to account for the combined weight of fresh concrete, formwork itself, and any additional loads like workers or equipment, along with typical prop spacing guidelines.

This section defines the support structures integral to concrete formwork, including suspended formwork and preassembled table units. It discusses load requirements to safely carry the weight of fresh concrete and construction activities, with design parameters such as deflection limits and safety factors. Typical load formulas and standard load values are provided to guide the design of durable and stable formwork support systems.

IS 6461 Part 5 elaborates on the function and types of form ties and clamps. Form ties are tensile elements that hold opposing form faces against lateral pressure from concrete. Through ties extend through the concrete and are removed after formwork removal. Form anchors secure formwork to hardened concrete permanently, while snap ties break off below the surface after use. Design considerations include tensile strength, spacing, material selection, and controlled break-off forces to maintain structural integrity.

This portion addresses the various materials used in formwork construction and their corresponding surface finishes. Timber, plywood, steel sheets, and plastic laminates are covered with respect to their texture, durability, reusability, and impact on concrete surface quality. It distinguishes rough formwork for textured finishes from smooth formwork requiring precise joints and surface preparation. The importance of rigidity, leak-proof design, and ease of dismantling is emphasized.

Here, the standard explains the pressures exerted on formwork by fresh concrete, particularly hydrostatic pressure which increases linearly with concrete depth. It also covers live loads from workers and equipment, and the self-weight of formwork components. Design guidance includes formulas to calculate these loads, ensuring formwork strength and stability during concreting operations.

This section defines stop ends used at vertical construction joints and fillers or stoppings applied to seal gaps, screw holes, and joints in formwork. Specifications stress the need for tight, leak-proof joints that allow minimal movement, and filler materials that are flexible, non-absorbent, and compatible with formwork surfaces. Proper application ensures smooth concrete finishes and structural soundness.

Guidelines for the timing and procedure of formwork removal are presented here. Striking time depends on concrete strength, mix, temperature, and element type, with typical minimum periods outlined for walls, slabs, beams, props, and foundations. The standard emphasizes ensuring concrete has attained a sufficient percentage of design strength before formwork removal, and addresses the safe handling of movable formwork during relocation.

Special formwork systems such as table formwork for suspended floors are described. These are preassembled units that rest on previously cast floors and are moved as a single entity to expedite construction. The section covers load requirements, material considerations, and safety measures during lifting and movement, along with fundamental design principles like pressure calculations and deflection limits.

This part focuses on formwork designed for specific structural members, especially suspended floors using table formwork. It outlines typical pressure formulas, minimum thicknesses for timber forms, allowable deflections, and requirements for stability and rigidity during casting and curing. Emphasis is placed on ease of removal without harming the concrete surface.

The standard defines inspection doors as removable panels in formwork to facilitate inspection, concrete placement, and compaction. Typical dimensions and locations are specified to ensure accessibility without compromising formwork integrity. Construction requirements include secure fitting, sealed edges, and provisions for repeated use. Related features like scaffolding and top forms are also referenced.

Definitions include mechanical vibrators used to consolidate concrete, distinguishing external vibrators attached to formwork, internal vibrators inserted into concrete, and surface vibrators applied atop concrete. Specifications cover typical frequencies and amplitudes, explaining the importance of proper vibration to eliminate air pockets and achieve uniform density, while cautioning against over- or under-vibration.

This section covers safety-related terms such as formwork, shoring, falsework, stripping, and camber. While IS 6461 Part 5 is primarily a glossary, it highlights the importance of load calculations including dead, live, and concrete loads, adequate bracing to prevent collapse, and inspection before reuse. For detailed safety and handling calculations, references to IS 456 and IS 875 are recommended.

IS 6461 Part 5 is part of a 12-part series covering terminologies for cement concrete. This part specifically details formwork terms. Other parts address aggregates, materials, reinforcement, concrete types, equipment, construction processes, properties, structural aspects, testing, prestressed concrete, and miscellaneous topics. For design formulas and detailed construction practices, IS 456, IS 3370, and IS 15916 are relevant complementary standards.