What is the correct sequence for concreting a shell roof?

Concreting should begin at the lowest points (springing or edge beams) and proceed upwards simultaneously towards the crown.

How should decentering (striking of formwork) be handled safely?

Centering must be lowered gradually and uniformly over the entire area to transfer the load smoothly to the concrete structure without shock.

Why is the maximum aggregate size restricted in shell roofs?

Because shell structures are inherently thin, smaller maximum aggregate sizes (typically 10 mm to 12.5 mm) are required to prevent voids and ensure proper compaction around congested reinforcement.

IS 2204

: 1962

Code of practice for construction of reinforced concrete shell roof

CurrentSpecializedCode of PracticeBIMStructural Engineering · Building Construction Practices incl. Painting, Varnishing

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This code specifies the construction practices for reinforced concrete shell roofs, detailing requirements for formwork, reinforcement placement, concreting methods on curved slopes, and the safe sequence of decentering. It serves as a practical execution companion to the design criteria provided in IS 2210.

Code of practice for construction of reinforced concrete shell roof

Quick Reference Values

Minimum clear cover to reinforcement12 mm (or diameter of bar, whichever is greater)

Nominal maximum size of coarse aggregate12.5 mm (for typical thin sections)

Concrete slump for curved/steep slopes25 mm to 50 mm

Practical Notes

Concreting should always start from the edge beams or springings and work simultaneously up towards the crown to maintain balanced loading on the centering.

Strict control over concrete workability is crucial; a highly workable (high slump) mix will slide down the steep slopes of the shell.

Decentering must be executed gradually, uniformly, and symmetrically to avoid introducing unbalanced stresses into the newly formed shell.