---
title: "Formwork for beam and slab (column)"
subject: "Building Technology"
chapter: 8
key: "semester_6/building_technology:formwork-beam-slab"
source: https://www.bctengineer.com/q/semester_6/building_technology/formwork-beam-slab
site: BCT Engineering
---

# Formwork for beam and slab (column)

Building Technology · Chapter 8: Temporary construction

- Asked in: 2079 Chaitra, 4 marks; 2077 Chaitra, 4 marks (asked 2 times)
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/building_technology/formwork-beam-slab
- Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-8

## Question

Explain the formwork for beam and slab (column and beam) with necessary sketch.

## Short answer

Formwork for beams includes a bottom soffit plank on props with sole plates and wedges, and vertical side cheeks with cleats and struts. Slab formwork uses plywood sheathing on joists supported by runners and props with sole plates. Column formwork has four side panels stiffened by battens and clamped by yokes with inclined props. Striking times per IS 456: vertical faces 16-24 hours, slab soffits 3 days, beam soffits 7 days.

## Answer

**Formwork (shuttering)** is the temporary mould into which wet concrete is poured and kept until it gains enough strength to support itself. It is made of timber, plywood, steel or aluminium.

#### Formwork for beam
- **Beam bottom (soffit) plank:** a 25-40 mm thick board, as wide as the beam, supported on **head trees/props** at 0.6-1.2 m spacing, standing on **sole plates** and **wedges**.
- **Beam sides (cheeks):** vertical boards fixed on both sides with **cleats** and **struts** at 0.6-0.9 m spacing, to hold the sides in place.
- The props are braced to each other horizontally and diagonally.

#### Formwork for slab
- **Sheathing/decking:** plywood or boards (18-25 mm).
- **Joists** (75 x 50 mm at 400-500 mm c/c) under the sheathing, supported on **runners** (ledgers) and **props** (vertical posts of steel or ballies) at 1-1.2 m, with a **sole plate** and wedges for easy removal.
- The edges are closed by a side form (stop board).

#### Formwork for column
- **Sheathing:** four side panels of boards (about 40 mm) or plywood (18 mm), stiffened by battens.
- **Yokes/clamps:** timber yokes or steel column clamps around the panels, placed closer at the bottom (where the concrete pressure is greatest) and wider apart at the top.
- **Props:** inclined props on two faces keep the column plumb; a cleaning hole is left at the foot.

```text
 Beam & slab form (section)
   ___slab sheathing_________
   ___joists |  |  |  |  ___
        |cheek| beam |cheek|
        |     |soffit|     |
        |    head tree     |
        |      prop        |
        |_____ sole plate__|
```
**Striking time** (IS 456, OPC): vertical faces of beams, columns and walls 16-24 hours; slab soffits 3 days (props refixed); beam soffits 7 days (props refixed); props to slabs 7 days up to 4.5 m span and 14 days over 4.5 m; props to beams 14 days up to 6 m span and 21 days over 6 m. Surfaces should be oiled for easy removal.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Which parts form the beam formwork?
   A. Rakers and sole plates
   B. Only vertical sheeting and walings
   C. Soffit plank on head trees/props with side cheeks held by cleats and struts
   D. Standards and ledgers
   Answer: C. The beam soffit plank sits on props and the cheeks are fixed at the sides with cleats and struts. (Key point: Beam formwork parts)

2. How is slab formwork supported?
   A. On rakers
   B. Sheathing hanging from the beams by ropes
   C. Directly on the ground without props
   D. Sheathing on joists, which rest on runners and props with sole plate and wedges
   Answer: D. Sheathing is supported by joists, runners and props, with sole plates and wedges for easy removal. (Key point: Slab formwork parts)

3. According to IS 456, the sides of beams, columns and walls can be struck after about:
   A. 3 days
   B. 16-24 hours
   C. 14 days
   D. 28 days
   Answer: B. Vertical sides need only 16-24 hours because they carry no load, unlike soffits which stay propped longer. (Key point: Striking time)

## Related in Building Technology

- [Formwork for excavation, timbering, RCC formwork](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aformwork-timbering-062p) — Building Technology, chapter 8

## Related in other subjects

- [Column slab base: sketch and design steps](https://www.bctengineer.com/question.md?key=semester_6%2Fdesign_of_steel_and_timber_structure%3Aslab-base-procedure-sketch) — Design of Steel and Timber Structure, chapter 6, asked 3×
- [Slab three edges continuous, one short edge discontinuous (5x4 m, 250 beam)](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Aslab-three-edges-continuous-one-short) — Design of RCC Structure, chapter 9, asked 3×
- [Beam supporting RCC slab, DL 10 kN/m, IL 30 kN](https://www.bctengineer.com/question.md?key=semester_6%2Fdesign_of_steel_and_timber_structure%3Abeam-6m-rcc-slab-10dl-30il) — Design of Steel and Timber Structure, chapter 7, asked 2×
- [Beam supporting RCC slab, DL 25, IL 20 kN/m](https://www.bctengineer.com/question.md?key=semester_6%2Fdesign_of_steel_and_timber_structure%3Abeam-rcc-slab-6m-25dl-20il) — Design of Steel and Timber Structure, chapter 7, asked 2×