---
title: "Permissible stresses as per IS 800"
subject: "Design of Steel and Timber Structure"
chapter: 2
key: "semester_6/design_of_steel_and_timber_structure:permissible-stresses-is800"
source: https://www.bctengineer.com/q/semester_6/design_of_steel_and_timber_structure/permissible-stresses-is800
site: BCT Engineering
---

# Permissible stresses as per IS 800

Design of Steel and Timber Structure · Chapter 2: Working Stress Design Method

- Asked in: 2068 Bhadra (old course), 6 marks
- Video: [PERMISSIBLE STRESS IN STEEL STRUCTURE - DEFLECTION CRITERIA](https://www.youtube.com/watch?v=AgdzxEVsP_w) — CIVIL ENGINEERING TALENT
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/design_of_steel_and_timber_structure/permissible-stresses-is800
- Whole chapter: https://www.bctengineer.com/md/semester_6/design_of_steel_and_timber_structure/chapter-2

## Question

For a steel of yield stress as $f_y$, what are the permissible stresses in tension, compression, bending, shear and bearing according to IS 800?

## Short answer

Permissible stresses per IS 800:1984: axial tension 0.6f_y, bending 0.66f_y (laterally supported), average shear 0.4f_y, maximum shear 0.45f_y, bearing 0.75f_y. For f_y=250 N/mm², these are 150, 165, 100, 112.5, and 187.5 N/mm² respectively.

## Answer

As per IS 800:1984 (working stress method), with $f_y$ the yield stress of steel (the 2007 code uses limit states instead):

| Stress | Clause | Permissible value |
|---|---|---|
| Axial tension, $\sigma_{at}$ | 4.1 | $0.6f_y$ |
| Axial compression, $\sigma_{ac}$ | 5.1 | $0.6\dfrac{f_{cc}f_y}{[(f_{cc})^n+(f_y)^n]^{1/n}}$ with $n=1.4$, $f_{cc}=\pi^2E/\lambda^2$; maximum $0.6f_y$ |
| Bending, tension & compression, $\sigma_{bt},\sigma_{bc}$ | 6.2 | $0.66f_y$ (laterally supported); lower for a compression flange with high slenderness (table) |
| Average shear, $\tau_{va}$ | 6.4.2 | $0.4f_y$ |
| Maximum shear (in web of I-section), $\tau_{vm}$ | 6.4.1 | $0.45f_y$ |
| Bearing, $\sigma_p$ | 6.3 | $0.75f_y$ |

For $f_y=250$ N/mm²: tension 150, bending 165, average shear 100, maximum shear 112.5 and bearing 187.5 N/mm². For connections (IS 800:1984), black bolts of grade 4.6 have permissible shear 80 N/mm² and bearing 250 N/mm², and shop fillet welds have permissible shear 108 N/mm².

## Check yourself

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

1. For fy = 250 N/mm2, the permissible axial tension and bending stresses are:
   A. 165 and 150 N/mm2
   B. 100 and 150 N/mm2
   C. 150 and 165 N/mm2
   D. 187.5 and 165 N/mm2
   Answer: C. 0.6fy = 150 for tension and 0.66fy = 165 for bending. (Key point: Tension and bending)

2. What are the permissible average shear and maximum shear stress values?
   A. 0.4fy and 0.45fy
   B. 0.6fy and 0.66fy
   C. 0.45fy and 0.4fy
   D. 0.75fy and 0.4fy
   Answer: A. Average shear is 0.4fy (100 N/mm2 for fy 250) and maximum shear at the web is 0.45fy. (Key point: Shear stresses)

3. What is the permissible bearing stress for steel?
   A. 0.6fy
   B. 0.45fy
   C. 0.66fy
   D. 0.75fy
   Answer: D. Permissible bearing stress is 0.75fy, i.e. 187.5 N/mm2 for fy = 250. (Key point: Bearing)

## Related in Design of Steel and Timber Structure

- [Shear stress in rivets B and C](https://www.bctengineer.com/question.md?key=semester_6%2Fdesign_of_steel_and_timber_structure%3Arivet-shear-stress-b-c) — Design of Steel and Timber Structure, chapter 4
- [Idealized stress-strain diagram of steel](https://www.bctengineer.com/question.md?key=semester_6%2Fdesign_of_steel_and_timber_structure%3Astress-strain-mild-steel) — Design of Steel and Timber Structure, chapter 1
- [Single angle tension member, 100 kN](https://www.bctengineer.com/question.md?key=semester_6%2Fdesign_of_steel_and_timber_structure%3Atension-single-angle-100kn-m20) — Design of Steel and Timber Structure, chapter 5
- [Single channel tension member, 280 kN](https://www.bctengineer.com/question.md?key=semester_6%2Fdesign_of_steel_and_timber_structure%3Atension-single-channel-280kn) — Design of Steel and Timber Structure, chapter 5
- [Bridge compression member, ISLC 400, toe to toe](https://www.bctengineer.com/question.md?key=semester_6%2Fdesign_of_steel_and_timber_structure%3Abridge-compression-islc400) — Design of Steel and Timber Structure, chapter 6
- [Bridge compression member, 1200 kN, tie bar lacing](https://www.bctengineer.com/question.md?key=semester_6%2Fdesign_of_steel_and_timber_structure%3Abridge-compression-1200kn-tie-bar) — Design of Steel and Timber Structure, chapter 6

## Related in other subjects

- [Permissible compressive stress of masonry as per IS 1905](https://www.bctengineer.com/question.md?key=semester_5%2Fdesign_of_timber_and_masonry_structures%3Amasonry-permissible-stress-factors-code) — Design of Timber and Masonry Structures, chapter 5
- [Max shear for 150 MPa stress limit; principal stresses](https://www.bctengineer.com/question.md?key=semester_3%2Fstrength_of_materials%3Adirect-stresses-100t-60c-shear-limit) — Strength of Materials, chapter 4
- [Normal, shear, bearing stress and factor of safety](https://www.bctengineer.com/question.md?key=semester_4%2Fstrength_of_materials_mechanical%3Astress-types-factor-of-safety) — Strength of Materials, chapter 1
- [Normal/shear stress on 25 degree plane, principal stresses](https://www.bctengineer.com/question.md?key=semester_3%2Fstrength_of_materials%3Ainclined-plane-30-25deg-mohr-verify) — Strength of Materials, chapter 4, asked 3×