---
title: "Fillet weld size for bracket plate, 100 kN"
subject: "Design of Steel and Timber Structure"
chapter: 4
key: "semester_6/design_of_steel_and_timber_structure:bracket-weld-100kn-working"
source: https://www.bctengineer.com/q/semester_6/design_of_steel_and_timber_structure/bracket-weld-100kn-working
site: BCT Engineering
---

# Fillet weld size for bracket plate, 100 kN

Design of Steel and Timber Structure · Chapter 4: Connections in Steel Structures

- Asked in: 2076 Baisakh, 14 marks
- Video: [How To Determine the Weld Size of a Bracket](https://www.youtube.com/watch?v=W1sSGsdC1po) — Prof One YT
- 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/bracket-weld-100kn-working
- Whole chapter: https://www.bctengineer.com/md/semester_6/design_of_steel_and_timber_structure/chapter-4

## Question

Determine the size of fillet weld required to connect a bracket plate to the flange of a column as shown.
[Figure: 12 mm thick bracket plate welded to the flange of ISMB 350; 100 kN (working load) acts at 14 cm from the column face; weld is 10 cm wide at top and bottom and 16 cm deep; 10 cm dimension shown at the bottom]

## Short answer

Working load 100 kN, factored 150 kN at 140 mm eccentricity. Weld group length 360 mm, Ixx=1.62e6 mm³, resultant force 1116.8 N/mm. Required throat 5.90 mm, size 8.43 mm. Use 9 mm fillet weld on three sides.

## Answer

**Assumptions:** the 12 mm bracket plate is welded to the ISMB 350 flange ($t_f=14.2$ mm) by a C-shaped weld: top and bottom 100 mm and vertical 160 mm. The working load of 100 kN acts parallel to the flange at $e=140$ mm from the weld plane, giving direct shear and bending in the weld. Factored load $P_u=1.5\times100=150$ kN. Shop weld, E250.

#### Weld group (per mm of throat)
- $L=2\times100+160=360$ mm
- $I_{xx}=\dfrac{160^3}{12}+2\times100\times80^2=1621333$ mm³
- $M=150\times10^3\times140=21.0\times10^6$ N·mm

#### Force per mm at the extreme weld (y = 80 mm)
- Shear: $q_s=\dfrac{150\times10^3}{360}=416.7$ N/mm
- Bending: $q_b=\dfrac{My}{I_{xx}}=\dfrac{21.0\times10^6\times80}{1621333}=1036.2$ N/mm
- Resultant: $q=\sqrt{q_s^2+q_b^2}=1116.8$ N/mm

#### Size of weld
$$
f_{wd}=\frac{410}{\sqrt3\times1.25}=189.4\ \text{N/mm}^2,\qquad t_t=\frac{1116.8}{189.4}=5.90\ \text{mm},\qquad s=\frac{t_t}{0.7}=8.43\ \text{mm}
$$
Take **$s=9$ mm** (capacity $0.7\times9\times189.4=1193$ N/mm $>1116.8$ N/mm; an 8 mm weld gives only 1060 N/mm).

Checks: minimum size for 14.2 mm flange = 5 mm; maximum size = plate thickness $-1.5=10.5$ mm (12 mm plate), so 9 mm is acceptable.

**Answer: 9 mm fillet weld (shop) on all three sides.**

## Check yourself

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

1. The 100 kN load is a working load. What load is used for the weld design in this answer?
   A. 100 kN
   B. 150 kN (1.5 x 100)
   C. 125 kN
   D. 66.7 kN
   Answer: B. Limit-state design uses factored load: 1.5 x 100 = 150 kN. (Key point: Factored load)

2. With e = 140 mm and P_u = 150 kN, what is the moment M used for the bending force in the weld?
   A. 14 x 10^6 N·mm
   B. 15.0 x 10^6 N·mm
   C. 21.0 x 10^6 N·mm
   D. 10.5 x 10^6 N·mm
   Answer: C. M = P_u x e = 150 x 10^3 x 140 = 21.0 x 10^6 N·mm. (Key point: Moment on weld)

3. At which part of the weld group is the force per mm greatest and used for sizing?
   A. At the neutral axis
   B. At the extreme top and bottom welds (y = 80 mm)
   C. At the middle of the vertical weld
   D. Equal everywhere
   Answer: B. Bending force q_b = My/I grows with y, so the extreme weld at y = 80 mm gives the largest resultant (1116.8 N/mm). (Key point: Extreme weld governs)

4. The calculated size is 8.43 mm. Why is 9 mm chosen?
   A. Weld sizes must be odd numbers
   B. An 8 mm weld carries only about 1060 N/mm, less than the 1116.8 N/mm demand
   C. The plate thickness is 9 mm
   D. The minimum size is 9 mm
   Answer: B. Size must be rounded up to a practical size that has capacity above demand; 9 mm gives 1193 N/mm while 8 mm gives only 1060 N/mm. (Key point: Why 9 mm not 8 mm)

## Related in Design of Steel and Timber Structure

- [Check eccentric fillet weld, 8 mm, P=100 kN](https://www.bctengineer.com/question.md?key=semester_6%2Fdesign_of_steel_and_timber_structure%3Arivet-eccentric-weld-p100) — Design of Steel and Timber Structure, chapter 4
- [Shop welded bracket, 5 mm fillet, safe load](https://www.bctengineer.com/question.md?key=semester_6%2Fdesign_of_steel_and_timber_structure%3Abracket-weld-safe-load-5mm) — Design of Steel and Timber Structure, chapter 4
- [Weld size for bracket on ISMB 400](https://www.bctengineer.com/question.md?key=semester_6%2Fdesign_of_steel_and_timber_structure%3Abracket-weld-ismb400) — Design of Steel and Timber Structure, chapter 4
- [Bracket plate on column flange, 5 M20 bolts](https://www.bctengineer.com/question.md?key=semester_6%2Fdesign_of_steel_and_timber_structure%3Abracket-bolted-5-m20) — Design of Steel and Timber Structure, chapter 4
- [Eccentric bolted bracket, ISMB 300, 220 kN](https://www.bctengineer.com/question.md?key=semester_6%2Fdesign_of_steel_and_timber_structure%3Abracket-bolted-ismb300-220kn) — Design of Steel and Timber Structure, chapter 4
- [Bolted bracket connection, 200 kN at 250 mm](https://www.bctengineer.com/question.md?key=semester_6%2Fdesign_of_steel_and_timber_structure%3Abracket-bolted-200kn-250mm) — Design of Steel and Timber Structure, chapter 4

## Related in other subjects

- [Footing size from plate load test curve](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Aplate-load-footing-size-3200kn) — Foundation Engineering, chapter 6
- [Brick and mortar for 250 mm wall (350 kN/m)](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Awall-eccentric-250mm-350kn) — Concrete Technology and Masonry Structure, chapter 8, asked 7×
- [Brick column 35 cm x 50 cm allowable load](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Acolumn-35x50-axial-eccentric) — Concrete Technology and Masonry Structure, chapter 8
- [Friction pile length, 350 mm, 1200 kN](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Afriction-pile-350mm-1200kn) — Foundation Engineering, chapter 8