---
title: "Define shear lag effect"
subject: "Design of Steel and Timber Structure"
chapter: 5
key: "semester_6/design_of_steel_and_timber_structure:shear-lag-effect"
source: https://www.bctengineer.com/q/semester_6/design_of_steel_and_timber_structure/shear-lag-effect
site: BCT Engineering
---

# Define shear lag effect

Design of Steel and Timber Structure · Chapter 5: Tension Members

- Asked in: 2079 Chaitra, 2 marks
- Video: [Shear Lag Effect - Design and drawing of Steel Structure](https://www.youtube.com/watch?v=fkiAsTXN1kk) — Ekeeda
- 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/shear-lag-effect
- Whole chapter: https://www.bctengineer.com/md/semester_6/design_of_steel_and_timber_structure/chapter-5

## Question

Define the terms shear lag effect.

## Short answer

Shear lag is non-uniform stress in a tension member when only part of the cross-section is connected, causing the outstanding leg to be less effective. It reduces net section strength and is accounted by a β factor.

## Answer

**Shear lag** is the non-uniform distribution of stress in a tension member when only part of its cross-section (e.g. one leg of an angle or the web of a channel) is connected to the gusset. The force enters through the connected element, so the stress is highest near the connection and the outstanding element is less effective, especially over a short connection length.

Because the outstanding leg does not carry its full share, the net section reaches its strength earlier than the full area would suggest. IS 800:2007 (cl. 6.3.3) therefore reduces the net-section strength using a factor $\beta=1.4-0.076\dfrac{w}{t}\dfrac{f_y}{f_u}\dfrac{b_s}{L_c}$ for the outstanding leg:
$$
T_{dn}=\frac{0.9A_{nc}f_u}{\gamma_{m1}}+\frac{\beta A_{go}f_y}{\gamma_{m0}}
$$
Shear lag is reduced by a longer connection length $L_c$ and by connecting the outstanding leg as well (e.g. with a lug angle).

## Check yourself

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

1. What is shear lag in a tension member?
   A. Slip between two plates in a bolted joint
   B. Reduction of strength due to bolt holes alone
   C. Non-uniform stress because only part of the cross-section (e.g. one leg) is connected
   D. Delay in yielding of the whole section under high temperature
   Answer: C. Force enters through the connected element, so stress is highest near the connection and the outstanding element is less effective. (Key point: Meaning of shear lag)

2. Because of shear lag, how does IS 800:2007 cl. 6.3.3 treat the outstanding leg in net-section rupture?
   A. It ignores the outstanding leg completely
   B. It reduces its contribution using the factor beta
   C. It increases the partial safety factor on bolts
   D. It uses the gross area of the whole angle at fy
   Answer: B. The outstanding leg term is multiplied by beta (limited to a range), which accounts for its reduced effectiveness. (Key point: Effect on net-section strength)

3. Which measure reduces shear lag?
   A. Shortening the connection length
   B. Using fewer bolts in the connected leg
   C. Using a thinner gusset plate
   D. Increasing the connection length or connecting the outstanding leg with a lug angle
   Answer: D. Shear lag decreases with a longer connection length and by connecting the outstanding leg, e.g. with a lug angle. (Key point: Reducing shear lag)

## Related in other subjects

- [Derive tractive force ratio (shear reduction factor)](https://www.bctengineer.com/question.md?key=semester_4%2Fhydraulics%3Atractive-force-ratio-derivation) — Hydraulics, chapter 10, asked 5×
- [Piezoelectric materials and piezoelectric effect](https://www.bctengineer.com/question.md?key=semester_3%2Felectrical_engineering_material%3Apiezoelectric-effect-polarization) — Electrical Engineering Material, chapter 3, asked 2×
- [Merchant circle and shear angle relation](https://www.bctengineer.com/question.md?key=semester_4%2Fmanufacturing_and_production_processes%3Amerchant-circle-force-relations-derivation) — Manufacturing and Production Processes, chapter 7
- [Sampling theorem; aliasing and aperture effect remedies](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Asampling-theorem-aliasing-aperture-remedy) — Communication Systems, chapter 4