---
title: "Behaviour and detailing of bolted and nailed joints"
subject: "Design of Timber and Masonry Structures"
chapter: 2
key: "semester_5/design_of_timber_and_masonry_structures:bolted-nailed-joint-behavior-detailing"
source: https://www.bctengineer.com/q/semester_5/design_of_timber_and_masonry_structures/bolted-nailed-joint-behavior-detailing
site: BCT Engineering
---

# Behaviour and detailing of bolted and nailed joints

Design of Timber and Masonry Structures · Chapter 2: Joints in Timber Structures

- Asked in: year not given, 6 marks
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/design_of_timber_and_masonry_structures/bolted-nailed-joint-behavior-detailing
- Whole chapter: https://www.bctengineer.com/md/semester_5/design_of_timber_and_masonry_structures/chapter-2

## Question

Describe the behaviour of bolted and nailed timber joints under load. State the failure modes and the detailing rules (spacing, end and edge distances) that must be followed.

## Answer

Mechanical fasteners (nails, screws, bolts) transfer load between timber members mainly by **bearing of the fastener on the wood** together with **bending of the fastener**.

#### Behaviour of bolted joints
- A bolt in a loaded joint bears against the wood. Early load–slip behaviour is nearly linear, then wood crushes under the bolt and the bolt bends, giving a ductile yielding response.
- A bolt placed in a hole 1–1.5 mm larger than its diameter first slips before taking load, so tight holes and washers (about $3d$ in size) under the head and nut are needed.
- Capacity depends on the bolt diameter $d$, member thickness $t$ (ratio $t/d$), the angle between load and grain (Hankinson's formula) and whether the joint is in single or double shear.

#### Behaviour of nailed joints
- Nails carry lateral load by bearing and bending; under axial load they resist withdrawal by friction.
- Joints with many small nails are ductile. Nails should not be used to carry permanent withdrawal loads.
- Hard timber is pre-drilled to avoid splitting.

#### Failure modes
1. Wood crushing under the fastener (bearing failure).
2. Bending / yielding of the fastener.
3. Splitting along the grain when end distance or spacing is too small.
4. Shear-out of a block (plug) at the loaded end.
5. Tension failure of the net section through the holes.
6. Withdrawal of nails or screws.

#### Detailing rules (typical code values; check the relevant code)
| Item | Typical minimum |
|---|---|
| Bolt spacing along grain | $7d$ |
| Bolt spacing across grain | $4d$ |
| Loaded end distance | $7d$ (not less than 80 mm) |
| Edge distance | $3d$ to $4d$ |
| Nail spacing along grain | $10d$ |
| Nail spacing across grain | $5d$ |
| Nail end distance | $15d$ |
| Nail edge distance | $5d$ |

Other rules: stagger the fasteners in adjacent rows, avoid placing all bolts on one grain line, provide at least two bolts per connection, and use nail penetration in the second member of not less than $10d$ (clinched where the nail passes through).

## Check yourself

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

1. How do mechanical fasteners mainly transfer lateral load between timber members?
   A. Bearing of the fastener on the wood together with bending of the fastener
   B. Friction between the two timber faces only
   C. Tension in the fastener shank only
   D. Shear of the wood fibres across the grain only
   Answer: A. Nails and bolts act by bearing on the wood and bending of the fastener, which gives a ductile yielding response. (Key point: Load transfer mechanism)

2. Which detailing error causes splitting along the grain in a bolted joint?
   A. Bolts staggered in adjacent rows
   B. Using two or more bolts per connection
   C. Too small an end distance or spacing
   D. Providing washers under the head and nut
   Answer: C. Splitting along the grain occurs when end distance or spacing is too small, so minimum distances must be provided. (Key point: Splitting failure)

3. Typical minimum bolt spacing is:
   A. 4d along the grain and 7d across the grain
   B. 7d along the grain and 4d across the grain
   C. 10d along the grain and 5d across the grain
   D. 3d in both directions
   Answer: B. Bolts need about 7d along the grain and 4d across it; 10d and 5d are the nail values. (Key point: Bolt spacing rules)

4. Why are tight holes and washers (about 3d) required for bolts?
   A. Because bolts carry withdrawal load by friction
   B. To prevent the bolt from bending
   C. To make the joint brittle
   D. A bolt in an oversize hole slips before taking load, and washers spread bearing under head and nut
   Answer: D. A hole 1-1.5 mm oversize lets the joint slip first; tight holes limit this and washers spread bearing under the head and nut. (Key point: Hole clearance and washers)

## Related in Design of Timber and Masonry Structures

- [Design of a nailed timber lap joint](https://www.bctengineer.com/question.md?key=semester_5%2Fdesign_of_timber_and_masonry_structures%3Anailed-lap-joint-design) — Design of Timber and Masonry Structures, chapter 2
- [Timber column under axial load and bending](https://www.bctengineer.com/question.md?key=semester_5%2Fdesign_of_timber_and_masonry_structures%3Atimber-column-combined-bending-axial) — Design of Timber and Masonry Structures, chapter 3
- [In-plane and out-of-plane behaviour of masonry walls](https://www.bctengineer.com/question.md?key=semester_5%2Fdesign_of_timber_and_masonry_structures%3Ain-plane-out-of-plane-behavior) — Design of Timber and Masonry Structures, chapter 6
- [Safe axial load on a timber column](https://www.bctengineer.com/question.md?key=semester_5%2Fdesign_of_timber_and_masonry_structures%3Aaxial-capacity-timber-column) — Design of Timber and Masonry Structures, chapter 3
- [Check of a solid brick wall under gravity load](https://www.bctengineer.com/question.md?key=semester_5%2Fdesign_of_timber_and_masonry_structures%3Asolid-masonry-wall-gravity-check) — Design of Timber and Masonry Structures, chapter 5
- [Masonry pier under axial load and in-plane moment](https://www.bctengineer.com/question.md?key=semester_5%2Fdesign_of_timber_and_masonry_structures%3Amasonry-pier-axial-moment-check) — Design of Timber and Masonry Structures, chapter 7

## Related in other subjects

- [Bolted joints in timber](https://www.bctengineer.com/question.md?key=semester_6%2Fdesign_of_steel_and_timber_structure%3Atimber-bolted-joints) — Design of Steel and Timber Structure, chapter 10
- [Failure mechanisms of bolted connection](https://www.bctengineer.com/question.md?key=semester_6%2Fdesign_of_steel_and_timber_structure%3Abolted-failure-mechanisms) — Design of Steel and Timber Structure, chapter 4
- [Why ductile detailing is needed in joints](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Awhy-ductile-detailing-is-needed-in) — Design of RCC Structure, chapter 12
- [Timber joist dimensions under UDL and point load](https://www.bctengineer.com/question.md?key=semester_3%2Fstrength_of_materials%3Atimber-joist-5kn-m-15kn) — Strength of Materials, chapter 7