--- title: "Bolted joints in timber" subject: "Design of Steel and Timber Structure" chapter: 10 key: "semester_6/design_of_steel_and_timber_structure:timber-bolted-joints" source: https://www.bctengineer.com/q/semester_6/design_of_steel_and_timber_structure/timber-bolted-joints site: BCT Engineering --- # Bolted joints in timber Design of Steel and Timber Structure · Chapter 10: Joints in Timber Structures - Asked in: 2076 Baisakh, 2 marks - Video: [Bolted Wood Connection Design Example - Part 1 - NDS #structuralengineering](https://www.youtube.com/watch?v=F-znsXEkOFg) — Kestävä - 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/timber-bolted-joints - Whole chapter: https://www.bctengineer.com/md/semester_6/design_of_steel_and_timber_structure/chapter-10 ## Question Explain about the bolted joints in timber. ## Short answer Bolted joints connect timber members with bolts in pre-drilled holes, transferring load by bearing and bolt bending. Types: lap joints, splices with timber/steel plates, single/double shear. Load per bolt depends on diameter, member thickness, species, and load angle to grain. Spacing rules: hole 1-1.5mm larger than bolt; along grain ≥4 diameters; end distance 7 diameters (tension), 4 diameters (compression); edge distance ≥1.5 diameters; row spacing 2.5-5 diameters. Washers prevent crushing; retighten after seasoning. ## Answer A **bolted joint** connects two or more timber members by bolts passing through holes bored in the members, with a washer under the head and the nut; the bolts transfer the load by bearing on the timber and by their own bending. - **Types:** lap joints and splices with timber or steel side plates, and tension or compression splices; the bolts act in single or double shear. - **Load per bolt** depends on the bolt diameter, the thickness of the members, the species and the angle of the load to the grain (it is higher parallel to the grain than perpendicular to it). - **Spacing rules** (IS 883, typical): holes $1$ to $1.5$ mm larger than the bolt; spacing of bolts in a row along the grain at least 4 diameters; end distance 7 diameters in tension members and 4 diameters in compression members; edge distance at least 1.5 diameters (4 diameters at the loaded edge when the load is perpendicular to the grain); spacing between rows about 2.5 to 5 diameters, depending on the ratio of member thickness to bolt diameter. - **Details:** washers prevent crushing of the timber; bolts are tightened again after the timber has seasoned; avoid bolts of very large diameter in thin members. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. How does a bolted timber joint transfer load? A. By friction of the nuts only B. By glue in the holes C. By tension in the bolts only D. By bearing on the timber and by bolt bending, with the bolts in single or double shear Answer: D. Bolts bear on the hole sides and bend; this is shear on the bolt. (Key point: How bolts transfer load) 2. How does grain direction affect load per bolt? A. Load per bolt is higher parallel to the grain than perpendicular B. It is the same in both directions C. It is higher perpendicular to the grain D. It depends only on bolt colour Answer: A. Timber bearing strength is much greater along the grain. (Key point: Grain direction) 3. Which statement about details is true? A. Holes are drilled 5 mm larger B. Washers prevent crushing and bolts are tightened again after seasoning C. Bolts are never retightened D. Washers are omitted to avoid crushing Answer: B. Timber shrinks as it seasons, so bolts need retightening; holes are only 1 to 1.5 mm oversize. 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