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IS 11096:1984 is the Indian Standard (BIS) for design and construction of bolt-jointed timber construction. This standard provides guidelines for the design and construction of structural joints in timber using steel bolts. It covers material specifications for timber and bolts, fabrication details, design criteria for joint strength, and requirements for bolt spacing, edge, and end distances.
Code of practice for design and construction of bolt-jointed timber construction
Overview
Status
Current
Usage level
Specialized
Domain
Structural Engineering — Building Construction Practices incl. Painting, Varnishing
! Ensure moisture content of timber is at or near equilibrium moisture content for the intended service location to minimize issues from shrinkage.
! Use of large-diameter washers under bolt heads and nuts is essential to prevent localized crushing of the wood fibers.
! The alignment of holes is critical in multi-bolt joints; mismatched holes can induce secondary stresses and lead to uneven load distribution among bolts.
EN 1995-1-1:2004CEN (European Committee for Standardization), Europe
HighCurrent
Eurocode 5: Design of timber structures — Part 1-1: General — Common rules and rules for buildings
Covers design of timber structures, including detailed rules for bolted connections based on Limit State Design.
ANSI/AWC NDS-2018American Wood Council (AWC), USA
HighCurrent
National Design Specification (NDS) for Wood Construction
The primary US standard for wood design, with comprehensive chapters on bolted connection design.
CSA O86-19Canadian Standards Association (CSA), Canada
HighCurrent
Engineering design in wood
The Canadian national standard for wood engineering, providing detailed guidance on bolted joints.
BS 5268-2:2002British Standards Institution (BSI), UK
MediumWithdrawn
Structural use of timber — Part 2: Code of practice for permissible stress design, materials and workmanship
Previous UK standard using a permissible stress design philosophy, conceptually similar to the IS code.
Key Differences
≠Design Philosophy: IS 11096 uses Allowable Stress Design (ASD), where stresses under service loads must be below specified permissible limits. Modern codes like Eurocode 5 and NDS use Limit State Design (LSD/LRFD), a more rigorous method considering ultimate and serviceability failure states with factored loads and material resistances.
≠Failure Mode Analysis: International standards like Eurocode 5 are based on Johansen's Yield Theory, which models multiple complex failure modes (timber crushing, bolt bending in single/double shear). IS 11096 uses a more simplified empirical approach based on safe bearing stresses on the timber and bolt.
≠Material Strength Basis: IS 11096 specifies permissible stresses for Indian timber species and steel grades. Modern codes use characteristic strength values (e.g., 5th percentile strength) which are then modified by factors in the design equations, providing a probabilistic basis for safety.
≠Modification Factors: Eurocode 5 and NDS have a more extensive and refined system of modification factors for effects like load duration, moisture content, temperature, and group action of fasteners. The Indian code's treatment of these variables is generally less detailed.
Key Similarities
≈Anisotropy of Wood: All standards fundamentally recognize that wood's strength is highly directional, providing different strength values and design rules for loads applied parallel to the grain versus perpendicular to the grain.
≈Geometric Requirements: Both the IS code and international standards mandate minimum spacing between bolts, and minimum edge and end distances. These rules, typically expressed as multiples of the bolt diameter, are crucial to prevent premature splitting and tear-out failures.
≈Use of Washers: The requirement to use washers under the bolt head and nut is common across all standards to prevent localized crushing of wood fibers and to effectively distribute clamping forces.
≈Consideration of Multiple Members: All codes provide different calculation methods for joints with two members (single shear) versus three or more members (double shear), acknowledging the difference in bolt bending and load transfer.
Parameter Comparison
Parameter
IS Value
International
Source
Design Method
Allowable Stress Design (ASD)
Limit State Design (LSD / LRFD)
EN 1995-1-1 / NDS-2018
Minimum Bolt Spacing (parallel to grain)
4 times bolt diameter (4d)
4 times bolt diameter (4d)
NDS-2018
Minimum End Distance (in tension)
7d for softwoods (conifers), 5d for hardwoods
7d for softwoods (parallel to grain loading)
NDS-2018
Bolt Hole Oversize
Bolt diameter + 1.5 mm
Bolt diameter + 1/16 inch (~1.6 mm)
NDS-2018
Basis for Timber Strength in Joint
Permissible bearing stress of timber species (from IS 883)
Characteristic embedment strength (f_h,k) derived from density
EN 1995-1-1
Basis for Bolt Strength in Joint
Permissible stress in shear and bearing for steel (from IS 800)
What is the minimum spacing between bolts in a row?+
For loads parallel to the grain, the minimum spacing is 4 times the bolt diameter (4d), as per Table 3.
What is the maximum permissible diameter for a bolt hole?+
The hole diameter should not exceed the bolt diameter by more than 1.5 mm, according to Clause 5.2.1.
How is the load capacity of a bolted joint calculated?+
The capacity is determined by the lesser of the bolt's bearing strength against the timber and the timber's bearing strength, considering factors like load direction, number of shear planes, and bolt spacing (Clause 7).
Are washers mandatory for bolted timber connections?+
Yes, washers of adequate size are required under the bolt head and nut to properly distribute the load onto the timber surface (Clause 5.3).