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).

IS 11096

: 1984

Code of practice for design and construction of bolt-jointed timber construction

CurrentSpecializedCode of PracticeStructural Engineering · Building Construction Practices incl. Painting, Varnishing

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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

Quick Reference Values

Minimum recommended bolt diameter12 mm

Maximum tolerance for drilled hole diameterBolt diameter + 1.5 mm

Minimum end distance for tension member (parallel to grain)7d for Group C timber (d=bolt diameter)

Minimum edge distance for bolts1.5d (d=bolt diameter)

Minimum spacing between bolts in a row (parallel to grain)4d (d=bolt diameter)

Key Formulas

P = f(timber bearing strength, bolt bending strength) — Formula for calculating safe load on a single bolt in single shear.

N = P / p — Formula for determining the number of bolts required in a joint, where P is total load and p is the safe load per bolt.

Practical Notes

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.