Bolting
Bolt assembly count and weight for a connection schedule
- where
- bolt assemblies to order
- number of connections
- bolts per connection
- spares allowance (%)
- weight of bolt assemblies (kg)
- mass of one assembly (kg)
Explain this equation
Counts how many bolt assemblies to order for one size and grade, with a spares allowance, and what they weigh. Use it when making up a bolt list from the connection schedule.
n_c is the number of connections of a type and n_b the bolts in each. s_p is a percentage added for losses and damage. N is the number to order, rounded up to whole assemblies. m_a is the mass of one bolt with its nut and washers, and M_b is the total weight.
The bolts needed are simply connections times bolts per connection. The bracket turns the spares percentage into a multiplier, and the ceiling brackets round up because you cannot order part of a bolt.
Sense check: 120 connections of four bolts is 480 bolts; with 5% spares that is 504.
Watch out: count each length and grade separately, and keep preloaded assemblies as matched sets from one supplier.
Number of bolt assemblies to order for one bolt size and grade, with a spares allowance, and their weight for handling and delivery.
Enter your values to see the result.
Good to know
Count each size, length and grade separately: BS EN 14399 preloaded assemblies must be supplied and used as matched sets from one manufacturer, so do not mix nuts and bolts from different sets. Assembly mass depends on length and washer type, so take it from the supplier’s catalogue. The spares allowance is your own choice for losses and damaged threads.
Common mistake
Mixing preloaded and non-preloaded bolts, or counting bolts without washers when the specification needs a washer under the turned part.
Limits
Quantity only. Bolt length must suit the grip with the thread protrusion required by BS EN 1090-2 8.2.2.
Sources
- BS EN 14399-1 and -3/-4 High-strength structural bolting assemblies for preloading (systems HR and HV, property classes 8.8 and 10.9, k-class declared on the certificate)
- BS EN 15048-1 Non-preloaded structural bolting assemblies – General requirements
- BS EN 1090-2:2018+A1:2024 Execution of steel structures and aluminium structures – Technical requirements for steel structures (8.2.2 bolt protrusion; 8.5 preloaded bolts: Fp,C = 0.7 fub As; torque method Mr,2 = km d Fp,C, first step about 0.75 Mr,i, second step 1.10 Mr,i; combined method Mr,1 = 0.13 d Fp,C simplification; k-classes K0, K1, K2; Annex B tolerances)
Results are calculations from the published methods and figures shown, and depend on the data you enter. Always work to the engineer’s drawings and bending schedules, BS 8666, BS EN 1992, BS EN 1090-2, BS 5531/the BCSA National Structural Steelwork Specification and manufacturers’ data. Lifting must be planned under LOLER by a competent person.