AD 264: Longitudinal Stability of single storey frames in fire boundary conditions
The guidance given on the requirements for longitudinal restraint to columns supporting boundary walls in P313 Single Storey Steel Framed Buildings in Fire Boundary Conditions contains an error. On page 18 the guidance states that longitudinal members require fire protection. However this is an overly onerous requirement.
If the frame and horizontal members restraining the columns are designed to BS 5950-1 for normal limit state design these members will also provide adequate restraint to the column in the fire limit state. Fire protection is not required for these members because, in the fire limit state, significant horizontal forces are unlikely to occur and the members will retain sufficient strength to perform their function as longitudinal restraints.
The text in the second paragraph of ‘2.8.2 Longitudinal restraint to column’ on page 18 should read as follows: ‘If the frame and horizontal members restraining the column are designed to the appropriate part of BS 5950, this will also be adequate for fire. The horizontal members do not require fire protection.’ This guidance remains unchanged from P087 The behaviour of steel portal frames in boundary conditions.