Specification 8 Performance of external walls in fire

This Specification contains measures to minimise, in the event of fire, the likelihood of external walls covered by S8C2 collapsing outwards as complete panels and the likelihood of panels separating from supporting members.

This Specification applies to buildings having a rise in storeys of not more than 2 with concrete external walls that could collapse as complete panels (e.g. tilt-up and precast concrete) which—

1. consist of either single or multiple panels attached by steel connections to lateral supporting members; and
2. depend on those connections to resist outward movement of the panels relative to the supporting members; and
3. have height to thickness ratio not greater than 50.

(1) Cast-in inserts and fixings must be anchored into the panel with welded bars or be fixed to the panel reinforcement.

(2) Cast-in inserts for top connections and fixings acting together must be able to resist an ultimate load of two times the larger of the forces required to develop—

1. the ultimate bending moment capacity of the panel at its base; or
2. the overturning moment at the base of the panel arising from an outwards lateral displacement at the top of the panel equal to one tenth of the panel height.

(3) Top connections of the panel exposed to fire, such as clips and drilled-in inserts, acting together must be able to resist an ultimate load of six times the larger of the forces required to develop the moment specified in (2)(a) or (b).

(4) Lateral supporting members and their connections must be designed to resist the connection forces specified in (2) and (3) and in the case of an eaves tie member the force in the member must be determined assuming that it deforms in a manner compatible with the lateral displacement of the wall panels, and that it acts in tension only.

(5) External wall panels that span vertically must have at least two upper connections per panel to the supporting member, except that where a number of panels are designed to act as one unit, (e.g. tongue and groove hollow-core panels), only two upper connections are required for each unit.

(6) External wall panels that span horizontally between columns must have at least two connections at each column.

(7) Connections providing lateral support to a panel must be designed to remain engaged to the supported panel both before and during a fire.

(1) Where vertically spanning external wall panels are located adjacent to columns, connections to the panels must be located and/or detailed to minimise forces that may develop between the panels and columns arising from the restraint of differential displacement.

(2) The requirements of (1) are satisfied by—

1. detailing the connections and/or the supporting member to sustain a relative outward displacement of (d) between the panels and columns at the connection height where d(m) is calculated as—
   1. the square of the connection height (m) divided by one hundred and twenty-five, when the connection height is less than 5 m; or
   2. the connection height (m) divided by twenty-five, when the connection height (m) is greater than or equal to 5 m; or
2. in situations where an eaves tie member is used to provide lateral support to external wall panels, the tie member is connected to the panels no closer than a distance (s) from the column where s(m) is taken as one quarter of the panel height (m).