disproportionate collapse requirements
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Disproportionate collapse requirements with British Standard clause references
Building
class
Building type and occupancy Building regulations
requirements
British standard material references and summary outline guidance
BS 5268 – Timber BS 5628 – Masonry BS 5950 – Steel BS 8110 – Concrete
1
Houses not exceeding 4 storeys.
Agricultural buildings.
Buildings into which people rarely go or come
close to.
Basic Requirements
Structures should be constructed so that no collapse should be disproportionate to the cause and reduce the risk of localized damage
spreading – but that permanent deformation of members/connections is acceptable.
C1.6.1.1: suitable geometry,
connections and bracing.
C1.16.3: robustness, interaction of
components and containment of
spread of damage.
C1.2.1.1.1 and C1.2.4.5.2: effective
horizontal ties as Class 2 A Option 2.
C1.2.2.2.2: effective horizontal
ties AND designed resistance to
notional lateral load of 1.5% design
dead load.
2A
5 storey single occupancy house.
Hotels not exceeding 4 storeys.
Flats, apartments and other residential buildings
not exceeding 4 storeys.
Offi ces not exceeding 4 storeys.
Industrial buildings not exceeding 3 storeys.
Retailing premises not exceeding 3 storeys and
less than 2000 m 2 at each storey.
Option 1:
Effective anchorage of suspended
fl oors to walls
C1.1.6.3.2: Figure M.3 or details in
BS 5628-1 Annex D.
As for Class 1 plus C1.33.4: details in
BS 5628-1 Annex D or BS 8103-1.
Generally N/A but C1.2.4.5.2:
bearing details of precast concrete
units to conform to C1.5.2.3 of
BS 8110-1.
C1.5.2.3: precast bearings not less
than 90 mm or half load bearing
wall/leaf thickness.
Option 2:
Provision of horizontal ties
C1.1.6.3.3 and Figure M.1. As for Class 1 plus C1.33.4 and
Table 12.
C1.2.1.1.1 and C1.2.4.5.2. As Class 1 plus C1.2.2.2.2 and
C1.3.12.3.6 .
2B
Hotels, fl ats, apartments and other residential
buildings greater than 4 storeys but not exceeding
15 storeys.
Educational buildings greater than 1 storey but less
than 15 storeys.
Retailing premises greater than 3 storeys but less
than 15 storeys.
Hospitals not exceeding 3 storeys.
Offi ces greater than 4 storeys but less than
15 storeys.
All buildings to which members of the public are
admitted which contain fl oor areas exceeding
2000 m 2 but are less than 5000 m 2 at each storey.
Car parking not exceeding 6 storeys.
Option 1:
Provision of horizontal and
vertical ties
As Class 2A Option 2 plus
C1.1.6.3.4.
As Class 2A Option 2 plus C1.33.5
and Table 13.
As Class 2A Option 2 plus
C1.2.4.5.3.
As Class 2A Option 2 plus C1.2.2.2.2
and C1.3.12.3.7.
Option 2:
Check notional removal of load
bearing elements
C1.1.6.3.5 .
As for Class 1 plus Table 11:
‘without collapse ’ rather than
limited areas.
C1.2.4.5.3 if Class 2B Option 1
cannot be satisfi ed.
C1.2.6.3 of BS 8110-2.
Check notional removal of load bearing elements such that for removal of any element the building remains stable and that the area of fl oor at any storey
at risk of collapse is less than the lesser of 70 m 2 or 15% of the fl oor area of that storey. The nominal length of load bearing wall should be the distance
between vertical lateral restraints (not exceeding 2.25H for reinforced concrete walls or internal walls of masonry, timber or steel stud). If catenary action is
assumed allowance should be made for the necessary horizontal reactions.
Option 3:
Key element design
C1.1.6.3.6 .
As for Class 1 plus C1.33.2 .
C1.2.4.5.4 if Class 2B Options 1 and
2 cannot be satisfi ed.
C1.2.6.2 of BS 8110-2.
Design of key elements to be capable of withstanding 34 kN/m 2 applied one direction at a time to the member and attached components subject to the
limitations of their strength and connections, such accidental loading should be considered to act simultaneously with full dead loading and 1/3 of all
normal wind/imposed loadings unless permanent storage loads etc. Where relevant, partial load factors of 1.05 or 0.9 should be applied for overturning and
restoring loads respectively. Elements providing stability to key elements should be designed as key elements themselves.
3
All buildings defi ned above as Class 2A and 2B that
exceed the limits of area or number of storeys.
Grandstands accommodating more than 5000
spectators.
Buildings containing hazardous substances and/or
processes.
Systematic risk assessment of the
building should be undertaken
taking into account all the normal
hazards that may be reasonably
forseen, together with any abnormal
hazards.
Lack of clear guidance . Lack of clear guidance. C1.2.4.5.1: Class 2B required as
a minimum.
Class 2B required as a minimum.
NOTES:
1. Refer to the detailed British Standard clauses for full details of design and detailing requirements.
2. Where provided, horizontal and vertical ties should be safeguarded against damage and corrosion.
3. Key elements may be present in any class of structure and should be designed accordingly.
4. The construction details required by Class 2B can make buildings with load bearing walls diffi cult to justify economically.
5. In Class 2B and 3 buildings, precast concrete elements not acting as ties should be effectively anchored (C1.5.1.8.3), such anchorage being capable of carrying the dead weight of the member.
Source: Adapted from Table 11, Part A3 Approved Document A, HMSO.
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