Part B1 Structural provisions (DtS)
B1.0 Deemed-to-Satisfy Provisions
Where a Deemed-to-Satisfy Solution is proposed, Performance Requirements BP1.1 to BP1.4 are satisfied by complying with B1.1, B1.2, B1.4, B1.5 and B1.6.
Where a Performance Solution is proposed, the relevant Performance Requirements must be determined in accordance with A2.2(3) and A2.4(3) as applicable.
To clarify that BP1.1 to BP1.4 will be satisfied if compliance is achieved with B1.1, B1.2, B1.4, B1.5 and B1.6.
Where a solution is proposed to comply with the Deemed-to-Satisfy Provisions, the requirements of BP1.1 to BP1.4 may be satisfied by complying with B1.1, B1.2, B1.4, B1.5 and B1.6.
Where a Performance Solution is proposed, the relevant Performance Requirements must be determined in accordance with A2.2(3) and A2.4(3) as applicable. (See commentary on Part A2).
B1.1 Resistance to actions
The resistance of a building or structure must be greater than the most critical action effect resulting from different combinations of actions, where—
the most critical action effect on a building or structure is determined in accordance with B1.2 and the general design procedures contained in AS/NZS 1170.0; and
the resistance of a building or structure is determined in accordance with B1.4.
To specify the method of achieving compliance with BP1.1 and BP1.2.
A building or structure must be designed to resist the most critical effect resulting from different combinations of actions. The actions must be combined taking into account the characteristics of the actions and the probability of the simultaneous occurrence of two or more actions. The levels of reliability of the structure when subject to combined actions should be consistent with the levels of reliability implicit in the design events for natural phenomenon (see comments on Table B1.2(b)). When designing for the maximum combined actions, a principle frequently adopted is that the maximum is likely to occur when at least one of the actions is at its maximum value.
B1.2 Determination of individual actions
The magnitude of individual actions must be determined in accordance with the following:
the design or known dimensions of the building or structure; and
the unit weight of the construction; and
the known loads that will be imposed during the occupation or use of the building or structure; and
Wind, snow and ice and earthquake actions:
the applicable annual probability of design event for safety, determined by—
assigning the building or structure an Importance Level in accordance with Table B1.2a; and
determining the corresponding annual probability of exceedance in accordance with Table B1.2b; and
AS/NZS 1170.2; and
AS/NZS 1170.3 and AS 1170.4 as appropriate; and
in cyclonic areas, metal roof cladding, its connections and immediate supporting members must comply with Specification B1.2; and
for the purposes of (iv), cyclonic areas are those determined as being located in wind regions C and D in accordance with AS/NZS 1170.2.
Actions not covered in (a), (b) and (c) above:
the nature of the action; and
the nature of the building or structure; and
the Importance Level of the building or structure determined in accordance with Table B1.2a; and
For the purposes of (d) the actions include but are not limited to—
liquid pressure action; and
ground water action; and
rainwater action (including ponding action); and
earth pressure action; and
differential movement; and
time dependent effects (including creep and shrinkage); and
thermal effects; and
ground movement caused by—
swelling, shrinkage or freezing of the subsoil; and
landslip or subsidence; and
siteworks associated with the building or structure; and
|Importance Level||Building Types|
|1||Buildings or structures presenting a low degree of hazard to life and other property in the case of failure.|
|2||Buildings or structures not included in Importance Levels 1, 3 and 4.|
|3||Buildings or structures that are designed to contain a large number of people.|
|4||Buildings or structures that are essential to post-disaster recovery or associated with hazardous facilities.|
|Importance Level||Annual probability of exceedance for non-cyclonic wind||Annual probability of exceedance for cyclonic wind||Annual probability of exceedance for snow||Annual probability of exceedance for earthquake|
To specify the principles for the determination of each action referred to in BP1.1(b) using the relevant editions of AS/NZS 1170 Parts 0, 1, 2 and 3, and AS 1170 Part 4.
Construction activity actions
The term “construction activity action” only refers to construction activities that may need to be accounted for in the final design such as stacking of materials and floor to floor propping.
Windows forming part of a barrier
A window forming part of a barrier is not required to comply with AS/NZS 1170.1. However, a window serving as a barrier must comply with the glazing assembly provisions of AS 2047 or AS 1288. These provisions consider the wind loading on the glass and human impact requirements.
A generic description of building types has been provided to which Importance Levels have been assigned. The “Importance Level” concept is applicable to building structural safety only. More specific examples are provided below. The examples are not exhaustive.
Importance Level 1:
- Farm buildings and farm sheds.
- Isolated minor storage facilities.
- Minor temporary facilities.
Importance Level 2:
- Low rise residential construction.
- Buildings and facilities below the limits set for Importance Level 3.
Importance Level 3:
- Buildings and facilities where more than 300 people can congregate in one area.
- Buildings and facilities with a primary school, a secondary school or day care facilities with a capacity greater than 250.
- Buildings and facilities with a capacity greater than 500 for colleges or adult educational facilities.
- Health care facilities with a capacity of 50 or more residents but not having surgery or emergency treatment facilities.
- Jails and detention facilities.
- Any occupancy with an occupant load greater than 5000.
- Power generating facilities, water treatment and waste water treatment facilities, any other public utilities not included in Importance Level 4.
- Buildings and facilities not included in Importance Level 4 containing hazardous materials capable of causing hazardous conditions that do not extend beyond property boundaries.
Importance Level 4:
- Buildings and facilities designated as essential facilities.
- Buildings and facilities with special post disaster functions.
- Medical emergency or surgery facilities.
- Emergency service facilities: fire, rescue, police station and emergency vehicle garages.
- Utilities required as backup for buildings and facilities of Importance Level 4.
- Designated emergency shelters.
- Designated emergency centres and ancillary facilities.
- Buildings and facilities containing hazardous materials capable of causing hazardous conditions that extend beyond property boundaries.
Importance Levels must be assigned on a case by case basis.
A hospital may be of Importance Level 4 if it is the only hospital in an area. The same hospital may be of Importance Level 3 if it is one of many in an area.
A general method for the determination of the Importance Level of any building is to assess the hazard to human life and the impact on the public in the event of building failure as follows:
Hazard To human life
Impact on the public
Impact on the public
Impact on the public
Impact on the public
The annual probability of exceedance varies with the type of action.
Building failures due to earthquake or cyclone may be widespread and therefore have more impact on the public than say thunderstorms, that affect relatively smaller areas.
The annual probabilities of exceedance in Table B1.2(b) originated from calibrations derived from experience with minor adjustments carried out to achieve consistency.
In cyclonic areas (wind regions C and D as described in AS/NZS 1170.2) it is necessary for metal roof assemblies to be tested in accordance with Specification B1.2. (See B1.2(c)(iv)).
B1.3 * * * * *
B1.4 Determination of structural resistance of materials and forms of construction
The structural resistance of materials and forms of construction must be determined in accordance with the following, as appropriate:
Masonry (including masonry-veneer, unreinforced masonry and reinforced masonry): AS 3700, except—
'(for piers—isolated or engaged)' is removed from Clause 8.5.1(d); and
where Clause 8.5.1 requires design as for unreinforced masonry in accordance with Section 7, the member must also be designed as unreinforced masonry in accordance with Tables 10.3 and 4.1(a)(i)(C) of AS 3700.
Concrete construction (including reinforced and prestressed concrete): AS 3600.
Autoclaved aerated concrete: AS 5146.1.
Post-installed and cast-in fastenings: AS 5216.
Steel structures: AS 4100.
Cold-formed steel structures: AS/NZS 4600.
Residential and low-rise steel framing: NASH Standard – Residential and Low-Rise Steel Framing Part 1 or Part 2.
Composite steel and concrete: AS/NZS 2327.
Aluminium construction: AS/NZS 1664.1 or AS/NZS 1664.2.
Design of timber structures: AS 1720.1.
* * * * *
Timber structures: AS 1684.2, AS 1684.3 or AS 1684.4.
Nailplated timber roof trusses: AS 1720.5.
Piling: AS 2159.
The following glazed assemblies in an external wall must comply with AS 2047:
Windows excluding those listed in (ii).
Sliding and swinging glazed doors with a frame, including french and bi-fold doors with a frame.
Window walls with one piece framing.
All glazed assemblies not covered by (i) and the following glazed assemblies must comply with AS 1288:
All glazed assemblies not in an external wall.
Skylights, roof lights and windows in other than the vertical plane.
Sliding and swinging doors without a frame.
Windows constructed on site and architectural one-off windows, which are not design tested in accordance with AS 2047.
Second-hand windows, re-used windows and recycled windows.
Glazing used in balustrades and sloping overhead glazing.
Termite Risk Management: Where a primary building element is subject to attack by subterranean termites: AS 3660.1, and—
for the purposes of this provision, a primary building element consisting entirely of, or a combination of, any of the following materials is considered not subject to termite attack:
Steel, aluminium or other metals.
Timber — naturally termite resistant in accordance with Appendix C of AS 3660.1.
Timber — preservative treated in accordance with Appendix D of AS 3660.1; and
a durable notice must be permanently fixed to the building in a prominent location, such as a meter box or the like, indicating—
the termite management system used; and
the date of installation of the system; and
where a chemical is used, its life expectancy as listed on the appropriate authority's pesticides register label; and
the installer’s or manufacturer’s recommendations for the scope and frequency of future inspections for termite activity.
Roof construction (except in cyclonic areas):
Terracotta, fibre-cement and timber slates and shingles: AS 4597.
Roof tiling: AS 2050.
Cellulose cement corrugated sheets: AS/NZS 2908.1 with safety mesh installed in accordance with AS/NZS 1562.3 clause 184.108.40.206 except for sub-clause (g) for plastic sheeting.
Metal roofing: AS 1562.1.
Particleboard structural flooring: AS 1860.2.
Garage doors and other large access doors in openings not more than 3 m in height in external walls of buildings determined as being located in wind region C or D in accordance with AS/NZS 1170.2: AS/NZS 4505.
Lift shafts which are not required to have an FRL, must—
except as required by (ii), be completely enclosed with non-perforated material between the bottom of the pit and the ceiling of the lift shaft, other than—
at landing doors, emergency doors and pit access doors; and
in atrium and observation areas, be protected with non-perforated material not less than 2.5 m in height—
above any places on which a person can stand, which are within 800 mm horizontal reach of any vertical moving lift component including ropes and counterweights; and
at the lowest level of the atrium area that the lift serves, on all sides except the door opening, for not less than 2.5 m in height, by enclosure with non-perforated material; and
be of non-brittle material; and
where glazing is used—
comply with Table B1.4; or
not fail the deflection criteria required by Clause 6(c)(iii) of Specification C1.8.
Lift shaft vision panels more than 65 000 mm 2 , door panels, and lift shafts
Lift shaft vision panels less than or equal to 65 000 mm 2
10 mm (0.76 mm interlayer)
6 mm (0.76 mm interlayer)
10 mm (0.76 mm interlayer)
6 mm (0.76 mm interlayer)
Annealed glass with security polyester film coating
Safety wire glass
Subject to fire test
To specify deemed-to-satisfy materials and forms of construction.
If the materials and construction listed in B1.4 are used, they must comply with the requirements outlined in the relevant sub-clauses.
The structural performance of a building is dependent, not only on the determining of the applicable actions, but also on the methods used to determine resistance to those actions. B1.4 provides a list of material design standards that can be used together with B1.2.
The weight of roof or ceiling insulation, particularly if additional ceiling insulation is used for compliance with the energy efficiency provisions, needs to be considered in the selection of plasterboard, plasterboard fixings and building framing.
For designers seeking structural compliance via Performance Solutions, a major principle in determining structural resistance is that the reliability level of the structure or its components may be at least equal to that already achieved in the Deemed-to-Satisfy Provisions. For a more complete explanation, the reader is referred to ISO 2394—General principles on reliability of structures.
B1.4(h) clarifies which type of glazed assemblies must comply with AS 2047 and which must comply with AS 1288. The reference to heritage windows is intended to apply to windows in heritage buildings. The method of determining a heritage building is normally covered by the appropriate State or Territory authority.
B1.4(i) only applies where a “primary building element” is considered susceptible to attack by subterranean termites. “Primary building element” excludes from the coverage of B1.4(i) building elements which may provide some bracing to a wall, but it is not required as part of their primary function. An example would be plasterboard not required for bracing or external cladding.
B1.4(i)(i) deems that several specified primary building elements are not subject to termite attack (see Figure B1.4).
B1.4(i)(ii) only requires the attachment of a notice regarding the method or system used to protect against termite attack where that method or system is one described in AS 3660.1.
Table B1.4 describes acceptable glazing permitted in the construction of lift shafts. The inherent strengthened qualities of these glazing types is considered for the purposes of B1.4(m)(iii) 'non brittle'.
B1.5 Structural software
Structural software used in computer aided design of a building or structure, that uses design criteria based on the Deemed-to-Satisfy Provisions of the BCA, including its referenced documents, for the design of steel or timber trussed roof and floor systems and framed building systems, must comply with the ABCB Protocol for Structural Software.
Structural software referred to in (a) can only be used for buildings within the following geometrical limits:
The distance from ground level to the underside of eaves must not exceed 6 m.
The distance from ground level to the highest point of the roof, neglecting chimneys, must not exceed 8.5 m.
The building width including roofed verandahs, excluding eaves, must not exceed 16 m.
The building length must not exceed five times the building width.
The roof pitch must not exceed 35 degrees.
The requirements of (a) do not apply to design software for individual frame members such as electronic tables similar to those provided in—
AS 1684; or
NASH Standard Residential and Low-Rise Steel Framing Part 2.
B1.5 does not apply where a software package simply eliminates manual calculations and the process of the package requires identical methodology as that undertaken manually, e.g. AS 1684 span tables and bracing calculations.
B1.6 Construction of buildings in flood hazard areas
A Class 2 or 3 building, Class 9a health-care building, Class 9c building or Class 4 part of a building, in a flood hazard area must comply with the ABCB Standard for Construction of Buildings in Flood Hazard Areas.
B1.6 requires the specified buildings in a flood hazard area to comply with the ABCB Standard for Construction of Buildings in Flood Hazard Areas. Under the definition of a 'flood hazard area' the appropriate authority (usually the relevant local government) is responsible for determining the extent of land lower than the flood hazard level. The flood hazard level is used to determine the minimum height of floors of a building above the flood waters. The flood hazard area may be mapped in a local government planning instrument.
The prescriptive provisions of the ABCB Standard only apply to flood hazard areas where the maximum flow velocity is not greater than 1.5 m/s. Where the appropriate authority is unable to determine whether the maximum flow velocity is not greater than 1.5 m/s, the prescriptive provisions only apply to inactive flow or backwater areas, i.e. not directly adjacent to a watercourse or floodway.
Where the maximum flow velocity is greater than 1.5 m/s, it would be necessary to formulate a Performance Solution which complies with the relevant Performance Requirements. This would involve the application of engineering practice to determine appropriate design solutions.