updated may 2009 - metroglass.co.nz balustrade... · specific design is required for structural...
TRANSCRIPT
Updated May 2009
13.23 BALUSTRADE & FENCE DESIGN
A glass balustrade is a modern and stylish safety
barrier, which provides strength and safety in
conjunction with maximum unobstructed views.
Glass balustrades can be free-standing cantilever glass
without vertical support, or infill balustrades supported
by post, glass fins or other frame members, or
combinations of these systems.
Infill types are normally two or three side supported by
channels clamps or disc clamp fittings.
The NZ Building Code specifies performance
requirements and design principles for balustrades.
It is important that all the requirements are met and a
producer statement of compliance is provided.
It is not acceptable to install a balustrade purely on the
basis of an architectural design drawing, and the
installer must ensure it has been engineered and the
product is fit for purpose.
NZ Building Code Compliance
The following sets out compliance with NZBC
Acceptable Solutions.
F2 Hazardous Building Materials
F2/AS1 refers to NZS 4223:Part 3:1999 as a means of
compliance and requires Grade A Safety Glass to be
used. Infill panels are required to be not less than 6mm
thick and Table 3.8 is provided for glass requirements
to some balustrade types. However, recent changes to
B1/VM1 mean that these tables do not comply with
AS/NZS 1170, so now tables are provided in this
section.
Specific design is required for structural balustrades
and fences and design tables are provided in this
section based on the new AS/NZS 1170 whic h replaces
NZS 4203.
B1 Structure
The compliance document B1/VM1 was amended in June 2008 and
became effective in 1 December 2008.
It now cites AS/NZS 1170 .1 which details the design actions for barriers in
Table 3.3
This has changed the requirements for barrier loads, and has increased
the number of occupancy types, increased the magnitude of some top
edge and infill loads , and has introduced a concentrated load case.
In B1/VM1, paragraph 2.2.7 provides specific information on the height of
application of the loads.
Wind loads must also be considered and this is important in high rise or
high wind load situations as the wind load may dominate design over the
other loads
AS/NZS 1170 also provides recommendations for deflection limits in Table
C1 and these are more stringent than the normal allowable deflection
requirements for toughened glass balustrades, which are span/60 for infill
panels and height/30 or 30mm maximum for freestanding glass.
It is important to remember that when balustrades have no handrail, the
glass is required to support the handrail load and this can be very
restrictive on design.
In addition consideration must be given to the result of glass failure and
Metro GlassTech recommends interlinking handrails on structural
balustrades in case of glass failure.
Type of occupancy
for part of the
building or structure
Specific uses
A - Domestic and
residential activities
All areas within or serving exclusively one
dwelling including stairs, landings, etc. but
excluding external balconies and edges of
roofs (see C3)
Other residential, (see also C)
B,E - Offices and work
areas not included
elsewhere including
storage areas
Light access stairs and gangways not
more than 600 mm wide.
Fixed platforms, walkways, stairways and
ladders for access (see note)
Areas not susceptible to overcrowding in
office and institutional buildings also
industrial and storage buildings
C - Areas where people may congregate
C1/C2 – Areas with tables
or fixed seating
Areas with fixed seating adjacent to a
balustrade, restaurants, bars, etc.
C3 – Areas without
obstacles for moving
people and not
susceptible to over-
crowding
Stairs, landings, external, balconies,
edges of roofs, etc.
C5 – Areas susceptible to
over-crowding
Theatres, cinemas, grandstands,
discotheques, bars, auditoria, shopping
malls (see also D), assembly areas,
studios, etc.
D – Retail areas All retail areas including public areas of
banks/building societies (see C5 for areas
where overcrowding may occur)
F4 Safety from Falling
F4/AS1sets out barrier heights and construction
requirements for buildings including balconies,
swimming pools and opening windows.
Barriers or balustrades are required when people can
fall 1m or more from an opening in the external
envelope or floor of a building or from a sudden change
in level within or associated with a building
The minimum barrier heights are;
Detached dwellings and within household units of multi-
unit dwellings.
900mm on stairs and ramps and their landings
1000mm on balconies, and decks, and edges
of internal floors or mezzanine floors edges of
internal floors.
All other buildings and common areas of multi-unit
dwellings:
900mm on stairs and ramps
800mm for barriers within 530mm of the front
of fixed seating
1100mm in all other areas
1200mm for swimming and spa pools.
Note - Heights are measure vertically from the floor level
(ignoring coverings) on floors landings and ramps and from the
pitch line or stair nosing on stairways
Toe holds are defined as 15mm ledge over the height
of the barrier, and if greater than 15 mm a 60 degree
fillet angle to the horizontal is required.
Openings in barriers frequented by children under 6
should not be more than 100mm, and not allow a
100mm sphere to pass through.
The triangular opening formed by the stair riser and the
bottom of the balustrade shall allow a 150mm diameter
sphere to pass through.
D1 Access Routes
D1/AS1 sets out the requirements for handrails for access routes including
stairs, to or within buildings.
Handrails are required on all stairs and Accessible Routes (for people with
disabilities) if the slope exceeds 1 in 20 and they must comply with the
requirements of D1/AS1. The handrail must have features to cope with
people with disabilities in Accessible Routes and the handrail must be 32
to 50 mm diameter. This is less than many standard handrail designs.
B2 Durability
B2/AS1 deals with durability and minimum durability requirements for
materials and fixings used in balustrades and barriers. The requirements
range from 5,15 to 50 years depending on whether the element is
structural and how difficult it is to replace. In some cases the 50 year
requirement will apply to fixings for structural elements of safety barriers
E2 External Moisture
E2/AS1 deals with balustrade to wall and deck drainage junctions and
balustrade fixing to ensure the building is water tight, and covers
compatibility of materials
Fencing of Swimming Pools Act 1987 (FOSPA)
F4 and F4/AS1 still refer to the FOSPA, however a new standard NZS
8500:2006 S afety Barriers and Fences around Swimming Pools and Spas
and Hot Tubs is available.
Fencing requirements under this act apply to pools altered since 1991.
Refer to the FOSPA for the requirements, but as a guide the key
performance requirements are:
Pools having a depth of water exceeding 400mm shall have
barriers
Barriers shall restrict the access of children under 6 years
All gates and doors shall be fitted with latching devices not
readily operated by children and must automatically close from
150mm or more from the closed position
Gates must not open inwards to the pool area
Latches must be fitted which are only accessible by reaching
1.5 m above ground on the outside
Barriers shall have no permanent objects on the outside that can
provide a climbing step.
If the pools side walls exceed 1.2 m height or the maximum depth of water
is less than 400mm then fences are not required.
For balconies overlooking a pool area – refer to NZS 8500 .
Balustrade Design Types
Balustrade glass designs normally fall into the following
types;
Type SB1. Structural Balustrade – Cantilevered glass
Type SB2. Structural Balustrade – 2 Edge-Point fixed
Type SB3. Structural Balustrade – 2 Edge support
Type SB4. Structural Balustrade – 3 Edge support
Type IB1. Infill Balustrade – 4 Edge support
Type IB2. Infill Balustrade – 2 Edge support
Type IB3. Infill Balustrade – 2 Edge-Point fixed with
handrail in front of glass
Tables
GANZ have prepared a series of design charts for the
above types based on design loads from AS/NZS
1170.1 and B1/VM1. These are an alternative solution
for compliance with the NZBC
The tables show the maximum ULS wind pressure for
each thickness and if the wind loads for the glazing
location exceed these pressures specific design will be
required. This can occur in some high rise buildings –
or exposed sites.
For other design types specific design is required.
Handrails
Handrails are not always required, but they normally fall
into three categories
Load Supporting Handrail (handrail takes the
load). This infers that the handrail
mechanically fixed to the structure,
independent of the glass, but the glass can be
connected to it. These handrails must be
designed to support the barrier loads. This is
normal with an infill balustrade.
Non Load Supporting Handrail (Glass takes
the Load).
This infers that either the top edge of the glass
acts as the handrail or the glass supports a
handrail that is fixed to the glass and relies on
the glass for structurally support. The glass
must be designed to support the barrier loads.
Interlinking Handrail
This infers the handrail is non load supporting,
unless an panel breakage occurs, and is
connected to adjacent panels of glass, or the
building, where the adjacent panels are at
least 1000mm wide and three or more panels
of glass form the balustrade. If any one panel
fails the remaining panels and handrail shall
be capable of resisting the barrier
.
NOTE. Metro Glasstech recommends interlinking
handrails on all structural balustrades