Updated May BALUSTRADE & FENCE DESIGN

Transcription

1 Updated May 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 B1 Structure The compliance document B1/VM1 was amended in June 2008 and became effective in 1 December It now cites AS/NZS 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 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 A - Domestic and residential activities B,E - Offices and work areas not included elsewhere including storage areas C - C1/C2 Areas with tables or fixed seating C3 Areas without obstacles for moving people and not susceptible to overcrowding C5 Areas susceptible to over-crowding D Retail areas Specific uses 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) 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 Areas where people may congregate Areas with fixed seating adjacent to a balustrade, restaurants, bars, etc. Stairs, landings, external, balconies, edges of roofs, etc. Theatres, cinemas, grandstands, discotheques, bars, auditoria, shopping malls (see also D), assembly areas, studios, etc. All retail areas including public areas of banks/building societies (see C5 for areas where overcrowding may occur)

2 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 multiunit 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 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.

3 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 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 fal 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

4

5

6

7