Annex H

(Foreword)

Glass Railings

H-1 General

Glass railings are generally sought in commercial applications (such as in malls) and in certain domestic villas, etc. Glass of appropriate thickness when used as a railing can provide transparency and when engineered properly can provide structural performance too.

The basic requirement of a parapet which a glass railing (if so used) intends to substitute shall be met with. This

includes protecting people from falling and in some cases to control movement. Careful consideration including in design shall be made where glass railings are used.

NOTE — Notwithstanding the above, the potential benefits including safety (through psychological aspects) of regular railings shall be borne in mind.

In the assessment of the need for a railing and the type

PART 6 STRUCTURAL DESIGN — SECTION 8 GLASS AND GLAZING

of railing to be provided, the designer should give consideration to the likely hazards, the building use and the risks to building users. Where, in a building, more than one use of the building is anticipated, either the railing design should be chosen to suit the worst case, or more than one type of railing should be provided, as appropriate, to the location. Generally when there is a change in adjacent levels (600 mm in dwellings, 380 mm in other buildings) a railing is needed to restrict movement of people.

The railing adopted should be designed so as to minimise the risk of persons falling, rolling, sliding or slipping through gaps in the railing. In dwellings and other buildings which can be accessed by children, gaps in railing or infill should not be large enough to permit a sphere of 100 mm diameter to pass through, making due allowance for deflection under load.

The designer should ensure all the elements of the railing system satisfy the criteria given in available relevant standards.

For general safety, the finished barrier should have no sharp edges or projections that could cause injury to persons or clothing. Infill panels and balusters are intended to provide support and protection to users, and should be designed to restrain people without causing additional injury from sharp edges, thin sections, open-ended tubes, projecting details, etc.

The design shall be based on the horizontal UDL (uniformly distributed load) should be applied at a notional height of 1.1 m above finished floor level, even though the minimum permissible height of the railing may be less (The notional design height of 1.1 m is chosen as being representative of the height of the centre of gravity of a human being above the datum level).

There are four common types of railing that used to fix glass.

a) Full height railing — Where glass forms part or whole of a wall element, the railing should be carefully designed as per the relevant existing standards and as per this Section, if any part of the glass comes below the minimum railing height (see Table 35).

b) Railings with a glass infill panel — In this type of railing, the main frame of the railing (that is, top rail and baluster) should be designed to withstand the loads applied to the top rail and the glass should be used to form infill panels. It should be noted that the glass provides no support to the main frame. This can be further sub-categorized into 4 types:

3. Glass supported on vertical edges only—This may involve the vertical edges of the glass being supported in a rebate into the side of each vertical post. The top and bottom edges of the glass are exposed. The glass may also be supported by patch fittings fixed to the posts. In all cases a handrail is required.

Glass supported on horizontal edges only — This may involve a handrail at the top, and a channel or a rail at the base of the glass. In this case the handrail should be designed to carry the railing load with the glass designed to carry the infill load. Glass supported on all four edges.

4. Glass fixed by patch/bolted fittings — This system requires the use of two rows of bolts (commonly) to provide a stiff fixing which minimises panel deflection. There are a variety of bolt fixing types available in the market so design and performance information should be sought for each type. The purpose of these fixings is to transfer the force applied to the railing into the support structure. These fixings occupy a small surface area on the glass which can produce high stresses in the glass, so careful analysis is required to determine suitable glass thickness, fixing spacing and size.

c) Free standing glass protective railing — In this type of railing, the glass should be designed to withstand the design loads. Each glass plate should be rigidly clamped to the structure along its bottom edge, the handrail attached to the top edge of the glass and there should be no balusters. In the event that a free standing railing is supplied without a handrail, each panel should be able to withstand the entire appropriate design load. This applies to vertical glazing and glass within 15° of vertical. Adequate provision for drainage of water should be made in the base structure to avoid any water ponding which may cause delamination issue

d) Bracket systems — These systems are an extension of the bolt fixed system where the bolts are part of a bracket and the bracket is fixed to the floor or the face of a concrete slab, steel or timber structure. The use of these systems shall be investigated carefully as they can develop very high stresses in the glass where the brackets are located. The design shall balance glass thickness and bracket location to produce an adequate system. Some systems may be designed to produce test data,

to justify their use. This data shall be studied carefully as there have been some cases where such data has been shown to be inadequate. Proper interpretation of these test data shall also become necessary.

H-4 Design Considerations

The designer shall first determine the purpose of the railing. Once this is done, the appropriate load requirement can be derived. Typical values (minimum requirements) of railing loads to be chosen are given in Table 36. (If so desired by the designer, higher values than that in the Table 36 may also be chosen.)