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.)

Railings should be designed to resist the most unfavourable likely imposed loads and wind loads separately without unacceptable deflections or distortions. Heights of railings shall be same as that for parapet walls as per other Parts of the Code. The railing height above datum is defined in Fig. 22. The minimum heights for each railing location shall be as given in Table 35.

The height of glass railings installed on top of low parapet walls should be measured from the top of the parapet and not at walk level.

For railings, either permissible stress or limit state design procedure should be used, according to the recommended procedures. When using limit state design, the partial safety factors for loads and materials should be those recommended by the appropriate standard for relevant materials. The deflection of the railing shall be determined as per serviceability limit state.

Minimum horizontal imposed loads appropriate to the design of parapets, railings, balustrades and other

NOTE — In design, the horizontal uniformly distributed line load acts at a height of $1.1\mathrm{m}$ above datum level, irrespective of the actual height of the element.

FIG. 22 DATUM, BARRIER HEIGHT AND DESIGN HEIGHT

PART 6 STRUCTURAL DESIGN — SECTION 8 GLASS AND GLAZING

NOTE — $H$ is the height at which the applied load (horizontal design load) is located and it need not be the height of the barrier itself.

elements of structure intended to retain, stop or guide people, should be determined in accordance with Table 36, which recommends a uniformly distributed line load for the railing and a uniformly distributed and point load applied to the infill.

NOTE — These are not additive and should be considered as three separate load cases, all loads being determined according to the type of occupancy which reflects the possible in-service conditions.

Horizontal uniformly distributed line load should be applied at design height as presented in Table 36 or at

design level (1 100 mm) for railings higher than the design height.

Uniformly distributed load should be applied to the area below the design height.

Point load should be applied at the most onerous point anywhere on the railing structure.

NOTE — For clarity, the design level (the level at which the horizontal uniformly distributed line load ought to be considered to act) is shown in Fig. 23.

In general, the load combinations as described in H-4.2.1 to H-4.2.3 should be applied.

FIG. 23 HEIGHT LIMIT FOR THE UNIFORM LOADING FOR VARIOUS CATEGORY OF BUILDINGS

H-4.2.1 Free Standing Glass Protective Railing (Without any Balusters)

It requires five design loadings to be taken into account:

a) Line load (Horizontal UDL), in kN/m

b) UDL (Infill UDL), in $\mathrm{kN / m^2}$.

c) Concentrated load, in kN.

d) Impact force.

e) Shot bag test load (see Annex E).

H-4.2.2 Railing with Glass Infill Panel

It requires three design loadings to be taken into account:

a) UDL (Infill UDL), in kN/m².

b) Concentrated load, in kN.

c) Impact force, in kN.

H-4.2.3 Full Height Railing

It requires three design loadings to be taken into account:

a) Line load (Horizontal UDL), in kN/m.

b) UDL (Infill UDL), in kN/m².

c) Concentrated load, in kN.

H-4.3 Wind Loads

External railings should be designed to resist the wind loads given in good practice [8-5(7)].

PART 6 STRUCTURAL DESIGN — SECTION 8 GLASS AND GLAZING

Railings for the protection of people should be of adequate strength and stiffness to sustain the applied loads given in Table 36. In addition, a railing that is structurally safe should not possess flexibility to such an extent so as to create a false alarm to building users when subject to normal service conditions. Therefore, for serviceability considerations, the limiting condition for deflection appropriate for a railing for the protection of people is that the total horizontal displacement of the railing at any point from its original unloaded position and should not exceed the deflection limits determined from the relevant structural design code (where applicable) for the material used, or 25 mm, whichever is the smaller. Where the infill of a railing is subjected to the imposed loads given in Table 36, or if appropriate, other calculated design loads, the displacement of any point of the railing should not exceed H/65 or 25 mm, whichever is lower.

The strength of fixings, attachments and anchorage securing the railing to a substrate should be adequate to sustain a loading greater than that to which the railing will be subjected. All joints should be designed to provide the full strength of the members being joined. To that end, where any uncertainty exists with regard to the strength of any component in the fixing, the design loading factors should be increased by 50 percent.

While designing fixings, particular care should be taken to account for the material into which the fixing is placed, the spacing between fixings, the edge distance, and where the substrate is concrete, the position of reinforcement. Designs based on the pull out capacity of a single fixing should be avoided.

NOTES

1 The recommendation of an additional load factor of 1.5 is intended to ensure that under an extreme load condition, railings give an indication of failure by deflection distortion and not by total collapse, as may be brought about by a failure of the fixing, attachment or anchorage system. Where the design strength of a proposed system of fixing to an existing substrate cannot be determined with reasonable accuracy by theoretical consideration, load testing should be used to validate the design. 2 A factor greater than 1.5 on railing load design might also be chosen based on the importance desired by the designer/parties concerned.

H-4.6 Testing

The standard tests, performance criteria of glass in permanent glass railing systems, guards and balustrades shall be mutually decided between the parties concerned.

The use of glass in railings, the type and thickness of glass required for various support conditions shall be as given below. If designed properly, glass can form a structural component of the railing, or the railing may be designed to have a structural component made from another material such as steel or aluminium, with glass acting as an infill panel only. This places a lesser load on the glass as the major load is taken by the structural component.

NOTE — There are certain situations, particularly under some lighting conditions, where the presence of transparent glass is not readily evident and suitable manifestation should be provided.

For the purpose of this annex, safety glass used in railing shall be any of the following:

a) Laminated glass,

b) Heat strengthened laminated glass, and

c) Toughened laminated glass.

The designer shall ensure that in the case of accidental or deliberate damage, there is no glass fallout to rule out any kind of danger to public. In these situations, it is recommended to use a toughened laminated glass or fully framed laminated glass. Exposed edges of laminated glass are not recommended unless it is with a non-hygroscopic layer.

It is recommended that all monolithic toughened glass used in frameless or bolted structural railings be specified as heat soak treated.

The type of glass should be chosen to suit the design of the railing. For the use of laminated glass, where the glass is not fully framed, the manufacturer should be consulted. Toughened glass and laminated toughened glass should be used for all railings where the glass is fully or partially framed or is free standing. The selection of glass should include consideration of the post breakage behaviour.

NOTES

1 Laminated safety glass can be used for all railings, where the glass is used, fully framed.

2 Monolithic toughened glass might fall from its retention system if broken in free-standing and infill railings. In such cases, additional protection shall be required if this type of glass is used above areas of fixed seating.

H-5.2 Working of Glass

The size, position and shape of holes and notches in toughened glass, and the production of shapes other than rectangles, should be decided in consultation with

the manufacturer, as shaping, drilling, cutting, etc, should be undertaken prior to toughening.

Contact between glass and any other hard material (including other glass parts) should be prevented. Rubber gaskets or other glazing materials should be used with frame sections. The frame section should give a minimum of 15 mm edge cover to the glass unless it can be shown by test or calculation that the frame will retain the glass under load while conforming to design requirements.

The frame and/or fastenings should be designed so that they do not tend to distort the glass panel. This is particularly important with bolted connections, which can exert considerable forces on the glass, where particular attention should be paid to the alignment and position of the fasteners in order to avoid unnecessary stresses being developed.

At the bolted connections there should be clamping plates and gaskets on both sides of the glass that provide a minimum of 50 mm diameter cover to the glass. These plates should be not less than 6 mm thick in steel or 10 mm thick in other suitable metals.

Where the length of a glass pane is greater than the span between the bolted connectors, giving rise to a cantilevered portion of the pane, the cantilevered portion should be less than one-quarter of the span between the bolted connectors.

Under the design loads, the railing should be designed so that the relative in plane movement of the bolted connections in the same panel is not greater than $2\mathrm{mm}$.

The glass, framing system and connections of railings and infill panels should be capable of sustaining and safely transmitting the design loads to the supporting structure.

H-5.4 Design of Glass

H-5.4.1 Design of Glass in Full Height Protective Railings

Glass partly or totally below the minimum railing height should be designed to satisfy the appropriate design criteria. Any part of a glass pane below the minimum railing height should sustain the infill loads. Where there is glass at the minimum railing height given in Table 36, the glass should also sustain the line load applied at the design level.

For any specific information on the glass size relative to the glass type, support system, loadings and thickness, available standards or the manufacturer recommendations should be sought.

Infill panels should be designed to satisfy the appropriate design criteria as below:

a) Fully framed infill panels — The deflection of the glass in fully framed infill panels should be as per recommended deflections.

b) Two-edge framed infill panels — The deflection of the glass in two edge framed infill panels should be as recommended under H-4.4 taking L as the distance between the supports.

c) Clipped infill panels — The clips should be positioned around the periphery of the infill panel, at a maximum spacing of 600 mm. Each clip should be not less than 50 mm in length and should give a minimum depth of cover to the glass of 25 mm.

d) Bolt fixing of glass infill panels — Where glass is supported by bolted connections through holes in the glass, toughened/toughened laminated glass should be used.

e) Position of infill panels relative to the main frame — Infill panels should be fully contained within the supporting structure. In order not to apply unintended loads to the infill panels, they should have handrails above the glass or attached to the side to which the public have access.

H-5.4.3 Design of Free Standing Glass Protective Railings

The glass should be designed to satisfy the appropriate design criteria given in H-4. The deflection of the glass should not be more than $25\mathrm{mm}$ at any point.

Where the railing protects a difference in level greater than 600 mm, a handrail shall be used unless a laminated toughened glass construction is used that remains in-situ, if a panel fails. Continuous fixing should be used for fixing the handrail to the glass, or individual fixings where calculations or tests demonstrate that component failure will not occur.

Where handrail is not desired, the laminated toughened glass should have a stiff interlayer such as ionoplast interlayer or structural PVB interlayer.

The handrail should be attached to the glass in such a manner that, should a glass panel gets fractured, the handrail,

PART 6 STRUCTURAL DESIGN — SECTION 8 GLASS AND GLAZING

a) will remain in position; and

b) will not fail if the design load is applied across the resulting gap.

NOTE — The above condition (b) can be relaxed where the glass pane is an end pane and protects a difference in level of 600 mm or less, for example at the foot of a flight of stairs. In cases where an end pane protects a difference in level greater than 600 mm, there may normally be some adjacent structure to which the handrail could be attached, thus enabling it to meet condition (b).

H-5.4.4 Base Fixing of Free Standing Railings

H-5.4.4.1 Point of fixing clamps

The fixing clamps on each side of the glass should be not less than 100 mm to 150 mm and should be made of a suitable metal of minimum thickness 12 mm. There should be not less than two fixing clamps for every 1 m length of railing.

H-5.4.4.2 Continuous fixing clamps

The fixing clamps on each side of the glass should be not less than 100 mm wide and should be made of a suitable metal of minimum thickness 12 mm. The clamps should be continuous for the entire length of the glass pane and have a maximum bolt spacing of 500 mm.

H-5.4.4.3 Other clamping systems

Different clamping methods could be used, provided they cater for an effective continuous clamping over the length of the glass pane. Where a clamping system that does not rely on bolts through the glass is used, the depth over which the clamping force operates should be not less than 75 mm, unless specific tests have been carried out to prove the integrity of the system and that it meets the design criteria given.

H-5.4.4.5 Structural movement

The structural movement due to live or dead loads or creep of the structure to which a railing pane is clamped should be not greater than 2 mm over the length of any railing panel, if more than two bolts are used to clamp that panel.

H-5.4.4.6 Fixing clamps

The attachment of the fixing clamps to the structure should be capable of withstanding the turning moment induced at the fixing clamps.

H-6 Impact Resistance and Containment

H-6.1 General

In addition to resisting the design loads given, glass below the minimum railing height (see Table 1) should also be able to resist impact forces appropriate to whether the railing indicates a route or protects people from a hazard.

H-6.2 Glass in Full Height Railings

The glass in full height railings should be selected to resist the appropriate design loads given and for its impact performance in accordance with the safety glazing recommendations.

H-6.3 Railing with Glass In-Fills or Free-Standing Balustrades

The glass in railings with glass in-fills or free-standing should be selected to resist the appropriate design loads given, and to provide containment, that is, it should meet the recommended impact class without penetration.

H-7 Installation

The installation of a railing should be supervised by a suitably qualified person or persons, who should ensure that the design assumptions have been effectively implemented. Inspections and investigations should be carried out as necessary to establish the integrity of the materials and the elements of construction used.

H-7.1 Fasteners and Fittings

Fasteners and fittings should be of stainless steel, or should be hot-dip galvanized. Thin zinc plated or cadmium plated coatings should not be used for external exposure without additional protection.