Glass: Glasses are used in doors and windows because it transmit diffused light, to achieve privacy with dark glass and to get some decorative features to the building. Many types and varieties of glasses are available in the market. Out of these, ordinary glass, tinted glass, tempered glass and laminated glass are normally Industry Buying INused in building construction.

Types of Glass:

Sheet Glass or ordinary glass: It is made by Soda, Silica and lime. The combination of this material is heated in the furnace to melt and fuse. Molten glass is pulled vertically through rollers. This glass goes through the annealing process and is also known as annealed glass.

Tinted glass: While making sheet glass different colours are added to it. This reduces the sun light entering inside and also reduces solar heat in the building. It is used in the Air-conditioned premises and wherever sun light has to be reduced. Apart from colour it has the same properties as that of parent glass.
Tempered glass: Tempered glass is strong and has more resistance power to wind pressure. If it breaks, the resultant shards are granular in shape and prevent injury to people. The glass is heated to its softening temperature and then suddenly cooled down. It is used in commercial building, Shops as curtain walls and main doors etc. As this glass is stronger, it is used for frameless doors also.

Laminated glass: While making this type of glass, two elastic lamination films are provided from both the sides to the glass. The glass is bounded in the two films. If this glass is broken the glass particles remain there in broken condition.

Wired glass: In this glass steel wire mesh is used as reinforcement. This type of glass is stronger than the normal glass. The wire mesh prevents the broken glass pieces from falling out.
Guidelines for use of Glass in Structures: The glass sheets when used as structural elements receive mainly load due to wind and also accidentally human impact. It is considered that if the glass is located between final floor level and 750 mm above it, it is the most vulnerable condition when maximum load can come due to human impact. Accordingly, certain conditions based on i) edge support ii) Location of glass sheet with reference to final floor level and iii) type of glass are recommended as under,
Four sides framed glass: In case of framed glass panels supported on four sides and placed between the finished floor level and 750 mm, the maximum allowable area of the glass panel is as follows:image249 image250
The maximum area of the normal or annealed glass shall be less than equal to 0.5 sq.m. The maximum area of the safety glass depending upon its thickness shall be within the permissible maximum area as defined in the table (A) given below.
Table A : Thickness and permissible area of glass
Type of Glass
Nominal thickness (mm)
Maximum allowable area (sq.m.)
Tempered Safety Glass
4
2
5
3
6
4
8
6
10
8
12
10
 Laminated Safety Glass
6
2
8
3
10
5
12
7
     
In the case of ordinary annealed glass panels supported on all four sides starting above 750mm or a protection / transom / chair rail is in place permanently from the finished floor level, the thickness of annealed glass shall be within the permissible maximum area as defined in the table B.image251
Table B: Annealed glass (Ordinary Glass)
Nominal Thickness (mm)
Maximum allowable area (sq.m.)
4
0.8
5
1.2
6
2.1
8
3.2
10
4.4
12
6.3
Two / Three sides Framed Glass: In case of glass panel supported on two/three sides above 750 mm or has a protection from the finished floor level, then annealed glass can be used in following cases as mentioned in the Table C, else tempered or laminated glass shall be used.
Table C:
Nominal Thickness
(mm)
Maximum allowable
height of glass (m)
Maximum allowable
glass area (sq.m.)
6 mm
= 1.2
0.9
8 mm
> 1.2 to = 1.6
1.8
10 mm
> 1.6 to = 2
2.7
Frameless / Non-framed Glass: In case of frameless or non-framed glass panel toughened safety or laminated safety glass only shall be used. The thickness of safety glass and corresponding maximum permissible area is given in the following table D.
Table D:
Nominal Thickness (mm)
Maximum allowable area (sq.m.)
6
3.0
8
4.5
10
6.0
12
7.5
In cases wherein the glass area exceeds 7.5 sq.m., it is not recommended to glaze the area or else determine thickness of the glass using advanced analysis under wind load as per IS : 875 (part 3 1987; reaffirmed 1997) for external glazing and / or loads, in case of internal glazing or glazing wherein there are chances of human impact.
Point Supported glass: It is not recommended for point fixed system unless the glass area and glass thickness is determined by the specific strength analysis and type of point fixing hardware.
Fixing glass: Glass sheets may be fixed in wooden frame or metal frame. There is minor difference in the two cases. In wooden frame, rebates are provided in the glazing bar which support the glass pane, with the help of putty and beading. In some steel window frames the same may be possible, especially in smaller glazed areas, but in cases where extruded aluminum or steel sections are used for glazed walls, it shall not be feasible and special arrangements are available consisting of Shoe stop, storm clip, cover strip, lead wing, fixing bolt, drought excluder, PVC cushion etc.
The fixing of glass on wooden frame or some steel frames not using extruded sections is described below,
Glass is fitted in the window over a thin layer of beading made with putty and back putty. In other words, the glass edges are embedded in putty. It seals the gap between the glass and the rebate in the glazing bar.
The pane is secured by means of triangular pins, called ‘Sprig’ or panel pins to remain in position. In case of steel glazing bar, machine screws are fixed in the holes provided in the rebate to secure the glass.
A wooden beading of appropriate size is fixed in front of the glass pane in the rebate in case of wooden frame. In case of steel frame, front putty is placed to form a triangular fillet with the help of knife blade. In case of wooden frame also, similar fillet can be placed by front putty instead of the beading. However, the finish is not very pleasing and is adopted for doors windows which do not come in the eyes of the occupants, such as for windows opening on the street on higher floors etc. but rarely used for doors. The details are shown in the figure below.
Glazing Putty (Lamb): Putty is a mixture of linseed oil, white lead and chalk powder. It is in the form of thick paste. Boiled linseed oil is added to the above mixture to form a stiff paste of desired consistency. Readymade putty is nowadays available in the market under different brand.image252
Putty for glass fixing: Following precautions should be taken while using putty for glass fixing:
·              Mix the putty at site with the help of linseed oil and form a roll for better consistency.
·              See that second coat oil paint is applied after semi drying of putty.
·              Finishing of putty should be made smooth with the help of glass cut piece.
·              See that sufficient quantity of putty is applied to every panel.
·              Before applying putty, check that glazing clips are fixed in each and every hole provided in the   frame.
·              Position and tension of each glazing clip should be as such to hold the glass in position.
·              Check that glass size is not under cut.
·              Use glass diamond cutter to cut the glass of required size.
·              Do not disturb the glass panes when putty is wet.
image253Glazed Walls: The patented extruded aluminum and other metal sections are being used extensively in construction walls with glazing. This form of glazing has systems inbuilt for collecting and removing water in channels or glazing bars different from putty and beading to seal the joints. Typical details are shown in the figure below
The various fixtures are required to be fixed as per the figure shown, however except for I.S.10439-1983 which also gives general specification, one has to go by the specifications provided by manufacturers of Aluminum doors and windows. Their brief function is as under,
Capping or cover strip: It is a preformed metallic or plastic strip fitted externally to a glazing bar and prevents penetration of water and also restrains the glass from being lifted due to suction forces.
Storm clip: A fitment fixed externally to the glazing bar to restrain the glass against suction pressure.
Draught excluder: A strip to fill the space between the underside of glass and structural member to prevent penetration of driving rain or snow.
Flashing: Astrip of flexible, impervious material usually metal or plastic used to exclude water from the junction between glazing and adjacent part.
Shoe Stop: A fitting secured to the lower end of glazing bar and acting as a stop to the glass.image254
Muntins section: A light bar of suitable material, such as thin preformed aluminum strip or a plastic section in the shape of ‘H’ or ‘A’ to weather horizontal butt joint between two panes of glass held vertically in the same plane by glazing bars.
Lead wings: A projection lead for forming an integral part of a glazing bar, it is dressed down to the glass to form a barrier against penetration by water. The detailed assembly is shown in sketch below.


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