CURTAIN GLAZING

REPORT

•Curtain wall systems are a non-structural cladding systems for the external walls of buildings. They are generally associated with large, multi-storey buildings.

•Curtain walls separate the interior from the exterior, but only support their own weight and the loads imposed on them (such as wind loads, seismic loads and so on) which they transfer back to the primary structure of the building.

•Typically curtain wall systems comprise a lightweight aluminium frame onto which glazed or opaque infill panels can be fixed. These infill panels are often described as ‘glazing’ whether or not they are made of glass.

•Curtain wall systems can be custom designed and manufactured, but are often manufacturer's proprietary systems that can be bought ‘off the shelf’. Custom-designed systems are generally only cost effective for larger buildings.

CURTAIN WALLS ??

THE UNITIZED CURTAIN WALL• A glass and aluminum curtain wall fabricated and

installed as a panel system is referred to as a unitized curtain wall system. A unitized curtain wall will have the same components as a stick built curtain wall system. It will comprise aluminum mullions, an IGU and a spandrel panel mounted in a prefabricated aluminum frame. However, instead of assembling the glass and aluminum curtain wall in the field, most of the system components are assembled in a plant under controlled working conditions.

• This promotes quality assembly and allows for fabrication lead-time and rapid closure of the building. The unitized system is assembled on the building as panels (see Fig. 4, page 4). The mullions and rails are fabricated as half sections instead of tubular sections, which mate at assembly time to form the curtain wall system. The panels are installed in shingle fashion, starting from the bottom of the building and going around each floor and up the building.

• While the unitized system offers many advantages with respect to quality assembly and speed of on building closure, there is one design concern with respect to installed performance and durability. In a stick built system, there are two joints along every mullion and rail. In a unitized system, there are three joints along every mullion and rail. These include the two glass to aluminum joints and a third joint at the junction between the half mullions and half rails.

• Three joints instead of two increases the potential air and water leaks by 50% over a stick built system. Should an air or water leak develop at the third joint, there is usually no practical method of accessing the in-between panel joint for repair (see Fig. 5) unless the manufacturer has provided a serviceable joint system design. In a unitized system, the manufacturer must rely on qualified installers to ensure that the air seals are properly installed between the split mullions.

• Nevertheless, the unitized system is now as popular as the stick system according to one manufacturer and it has performed satisfactorily when installed correctly.

Curtain walls can adopt a ‘stick’ system, or can be unitised:

• Stick systems are installed piece by piece on site, with the glazing inserted into the frame from the inside or the outside depending on access conditions.

• Unitised systems are pre-fabricated in modules off-site and delivered in panels. Unitised systems are better able to exploit the benefits of factory condition manufacturing and quality control and require lower installation time on site.

There are a wide range of possible infill panels for curtain wall systems, including:

• Vision glass (which may be double or triple glazed, may include low-e coatings, reflective coatings and so on).

• Spandrel (non-vision) glass.• Aluminium or other metals.• Stone veneer.• Fibre-reinforced plastic (FRP).• Louvres or vents.• Panels are often composites, with the facing

materials bonded to, or ‘sandwiching’ insulation.

STICK BUILT SYSTEM

Structural Glass Systems Structural Glass Systems, often called “Spider Systems” or

“Bolted Systems”, have been used on many high profile buildings. Holes are typically drilled

in each corner of each glass pane and the glass is attached mechanically with stainless

steel “spiders”. These systems are not structural glazing although they have a similar

appearance from the exterior. In certain designs, the “spider” only attaches to the internal pane of an insulating glass unit. In

such designs, the insulating glass sealant will have a structural function. In all types of

Structural Glass Systems, silicone sealants play an important role in maintaining a

watertight weatherseal and in the performance of the insulating glass units.

Glass Systems

Toughened glassToughened or tempered glass is glass that has undergone processes of controlled thermal treatment to increase its strength. Toughened glass is made from annealed glass that has been heated to approximately 650⁰C and then rapidly cooled. Due to the increased heat treatment and rapid cooling of the glass, especially between the surface and the inside of the glass, the treatment produces different physical properties. This results in compressive stress on the surface and improved bending strength of glass. Before toughening, the glass must be cut to size or pressed to shape. This is because once it is toughened, it cannot be re-worked on. Toughened glass is widely used in a number of applications

Laminated glass is a kind of safety glaSS that is commonly used for automobile windshields. It consists of two layers of glass with a layer of film, called the interlayer, in between them. The glass is designed this way in order to prevent it from shattering into sharp pieces when struck by an object or when the car is in an crash.The interlayer in the glass is a film of a tough, yet pliable material known as POLY VYNIL (PVB). In the event that the glass breaks, the two layers are held together by the PVB, allowing the sheet as a whole to bend and absorb the impact. This characteristic is especially important for car windshields since, ideally, the film will keep objects from penetrating through the glass and possibly injuring the car’s occupants. Laminated glass is also used in prisons, jewelry stores, hospitals, and other places where safety or security are paramount.

SPIDER FITTINGS

SINGLE ARM SPIDER

2 WAY SPIDER

4 WAY SPIDER FITTING

Frame and panel designs are very complex, as they need to perform multiple functions:

• Transferring loads back to the primary structure of the building.

• Providing thermal insulation and avoiding cold bridging and condensation.

• Providing fire, smoke and acoustic separation. This is particularly difficult at joints between the curtain wall system and interior walls and floors.

• Creating a barrier to water penetration.• Accommodating differential movement and deflection.• Preventing panels from falling out of the frame.• Allowing for opening windows.• Preventing the accumulation of dirt.

On tall buildings, access systems must be provided to allow regular inspection, maintenance, cleaning and replacement (in particular, replacement of external seals).

Systems used to prevent the passage of water through joints (driven by pressure differences between the inside and outside) include; face-sealed, water-managed and pressure-equalised (PE or ‘rainscreen’) systems.

Pressure-equalised systems create a rebate between the internal and external gasket that is ventilated to the outside so that there is no pressure difference between the outside and the rebate.

As a result, water is not driven into the rebate by a pressure difference that would otherwise build up across the outer gasket. Any rain that penetrates the outer seal can be drained to the outside through the vents, or weep holes. This is considered to be more reliable than face-sealed systems that attempt to create a ‘perfect’ seal which inevitably fails due to pressure-driven moisture.

Water-managed systems are similar to pressure-equalised systems, but there is no attempt to prevent water penetrating the outer seal, and so the primary function of weep holes or drains is to drain water rather than to allow pressure equalisation.