A curtain wall system can be defined as a light weight exterior cladding that is hung on the structure of a building. This usually extends from one of the floor to the other floor. It is characterized by its vertical or horizontal caps that are narrowly spaced , with metal or glass infill panels. Finished exterior and semi finished interior appearances are provided by these materials. The most commonly used material for the curtain wall manufacture is aluminium. Sometimes steel is also used.
The main components of the curtain wall are:
Categories of Curtain Wall System
The curtain wall are grouped into four categories:
The mullion design focus on the vertical member i.e. the mullion and the column cover. The horizontal line of the structure is focused by the spandrel design. A design expressing both the vertical and the horizontal elements is the grid system.
The sheath construction is also referred as panel construction. Without the help of intermediate elements, the panels are directly joined. A secondary framing is used to fasten the panels to the supporting structure.
Types of Curtain Wall System
Based on the method of installation of curtain wall system, it can be classified as:
- Stick -built system
- Structural Glazing System
- Unitized System
Stick - built Curtain Wall System
- Description: The stick built wall system involves a cladding and exterior wall system. This is hung on the building structure from floor to floor. The installation is carried out piece by piece. This is an oldest type of curtain wall system. The installing is represented in the schematic figure below.
- Installation: The assembling of this system is carried out sequentially using different components like steel or aluminium anchors, mullions (vertical tubes), horizontal mullions or rails, vision glass, spandrel glass, insulation and metal back pans.
- Design Considerations : Depending on the column spacing, the wind load & the desired appearance of the facades, the vertical mullions are spaced from 4 to 6 feet. The vertical mullions arrangement will result in joints after their arrangement. This spacing will behave as an expansion joint for the live load deflections from floor to floor. These joints also accommodates movements due to creep and thermal expansion.
Unitized Curtain Wall System
- Description: In this system the glass and the aluminium curtain wall are installed in the form of a panel. The components that are involved in the unitized curtain wall system is same as that of stick-built system. Here unlike the stick built, the panel is completely connected and assembled at the workshop. During the time of installation, the panel is bought to the site and installed. As most of the connection procedure are carried out in special working conditions, the quality is assured. This also allows in fabrication lead time.
- Installation: As mentioned, the unitized system is installed in the buildings in the form of panels. Instead of fabricating the mullions and the rails as tubular systems, they are made as half sections. This will form the curtain wall systems during the assembling. The assembling starts from the bottom of the building then going around each floor and to the top of the building.
|Fig.5: Unitized Curtain Wall System|
Fig.5.Unit Wall System; Will units prefabricated , brought to site and Installation Carried out
- Design Consideration:The main design aspect in this system is performance and durability in the installation. How good be the quality of panels; the installation of the panel will judge the final performance of the wall system. In case of a stick-built system two joints are there along every mullion and the rail. But in the case of unitized system there are three joint along every mullion and the rail. In the three, two are placed between the glass and the aluminium joints. The third one is between half mullions and half rails. There is an increase of potential air and water by 50% compared to stick built system. Hence a serviceable joint has to be designed.
Structural Glazing System
Description: This system use the same aluminium mullion components that are used in the stick built system. The only difference is that here the mullion nose or the neck is omitted. This will create a capless vertical joint, as shown in figure 5.
|Fig.5: Vertical Joint Detail|
Installation: To provide a flushed exterior appearance, the vertical joint between the IGUs is filled by a silicone sealant. Standard pressure plates and caps are used to construct the horizontal mullions. A gasket or spacer tape is used to hold the IGUs against the aluminium of the vertical mullion. Here the inner side of the IGUs is held apart from the same, by the gasket or spacer tape. Between the glass and the aluminium a structural silicone sealant is also provided.
Design Consideration: The contact width or the joint is around 12.5mm. An adhesive bond is provided by the silicone sealant. This have a minimum strength of 20psi.
Advantages of Curtain Wall System
- Curtain wall system have involvement in accommodating the structural deflections
- The air leakages and rain water driven by wind are controlled.
- The adverse effects of solar radiation is minimized, providing occupant comfort
- The system is maintenance free assuring long term performance.
- Curtain wall are light weight ; Hence reduces overall weight
- Fewer joint will reduce caulking or sealing problems
- Erection carried out through internal access help in eliminating scaffolding
- Mass production is possible
- Thinner wall construction from 2 to 5 inch