Product category:
Cladding and Facades
News Release from: ASD Architectural | Subject: Steel in glazed facades
Edited by the Buildingtalk Editorial
Team on 27 March 2008
ASD argue the case for steel in glazed
facades
The simplest method to maximise daylight within a space is to increase the glazing area.
The benefits of designing with natural light are well known in the building industry From energy and operating cost savings to improved occupancy productivity and enhanced aesthetics, architectural designs incorporating daylight are increasingly required
This article was originally published on Buildingtalk on 7 Mar 2008 at 8.00am (UK)
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This truism relates directly to the framing system.
In comparison to traditional aluminium curtain wall assemblies, newer steel framing systems, such as those available from ASD Architectural, enable narrower frame profiles and larger areas of uninterrupted glass, while meeting a range of other performance and design needs.
Whilst aluminium has controlled the market in the last few decades steel is now emerging as a pioneering material for glazed windows and doors, as well as curtain walls.
High tech manufacturing processes now allow steel to be formed into a wide range of framing profiles, matching the flexibility in profile choice provided by aluminium framing systems.
Architects and designers on the continent have used these advanced steel framing systems for years, and now they are available in the UK.
Steel frames are well adapted for numerous design applications, including large span straight curtain walls, curved and serpentine walls, and vaulted glazed roofs/ceilings and atria.
Due to steel's greater strength, larger spans of glass and minimal frame dimensions are also possible, which allow more natural light and can improve the buildings aesthetics.
Technical properties of steel.
In comparison to assemblies of traditional materials, steel has many physical properties that provide superior performance for glazed curtain walls and window and door framing systems .
Modulus of Elasticity (Young's Modulus).
Steel has a modulus of elasticity of about 210 million kPa (30million psi) compared to aluminium's 70 million kPa (10 million psi).
With three times the stiffness value, steel frames of a given profile or cross section deflect less, providing a substantially greater load capacity.
As a result, for a given framing profile cross section, steel can achieve much larger glazing spans than aluminium.
Or , for identical load and deflection requirements, narrower steel profiles can be employed.
In either case, steel enables larger areas of uninterrupted glass with less framing than aluminium.
The difference in frame profile sizes can be dramatic, with steel framing systems allowing much thinner profiles than a typical aluminium assembly A general rule of thumb is that for the same size frame profile, steel allows for glass panes approximately three times the surface area as possible with aluminium framing.
For fixed design criteria (e.g load), the primary benefit of steel is a more visually appealing system with thinner framing.
Thermal Expansion Co-efficient.
The thermal expansion of steel is approximately 7.3 which is of the same general order of magnitude as glass at 5.0 and concrete at 8.0, compared to an expansion coefficient for aluminium of 12.3.
Steel's lower susceptibility to thermal expansion allows for greater design and installation flexibility, as temperature changes, the glass, the steel framing, and surrounding concrete all expand together, requiring fewer, if any framing expansion joints.
A facade 167m long was fitted recently without need for expansion profiles.
Heat transfer.
Compared to aluminium, steel frames reduce heat transfer in two ways.
First , the steel has one quarter the thermal conductivity of aluminium ( approximately 31 Btu per hour for steel versus about 118 Btu per hour for aluminium).
Second, the potential for narrower frame profiles provides a smaller area of metal through which heat can pass.
Together, these characteristics result in lower heat loss and gain, and also reduced likelihood of interior condensation on frames.
Anti Corrosion and Durability.
To address earlier steel framing's propensity to rust, the ASD Architectural systems are available with high corrosion protection, such as pre-galvanization inside and outside of the tubes.
The zinc is applied to a thickness of 20 um leaving the surface incredibly smooth.
Powder coating is the general finish applied post fabrication for durable longevity , though wet spray applications are also suitable.
The durability of steel door and window and curtain wall systems is guaranteed by the durability of steel itself, the profile can take high levels of abuse in high traffic and high vandalism areas.
Installation and Costs.
Steel framing systems are installed in a similar fashion to aluminium assemblies.
There are now cleated steel assemblies using a ' plug and screw' method, this allows the framing to be readily assembled without welding, the result is crisp corner joints without visible fasteners or welding beads.
The result is a clean finished look with the profiles having tight linear edges due to state of the art roll forming processes.
The framing is made watertight by EPDM back seals, which cover the frame profile and are secured in grooves.
The pressure plate and cap which are external to the system are generally aluminium, though stainless steel is available for in the cap for alternative aesthetics and on the pressure plate for fire performance.
Weather Test Evidence.
The ASD curtain wall systems have been rigorously tested to EN standards for air permeability, water-tightness, wind loads static and dynamic, and impact resistance.
The system can resist water ingress under high pressure(1200Pa) because the profiles resist deflection, and because of the effectiveness of the drainage system.
Multi Top Steel Modular Facade system.
Multi top is a steel framing system which allows the back mullion to be customizable to any profile, including L shaped , U shaped, T shaped, I shaped, and hollow sections.
Instead of limiting them to traditional square tube Multi top allows designers to use almost any structural member as a curtain wall mullion including I beams, timber glue laminated beams, round steel tubes, and stainless steel profiles.
The advantages here are that spans can be even larger if back mullions are used with very high Ix values, and cost can be kept low as there is less time spent in fabrication.
Economy of Steel Facades.
Although aluminium is a competitive market steel can compete because it is able to use less frame transoms and mullions than aluminium, due to its higher strength and lower deflection.
Also the number of glass panels and system joints is lower so there is time is less on site and in the factory.
Steel framing is also available to meet fire ratings, and can be used for fire-rated curtain walls in areas such as large enclosed stairwells, left areas, partitions, and exterior walls .Before the advent of modern fire rated glass and framing systems, exit corridors had to be made of materials like masonry or gypsum.
Now, fire rated glazing can be used throughout a building, allowing natural light to filter in and open up the interior.
During the last two decades, the glazing industry has witnessed dramatic changes in the speciality field of fire rated glass and framing.
Modern fire rated glass looks like the glass of ordinary windows, outperforms wired glass in fire testing, and can provide substantially better impact safety and thermal insulation.
From an aesthetic point of view, fire rated glass is also available in large sizes, and a range of finishes such as etched surfaces and varied textures.
Fire rated framing has also considerably improved in recent years, advancing beyond the bulky frames of the past to the same sleek curtain wall systems already discussed.
There is even an overhead glazed roof system with 45mm mullion sight line.
Advances in fire rated steel framing have enabled the development of fire rated curtain walling across multiple stories.
Floor to ceiling fire rated curtain walls are sometimes used to divide interior spaces while offering security ,daylight, and aesthetic appeal , along with life safety.
Fire rated curtain walling is especially suitable for lobbies and atriums as they provide uninterrupted views.
More and more fire rated screens are specified externally for example when a building is close to another buildings property line.
Exterior fire rated curtain wall can also prevent the spread of fires within buildings as fire of bursts out of windows and leaps to the floors above.
Bullet Resistance.
Another advantage of steel is it's superior ability to resist bullets, and ASD Architectural have doors, screens and curtain walling which are certificated and tested toEN1522 for FB4 and FB6.
Security.
Because of the innate strength of steel it makes it the ideal material for security.
It is a natural barrier to intruders and has been widely used in the UK where security requirements are paramount.
Either in the battle against vandalism or in the field of high security anti - terrorism, steel has ready made solutions in this field.
Ecology.
There is much debate about the recycling of metals and its effect on the atmosphere.
It is true to say however in defence of steel that there is much less energy used in the production of steel and the recycling of steel, than in the production and recycling of aluminium.
Conclusion.
Steel has many advantages over it's rival aluminium.
When considering higher performance needs designers and architects should consider the benefits of steel framing systems to meet their design and challenges.
When specifying it is crucial to ensure the design takes advantage of this material's inherent strengths .
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