No compromise in steel structures

The challenge of ensuring fire safety for those people using modern steel structures is becoming even more complex. As modern design of complex buildings is pushed to the limits, we should not forget the critical need to ensure that fire safety is not compromised along the way.

Architects and design engineers can use cellular beams for example to great effect, sometimes left exposed as part of the aesthetic finish, and adding to the fascination of tall, complex structures.

As the design becomes more sophisticated, so the load-bearing equations can alter and as other considerations come to the fore the need for the appropriate level of fire safety becomes paramount.

In the Middle East, high rise buildings are becoming a feature of modern living, often designed to look attractive and to blend with existing construction in the area. However, serious fires in high-rise buildings are occurring with increasing frequency.

In London in 2009, six people were killed in Lakanal House, a relatively low-rise 15 storey residential building. The fire started in a dwelling on the seventh floor and quickly spread internally and externally to the ninth floor.

It is important to understand that although the various codes of practice require the external walls to be fire resisting in load bearing capacity, there is rarely a requirement for the walls themselves to restrict fire penetration through them i.e. the load bearing capacity is often provided by columns and beams thereby enabling the incorporation of unprotected areas within the walls such as windows.

The use of glazing for windows is entirely desirable, it would be impractical and cost prohibitive to have fixed shut fire resisting glazing on all the exterior walls.

The percentage of the wall area that may be unprotected depends on the height, use and proximity of neighbouring buildings.

The new regulations introduced in the UAE in 2013 require the use of fire resistant aluminium composite panels with a mineral core rated as per international fire regulations, in the place of an inflammable core. They disallow the use of Silicon or fillers in the cladding assembly joints, and specify an open joint ventilated sub-structure backed with fire resistant and high density insulation.

At the same time as these design approaches are changing, there is an increasing blurring of the lines of responsibility for fire safety through the process of concept, design and installation.

It can change project by project but should in practice lie with the designer along with other specification details, whether they are amended through the development stages or not.

The reality is becoming slightly different, and worrying. Quite often the steelwork contractor or specialist site fire protection contractor is now expected to take on this responsibility as the project build moves through the process.

They in turn will often rely on other suppliers in the chain for advice such as coatings experts. We at Sherwin-Williams often provide guidance on products to all known standards and are happy to do so as part of our own role in the supply chain.

Building owners and managers need to identify whether or not their buildings are code compliant. If they are not, or cannot be confirmed to be, appropriate mitigating measures will need to be introduced to reduce the risk to building occupants and persons in the vicinity so far as is reasonable practicable.

Such measures could include the replacement or treatment of existing panels or the provision of active fire safety measures such as external sprinklers.

Extensive testing and modelling would need to be carried out before safety systems such as external sprinklers were installed to ensure they would be effective in the particular circumstances.

There are potentially a number of different approaches and it would be a case of looking at each one individually.

A suitable and sufficient fire risk assessment must be carried out by a suitably competent person to determine what needs to be done and what would work on each particular design.

Once they have identified the risks, they can take appropriate action to control them, remove the risk altogether or reduce the risk and manage them. They should also consider how they will protect people if there is a fire. How is the building owner or manager to understand and act to cover these issues? The only way very often is to employ fire safety experts, which in turn comes with a cost.

A worrying trend is emerging where the complexity of fire safe design means it can be out of the sphere of knowledge of the owner or manager, the steel frame designers and indeed, where employed, the fire consultant, particularly if employed to consider non-structural aspects of fire safety.

Designing structures in the ambient state with no consideration for the fire condition is unacceptably risky and irresponsible. Our current industry procedures mean that this can easily happen and the burden of ensuring fire safe design, which may well include additional costly measures, is placed with either the wrong party or, in the worse case, missed altogether.

The danger in cutting corners is that the fire safety measures will be compromised. We believe the responsibility in modern building design should lie with the designer up to handover of the building and then, with full knowledge of all fire safety requirements, it becomes the responsibility of the owner/manager.

We believe there is a need for clarity here as building design develops against legislation potentially scoped out some years ago to different design models/codes, particularly in relation to beams with web openings.

The level of protection afforded on any building where large numbers of people move about has to be proportionate to the structure. If this falls short, the time the protection provides for rescue services in the event of a real fire could be reduced and potentially the load bearing capacity of the steel breached much more quickly than anticipated, threatening the safe evacuation of people.

At Sherwin-Williams, we have developed our own piece of software to make sure these calculations can be specific and measurable.

For the first time, the software in the new Firetex Design Estimator 2.0 (FDE) offers the capability of providing calculations for all shapes and configurations of apertures within cellular beams as well as efficient handling of unfilled voids with trapezoidal profiled metal decking systems.

Other benefits of this package include project sharing as well as designs to the emerging Eurocodes. The FDE is independently tested and fully verified under the Exova Certifire scheme and, in the case of cellular and fire engineered beams, further verified by the University of Manchester. Of real interest to the contracting world is that the FDE is also fully Building Information Modelling (BIM) enabled.

The benefits of best practice in fire safety engineering can be seen as an integrated package of measures within the FDE, designed to achieve the maximum benefit from the available methods of preventing, controlling or limiting the consequences of fire.

Some of those in the supply chain may question why steel parts for new buildings – whether a beam, column or brace for example – would be overly-specified and under-utilised in terms of their load bearing capacity in their ambient design state.

In reality, this performance-based approach allows designers to account for different applied loads being used in various parts of a building for a diverse set of reasons rather than the ‘one-size-fits-all’ prescriptive approach which assumes loads and tolerance.

The trend to assume loads well under the reality of performance-based modelling on each section of steel in today’s complex buildings – thus creating savings for the project in fire protection – is dangerous indeed.

This issue is becoming more complex as designers factor in longer span beams as the pressure to create more letting space becomes more intense.

With more openings and fewer columns, the flexibility of buildings also increases to meet the needs of usage today, with many new steel structures accommodating commercial use as well as living, retail and leisure within the same structure.

Increased knowledge of how real buildings react in fire and of how real fires behave, has led many authorities to acknowledge that improvements in fire safety may now be possible in many instances.

At the heart of fire engineering is safety, no matter how complex and demanding the buildings, in the interests of lives and property.

For more information, go to www.sherwin-williams.com/protectiveEMEA