Widely used since the 18th century, steel framing is a reference in terms of low weight and ease of assembly. Iconic historical structures such as the Empire State Building in the United States have long been erected in steel.
Steel frames are associated to modernity and innovation and stand out mainly for their erection speed which results from optimized processes from the conception to the assembly, resulting in shorter schedules than mainstream construction techniques.
Despite the advantages, a great number of myths and doubts regarding its use still linger, especially in Brazil, where the ‘concrete culture’ is very strong. In this article we’ll discuss where and how steel frames can be used as well as its features, advantages and financial feasibility.
Besides overall manpower productivity increases in a development, the most often cited advantages of steel framing are its assembly speed, long spans without intermediate supports and the meaningful reduction and optimization of materials and resources.
However, the advantages of steel framing go far beyond that:
Fast production and assembly is definitely one of the highlights of steel framing. This becomes clear from the first construction stages, once the sections and pieces will be able to be manufactured while the foundations are being laid and several work fronts will be carried out simultaneously (such as services installation, slabs molding, enveloping and so on). A precise schedule of works may cut down your construction delivery in up to 40% when compared to that of mainstream building systems.
If you are aiming at reducing your framework total dead load, steel can be an invaluable asset, as steel framing often weights from 6 to 10 times less than concrete ones (without the slabs). At the end of the day, if you take into account all the building systems, the loads carried to the foundations may be cut by up to 20%. This reduction will directly impact the foundation execution costs and abbreviate the project delivery.
Delivering and assembling the framework parts is a standardized and eased process as we are talking about an industrialized system. The sections and pieces delivered to the site are ready to be hoisted and bolted or welded, considerably reducing labor resources needs. Besides cutting down the bottom-line costs, your limited gang sizes on site will mean better workers’ safety and control.
As steel framing is lighter than reinforced concrete framing, its transportation, hoisting and moving results easier. Steel frames may also reduce substantially the interference on neighboring lots, especially in hard-to-access sites such as those in residential areas or near schools and hospitals. Execution is shorter, less dust and waste are produced and both the framework delivery to the site and its assembly can be scheduled to those times when traffic is lighter, minimizing problems on access roads and disturbance to the surrounding areas.
As every construction system has its own characteristics and specific requirements, a development designed life involves a thorough assessment of the whole building process, class and objective.
Long-framed and low-rise structures such as warehouses call for periodic maintenance especially in those framework parts exposed to the elements. Regular coating and cleaning of gutters, and skylights, for instance, are paramount to ensure a longer lifespan. Bridges, viaducts and other structures with accelerated weather exposure also require a preventive follow-up.
High-rise structures (commercial or residential buildings), on the other hand, demand next to nothing framework maintenance.
Additions, either high-rise or low-rise, are also facilitated by the use of metal frameworks. This is especially true when load increases on existing structures must be limited.
Steel is the world’s most recyclable material and it can be 100% reused. Furthermore, steel frames are inherently industrialized and custom milled so waste generation, sound pollution and on-site losses are minimal.
All this will be an important contribution if you aim at the LEED certification.
Leadership in Energy and Environmental Design – LEED – is the accreditation attributed by an American NGO focused on sustainable construction. Steel frameworks are classified in their category of recyclable materials and low environmental impact resources. LEED is a highly regarded and valued certification system adopted by socially and environmentally conscious companies and organizations.
Steel frameworks are manufactured through top precision processes that assure standardization and quality in the end products. As the framework construction technique is totally controlled from the industry to the on-site assembly, levels of building workers’ safety are similar to those achieved in factories.
Another meaningful advantage of using steel frameworks is getting rid of temporary struts to support the slabs and other horizontal components. A proper planning will also allow the immediate start of following construction phases, such as servicing, enveloping, cladding and so on, freeing your schedule of the typical waiting time of 21 to 28 days needed for a concrete member to set.
Supporting activities which do not add value to the end product such as scaffolding transportation, assembly and disassembly will also be reduced, especially in tall structures or buildings with high ceilings.
A steel framework means a cleaner and safer construction environment for the workers, preventing endless incidents, generating less waste and preventing costs with the removal of temporary structures.
Of course the development details and objectives as well as the site features and the schedule have to be analyzed in order to assure the most appropriate and economical solution. The financial gains obtained with the shorter delivery time of a commercial building, for instance, may offset the extra initial investment made on the framework. The point is to realize that the fact that the steel framework per se is more expensive often means it is optimizing the end results and the cost-benefit ratio.
It is also worth considering the present costs of the several construction methods in the long run taking into account the forecast whole life cost in maintenance and repairing.
Depending on the design, your average final cost may be around 35% lower than that for mainstream solutions. (Source: Pinho, Fernando Ottoboni. Viabilidade Econômica. Série Manual da Construção em Aço, 2008.)
Less interference on urban roads is another advantage of this type of framework.
Saying that steel framing is only interesting in high-rise or high-loaded structures (as bridges and viaducts) is another myth.
Structural steel can be used to great advantage in endless types of constructions and buildings, from small sheds to bridges, viaducts, wide-span roofs and special work such as harbors, airports and soccer stadia. Limited road access, constrained sites or soil or weather issues very often make steel frames a much more practical and economical solution to turn a development viable.
Every frame has to be assessed in terms of its resistance in the event of fire. National and local standards establish a fire rating for every kind of use. In the case of steel, different protective coatings and claddings are used to reach the required fire resistance. This can be achieved with blown plaster, fire-retardant coating or even an increase in the cover usually applied to the components. Some of these approaches have a double function of adding to the corrosion resistance.
The Brazilian standards that must be followed are NBR 14323 and NBR 14432.
Contrary to the common belief, reinforced concrete frames are nearly seven decades newer than steel frameworks. Both started in Europe, and have been widely adopted ever since. In Brazil, the ‘concrete culture’ is deeply rooted among architects and engineers, unlikely those in Europe, Asia and North America, where steel frames largely dominate.
In a feasibility study it is important to consider the design features, the site location and the delivery deadline. Such data is paramount in an economical assessment of every solution. Having said that, it is a fact that steel frameworks are faster to build, what render then more interesting in commercial structures, when the deadline impacts the investment return rate. Other factors to be compared:
As an industrialized system, steel framing benefits from budgets that tend to be more accurate and from very precise assembly systems. Costs are seldom revised. The production of components in a better-controlled environment also cuts risks that may postpone deliveries and generate extra costs.
Whereas in-situ construction requires a wide variety of materials and components (e.g., formwork, bracing, woodwork, etc.), steel frames are just assembled there as the sections and connectors are manufactured in an industrial facility and delivered to the site.
Pre-cast reinforced concrete components are structural members which reach a certain level of strength before being placed in their definite positions in a framework.
One of the main advantages of metal frames in relation to pre-cast concrete ones is related to the logistics and equipment necessary for the assembly. Concrete members are usually heavier and bulkier than metal ones, which means more room will be taken in the site and larger hoisting devices will be required and, at the end of the day, higher costs.
Steel frames are extremely appropriate for slab blocks such as those typical of logistic condominiums, distribution centers and industrial estates. This is because they allow wide spans, freeing the interiors from columns that often disturb operations. Besides spatial optimization, steel frames for those applications can result in cost cuts of around 30% when compared to those of mainstream construction techniques. Besides costs and delivery deadlines, they are also advantageous when the case calls for an extension or a minor maintenance or repair job. Steel components can be widely used in such interventions, as sandwich panels or other metal tiles are often the components of choice for the whole fabric, i.e., roof and walls.
Tower buildings maximize the pros of choosing steel framing, mainly in commercial developments on constrained lots. Not only steel framing is much lighter and faster to assemble but results in a better use of internal space and does not take up large areas in the construction site. The more floors the structure has, the more economical the steel frame is and the shorter the schedule becomes.
Besides high-rise buildings, steel framing is an excellent option for infrastructure work, i.e. bridges, viaducts and subway stations. Such frames are cleaner and more sustainable. Being safer for the workers during erection is an important differential for such type of development, which often does not have a closed and safe building site. Steel solutions also cut down assembly times and hence reduce logistic and traffic issues in the surrounds. In some designs, steel can also account for meaningful economical advantages.