Pre Engineered Buildings

What are Pre Engineered Buildings?

Pre engineered buildings are literally building blocks for civil engineers. But is it the same as steel buildings? Today's article is regarding this new construction technique.

Pre Engineered Buildings (PEB), also known as Pre Engineered Steel/Metal Buildings is an upcoming technology used in constructing buildings. Simply put, PEBs are buildings Engineered at the factory and assembled on site. PEBs are commonly known as ‘metal boxes’ or ‘tin sheds’ by laymen, as they are basically rectangular box-shaped structures covered in corrugated metal sheets. Here the components are tailor-made to suit the customer requirement and raw material availability and assembled completely on-site using bolts.

PEB is a cost-effective method of constructing various buildings ranging from warehouses, sports stadiums, train stations or high rise buildings to name a few. PEBs help in constructing low maintenance and cost-effective buildings within short time periods.

Common PEB Warehouse
Custom designed PEB warehouse | Source: China Metal Buildings

There is a considerable difference between conventional steel buildings and PEBs. PEBs are designed to suit the final design and all components are fabricated off-site in factories. Therefore all basic components such as I-beams are tailor-made to the exact requirement in a factory and brought on site. These components are then fixed using bolts. Due to this process, the foundations can be laid while the factory prepares the remaining components, helping to save time (time consumed can be up to 3 times lesser than conventional steel buildings).

Incomplete PEB structure | Source: IndiaMart

PEBs were introduced in the United States to reduce the amount of steel used as steel prices rose. PEBs use a relatively lesser amount of steel than conventional steel buildings as each component is produced to the required dimensions. Due to this, the components tend to have tapered shapes which also help in reducing the steel consumption. The reduction of the amount of steel also has an added advantage as having lower weight (at least 30% lesser weight when compared to a conventional steel building of the same scale). Other components used include “Z” or “C” purlins (horizontal beams) and profiled sheets. The assembling of PEBs is also relatively easier as each component is bolted together in a predetermined order. In addition to this PEBs can be easily expanded by adding sections at each end.

How is the structure produced?

Once the building is designed, the construction firm fabricates each individual component as required. Usually, these components are designed to satisfy the exact loading conditions as determined by engineering calculations such as bending moment diagrams. This prevents the structures from being overdesigned. The required metal sheet thicknesses are selected and used to produce the main “I” beam components with the help of welding. In high-end factory lines, these all go through automated processes after the CAD model is provided.

While the components are produced the foundation of the building can be laid on-site including the preparation of the ground. The foundation is a usual concrete open foundation. As the buildings are lightweight, winds can cause uplift forces on the structure. Therefore the foundation should be strong enough to anchor the building. The floor can be placed directly on a prepared ground using a graded concrete. An epoxy or polyurethane floor could be attached to the concrete if required.

Exploded view of a typical pre-engineered building | Source: FT Infrastructures

The prepared beams have endplates with connection points for bolts. On-site the beams are placed in the predetermined order according to the design and fixed with the help of bolts. These beams are fixed with the help of cranes. Each connection is fitted with 6 to 20 bolts as required with the help of construction workers and tightened to the required amount using torque wrenches. It is important to note that absolutely no on-site welding or fabricating is required.

Internal view of a constructed pre-engineered building | Source: Jenish Infraworks

The whole structure is usually enveloped with corrugated 0.5mm steel sheets coated in aluminium-zinc alloy to provide attractive, durable protection. These sheets can be used as the external walls and roofing. Cold-formed “C” or “Z” purlins are used as horizontal beams for the roofing of the structure. The roofing can also include skylights to allow for natural lighting capabilities to save energy. Constructions may incorporate insulation sheets prior to attaching the sheets if required to act as insulators or vapour barriers. The addition of insulation also helps in making the building energy efficient by reducing costs for heating and cooling as the building can be sealed. Some PEBs also use an external masonry wall of about 10 feet for added protection and to attach doors and windows.

How to construct a Pre-Engineered Building?

First, identify the requirement. PEBs are best suited for buildings which are required with a short deadline, at a low cost and maintenance. PEBs also account for architectural versatility, design flexibility and further expansions.

Once the requirement is identified, it is a must to contact a PEB constructor. The entire production procedure from designing, component production and assembly are handled by a single contractor. Due to this, if one is interested in going for a PEB solution for their construction he/she should make sure to select a contractor that matches the requirement, with previous experience in the field and an agreeable price.

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A. Wanasinghe
Department of Mechanical Engineering, University of Moratuwa

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