Construction World - Indian Edition | May 2009

Feature – PEB

Pre-engineered to Last

Pre-engineered buildings made of prefabricated components, which offer a host of advantages, are making inroads in the construction industry. CHARU BAHRI discovers how this building concept stacks up against the competition.

A s a concept, customisation is seen as diametrically opposed to the readymade. But the two are seamlessly reconciled in the construction industry in the form of pre-engineered buildings (PEBs) made of prefabricated components. Computer-aided designed pre-engineered buildings featuring a structural steel framework of primary and secondary members to which factory-finished cladding and roofing components available in knock-down condition are attached, have slowly made inroads in the construction industry.

The scope
“Warehouses of varied descriptions and functionalities required at seaports, airports, in the supply and distribution channel network for bulk commodities and as part of cold chain infrastructure for perishables for export and retail businesses are increasingly being constructed as pre-engineered buildings made up of prefabricated components,” notes N Srinivas, Director - Technical, Lloyd Insulations (India) Ltd.

The almost unlimited possibilities for customisation inherent in this mode of construction easily take care of the differing storage configurations required by different commodities. For example, some products may require stacker reclaimers to be mounted on the building structure, while cold chain facilities would require insulated temperature controlled enclosure to be accommodated within. PEBs with pre-fabricated insulated or un-insulated external panels are precisely what are most appropriate for these needs.

Advantage PEB
The benefits are not limited to customisation making use of readily available components (See Box 2 for more advantages). Strategically well planned facilities with optimised engineering also offer the twin advantages of overall economy (both in first cost as well as in maintenance, See Box 1) over their service life as well as speed of construction, a major requisite for any time-bound infrastructural project. In fact, the interest savings that ensue from a faster start-to-finish construction time could go a long way in enhancing commercial, industrial and institutional interest in the multi-storied versions of these structures, even in times of economic slowdown.

Manav Goel, Vice-President - Marketing, Minaean Habitat (India) Pvt Ltd, is quick to point out that these structures have less of an environmental impact. “Prefabricated pre-engineered building systems are more stable amid temperature fluctuations,” he says. “When optimally designed using light gauge steel and appropriate cladding material, these better withstand a temperature fluctuation from - 6o C to + 80o C. Traditional concrete constructions may develop cracks in extreme temperature, whereas suitable cladding material used as building components in these structures are a lot more stable. Moreover, the dry construction technology used to construct these structures may be taken up in any weather condition and is also eco-friendly as it completely does away with the cement and water slurry waste that seeps into and contaminates underground water supplies.

Arguably though, the absence of standards applicable to the prefabricated components industry is impeding its growth. “After all,” says Srinivas, “any built structure must deliver not only the functional needs of the end user, but also assure the highest levels of safety against all loads and exposure conditions that are expected to be imposed during construction as well as service phases of a building. Today, our accent is on green buildings, with energy efficiency and resource optimisation built in to each project.”

Lack of a dedicated PEB code plays spoilsport?
PEB design concepts incorporate all these vital factors and buildings built with prefabricated components have the potential to overhaul the more traditional ‘iron truss’ and ‘brick and mortar’ approach to design and construction owing to their inherent strengths of speed and economy. However, this evolution is largely depen-dent on the creation of a dedicated building code dedicated to these concepts.
“PEBs are currently based on Indian codes for earthquake forces and local wind forces,” explains Manish Garg, President, Everest Steel Building Solutions, Everest Industries Ltd. “Thereafter, customers have the choice of either following the AISC (American Institute of Steel Construction) or the IS code for the analysis of structures, as the IS 800 release 2007 is quite similar to the AISC code. So following either results in extremely safe and sound buildings as long as the manufacturer uses appropriate software tools to ensure that steel is used at the right places, which Everest is capable of doing using the customised software at its disposal. Steel buildings use ductile detailing that makes these buildings extremely safe during earthquake attacks.”

Even so, the Indian PEB industry would welcome a detailed code, as it would enhance the overall image of PEBs. “At present,” says Goel, “the absence of a building code laying down specifications for pre-engineered building systems created with light gauge steel prefabricated components forces us to follow American and British standards. Indian standards would boost consumer confidence in the industry as well as offer its players much-needed benchmarks.”

Given that PEB as a concept finds its strength in its innovative design process, which in turn derives its strength from the optimal deployment of metal to exactly match the loads that are incident on that element, Srinivas emphasises the need to optimise our mindset as well! Once comprehensive standards are in place, the scope of pre-engineered and prefabricated buildings would also widen, to include sports facilities offering an unobstructed view to spectators, creation of wide network of primary and secondary health centres, schools boasting an optimised layout of classrooms and facilities, and mass housing for rehabilitation of slum dwellers. These socially relevant development areas must attract highest priority while governments plan the rejuvenation of our economy.

Would standards stifle innovation?
In spite of the overwhelming endorsement of the need to standardise PEB systems, Dr M Pradyumna, Director - Design & Development, Geodesic Techniques Pvt Ltd, says that any building code would probably not do justice to all the various combinations of RC-based prefabricated components that would be required to implement these designs. As these components are generally designed for a specific purpose to resist a specific
set of forces, standardisation is best attempted in individual projects that are sufficiently large. However, standardi-sation is mandated in the manufacture of steel-based components made by indivi-dual manufacturers, a typical case being that of space frames. Each manufacturer has an internal set of standard compon-ents that are reused in practically every project. In this example, if a code were specified, it would take away the freedom that exists today in the marketplace to develop newer and better designed components.

Innovations in the PEB realm
Rapid advancements in the compo-nents available to construct these structures are ensuring a lot more than functional efficiency to end-users. For instance, innovative concepts like hidden fasteners and the wide array of colours in which these are available offer architects an exciting set of aesthetic options. Occupants also benefit from a favourable inner ambience, thanks to the use of sandwich panels that offer high-efficiency thermal insulation, excellent noise transmission rating and good internal noise absorption. In this category, PUF as a material is fast catching up as it offers better insulation, is lightweight and has a considerably long life.

Speaking of the ease and economy of ambience control in pre-engineered buildings, HG Chandrashekhar, Vice President - Building Solutions, Tata BlueScope Steel Ltd (a member of Indian Green Building Council, Hyderabad, which works on LEED rating system for Green Building Certification), explains that BUTLERTM Building Systems come with several green building features that help reduce the load on air-conditioning. “Fibreglass insulation material in the roof system is coupled with the excellent thermal reflectivity property of ZINCALUME® used as roofing material. This helps reduce the impact of outdoor temperature variations, thus consequently reducing the load on air-conditioning. Wind-driven turbo vents and ridge vents ensure natural ventilation. Moreover, a specially designed water and sand-resistant industrial louvre system ensures free inflow of air.” In April 2009, the Building Solutions (BS) division of Tata BlueScope Steel received the prestigious Factory Mutual Approval (FM Approval) for its MR-24® standing seam roof system and BR-II™ roof panel lap seam roof system, both roofing systems of BUTLER Building Systems. This approval from FM Approvals, an independent, third-party testing laboratory that certifies products and services that meet the highest property loss prevention standards, certifies the high product quality and reliability of these roof systems, and thereby qualifies the company to provide world-class PEB solutions to all FM Global insured clients inves-ting in India and the SAARC region.

As long as the industry lays stress upon innovation and works towards ensuring that its new solutions meet the most rigorous standards of the industry, this innovative construction technique is bound to find more takers over time.

Quick Bytes
Computer-aided designed pre-engineered buildings have slowly made inroads in the construction industry.
PEBs have the potential to overhaul the more traditional ‘iron truss’ and ‘brick and mortar’ approach to design and construction owing to their inherent strengths of speed and economy.
Rapid advancements in the components of PEBs are ensuring a lot more than functional efficiency to end-users.
PUF as a material is fast catching up as it offers better insulation, is lightweight and has a considerably long life.

The Pros
Prefabricated pre-engineered buildings offer significant advantages over conventional structures. We list a few:
• Lightweight: Steel structures offer a
higher strength-to-weight ratio vis-à-vis conventional RCC beam slab or plane truss and purlin configuration.
• Stable configuration: Steel structures can be designed to be far more stable than conventional structures.
• Speed of construction: Steel-based structures are constructed far more rapidly than conventional systems. This translates
into a saving of interest and increases operational revenues.
• Column-free space: Framed structures provide larger column-free spaces ideal
for machine shop floor or storage applications where freedom of materials movement
is necessary.
• Flexibility: These structures may be easily dismantled and relocated or extended without damaging the structural integrity of the frame.
• Integrated services: The framework of these structures functions as a natural deck for building services like HVAC or to fix a false ceiling without burdening the structure with an additional supportive framework.
• Accuracy: Components prefabricated in machines are far more accurate and relatively smaller than the components used in conventional construction which makes them easier to handle and transport.
• Fire and blast-resistance: Double-layer grids are more fire-resistant than conventional structures and better resist aerial or terrorist attacks and explosions.
• Versatile: These structures can be clad with a wide range of materials such as aluminium, steel, asbestos cement sheet, glass, polycarbonate sheet and pre-cast concrete.
• Economy: This method makes for cheaper buildings of larger spans and/or heavy loads.

Tax Structure Reform Boosts Prefabrication
Prefabricated components are an essential part of pre-engineered buil-dings.Given thourgh these components offer intangible benefits like better quality of end products, safer and better working environment, improved reliability of delivery and speed of construction, Dr M Pradyumna, Director - Design & Development, Geodesic Techniques Pvt Ltd, points out that “earlier, the excise duty levied on factory-made goods ensured that investors did not see this style of construction as a viable proposition. Now, the levying of service tax on site fabrication and the recent reduction in excise duty on factory-made components has made prefabricated components a financially viable option.”

Standards and Codes: What has been done? What remains? N Srinivas, Director - Technical, Lloyd Insulations (India) Ltd, shares some pointers
• Steel design: The revision in the Code of Practice for structural steel design (IS:800-2007) is substantially in line with this building concept. But new standardisation work is needed to cover materials such as composites (like sandwich panels), and codes for fire safety.
• Fire safety: In the absence of good fire safety codes, panels with highly combustible inner cores like foam polystyrene are being propagated and used owing to their low cost when highly researched fire safe panels incorporating polyisocyanurate and mineral wool cores with excellent fire rating are widely available.
• Panel facings: Today’s PEB structures incorporate panels with steel facings with proven advanced metallurgical protection like aluminium plus zinc coatings. While standards exist for galvanised steel, we need a National Standard for advanced metal protection systems. Metal exterior surfaces must be engineered precisely to meet the aggressiveness of the diverse climatic and environmental conditions where they have to perform. Exterior finishes like organic coating (paint systems) also need to be covered by National Standards specific to these colour-coated products.
• Components: A large number of components like windows, doors, louvres, ventilators, awnings, canopies and loading bays need to be standardised with respect to dimensions, functional features, etc. Standards must integrate functional requirements with manufacturing parameters for building components.

Why do pre-engineered buildings have a lower life cycle cost vis-à-vis conventional steel buildings?
Conventional steel buildings use primary steel members selected from standard hot rolled I or H Sections owing to which the structure is much heavier than required by design. Primary steel members have constant cross-sections regardless of the varying magnitude of internal stresses along the length of the member. Also, owing to the unavailability of the required standard hot-rolled sections for a particular load, consultants are compelled to select a higher standard section, which leads to uneconomical and heavy designs. In a pre-engineered building, typically, primary framing members are tapered, i.e. of varying depth built-up sections with smaller depths in areas of lower stress.
Traditionally, conventional buildings also use cement roofing sheets and a plastered brick wall. Roofing requires replacement every 10 years and brickwork requires repainting and repair every three years. In PEBs, the roof is high-grade galvalume and the walls are made up of permanently colour-coated metal wall. These roofs and walls require no repainting or maintenance over at least 25 years. Therefore, PEBs are actually zero- maintenance structures. Over a lifecycle analysis of just five years, PEBs prove to be at least 20 per cent more economical than conventional buildings.



 

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