Few days back, I was part of a meeting that our team was having with a key Client to discuss a project encompassing Civil and PEB works and Planning. The discussion gradually veered towards the commercial domain, when suddenly the Client dismissed most of the work including PEB work as “petty works”. Having a PEB (Pre-Engineered Buildings) background and a habit of introspecting each and every sentence that comes out of everyone around me, I felt I should set straight the perception on quality engineering and planning and its importance in execution, operations and maintenance. Although, after few moments of scrutiny I realised the Client’s observation was absolutely justified since PEB design and its implementation is absolutely simple, cost effective and takes very less time. However, when someone calls it petty work, I thought of penning down my views on what it entails to make these structures simple, elegant and cost effective.
PEB structures are essentially metal structures consisting of members that are project specific (Steel is the most widely used material in PEB because of its excellent strength and material properties). Various components are assembled off site and transported to site for final erection and finishing. The time required for such assembly erection is very less. The primary load bearing members of a PEB structure are usually Built-up members, which are made by machine cutting high grade steel sheets and welding them under controlled environment inside a factory (most probably a PEB structure). This means that the structural engineer who designs the structure has the liberty to provide tapering member sizes that match the exact design requirement w.r.t stress and serviceability, unlike the case of hot-rolled sections, where the members are straight. This shall help to reduce the weight of the structure. Since the structure is light weight, they are ideal for regions prone to seismic events. From a sustainability point of view, steel is ideal for construction as steel can be recycled. In 2021, the steel industry recycled 680 million tons of scraps, avoiding over 1 billion tonnes of CO2 emissions that would have been emitted from the production of virgin steel.1
Alternate to Built-up members
Hollow Steel Sections (HSS) have been extensively used in recent years in PEB structures, because of its closed shape and high moment of Inertia about the weak axis. It has high axial strength and bending capacity in both major / minor axis. It has good resistance against buckling, twisting and shear. Architects and Engineers have used the aesthetic appearance of exposed HSS to their advantage. As the section is a closed one, it will be easier to handle and work with. In a recent study conducted by APL Apollo Tubes Limited in collaboration with Indian Institute of Technology, Roorkee, where various buildings were modelled using HSS and Built-up and compared for its steel savings, it was found that using HSS reduced the use of steel by 15-25%.2
Previously, the use of cold formed sections was restricted to the role of purlins, girts and other non-structural components as its limited thickness makes it susceptible to buckling instabilities. Recently, they have been employed as primary and secondary load bearing elements due to its light-weight and dimensional flexibility. To minimise the buckling instabilities, hollow flange sections have been developed and studied. The Direct Strength Method has led to exploring innovative and complex sections for Cold formed sections. This method considers the member buckling loads under local, distortional and global buckling under a given loading, bracing and supporting condition. The effective width of the member is irrelevant and buckling analysis is carried out for the cross-section. Irrespective of the width and shape of cross-section, a consistent approach can be adopted for analysis.3
Future of PEB
Integration of Artificial Intelligence and Machine Learning (AI and ML) with PEB technology can result in innovation and sustainable practices and can shape the future of PEB. AI powered software can analyse various design parameters and constraints to provide highly efficient designs and help in choosing the optimal design to reduce material usage. AI and ML in manufacturing phase will help streamline operations and enhance product quality. During construction phase, AI and ML contribute to project management, safety and efficiency.
In the last decade, many PEB builders have ventured into the Indian market space and more are on the way. PEB market in India is growing at a CAGR of 11.66% in the forecast period 2022-2030. 4 This clearly indicates that PEB construction is gaining popularity in India. This has forced the Government of India (GoI) to take steps to introduce standard practices in Indian PEB sector. As a first step, GoI has recently released the Handbook on Warehousing Standards – a guideline for planning, design and construction of warehouses. The guideline suggests ASTM (American Society for Testing and Materials) International to be adopted for PEB structures. For design purpose, we have the option of following AISC 2010 Edition (American Institute of Steel Construction). Thus, the use of High-grade steel with a non-conservative design code will make the structure light.5
With the rising demand for both commercial and residential spaces, adopting technology for sustainable construction is crucial. PEB, with its versatility, customizability, and strength, is poised to transform the construction industry in the days to come.
1.www.worldsteel.org “Steel- the permanent material in the circular economy” Worldsteel Association – Circular Economy (©2023 worldsteel)
3.Helen Chen Ph.D. P.E., Benjamin Schafer and Roger Laboub, “Direct Strength method for Cold formed sections” Structure magazine (August 2007)
4.Nikhil Bothra, “Pre-Engineered Buildings: The need of the hour to fulfil the burgeoning space demand quickly” The Financial Express (November 24, 2022)
5.Warehousing Association of India e-Handbook on Warehousing Standards (2022)