Prefabricated Construction Technologies for the Future of Sri Lanka s Construction Industry

Transcription

1 Prefabricated Construction Technologies for the Future of Sri Lanka s Construction Industry Tharaka Gunawardena 1*, Roshan Karunaratne 2, Priyan Mendis 3 and Tuan Ngo 4 1,2, 3 & 4 The University of Melbourne, Parkville, Australia * tgu@unimelb.edu.au, TP: Abstract: Prefabrication and off-site manufacturing have been a part of building construction for a long time in many countries. However, due to its many advantages such as construction speed, minimum work on site and higher quality assurance and issues such as scarcity of both human and material resources that are threatening traditional construction practices, prefabrication is rapidly evolving into an essential component in the construction industry. Although the Sri Lankan construction industry has traditionally been a labour-intensive practice, the skilled labour resource is now gradually diminishing. This phenomenon dictates that prefabrication would need to be introduced into the industry in significant proportions to replace on-site construction with off-site manufacturing. This paper presents a critical insight into such prefabrication technologies that are practiced successfully in the rest of the world. While showcasing some of the recent research that has been carried out on these technologies the paper provides a discussion into how such construction methods would suit the future of the Sri Lankan construction industry. Keywords: Prefabrication, Volumetric construction, Off-site manufacturing, Design for Manufacturing and Assembly (DfMA) 1 Introduction Skilled labour in the Sri Lankan construction industry is increasingly becoming a scarce resource. Prefabrication of building components and modular building systems offer an opportunity to replace this need for labour with a supply of trained building technicians. The building units are made in a factory production line with an improved quality control and a large saving of time. Many new urban development projects face common problems such as limited land availability and site access. As a result, many old buildings are demolished to make way for new ones. Prefabrication offers a unique opportunity to commence the construction even before the site is available owing to demolition works. It also ensures many other advantages that are discussed through this paper. Booming construction environments in many countries are increasingly resorting to prefabricated technologies. It is high time that Sri Lanka introduced prefabrication as a main component in its construction practice. In recent times as well as in the past, construction in Sri Lanka has used prefabrication from time to time especially in bridges and road works. However, the need for more prefabrication to be an essential part of construction in Sri Lanka will be inevitable in the near future. Therefore, this paper discusses the overall feasibility of adopting prefabricated technologies for the future of the construction industry in Sri Lanka. 2. Forms of Prefabrication Prefabrication has featured in building construction for many years in various forms. Dry wall systems, structural insulated panels (SIP), prefabricated roof trusses, prestressed beams, rebar cages etc. are such examples. Lusby-Taylor et al. [10] identified various forms of prefabricated construction in five categories

2 according to the way it is manufactured and assembled on site as; 1. Modular (Volumetric) construction: Production of three dimensional units including finishes in controlled factory conditions prior to transportation to site. 2. Panelised construction: Flat panel units are produced in a factory and assembled on-site to produce a three dimensional structure. This method usually leaves some finishes to be done on-site after assembly. 3. Hybrid (Semi-volumetric) construction: combines both panelised and modular approaches. Typically, modular units (also known as Pods ) are used for the highly serviced and more repeatable areas such as kitchens and bathrooms, with the remainder of the dwelling or building constructed using panels 4. OSM (Off-site manufacturing) subassemblies and components: covers approaches that fall short of being classified as systemic OSM but which utilise several factory-fabricated innovative subassemblies or components in an otherwise traditionally built structural fabric, e.g. roof cassettes, pre-cast concrete foundation assemblies, but excluding window, door sets, roof trusses. 5. Non-OSM: This category is intended to encompass schemes utilising innovative housing building techniques and structural systems that fall outside the OSM categories. The graphic in Figure 1 highlights the main two benefits of volumetric (modular) construction in the form of reduced labour and construction time compared to other conventional and modern methods of construction. Some of the other benefits and features of prefabricated modular construction are as follows; The modules can incorporate all components of a building including stairs, lift shafts, facades, corridors and services. The modules are mass produced in a quality controlled production facility. A unit s length, width and height may vary from project to project. There is minimal work on site to complete the buildings as the façade and interiors Figure 1: On-site labour requirement and construction duration of volumetric (modular) construction compared to other types of construction (National Audit Office, UK, [12]) themselves form parts of modules. This enables the construction process to move away from being a labour-oriented operation to a more process-oriented manufacturing and assembly process resulting in building sites with less congestion and pollution. The modules are able to be removed from the main structure for future reuse or relocation. The reusability of prefabricated modules adds a large impact on modular buildings having a much lower life cycle energy (Aye et al. [1]). Modular construction at present reduces construction time by over 50% from a siteintensive building (Lawson et al. [8]). This ensures that the Client of the project starts generating revenue from the project much faster and invests in the opportunity costs of having a different construction technology in earning further income.

3 The construction process is far less vulnerable to bad weather which will make the construction even faster especially in a country like Sri Lanka. 3. Modular Buildings Constructed Across the World Little Hero Building in Melbourne, Australia The low rise apartment building Little Hero that finished construction in June, 2010 in Melbourne, Australia is a great example of modular construction (Figure 2). The building consists of 58 single-storey apartment modules and 5 double-storey apartment modules. The 8 modular stories were assembled with finishes within 8 days and the building was constructed in a Melbourne CBD (central business district) site with a very narrow access road demonstrating many advantages of modular construction. This is also a noteworthy construction as it is one of the earliest multistorey modular buildings in Australia. SOHO Apartment Building in Darwin, Australia This 32 storey building (Figure 2) is presently the tallest modular building in the world. This building was completed in September 2014 and consists of 21 fully modular storeys. These modules have used concrete floors as a special feature in their construction. The concrete floors have been used as an alternative to any light weight material to better cater for the high humidity in the tropical Northern Territory of Australia and also serves better with improved fire rating. Figure 2: SOHO Apartments in Darwin, Australia (IrwinConsult, [7]) terms of savings in man-hours to an 80 per cent improvement from a site-intensive construction. Therefore, not only has modular technology proven time-efficient, but it has also proven to be more environmentally friendly, providing energy-efficient solutions. As discussed by Lawson et al. [8], in general, prefabricated modular buildings have proven to reduce construction waste considerably and this is mainly through means of minimised off-cuts (Osmani et al. [14]). One9 Apartment Building in Melbourne, Australia One9 Apartments (Figure 3) is a ten storey residential modular building built in one of the inner suburbs of Melbourne, Australia that consists of 34 apartments which are designed for energy efficiency and comfortable liveability. Student Housing Building in Wolverhampton, UK This 25 storey apartment building has been completed with only 27 weeks of on-site work. Lawson et al [8] explains that this has resulted in a 50 per cent saving from the on-site construction time estimated for a conventional site-intensive project. The productivity has been estimated in Figure 3: One9 Apartments during construction (Hickory Group, [6])

4 The above ground modular floors were assembled on site in as few as five days and opened to users by November, The site was constrained by a nearby large shopping mall which was strictly not to be disturbed. Modular technology proved to be the best solution to cater for the client s need in constructing a ten storey building in only a few days which helped saved many costs that he would otherwise have foregone in dealing with a challenging construction in a heavily congested suburb with a difficult set of constraints that limited the work flow on site. The One9 Apartments development also has secured a 6-star rating from Green Star Australia for its many features that promote sustainable construction. Modular construction has proven its value in many avenues in this project especially considering the fact that it was built in a land as small as 277 square metres. In addition to many examples where prefabricated modular structures have been used for commercial use, they have also been quite a productive solution for post disaster relief operations. Some post disaster housing reconstruction programmes where prefabricated modules were used are discussed below; Post Katrina Housing in Mississippi, USA Due to the large housing demand which followed the Hurricane Katrina disaster in 2005, extensive research has gone into improving the previously used FEMA Trailers and to implement modular construction for temporary housing. A design by Architect Marianne Cusato inspired these modular house type, which was named the Katrina Cottage. It was designed to be installed with a floor area of 27.8 square metres. However, this was improved to incorporate a more permanent housing solution with 20 different cottage models that allowed for future extensions (McIntosh [11]). installation of 46 modular housing units as temporary shelter for 75 individuals. This was however carried out as a temporary housing solution to serve for the immediate needs of disaster victims until more permanent housing solutions were arranged. However, Gunawardena et al. [5] explains how modular construction can serve better in providing permanent housing much faster in post-disaster reconstruction operations. 4. Research in Progress on the Performance of Prefabricated Buildings 4.1 Structural Systems and Performance A great amount of research is currently continuing with the involvement of the authors and many industry partners on the structural behaviour and performance of low rise and multi-storey prefabricated buildings. Modular (volumetric) construction methods are investigated in great detail on this regard. Prefabricated modules can be categorised into two main forms according to their load transfer mechanisms (Figure 4); 1. Load-bearing modules the perimeter wall structure of the module transfers the gravity loads to the modules below. This system is only feasible with low-rise applications. (a) Corner columns Reconstruction after Haiti Earthquake in 2010, Haiti Following the Haiti earthquake in 2010, the Canadian Embassy in Haiti had carried out the (b) Figure 4: (a) A corner-supported module and (b) a load bearing module (Lawson et al. [9])

5 2. Corner-supported modules externally connected columns in the module take up the floor loads and transfer them to the columns below. This system is also capable of resisting horizontal loads such as earthquake and wind forces, thus ideal for multi-storey applications. Most multi-storey modular buildings around the world can be observed as systems of cornersupported modules that are connected laterally to a cast in-situ concrete or prefabricated steel core which eventually acts as the primary lateral load resisting element. Further, in most instances, the floors are poured with concrete subsequent to placing the modules. Although these methods do still add value to the construction by saving construction time initially, they do not define the structure as a purely modular construction. As a result, these structures do not fully enjoy the previously presented benefits of modular construction. Gunawardena et al. [4] introduced a modified corner-supported structural system where an assembly of prefabricated modules alone could be used to engineer a structurally stable building, which in turn will reward the building with full benefits of modular construction. A cast in-situ or prefabricated core is not required to be the predominant lateral load resisting component in this structural system. The elevator shaft in this system is intended to be formed with steel elements as a part of some of the prefabricated modules themselves and therefore will not be the central component in the lateral load resisting system. The Table 1: Earthquake ground motions used to generate demand curves prefabricated modules are stacked vertically and connected horizontally through bolted plates. These connections need to be designed to take the full amount of shear forces generated by the design lateral loads. Therefore, lateral load transfer mechanism is provided primarily through these connections and improved greatly through the introduction of modules with stiff concrete walls. These stiff modules which are strategically placed in the main structure resist the majority of lateral loads and transfer them down to the foundation. As a result the structure would not require a traditional central structural core. The structure can now act as a purely modular system. This new system provides architects with a great degree of freedom with a structure that is not limited by the placement of a core. The structural behaviour of this system was critically evaluated through recent research and since it is a cornersupported system its performance against lateral loads such as earthquake forces is a key performance criteria. In this regard, a capacity spectrum analysis was carried out on a hypothetical ten-storey building (Figure 5) constructed with this new corner supported system to obtain an indication of the system s earthquake performance. Table 1 shows the six ground motion records that were used to generate the demand curves. While Gunawardena et al. [3] discusses the seismic performance of the system in detail, Figure 5 shows a summarised outcome of the above mentioned capacity spectrum analysis. The analysis was carried out with the aid of the software RUAUMOKO 3D. The outcome of the capacity spectrum analysis (Figure 5) shows that the structure is past its linear deformation zone at its performance points against all six earthquake time histories. The performance points are also far below the full capacity of the structure. Therefore, it can be deduced that the structure performs approximately in the Immediate Occupancy to Life Safety zone as per the performance levels described in FEMA 356 [2]. This is a valuable preliminary estimate of the performance of this structure against the earthquakes applied.

6 Spectral Acceleration (g) Performance Points (points of intersection) Chi chi Düzce Imperial Valley Kocaeli Loma Prieta Tabas Capacity Curve Spectral Displacement (m) The key technical challenge in this research is foreseen as overcoming the inherent limitations and developing a modular space system for diverse building applications. The new prefabricated paradigm offers the promising features of modern manufacturing and construction techniques with integration of several approaches previously overlooked including; modular flexibility, quick assembly, affordability, integrated building services, consistency, standardisation, automated manufacturing and predictable environmental control. The newly introduced mass customisation techniques will remodel the prefabricated housing market in Australia. 4.2 Energy Performance Figure 5: Outcome of the capacity spectrum analysis - 5% damped demand curves against capacity curve (Gunawardena et al., [3]) 4.2 Architectural Innovations The authors are engaged in research that aims to design and develop a sustainable, prefabricated hybrid modular system that fosters mass customisation to achieve variety and individuality in low and mid-rise projects. The proposed modular system with standardisation of modular components will achieve interchangeability of parts, simplicity of connecting parts, consistent sizes and predictable assembly processes. This research will engage a multi-disciplinary approach. The comprehensive evaluation will account for; Design novelty for flexible, smart modular and hybrid systems using sophisticated parametric modelling Reasonable building specifications to sustainability measures Efficient structural, MEP (mechanical electrical and plumbing) performance BIM (building information modelling) and Lean manufacturing and assembly for overall process coordination and DfMA. A fair amount of previous research has established a sound understanding of the energy performance of modular buildings. Aye et al. [1] compared conventional concrete construction to modular steel and timber construction methods. This study involved an assessment of the embodied and operational energy associated with the particular building, for the mentioned three construction approaches. The operational energy assessment also included a lifecycle energy analysis and a lifecycle greenhouse gas emissions estimation for both operational energy and embodied energy related emissions. This particular research showed that the modular buildings performed much better in all aspects when their reusability was taken into consideration. A summary of the outcome of this research is shown in Figure 6. The graph highlights the considerably higher energy savings by volume, mass and embodied energy of the modular steel and timber structures compared to the conventional concrete structure. 4.3 Economic and Financial Feasibility As explained previously the authors are involved in carrying out extensive industry-

7 Figure 6: Total volume, mass and embodied energy of concrete and prefabricated steel and timber building scenarios, with percentage of potential savings achieved from the reuse of materials through Modular Construction related research on advanced manufacturing of prefabricated housing. One of the main areas of research is to investigate the financial and economic benefits of prefabricated construction technologies and to determine more efficient financing methods especially to help the investors better plan for their ventures. The above mentioned research project is also carrying out extensive research and testing on the structural, services and energy performances of prefabricated buildings. 4.3 Other Attributes The innovative nature of the modern prefabricated construction technology invites many new composite materials as well, especially for facades and partition walls which are also at times structural insulated panels (SIPs). The recent study carried out by Nguyen et al. [13] shows the improvement in fire performance of modular units that consist of facades with GFRP (glass fibre reinforced polymer) laminates with 5% organo-clay concentration. Such innovative materials provide the flexibility to designers and builders to use non-traditional construction systems to produce better performing buildings. 5. Concluding Remarks With imminent challenges, such as depleting skilled labour resources, prefabrication technologies are becoming a necessary component of building construction. Modular construction in particular, provides designers, builders and developers with a means to realise challenging projects in a very short time with many other advantages included. The newly introduced modified corner supported system presents designers with many more attractive benefits including flexibility with arranging spaces without being restricted by an in-situ unmovable core. The presented research outcomes show the feasibility of the prefabricated architectural, structural and MEP systems. There are many positives in prefabrication in terms of the energy performance as well, especially when the reusability of prefabricated components is taken into consideration. This research also interconnects with other ongoing research on innovative lightweight and high performance materials (performance on fire resistance, acoustics, insulation and durability) which will help the design of the modules and other prefabricated structural systems to be more light weight while maintaining their stiffness. This aspect makes prefabricated members and systems more

8 transportable and easier as well as safer to handle on-site. Modular technology in particular has created a remarkable shift in modern construction from trying to make on-site activities more safe and efficient to making efficient off-site manufacturing (OSM), prototyping and assembly systems. This concept of Design for Manufacturing and Assembly (DfMA) is catching the construction market at a rapid rate in creating better performing modular systems which will realise projects even faster and generate more impressive profit margins for investors. With all the above aspects considered, prefabricated construction is sure to pave way to the next generation of building construction and many builders in the world are adopting it already in a large scale. In addition to rapid constructions, it will also create a more quality oriented product-line and a safer working environment for well-trained building technicians. References [1] Aye, L., Ngo, T., Crawford, R. H., Gammampila, R., & Mendis, P. (2012). Life cycle greenhouse gas emissions and energy analysis of prefabricated reusable building modules. Energy and Buildings, 47(0), [2] Federal Emergency Federal Agency, FEMA-356 (2000), Pre-standard and Commentary for Seismic Rehabilitation of Buildings. Washington DC [3] Gunawardena, T., Mendis, P. & Ngo, T. (2016). Behaviour of Multi-Storey Prefabricated Modular Buildings under seismic loads. Earthquakes and Structures, 11(6), Techno Press. [4] Gunawardena, T., Mendis, P. & Ngo, T. (2016). Innovative Flexible Structural System Using Prefabricated Modules. Journal of Architectural Engineering, 22(2). American Society of Civil Engineers. [5] Gunawardena, T., Ngo, T., Aye, L., Mendis, P. & Crawford R. (2014). Time Efficient Post Disaster Housing Reconstruction with Prefabricated Modular Structures. Open House International, 39(3), [6] Hickory Group. (n.d.). Retrieved December 20, 2014, from projects/one9-apartments [7] IrwinConsult Engineering Consultants. (n.d.). Visited, 27 th August, 2016 [8] Lawson, R. Mark., Ogden, Ray G., & Bergin, Rory. (2012). Application of Modular Construction in High-rise Buildings. Journal of Architectural Engineering, American Society of Civil Engineers. [9] Lawson, RM, Ogden, R, & Goodier, CI (2014), Design in modular construction, Boca Raton: Taylor & Francis. [10] Lusby-Taylor, P., Morrison, S., Ainger, C. & Ogden, R. (2004). Design and Modern Methods of Construction, The Commission for Architecture and the Built Environment (CABE), London. [11] McIntosh, J. 2013, The Implications of Post Disaster Recovery for Affordable Housing in Tiefenbacher, J. (ed.) Approaches to Disaster Management: Examining the Implications of Hazards, Emergencies and Disasters. Rijeka (Croatia), Intech. [12] National Audit Office, UK (2005). Using modern methods of construction to build more homes quickly and efficiently. [13] Nguyen, Q., Ngo, T., Tran, J. P., Mendis, P., Zobec, M. & Aye, L. (2016). Fire performance of prefabricated modular units using organoclay/glass fibre reinforced polymer composite. Construction and Building Materials, 129. [14] Osmani, M., Glass, J. & Price, A. (2006). Architect and Contractor Attitudes to Waste Minimisation. Waste and Resource Management, 2(1),