Modular construction or Prefabricated Prefinished Volumetric Construction (PPVC) is becoming a common sight in Singapore due to a government policy promoting the industrialisation of the construction process, which is in line with the vision of continuous increase of prod uctivity in the industry.
Although modular construction has been around for many years in other parts of the world, this technology is fairly new to Singapore and needs to be adapted to meet the particular local requirements and constraints—regulatory, economic, market and high-rise building type.
BENEFITS AND ADVANTAGES
The main advantage of modular construction is clearly the reduction of programme relative to conventional construction, which can be as much as six months. As a consequence, a modular project provides additional revenue to developers through reduced financial costs and earlier market launch.
Modular construction is also very well-suited for implementation in urban and congested areas. As the construction process is delocalised off-site, it is generating almost no nuisance (sound, dust, traffic, etc.). The installation process on-site takes only a few weeks, as compared to a few months for a conventional in situ construction.
The key advantage of modular construction is the industrialisation of the construction process. Most of the construction activities are done in a factory, in a more productive and safer environment. There are no more stairs to climb for the workers and the materials can be delivered at any time without having to wait for the construction site hoist to be available. The quality of each task can be improved and wastages can be reduced, as the working environment is more systematic and controlled.
Cost wise, modular construction currently comes with a premium. However, we can expect that construction cost will reduce in the near future as the systems and the fabrication process will be improved.
CREATIVE DESIGN AND ADAPTATION CHALLENGES
The modular construction method is best suited for projects with repetitive, standardised floor layouts and with rooms confined within a single module—such as in hotels or student residences. However, this technology can also be applied to a residential building where a few adjacent modules are used to form an apartment. Some implementation principles may restrict the layout of the development, but in most cases design intent can be maintained. Often, the process of rationalisation brings added efficiency to the floor layout. It is often assumed that modular construction either derives from container or temporary site office concept, hence limiting outcomes to an industrial boxy appearance. In reality, modular construction opens new possibilities in terms of architecture as the structure is much lighter than in situ construction. Change in geometry is achievable and transfer can also be accommodated. The façade does not need to be a single plane and the joints between modules can be easily concealed.
MODULAR CONSTRUCTION METHODOLOGY
PPVC systems can be based on a number of different models, each one having its own advantages and drawbacks, and each being most suitable for a particular type of project:
• Modules made of steel framing that is infilled with wall, floor and ceiling board: This system is rather light and suitable for a high-rise building. However, its water tightness before installation can be problematic, and the hollow feeling of the walls and floor is often not well-accepted by the end-users in the market.
• Modules made of steel frame with walls and ceilings of corrugated steel sheet infill and floor boards on steel joist: This system is very robust and lightweight, but corrosion and fire protection are challenging. It is also a rather expensive system.
• Modules made of reinforced concrete: They are cost-effective and provide a good response to fire and corrosion protection. This type of system is heavier and design and installation requirements
are closely interlinked.
• Modules made of timber frame with Cross Laminated Timber (CLT) panels infill: This structure is rather light and suitable for low-rise construction. Water tightness before installation is a concern. This technique of construction is not available in Asia and the timber elements needs to be sourced.
• Hybrid modules that incorporate some of the elements listed above: Although they require multidisciplinary expertise, those systems provide a good response to both market and technical requirements.
OVERCOMING INHERENT MATERIAL PROPERTY CONSTRAINTS
The transfer of construction activity from the site to a factory controlled environment not only procures more productive and safer working conditions for the workforce, it also reduces downtime due to inclement weather and enables the implementation of alternative materials that would be difficult to transport to the site or could not be exposed to climatic conditions. New construction methods can also be envisaged to increase productivity with the industrialisation of some tasks that could rely on machinery or robotisation, in the same manner that the automobile and aviation industries have embraced those techniques several decades ago.
One interesting feature of PPVC is the possibility of implementing a combination of multiple materials within a single element so as to make best use of each material’s properties (weight, resistance to fire or corrosion, mechanical strength, etc.), while minimising any adverse impact.
Modular construction enables the usage of greener materials and reduction of wastage, resulting in more sustainable construction. The creation of fully demountable buildings that can be dismantled and transported to another location for reusage is also a potential additional benefit of the system.
These benefits will be achieved along with a marked improvement in the quality of workmanship, which is made possible by fabrication in a controlled environment and repetition of modules of similar nature and dimensions.
Although modular construction has been around for several decades, it is still in its infancy as it has only recently been regularly employed in medium- and high-rise buildings. Therefore the systems that are currently available are constantly being refined to improve the performance of the modules so as to better meet the particular requirements of each project.
Gilles Chaillan is a French civil engineer with 25 years of experience in construction, especially in the design of unconventional structures, such as the Sports Hub’s movable roof and movable tiers. With his team, Chaillan has developed a hybrid PPVC system that can be implemented in a wide range of buildings, including high-rise structures. He has also developed a new type of PPVC connection system that relies on composite material. He is currently fully dedicated to PPVC system improvement by refining current systems through the introduction of new material and construction techniques.
ABOUT DRAGAGES SINGAPORE
Dragages Singapore is a member of the Bouygues Construction Group. Dragages is currently building its third PPVC project in Singapore and has developed two types of PPVC systems in-house—one that relies on a steel structural frame that is infilled with concrete (hybrid system), and another one that is entirely in reinforced concrete. Dragages’ engineering department is now developing the next generation of modules and exploring the use of new materials to be installed in a more industrialised process. This will improve both the sustainability and quality of the product, which enhances commercial competitiveness.