Ajay Chourasia, Sr. Principal Scientist, CSIR-Central Building Research Institute (CBRI), Roorkee, reviews the general concepts, PVMC connections, and recommendations for technological interventions and alternate connection systems.

Prefabricated Volumetric Modular Construction (PVMC) is an efficacious construction technique which has a sustainable behaviour that reduces construction time, waste of resources, and onsite workload, resulting in improved quality, faster, safer, and more environmentally sustainable construction.

PVMC’s adaptation to modern urbanisation is an acceptable alternative to traditional construction in multi-storey structures. Although, its use in low-rise and low seismic region is common, it poses challenges in contrast conditions due to inadequate understanding and knowledge as a result of extreme multi-direction forces.

The seismic behaviour of prefabricated volumetric modular buildings depends on joint connections between modular components. Thus, it is of utmost importance to improve the joint connection details and deploy seismic resisting features in PVMC. Researchers across the world have performed experimental and numerical studies to evaluate the response of such buildings under lateral loading.

PVMC is an industrialized construction process which involves manufacturing of prefabricated volumetric modular components in a factory, followed by transportation to the construction site, where they are assembled and joined, using specially designed connections. PVMC buildings are distinguished by their assembly process, design system, and detailing requirements, as well as a reduction in deadweight, and improved efficiency over traditional structures. Fig. 1 shows the volumetric building construction process from manufacturing stage to installation.

Prefabricated Volumetric Modular Construction Prospects & ChallengesFigure 1: Volumetric Modular Construction: Offsite Manufacturing to Installation Process

There are three classes of prefabricated construction: 1D single element, 2D panelised system, and 3D volumetric system, based on the degree of prefabrication. Panelised and volumetric construction, also known as modular construction, is the most efficient class of prefabricated construction as it allows for 70% to 95% of a building to be prefabricated in a factory before transporting it for on-site assembly.

The connections between prefabricated modules can be achieved by on-site simple inter-modular connections. Although PVMC has been extensively applied for low-rise buildings over the last three decades, its application for high-rise buildings is still limited at less than 1%.

Structural Systems for Improving Multi-Directional Stability
Joint Connections: The performance of PVMC under lateral loading is the function of its seismic parameters such as lateral strength, deformation characteristics and energy dissipation capacity.

Inter-modular joint connections in PVMC result in movement and volumetric changes due to the consequences of loading, stresses, shrinkage, thermal effect, and other factors. Thus, to reduce the movement and deformation, internal friction between the elements is induced by providing connectors.

Prefabricated modules should be designed to sustain gravity as well as lateral loads in order to deliver highly efficient seismic resistant system, which can be ensured by evaluating and studying mechanism of inter-modular joint connections. The mechanical behaviour of a joint connection can be designated by load-deformation curve (Fig. 2).

Prefabricated Volumetric Modular Construction Prospects & ChallengesFigure 2: Load Deformation Curve for Joint Connection (fib 2008)

Apart from structural requirements, joints between precast panels should also fulfil the functional requirements with regards to sound insulation, thermal insulation and water proofing. Hardware materials used for connections between precast walls include reinforcing bars, bolts, threaded connectors, welds, post-tensioning steel, steel plates, etc. In modular high-rise buildings, the connections between modular units play an important role to ensure the overall structural integrity, stability, and robustness of the entire building. Although welded connections can provide rigidity between adjacent modules, it is not preferred onsite as it requires highly skilled labour, a large working space, and time-consuming inspections after welding.

Inter-modular Joint Connections: An increased number of joining techniques have been developed for the inter-modular connection of modular steel buildings as illustrated in Fig. 3. These connections can be classified into three different types: inter-module connection using tie rod; inter-module connection using connector; and inter-module connection using bolt.

Prefabricated Volumetric Modular Construction Prospects & ChallengesFigure 3: Typical inter-module connections of modular buildings
(Thai 2020)

Inter-Module Connection using Tie Rod: This type of connection has been developed to vertically connect the columns of the lower modules to those of the upper modules (i.e. column-to-column connection). In this connection, the vertical tying between lower and upper modules is provided by using a vertical rod, whilst the shear force between the lower and upper columns is resisted by shear keys. The advantage of this type of connection is that it can be installed outside the modules, which thereby prevents any potential damages to internal finishes. In addition, this joining technique can be applied for columns with both hollow bare steel sections and CFST sections, which are necessary for high-rise buildings to retain the same column size.

Inter-Module Connection using Connector: Unlike the tie-rod system, the installation of the connector system is quite simple and flexible because the connector can be easily welded to the beam and column of the module offsite, which have different shapes of cross-sections. Various connector systems have been developed such as Vectorbloc, self-lock, rotary, and bracket connectors.

Inter-Module Connection using Bolt: Bolted connection is considered as an alternative solution to the onside welding approach due to its fast and easy installation and better quality control. Various bolting techniques have been developed for inter-modular connections of modular steel buildings, such as bolted connection with plugin device, wherein a high-strength bolting system is used to establish the vertical connection between the lower and upper modules, whilst a cast plugin device is adopted to establish the horizontal connection between adjacent modules. The seismic behaviour of the connection was experimentally and numerically investigated by Chen et al. (2017) for the corner joint and perimeter joint of modular steel buildings. The results showed that all connection specimens have reasonable energy dissipation capacity, post yielding deformation capacity and connection ductility, although fracture is their governing failure mode. In addition, the connection stiffness is also pronounced and needs to be considered in the design.

Impediments in Current Connection Systems
There have been an increasing number of joining techniques developed recently for modular buildings. However, the current techniques result in limited strength and stiffness, which may not be suitable for high-rise building applications. They also require a certain level of on-site labour. Therefore, there is a need for future research to develop smart joining techniques, which are not only stronger for high-rise applications, but also easy to install.

In addition, the new joining technique should be robust enough to be applicable to a wide range of joint configurations and novel modules with composite members. With these techniques, modular buildings can be built taller, faster and cheaper. For concrete modules, the current inter-module connections require significant on-site labour for laying the rebars and site grouting.

Tie-rod connection has limited moment resistance and its performance is similar to that of a weak semi-rigid connection. This leads to a weak framing action and lateral resistance of the whole building. Therefore, this type of connection is not suitable for high-rise buildings.

Bolted connection using welded plate can provide satisfactory connection ductility, but its strength and stiffness are limited and consequently, it can be classified as semi-rigid connection. This connection is not suitable for the inter-module connections of modular steel buildings as it requires highly skilled labour and working space.

Alternate Connection System: Headed Bars
Headed bars are formed by attaching a steel anchor at the end of beam reinforcement bar through welding or threading. Headed bars are highly advocated by the researchers due to their cost-effectiveness, easy installation, time saving fabrication and construction efficiency, without affecting the structural performance.

Prefabricated Volumetric Modular Construction Prospects & ChallengesFigure 4: Types of Headed Bars

Behaviour of Headed Bars: Experimental program
Prefabricated Volumetric Modular Construction Prospects & ChallengesFigure 5: Connection using: (a) Conventional Development Length using Reinforcing Bars; (b) Partial Development Length; and (c) Ribbed Headed Bars

Prefabricated Volumetric Modular Construction Prospects & ChallengesFigure 6: Test set-up for cyclic loading on prefab RC beam-column joint specimens
At first intance, headed bars are tested for prefab RC beam-column joints. Ribbed headed bars were tested under displacement controlled cyclic loading and its strength was compared with conventional system of ductile detailed system and partial development length. Fig 5 shows the prefab RC beam-column joint with headed bar and development lengths and Fig. 6 shows the experimental set-up of tested precast RC beam-column joint specimens.

Headed bar specimens demonstrated satisfactory structural performance by surpassing nominal moment strength and design joint shear capacity. The load carrying capacity of headed bar specimens was well comparable with the conventionally detailed specimens, even marginally higher in most of the cases. Thus, headed bars are efficacious in imparting adequate bond strength inspite of absence of development length. Headed bar specimens satisfied the performance criteria of ACI 374.1-05 with regards to minimum drift, strength degradation, relative energy ratio and stiffness, which is considered as an important milestone for their acceptance. Fig. 7 shows the typical hysteretic curves for the three connection systems tested.

Prefabricated Volumetric Modular Construction Prospects & ChallengesFigure 7: Load-displacement hysteresis curves of prefab RC beam-column joint with (a) Conventional detailed (b) Partially detailed (c) Headed Bar

Prefabricated Volumetric Modular Construction Prospects & Challenges

Cost Analysis
Cost of implementing headed bars in beam-column joints was estimated and compared to the cost of conventional development length for different rebar diameters. Cost of anchor is considered as per manufacturer’s rate. Rate of steel work is considered as ₹ 60/kg, including labor charges as prevalent in construction. Rebar embedment depth into the joint is considered as 300 mm in case of headed bars, while embedment depth for development length is determined as per IS 456-2000 and IS 13920-2016. Table 1 illustrates the cost analysis and comparison of headed bars and development length for different rebar diameters. Cost analysis indicated that the headed bars are economic substitute to development length, with percentage saving increasing with the increasing rebar diameter (Fig. 8).

Prefabricated Volumetric Modular Construction Prospects & ChallengesFigure 8: Percent Saving in Headed Bars with Respect to Rebar Diameter

Prefabricated volumetric modular construction reduces construction time, resource waste and onsite workload using a volumetric modular construction method. It provides more cost-effective, faster, safer, and eco-sustainable building solutions than traditional onsite construction. In addition to many advantages, the success shown by PVMC in multidirectional forces is increasingly encouraging its adaptation as an acceptable alternative to conventional construction.

PVMC offer a wide range of benefits over cast-in-situ structures, yet their acceptance is uncommon in construction industry, owing to scarce knowledge on the design and force transfer mechanism of joint connections. Previous studies on PVMC revealed that behaviour of modular buildings can be enhanced by providing effective connection systems which impart adequate lateral strength and ductility to the building. Existing research, although competent to understand the response of connections at component level, cannot completely envisage the global seismic performance of modular buildings.

Structural behaviour of existing connection types is still ambiguous when practically implemented to the buildings, for which full-scale prefabricated modular buildings with inter-modular connections should be tested experimentally under lateral loading. Alternate inter-modular connections for PVMC include headed bars which have shown superior structural performance and cost-effectiveness as compared to conventional development length using reinforcing bars.

Current design practices for modular buildings are based on conventional design guidelines for traditional buildings, which are not suitable and joint connections require special design. The structural design guidelines for modular connections remain unavailable. Therefore, there is a need for future research to develop provisions for the structural design of inter-modular connections. With the new design codes, modular buildings can be built safer, which will enable the construction industry to implement advanced modular technologies for high-rise buildings. These endeavors may encourage widespread adoption of PVMC in seismic prone regions of the world.

  1. ACI Committee 374, “Acceptance Criteria for Moment Frames Based on Structural Testing and Commentary (ACI 374.1-05),” American Concrete Institute, Farmington Hills, MI, 2005.
  2. Boafo FE, Kim J-H, Kim J-T. Performance of modular prefabricated architecture: Case study-based review and future pathways. Sustainability 2016;8:558.
  3. Chen Z, Liu J, Yu Y, Zhou C, Yan R. Experimental study of an innovative modular steel building connection. J Constr Steel Res 2017;139:69–82.
  4. Chen Z, Liu J, Yu Y. Experimental study on interior connections in modular steel buildings. Eng Struct 2017;147:625–38.
  5. Chourasia, A., Singhal, S. and Chourasia, A., 2019. “Pull-out behaviour of headed bars embedded in concrete.” In 8th International Engineering Symposium, Kumamoto University, Japan.
  6. Deng E-F, Zong L, Ding Y, Dai X-M, Lou N, Chen Y. Monotonic and cyclic response of bolted connections with welded cover plate for modular steel construction. Eng Struct 2018;167:407–19.
  7. Deng E-F, Zong L, Ding Y, Luo Y-B. Seismic behavior and design of cruciform bolted module-to-module connection with various reinforcing details. Thin- Walled Struct 2018;133:106–19.
  8. Fib Commission C 7: Bulletin 27. Seismic design of precast concrete building
  9. IS 13920-2016. Ductile detailing of reinforced concrete structures subjected to seismic forces- Code of Practice. Bureau of Indian Standards, New Delhi, India.
  10. IS 456-2000. Plain and reinforced concrete-Code of Practice. Bureau of Indian Standards, New Delhi, India.
  11. Kamali M, Hewage K. Life cycle performance of modular buildings: A critical review. Renew Sustain Energy Rev 2016;62:1171–83.
  12. Liew JYR. Innovation in modular building construction. Proceedings of the 9th International Conference on Advances in Steel Structures - (ICASS 2018) 2018: 1–14.
  13. McKinsey. Modular construction: From projects to products, from https://www. mckinsey.com/industries/capital-projects-and-infrastructure/our-insights/mo dular-construction-from-projects-to-products; 2019.
  14. Mortice Z. Can this Chicago apartment factory make new homes affordable? from https://www.citylab.com/design/2019/07/chicago-new-construction-apartment -affordable-rent-skender/592444/; 2019.
  15. Pan W, Yang Y, Yang L. High-rise modular building: Ten-year journey and future development. Construction Research Congress 2018:523–532.
  16. Pang DS, Liew JR, Dai Z, Wang Y. Prefabricated prefinished volumetric construction joining techniques review. Proceedings of the Modular and Offsite Construction (MOC) Summit 2016:249–256.
  17. Singhal, S., Chourasia, A. and Parashar, J., 2020, October. Anchorage behaviour of headed bars as connection system for precast reinforced concrete structural components. In Structures (Vol. 27, pp. 1405-1418). Elsevier.
  18. Smith RE. Prefab Architecture: A Guide to Modular Design and Construction. John Wiley & Sons; 2011.
  19. Thai H-T. Numerical study of a novel self-lock connection for modular tall buildings. Proceedings of Indian Structural Steel Conference - (ISSC 2020), Hyderabad, India 2020.
  20. Thomson J. Modular construction: A solution to affordable housing challenges. Cornell Real Estate Rev 2019; 17:90–7.
Brimax AAC: An Indian Lighthouse Project from HESS AAC SYSTEMS, Netherlands
Brimax AAC Products LLP contracted Hess AAC Systems to supply a new AAC plant in Vadodara, India, with a capacity of 680 cbm/day (expandable up to 900 cbm/day with reinforcement for panel production). This order strengthens Hess´ position as

Read more ...

Vollert India Expands Production Capacity to Cater to Infra Development Sector
Vollert India, based in Sikandrabad, near Greater Noida (UP) since 2017, is strengthening its commitment to India; it is now expanding its production capacity of precast machinery and components to meet the greater demand from India’s fast

Read more ...

Elematic Precast Technology Solutions for Building, Industrial and Infra segments
Elematic offers a comprehensive range of precast technology solutions for the Building, Industrial and Infra segments. Elematic precast technology enables clients to automate the production of walls, slabs, columns, beams, and stairs, providing an efficient

Read more ...

Advanced Concrete Curing Systems from Kraft Curing
Kraft Curing Systems GmbH is offering advanced concrete curing systems that optimize the hardening process of concrete. Kraft Curing’s Advanced Concrete Curing System provides numerous solutions, from vapor-based (steam) systems mainly for the precast

Read more ...

Why Automating Production is the Solution
Automating the production processes will lead to reduced wastage, fewer errors, more precision, greater safety, and higher quality of the end-products, and in a shorter period of time. First, we need to understand where we stand today as regards industrialisation

Read more ...

Elematic India confident of the future of Precast Business
Elematic India sees growing demand for its precast plants in India due to the growth in precast construction across segments. What gives the company an edge is its ability to support the customer through the entire value chain. Says Sridhar Rao, Sales

Read more ...

F.B.I. Tasbud Partners With Progress Group
Progress Group is helping companies like Tasbud stay ahead in a changing market with automation and software integration. Automated machinery to produce precast elements as well as the reinforcement and the integration of the fitting software are

Read more ...

Mekuba Petro Products - Catering to Mega Precast Concrete Projects
Mekuba Petro Products has a strong presence in the petrochemicals industry since 47 years and has been growing rapidly in the construction chemicals segment over the past decade. An expert in the formulation and production of mould-releasing agents, its

Read more ...

Precast & PEB Construction Opportunities for Entrepreneurs
C. A. Prasad, Director, Metey Engineering & Consultancy and President, PSI, Hyderabad, guides entrepreneurs on the various aspects of Precast and PEB construction business. Quality assurance and timely construction using Precast and PEB produced

Read more ...

Autoclaved Aerated Concrete Blocks
A sunrise segment in India’s building materials industry, the AAC block is finding preference over the red brick and emerging as the future of building construction. Mohit Saboo, Director & CFO BigBloc Construction

Read more ...

A Stellar Modernization of Construction With Precast in NCR, India
What influenced the Stellar Group’s decision to build with precast and invest in a precast plant. The well-known Indian ‘Stellar Group’, which has been successfully working in the construction business for over 25 years, is convinced that precast is the future

Read more ...

Sardinian industry leader invests in automated mould from Progress Group to advance production
Recently, a highly automated mould for the production of pillars from Tecnocom, a company of the Progress Group, has been installed to help industry leader Consultecna stay ahead. Francesco Pireddu explains the decision made in favour of automation although

Read more ...

AHCT’s Smart Solutions for Smart Contractors
Technology companies have developed hardware and software solutions to help manage every aspect of a construction project, no matter how complex or massive the project may be. Harsh Pareek, Regional Sales Director, India and SAARC, Trimble Solutions

Read more ...

Echo Precast Engineering Helps Modernize Pruksa’s Precast Plants
Thailand’s real estate developer Pruksa, a leader in the building sector, modernizes its building solutions with automated hollow core production plant equipped with machinery from Echo Precast Engineering, a company of the PROGRESS GROUP. Real estate developer Pruksa

Read more ...

Dongyue Machinery Group gearing up to meet rising demand for AAC Bricks in India
Dongyue Machinery Group is offering Autoclaves Aerated Concrete (AAC) blocks, brick blocks, hollow blocks, curb stones, color blocks etc. AAC Blocks, which are lightweight concrete blocks, use less cement compared to traditional cement bricks, and are therefore eco-friendly

Read more ...

B.E. Billimoria Changing the Face of India
BE Billimoria & Company is one of India’s leading firms of civil engineering construction contractors. Ranging from commercial, residential spaces to some of the most iconic buildings in the country, like the 316-meter Namaste Tower, are among their project list

Read more ...

Advanced Concrete Curing Systems from Kraft Curing Systems GmbH
Kraft Curing Systems GmbH is offering advanced concrete curing systems that optimize the hardening process of concrete. Kraft provide numerous solutions, from vapor-based (steam) systems mainly for the precast industry, to heating/air circulation systems

Read more ...

LARCO partners with ECHO Precast to set up production site for prefab elements
The production site of LARCO PREFAB S.A. in Welkenraedt, Belgium opened in 2018 and has grown consistently over the years. LARCO produces a range of prefabricated concrete elements such as hollow core slabs, columns, wall panels, soccles

Read more ...

Special prefabricated elements specialist Klaus relies on fully individualised automation solutions
Klaus Hoch- und Tiefbau GmbH is upgrading its machines in the precast concrete plant with several automated systems from progress Maschinen & Automation and Tecnocom - companies of the Progress Group. With the individualised reinforcement machines

Read more ...

Prefab Housing
Civil Construction in India has not been as much industrialized as it has been in the West. Presently, it shares barely 1-2% of the real estate market, though as per a recent study, it is expected to grow @8.5% in the decade of 2016-2026

Read more ...