Modular construction: Pros and cons

The challenge that structural engineers often face is will modular construction be worth it or not? What are the pros and cons? Are there any special considerations for its engineering design?

In general, three scenarios are required for modular structures in an engineering analysis: the permanent use, the lifting and its transport.

Scenario 1: Permanent use

This scenario is where all modules, together with their equipment, are assembled and installed at the final location on site. The engineering analysis is as per conventional construction.

Scenario 2: Lifting

This scenario is when a single module is assembled in the shop and ready to be lifted onto the truck for delivery to the construction site, as well as when the module arrives on site for off-loading and installation. The client is involved in selecting contractors, lifting equipment and laydown area availability, while the engineering firm and lifting contractor are both engaged in the lifting analysis.

The engineering firm is responsible for the lifting plan and the modular structure itself, including the lifting arrangement schema, lifting lugs and any temporary braces, if required. The lifting impact and balancing the module are the major concerns, other than the integrity of the module itself.

Lifting contractors are responsible for designing all shackles, slings and spreader bars. They must also ensure that all module lifting is carried out as per the lifting plan.

Scenario 3: Transport

This scenario is where the module is being transported to the construction site. The client is involved in contractor selection, transport equipment and method availability, route selection and local authority confirmation, etc., while the engineering firm and transport contractor are both engaged in the transport analysis.

The engineering firm is responsible for the transport plan and the module structure itself, including the transport arrangement schema, the module base supports and any temporary braces, if required. The impact of the load moving in any direction and the climatic loads during transport are the major concerns, other than the integrity of the module itself.

Transport contractors are responsible for securing the cargo and must also ensure the transport plan is executed properly.

It’s essential to be aware of the pros and cons for a modular construction so the client and the engineering firm can decide whether to go with a modular construction or carry out the project conventionally using the stick-built method. This includes, but is not limited to, the cost, schedule and environmental considerations.

Pros

• Construction schedule: Regardless of the weather, modular structures are completed inside a factory, which mitigates any risks of delay. The project is delivered much sooner, which offers a faster return on investment.
• Labour: There are much fewer onsite construction staff members, which provides a major direct reduction in construction costs.
• Quality: Modular structures are fabricated and assembled in well-equipped shops, which makes it much easier to control and meet or even exceed product quality.
• Safety: The indoor construction environment reduces risks of accidents and related liabilities for workers.
• Environmentally friendly: Modular construction considerably reduces CO₂ emissions by creating less material waste, greater flexibility and reuse, and improved air quality.

Cons

• Engineering: Compared to stick-built construction, though it won’t take much more time, modular structures require more analysis for different scenarios.
• Manufacturing: The plant may need to be larger for fabrication and assembly and a higher lifting capacity is required for the plant to lift the assembled modules.
• Transport: A special road permit may be required if the module is oversized and overweight, and damages may occur during transport.
• Installation: The site access road will require stricter requirements regarding its size and capacity. A higher lifting capacity is required for off-loading and installing the assembled modules. Higher fabrication and assembly accuracy is also required to connect both the structures and the equipment together for different modules. Challenges in change management could result if modifications are required after fabrication, assembly and installation.

The EPCM team, together with our engineering and estimation teams, take care of estimating costs and schedules for different options. This helps clients make decisions regarding modular or conventional construction.

Our engineers have shown ingenuity in finding simple solutions to complex problems. This, in turn, creates project value by using a modular construction approach on many heavy industrial projects. BBA also provides expert services in constructability analyses and technical assistance during modular construction regarding lifting, transport and installation.

You can count on BBA to help you get the job done well! To learn more, contact our expert: xing.li@bba.ca

• National Building Code of Canada, NRCC – National Research Council of Canada
• CSA S16 Design of steel structures, National Standard of Canada
• Design loads on structures during construction, ASCE – American Society of Civil Engineers
• Structural design criteria, PIP – Process Industry Practice
• Standard Specifications for Highway Bridges, AASHTO – American Association of State Highway and Transportation Officials
• North American Cargo Securement Standard, CCMTA – Canadian Council of Motor Transport Administrators
• Cargo Securement Guide, MTQ – Ministère des Transports du Québec