Introducing fully modular multi-storey buildings for New Zealand
The two key issues facing housing for New Zealanders are affordability and availability. Fortunately, modular homes, prefab buildings and pre-built homes are set to become part of the solution (Ashcroft et al., 2019). Since 2008, Dr John Jing has been conducting leading research to address structural design issues for fully modular multi-storey buildings in New Zealand (Jing, 2016; Jing and Clifton, 2016; Jing et al., 2020).
New Zealand’s seismic challenges
Not surprisingly, a key challenge with multi-storey buildings is in meeting New Zealand's seismic requirements. The good news is, the answer is finally here. With our proprietary inter-module connection technology, Tino Structures is able to:
Design an earthquake-resilient fully modular multi-storey building
At a significantly lower cost
And within a much shorter construction timeframe compared to any other options available currently
More on this in a moment. First, let’s take a look at modular structure design for multi-storey buildings.
Categories of Modules
Generally, fully modular multi-storey buildings consist of structural modules in two categories based on the vertical load transfer mechanisms:
Continuous bearing modules
Selective bearing modules
It should be noted that buildings with modules supported by a conventional RC/steel structure are partially modular – it is a mixed form of construction. Figure 1 shows the continuous and selective bearing modules in fully modular multi-storey buildings (Jing, 2016; Jing and Clifton, 2016; Jing et al., 2020; Srisangeerthanan et al., 2018).
FIGURE 1 – CONTINUOUS AND SELECTIVE BEARING MODULES (SRISANGEERTHANAN ET AL., 2018)
Continuous Bearing Modules
The continuous bearing modules are also known as ‘four-sided modules’. They are commonly used for rooms in hotel, student accommodation and apartment buildings. As the name suggests, these modules have four enclosed sides; openings are permitted but limited to the two sizes of windows and doors. Gravity loads are transferred continuously through the walls from one module to another below and eventually to the foundations and ground (Jing, 2016; Jing et al., 2020).
Four-sided modules are typically light steel framed in a multi-storey modular building. The framing members are cold-formed steel C-sections. Typical sections of the wall studs are 89 and 100mm deep. The ceiling and floor joists are 65 and 150mm deep, respectively. Both the joists and studs are spaced at 400–600mm centres with nogs. In some areas, double studs may be required due to concentrated loads. For lateral stability, the wall frames and ceiling and floor diaphragms of each module may be X- or K-braced. Alternatively, they may reply on the diaphragm actions of the board materials, such as plasterboards, to resist lateral loads. Figure 2 shows a typical four-sided module for multi-storey buildings (Jing, 2016; Jing et al., 2020).
FIGURE 2 – TYPICAL FOUR-SIDED MODULE FOR MULTI-STOREY BUILDINGS
Selective Bearing Modules
Selective bearing modules may be partially or fully open-sided. A partially open-sided module is similar to the four-sided version but has larger openings. The openings are created by introduction of intermediate and corner posts and by using stiff continuous edge beams. The post and edge beams are usually Square Hollow Sections (SHS) and Parallel Flange Channels (PFC) respectively. Gravity loads are transferred through the edge beams to the intermediate and corner posts and then down to the module below. Lateral loads are resisted in the same way as a four-side module. Figure 3 shows a partially open-sided module (Jing, 2016; Jing et al., 2020).
Fully open-sided modules are also known as corner-supported modules. They are designed to have fully open sides. Gravity loads are transferred through deep edge beams to the corner posts and then down to the module below. The edge beams and corner posts are Rectangular Hollow Sections (RHS) and are welded together to form Moment-Resisting Frames (MRFs) for lateral stability. These modules can be placed together to create larger rooms and corridors within a building. Figure 4 shows a fully open-sided module (Jing, 2016; Jing et al., 2020).
Seismic issues in New Zealand
Fully modular multi-storey buildings generally have a uniform lateral strength along their height. However, during a major earthquake, the seismic demands are concentrated at the lower levels. This means that the building is prone to a soft-storey failure mechanism at lower levels. To address this issue in New Zealand, modules are typically designed to be supported by a separate conventional RC / steel structure. For example, the Elam University Hall building consists of 468 timber-framed modules supported by conventional structural steel framing and concrete double-tee flooring. Unfortunately, this mixed form of construction reduces modularity and hence the benefits of modular construction, such as savings of construction costs and time (Jing, 2016; Jing et al., 2020).
Inter-Module Connectivity: A better solution
To find a better solution, Dr John Jing has spent the past decade on conducting the world’s leading research and development in structural engineering. According to Dr John, inter-module connectivity is the key in addressing the seismic challenge. It is also the enabler for future development of fully modular multi-storey buildings in New Zealand (Jing, 2016; Jing et al., 2020).
Proprietary Inter-Module Connections
To achieve full modularity, earthquake resilience, and cost and time savings in light steel framed multi-storey buildings, Dr John Jing has developed a novel inter-module connection device that has been fully patented in New Zealand (Jing, 2019). To find out more on how it works and the benefits it brings, read our Elam University Hall project.
For heavy steel framed fully modular multi-storey buildings, modules are connected together to assemble braced frames and diaphragms to transfer earthquake loading to the ground as shown in Figure 5. Inter-module connectivity is crucial to achieve the desired seismic performance.
While we are able to design rigid bolted or welded connections to the requirements of NZS 3404, we have been undertaking further research and development of our proprietary inter-module connection device aiming to provide the required strength, stiffness and ductility, as well as satisfy certain functional needs in accordance with the Industry 4.0 initiative for heavy steel framed fully modular multi-storey buildings.
FIGURE 5 – HEAVY STEEL FRAMED FULLY MODULAR MULTI-STOREY BUILDING (SRISANGEERTHANAN ET AL., 2018)
Find out how we CAN help you
At Tino Structures, we offer the full range of structural engineering services including Producer Statements 1, 2 and 4 at low, medium and high-risk levels to take your modular project of any scale, material and complexity from concept to reality. If you have a project and are keen on modular construction, please contact us today to find out more. As you will discover, there is no need to reinvent the wheel.
REFERENCES
Jing, J, G.C. Clifton, K. Roy and J.B.P. Lim, 2020. Three-storey modular steel building with a novel slider device: Shake table tests on a scaled down model and numerical investigation. Thin-Walled Structures, 155.
Jing, J, G.C. Clifton, K. Roy and J.B.P. Lim, 2020. Seismic protection of modular buildings with bonded rubber unit sliders: Experimental study. Thin-Walled Structures, 154.
Jing, J, G.C. Clifton, K. Roy and J.B.P. Lim, 2020. Performance of a novel slider device in multi-storey cold-formed steel modular buildings under seismic loading. Structures, 27.
Ashcroft, D., T. Egbelakin, J. Jing and E.O. Rasheed, 2019. Cost comparison of seismic damage resisting systems for modules in multi-storey buildings. Journal of Engineering, Design and Technology, 17(2), 330-346.
Jing, J, 2019. Seismic Damage-Resistant System for Multi-Storey Buildings. New Zealand Patent Number 740105. New Zealand Intellectual Office, available at http://www.iponz.govt.nz
Jing, J, 2016. Seismic Damage-Resistant System for Modular Steel Structures. University of Auckland, Auckland.
Jing, J and G.C. Clifton, 2016. Seismic Damage-Resistant System for Multi-Storey Modular Light Steel Framed Buildings. Proceedings of Australian Earthquake Engineering Society 2016 Conference, Melbourne, Australia, Nov 25-27.
Lawson, R.M., 2007. Building Design Using Modules. The Steel Construction Institute (SCI).
Srisangeerthanan, S., J. Hashemi, P. Rajeev, E. Gad and S. Fernando, 2018. A review on diaphragm behaviour and connections for multi-storey modular buildings. Proceedings of Australasian Structural Engineering Conference, Adelaide, Australia, September 25-28.