Petia Tzokova
Tall modular buildings:
Figure 5 shows a 90m (28 storeys) modular building in
Australia which has stacked modules combining steel
frames and thin-walled boxes, also with concrete inside
the steel columns [7].
Heights of existing tall modular buildings were
compared with predictions.
Modular buildings are made from room-sized units
produced in a factory and assembled on site [1].
Their “off-site” nature can help to accommodate
increasing population and urban density in cities [2],
if these buildings can become much taller.
Existing modules can consist of either thin structural
walls or beams and columns, as shown in Figure 1.
The modules can then be stacked, forming a modular
building [3].
The following aims are considered:
• To find the height limit of simple stacked modular
buildings.
• To find the variation of this height limit between
different types of module.
I would like to thank Janet Lees and Keith Seffen for their help and support during this project. I would also like to thank
Allan McRobie, Andrew Lennon, Rod Lynch, Kati Sexton, Paula Block and the EPSRC (CDT grant, ref: EP/L016095/1).
Advanced Structures Group Lab, Department of Engineering, University of Cambridge, Cambridge CB2 1PZ, UK
Introduction
Project aims
Methodology
Results
Case studies
Conclusions
Acknowledgements
References
A single stack of perfectly
connected steel modules was
investigated – a modular
tower. Figure 2 shows the
loadings considered.
Different generic module
types were investigated, as
shown in Figure 3;
variations in manufacture
were also considered.
Figure 7 shows an Ashby Chart of maximum number of storeys vs
weight of module in each tower. Each point on the chart is a different
modular tower, coloured accordingly; clusters of the same module type
have been highlighted.
Solid block modules (blue cluster) give maximum height but are very
heavy (and unrealistic). Thin-walled boxes (red cluster) give modules
generally lighter than the other module types (furthest to the left of the
plot). Braced frame modules (yellow cluster) give a similar maximum
height as thin-walled boxes, but have a larger weight variability.
Unbraced frames (green cluster) generally give heavier modules than
thin-walled boxes, but also give the tallest practical tower at 78 storeys
(see Figure 7). A summary of the results is given in Table 1 showing this
unintuitive result – the unbraced frames greatly outperform the braced
frames as well as the thin-walled boxes. The reason is because the
sections used in the unbraced frame may work better in bending than
when pinned and braced, as demonstrated in Figure 8 for a single storey.
The tallest realistic modular tower (78 storeys) uses an unbraced frame module. The lightest
tower for its height uses a thin-walled box. However, all case study buildings fall below the
tallest modular towers in this analysis, suggesting that higher towers may be possible. Note that
this Ashby Chart is the first to consider actual structural forms.
Further research after this preliminary study will focus on the dynamics of tall modular
buildings, in particular control and hence mitigation of excessive lateral displacements due to
extreme events such as earthquakes or strong winds.
Figure 4 shows the tallest modular building in the
world at 200m (57 storeys). The modules are steel
frames (also including intermediate columns) and are
stacked along the height of the building [6, 9].
Figure 6 shows a student accommodation building in
Wolverhampton, UK, which is 75m (25 storeys) high. It
has steel frame modules (with concrete floors) stacked
along the building height [10].
[1] Lawson, R. M. Modular construction using light steel framing: An architect's guide. Ascot: Steel Construction
Institute, 1999.
[2] Miles, J. and Whitehouse, N. (2013) Offsite Housing Review, Construction Industry Council, London.
[3] Lawson, R. M. P348: Building Design Using Modules. Ascot: Steel Construction Institute, 2007.
[4] Arup. Oasys GSA. Computer program. Version 8. 2015. url: www.oasys-software.com.
[5] Ashby, M. F. (2005). Materials selection in mechanical design, Butterworth-Heinemann, Boston.
[6] The Guardian. Chinese construction firm erects 57-storey skyscraper in 19 days. News website. Apr. 2015. url:
www.theguardian.com/world/2015/apr/30/chinese-construction-firm-erects-57-storey-skyscraper-in-19-days
(visited 07/03/16).
[7] IrwinConsult. SOHO Apartments. Consulting engineer's website. 2013. url: www.irwinconsult.com.au/
case_studies/soho-apartments-case-study/ (visited 07/03/16).
[8] Architectural Profiles Ltd. Victoria Hall: Architectural Profiles Limited and Europe's tallest modular building.
Website. url: www.archprof.co.uk/news/victoria_hall.php (visited 07/03/16).
[9] Coonan, C. Skyscraper 57 storeys tall built in 19 days in Chinese city. News website. Mar. 2015. url:
www.irishtimes.com/business/construction/skyscraper-57-storeys-tall-built-in-19-days-in-chinese-city-
1.2150064 (visited 07/03/16).
[10] Guthrie, J. B. An American perspective: skyscraper architecture goes modular in the UK. Website. Sept. 2009.
url: www.bdcnetwork.com/american-perspective-skyscraper-architecture-goes-modular-uk (visited 07/03/16).
Module typeTallest
(no. of storeys)
Lightest
(storeys/kN)
Blocks 103 0.0268
Thin-walled boxes 38 4.68
Unbraced frames 78 0.89
Braced frames 36 1.74Large beam and column
sections work well in bending
δ𝑢𝑛𝑏𝑟𝑎𝑐𝑒𝑑Large beam and column sections
under axial load are not limiting
δ𝑏𝑟𝑎𝑐𝑒𝑑
Brace will be a smaller section and under axial load this is the limiting factor
Victoria Hall and SOHO Apartments fall
well within the clusters, with Mini Sky City
on the edge of the data, having slightly
lighter modules. Note, many of the existing
buildings have separate lateral systems,
unlike the modular towers in this analysis.
Figure 1 Thin-walled module (a) and frame module (b) [3]
Figure 3
Module
types;
solid
block (a),
thin-
walled
box (b),
unbraced
frame (c)
and
braced
frame (d)
[4]
Figure 2 Modular tower, with
vertical and horizontal loads [4]
Figure 8
Unbraced
frame with
smaller
deflection
than braced
frame [4]
Table 1 Summary of results
Figure 6
Victoria Hall [8]
Figure 5
SOHO Apartments [7]
Figure 4
Mini Sky City [6]
wind
load
self weight
+
floor load
Limits of strength, buckling and horizontal
deflection were combined to find the maximum
height of tower in each case, presented later as
an Ashby Chart [5].
Figure 7 Final Ashby Chart
(a) (b)
(c) (d)
height limits of stacked steel modules
(a) (b)