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]

pst29@cam.ac.uk

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)