Safer and more economical slender structures
Submitting InstitutionOxford Brookes University
Unit of AssessmentGeneral Engineering
Summary Impact TypeTechnological
Research Subject Area(s)
Engineering: Biomedical Engineering, Civil Engineering
Summary of the impact
Research, led by Oxford Brookes University's Dr Mike Godley and Dr Rob
Beale, into the design and analysis of scaffold structures has enabled a
better understanding of their behaviour, higher standards of safety and
improved design. The Group produced technical guidance to the HSE and
authored the design guide TG20:08 (2008); the basis for scaffold design in
the UK. The Group contributed to new Euronorms for scaffolding and the UK
design guide is compatible with these. Furthermore, the Group informed a
pan- European design guide for storage racking systems (2000) that later
transformed with little modification into EN 15512 (2009). This is now the
basis for the design of all such storage racks across Europe.
Scaffold and storage rack structures are slender structures with semi
rigid joints and splices and both exhibit looseness. Additionally, rack
structures are sensitive to local buckling1. The Group was
amongst the first to demonstrate that traditional methods of design for
access scaffolds, that assumed lift-height effective lengths, could
produce unsafe scaffold structures. Such methods erroneously assumed that
horizontal members (ledgers) acted as ties restraining deflections
parallel to the facade2. The true behaviour is that the
restraint is only partial. Scaffold structures also require ties to the
facade to give them their structural integrity. The Group demonstrated
that the buckling behaviour of scaffolds is dependent on the pattern of
such ties in addition to the degree of horizontal restraint provided by
the ledgers. These results were confirmed by tests of full size scaffolds
For both scaffolding and storage racking systems the structural behaviour
of the connection between beam and column has a crucial effect of
performance3. Currently available software allows only a
simplified linear model of the connection to be used, but work by
Pabrakhan4 demonstrated ways of successfully introducing
non-linear characteristics into the structural joint models.
The configuration of access scaffolds is much less regular than that of
storage structures, and was lightly regulated during the early days of the
research. There was concern that safety levels might be compromised and
premature failures might occur due to common errors in construction. With
the support of the Health and Safety Executive (HSE) site surveys were
made and some indication of the types of construction errors that occurred
and their frequency was obtained. Reliability analyses of typical scaffold
constructions were made to determine failure risks. It was discovered that
these faults are usually caused by poor site supervision and practice and
in 1997 HSE inspectors were issued with guidelines to ensure safer work.
A major shortcoming of scaffold design is the lack of a thorough
investigation into the effects of wind. To rectify this, Irtaza5
carried out extensive experimental work on wind tunnel models and a
parallel computational fluid dynamics (CFD) study, to successfully
identify the wind loads applied to scaffolds with and without sheeting and
netting. He calibrated the CFD model against full scale tests made at
Silsoe and derived pressure coefficients for scaffolds erected around a
cubical building. A large data set derived from experimental work on
models in a wind tunnel was deposited in the British Library for use by
Both scaffolds and storage racks have relatively short lives and there is
therefore a reluctance to invest heavily in permanent column foundations.
Temporary lightweight foundations are susceptible to failure due to the
effects of lack of fixity, imperfections and column flexure. This problem
was initially investigated by Feng1who designed a simple model
of a base-plate which peeled off the substrate as column bending
increased. Further work by Lau9 demonstrated the consequences
of column flexure on flat ended column bases experimentally, confirming
his theoretical predictions. The research is being extended into the
reliability of scaffold stuctures6.
References to the research
1. Godley M H R, Beale R G and Feng X, 2000. "Analysis and Design of
down-aisle pallet rack structures", Computers and Structures, Vol. 77, No.
4, 391-401. doi:10.1016/S0045-7949
This paper presented the results of doctoral research by Ms Feng under the
supervision of Dr Godley and Dr Beale into a single column non-linear
model of pallet rack structures including imperfections which was shown to
give results that were within 4% of full three-dimensional analyses. The
model formed the basis of the state-of-the-art commercial program
Palletsoft which designed storage structures to FEM10.2.02, 2000 and which
had international sales. The program was able to design racks in
significantly less time than the use of standard finite element programs
enabling efficient and economical designs to be produced
Submitted to RAE2001, Oxford Brookes University, UoA33-Built
Environment, RA2, MHR Godley, Output 4.
2. Godley M H R and Beale R G, 2001. "Analysis of large proprietary
access scaffold structures", Proc. Inst. Civil Eng. Structures and
Buildings, Vol. 146; Part 1, 31-40. doi:10.680/stub.2001.146.1131
This paper presents bi-linear models of the non-linear elasto-plastic
behaviour of scaffold connections and shows that the different
moment-rotation curves for clockwise and anticlockwise rotation need to be
considered in analyses. Finally it presents new two-dimensional models
which accurately model the interconnection between elements in a full
three-dimensional scaffold structure.
3. Ng A L Y, Beale R G and Godley M H R, 2009. "Methods of restraining
progressive collapse in rack structures", Engineering Structures, Vol. 31,
No. 7, 1460-1468. doi:10.1016/engstruct.2009.02.029
This paper presents the results of doctoral research by Ms Ng under the
supervision of Dr Godley and Dr Beale into the dynamic collapse of pallet
racks under impact conditions. The research demonstrated an economical way
of increasing the resistance of a rack to impacts by the insertion of
4. Prabhakaran, U, Beale R G and Godley M H R G, 2011. "Analysis of
scaffolds with connections containing looseness", Computers and
Structures, Vol. 89, No 21-22, 1944-1955.
Continuing the research into scaffolds the effects of looseness which is
prevalent in all scaffold connections was investigated by Miss Prabhakaran
under the supervision of Dr Godley and Dr Beale. The resulting new models
developed in this paper have shown that the traditional way of dealing
with looseness by applying an equivalent side load can lead to incorrect
Submitted to REF2014, Oxford Brookes University, UoA15-General
Engineering, REF2, RG Beale, Output identifier 8533.
5. Irtaza, H, Beale R G and Godley M H R, 2012, "A wind tunnel
investigation into the pressure distribution around sheet-clad scaffolds",
Journal of Wind Engineering & Industrial Aerodynamics, Vol. 103,
The research into scaffolding was continued by Irtaza as part of a
doctoral programme supervised by Dr Beale and Dr Godley. The paper extends
the previous research which was primarily structural analysis into the
determination of wind loads applied to access scaffolds. The study
included a consideration of the porosity of the sheeting around the
Submitted to REF2014, Oxford Brookes University, UoA15-General
Engineering, REF2, MHR Godley, Output identifier 9123.
6. Andre, J, Beale R G and Baptista A M, 2013,"Recent advances and
existing challenges in the design of bridge falsework systems", Civil
Engineering and Environmental Systems, Vol. 30, Issue 2, 130-145.
The slender structures group have obtained funding from the Portuguese
Research Council (FCT) for a doctoral student, Mr Andre, to investigate
failures of bridge scaffold structures to extend the work into devising
procedures for improving the safety of the structures. This paper
represents the preliminary results of the research.
Details of the impact
Research into the design and analysis of scaffold structures has enabled
a better understanding of their behaviour, higher standards of safety and
in improved design. The design guides TG20.05 and its revision TG20.087,8
are extensively used throughout the UK and, together with the suggested
revisions to testing procedures for scaffold connections, will enable
proprietary scaffold systems to also be erected safely so that the number
of scaffold collapses within the country will be reduced. As a consequence
of the authors' involvement in the development of the Euronorms for access
scaffolding, they are compatible with the Euronorms. Recently the group
has attracted funding from the Portuguese government to extend the
research into the reliability of bridge scaffolds, several of which have
collapsed in the last few years in Portugal causing fatalities. The
results of this research have been presented at conferences and in journal
Although the research has been primarily applied to UK scaffolds it has
also been referenced and used by scaffold designers in developing
countries where Dr Beale through his research expertise has given seminars
to Structural Engineers9 on causes of scaffold collapses and
the improvements required for safe design (Hong Kong,2003 and 2008 and
The earlier research for the HSE has led to scaffold contractors and
users being made aware of the importance of tying and bracing on the
behaviour of the systems and to the HSE Inspectors being given a set of
strict guidelines to enforce when inspecting scaffolds. Test results on
scaffold connections were used to help draw up the models used in
producing the design guides referred above. The implication of looseness
on scaffold designs has yet to make an impact but the work was only
published in 2011 with recommendations for changes to the European
The testing procedures developed for rack structure10,11,12
were used in developing the procedures for testing scaffold structures and
as part of its consultancy programme the University has tested nearly
every scaffold manufacturer/distributor in the UK to enable the
manufacturers and designers to correctly determine their products'
performances (income generated in excess of £400,000 over 15 years).
During the period in question about 200 reports on structural testing of
scaffolds and racking system components were completed.
Research-led consultancy work for Interserve UK13 resulted in
new design tables for `Kwickstage' scaffold structures being produced.
These tables were immediately used by competitors supplying look-alikes
although the university established that the alternative manufacturers'
products could be 10% less safe13. Following this consultancy
the group, with Interserve, developed a new economical scaffold structure
(K2 system) requiring 20% less components and steel and being erectable in
less than 50% of the time of its competitors.
The profits from the consultancy enabled several PhD students to be
funded, many from developing countries. Some of these students have since
gone on to become University lecturers in Malaysia 9(2),
Jordan14 (2) and India where they are using the knowledge
gained in their research and disseminating it there. Other ex-PhD students
have become leading designers and engineers working in the UK and the US.
The extensive research into pallet rack properties has led to the
Euronorm BS EN1551215 being accepted. It requires racking
manufacturers to take into account second order elastic effects in the
stability of the racks so as to produce safer and more economic racks.
Small reductions in the amount of material used in modern designs
(typically from the new procedures) of around 15% can make a rack fully
competitive in international marketplaces as material costs are around 85%
of the total cost of an installed rack. Although there are only a limited
number of UK pallet rack manufacturers the University has commercially
tested the products of most of them. In addition a state-of-the-art
computer program `Palletsoft' written by the group and marketed by the
University had international sales and is used in Australia and the UK to
produce safe, economical designs efficiently and quickly.
The looseness effects on cross-aisle stability of pallet racks have been
reported to the industry where they have caused some manufacturers to
amend their procedures. Latest research has led to a very cost effective
way of reducing the number of rack collapses under impact by fork lift
trucks which is to insert additional plan bracing at the first level of
Insights from the research of Dr Godley and Dr Beale, at Oxford Brookes
University, to better understand the analysis and design of slender
structures has not only informed design guides and safety policy but also
influenced construction standards in the UK and Europe with improved
practice and safety measures for construction workers
Sources to corroborate the impact
- Corroborating contact 1. Managing Director, The National Access
- NASC TG20:08 :Technical Guidance on the use of BS EN 12811-1, 2008
- Corroborating contact 2. Head of Department of Civil Engineering,
Curtin University, Sarawak Malaysia.
- FEM 10.2.02, The Design of static Steel Pallet Racking, Section X of
the Equipment et Proceeds de Stockage` ,2000(design code).
- Corroborating contact 3. Engineer, Harsco Infrastructure Ltd ,
(scaffolding and pallet rack structures).
- Corroborating contact 4. Secretary General, FEM Racking and Shelving
product Group (European Racking Federation).
- Corroborating contact 5. Chief Engineer, Interserve Construction
Limited (scaffold structures).
- Assistant Professor, Department of Civil Engineering, Faculty of
Engineering and Technology, University of Jordan (Contact details
available from Oxford Brookes University Research & Business
Development Office upon request)
- BS EN 15512 `Steel static storage systems — adjustable pallet racking
systems — Principles for structural design', 2009.(Euronorm)