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Constructability:
A guide to reducing
temporary works
Published – October 2020
This TWF Guidance is available
as a free download from
www.twforum.org.uk
Document: TWf2020: 02
NOTE: If you need to print this
document, be aware that the pages
are prepared with alternate (even)
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Temporary Works forum Constructability: A guide to reducing temporary works – TWf2020: 02
Members of the Working Party
This guidance has been prepared by Working Group 25:
Convenor Jim Tod Tony Gee and Partners LLP
Secretary David Thomas Temporary Works Forum (TWf)
Chris Bennion Chris Bennion Consultancy Ltd
Paul Boddy Interserve Construction
Tim Bowes Atkins
Godfrey Bowring Retired
Nick Boyle Balfour Beatty Civil Engineering Ltd
Andrew Finch Jacobs UK Ltd
Tim Lohmann Wentworth House Partnership
Chris Maher Highways England
Doug Potter Arcadis Consulting (UK) Ltd
Jim Richings Vinci Construction UK
Malachy Ryan Alan White Design Ltd
Mike Webster MPW R&R Ltd
Aleksander Widernik Lendlease Construction (Europe) Ltd
Rob Williams Murphy Group
Steve Williams Network Rail
John Winson Atkins
Contributors also included: James Appleby Network Rail
Natalie Cropp Tony Gee and Partners LLP
Ray Filip RKF Consult
Jon Hodgins Galliford Try
Mathew Howells Tony Gee and Partners LLP
Andrew Jarman Network Rail
Sinead Lawlor Network Rail
Andy Marshall Tony Gee and Partners LLP
Kirsten Morris Hewson Consulting
Neil Robinson Galliford Try
Mike Southall Galliford Try
Andrew Stotesbury Lendlease
The Temporary Works Forum gratefully acknowledges the contribution made by the working group and contributors in
the preparation of this guidance.
Acknowledgement or type of project, from conception to decommissioning.
Some of the information (e.g. tables, etc.) was supplied by The guide also contains suggested further reading
- and is the copyright of - Tony Gee and Partners LLP and and examples where the principles have been applied
may appear elsewhere. successfully.
Editorial note Disclaimer
The information provided in Chapters 6 to 8 is available Although the Temporary Works Forum (TWf) does its
in ‘Word’ format on the Temporary Works Forum (TWf) best to ensure that any advice, recommendations
website (www.twforum.org.uk . . . select . . . Resources/ or information it may give either in this publication or
Library Folders/TWfGuidance). These lists do not set elsewhere is accurate, no liability or responsibility of any
out to be prescriptive and should be amended to suit kind (including liability for negligence) howsoever and from
individual company operations and preferences. They whatsoever cause arising, is accepted in this respect by
may be updated from time-to-time (and the Secretary the Forum, its servants or agents.
invites contributions to them (secretary@twforum.org.uk). Readers should note that the documents referenced in
Synopsis this TWf Guide are subject to revision from time to time
and should therefore ensure that they are in possession of
This guide provides a definition of what is meant by the latest version.
“constructability”; guidance on the legal requirements
on clients and designers; and suggests aspects of
constructability that should be considered throughout the
project lifecycle. The principles can be applied to any size
2 Return to the contents
Constructability: A guide to reducing temporary works – TWf2020: 02 Temporary Works forum
Contents
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Section Page Section Page
1.0 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 8.4.1 Actions to be complete before
holding constructability review . . . . . . 19
2.0 Statutory legal aspects . . . . . . . . . . . . . . . . . . . 4
8.4.2 Aim of the constructability review: . . . . 19
3.0 Construction process . . . . . . . . . . . . . . . . . . . . 5 8.4.3 Actions to be carried out after
4.0 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 constructability review . . . . . . . . . . . . 20
5.0 Procurement models (UK) . . . . . . . . . . . . . . . . . 6 9.0 Summary and concluding remarks . . . . . . . . . 20
6.0 Constructability principles . . . . . . . . . . . . . . . . 8 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
6.1 Lean construction . . . . . . . . . . . . . . . . . . . . . . 8 Further reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
6.2 Low carbon design . . . . . . . . . . . . . . . . . . . . . 9 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
6.3 Off-site fabrication – aspects of construction Appendix 1: Other definitions and terms . . . . . . . . 24
that can influence the design . . . . . . . . . . . . 10 Appendix 2: Projects that benefited from early
6.4 Reasons to consider off-site construction . . . 10 contractor involvement . . . . . . . . . . . . . . . . . . . . . . . 25
6.5 How the components get to and 1. Bar Hill bridge deck . . . . . . . . . . . . . . . . . . . 25
across site . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2. Installation of bridge deck (A14) . . . . . . . . . . 25
6.6 The design of fabricated elements 3. Pre-cast slabs form viaduct deck . . . . . . . . . 25
required to be lifted or moved . . . . . . . . . . . . 11
4. Dover Western Docks Revival –
6.7 The handling and installation of New Marina Pier . . . . . . . . . . . . . . . . . . . . . . 26
pre-fabricated elements on site . . . . . . . . . . . 13
5. Dover Western Docks Revival –
7.0 When to consider constructability . . . . . . . . . 13 Wellington Dock Navigational Access . . . . . . 26
7.1 Notes on the practical aspects of 6. Blackfriars Thameslink Project . . . . . . . . . . . 27
carrying out constructability reviews . . . . . . . 15
7. Landmark, Manchester . . . . . . . . . . . . . . . . . 27
7.2 Who should undertake reviews . . . . . . . . . . . 15
Appendix 3: Good practice in BIM . . . . . . . . . . . . . . 29
7.3 Information . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Example 1 - Manchester Victoria Station . . . . . . 29
8.0 A methodological approach to
Example 2 - Birmingham New Street
constructability reviews . . . . . . . . . . . . . . . . . . 15
Station . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
8.1 Constructability at project initiation,
Appendix 4: Construction issues resulting
option development and selection . . . . . . . . 16
from aspects of the design . . . . . . . . . . . . . . . . . . . . 30
8.1.1 Constructability at project initiation . . . 16
8.1.2 Constructability at option A4.1 Stability of reinforcement . . . . . . . . . . . . . . 30
development and selection . . . . . . . . . 16 A4.2 Temporary piers . . . . . . . . . . . . . . . . . . . . 30
8.1.3 The importance of constructability at A4.3 Stability of precast element . . . . . . . . . . . . 30
project initiation, option development
A4.4 Precast concrete ceiling planks
and selection . . . . . . . . . . . . . . . . . . . 16
in a school . . . . . . . . . . . . . . . . . . . . . . . . . 31
8.1.4 Actions to be complete before
holding constructability review . . . . . . 16 A4.5 Insitu cast earth retaining wall –
8.1.5 Aim of the constructability review . . . . 17 concrete finish . . . . . . . . . . . . . . . . . . . . . . 31
8.1.6 Actions to be carried out after A4.6 Suspended ground floor slabs . . . . . . . . . . 32
constructability review . . . . . . . . . . . . 17 A4.7 Nearby buildings and party wall issues . . . 32
8.2 Constructability at preliminary and A4.8 Composite decking . . . . . . . . . . . . . . . . . . 32
detailed design . . . . . . . . . . . . . . . . . . . . . . . 17
A4.9 Reinforced concrete slab design/back
8.2.1 Actions to be complete before
propping . . . . . . . . . . . . . . . . . . . . . . . . . . 32
holding constructability review . . . . . . 17
8.2.2 Aim of the constructability review: . . . . 17 A4.10 Limited soil investigations . . . . . . . . . . . . . 33
8.2.3 Actions to be carried out after A4.11 Limited investigation of existing
constructability review . . . . . . . . . . . . 18 structures . . . . . . . . . . . . . . . . . . . . . . . . . 33
8.3 Constructability at pre-construction cost A4.12 Integrating permanent and temporary
estimate build up (‘tender’) . . . . . . . . . . . . . . 18 works design: needling and propping . . . . 33
8.3.1 Actions to be complete before holding A4.13 Integrating permanent and temporary
constructability review . . . . . . . . . . . . 18 works design: basements . . . . . . . . . . . . . 33
8.3.2 Aim of the constructability review: . . . . 19
Appendix 5: Construction issues resulting
8.3.3 Actions to be carried out after
from aspects of the site work . . . . . . . . . . . . . . . . . 34
constructability review . . . . . . . . . . . . 19
A5.1 Stability of reinforcement . . . . . . . . . . . . . . 34
8.4 Constructability at pre-construction stage (‘site
work’) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 A5.2 Precast concrete bridge fascia panels . . . . 34
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Temporary Works forum Constructability: A guide to reducing temporary works – TWf2020: 02
1.0 Introduction Regulation 4 - Client duties in relation to
This document aims to provide guidance to all managing projects
those in project teams on the consideration of 4.—(1) A client must make suitable arrangements
constructability. for managing a project, including the allocation of
1.1 The constructability of a project results from sufficient time and other resources.
decisions made by the client, architect, (2) Arrangements are suitable if they ensure
designer(s) and contractor(s) at the pre-project, that—
options, development, construction and (a) the construction work can be carried out, so
decommissioning/ demolition phases on aspects far as is reasonably practicable, without risks to
such as location, land-take, form, programme the health or safety of any person affected by the
and cost. project; ….
1.2 For the purpose of this guidance the following 2.2 In relation to designers:
definition is adopted1:
Regulation 8 - General duties
Constructability
8. - (1) A designer (including a principal designer)
“the extent to which the design of a building or contractor (including a principal contractor)
or construction project and its environment appointed to work on a project must have the
facilitates ease of construction, subject to skills, knowledge and experience, and, if they
the overall requirements of the building or are an organisation, the organisational capability,
construction project and its environment.” necessary to fulfil the role that they are appointed
Source: Network Rail Safe by Design, Guidance to undertake, in a manner that secures the health
Note – Early Focus on Constructability and safety of any person affected by the project.
and Temporary Works (2019) [1.]
Regulation 9 Duties of designers
1.3 This guidance makes recommendations for 9. - (2) When preparing or modifying a design
the stages when it is sensible to consider the the designer must take into account the general
constructability of the project. It also identifies principles of prevention and any pre-construction
some of the factors that affect constructability information to eliminate, so far as is reasonably
and which are common to many sites. Finally, it practicable, foreseeable risks to the health or
gives examples of projects where constructability safety of any person ….
has been considered early in the project
development and incorporated into the design; 2.3 The role of the designer is recognised in HSE
and other projects where details of the design Guidance:
have left room for improvement. “A designer has a strong influence during the
1.4 The practical result of considering constructability concept and feasibility stage of a project. The
during the development and design stages is that earliest decisions can fundamentally affect the
projects will be easier to build. health and safety of those who will construct,
maintain, repair, clean, refurbish and eventually
NOTE: A peer review may include some aspects demolish a building …”
of a constructability review.
Source: HSE, L153, Para 75 [3.]
2.0 Statutory legal aspects
2.4 CIRIA has published Construction work
2.1 Constructability should be considered by the sector guidance for designers (C755) [4.].
client, the designer(s) and the contractor(s). The The document has been produced to assist
legal aspects of constructability are many and designers in complying with CDM2015,
varied. The following extracts highlight key issues Regulations 8, 9 and 10. It provides a description
in the Construction (Design and Management) of the risks typically associated with various
Regulations 2015 (CDM2015) [2.]2 with which construction methods and how the designer can
the reader should be familiar: consider overcoming them.
1
‘Constructability’ isn’t new and other definitions and terms have been in use for many years. See Appendix 1.
2
CDM came effect first on 31st March 1995 as the Construction (Design and Management) Regulations 1994, following the introduction
of European Directive 92/57/EEC on the minimum safety and health standards for temporary or mobile construction sites. The
Regulations were, and still are, aimed at improving the overall management and co-ordination of health, safety and welfare throughout
all stages of a construction project. They place duties on all those who can contribute to the health and safety of a construction project:
clients, designers and contractors.
4 Return to the contentsConstructability: A guide to reducing temporary works – TWf2020: 02 Temporary Works forum
2.5 C755 states: f) replace the dangerous by the non-dangerous
“Designers have to weigh many factors as they or the less dangerous
prepare their designs. H&S considerations have g) develop a coherent overall prevention policy
to be weighed alongside other considerations, which covers technology, organisation of
including cost, fitness for purpose, aesthetics, work, working conditions, social relationships
buildability, maintainability and environmental and the influence of factors relating to the
impact. …” working environment
and provides a discourse3 on the issues that h) give collective protective measures priority
should be taken into account. over individual protective measures
2.6 It repeats the definition in L153 of what is meant i) give appropriate instructions to employees
by the term reasonably practicable4 and contains 2.9 In summary6, the legal context to the need to
some salutary advice 9 [emphasis added]: consider constructability has been around for
“There is a feeling that after an accident, many years. The concept is not new.
in retrospect, it is always obvious what 3.0 Construction process
more could have been done to prevent
it occurring. Any decision in which cost 3.1 The construction process is the delivery of the
plays a major part will be likely to be (in whole permanent works. The permanent works
retrospect) particularly criticised.” are usually an assembly of component parts.
There is an interdependent relationship between
2.7 BS 5975: 2019 [5.], states: the choice of component and method of
8.1.2 Designers should address the buildability assembly.
of permanent works, temporary works, 3.2 Components are defined by their material,
their interfaces, their proposed methods size, shape, weight and structural properties.
of construction and any related design These may be dependent on the manufacturing
assumptions. process, any post-processing assembly, the
8.3.1 Permanent works designers should weight that can be lifted, the position that they
address the buildability of the permanent can be supported in during the temporary
works and identify, and make provision stage(s), the stability of the component(s) under
for, any temporary works and temporary their own self weight and environmental loads
conditions required by their design and and the way in which they are incorporated into
their assumed method of construction … the other permanent works.
2.8 The Management of Health and Safety at Work 3.3 These are in turn affected by the availability of
Regulations 1999 [6.] were the first to set out the raw materials, skilled workforce, manufacturing
requirements for ‘risk assessment’ (Reg. 3) and facilities, transport, the type and size of plant
introduced the ‘general principles of prevention’ and any limitations on access and egress
(Reg. 4). The latter are summarised in CDM2015 arrangements. Where transport is problematic
[3.] as an hierarchy5: the smallest transported components are - for
a) avoid risks example - clay bricks, bagged cement, steel
reinforcing bars, locally won sand and aggregate,
b) evaluate the risks which cannot be avoided locally sourced timber. It may also be feasible
c) combat the risks at source to set up on site pre-assembly manufacturing
facilities (e.g. from concrete batching plants
d) adapt the work to the individual, especially
to production lines for match-cast segmental
regarding the design of workplaces, the
concrete bridges).
choice of work equipment and the choice of
working and production methods, with a view, 3.4 Constructability exists on a varying scale
in particular, to alleviating monotonous work, and every structure (or building) has overall
work at a predetermined work rate and to requirements which may necessitate some
reducing their effect on health degree of compromise.
e) adapt to technical progress
C755, Section 1.4.6
3
4
The term ‘reasonably practicable’ has been defined as: “balancing the level of risk against the measures needed to control the real
risk in terms of money, time and trouble. However, you do not need to take action if it would be grossly disproportionate to the level of
risk. (See www.gov.uk/risk/faq.htm for the most up to date explanation of what ‘reasonably practicable’ means)” (Source: Glossary of
acronyms and terms, L153 (HSE, 2015) [3.])
This hierarchy is often referred to as ‘ERIC’ – Eliminate, Reduce, Inform and Control
5
There may be commercial and/or contractual aspects in the delivery of a project, not considered here
6
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3.5 In some instances, a design which increases to input ideas at an earlier stage, enabling
the material content of the permanent works more effective communication, improving
but reduces the need for temporary works may design empathy for production and simplifying
be safer, less disruptive, more cost-effective, construction techniques. In some cases the
more carbon-efficient and cheaper. For example, Client enters into a contract with a single
the overall combination of factors should be administrative party who then delivers the whole
aggregated and where a more substantial project. In theory, the designer and constructor
permanent works solution might significantly are an integrated team with the function of
reduce the temporary works required then delivering the project (CIRIA C534 [9.]).
this should be given due consideration as the 4.3 There remain some challenges in the UK of the
preferred solution, particularly where it results in resulting arrangements, which do not appear
reduced construction time and risk exposure on to have delivered all the improvements sought8,
site. but in respect of the consideration of temporary
3.6 Decisions made about the design of the works these forms of procurements have
permanent works have a fundamental impact on advantages.
the materials available, even at early stages. 5.0 Procurement models (UK)
3.7 The plant and techniques which are available to 5.1 There are now several programme management
the constructor evolve constantly. For instance, in models within the UK construction industry which
the 25 years since the drafting of CIRIA R155 [7.] define the progress of the project through the
and CIRIA C543 [8.] there has been an increase stages from initial briefing to final completion,
in the capacity of cranage, allowing larger parts including:
of the construction to be prefabricated/pre-
assembled and lifted into position (so minimising • Network Rail ‘Governance for Railway
the need for insitu falsework and formwork and Investment Projects (GRIP)’ (2018) [10.]
reducing the impact on the site) as well as self- • Highways England ‘Project Controls
propelled modular transporters (SPMTs). Framework’ v4 (2018) [11.]
4.0 Background • Royal Institute of British Architects (RIBA) ‘Plan
Constructability; temporary works; safety; of Work’ (2013) [12.]
construction methodology • Office of Government Commerce ‘Gateway
4.1 For many years the typical form of procurement Review Process’ (2011) [13.]
was for a Client to have separate contracts with • Institution of Structural Engineers ‘The
the Engineer and Contractor. The Contractor built Structural Plan of Work’ (2020) [14.]
what the Engineer specified and there was little
5.2 All the procurement methods follow a similar
opportunity to suggest improvements in design
pattern (see Figure 1):
which would increase buildability and reduce
cost, risk and project duration. This contract • pre-project
arrangement was also thought to lead to poor • options phase
project delivery, quality of finished construction,
• development phase
delays, cost overruns and claims7.
• construction phase (to ‘completion’ or
4.2 These issues led to a general change in the
‘hand back’)
typical forms of procurement to the Early
Contractor Involvement (ECI) and Design and • use phase (including operation and
Build (D&B) contracts common today. The maintenance)
intention is that the constructor is allowed • decommissioning / demolition phase
7
UK: Emerson 1962; Banwell 1964; EDC 1967; Wood 1975; CIRIA 1983; CIRIA 1989; Latham 1994; Egan 1998; USA: ASCE 1974; CII
1986; CII 1987; Australia: Gyles 1992
8
NAO 2001; RCTF 2001; SFC 2002; NAO 2005; Wolstenholme 2009; Laidlaw 2012; May 2013; CO 2013; HMSO 2013; Public
Accounts 2016
6 Return to the contentsEnd of
Construction
Pre-project/ Initiation Options phase Development phase Use/operation use and
phase
demolition
Return to the contents
Decision point:
HE Project 0 6
1 2 3 4 5
Control Strategy Construct, 7
Option Option Preliminary Statutory Construction
Framework shaping and commission Closeout
identification selection design procedures preparation
(PCF) 2008 prioritisation and handover
and powers
6 7
1 3 4 5 8
Network Rail 2 Construct, Scheme
Output Option Single option Detailed Project
GRIP Feasibility test and hand
definition selection development design closeout
commission back
6
0 1 2 3 4
Constructability: A guide to reducing temporary works – TWf2020: 02
RIBA Plan of 5 Handover 7
Strategic Preparation Concept Developed Technical
Work 2013 Construction and In use
Figure 1 - Summary of some programme management models (UK)
definition and brief design design design
closeout
Stage 5
Stage 6
Construction Stage 3 Stage 4 (Manufacture,
Stage 1 Stage 2 (Handover Stage 7
Industry (Design (Production installation and
(Preparation) (Concept) and (In use)
Council (CIC) development) information) construction
closeout)
information)
model for this stage (from pre-project to implementation)
End of use, decommissioning and demolition may have such significant
The Structural 5
0 2 3 4 4.5
Plan of Manufacturing 6 7
Strategic Concept Spacial Technical Production
consequences that it is appropriate to use the full project/ programme management
Work 2020 and Handover In use
definition design coordination design information
(IStructE) construction
7
Temporary Works forumTemporary Works forum Constructability: A guide to reducing temporary works – TWf2020: 02
5.3 The consequences of the end of use, i.e. the management; quality assurance; operational
decommissioning and demolition phases, may research; and lean manufacturing.
in themselves be significant enough that it would 6.1 Lean construction
be appropriate to consider all these stages in this
approach, e.g. from pre-project through to use 6.1.1 ‘Lean’ in its simplest form means eliminating
(including operation and maintenance). waste from everything we do.
5.4 Irrespective of the management model adopted, 6.1.2 Essentially, ‘lean’ is a collection of ‘Work Study
constructability reviews should be undertaken. and Operational Research’ techniques some
of which have been used for decades. These
6.0 Constructability principles techniques have been used by contractors
There have been many works published recently to gain a competitive edge. It has now been
on the subject of “Lean Construction”. However, re-branded and is covered by a suite of CIRIA
the application of science to manufacturing is not guides11. One of most valuable concepts is the
new. To help achieve a sense of perspective, the definition of waste in CIRIA C730 [15.] (see
following are offered: Figure 2):
Charles Babbage (1791-1871)9 6.1.3 Applied simply to construction:
Charles Babbage was credited as the inventor of Value adding (VA) = permanent works
the digital (mechanical) computer and his ideas Essential non-value = temporary works
helped shape the “Industrial Revolution” as well adding (enVA)
as the Victorian expansion in manufacturing.
Waste = waste and inefficiency
Fredrick Taylor (1856-1915)10
Fredrick Taylor was one of the first Management
Consultants. His legacy to us is: knowledge
Any work activity will comprise
all three elements of work. It
adding (VA) content will be a
lot less than other elements.
Operator time
When improving the way
work is carried out:
Step 1: aim to eliminate waste
Waste EN VA VA Step 2: improve the way
ENVA is carried out
E liminate Reduce of VA
Lean improvement reduces
Increased capacity the time taken to carry out
to do more work a particular task, releasing
more capacity: ‘more for the
same’ or ‘more for less’.
Figure 1.1 Eliminating waste
Figure 2 – Defining waste
Source: CIRIA C730, Lean tools and techniques – an introduction
9
Babbage wrote, “On the Economics of Machinery and Manufactures” (1832). This book described differentiating task with skills, bonus
systems, “piece work” and profit sharing. His ideas are said to have influenced Marx.
Taylor wrote the very influential book, “The Principles of Scientific Management” (1911). It is reported that his principles have been
10
adopted by everyone from Henry Ford to Lenin, Trotsky and Stalin.
CIRIA: Implementing Lean in Construction (RP978); Build Lean (C696); Lean construction and BIM (C725); Lean and the sustainability
11
agenda (C726); Lean benefits realisation management (C727); A Lean guide for client organisations (C728); Selecting and working with
a Lean consultant (C729); Lean tools and techniques – an introduction (C730); Health and Safety Synergies of Lean (C769)
8 Return to the contentsConstructability: A guide to reducing temporary works – TWf2020: 02 Temporary Works forum
6.2 Low carbon design 6.2.4 The permanent works designer (PWD) needs
6.2.1 The term embodied carbon is used to describe to engage with the temporary works designer
the greenhouse gas (GHG) emissions associated (TWD) to ensure greater consideration of
with the production of materials or products constructability, e.g. through constructability
to the factory gate. Carbon dioxide equivalent reviews.
(CO2e) is used as a proxy for the impact of
different greenhouse gases included in carbon
assessments. In line with PAS 2080: 2016,
Carbon management in infrastructure [16.],
carbon assessments should consider the whole
life of the asset from manufacture of materials, VA enVA
through construction, operation and end of life.
To this end the trade-offs between more carbon
intensive stages can be made with other lower • Lowest VA – Design driven by lowest material
carbon stages. However, often the scope is cost: low material cost, but may have high
limited to embodied carbon assessments that are
construction cost
carried out without consideration of construction
techniques or temporary works.
VA enVA
6.2.2 Cost is also subject to the some of the same
drivers as carbon (In general terms more
embodied carbon equals more cost [17.]). This
• Lowest enVA - Design driven by lowest
can lead to designs which at first sight appear construction cost: material costs may be higher,
efficient because they have low “Value Adding” but the construction costs are lower
(VA) content but require more temporary works - • The overall cost of the project is a combination
“essential non-Value Adding” (enVA) - content to of material and construction costs. A project
with greater material content may be
construct them. sufficiently lower in construction cost for this
to be the most economic solution
6.2.3 It may be cheaper overall - and therefore produce
less embodied carbon - to construct permanent
works with a higher material content and which Figure 3 – Consequences of different
requires less temporary works, i.e. is easier to approaches to constructability
build (see Figure 3 and Figure 4).
In this instance the designer
aimed to make savings by
reducing the thickness of
the abutment wall below the
level of the bearing shelf.
While reducing the
concrete content of the
PROFILE FINISH
wall the complexity of the
reinforcement detailing and
the formwork costs were
increased.
A straight wall would have
resulted in simpler and
cheaper reinforcement,
reduced formwork costs,
exposure to less risk and
faster construction.
Figure 4 – Example of a design driven by material reduction rather than constructability
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6.3 Off-site fabrication - aspects of construction • Presence of obstructions, e.g. something
that can influence the design already on site, especially if an existing
6.3.1 The plant available for construction is constantly structure is being replaced.
evolving. • Potential for an improvement in programme
6.3.2 Developments in fabrication facilities, delivery, e.g. working on several different parts
transportation and means of placing (e.g. of the project concurrently.
larger cranes, SPMTs) allow structures to be • Protection from the environment during
constructed from components of greater size. fabrication.
This can reduce the need for in-situ falsework • Potential reduction production costs.
and formwork and so reduce the work on the
site. • Improved quality control, e.g. concrete
finishes, welding, etc.
6.3.3 Sections 6.4 to 6.7 list some of the aspects of
the construction process that can influence the 6.5 How the components get to and across site
design for off-site fabrication: 6.5.1 There are many issues to be considered when
• Reasons to consider off-site construction (see assessing any access route(s), i.e. how the
6.4) components get to and across site:
• How the components get to and across site • Components and/or plant being delivered to
(see 6.5) and across site:
• The design of fabricated elements required to • weight
be lifted or moved (see 6.6) • dimensions including protrusions
• The handling and installation of pre-fabricated • number of vehicles
elements on site (see 6.7)
• Restrictions on the existing route:
6.3.4 Similarly, some of the design choices will affect
• width; height restrictions under, through
the construction. They should be adapted by the
bridges and/or tunnels; between buildings
reader to suit their own project-specific needs.
• length restrictions, e.g. tight bends, street
6.3.5 Designers should be aware of the problems
furniture
the Contractor will face. However, to obtain
the best solution dialogue with the contractor • gradient of road route
(a construction method specialist) should be • weight restrictions, e.g. bridges, roads
arranged.
• availability of railway (viz. route availability
6.4 Reasons to consider off-site construction (RA) rating)
6.4.1 There are many reasons to consider off-site • whether permits are required to use the
construction: route (and how long they will take to obtain)
• Enhance safety - e.g. to avoid building at • can bollards, etc. be removed temporarily
height or over water; avoid live transport to assist the movement of Abnormal
routes. Indivisible Loads, by agreement with the
• Less interfaces to manage on site. relevant highway authority
• Potential reduction in the amount of temporary • Is the route affected by tides?
works required on site (and the associated • This will affect the timing of operations
reduction in risk exposure for site workers)
• Is the route in the inter-tidal zone?
• Absence of foundations and working space
• This significantly restricts the access by
available beneath the structure, e.g. in rivers,
both land based and floating plant
over valleys, on poor ground, or above roads,
railways, sewers and tunnels. • How exposed is the route to weather (and will
it flood or become blocked by snow)?
• Potential disruption to adjacent sites, e.g.
when working near or over railways and/or • Resilience of the route
roads. • Will it deteriorate rapidly under adverse
• Absence of or unsuitable working space weather? Will it take the traffic?
adjacent to (or above) the structure, e.g. in • Speed
a congested city centre site, near airports,
• Can the route accommodate the number of
under overhead lines.
vehicles in the required duration?
• Limited period of access to the site, e.g. rail or
road possession, tidal working.
10 Return to the contentsConstructability: A guide to reducing temporary works – TWf2020: 02 Temporary Works forum
• Do precast concrete elements have
Example 1 – Bringing in material by rail protruding reinforcement?
The Birmingham New Street Gateway • Does the load have to be tilted?
programme was a £650m refurbishment
of the old railway station into an iconic • Can the element be transported in its
permanent orientation such that it does
passenger Hub; completed whilst keeping the
not have to be adjusted when lifted into
operational railway working at all times in a
position (e.g. a bridge beam for placing
very congested city centre site.
on abutments at different levels can be
In order to maximise project efficiency and transported on temporary supports that
minimise the effects on the neighbourhood have the same level difference as the
an early decision was made to deliver most permanent supports)?
materials/small plant - and remove most • What is the structural and material form of the
waste products - by train. Only one of 12 load to be moved?
platforms could be closed at any time, so
• What is its strength and rigidity?
the closed platform was utilised to receive
materials at the start of each shift and remove • If considering prefabricating or lifting
waste at the end. reinforcement cages, remember that
reinforcement ties are poor structural
Materials and plant were delivered to and
connections
stored at the Bordesley sidings, just outside
the city centre, minimising disruption • If the element is made from concrete,
throughout the project. what strength should have been
achieved before handling?
This was a good example of thinking
• How is it supported before moving?
strategically at an early stage in order
to facilitate efficient construction, whilst • Where are the attachment points?
minimising the impact on others. • What is the maximum reaction at each
attachment point?
• The proximity of being able to bring in material
• Is relative movement between supports
by rail (see Example 1)
(temporary and permanent) important?
• The need for haul roads and/or temporary
• Will load be transmitted through two, three or
bridges
four points?
• The impact on residents in the urban
• Can it rock on just two supports (e.g. when
environment
considering 4 lifting points theoretically
• Splice positions: equidistant from the centre of gravity,
• Ensure that they are in the most due to minor variations in setting out, all
appropriate and optimal area the load could be taken by only 2 lifting
points)?
• Contingency plans, e.g. redundancy;
alternative delivery methods: • Will the load need to be stored in a temporary
position on site prior to be lifting into its
• Ensuring that there is a robust approach to permanent position?
minimise failed manoeuvres
• What type of area is required for storage
6.6 The design of fabricated elements required purposes?
to be lifted or moved
• How will the load be supported after placing?
6.6.1 There are considerations for the design of
fabricated elements required to be lifted or • Will it be supported immediately, without
moved12: the need for grout to set?
• What is the size, weight and position of the • It must be lined and levelled accurately.
centre of gravity (CoG)? Does the detailing allow for this? Temporary
jacks can be used for fine adjustment
• The point of application of the lift must pass
through the CoG, or movement will take • The temporary supports and any
place; the load will slew, twist or rotate (see permanent works they are attached
Figure 5) to, must have adequate strength and
stability for all ongoing environmental and
NOTE: The position of the CofG varies construction loads (e.g. accidental impact,
during the assembly of component parts wind and hydrostatic concrete loads), until
incorporated into the permanent works.
See also ‘Precast concrete: Good practice and common issues in temporary works’ (TWf2019: 01, TWf, 2019) (https://www.twforum.
12
org.uk/viewdocument/precast-concrete-good-practice-and)
Return to the contents 11Temporary Works forum Constructability: A guide to reducing temporary works – TWf2020: 02
• Can it be adequately supported about its • Have lifting checks been made in all temporary
CoG? Is there any novelty in the design states (i.e. at all stages and not just off-site)?
of the permanent works which makes the • Is off-line construction an option, e.g.
temporary support particularly difficult (e.g. bridge slides, transportation by SMPT or
inclined members, cantilever members)? bridge launches (where the road is diverted/
• How is the member required to connect with constructed afterwards)
the existing structure? • Consider temporary states of the
• Will protruding reinforcement clash with permanent works
existing reinforcement? • For multiple lifting operations, ensure the
• How will the component be lifted? attachments are designed to suit
• Are screw-in loops (eyes) required? Has the • For complex lifts load compensating devices
size and position been required, in order to may be required
accommodate later construction? • Consider the possibility of redundancy in
• Consider the stability of modules lifting equipment
• Are braced beams required?
NOTE: Beams in pairs are preferred to an
odd number of beams
• Have any splice positions been
considered?
Figure 5 - Example of eccentric lift. Centre of gravity is very close to lifting eye
NOTE: If the hook is not directly above the centre-of-gravity the load will rotate
(In this example, unequal chain lengths were used to achieve a level lift).
12 Return to the contentsConstructability: A guide to reducing temporary works – TWf2020: 02 Temporary Works forum
6.7 The handling and installation of pre- • Consider the stability of precast concrete
fabricated elements on site beams13 and steel girders
6.7.1 The considerations for handling and installing • These may be separate or combined
fabricated elements on site include: • Are trial lift(s) and/or erection required?
• Will pre-fabrication result in ‘locked-in’ • When lifting, consider the access required at
stresses in the permanent works? any landing points to make connections and
• Consider the effect of the construction remove lifting chains
sequence on the final arrangement • Can cross-bracing of girders and similar
• Have all the construction load cases been features required during the temporary state
considered, e.g. prior to composite action be left permanently in place as sacrificial
being achieved elements to reduce dismantling works?
• Include horizontal loads 7.0 When to consider constructability
• What is the availability of plant? It is suggested that there is benefit in carrying
• How does this affect the robustness of the out a formal constructability review at each of the
programme to meet the installation date? four phases of the procurement management
model (see Figure 6):
• What size vehicle is required?
• pre project/ initiation (see 8.1.1)
• Consider:
• options (see 8.1.2)
• Dimensions including protrusions
• development (see 8.2 and 8.3)
• Weight
• construction (see 8.4)
• Applied ground bearing pressure
These are considered in more detail in Sections
• What space and/or additional cranage 8.1 to 8.4. It may be appropriate to have a
requirements are necessary for rigging and number of constructability reviews during the
de-rigging large cranes same phase. These can have the same goal (e.g.
• Consider space for additional ballast, as an aid to the selection between alternatives
delivery vehicles and turning circles during the initiation phase) or be different (e.g.
as in the development phase when the design
• What is the direction, distance and height to
develops from preliminary design to a pre-
be moved?
construction cost estimate).
• Are there changes in direction of travel and
The design develops by a succession of choices
slope or fall?
between alternative solutions. As the alternatives
• What are the site conditions? are considered and preferences selected the
• What are the ground conditions, design and detail become more defined. At each
topography and foundation requirements? phase the choice of alternatives is limited by the
preceding decisions. As the definition increases
• Are there constraints from adjacent sites, the range of possibilities for future choices
such as headroom near airports, over reduce, until eventually the design is completely
railways or near nuclear facilities? defined.
• What is the route of transportation (e.g. If, after considering constructability, a decision
road, rail, river or sea) and what limitations on which the design has been based needs
does this route impose? to be changed, this may invalidate the design
• Is on-site assembly of sub-assemblies work that had been based on it. The earlier
constructed off site required? the original decision was made, or the later
the change is made, the more chance there is
• How many items need to be moved, e.g. one-
that it would affect other parts of the design;
off move or multiple items?
and the more re-working necessary. The earlier
• Is speed critical (both programme duration that constructability is considered in design
and velocity)? development, the more opportunity to influence
• What site storage is required? the design and the less need for reworking.
• Is delivery ‘just in time’? It should be noted, there is evidence from past
projects that constructability was undertaken well
• Are there environmental constraints, e.g. during some stages but was absent from others
weather, tide and season? (e.g. considered well at the design options stage
• What provides the fail-safe in case of but undertaken poorly at the design stage).
malfunction?
• Is there any aspect in the design of the
permanent works which makes its temporary
support particularly difficult?
13
Technical Advice Note: Handling of Bridge Beams on Site (PCA) (Now available at: https://www.twforum.org.uk/viewdocument/
technical-advice-note-handling-of)
Return to the contents 13Temporary Works forum Constructability: A guide to reducing temporary works – TWf2020: 02
High Influence Low Influence Results
Low Cost High Cost
100% 100%
Decreasing Increasing
influence cost
0% 0%
Project Time
Pre project/ Options Development Construction Use / End of use
initiation phase phase phase Operation and
demolition
HE Project 0 Strategy, 1 Option 2 Option 3 Decision 5 6 Construct, 7 Closeout
Control shaping and identification selection Preliminary point: Construction commission
Framework prioritisation design 4 Statutory preparation and
PCF 2008 procedures handover
and powers
Network Rail 1 Output 2 Feasibility 3 Option 4 Single 5 Detailed 6 Construct, 7 Scheme 8 Project End of use,
GRIP definition selection option design test, handback closeout decommis-
development commission -sioning and
demolition
may have
such
significant
2013 RIBA 0 Strategic 1 2 Concept 3 Developed 4 Technical 5 6 Handover 7 In use consequences
Plan of Work definition Preparation design design design Construction and closeout that it is
and brief
appropriate
to use the
full Project /
programme
Construction Stage 1 Stage 2 Stage 3 Stage 4 Stage 5 Stage 6 Stage 7 (in management
Industry (Preparation) (Concept ) (Design (Production (Manufacture, (Handover use) model for
Council Development) Information) Installation & and this stage
(CIC) Construction closeout) (from pre
Information) project to
impementation)
The 0 Strategic 1 2 Concept 3 Spatial 4 Technical 4.5 5 6 Handover 7 In use
Structural definition Preparation design Cordination design Production Manufacturing
Plan of Work and brief Information and
IStructE Construction
2020
8.1.1 8.1.1 8.1.2 8.2 8.2 8.3 8.4
Project Project Options Preliminary Detail Tender Project
Initiation Initiation Selection Design Design Construction
Figure 6 - How a constructability review can improve the design of permanent works
NOTE: A diagram – based on figure 1 – showing the idealised change in the influence and cost of design and
constructability decisions on the project cost with respect to project duration, overlaid with project
procurement management model and suggested opportunities for formal constructability reviews
14 Return to the contentsConstructability: A guide to reducing temporary works – TWf2020: 02 Temporary Works forum
7.1 Notes on the practical aspects of carrying 7.2 Who should undertake reviews
out constructability reviews 7.2.1 To be considered an effective way of ensuring
There are a number of issues to consider: constructability, at any stage, constructability
Positives: reviews should be undertaken by all parties to a
project, bringing together different expertise from
7.1.1 Constructability reviews: all duty-holders:
• should be polite and inclusive; • project manager;
• can be a team-building exercise, when done • client;
well;
• permanent works designer (consultant);
• will highlight issues which may affect safety,
operations, temporary works requirements, • construction expert (temporary works);
etc. and may inform ‘design change’; • principal designer;
• should consider the likely impact on • specialist construction experts (e.g.
neighbours and test whether the proposals proprietary suppliers);
have the potential to disadvantage particular • stakeholder technical representative(s);
groups in the community;
• facility operator;
• can enable efficiency for design and execution
of the works, enable contingency plans to be • safety expert(s).
developed and will troubleshoot issues before 7.2.2 Sometimes, the best constructability advice
they get to site. comes from the site team, e.g. foreman.
7.1.2 A constructability review can also: 7.3 Information
• ‘de-risk’ a project by ensuring that it can be 7.3.1 The project needs to be defined to a sufficient
constructed and in what sequence (allowing a level of detail to be able to carry out a
better focus on the most effective options); constructability review. This information may take
• facilitate early identification of temporary works the form of reports, surveys, archive information,
requirements, to enable early procurement; calculations, drawings and models.
• facilitate the production of temporary 7.3.2 Building Information Modelling (BIM) - see
works solutions that suit chosen temporary Appendix 3 - can be an effective way of
conditions and sequencing; capturing, collating and presenting this
information14.
• enable early decisions to be made on whether
the permanent works design can be amended 8.0 A methodological approach to
to improve constructability; constructability reviews
• improve constructability to facilitate improved Sections 8.1 to 8.4 show a methodical approach
safety, programme and cost. to reviewing constructability. They identify the
stages when a constructability review may be
Hazards/pitfalls: useful and list some of the pre-requisites, aims
7.1.3 It should be remembered that: and outputs of the review process.
• There is more than one way to build The items listed and the topics covered should
something and different construction experts be adapted and changed to suit the requirements
may have preferred techniques; of a particular project.
• The people best at constructing are most More than one constructability review may be
likely be on site constructing - the most required during each stage of the project delivery
experienced or best construction expert(s) process. For example, it may be appropriate to
may be not be available for the constructability have a constructability review at the preliminary
review; design stage and another at detailed design.
• The continuity of construction experts It is expected that as the use of BIM develops
at subsequent constructability reviews within the industry it will become a key tool
may depend upon staff retention and the in carrying out and recording constructability
contractor’s work commitments. reviews.
14
The TWf [September 2020] is preparing some advice, ‘An open standardized approach to the management of temporary works design
– digital collaboration’.
Return to the contents 15Temporary Works forum Constructability: A guide to reducing temporary works – TWf2020: 02
It is important to identify early on any technical
NOTE: Engineering assurance and approval authorities, e.g. highways, rail. Large
constructability reviews clients may have their own technical approval
Large infrastructure organisations such as process and should be engaged.
Network Rail and Highways England have 8.1.2 Constructability at option development and
engineering assurance processes that seek selection
to de-risk designs against numerous criteria -
Design development and options selection GRIP
such as maintaining open railways and open
1/2/3; RIBA 0/1/2; HE 0/1/2
roads as far as is reasonably practicable – in
order to minimise the effects of repairs and The brief (requirements) should be identified.
enhancements on rail and road users. Consider the variety of options (forms)
developed, e.g. location, number of spans,
Undertaking constructability reviews will
concrete or steel, practicalities, sequence of
enable the project team to home in on the
construction, aesthetics, etc.
most appropriate, constructible solutions and
ensure operations continue without undue The deliverability – in addition to
disruption. constructability - should also be assessed. A
project risk workshop may, for example, be
Such procedures call for schedules of
the way to do this. This process may repeat in
temporary works to be developed, to include
later stages.
the following:
8.1.3 The importance of constructability at project
• location/description of temporary works
initiation, option development and selection
• design check category
If constructability and temporary works are not
• high- or low-risk check category for work considered from the outset the structure may be
package planning very difficult (unsafe) and/or impossible (too risky)
• confirmation and consideration of to build; as well as too expensive.
coordination between all permanent and Decisions on land-take, programme and
temporary works aesthetics taken at the project initiation
• dates for submission and acceptance for and option development stages will have a
deliverables fundamental impact on the delivery of the
scheme, e.g. space for site access and cranage,
• details of temporary work design
key possession dates and length of programme.
organisation
The designer may introduce risks that could be
• details of interdisciplinary interfaces
avoided or increase exposure. CIRIA C755 [4.]
• requirements for inspections and testing advises:
A constructability review will enable early • “Designers would be wise to stray on the
determination of the need for such works. side of caution – especially when considering
significant (‘life or death’) risks because after a
8.1 Constructability at project initiation, option death legal analysis of reasonableness will be
development and selection tinged by the reality and emotion of what has
actually happened …
8.1.1 Constructability at project initiation
8.1.4 Actions to be complete before holding
Grip 1, RIBA 0, HE 0
constructability review
It is never too early to consider constructability;
The following actions should be completed:
and as early as project initiation stage. A
constructability review at this stage should be a • Functional requirements established
swift process, as there will be many unknowns • Alternative geographical locations identified
and many options to home in on. Such a review
• Stakeholders identified
will enable appropriate conversations about how
a proposal can be built; to test its feasibility for • Value criteria established
construction. • Outline solutions determined
As early solutions are developed, the basics will • Options preliminary design and feasibility
then be better understood and key decisions can
be made in principle, e.g. access arrangements, • Site investigation(s) carried out
logistics, materials storage, cranage. This will • Restrictions on timing and boundaries of
enable key issues to be resolved, e.g. the need site possession identified, e.g. rail interface,
to buy or hire land owned by others to facilitate airport/flightpath, tidal working, nearby power
construction in good time. transmission
16 Return to the contentsConstructability: A guide to reducing temporary works – TWf2020: 02 Temporary Works forum
8.1.5 Aim of the constructability review 8.2.1 Actions to be complete before holding
The aim of the constructability review is to constructability review
determine: The following actions should be completed:
• whether the project can be built safely in the • Form of structure established
time allowed • Geographical locations established
• construction materials and methodology • Stakeholders engaged
• what specialist plant and contractors are • Check that value criteria are being met
required
• Determine outline solutions
• what geotechnical work has to be carried out
• Advanced the options preliminary design
• the obstacles that must be overcome
• Identify interfaces between functions of works
For example, site access and egress (e.g.
timings: tides/possessions; environmental, site of • Identify interfaces with other contracts
special scientific interest); weather and seasonal • Carry out further site investigation(s)
conditions (e.g. monsoon season, school term
• Draw up a schedule of site possessions
times)
8.2.2 Aim of the constructability review
• major items of temporary works; better
still, what can be done to design them out The aim of the constructability review is to
(elimination) determine:
• potential logistics problems • Method for choosing the location of
construction joints
For example: can the materials and resources be
made available; where will they be coming from; • Determine the size of pre-assembled
does a mine, quarry or borrow-pit need to be components to be delivered to site
established; do people need to be trained • Method of handling (craning) pre-assembled
• potential transport problems components.
For example: can the materials and resources be NOTE: If reinforcement has to be pre-
delivered to site at the correct time fabricated, how will the reinforcement cage
temporary structure be designed?
• any sources of uncertainty
• Method of connecting pre-assembled
8.1.6 Actions to be carried out after
components
constructability review
• Method of supporting pre-assembled
The following actions should be completed:
components before they become incorporated
• best (compromise) solution chosen from into the works and are self-supporting
options
NOTE: This includes reinforcement, steelwork
• safety case developed and precast concrete
• hazard identification carried out • Method of providing strength and stability
• risks designed out or reduced during early maturity (e.g. concrete strength
for slip-forming)
• risk register developed
• Method of providing stability during early
8.2 Constructability at preliminary and detailed stages of construction
design
For example: additional bracing in composite
Development phase: GRIP 4/5; RIBA 3/4; HE bridges where the steel beams would rely on
3/4/5 the deck to restrain the top flange; longitudinal
Consider the form to be chosen: For example, restraint of continuous span bridges that are
sequence of construction; bearing details (and constructed in incremental spans
temporary fixity/restraint); thermal movements; • Assess the stability of any existing structures
residual stresses; temporary support to follow on during the works, e.g. masonry walls upon
construction (e.g. temporary support to precast; removal of any adjacent walls, roof or floor
precast acting as formwork resisting hydrostatic support; the support of wet concrete on
loads; precast acting as edge protection); masonry walls; wind loading on previously
unsupported reinforcement; correct poor protected walls and/or structures
buildability; eliminate unnecessary temporary
works.
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