Civil Engineering Reference
In-Depth Information
5.3.6 Service life and sustainability considerations
The concepts and processes required to balance the various and
potentially conflicting components of sustainable construction
have collectively been termed 'lifetime engineering'. Research
in this field is leading towards the development of an integrated,
holistic approach to the design and management of buildings
and structures which takes account of all aspects of design and
construction practice, including recognising the benefit of inte-
grated teams and supply chains. This type of approach is seek-
ing to encompass both cost-driven and sustainability-driven
initiatives aimed at delivering sustainable construction at an
affordable life-cycle cost. It should also be recognised that
through careful and intelligent choices, good design solutions
for constructed assets that achieve a lower overall environmen-
tal impact can potentially be made even with materials that
have a relatively high environmental impact per tonne. Voo and
Foster (2010) present several examples where such a design
approach produces a more sustainable solution. They compare
the use of ultra-high performance concrete, which has a sig-
nificantly higher environmental impact per tonne, with con-
ventional Portland cement concrete, firstly, for a 40 m span
highway bridge in Australia and, secondly, for a 1.5 m high
retaining wall to a monsoon storm water drain.
Service life design concepts (see Boxes 5.4 and 5.5) can
be key facilitators for the delivery of sustainable construction.
When used in conjunction with appropriate conceptual and
detailed design, in association with properly planned and deliv-
ered execution, it can help meet the owner's needs in terms of
the performance of the structure over its lifetime in an economic
manner. An important facet of a sustainable construction strategy
is the quality of construction and whether this is appropriate for
the envisaged service life requirements of the structure. Failure
in sustainability terms can arise from both over- and underd-
esign. For example, overdesign might occur where more or
higher quality materials have been used than are needed to meet
the design requirements. It might also arise through underdesign
or as a result of poor quality materials, design or workmanship
which results in the need for premature repair or replacement.
Significant progress towards these overall objectives can be
made by making relatively simple, but intelligent, decisions
about design and detailing, taking account of the characteris-
tics of the structure's service environment. Overwhelmingly
these considerations involve the control of water and limiting
the access of moisture to the structure. It is suspected that con-
siderable improvements could be achieved simply by getting
more of the 'basics' correct, without recourse to special mate-
rials or sophisticated analyses of failure mechanisms.
A service life design approach provides a basis for addressing
many aspects of these issues. The key elements of the service
life design system are reproduced in the list below. These items
act as a reminder that durability problems can arise as a result
of deficiencies which occur in any one of a number of stages
throughout the design, specification and construction process.
Owner brief.
■
■
Assessment of environmental loads.
Definition of required performance under environmental loads.
■
■
Development of project specification.■■
Conceptual and detailed design phases.
■
■
Execution of works.
Through-life care and maintenance.
■
Figure 5.10
presents a simplified schematic diagram of the
overall design and construction (execution) process for a con-
structed asset, with associated links to the service life design
process being shown on the left-hand side of the diagram and
construction process sustainability related activities being
shown on the right-hand side of the diagram.
In this context items such as 'loads' are intended to relate
to both physical loads and actions associated with structural
design and also to the environmental loads associated with
service life design/durability considerations. The diagram is
intended to illustrate the interactions between the structural
design and service life design processes. All the above activ-
ities are carried out in parallel and typically proceed in an
iterative manner.
Clearly the actual service life design process is somewhat
more complicated than the above diagrammatic representation
portrays.
Figure 5.17
, which presents a more specific represen-
tation of the service life procedure for a concrete structure, puts
a strong emphasis on the owner (client) brief and conceptual
design stages, whilst embracing structural design. Execution,
construction quality and through-life care and maintenance in
use are crucial if the intended performance is to be achieved in
practice. As noted previously, these factors need be considered
at the conceptual design stage. The importance of good com-
munication up and down the supply chain and across the ser-
vice life design process is also highlighted in
Figure 5.18
.
Figure 5.10
also makes reference to a durability assessment
review procedure, which is an auditing procedure applied
throughout the service life design process. This type of add-
itional activity, linked to wider quality assurance goals, would
be intended to improve the likelihood of achieving the owner's
and user's requirements in terms of durability, sustainability
and functional performance for the anticipated structural/life-
cycle cost and environmental impacts.
5.3.7 Overview of environmental assessment
methodologies
Environmental assessment methodologies have to encompass
the complexity of the relationships that exist between different
sustainability issues, whilst employing practicable means of
evaluating the environmental and other aspects of the 'impacts'
arising from a building or other constructed asset. Many of
these issues are interrelated, which adds to the complexity of
making the desired assessment.
