Download Life Cycle Assessment of buildings comparing structural steelwork

Life Cycle Assessment of buildings comparing structural steelwork with
other construction techniques
Alexander Passer, Guido Cresnik, Danilo Schulter, Peter Maydl
Institute of Technology and Testing of Building Materials, Graz University of Technology,
Stremayrgasse 11, 8010 Graz, Tel.: +43/316/873-7153, Fax: +43/316/873-7650
[email protected], http://www.tvfa.tugraz.at
Keywords: Integrated Environmental Performance of Buildings, Life Cycle Assessment, EPD, Sustainable
Construction, Construction Products
ABSTRACT
This paper shows the results of a pre-feasibility study to identify future calls for actions for the construction
industry towards sustainability: Three office buildings with load bearings systems made of reinforced concrete,
steel and timber were compared. For the assessment a life cycle assessment (LCA) was undertaken. It is
investigated how benefits of sustainable construction regarding different construction techniques can already be
assessed.
The main result is that the three construction techniques are very close to each other and no construction
technique is preferable only on the basis of the life cycle assessment. It is necessary to extend the onedimensional environmental assessment by adding the two other pillars of sustainability to be in the line with
holistic considerations to fulfil the three dimensions of sustainability. It follows that in the context of buildings
requirements such as safety and fitness for use must also be considered in a new dimension called structural
sustainability.
Introduction
Since the Brundtland Report "Our Common Future" 1985 and the Earth Summit of Rio 1992 "Sustainable
Development" is omnipresent in our society: “Sustainable development is a development that meets the needs of
the present without compromising the ability of future generations to meet their own needs” [10].
Nowadays even the building sector is changing towards sustainability. The transmission of this concept into the
building sector is called “Sustainable Construction”. Sustainable construction means to design and construct
buildings with a holistic approach considering ecological, economical and socio-cultural aspects - a paradigm
shift for the entire building sector.
Whereas in the past, considerations to guarantee the long-term stability and fitness for use of buildings used to
concentrate primarily on the influences of the environment on the building and its structural components, it is
now – additionally! – necessary to consider the effects of the building on the environment. This has made the
task of architects and engineers much more demanding. Building design has to satisfy the extended requirements
throughout the entire life-cycle and additionally be technically, ecologically and economically optimized.
The importance of the construction sector led 2004 to the mandate M/350 “Integrated Environmental
Performance of Buildings” [6] of the European Commission assigning the European Committee of
Standardization (CEN) to develop a European set of regulations for the field of “Sustainability of construction
works”. Voluntary environmental declaration of construction products (EPD) based on the mandate should lead
to a product specific and EU-wide harmonized assessment. The increasing interest for sustainability combined
with financial incentives will motivate the producers to assess the performance of their construction products so
that they can show their individual environmental responsibility with a high acceptance of stakeholders.
LCA Case Study
The aim of this paper is to determine the performance of office buildings with different construction techniques
for load bearing systems based on the results of a pre-feasibility study undertaken for the “Austrian Steel
Association” entitled “steel for buildings – a sustainable construction material?” [8]. A life cycle assessment
(LCA) on the basis of the ISO 14040 [1] was performed. It is investigated to which extend it is possible today to
determine benefits of sustainable construction regarding different construction techniques.
Life Cycle Assessment:
According to ISO 14040, an LCA is a methodical approach to evaluate the environmental impacts associated
with a product, process or service by identifying and quantifying material and energy flows. On the basis of the
inventory data an impact assessment can be carried out. The results can be used for identifying and evaluating
opportunities for improvement.
System boundary, functional unit and indicators used for the LCA:
The spatial system boundary is the load bearing structure of the buildings. It follows thus that foundations, walls
and pillars, floor ceilings and the roofs are included. Cladding, interior fittings and building services are
neglected. Due to the explicit objective of the study, only the construction phase (construction materials) is
investigated representing only the first step towards a complete life cycle assessment demanded in the near
future. For this study the heat/cooling demand and the electricity consumption is estimated to be the same at all
three buildings. These factors cannot be influenced by the construction technique, that’s why they are excluded
in this study.
The functional unit is defined as square meter (m²) net area. Hence the influence of the building size can be
disregarded. The selection of the indicators used for the life cycle impact assessment is chosen according to the
ISO/DIS 21930 [7] and the drafts of the CEN TC350 [3]. The results of the impact assessment are calculated
using the ecoinvent data v1.3 [4].
LCI results:
The top section in figure 1 illustrates the three buildings; reinforced concrete, steel skeleton and timber skeleton
construction (f. l. t. r.). The results of the life cycle inventory (LCI) for the total mass of construction materials
are shown below. The pie chart compares the mass fraction arranged by construction materials (total load
bearing construction in mass percent). The table below subdivides the employed input of construction materials
by showing the amount of construction materials used per m² net area.
Figure 1: Analyzed buildings, comparison of mass fraction per m² net area arranged by construction materials
(load bearing construction in kg per m² respectively in mass-%).
The striking dominance of concrete used for load bearing constructions is particularly noteworthy. In the case of
the steel- and timber skeleton construction this results primarily from the usage of concrete for the building
foundations and staircases (safety in case of fire). Steel- and timber skeleton constructions need less construction
materials per m² net area as the reinforced concrete construction due to their more efficient material usage.
LCIA Results:
The main results of the life cycle impact assessment (LCIA), as illustrated in figure 2, are harmonized on the
basis of the reinforced concrete construction (100%). This chart illustrates how the different construction
techniques perform within each indicator at the building level. However, the different indicators (e.g. GWP and
ODP) cannot be compared in their relation to one another due to their different absolute values. It shows that the
environmental performance of all load bearing construction systems is very similar, even though their ranking
differs in various indicators.
In contrary to the results of the LCI the dominance of concrete cannot be proven on the LCIA level. Looking at
this in more detail, the unexpected high POCP-value of the timber skeleton construction is caused by the
relatively high use of glued laminated timber (GLT), affecting also the other indicator results ODP, AP, EP, HTP
and CEDnr. Regarding the indicators HTP and TEPT, a significant environmental burden from steel products
can be seen, whereas concrete doesn’t influence these indicators too much.
The results also indicate that structural steel and connecting plates for timber skeleton constructions play a
significant role in LCIA and should always be included in the system boundaries. It can be seen that the
influence on the indicators vary between 2 and 4% at the building level. Comparing the employed timber with
the structural steel and connecting plates for skeleton technique, the influence on the indicators rises to 33% in
the case of EP and to 260% in the case of TETP. The influence on the assessment should never be
underestimated.
Figure 2: Comparison of construction techniques in alphabetical order with their environmental performance.
Conclusion
From the authors’ point of view, there is no specific construction technique which is preferable only on the basis
of the LCIA. Aspects such as structural design and service life of building products depending on the in-use
condition and maintenance of the used materials in the building are not considered in life cycle assessments at
the moment.
The results indicate that generic data sets of construction products used for life cycle assessment can be
improved upon and can vary significantly as a result of inappropriate assumed transport routes or a lack of
knowledge about various material characteristics of construction products and their multiple field of application
(e.g. use of cement types in concrete). In future, this undesirable circumstance should be improved by using
environmental product declarations based on product specific- and EU-wide harmonized data and rules for
assessing constructions.
Outlook
While many scientists dedicate much time and resources to the establishment and assessment of environmental
impacts, an equally important issue is neglected all too often: How can architects and engineers implement these
considerations in the planning and design of buildings. In particular, the tools available today, for comparing and
assessing the long-term safety and the fitness for use of structures are still unsatisfactory. That includes aspects
like maintenance, lifecycle costs and environmental impacts.
Contrary to the principles of sustainable development, namely the equal consideration of the three dimensions of
sustainability, the mandate to CEN focuses mainly on ecological sustainability. It is a given fact that assessing
sustainability must take the form of total life cycle assessment. This necessitates considering the entire life of a
structure or building in the three dimensions of sustainability in accordance with the assessment framework.
However, in this framework document, the social sustainability is restricted to “health and comfort”, which is
undoubtedly too narrow a view of this dimension. But the environmental impact as well as the environmental
costs can only be assessed if they are compared with the benefit of a building or structural component in mind.
Consequently, it is necessary to define a suitable parameter as a “functional unit” for considering all factors on a
quantitative level. The framework document therefore also includes the columns “Functional Performance” and
“Technical Performance”.
Fig. 3 Simplified structure of the CEN/TC 350 framework and the 4th dimension of sustainability [9]
Hence, the big challenge for architects and engineers in the future will be the necessity to integrate holistic
considerations about the lifecycle of buildings in their planning. This means that the three dimensions of
sustainability need to be networked with the requirements profile of the Construction Products Directive
(CPD)_[5] and the Eurocodes [2], i.e. with the Technical and Functional Performance of Construction Works.
Therefore, a fourth dimension needs to be added to the three “classical” dimensions of sustainability, namely the
dimension of “structural sustainability”, as seen in figure 3.
Consequently, there appears to be an urgent need for civil engineers to study these issues more intensively. It is
the duty of the universities to ensure that their education programmes create the necessary conditions to
empower the civil engineers to shape our future and the future of our children rather than being mere
constructors. Otherwise, the role of the civil engineer would be reduced to accepting the responsibility for costs
and structural damages after the building has been designed and constructed.
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CEN TC 250: EN 1990, Eurocode – Basis of Structural Design, 2003.
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