1 INTRODUCTION

1.1 Sustainable development and the built environment

Sustainable development has become in the last decade the conceptual framework for almost all areas of social and economic life. The steps of integrating the sustainability concept in construc-tion are easy to understand. As long as the discourse on sustainable development has been fo-cused on environmental component, the construction industry has found the answer in the en-ergy consumption and environmental loadings, namely the green building model. In the last decade the focus has shifted on integrating the four pillars of sustainable development (not only the environmental component, but also economic, social and cultural ones), which in the con-struction industry led to the birth of the sustainable building model (Dall’O & Galante 2010).

As such, in terms of scientific research, any topic of sustainable development requires an in-tegrative way of thinking and an interdisciplinary approach. This goal is difficult to achieve in practice due to thinking patterns and the design process. Even in the developed countries, the integrated design process is only at the beginning.

1.2 Approaches and barriers to sustainable design in a developing country

The most important issues acting as barriers to implement sustainability in the construction in-

dustry in Eastern European countries are: a lack of awareness among investors, a limited ex-

perience among developers and the limited number of professionals specialized in sustainable

buildings. In recent years in Europe the problems were also related to the global recession with negative

effect on building industry, the lack of a comprehensive data that form the basis of decision making in European Union and lack of universal mandatory standards that can define and measure sustainability of construction. In order to make a step forward in this direction, the

Sustainable design of a multistory welded steel structure located in a seismic area

M. Georgescu, V. Ungureanu & M.Szitar “Politehnica” University of Timisoara, Romania

ABSTRACT: The paper presents the case of an existing steel structure, located in the city of Arad / Romania and made of built-up welded elements, which has been practically abandoned after main frame erection. As the new owner required to refurbish and to transform the building for modern office purposes, a resistance and stability investigation plus structural measures were necessary, as part of the refurbishment procedure, described in the paper. A building sus-tainability assessment resulting from the restoration /refurbishment procedure is performed in order to evaluate practical application of specific criteria. The sustainability building assessment that takes into account all the pillars of sustainability can help each team member to understand its place in a project and the way all the things are related. This understanding is crucial in order to achieve a long-term visible improvement of the built environment.

European Committee for Standardization is preparing a common framework: CEN/ TC350 - Sustainability of construction works and ISO TC 59 “Building construction” with its subcom-mittee SC 17 “Sustainability in building construction” is developing a series of related stan-dards.

What must be mentioned as a possible barrier, but also as a challenge at the same time is the specific conditions related to the built environment, namely: the chaotic development of the cit-ies after 1989, the investors pressure for buildings with low construction costs and low quality, erected in a short period of time, the continuous pressure on land-use and site development. Last, but not least, the step by step design approach is to be mentioned. In the developing coun-tries it is a long way to the integrated design process. Thus, the design approach in terms of sus-tainability is rather at the beginning at it is done fragmented (different specialties and parts of the project may treat very differently these issues). It is also the case of the refurbishment pro-ject presented and analyzed.

2 DESCRIPTION OF THE BUILDING AND THE REFURBISHMENT PROJECT

2.1 Description of the existing structure before refurbishment

The reality of the construction market is often offering quite interesting cases, as the one pre-sented in the paper, an existing building centrally located in the city of Arad (close to the west-ern border of Romania).

Probably out of economic reasons, the building could not be finished and was abandoned for 14 years in this partially finished phase, without proper roofing and practically with no clad-ding. This caused an exposure of the steel structure (protected only with a layer of primer) and to the concrete of the prefabricated strips, to climatic factors characteristic to an inner continen-tal area (wind, rain, snow, or quite severe temperature variations) causing metal corrosion. As the site was located near one of the most important transport arteries of the city, quite near to the road, the intense heavy traffic caused vibrations which gradually shifted the simple sup-ported concrete strips and caused some of them to fall down inside the building. All that, com-bined with an incomplete and improper wind bracing, suggested an insecure and really danger-ous location, in degradation, which needed quick intervention (Fig. 1).

The ground floor of the abandoned construction was in fact a deposit for all kind of debris and garbage (typical to such situations) and extremely harmful to environment, especially in the middle of a large city.

The steel structure of the building was erected in 1993, in two distinct phases: one initial phase consisting into ground floor plus two floors, followed by a second phase consisting into a third floor, linked by bolted hinged connections to the top of the previous zone. Prefabricated 19 cm thick concrete hollow strips were used to build the floor decking, however, without suc-ceeding to cover completely the required surface and with practically no connection to the un-derneath steel beams except the simple support. The initial idea was to build the roofing using tiles on steel skeleton, further on renounced to and replaced by the third floor steel structure, with terrace roof of prefabricated concrete decking. Furthermore, the prefabricated concrete strips (which were not connected to the metal beam underneath) continued to represent a danger by threatening to fall down again and thereby cause fatal accidents under the continued action of vibrations induced by traffic.

2.2 Sustainability principles and refurbishment projects – theoretical issues

Modern design has to comply with several objectives, clearly defined and accepted at the level of international practice: accessibility, aesthetics in relation with the location specificities, flexi-bility, durability, low maintenance operations, health and well being of the occupants, structural safety and fire protection, sustainability of the site and the construction.

As proved by this complex list of objectives, the design procedure nowadays has to comply with a large number of criteria, which makes it considerably difficult and which requires com-promise in some situations. All this implies an integrated approach of building design, by com-plex teams of different specialists, promoting science-based developments.

Figure 1. The existing abandoned structure.

Though sustainable construction approach is only one aspect to treat in relation with whole

building design, it is an aspect of paramount importance as it includes not only environmental requirements generally accepted nowadays (optimize site/existing structure potential, optimize energy use, protect and conserve water, use environmentally preferable products and local ma-terials, minimize emissions), but also economic aspects (quality related with life-cycle costs, minimize construction and operation costs, the stability value on the local market) and socio-cultural aspects (enhance indoor environmental quality, optimize functional and technical qual-ity, optimize operational and maintenance practices, innovation and process quality).

A building project can be regarded as sustainable only when all the various dimensions of sustainability – environmental, economic, social and cultural ones are dealt with, otherwise it will provide only a partial solution, without noticeable effects concerning a long term strategy (Bragança et al. 2007). This is the case of most buildings erected during last decade in Romania, and also the case of the building analyzed, as shown in the sustainability assessment and the analysis of strengths and weaknesses.

Among mentioned requirements, the evaluation performed by the authors on the practical de-sign case described in this paper is strongly related to the optimization of site/existing structure potential. The existing construction experience has shown that it is more sustainable to renovate an existing building than to tear it down and construct a new one. It is highly advisable to con-sider reuse and retrofit of available existing buildings before deciding to build new. From this point of view, the decision taken by the owner of the analyzed structure (together with the archi-tect and structural engineer) of refurbish the partially erected frame, is fully complying with sustainability requirements.

The structural retrofitting performed on ordinary buildings has the aim of repairing and strengthening these to keep them in use at a specified safety level. The reanalysis and redesign process of the existing structure implies a certain level of intervention, aiming to preserve the original structural system with proper strengthening of its weak elements, if necessary. The na-ture of performed interventions may be either of local or of general type, as required.

Any structural restoration or retrofitting process implies some necessary steps: - Set-up of a restoration scheme, as core of the whole procedure; this should be the output of

an interrelated approach from the structural, architectural and client point of view; - A deep knowledge of the existing structural system, properties of materials and their change

in time and knowledge of structural response to gravity loads and seismic loads; - In-situ investigations including a geometrical and constructional survey, pathology of the

structure, in-situ non-destructive tests and soil investigations; - Laboratory tests (if required) on the mechanical properties of the original materials, soil

tests and possibly model tests;

- The analysis and design of the original structure using various analytical approaches, plus stress determination and comparison with strength;

- Assessment of the residual resistance of the structure, as a crucial step for the decision mak-ing on structural restoration procedure (Penelis 2009).

As a result of the described steps, the retrofitting project is obtained, after reanalysis and re-design of the modified structure using the upper scheme, followed by drawings, technical de-scriptions and specifications.

The next paragraphs are presenting some of the procedure steps, as applied by the design team in the restoration process.

2.3 Design decisions concerning architectural project that affect projects sustainability

The choice to retrofit the structure, instead of demolish and erect a new one was beneficial, so from this perspective it was a sustainable decision regarding the building use. The site location and characteristics instead were difficult: a plot of land of only 418 sqm, a problem in solving properly the places for parking, heterogeneous neighborhoods not far from the city center, the pressure on land with a high percentage of occupancy. It can be said that although the building is correctly located on the site, the rest of the choices regarding the relationship of the building with the context are not driven by sustainability issues: the material used for the façade does not fit into the surroundings, is not regional and has a high degree of toxicity and the idea of a pos-sible green space or a green roof terrace was left aside.

The new owner of the building has decided to reuse and retrofit the old steel and concrete structure, in view of creating a modern multistory building of offices with glazing working as cladding. This decision brought strengths to the project, such as: reducing weight of the struc-ture and especially the good natural lightning. At the same time, it brought some weaknesses in respect to sustainability issues, as the choice of the material was mainly determined by the con-struction cost, thus a material with poor thermal characteristics was chosen, that will increase the operational costs and will have a negative impact on the quality of indoor environment.

In order to maximize the space for offices, it was decided to build the new staircase and ele-vator structure outside the reconstructed building, in form of a tower of masonry and reinforced concrete (materials imposed by fire protection reasons) with links at every level to the corre-sponding storey. The separate staircase would have to be located in the backyard of the build-ing. This was a good choice for the functional and technical quality of the project and also for the stability value, providing further flexibility and adaptability of the space.

2.4 Resistance and stability checking of the existing structure

The analyzed steel structure layout is schematically presented (the initial project was available). As evident from the layout dimensions, the span values 5,50 m + 1,80 m +5,50 m adopted by the initial designer are not entirely suitable and correspond more to concrete than to steel struc-tures. Also, quite small bay values were adopted (i.e. 3 x 3,30 m + 4,20 m).

In order to evaluate the existing structure and its capacity to resist loading, the first structural analysis was performed on this initial configuration, with transverse vertical wind bracing in axes 1 and 4 and without vertical bracing on the longitudinal direction (sway frame). Further-more, the hinged connection of the 3

rd floor structure to the rest of the building is plenty con-

tributing to increase the deformability of the structure. Another important aspect related to the existing steel structure refers to the vertical bracing system. As a matter of fact, the initial pro-ject provisions haven’t been respected by the constructor and the existing vertical bracings were placed in the transverse frames of axes 1 and 4. No longitudinal vertical bracings were pro-vided. Thus, the existing bracing system was also incomplete, living a sway frame on the longitudinal direction.

Some results of the FEM analysis in SAP 2000 Nonlinear are quite relevant. The high value of the first eigen period (i.e. T1=1,068 sec) indicates an excessive deformability of the structure on the longitudinal direction (no bracing system provided on that direction). The longitudinal beams and the ground floor columns resistance is exceeded under the load combinations includ-ing longitudinal earthquake. The lateral sway at the top of the structure was found of 138 mm > H/200. This makes the initial structure totally unacceptable and clearly indicates the necessity

of structural measures by the designer. A certain number of other bracing configurations were therefore analyzed in order to find the optimum one.

In the end of the study, from all the studied cases, the bracing configuration presented in Fig-ure 2 has been chosen. As mentioned before, the architect/ client requirement of free space in the front façade at ground floor level (no bracings) has been considered in this choice, together with a reversed position of the lateral bracing at ground floor between axes A and B required by street circulation reasons.

The column and beams cross section made of built-up steel plates, were found to be of class 1 according to EUROCODE 3 and Romanian code (P100-2006) classification. Typical geometri-cal dimensions for column and beam cross sections, built of welded steel plates and actually checked for section class were used. The beam to column connections are single bevel welded in the initial configuration. No over strength measures for the connections were taken by the ini-tial designer.

After choosing the optimum structural configuration and performing a FEM structural analy-sis, a maximum level of solicitation of 35-40% (compared to member capacity) was found for the whole structure. This shows an over strength of the whole structure, probably due to an ex-aggerated prudence of the initial designer, and also to the elimination (in the new configuration) of the previously intended masonry outer walls, leading to concentrated masses reduction and thus to reduced seismic forces. Therefore, the decision was taken not to take supplementary measures for over strength in the beam-to-column connections of the new structure. Upper ob-servations allow for the adoption in the earthquake analysis of the seismic behavior factor q=5 characteristic to a ductile steel structure. This dissipation level was very important to reduce column base reactions and thus to avoid exceeding of foundations capacity under the new struc-tural configuration.

Figure 2. Bracing configuration chosen in order to reinforce the structure.

2.5 Discussion on structural retrofitting procedure

As a positive start for the retrofitting procedure, the new owner of the building did not request any major modification in the metal structure geometry and only asked for a multistory office building having glazing as cladding and with an outer staircase located in the backyard. The in-ner partition walls would be of gypsum board on light metal structure, bringing no significant supplementary dead load. The cladding would be glazed, much lighter than the initially planned masonry cladding. The performed structure analysis on the existing building, as previously pre-sented, results in a number of intervention techniques aiming to consolidate and adapt the struc-ture to the new requirements and simultaneously provide a satisfactory level of safety.

The intervention techniques are all included in the category of irreversible ones, as the re-stored building is an ordinary building and considering the environment requirements plus (last but not least) the financial acceptance by the client. The irreversible interventions adopted in the frame of the reconstruction procedure, mostly comply with sustainable design principles and lead to a better impact of the resulting structure on the environment.

Figure 3. The final result – the new office building.

3 SUSTAINABLILTY BUILDING ASSESSMENT FOR THE NEW BUILDING

3.1 Performing a simplified building sustainability assessment

A simplified building sustainability assessment was performed on the building, after the refur-

bishment. The model used is based on the study of existing systems (Szitar & Grecea 2011) and

the CEN/ TC350 and ISO sustainability standardization, adapted to the local conditions, a sys-

tem that is flexible enough, clear and can be easily understood and used in the first phases of a

project in order to assess alternative solutions (Grecea et al. 2011).

In the development of this methodology there were stated some priorities (after studying the

state of art methodologies related to local conditions of a developing country). The most impor-

tant ideas were: balancing between all the dimensions of sustainable development, the list of pa-

rameters, indicators and criteria has to be limited enough in order to be practical, but wide

enough in order to comprise the most relevant characteristics, limitation of qualitative criteria

that are hard to validate, a user-friendly tool (with the main purpose of using it in the design

phase in order to compare different options) with a graphical output that can be easily under-

stood and interpret (radar diagram), following the Bellagio priciples (Hardi & Zdan 1997). The methodology and the steps made in creating such a system are presented in other papers

dealing with methodological aspects of building sustainability assessment (Zavrl et al. 2009, Bragança et al. 2010). In brief, there are four stages in preparing a rating system: selection of main criteria and parameters, quantification of parameters, normalization and aggregation of pa-rameters and representation of the global assessment of the project.

There are 8 criteria and 27 parameters used in this simplified sustainability framework (table 1-3). In this simplified assessment the authors have not used coefficients for normalization the score, as the main purpose was not to obtain a rating, but to analyze the building as a whole and to understand its benefits and drawbacks from this perspective. The radar diagram shows how the project scores in different areas and where is place for improvement (Fig 4).

The differences between various dimensions of sustainability become in this way more clear. The strengths of the project are in area EC2 (stability value) and S2 (functional and technical quality),mainly due to the fact that the architectural design is well balanced and the fact that it provided an open space (that can be easily transformed) and due to innovative structural solu-

tion that meet the architect and customer requirements. The weaknesses can be found in the area EN2 (land use, ecology, water) due to the fact that the project disregards context specificities it lacks green space and EN3 (energy) due to the fact that it uses a type of a curtain wall with low insulation properties and does not use any type of renewable energy.

Table 1. Environmental criteria and parameters used in the assessment _____________________________________________________________________________

Nr Environmental quality Parameters _____________________________________________________________________________

EN1 Climate change -GWP – global warming potential and atmosphere -CO2 emissions -Other emissions EN2 Land use, ecology, water -land use and site development -heat island effect -potable and rain water use EN3 Energy -energy efficiency -renewable energy EN 4 Materials, resources, waste -non-toxic materials -reused or regional materials -waste management _____________________________________________________________________________

Table 2. Social and functional criteria and parameters used in the assessment _____________________________________________________________________________

Nr Social quality Parameters _____________________________________________________________________________

S1 Quality of indoor -hydrothermal comfort environment and health -acoustic comfort -visual comfort -indoor hygiene -natural and artificial light S2 Functional and technical -barrier free accessibility quality -area efficiency -functional relationships -feasibility of conversion -structural safety -fire safety _____________________________________________________________________________

Table 3. Economic criteria and parameters used in the assessment _____________________________________________________________________________

Nr Economic quality Parameters _____________________________________________________________________________

EC1 Life-cycle costs -quality / life-cycle costs -minimize operation costs EC2 Stability value -flexibility and adaptability -adaptation to local economy -viability and affordability _____________________________________________________________________________

4 CONCLUSIONS

As a result of the performed structural conversion, the existing structure, already obsolete in the central area of Arad, was transformed into an office building, having a much better environ-mental impact, even if the project has some weaknesses in this area, as shown in the sustainabil-ity assessment. The structure, built of both old and new structural elements, is in function at pre-sent time. However, by analyzing the whole design and construction procedure in the light of sustainable design principles, the research team concluded that the building is still tributary to old ways and to specific constrains of the economical conditions.

A sustainability building assessment that takes into account all the pillars of sustainability performed in the first phases of a project can help each team member to understand its place in

a project and the way all the things are related. This understanding is crucial in order to achieve a long-term visible improvement of the built environment. Planning and building a sustainable construction implies communication among all parties that could be involved in the project.

Figure 4. Radar diagram for the sustainability assessment.

5 REFERENCES

Bragança, L., Mateus, R. & Koukkari, H. 2007. Perspectives of building sustainability assessment. SB07. Sustainable Construction, Materials and Practices - Challenge of the Industry for the New Millen-nium: 356-365. IOS Press

Bragança, L., Mateus, R. & Koukkari, H. 2010. Building Sustainability Assessment. Sustainability, 12(7): 2010-2023

Dall’O, G. & Galante, A. 2010. Abitare sostenibile. Bologna: Il Mulino Grecea, D., Szitar, M., Ciutina, A. 2011. Criterii si sisteme de evaluare ale mediului construit in contextul

dezvoltarii durabile, Buletinul AGIR XVI(2): 28-38 Hardi, P. & Zdan, T. 1997. Assessing Sustainable Development: Principles in Practice. Winnipeg: Inter-

national Institute for Sustainable Development. Penelis, G. 2009. Structural restoration of monumental buildings in seismic areas. Proc. in-

tern.symp.COST C25 & C26, Thessaloniki , 17-24 May 2009. Szitar, M. & Grecea, D. 2011 Sustainable building assessment tools and the quality of the built environ-

ment; COST C25 Sustainability of Construction – Towards a Better Built Environment, Proc. intern. Conference Innsbruck, 03-05 February 2011.

Zavrl, M.S., Zarnic R. & Selih J. 2009 Multicriterial sustainability assessment of residential buildings. Technological and Economical Development of Economy, Baltic Journal of Sustainability 15(4): 612-630.

*** P100-1 / 2006 – Cod de proiectare seismica. Prevederi de proiectare pentru cladiri.