performance-based approaches for concrete structures

fib SYMPOSIUM 2016

PERFORMANCE-BASED APPROACHES FOR CONCRETE STRUCTURES PROCEEDINGS Editor: H. Beushausen

Image © 2016 by BBT SE

CAPE TOWN, SOUTH AFRICA · 21–23 NOVEMBER 2016

The fib Symposium 2016 in Cape Town, South Africa brings together engineers, scientists, specifiers, concrete technologists, researchers and other practitioners from around the world. The goal is to share knowledge and experience of current developments in concrete technology and structural concrete design, with a particular focus on performance-based approaches. With 250 articles and ten keynote lectures, authors from more than 40 countries have contributed to the fib Symposium 2016 and to this book. INTERNATIONAL FEDERATION FOR STRUCTURAL CONCRETE FÉDÉRATION INTERNATIONALE DU BÉTON

fib-international.org

Conference themes include: modelling and testing of concrete properties; materials technology; structural design aspects; durability and service life; sustainability aspects; construction systems; and the fib Model Code.

PERFORMANCE-BA SED APPROACHE S FOR CONCRE TE S TRUC TURE S

fib Symposium 2016. Performance-Based Approaches for Concrete Structures. Proceedings. University of Cape Town, Cape Town, South Africa, 21–23 November 2016 Editor: Hans Beushausen (Dept. of Civil Engineering, Univ. of Cape Town, South Africa) Copyright © 2016 by the fib. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage or retrieval system, without permission in writing from the publisher. For permission requests, please contact the fib at the address below. Published by Fédération internationale du béton ( fib), Case Postale 88, 1015 Lausanne, Switzerland fib-international.org ISBN 978-2-88394-122-9 Every effort is made to ensure that all published information has been reviewed by suitably qualified professionals and that all information submitted is original, has not been published previously and is not being considered for publication elsewhere. Further, the fib has made every effort to ensure that any and all permissions to quote from other sources has been obtained. The editor and the publisher are not responsible for the statements or opinions expressed in this publication. fib publications are not able to, nor intended to, supplant individual training, responsibility or judgement of the user, or the supplier, of the information presented. Although the International Federation for Structural Concrete ( fib) does its best to ensure that all the information presented in this publication is accurate, no liability or responsibility of any kind, including liability for negligence, is accepted in this respect by the organization, its members, employees or agents. Cover images: Brenner Base Tunnel. Copyright © 2016 by BBT SE. Reproduced with the kind permission of BBT SE. Printed in South Africa

PERFORMANCE-BA SED APPROACHE S FOR CONCRE TE S TRUC TURE S

CONTENTS Preface I Sponsors and Supporters II Scientific Committee and Advisory Board Organising Committee IV Overview of Papers V

III

Keynote Lectures Chapter 1: Structural Analysis and Design Chapter 2: Analysis and Design: Flexural and Prestressed Members Chapter 3: Analysis and Design: Shear and Torsion Chapter 4: Structures Exposed to Seismic Loading Chapter 5: Shrinkage and Creep Chapter 6: Materials, Production, Testing, Modelling, Construction Chapter 7: Fibre Reinforced Concrete Chapter 8: Precast Concrete Technology Chapter 9: Bridge Structures Chapter 10: Durability and Service Life Chapter 11: Deterioration Mechanisms and Reinforcement Corrosion Chapter 12: Condition Assessment Chapter 13: Protection and Repair Chapter 14: Structural Strengthening Author Index

KE YNOTE LEC TURES

13

Sustainability and Performance Design of Structures With Precast Elements D. Fernández-Ordóñez Past Chairman of fib Commission 6, Prefabrication. fib Secretary General, Lausanne, Switzerland

Abstract Prefabrication has evolved in depth and breadth from its beginnings, bringing many of the advantages of industrialisation to construction, while solving some of the problems that arose in the early years. Today prefabrication, compared to traditional construction methods, and concrete as a material, feature a number of beneficial characteristics. Precast elements are factory made products. The only way to industrialise the construction industry is to shift work from temporary construction sites to modern permanent facilities. Factory production entails rational and efficient manufacturing processes, skilled workers, systematization of repetitive tasks, and lower labour costs per m² as a result of automated production. Factory products are process-based and lean manufacturing principles are deployed. Automation is gradually being implemented in factories and is already in place in areas such as the preparation of reinforcing steel, mould assembly, concrete casting, and surface finishing on architectural concrete. And other stages in the process are sure to follow. Performance design as defined already in the fib MC2010 could be implemented in precast structures in many ways. This implementation could bring relevant improvements for the design and construction with precast elements. Sustainability is becoming a key aspect for decision taking when building structures. In any case it means that considerations regarding economic, environmental and social aspects have to be considered. Also it is of the greatest relevance that the whole life cycle of the structure should be considered, that includes as commonly said, from the cradle to the grave. In the case of precast structures, as industrialised construction, has at the earliest level a greater input of manufacturing and thus to take into account all aspects of sustainability and also the whole life cycle is relevant. Keywords: prefabrication · precast structures · performance design · design by use · sustainability · fib Model Code 2010

1. Introduction As prefabrication makes optimal use of materials, its potential for savings is much greater than in cast-in-situ construction. Structural performance and durability are also enhanced through design, modern manufacturing equipment and carefully planned working procedures. The production of precast concrete elements normally takes place under controlled climatic conditions in enclosed factories. This makes control of waste, emissions, noise levels, etc. easy compared to the same process at a traditional building site. Working environment is also easily controlled. Flexible building use may be another key aspect in design. Certain types of buildings, office buildings in particular, often need to be adaptable to user needs. The most suitable solution in such cases is open plan design. Precast structures are flexible in many respects. First, when using prestressing, design spans are usually long, so it is easy to adapt the building to future needs of change or forthcoming use demands. After then, life design for the structure and external walls is at least 50 to 100 years, while for the inner partitions is just about 10 years.

14

KE YNOTE LEC TURE S

The environmental burden of prefabrication is mainly the burden caused by the raw materials of concrete (especially production of cement and steel). The environmental burden caused by raw materials is approximately three times larger than that caused by the production process of the elements, as indicated by the examples of environmental product declarations [3-4]. fib Commission 6 Prefabrication is working on the development a document about sustainability of precast structures. Some of the ideas developed in the document are expressed in this paper.

2. Sustainability of precast structures In the MC2010 the purpose of design for sustainability is to reduce impacts on the environment, society, and economy by evaluating and verifying the performance of concrete, concrete components or structures. The fulfilment of sustainability requirements for a structure presumes that all aspects of design, construction, use, conservation, demolition as well as recycling and disposal that are relevant for the environment and society are taken into account in the MC2010. Economic requirements are not taken into account. Thus the performance requirements for sustainability in the MC2010 are related to: –– impact on the environment, which is defined as the influence of the activities, from the design to disposal, on the environment, –– impact on society, which is defined as the influence of the activities from the design to disposal, on society [1-16-17]. Performance requirements are then taken into account for environmental and social aspects. For environmental aspects, a structure shall be designed in such a way that the impact on environment is appropriately taken into consideration in the life cycle. Regarding the impact on society, a structure shall be designed in such a way that the impact on society is appropriately taken into consideration in the life cycle [1-4]. The assessment of impacts on society addresses the intended and unintended social effects, both positive and negative, of the project and any social change processes caused by the project. At present there are defined not clear indicators regarding social aspects for sustainability [18-19]. Among other aspects is the short construction period leads to less public troubles as noise and dust normally associated with construction. Due to the size of the prefabricated units, large parts of the building is carried on with each transport, compared to putting on scaffolding, shuttering material, cement, aggregates, among others, that is transported separately. Hence the considerable reduction in traffic and less obstruction to the general public leads to lesser troubles for the public. Many works are in densely populated areas within urban centres, and therefore the work activities can disturb a large number of people. Also for the model developed in T6.3 of fib it has been taken into account the interaction with third parties like the comfort including the thermal comfort the noise and quality of air. Also it has been taken into account the noise and particle pollution and traffic disturbances during construction. On the risks point of view, it has been taken into account the health and safety during construction and production and the users safety. EN 15978 specifies the calculation method, based on Life Cycle Assessment (LCA) and other quantified environmental information, to assess the environmental performance of a building, and gives the means for the reporting and communication of the outcome of the assessment. The standard is applicable to new and existing buildings and refurbishment projects. The standard gives: – the description of the object of assessment; – the system boundary that applies at the building level; – the procedure to be used for the inventory analysis; – the list of indicators and procedures for the calculations of these indicators; – the requirements for presentation of the results in reporting and communication; – and the requirements for the data necessary for the calculation. Only the LCA

KE YNOTE LEC TURES

15

of a building can provide estimates of the full range of environmental burdens, such as embodied energy use and related fossil fuel depletion; other resource use; greenhouse gas emissions; and toxic releases to air, water, and land [1-2-5]. When applied to buildings, an LCA includes: –– resource extraction; –– manufacturing and transportation of materials and prefabricated components; –– on-site construction; –– building operations, including energy consumption and maintenance; [6] –– end-of-life reuse, recycling, or disposal. CEN Technical Committees in charge of building materials and products will now develop, on the basis of the general rules given in EN 15804, specific standards for their products adding the characterisations factors missing in EN 15804. A precast concrete beam could not be considered a sustainable element everywhere and/or every time if the whole structure is not assessed. Nevertheless, some sustainable (environmental) characteristics may be remarked about precast concrete solutions are really competitive as seen in Table 1: [8-9-10]. Table 1. Precast concrete contribution to sustainability Precast concrete contributions Thermal inertia Fire protection

ENVIRONMENTAL Savings in energy consumption CO2 emissions avoided Lack of toxic emissions

Acoustic insulation Resilience (robustness) Durability

Longer period of environmental impacts amortization

SOCIAL

ECONOMIC

Higher comfort

Fewer operational costs: heating and cooling Better protection to Fewer insurance persons (and firefighters) Higher possibility of Better protection to reconstruction patrimony Higher comfort Higher privacy level Better performance Fewer expenses in against natural recovery the original construction disasters Less maintenance

Important positive sustainability aspects of the use of concrete in building structures and in particular in precast concrete buildings are: –– High thermal mass of concrete – Concrete elements can serve due to their density as thermal energy storage. It means that they are able to absorb and release heat or cold at a rate that roughly corresponds to a building’s daily heating and cooling cycle. This can result into savings in energy use for heating and cooling. Precast elements in precast structures can use thermal mass to drastically reduce the use of energy in heating and cooling of buildings. Also precast sandwich panels can have all necessary insulation incorporated from the construction of the element. –– Acoustic parameters (air born sound insulation properties) of concrete plane elements – Concrete walls and floors provide the mass that is required for effective reduction of sound transmission, particularly low frequency sounds. –– High resistance of concrete structures against climatic effects (in environmental exposition) – High mechanical resistance of concrete structures; high durability of concrete surface (advantage for bridges, roads and other civil structures); resistance against floods, winds, frost, sun radiation, abrasion etc. Durability and water tightness of HPC and UHPC. Normally in precast concrete structures and panels HPC and SCC is used and therefore good properties of these concretes are incorporated in precast buildings. [12-13-14-15].

16

KE YNOTE LEC TURE S

–– High fire resistance of concrete structures – In comparison to the most steel or timber structures concrete structures provide significantly higher fire resistance. –– High durability, low maintenance requirements – especially in inside building environment, where concrete is protected against direct climatic impacts. –– Demountability and Reuse of materials. Precast structures can be designed to be easily demountable and the possibility to recycle precast concrete is high compared to other materials. This is also in development by the Commission of Prefabrication of fib in its Task Group 6.3 Sustainability of Precast Structures. It has been developed a model for Sustainability of Precast Structures using MIVES is presented in Table 2. Table 2. Requirements tree proposed by the fib TG 6.3 for the sustainability assessment of structural concrete Requirement

R1 Economic (λ R1 = 40%)

Criteria C1 Total Costs (λC1 = 50%) C2 Quality (λC2 = 10%) C3 Dismantling (λC3 = 10%) C 4 Service Life (λC4 = 30%)

Indicator

Units

Value function

I1 Total costs (λ I1 = 100%)

€

DS

I 2 Non quality costs (λ I2 = 100%)

Attrib.

DL

I 3 Dismantling costs (λ I3 = 100%)

€

DS

I4 Maintenance I4 = 50%)

€

IS

I 5 Resilience (λ I5 = 50%)

€

IS

Tn

DS

IS

I6 Cement (λ I6 = 20%)

R 2 Environmental (λ R2 = 45%)

R 3 Social (λ R3 = 15%)

C5 Materials consumption (λC5 = 55%)

I7 Aggregates (λ I7 = 20%) I8 Steel (λ I8 = 30%) I9 Water (λ I9 = 10%) I10 Plastics and others (λ I10 = 10%) I11 Reused Material (λ I11= 10%)

Tn

C 6 Emissions (λC6 = 55%)

I12 CO2 emissions (λ I12 = 60%)

TnCO2 -eq

I13 Total waste (λ I13 = 40%)

Tn

C7 Energy consumption (λC7 = 10%)

I14 Embodied Energy (I14 = 33%)

MWh

C8 Interaction with third parties (λC8 = 50%)

C9 Risks (λC9 = 50%)

I15 Construction Energy (λ I15= 33%)

MWh

I16 Service Energy (λ I16= 33%)

MWh

I17 Comfort. Thermal, air, noise (λ I17 = 50%) I18 Noise pollution. Construction (λ I18 =10%) I19 Particles pollution. Construction (λ I19 = 30%) I 20 Traffic disturbances. Construction (λ I20 = 10%) I 21 Health and Safety. Production (λ I21 = 33%) I 22 Health and Safety. Construction (λ I22 = 33%) I 23 User’s Safety (λ I23 = 33%)

DS: decreasing S-shape; IS: Increasing S-shape; DL: decreasing linear

Attrib. Db

DS

Tn Attrib. Attrib. Attrib. Attrib.

DS

KE YNOTE LEC TURES

17

As it can be noticed, the requirements tree consists of 23 indicators (I) groups in 9 criteria (C). The number and type of indicators result from the different meetings carried out by the members of the committee; these indicators have been considered as those representatives to dealt with the sustainability assessment of construction systems or structural elements (in particular precast and in-situ constructed structural concrete elements) covering from the extraction of the materials to the dismantling operations. The economic requirement (R 1) is represented by four criteria related to costs: total (C1), quality (C2), dismantling (C3) and service life (C 4) costs. Five indicators have been included; among these, the resilience, as beneficial property, is taken into account. The environmental requirement (R 2) gathers three criteria: material consumption (C5), emissions (C 6) and energy consumption (C7) and eleven indicators. Finally, the social requirement (R 3) consist of two criteria: interaction with third parties (C8) and risks (C9). The experts’ panel have fixed and defined these indicators aiming at guaranteeing the independence of these and avoiding potential overlapping. In this regard, more indicators could have been included; nevertheless, the addition of extra indicators (with weight below 5%) can: (1) difficult the application of the method (more indicators to be assessed); (2) potential overlapping between the indicators and (3) lead to lose the general view of the problem. Thus, indicators with less than 5% of weight have been disregarded. Finally, the distribution of weights proposed for this initial requirements’ tree has been fixed by using the direct assignment method; that is: the experts agreed the weights of each indicator based on the own experience. Needless to say that this distribution can be adjusted to other stakeholders’ preferences in order to take into account other economic scenarios or environmental and social sensitivities. In this regard, the next step to be carried out by the fib TG 6.3 is to send this requirements tree to the members of other fib commissions so that other distributions can be assumed. This process would help to guarantee the representativeness of the sustainability assessment method proposed.

3. Performance design in the Model Code 2010 As defined by the fib Model Code 2010 (MC2010), the performance of a structure or a structural component refers to its behaviour as a consequence of actions to which it is subjected or which it generates. It says that structures and structural members shall be designed, constructed and maintained in such a way that they perform adequately and in an economically reasonable way during construction, service life and dismantlement [11]. This means that, in general all structures shall meet the following: –– structures and structural members shall remain fit for the use for which they have been designed; –– structures and structural members shall withstand extreme and/or frequently repeated actions and environmental influences liable to occur during their construction and anticipated use, and shall not be damaged by accidental and/or exceptional events to an extent that is disproportional to the triggering event; –– structures and structural members shall be able to contribute positively to the needs of humankind with regard to nature, society, economy and wellbeing, which is the definition of sustainability taking into account the three main characteristics of social, economic and environmental aspects. For structures there are three categories, for which further needs shall be met: –– serviceability, i.e. ability of a structure or structural members to perform, with appropriate levels of reliability, adequately for normal use under all (combinations of) actions expected during service life; –– structural safety i.e. ability of a structure and its structural members to guarantee the overall stability, adequate deformability and ultimate bearing resistance, corresponding to the assumed actions (both extreme and/or frequently repeated actions and accidental and/or exceptional events) with appropriate levels of reliability for the specified reference periods. The structural

18

KE YNOTE LEC TURE S

safety shall be analysed for all possible damage states and exposure events relevant for the design situation under consideration; –– sustainability, i.e. ability of a material, structure or structural members to contribute positively to the fulfilment of the present needs of humankind with respect to nature, society and humans, without compromising the ability of future generations to meet their needs in a similar manner Robustness is a specific aspect of structural safety that refers to the ability of a system subject to accidental or exceptional loadings (such as fire, explosions, impact or consequences of human errors) to sustain local damage to some structural components without experiencing a disproportional degree of overall distress or collapse.

Performance Design Using a performance-based approach, a structure or a structural component is designed to perform in a required manner during their entire life cycle. In case of existing structures, by a performancebased approach it is assessed whether the actual performance of an existing structure or a structural members and their performance during the residual life satisfy the demands of the stakeholders. Performance is evaluated by verifying the behaviour of a structure or a structural component against the specified performance requirements. Constraints related to service life are given by means of a specified (design) service life (relevant for the design of new structures) or a residual service life (relevant for the re-design of existing structures). The specified (design) service life and the residual service life refer to the period in which the required performance shall be achieved for structures to be designed and for existing structures, respectively as seen in Table 3. Table 3. Example of performance requirements for the design of a new structure, Source MC2010 Performance category Serviceability Structural safety Sustainability

Performance criteria Deformation limit Crack width limit Vibration limit, etc. Stress limit Capacity limit Progressive collapse limit, etc. Emission limits Impact on society Aesthetics, etc.

Constraints Specified (design) service life: Target reliability level: Specified (design) service life: Target reliability level:

50 year β = 1.5 50 year β = 3.8

4. Performance design applied to precast structures After the general statements defined in the MC2010 about performance design, in some aspects, this particular kind of design has been developed to a more detailed level and in some cases it could be applied to precast concrete applications. MC2010 gives some ideas about several of these aspects like Service Life Requirements, Ultimate Limit States, Robustness and Sustainability. In some of these aspects a performance-based design could be implemented directly in precast structures.

Service Life requirements In the MC2010, serviceability limit states correspond to the states beyond which specified demands for a structure or a structural component related to its normal use or function are no longer met. Frequently exceeding the serviceability limit states may affect the efficient use of a structure, its components (tanks, pipes, canals) or its appearance. In many cases, the risk of damage is indirectly excluded by ultimate limit state verifications or by detailing.

KE YNOTE LEC TURES

19

The serviceability limit states address fitness-for-use of a structure. Accordingly, the serviceability limit states that should be considered can be described as: –– operational limit states; –– immediate use limit states The corresponding serviceability limit state criteria are related to: –– f unctionality of the structure related to its normal use; –– comfort of using the structure. Traditional structural design involving the avoidance method includes a concept based on avoiding or reducing the detrimental effect, e.g. sheltering the structure from certain loads like environmental loads, wind, wave loads impact by vehicles or missiles, etc. In design for durability the avoidance-of-deterioration method implies that the deterioration process will not occur, due to for instance: –– separation of the environmental action from the structure or component, e.g. by cladding or membranes; –– using non-reactive materials, e.g. certain stainless steels or alkali-nonreactive aggregates; –– separation of reactants, e.g. keeping the structure or component below a critical degree of moisture; –– suppressing the harmful reaction, e.g. by electrochemical methods. Traditionally, national and international concrete standards give requirements to achieve the desired design service life based on the “deemed to-satisfy” and the “avoidance of deterioration” approach. When we design for durability we are in some way avoiding the corrosion of the steel by having an adequate material that separates the corrosion agents from the steel. This finally results on a dimension of the cover and a quality of the cover. In our present codes instead of defining the separation material and the time that has to resist for the service life of the structures we are giving other rules. This is due to our lack of definition of the separation material in a more technical way. Some codes are already giving information to be able to define the quality of the separation material to the steel as a characteristic and then they are able to avoid other simplified rules. For example, Spanish Code on Structural Concrete EHE in its Annex 9 allows to define and calculate beforehand the quality of the cover and the concrete and to define the transfer of external agents in the concrete to be able to define a cover related to the life span and the type of concrete tested [7]. In the case of corrosion, both by carbonation and by chlorides, the total time t L needed for the attack or deterioration to become significant can be expressed as: t L =t i+tp where: ti tp

Corrosion initiation period, understood as the time taken by the penetration front of the aggressive agent to reach the reinforcement thereby causing the corrosion to start. Propagation period (propagation time of the corrosion until the structural element suffers significant deterioration).

Using a similar model, it is possible today to design for durability using performance models in precast elements. This design could be very beneficial for the definition of covers which are relevant in slender elements and thus can lead to relevant optimisation of the structure.

20

KE YNOTE LEC TURE S

The problem arises when the application of the normal rules intended as just for design for avoidance is enforced directly by the codes and the effort to explain or convince the designers that the more detailed rules can be applied is so great that in the normal cases is not used.

Design by Testing In the MC2010, ultimate limit states are limit states associated with the various modes of structural collapse or stages close to structural collapse, which for practical purposes are also considered as ultimate limit states. In MC2010 there is a definition of how to define structural elements designed by testing. Verification assisted by testing is considered as a procedure where loading tests on limited series of representative specimens are used for the determination of the response of structural members or structural systems. The aim of the verification assisted by testing is to obtain design values for the parameters governing the response of structural members and structural systems under specified load conditions with respect to a certain limit state. Design by testing is an aspect of performance design that can be applied directly to industrialised construction. In some special cases it has been used when large quantities of products are designed in the same way. Then systematic testing has been developed to check design rules. An example of this case is the design of shear for hollow core slabs. Hollow core slab is a very common precast product that has no shear reinforcement and therefore it needs to be designed normally as a prestressed element without stirrups. Since the 1950`s large programs of testing were developed to cover shear design of hollow core slabs. In the last years also other testing programs have been developed for the design of shear and torsion in hollow core slabs and also fire design in hollow core slab floors. Design by testing is a design tool that should be more clearly developed to assign adequate safety levels. Also future development of design by testing rules should define and relate safety levels with number of testing and variability of the tests so they could be used in reality. With these clear rules many of precast products produced today in the industry could be largely optimised using design by testing.

5. Conclusions This paper emphasizes the importance of sustainability and performance design in precast concrete buildings. It is necessary to take into account the full life of the structure, even with the consideration and recycling. Taking into account these aspects, the use of the help of the thermal mass specific uses in precast concrete should also be considered. The use of industrialization or prefabrication in construction provides the advantage of using industrial methods for construction into the work site. The greatest impact that involves industrialized elements transfer at site is compensated by the advantages of industrial means within controlled premises. The use of available resources in industry provides materials optimisation and means of implementation for structures. It can be either because they minimize work at site, or because structures can be performed with less materials and higher quality. It also results in a more controlled environment in which it is possible and economically viable to make tests on special aspect of the materials or the structure to optimise the design thus avoiding costlier simplifications that come from the codes that need to take into account for more general design conditions.

KE YNOTE LEC TURES

21

Design of precast element using performance criteria is a real possibility today. As a matter of fact, precast structures, as they are an industrialization of construction, are developed under highly controlled conditions, can be designed in many aspects using performance criteria. This approach to design of precast structures can optimise it design in a very relevant way.

6. Acknowledgements The author would like to acknowledge past fib Commission 6 Chairs and many colleagues for sharing for many years very valuable information and personal experiences, to the ETS Ingenieria Civil of the Universidad Politecnica de Madrid in which I have been teaching for the last years and to fib, the organization in which I am now delightfully working. References 1 Aguado, A., Manga, M., and Ormazábal, G. (2006). “Los aspectos conceptuales del proyecto MIVES.” La medida de la sostenibilidad en edificación industrial, R. Losada, E. Rojí, and J. Cuadrado, eds., UPV, UPC, Labein‐Tecnalia, Bilbao, Spain, 113–134 (in Spanish). 2 Alanne, K. (2004). “Selection of renovation actions using multicriteria “knapsack” model” Autom. Constr., 13(3), 377–391. 3 Alexander, Sven (1997) Taking advantage of the environmental challenges facing the precasting industry. FTP symposium proceedings, The concrete way to development. Johannesburg. 4 Asunmaa, Otto-Ville Anttoni (1999) Optimising Environmental Effects of Prefabricated Concrete Building Frames. Helsinki University of Technology 5 ClMbéton (2002) Bétons & environnement. Analyses de cycle de vie de bétons. Paris. 6 Concrete for energy efficient buildings The benefits of thermal mass. Published by the European Concrete Platform ASBL Editor, Belgium 7 EHE, Code on Structural Concrete (EHE-08), Ministerio de Fomento, Spain 8 fib (2003) Environmental issues in Prefabrication. Bulletin 21 fib 9 fib (2004) Environmental Design. Bulletin 28. fib 10 fib (2008) Environmental Design of Concrete Structures. Bulletin 47. fib 11 fib (2013) Model Code for Concrete Structures 2010. fib. Ernst & Sohn. 12 Fluitman, A; deLange, V.P.A. (1996) Comparison of the environmental effects of three concrete story floors. CREM Report no. 95.107Amsterdam. 13 Hendriks, Ch. F. (2000) Durable and sustainable construction materials, Aeneas,. 14 Jacobs, F.; Hunkeler, F. (1999) Design of self compacting concrete for durable concrete structures. RILEM symposium proceedings, Self-compacting concrete. Stockholm. 15 Óberg, Mats (2000) The optimal concrete building. Lund Technical University. Division of Building Materials. Lund. 16 Punkki, Jouni (2001) Sustainable Prefabrication. fib Symposium proceedings, Concrete and Environment. Berlin. 17 Ríos, S., Ríos‐Insua, M. J., and Ríos‐Insua, S. (1989). Procesos de decision multicriterio, EUDEMA Universidad Complutense de Madrid, Madrid, Spain. 18 Straatman, Remco (2000) Environmental Related Issues in Precast Demountable Construction. Delft University of Technology, Faculty of Civil Engineering, 19 Swiss Society of Engineers and Architects (1998) Environmental Aspects of Concrete. Information on environmental compatibility, Zurich.