Structural Concrete 2015 01

1

Volume 16 March 2015 ISSN 1464-4177

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Eurocode 2 – analysis of National Annexes

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Extended design parameters for columns in fire with 2nd order effects

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Low-strength mortars – EC/US code approaches

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Bond/Anchorage of steel bars in fib Model Code 2010

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Bond behaviour of normal- and high-strength RAC

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5-spring model for full shear behaviour of deep beams

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Transverse stresses and bursting forces in post-tensioned anchorages

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Derivation of

σ-w relationship for SFRC with bending tests

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Thin-walled TRC shells – Part I: Design and construction

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Thin-walled TRC shells – Part II: ULS assessment, simulation

HALFEN GmbH • Liebigstrasse 14 • 40764 Langenfeld • Germany Tel.: +49 (0) 2173 970-9020 • Fax: +49 (0) 2173 970-450 • www.halfen.com

European.

Technical.

Approved.

March 2015 ISSN 1464-4177 (print) ISSN 1751-7648 (online)

Contents

Structural

Concrete

Vol. 16 / 1

Message from the president

1 Harald S. Müller

From accomplishments to challenges

Technical Papers

3 Anett Ignatiadis, Frank Fingerloos, Josef Hegger, Frederik Teworte

Eurocode 2 – analysis of National Annexes

17 Lijie Wang, Robby Caspeele, Ruben Van Coile, Luc Taerwe

Extension of tabulated design parameters for rectangular columns exposed to fire taking into account second-order effects and various fire models

36 François Duplan, Ariane Abou-Chakra, Anaclet Turatsinze, Gilles Escadeillas, Stéphane Brûlé, Emmanuel Javelaud, Frédéric Massé

On the use of European and American building codes with low-strength mortars

45 John Cairns

Bond and anchorage of embedded steel reinforcement in fib Model Code 2010

56 M. John Robert Prince, Bhupinder Singh

Bond behaviour of normal- and high-strength recycled aggregate concrete

71 Boyan Mihaylov

Five-spring model for complete shear behaviour of deep beams

84 Lin-Yun Zhou, Zhao Liu, Zhi-Qi He

Further investigation of transverse stresses and bursting forces in post-tensioned anchorage zones

93 Ali Amin, Stephen J. Foster, Aurelio Muttoni

Derivation of the σ-w relationship for SFRC from prism bending tests 106 Alexander Scholzen, Rostislav Chudoba, Josef Hegger

Thin-walled shell structures made of textile-reinforced concrete

Part I: Structural design and construction 115 Alexander Scholzen, Rostislav Chudoba, Josef Hegger

Thin-walled shell structures made of textile-reinforced concrete

Part II: Experimental characterization, ultimate limit state assessment and numerical simulation

125 Bastian Jung, Guido Morgenthal, Dong Xu, Hendrik Schröter

Quality assessment of material models for reinforced concrete flexural members

137 Josef Holomek, Miroslav Bajer, Jan Barnat, Pavel Schmid

Design of composite slabs with prepressed embossments using small-scale tests

fib-news

149 The fib in Russia: new standards

150 Worldwide representation at ACF 2014 151 DISC2014: the past and the future 151 Old for new: Penang Bridge 152 A venerable institute turns 80 152 JPEE2014 in Lisbon

153 fib MC2010 course in Brazil

153 Short notes

155 Nigel Priestley † 1943–2014 156 Congresses and symposia 157 Acknowledgement A5 Products and Projects

They have already become a new landmark: The six new water towers in the Al Jahra area in Kuwait City. Their mushroom-shaped water tanks were post-tensioned using DYWIDAG Strand Tendons. It goes without saying, that these buildings are of decisive importance for the inhabitants of cities in Kuwait, see page A5 (photo: DSI).

fédération internationale du béton

International Federation for Structural Concrete www.fib-international.org

Journal of the fib

Peer reviewed journal

Since 2009, Structural Concrete is indexed

in Thomson Reuter’s Web of Knowledge (ISI Web of Science).

Impact Factor 2013: 0.857

www.ernst-und-sohn.de/structural-concrete http://wileyonlinelibrary.com/journal/suco

The journal “Structural Concrete”, the official journal of the Inter -national Federation for Structural Concrete (fib – fédération internationale du béton), provides conceptual and procedural guidance in the field of concrete construction, and features peer-reviewed papers, keynote research and industry news covering all aspects of the design, construction, performance in service and demolition of concrete structures.

“Structural Concrete” is published four times per year completely in English.

Except for a manuscript, the publisher Ernst & Sohn purchases exclusive publishing rights. Only works are accepted for publication, whose content has never been published before. The publishing rights for the pictures and drawings made available are to be obtained from the author. The author undertakes not to reprint his article without the express permission of the publisher Ernst & Sohn. The “Notes for authors” regulate the relationship between author and editorial staff or publisher, and the composition of articles. These can be obtained from the publisher or in the Internet at www.ernst-und-sohn.de/en/journals.

The articles published in the journal are protected by copyright. All rights, particularly that of translation into foreign languages, are reserved. No part of this journal may be reproduced in any form without the written approval of the publisher. Names of brands or trade names published in the journal are not to be considered free under the terms of the law regarding the protection of trademarks, even if they are not individually marked as registered trademarks. Manuscripts can be submitted via ScholarOne Manuscripts at www.ernst-und-sohn.de/suco/for_authors

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Editor-in-Chief

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 György L. Balázs (Hungary)  Josée Bastien (Canada)  Mikael Braestrup (Denmark)  Tom d’ Arcy (USA)

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 Petra Schumacher (Secretary General fib)  Tamon Ueda (Japan)

 Yong Yuan (China) Current prices

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Imprint

Structural Concrete 16 (2015), No. 1

Products & Projects

DYWIDAG Ring Tendons stabilize Kuwait’s new Landmark

Afterwards, concreting, post-tensioning and grouting of the ten-dons were carried out using the equipment that had been sup-plied by DSI.

Further Information: DSI Holding GmbH,

Destouchesstrasse 68, 80796 Munich, Germany,

Tel. +49 (0)89 – 30 90 50-200, Fax +49 (0)89 – 30 90 50-215, [email protected], www.dywidag-systems.com Water is a valuable commodity in Kuwait – bottled water is

even more expensive than petrol. Consequently, the six new water towers that were built in the Al Jahra area in Kuwait City are an investment of decisive importance for cities in that country.

The huge, mushroom-shaped water tanks have already become a new landmark of the country and can be seen from afar thanks to their blue and white stripes. The elevated tanks are 38.5m high and have diameters of 32m at the upper rim of the water tanks. This way, the tanks can store more than 2.4 million liters

or 650,000 gallons of fresh water.

The towers’ mushroom-shaped water tanks were post-tensioned using DYWIDAG Strand Ten-dons. DSI supplied 66 6-0.5“ DYWIDAG Ring Tendons with anchorages and accessories to post-tension each tank. Initially, the ducts and tendons were installed into the form-work at ground level. They were then hydraulically lifted onto the pillars of the water towers.

Fig. 1. They are an investment of decisive importance for cities in Kuwait: the six new water towers that were built in the Al Jahra area, Kuwait City

Fig. 3. The tanks are 38.5m high and have diameters of 32m at the upper rim

of the water tanks. (© DSI)

Fig. 2. A new landmark of the

Generation of Moving Loads on Surfaces

The RFEM add-on module RF-MOVE Surfaces creates load cases from various positions of moving loads such as vehicles on bridges. It is also possible to create an enveloping result combination.

The data is entered in only four input windows. In this way, and due to the quick load case generation for RFEM, you can save a lot of time.

Features

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– Access to different stored axle load models (database) – Favorable or unfavorable load application taking into account

influence lines and surfaces

– Summarizing several moving loads in one load scheme – Generation of a result combination to determine the most

unfavorable internal forces

– Option to save different sets of movements to use them in other structures

Working with RF-MOVE Surfaces

The surfaces on which the load is moving are selected graphical-ly in the RFEM model. It is possible to define a load on a sur-face with several different sets of movements at the same time.

You can define the „lane” by using sets of lines. They can be selected graphically in the model. The moving step of single load steps is also specified.

RF-MOVE Surfaces provides several load types such as single, linear, rectangular, circular loads as well as different axle loads. They can be applied in local and in global directions. The differ-ent loads are summarized in load models. The defined load models are allocated to the sets of lines and on the basis of this information, individual load cases are generated.

With a single mouse click, you can create a variety of load cases. When the generation has been completed, RF-MOVE Surfaces displays the numbers of the created load cases for information. The descriptions of the individual moving loads are deduced from the respective load step number. It is possible, however, to replace those names in RFEM by other load case descriptions. Finally, the entire window input can be exported to MS Excel or OpenOffice.org.Calc.

More Information and Trial Versions: Dlubal Software GmbH,

Am Zellweg 2, 93464 Tiefenbach,

Tel. +49 (0)96 73 – 92 03-0, Fax +49 (0)96 73 – 92 03-51, [email protected], www.dlubal.de

MAURER AG: Change of corporate form

with a view to the future

With effect from 15. December 2014 the tradition steeped Munich firm specializing in steel construction, mechanical and plant engineering, Maurer Söhne GmbH & Co. KG will become the MAURER AG. The change in corporate form to a stock corporation denotes a milestone in the company`s strat-egy: The path is leading in the direction of further internation-alization and the inter nationally recognized legal form of stock corporation is a logical step on this path. Maurer AG will be represented by a new Logo and a new internet presence.

Dr. Holger Krasmann (Chairman of the Executive board) and Dr. Christian Braun, the former managing directors, have been appointed to the board of the renamed Maurer AG. The com -pany will remain in the ownership of the Beutler and Grill fami-lies, with Jörg Beutler as Chairman of the Supervisory Board. A new, clearer brand image will support the changeover to a stock corporation. The Logo has been reworked: Clear, con -temporary and distinctive, the Logo communicates strength and unity. The company name now only consists of the name Maurer.

The new internet presence www.maurer.eu gives a clear visual message of technological orientation. “However it is not only a visual concept” explains head of marketing Judith Klein, “rather that we want to present a company cast from one piece, no longer separated into sub-divisions but one homogenous Company.” Naturally the new website is also optimized for mo-bile devices.

Further Information: MAURER AG,

Frankfurter Ring 193, 80807 München, Tel. +49 (0)89 – 323 94-0,

[email protected], www.maurer.eu

A6 Structural Concrete 16 (2015), No. 1 Responsible for Products & Projects: Publishing House Ernst & Sohn

Products & Projects

Fig. 1. Definition of the lane using sets of lines in RF-MOVE Surfaces

Fig. 2. Generated Loads in RFEM (© Dlubal)

The new Logo of the re-named MAURER AG. The M can stand alone. (© Maurer)

Strasbourg receives another clinic

PASCHAL gets things moving on the construction site in the Strasbourg district of Cronenbourg with its “TTR” Trapezoi-dal girder circular formwork and the speedy construction pro-gress for column formwork is supported with the multi-pur-pose panel.

EPSAN and ARS Alsace, partners for psychiatric care, commis-sioned the construction of a 140-bed hospital to provide better patient care.

The Alsace branch of the construction company EIFFAGE CONSTRUCTION in Strasbourg prepared the project for the clinic, which is scheduled to open at the end of 2015. The square building structure is broken up by two two-storey, elliptical reinforced concrete constructions and a rounded rein-forced concrete construction.

First choice for rounded reinforced concrete constructions

To form the two ellipses and the semi-circular rein-forced con-crete wall, Eiffrage, the construction company in charge, used the TTR Trapezoidal girder circular formwork from PASCHAL. The construction company relied on the materials being deliv-ered and also profited from PASCHAL’s specialist knowledge and experience, which they used for the preparations and com-pliance with the work safety regulations.

The application engineering department at PASCHAL was therefore involved in the construction project from the very be-ginning and delivered a de-tailed and practical formwork con-cept in close coordination with the other parties involved in the project.

Individual columns on individual foundations

Right at the start of the shell construction, the slim reinforced concrete columns (dimensions: 35 × 65 cm) were formed and concreted with the multi-purpose panel from the LOGO.3 form-work system.

Four multi-purpose panels can be used to form rectangular and square columns with edge lengths from 20 cm to 75 cm quickly and easily using the “windmill vane principle”. This was applied on the construction site in Strasbourg. To speed up the work progress and to meet the strict French accident prevention regu-lations, the column forms were each fitted with two preassem-bled work platforms opposite each other.

Curved concrete constructions

Both ellipses consist of a 20 cm thick C25/30 reinforced con-crete wall. The large ellipse has a length of 13.352 m and a width of 5.825 m. The small construction has a length of 6.50 m and a width of 4.26 m. Both ellipses have a height of 9.39 m to 9.75 m. The height difference is due to the sloping upper con-necting wall.

To optimally support the construction progress, PASCHAL sup-plied completely preassembled and rounded TTR formwork units for the first step, in-cluding preassembled folding work platforms for the construction site. For the height intervals of the working levels, attention was paid to the easy accessibility of

A8 Structural Concrete 16 (2015), No. 1 Responsible for Products & Projects: Publishing House Ernst & Sohn

Products & Projects

Anchor Profi

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The cross-vendor anchor design software makes the an-chor world transparent and saves you time and money.

Anchor Profi is probably the best tool available to you to

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For further information, please contact: Dr. Li Anchor Profi GmbH

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Fig. 1. The small ellipse is rounder and has 5 x 4 = 20 radii.

Fig. 2. The small ellipse with half of a Trapezoidal girder circular formwork

unit in the foreground; the assembled recess formwork for the penetrations is subsequently reinforced.

the ties during formwork planning, so that the formwork tasks could be com-pleted quickly and safely.

For each preassembled formwork unit, the dead weight and the admissible ca-pacity of the crane lifting eyes were calcu-lated exactly and recorded on the form-work drawings for the form-work phases. In this way, the crane operator knew the lift-ing weight for each movlift-ing process of the formwork units.

Formwork planning for ellipses

To shape each ellipse as planned, the en-gineers in application engineering “mir-rored” each ellipse along the longitudinal axis.

To form the large ellipse, the two infinite-ly “adjustable ranges” were combined with the “adjustable range” up to 5 me-tres inside diameter. When added togeth-er, this ellipse comprises

8 × 4 = 32 radii.

To ensure a smooth transition at the con-crete sections to the left and right of the longitudinal axis, the inner and outer formworks extended beyond the actual concrete section and 3/4 were covered with a panel of 1.25 m during concreting of the opposite halves of the formwork with the two formwork units.

All three rounded structural parts were built with system formwork and

form-work filler plates supplied by PASCHAL were used for compensation.

As the pioneer of circular formwork with adjustable radii, PASCHAL is constantly faced with diverse reinforced concrete construction shapes, as highlighted by the Strasbourg clinic example. Thanks to extensive practical experience,

PASCHAL’s specialist team is able to pre-pare system formwork even for such un-usual shapes.

The invaluable benefits come from the Trapezoidal girder circular formwork available in two versions:

– For inside diameters from 5.00 m (r = 2.50 m) to infinity (straight).

– For inside diameters from 2.00 m (r = 1.00 m) to inside dia meters of 5.00 m. These possible combinations allow all curvatures to be shaped exactly, as there is a matching outside segment for each inside segment.

The system only uses a few ties and reli-ably absorbs fresh concrete pressure of up to 60 kN/m². Further information: PASCHAL-Werk G. Maier GmbH, Kreuzbühlstraße 5, 77790 Steinach, Tel. +49 (0)78 32 – 71-0, Fax +49 (0)78 32 – 71-209, [email protected], www.paschal.de

Products & Projects

Structural Analysis and Design

Up-to-Date Information...

Free Trial Version at

www.dlubal.com

Further Information: Dlubal Software GmbH Am Zellweg 2, D-93464 Tiefenbach Tel.: +49 9673 9203-0

DESIGN according to EC 2, ACI 318-11,

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RF-/FOUNDATION Pro: foundations

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RF-MOVE Surfaces: generation

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The Ultimate FEA Program

Steel Construction

Solid Construction

Column Bases

3D Finite Elements

BIM/CAD Integration

Stability and Dynamics

© www.ibehlenz.de © www.ssp-muc.com 3D Frameworks Cross-Sections Follow us on: © www.isenmann-ingenieure.de

The Structural Beam Analysis Program

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Bridge Construction

Fig. 3. Completely

pre-assembled formwork units of the Trapezoidal girder circu-lar formwork with plywood and built-on, folding work platforms are ready for use.

Fig. 4. To the left, the

dis-mantled “large ellipse”. To the right, the mounted form-work unit consisting of TTR segments for the rounded reinforced concrete wall in “Block 11”. The three work-ing levels were coordinated with the formwork and rein-forcements to be executed so that the builders could work quickly and safely. (© Paschal)

Topping-out ceremony for New Office

Airport Stuttgart

Last year’s November saw the topping-out ceremony for New Office Airport Stuttgart (NOAS), a new office building and one of the largest construction projects at Stuttgart Airport in recent years. With its rounded contours, the striking new building will redefine the character of the entrance to Stuttgart’s Airport City. Züblin completed the structural works on time within the schedule provided and the build-ing’s first tenant, financial audit firm Ernst & Young, is slated to move its Germany headquarters into the complex in early 2016.

In his ceremonial speech, Walter Schoefer, managing director of Stuttgart Airport, stressed: “We are investing about € 130 mil-lion in this excellent office property as a symbol for the further state-driven development of our airport site. Over 1,500 employ-ees of Ernst & Young will relocate here in 2016, giving the cam-pus enormous economic strength. The move shows that optimal infrastructure and mobility are extremely important for globally positioned companies. In this respect, Stuttgart Airport is one of the best-developed locations in the state of Baden-Württem-berg.”

Michael Marbler, lead partner for southwest Germany at Ernst & Young, and Roland Wiehl, business unit manager for turnkey construction at Züblin, which is handling the project turnkey as general contractor, expressed their thanks to the workers for helping to complete the structural works so swiftly and perfect-ly.

The new office building was planned and is being built accord-ing to the latest standards in terms of efficiency, sustainability and comfort. The architectural design by Hascher Jehle Ar-chitekten consists of two building complexes in the form of a reclining figure eight plus a third complex housing a conference centre. The office building, which is clearly visible as a new landmark from the A8 motorway, comprises an aboveground area of around 40,000 m2_{as well as two underground floors} with approximately 20,000 m2_{for parking, storage and cellar} rooms.

Further Information: Ed. Züblin AG,

Albstadtweg 3, 70567 Stuttgart,

Tel. +49 (0)711 – 78 83-0, Fax +49 (0)711 – 78 83-390, [email protected], www.zueblin.de

A10 Structural Concrete 16 (2015), No. 1 Responsible for Products & Projects: Publishing House Ernst & Sohn

Products & Projects

Fig. 1. Bird’s eye view on one of the largest construction projects at

Stuttgart Airport in recent years

Fig. 2. With its rounded contours, the striking new building will redefine the

character of the entrance to Stuttgart’s Airport City.The structural works have been completed by Züblin on time within the schedule provided. (© Stuttgart Airport)

software

Dlubal Software GmbH Am Zellweg 2 93464 Tiefenbach Phone +49 (0) 96 73 92 03-0 Fax +49 (0) 96 73 92 03-51 Mail: [email protected] Web: www.dlubal.de

stay cables

DYWIDAG-Systems International GmbH Max-Planck-Ring 1 40764 Langenfeld/Germany Phone +49 (0)21 73/7 90 20 Mail: [email protected] Web: www.dywidag-systems.de

vibration isolation

BSW GmbH Am Hilgenacker 24 D-57319 Bad Berleburg Phone +49(0)2751 803-126 Mail: [email protected] Web: www.bsw-vibration-technology.com under-screed impact sound insulation with European Technical Approval, PUR foam & PUR rubber materials for vibration isolation

reinforcement

technologies

HALFEN Vertriebsgesellschaft mbH Katzbergstraße 3 D-40764 Langenfeld Phone +49 (0) 21 73 9 70-0 Fax +49 (0) 21 73 9 70-2 25 Mail: [email protected] Web: www.halfen.de concrete: fixing systems facade: fastening technology framing systems:

products and systems

Max Frank GmbH & Co. KG

Technologies for the construction industry Mitterweg 1 94339 Leiblfing Germany Phone +49 (0)94 27/1 89-0 Fax +49 (0)94 27/15 88 Mail: [email protected] Web: www.maxfrank.com

sealing technologies

Max Frank GmbH & Co. KG

Technologies for the construction industry Mitterweg 1 94339 Leiblfing Germany Phone +49 (0)94 27/1 89-0 Fax +49 (0)94 27/15 88 Mail: [email protected] Web: www.maxfrank.com

Provider directory

products & services

bridge accessories

Maurer Söhne GmbH & Co. KG

Frankfurter Ring 193 D-80807 München Phone +49(0)89 32394-341 Fax +49(0)89 32394-306 Mail: [email protected] Web: www.maurer-soehne.de Structural Protection Systems Expansion Joints

Structural Bearings Seismic Devices Vibration Absorbers

literature

Ernst & Sohn Verlag für Architektur und technische

Wissenschaften GmbH & Co. KG

Rotherstraße 21 10245 Berlin Phone +49 (0) 30 4 70 31-2 00 Fax +49 (0) 30 4 70 31-2 70 E-mail: [email protected] Web: www.ernst-und-sohn.de

fastening technology

HALFEN Vertriebsgesellschaft mbH Katzbergstraße 3 D-40764 Langenfeld Phone +49 (0) 21 73 9 70-0 Fax +49 (0) 21 73 9 70-2 25 Mail: [email protected] Web: www.halfen.de concrete: fixing systems facade: fastening technology framing systems:

products and systems

post-tensioning

DYWIDAG-Systems International GmbH Max-Planck-Ring 1 40764 Langenfeld/Germany Phone +49 (0)21 73/7 90 20 Mail: [email protected] Web: www.dywidag-systems.de

prestressed concrete

Paul Maschinenfabrik GmbH & Co. KG

Max-Paul-Straße 1 88525 Dürmentingen/Germany Phone +49 (0)73 71/5 00-0 Fax +49 (0)73 71/5 00-1 11 Mail: [email protected] Web: www.paul.eu

The potential and the limitations of

numerical methods

The book gives a compact review of fi nite element and other nu-merical methods. The key to these methods is through a proper description of material behavior. Thus, the book summarizes the essential material properties of concrete and reinforcement and their interaction through bond.

Most problems are illustrated by examples which are solved by the program package ConFem, based on the freely available Py-thon programming language. The ConFem source code together with the problem data is available under open source rules in combination with this book.

Table of content:

fi nite element in a nutschell

uniaxial structural concrete behavior 2D structural beams and frames strut-and-tie models

multiaxial concrete material behavior deep beams

slabs appendix

*€ Prices are valid in Germany, exclusively, and subject to alterations. Prices incl. VAT. excl. shipping. 1044106_dp Order online:

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Recommendations:

Ulrich Häussler-Combe

Computational Methods for Reinforced Concrete Structures

2014. 354 pages. € 59,–*

ISBN 978-3-433-03054-7 Also available as

fib Model Code for Concrete Structures 2010

Structural Concrete Journal of the fib

On 1 January I began my two-year term as fib president with emotions ranging from deep respect for the office to pleasure at the idea of serving the fib in such a prominent role. This outstanding international association has been my home for many years and I have occupied various po-sitions within it since I started in the CEB in 1979. I am truly humbled to fill the same role as such extraordinary individuals as Gordon Clark, György L. Balázs, and

Michael Fardis, to mention but a few.

When I think of the fib’s mission and look back at its recent history, I see significant contributions to the ad-vancement of knowledge and technical developments in the field of structural concrete. The greatest accomplish-ment was the publication of the fib Model Code for Con-crete Structures 2010 in September 2013, which exempli-fied the fib’s ambition to compile the most up-to-date knowledge in code-type form to serve as a model for new generations of standards. Following in-depth analyses and discussions that began in 2010, the new structure for the

fib’s commissions and task groups was implemented at the

beginning of this year and will help the fib to run more ef-ficiently. Finally, Structural Concrete, journal of the fib, has made great progress: last year its impact factor in-creased from 0.289 to 0.857, testimony to the high quality of its articles.

Therefore, it would seem that, as president, I have on-ly to steer the association forward with a steady hand on the wheel. Not so. I think such an approach would be haz-ardous in our rapidly changing world. Stagnation means regression. We have to build on our accomplishments. The true challenge consists of developing a vision that looks beyond the horizon.

With this in mind, I would define my main targets in these terms: strategy, development, and globalisation.

For me, ‘strategy’ comprises, for example, a concept for continuously updating the fib Model Code. Exactly 20 years elapsed between MC 1990 and MC 2010; MC 1990 was already partially outdated by the end of the 1990s. ‘Strategy’ also means finding the best framework for desig-nating fib membership status and future benefits.

By ‘development’, I mean defining the technical ad-vances to be promoted by the fib, one of which is of

course sustainability. Simply partially replacing Portland ce-ment in concrete with other binders will not solve future problems. Since concrete use will increase by a factor of five over the next 30 years, only the development of new concretes and design concepts will help to avert increased environmen-tal troubles. We need task groups to tackle these prob-lems. Developing a model code for existing structures is a logi-cal step, as maintenance and re-habilitation are the most effec-tive sustainable measures.

Referring to ‘globalisation’, I think firstly of the fib’s role within the international associations scene, where ISO, CEN, the ACI, RILEM, the ACF, and others, have missions that are partially similar and certain publications that are comparable to those of the fib. Defining our own position more clearly and developing closer official con-tacts, for example through cooperation agreements or memoranda of understanding, appears to be advanta-geous in many respects.

My approach may mean that I, along with my desig-nated successor, current Deputy President Hugo Corres, will face sizable challenges. I am, however, rather confi-dent that we will contribute to the progress of the fib, not because of our own aptitudes, but because of the support of the excellent engineers, scientists, and practitioners from all over the world who form the backbone and strength of the fib.

Univ.-Prof. Dr.-Ing. Harald S. Müller President,

International Federation for Structural Concrete (fib)

From accomplishments to challenges

Message from the president

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Themes: Landmark Projects, Conceptual Design, Innovative Construction Methods, Special Foundations and Geotechnical Site Investigations, Life Cycle, Monitoring & Maintenance & Management, Incidents and Accidents, Logistics, Durability, New Materials and Special Devices, Extreme Loads, Rehabilitation, Operational Risk Analysis, Safety and Serviceability.

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Eurocode 2 consists of four parts that have to be applied in con-junction with the respective National Annexes of the CEN mem-ber states. The National Annexes were introduced, in particular, to maintain national safety levels and to account for regional as-pects in the different states.

The CEN (European Committee for Standardization) will revise and extend all structural Eurocodes by 2018. As part of that process, two main objectives for revising Eurocodes have been formulated: a reduction in the number of Nationally Determined Parameters (NDP) and improving the “ease of use”.

In order to reduce the number of NDP, improve the ease of use and allow for further harmonization without changing the main structure and the design models of Eurocode 2, the National An-nexes of EN 1992-1-1 for the different CEN member states have been compared and analysed. Furthermore, the analysis of the National Annexes may help to identify some main aspects for the revision of Eurocode 2.

This paper summarizes the analysis of the National annexes of EN 1992-1-1 and makes first proposals for further harmonization.

Keywords: Eurocode 2, national annexes, NDP comparison, harmonization

1 Reason and introduction

The European Commission has initiated the amendment and evolution of the present Eurocode generation by 2018 in accordance with mandate M/515 [1]. The European standards organization CEN followed up the mandate with detailed proposals for the respective work pro-grammes [2]. As part of that process, two main objectives for the revision of Eurocodes have been formulated: a re-duction in the number of Nationally Determined Parame-ters (NDP) and improving the “ease of use”.

In Germany these objectives have been expressly supported. Therefore, the engineering offices and industri-al associations chiefly affected by the codes in their every-day business have established the Initiative PRB, an orga-nization that aims to make the Eurocodes easier to use. Based on collecting and evaluating the experience gained with the present Eurocodes, practice-oriented proposals will be developed for the next Eurocode generation.

Looking after concrete construction and Eurocode 2 within this organization are the German Committee for Structural Concrete (DAfStb) and the German Society for Concrete and Construction Technology (DBV). One of the first tasks was to analyse the implementation of Eu-rocode 2 in the National Annexes of the CEN member states (CEN-MS).

Eurocode 2 consists of four parts ([3], [4], [5], [6]), which have to be applied in conjunction with the respec-tive National Annexes. The National Annexes were intro-duced, in particular, to maintain national safety levels and to account for regional aspects in the different CEN-MS. Some CEN-MS also implemented additional national rules and explanations in the form of NCI (Non-contra-dictory Complementary Information) for further guid-ance. In order to reduce the number of NDP, improve the ease of use and allow for further harmonization without changing the main structure and the existing models, the National Annexes of EN 1992-1-1 of the different CEN-MS have been compared and analysed. Furthermore, the analysis of the National Annexes may help to identify some main aspects for the revision of Eurocode 2.

The German mirror committee for Eurocode 2 takes the view that, in principle, the present code structure and the design and detailing rules should remain largely unchanged, unless unacceptable safety deficits or other technical and economical reasons exist (e.g. “ease of use”).

The following sections summarize the results of an analysis of the National Annexes of EN 1992-1-1 and make the first proposals for further harmonization.

2 Analysis and comparison

The National Annexes contain two types of information: the Nationally Determined Parameters (NDP) and the non-contradictory complementary information (NCI). Whereas the NCI may contain additional or specific na-tional rules (e.g. application rules for cases not covered by Eurocode 2, links to national codes or literature), the NDP represent mostly single values, groups of values, ta-bles or methods from which choices can be made. Recom-mended values are given in Eurocode 2, which can be adopted or changed in the National Annexes of the many CEN-MS. Background information to the German Na-tional Annex [8] can be found in [7].

Technical Paper

Eurocode 2 – analysis of National Annexes

Anett Ignatiadis

Frank Fingerloos*

Josef Hegger

Frederik Teworte

DOI: 10.1002/suco.201400060

* Corresponding author: [email protected] Submitted for review: 21 July 2014

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Altogether, Eurocode 2 refers to more than 120 NDP in EN 1992-1-1 [3] and a further approx. 70 NDP in EN 1992-1-2 [4], EN 1992-2 [5] and EN 1992-3 [6]. The Nation-al Annexes of EN 1992-1-1 of 28 states ([8] to [36]) have been compared in the present analysis. Malta and Latvia do not have National Annexes and the Swiss document is still in print. Fig. 2 shows the implementation of the rec-ommended values given in Eurocode 2 in the different National Annexes. The resulting potential for harmoniza-tion is shown in Fig. 1.

In general, the concepts and models of Eurocode 2 are adopted by all states. Only the informative annexes do not apply in every state, and in some states single para-graphs are omitted via NDP or NCI. In many cases the NDP just change some values compared with [3]. Hence, the number of differences between the National Annexes and [3] does not necessarily reflect the acceptance of EC2 in the different countries. Larger changes to the models and concepts implemented are exceptions (e.g. Finland does not apply the sections concerning punching, which may be solved with the current amendment [37]; Denmark has introduced a more detailed concept for the material safety factors and a design concept based on plastic theo-ry).

Key to Fig. 1: Categories

A: Harmonization by fixing value

B: Harmonization possible by introducing classes C: Good chance for harmonization

D: Harmonization may be possible (fixed or classes) E: Harmonization very difficult

C: 48 (38%) D: 44 (34%) B: 23 (18%) A: 8 (6%) E: 5 (4%)

Fig. 1. Potential for harmonization of NDP in EN 1992-1-1 (28 states

analysed) NO BE LU NL BG GR RO CY IT PT ES HR PL SK SI CZ HU

NDP in EN 1992-1-1

Hungary Czech Republic Slovenia Slovakia Poland Croatia Spain Portugal Italy Cyprus Romania Greece Bulgaria Netherlands Luxembourg Belgium Norway 0 10 20 30 40 50 60 70 80 90 100 110 120 130 DE AT FR UK IE SE DK EE FI IS LT NO Number of NDP Norway Lithuania Iceland Finland Estonia Denmark Sweden Ireland United Kingdom France Austria Germany Key:

Recommended values adopted

In general, recommended values adopted, but special conditions for application or exceptions possible Different values

Section does not apply

Section not mentioned in NA / information incomplete or ambiguous

A. Ignatiadis/F. Fingerloos/J. Hegger/F. Teworte · Eurocode 2 – analysis of National Annexes To outline possibilities for further harmonization and

to identify main aspects for revision, the NDP were divid-ed into five categories. NDP with acceptance of the rec-ommended values according to EN 1992-1-1 in all states were classified as category A (e.g. safety factor for fatigue). Furthermore, there are several NDP where only two or three different values are used in all states. In this case, harmonization by introducing classes seems possible (cat-egory B). This concerns, for example, the factor αccused

when calculating the design value of concrete compres-sive strength, which only differs between 0.85 and 1.0. Cat-egory C describes NDP where the differences are quite small and only a few states do not apply the recommend-ed values, thus leading to a high potential for harmoniza-tion (see example in Table 1).

The values of NDP in category D show larger differ-ences, so there is greater need for discussion, see Table 2. NDP in categories C and D especially need further investi-gation concerning the reasons for the differences. The dif-ferences, particularly regarding the final result (e.g. dimen-sions, amount of reinforcing steel), may be identified by means of parameter studies or comparative calculations.

For some NDP the chance for further harmonization seems to be rather small (category E). This applies espe-cially to NDP that relate to other codes, e.g. determining the minimum concrete cover depending on the exposure classes with reference to EN 206-1:2000 [39] or the prop-erties of reinforcing steel with reference to EN 10080 [40]. Table 3 lists and classifies the NDP of EN 1992-1-1 con-cerning the potential for harmonization applying the five categories A to E described above.

3 Approaches for reducing the number of NDP and further harmonization

3.1 General

Different approaches can be applied to reduce the number of NDP, and hence also the volume of Eurocode 2 and the National Annexes. One approach, especially applicable to NDP in category A, is the use of the recommended values as fixed values. However, for safety factors it may be nec-essary to retain an opening clause for formal reasons. An-other approach is the introduction of classes, which seems to be promising for NDP in category B.

Furthermore, some NDP may be omitted due to the revision or reduction of the corresponding section (e.g. if special cases or application methods are shortened). After a discussion of the different national provisions, it may be possible to enhance the chance for harmonization by clar-ifying the corresponding section for some NDP (e.g. differ-ent recommended values for differdiffer-ent loads). In doing so, the existing concepts and models can generally be re-tained and there is no need to start harmonization based on a completely new document.

Owing to the number of parameters and the com-plexity of the Eurocodes, it cannot be ruled out that iden-tical or similar influences are considered in different para-graphs in the many CEN-MS. For this reason, many NDP cannot be dealt with independently, but have to be evalu-ated according to their final result accounting for the in-fluencing NDP. Therefore, some NDP may be summarized as one NDP without influence on the (national) final

re-Table 1. Example of NDP for category C (good chance for harmonization)

Section 5.10.2.2 (5)

Parameter k6

Description Coefficient used to determine maximum compressive stress at time of transfer of prestress for pretensioned elements Recommended value 0.70

Values in National Annexes1)

DE, AT, FR, UK, IE, SE, DK, EE, IS, LT, NO, LU, NL, BG, GR, RO, CY, IT, PT, HR, PL, SK, SI, CZ: recommended value

FI 0.65

BE 0.667 fcm(t)/fck(t)

ES 0.60

HU up to 0.90 (under defined conditions) 1)_{for CEN Member State codes see Fig. 2}

Table 2. Example of NDP for category D (average chance for harmonization)

Section 5.5 (4)

Parameter k1, k2, k3, k4, k5, k6

Description Coefficients to limit the redistribution of bending moments without an explicit check of the rotation capacity

Recommended values k1= 0.44; k2= 1.25 · (0.6 + 0.0014/εcu2); k3= 0.54; k4= 1.25 · (0.6 + 0.0014/εcu2); k5= 0.7; k6= 0.8

Values in National Annexes1)

AT, FR, SE, DK, EE, IS, LT, BE, LU, BG, GR, RO, CY, PT, HR, PL, SK, SI, CZ, HU: recommended values

IT Recommended values, except k6= 0.85 NO Recommended values, except k6= 0.9 ES Recommended values, except k6= 0.8εcu2 DE k1= 0.64; k2= 0.8; k3= 0.72; k4= 0.8;

k5= 0.7 and k6= 0.8 for fck≤ 50 MPa; k5= 0.8 and k6= 1.0 for fck> 50 MPa UK, IE For reinforcing steel with fyk≤ 500 MPa:

k1= 0.40, k2= 0.6 + 0.0014/εcu2; k3= 0.40, k4= 0.6 + 0.0014/εcu2; k5= 0.7; k6= 0.8

(more restrictive values for fyk> 500 MPa, further guidance in PD 6687 [38]) FI k1= 0.44; k2= 1.10; k3= 0.54; k4= 1.25 · (0.6 – 0.0014/εcu2); k5= k6= 1.0 for 100 · εuk· ft/fyk< 2.5; k5= k6= 0.9 – 3.21· εuk· ft/fyk≥ 0.67 for 100 · εuk· ft/fyk≥ 2.5 NL k1= f/(500 + f); k2= 0; k3= 7f/(εcu· 106 + 7f) with f = [(fpk/γS– σpm,∞) · Ap+ fyd· As)]/(Ap+ As) k4= 1.0; k5= 0.7; k6= 0.8

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A. Ignatiadis/F. Fingerloos/J. Hegger/F. Teworte · Eurocode 2 – analysis of National Annexes

sult, whereas in other cases a single NDP cannot be har-monized, instead a group of NDP has to be considered in combination (e.g. the permitted angle of the inclined com-pression strut determining the shear resistance and the maximum spacing of shear reinforcement).

During the revision of Eurocode 2, attention has to be paid to ensuring consistent recommended values in the remaining NDP, which means avoiding mixing up differ-ent national methods and philosophies so that the use of all recommended values is possible and on the safe side. Furthermore, the influences on the other parts of Eu-rocode 2, especially part 2, have to be considered.

It cannot be ruled out that new NDP have to be in-troduced during the revision. However, this may still lead to a reduction in the National Annexes if NCI can be omitted instead. In particular, in cases where NCI in the National Annex contradict the Eurocode or contain more restrictive requirements, the implementation of NDP will be a better solution.

Further research concerning the background to the national provisions, parameter studies and in some cases comparative analyses is necessary to make specific pro-posals. The classification of the NDP into categories A to E is explained in the following section. In addition, NDP related to other NDP are identified. Proposals for harmo-nization and further procedures are described for certain NDP.

3.2 Specific approach for certain NDP 3.2.1 Basis of design

In section 2.3.3 (3) a value of 30 m is recommended as the maximum spacing for joints to preclude temperature and shrinkage effects from the global structural analysis. Although only some CEN-MS have adopted this value, the chances for harmonization are high (category C). In the states not adopting the recommended value, this value has to be determined for each individual case (e.g. in Ger-many), or several values dependent on different influences are given (e.g. member geometry, concrete composition, foundation type, regional factors and others). Since this parameter can be dealt with independently from other NDP, the section could be revised, not recommending any specific value but instead pointing out factors to be con-sidered so that the NDP could be omitted. Detailed guid-ance and recommendations for several cases could be giv-en in background literature.

The recommended values for the partial factor for shrinkage action in section 2.4.2.1 (1), for the partial safe-ty factor for fatigue loading in section 2.4.2.3 (1) and for the partial safety factors for materials for serviceability limit states in section 2.4.2.4 (2) have been adopted by all states and could be fixed unless barred for formal reasons (category A).

The recommended value of 1.0 for the partial safety factor for favourable prestressing action in section 2.4.2.2 (1) has been adopted by most CEN-MS. In the United Kingdom, Ireland and Finland, a value of 0.9 is used, while in Norway and Romania values of 0.9 and 1.1 are applied. Therefore, this NDP was classified as category C. The recommended value of 1.3 for the partial safety factor for unfavourable external prestressing action at the

stabili-8

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Structural Concrete (2015), No. 1

ty limit state in section 2.4.2.2 (2) has been adopted by many states. The differing values range from 1.0 to 1.3 and so this NDP was classified as category D. The recom-mended value of 1.2 for the partial safety factor for un-favourable prestressing action for local effects in section 2.4.2.2 (3) has been adopted by most states; only Germany and Norway use other values (category C). These three NDP cannot be observed independently from other NDP concerning prestressing (especially in section 5.10). Since these NDP concern special cases (external prestressing with additional European Technical Approvals (ETAs)) or certain verifications (tensile splitting reinforcement, partly also requirements in ETAs), NDP in sections 2.4.2.2 (2) and (3) may eventually be omitted.

The recommended values for the partial safety fac-tors for materials for ultimate limit states in section 2.4.2.4 (1) have been adopted by many states. This NDP was clas-sified as category D even though the differences are not very great. Denmark has applied a more detailed system taking into account the type of failure and the level of in-spection. Here, it can be checked whether some of these influences are already covered by the current Annex A of Eurocode 2 as well. The values for reinforcing and pre-stressing steel with γS = 1.15 for the persistent, transient

and fatigue design situations and γS = 1.0 for the

acciden-tal design situation have been adopted by all other states, except The Netherlands, where the factor γS= 1.1 is applied

for prestressing steel in these situations. Further, γC= 1.5

for concrete in the persistent, transient and fatigue design situations has been adopted by almost all other states, with the following exceptions: Poland: γC = 1.4; Italy: other

values for special cases; The Netherlands: γC = 1.35 for

fatigue design. The maximum deviation occurs in the acci-dental design situation, where values of γChigher than the

recommended value (1.2) are applied (Germany, Spain: 1.3) as well as values lower than the recommended one (Italy: 1.0). Complete harmonization seems to be quite dif-ficult. In addition, these factors (especially γC) are used

several times in Eurocode 2, but eventually some of these values could be fixed unless barred for formal reasons.

The recommended value k_{f = 1.1 for the coefficient} for multiplying the partial safety factor for concrete when calculating the design resistance of cast-in-place piles without a permanent casing in section 2.4.2.5 (2) has been adopted by most CEN-MS (category C). In Germany and Austria, k_f= 1.0 is possible if the bored piles are built according to EN 1536 [41], and in Denmark and Italy a value of 1.0 is applied in general. In France the factor has to be determined according to the national code NF P94-262 [42]. It is necessary to check (also in section 9.8) which provisions for foundation members are necessary in Eurocode 2 and what is already covered in Eurocode 7 [43] or in the codes for execution of special geotechnical work (e.g. EN 1536).

3.2.2 Materials

The maximum concrete strength class of C90/105 for us-ing Eurocode 2 in section 3.1.2 (2) has been adopted by most CEN-MS (category C). Germany, Sweden and Nor-way allow a higher strength class (C100/115 or C95/110). In some states the use of strength classes higher than

A. Ignatiadis/F. Fingerloos/J. Hegger/F. Teworte · Eurocode 2 – analysis of National Annexes C50/60 requires the approval of the authority responsible

and in other states they can be used only with some re-strictions. The value for bridges may be different (EN 1992-2 NDP to 3.1.2 (102)P). Owing to developments in concrete technology, harmonization seems possible by the time the new generation of Eurocodes is published.

Factor k_t, for reducing coefficients _αccand _αctif the concrete strength is determined at age t_{> 28d, is defined} in section 3.1.2 (4). In most of the states the recommend-ed value of 0.85 or a value of 1.0 is applirecommend-ed. In some states the influence is considered by interpolation (Spain, Hun-gary), determination according to the development of the strength (Germany, Denmark) or by equation 1/αcc(t)

(Norway, Slovenia). The introduction of classes might be possible in this case (category B). This NDP could also be included in the NDP αccin 3.1.6 (1) and αctin 3.1.6 (2) as

it only can be observed in relation to these parameters. Coefficient _αccin section 3.1.6 (1) takes into account long-term effects on the compressive strength and un-favourable effects resulting from the load application. The recommended value of 1.0 is adopted in about half the states. Some states apply a value of 0.85 and some states apply values of 0.85 or 1.0 depending on the load (e.g. 0.85 for axial force and bending, 1.0 in other cases). The introduction of classes could be a way of harmonizing here (category B). It has to be considered that this para-meter influences many verifications indirectly via f_cd. To enhance the chances for harmonization, it has to be checked in the several sections as to whether the reduc-tion in compressive strength is justified and if other NDP in the several sections include a similar reduction, espe-cially in the states that apply αcc= 1.0. For this purpose,

careful investigation of which influences are considered precisely by coefficient αccis necessary. It is the same with

coefficient αct in section 3.1.6 (2), which takes into

ac-count long-term effects on the tensile strength and un-favourable effects resulting from load application. In most of the states the recommended value of 1.0 is adopted. Only Germany and Norway apply a value of 0.85 and Spain reduces the value for high ratios of permanent and full load. Furthermore, it should be confirmed whether the

applied values for NDP to 3.1.6 (101)P and NDP to 3.1.6 (102)P in EN 1992-2 are different in one state. If not, at least this NDP could be eliminated there.

The stress-strain diagram for reinforcing steel is de-fined in section 3.2.7 (2). Apart from the bilinear stress-strain diagram with horizontal top branch without stress-strain limit, a bilinear stress-strain diagram with inclined top branch and limitation of strains may be applied. The strain limit εuddepends on the National Annexes. The

rec-ommended value εud = 0.9εuk is applied in many states.

However, there are also differences, e.g. in Denmark only the stress-strain diagram with horizontal top branch is ap-plied, and in Germany and Finland one absolute value in-dependent of εukis defined. In Norway, for example, εudis

defined depending on the steel class, since different class-es exhibit different ductiliticlass-es. As the steel class used (wire fabrics _{= class A; reinforcing bars = class B) is not always} known during the design process, in Germany this ap-proach was not considered practical, leading to one dia-gram for all classes (and therefore to identical design tools).

Figs. 3 and 4 only reflect how the values determined influence the stress-strain diagrams and do not show the differences in, for example, the amount of reinforcement resulting from this. Hence, the parameter is classified as category D. To identify the potential for harmonization, further investigation is necessary. The impact on the rein-forcement required could be figured out by comparative analyses of different member types (e.g. beams, slabs, columns), also considering the minimum reinforcement and, where applicable, the stress limits. Therefore, the stress-strain diagram with horizontal top branch should al-so be considered. It is conceivable that the differences in the amount of reinforcement will be rather small, so this diagram may be sufficiently accurate in most cases (espe-cially for steel classes A and B) and the NDP could be eliminated.

The minimum value k= fpk/f0.1kto ensure adequate

ductility in tension for the prestressing tendons is defined in section 3.3.4 (5). The recommended value k_{= 1.1 has} been adopted by all CEN-MS and could be fixed.

440 450 460 470 σs [MPa] _B500A EC2 (b) EC2 (a) DE, BG (*) NO fyd BE, BG(**) FI, EE, ES DK, HU (b) BE (b) LU (b) 400 410 420 430 0 5 10 15 20 25 30 εs [‰] uk , ( )

EC2 (a) = AT, FR, UK, IE, SE, EE, IS, LT, LU, NE, BG, GR, RO, CY, IT, PT, HR, PL, SK, SI, CZ, HU BG (*) = ULS for axial force, non-prestressed members BG (**) = ULS for axial force, prestressed members (EE - two options possible) _ε

3.2.3 Durability

The minimum cover c_min,b for post-tensioned ducts and pretensioned tendons in order to transmit bond forces safely and ensure adequate compaction of the concrete is given in section 4.4.1.2 (3). Generally, there is good con-sensus regarding the values applied in different states, es-pecially concerning post-tensioned ducts. However, at least four values have to be defined, and the actual values in altogether 10 states deviate to some degree (category D). For post-tensioned circular ducts, the value c_min,b = φduct

is adopted by all states except Austria, where 0.5φductis

ap-plied. Also, the upper limit of 80 mm for circular ducts as well as for rectangular ducts is generally accepted. Only The Netherlands does not apply any upper limit and in Denmark the upper limit for circular ducts is 65 mm. Ad-ditional lower limits are applied in The Netherlands (25 mm for circular ducts) and Spain (40 mm). Essentially two groups can be identified for pretensioned tendons, i.e. one group adopting the recommended values of 1.5φp(for

strands or plain wires) and 2.5φp(for indented wires) and

another group (Belgium, Luxembourg, Italy, Cyprus, Spain) applying values of 2.0φpand 3.0φprespectively. No

difference between strands, plain and indented wires is made in Germany (generally 2.5φp) and France (generally

2.0φpor maximum aggregate size). Further harmonization

seems possible (maybe fixing the values for post-tensioned ducts and introducing classes for pretensioned tendons) provided the reasons for the differences are discussed.

The minimum concrete covers for reinforcement and prestressing tendons in normal-weight concrete, taking in-to account exposure and structural classes, are deter-mined in section 4.4.1.2 (5). Here, only a few states have adopted the recommended Tables 4.3N to 4.5N without any change. In some parts even the philosophy of the structural classes has not been applied. Therefore, this NDP was classified as category E, also concerning the def-inition of exposure classes in EN 206-1 [39]. In [44] a sur-vey of national requirements used in conjunction with EN 206-1 revealed that the application of the exposure classes

10

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Structural Concrete (2015), No. 1

cannot be harmonized further. Therefore, further investi-gation would seem to be unrewarding.

In most of the states the additive safety element for determining minimum concrete cover in section 4.4.1.2 (6) is not used (recommended value 0 mm) or integrated directly into section 4.4.1.2 (5) (category C). Only Ger-many, Ireland and Spain define values for _Δcdur,γ. Con-cerning the differences in section 4.4.1.2 (5), this NDP may be eliminated and the respective values may be inte-grated there as already done by some states.

Specific values for reducing minimum cover due to the use of stainless steel or other special measures in tion 4.4.1.2 (7) or because of additional protection in sec-tion 4.4.1.2 (8) are given in a few states only. Most states have adopted the recommended value of 0 mm without further specification (category C). In some states a reduc-tion is possible with further specificareduc-tion (approval, spe-cialist literature or tests). Here, mentioning the general possibility of reducing the minimum cover may be suffi-cient without giving any recommended value (elimination of NDP).

The NDP in sections 4.4.1.3 (1) and 4.4.1.3 (3) con-cerning the additive value to calculate the nominal cover (accepted negative deviation during execution) could be summarized, so that all cases for Δcdevare covered by one

paragraph. This is already done in some states.

3.2.4 Structural analysis

The coefficients to limit the redistribution of bending mo-ments without checking the rotation capacity are deter-mined in section 5.5 (4). This NDP consists of six values,

k₁to k₆, which define four different conditions for the per-mitted ratio of redistributed moment and elastic bending moment. The recommended values have been adopted in many CEN-MS, whereas in some states only one or two values differ and in other states all values have been changed (see Table 2). Hence, this NDP is classified as cat-egory D. The differences can be evaluated using Fig. 5. It can be seen that the permitted redistribution using rein-470 σs [MPa] B500B 460 EC2 (a) DE BE 450 FI EE ES BG (*) BG(**) 440 EC2 (b) NO fyd FI, EE, ES DK BE (b) LU (b) 420 430 410 420

EC2 (a) = AT, FR, UK, IE, SE, EE, IS, LT, LU, NE, BG, GR, RO, IT, CY, PT, HR, PL, SK, SI, CZ, HU BG (*) = ULS for axial force, non-prestressed members BG (**) ULS f i l f t d b 400

0 5 10 15 20 25 30 35 40 45 50 55εs

[‰] εuk

BG (**) = ULS for axial force, prestressed members (EE - two options possible)

A. Ignatiadis/F. Fingerloos/J. Hegger/F. Teworte · Eurocode 2 – analysis of National Annexes

forcing steel class A is generally lower than for class B or C. Furthermore, it decreases as the ratio between depth of neutral axis and effective section depth x_u/d increases in all states, but to a variable extent. This trend is more dis-tinct for concrete with higher strength. The differences be-tween the many CEN-MS are small (_{≤ 10 %) for concrete} with f_{ck ≤ 50 MPa and moderate degree of utilization} (small x_u/d) and increase with increasing concrete strength and increasing x_u/d. To discuss harmonization, research concerning the background to the differences is necessary.

The slenderness criterion in Eq. (5.13N) to check whether second-order effects may be ignored has been adopted by most CEN-MS (category C). Only Germany, Norway and Spain use other criteria, and in Slovakia and the Czech Republic an additional limit λlim≤ 75 has been

introduced. Since this is only a limit for using one method, there is no influence on the final result. There may be an influence on the computational cost in some cases. The NDP could be harmonized by getting all states to adopt Eq. (5.13N) or by changing the current voluminous limit to a simpler criterion that is on the safe side.

Three different methods considering second-order ef-fects are introduced in section 5.8.5 (1). Apart from the general method, based on non-linear second-order analy-sis, two simplified methods can be chosen. In most of the states, both methods can be applied without restrictions (category C). In Germany only method (b), based on nom-inal curvature, is used and in Denmark only method (a), based on nominal stiffness. In The Netherlands both methods apply with some restrictions or changes. In order to reduce the volume of Eurocode 2, one simplified method should be sufficient.

Several NDP calculating the permissible prestressing are given in sections 5.10.2, 5.10.3 and 7.2, limiting the stresses in prestressing steel or the compressive stress in the concrete at different times. As in most cases only three or four states define different values, these NDP have mainly been classified as category C. The coefficient to limit the compressive stress in the concrete under the

qua-si-permanent combination of loads in section 7.2 (3) can be fixed because all states have adopted the recommended value (category A). Furthermore, upper and lower partial safety factors for the increase in stress are defined in sec-tion 5.10.8 (3) and coefficients to consider possible varia-tions in prestress in section 5.10.9 (1). Here, it might be possible to introduce classes (category B). The differences in the final result can only be assessed by comparative analyses of different member types as all these NDP have to be considered together. In general, it should be investi-gated as to whether so many NDP are needed here or if one general NDP for stresses in the prestressing steel, one general NDP for stresses in the concrete and one or two NDP considering possible variations and safety factors are sufficient.

3.2.5 Ultimate limit states

There are several NDP in sections 6.2 and 6.4 for shear and punching design. These sections have already been identified as one main topic for the revision of Euro -code 2. The NDP for shear and punching resistance for members not requiring shear reinforcement in sections 6.2.2 (1) and 6.4.4 (1) respectively are classified as catego-ry C. The results do not depend on other NDP except γC.

Strength reduction factors for concrete cracked in shear are determined in 6.2.2 (6) and 6.2.3 (3). It should be con-firmed whether two NDP or even three, considering ν ′ in 6.5.2 (2) as well, are necessary for this purpose. Since the final results depend on f_cd, further NDP have to be consid-ered (see also remarks to 6.5.2 and 6.5.4). The NDP for limiting the angle of the inclined compression strut in sec-tion 6.2.3 (2) is classified as category D (see also remarks to sections 9.2.2 (6) to 9.2.2 (8)). The maximum punching shear resistance v_Rd,maxin section 6.4.5 (3) is determined quite differently in several CEN-MS. This even concerns the applicable control perimeter. Owing to an amendment [37], the general concept at least will be harmonized. How-ever, a new factor k_max for the maximum punching resis-tance as a multiple of v_Rd,c had to be introduced as an 0.80 0.90 1.00 δ DE (B,C) DE (A) IT (A) EC2 (B,C) UK, IE (B,C) NL (B,C) UK, IE (A) FI (A)

EC2 (A) NL (A) NO (A)

0.60 0.70

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 xu/d

EC2 (B, C) = AT, FR, SE, DK, EE, IS, LT, NO, BE, LU, BG, GR, RO, CY, IT, PT, ES, HR, PL, SK, SI, CZ, HU EC2 (A) = AT, FR, SE, DK, EE, IS, LT, BE, LU, BG, GR, RO, CY, PT, HR, PL, SK, SI, CZ, HU

NL for fyk= 500 MPa and without prestressing; UK, IE for fyk= 500 MPa

FI (B)

FI (C)