Precast Concrete Structures - Hubert Bachmann

Hubert Bachmann, Alfred Steinle

Precast Concrete Structures

Hubert Bachmann / Alfred Steinle

Precast ConcreteStructures

Dr.-Ing. Hubert Bachmann, Department Manager

Ed. Zublin AG

Structural Engineering (TBK-S)

Albstadtweg 3

D70 567 Stuttgart

Dr.-Ing. Alfred Steinle

Alte Weinsteige 92

D70 597 Stuttgart

Translated by Philip Thrift, Hannover/Germany

Cover photo: The Dancing Towers, Hamburg/Germany; two office towers of 80m and 70m height,

under construction.

(Photo: Ed. Zublin AG)

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in memoriam

Volker Hahn 10 April 1923 1 May 2009

The authors would like to dedicate this English edition to Prof. Dr.-Ing. Volker Hahn,their mentor and for many years their boss at Zublin, and also co-author of the first Ger-man edition.

Volker Hahn began his career at Ed. Zublin AG in 1949 and in his role as developmentengineer established the main engineering office, which is still the technological heartof the company. He was one of the pioneers as computers were introduced into construc-tion and with great farsightedness initiated important developments in precast concreteconstruction, transportation, specialist civil engineering, turnkey projects and environ-mental protection technology.

He was a member of the Board of Directors at Ed. Zublin AG from 1971 to 1987. It was inhis capacity as board member that he made major contributions to the dynamic growth ofthe company, its ongoing economic success and its position as a technology leader. Youngengineers were able to benefit from Volker Hahns superlative specialist knowledgethrough his lectures at the University of Stuttgart, where he was honorary professor.Zublin House was built under his leadership, a project that lent new momentum to precastconcrete construction.

Precast Concrete Structures. First Edition. Hubert Bachmann, Alfred Steinlec 2011 Ernst & Sohn GmbH & Co. KG. Published by Ernst & Sohn GmbH & Co. KG.

Preface

Building with precast concrete components is as old as building with concrete itself. Itwas only in the second half of the last century, however, that this form of constructiontook on its industrialised form. Factors that contributed to this were, in particular, the de-velopment of heavy lifting equipment, the use of mechanised steel moulds and, more re-cently, automated manufacturing systems, for suspended floor elements especially.

This work on precast concrete construction was first published in 1988 as part of theBeton-Kalender. A second version by the authors Alfred Steinle and Volker Hahn appea-red in the same publication in 1995. These essays were turned into a book which was pub-lished in 1998 as part of the Bauingenieur-Praxis series of the Ernst & Sohn publishinghouse. A further treatise appeared in the 2009 edition of the Beton-Kalender, this timewith Hubert Bachmann joining the original authors, and it was that version that becamethe second edition of the book in German.

Inevitably, there have been some changes to the standards over the past 10 years. Forexample, the publication, following a long period of preparation, of the new DIN 1045Concrete, reinforced and prestressed concrete structures.

This standard has been approved by the building authorities for use in the Federal Repub-lic of Germany since September 2002 and since 1 January 2005 is the only standard thatmay be used for concrete works. It was drawn up on the basis of the Euronorm EN 1992-1Design of concrete structures (previously known as Eurocode 2) and therefore repre-sents the translation of this Euronorm into national German practice.

Furthermore, we are witnessing a fundamental change in the design of precast concretecomponents.

The creation of the European Single Market led to the publication of the ConstructionProducts Directive, which has been in force in Germany in the form of the ConstructionProducts Act (Bauproduktengesetz) since 1992 and in the meantime has become part ofthe building regulations of the federal states which were revised to take account of this le-gislation. The directive renders it necessary to establish harmonised product standardsspecifically for the various precast concrete products so that in the end it will be possibleto use all such components labelled with the CE marking throughout the EuropeanUnion.

With modern methods of construction making use of industrial methods of manufacture,which includes construction with factory-precast concrete components, the design of theindividual elements, and also the entire structure, is heavily influenced by the factory pro-duction. On the manufacturing side, the growing trend towards mechanisation and auto-mation in production is evident.

The development of high-performance concrete provides us with the chance of em-ploying these for precast concrete construction in particular because factory productionpresents excellent conditions for their use. For example, the first precast concrete compo-


nents made from ultra-high-strength concrete for bridges and facades have already beenproduced. Besides the industrial production of batches and series of components, weare seeing more and more one-offs being produced, which take advantage of the excellentproduction options in order to achieve a high standard of quality. These tendencies willbecome even more obvious as more and more progress is made in the development ofconcrete as a building material.

The authors aim in writing this book is to map out the boundary conditions of factoryprefabrication for architects and structural engineers and also to demonstrate the opportu-nities presented by this method of construction in the expectation that this will contri-bute to the ongoing development of precast concrete structures.

Stuttgart, November 2010 A. Steinle H. Bachmann

Ed. Zublin AG

VIII Preface

Authors

Alfred Steinle (b. 1936) turned Hahns lecture notes into a manuscript in the early 1970s,which then became the starting point for this book. After a number of years in bridge-building, Alfred Steinle also became heavily involved in precast concrete constructionat Zublin. His theoretical work covered bridge-building with torsion and section defor-mations in box-girder bridges and in precast concrete structures within the scope of the6M system with corbels, notched beam ends and pocket foundations. In addition, hewas a key figure in many precast concrete projects such as the 6M schools, the Universityof Riyadh, schools with foamed concrete wall panels in Iraq, Zublin House and theconstruction of a modern automated precasting plant. Alfred Steinle retired in 1999 andby that time he had risen to the post of authorised signatory in the engineering office atZublin headquarters.

Hubert Bachmann (b. 1959) began his career in 1976 with a training course on concreteand precast concrete construction in a precasting plant. After studying construction engi-neering and completing his doctorate at the University of Karlsruhe, he accepted a post inthe structural engineering office of Ed. Zublin AG, where he has worked since 1993. Hisduties include the detailed design of structures of all kinds plus research and developmentin the civil and structural engineering sectors. He has been presenting the series of Hahnlectures at the University of Stuttgart on the subject of the prefabrication of concrete com-ponents since 2003.

The authors were or are also intensively involved in construction industry associations,numerous technical bodies plus national and international standards committees dealingwith precast concrete construction.


Contents

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VII

Authors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IX

Preliminary remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Standards, leaflets and directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.1 The advantages of factory production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51.2 Historical development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61.3 European standardisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2 Design of precast concrete structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2.1 Boundary conditions for precast concrete design . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162.1.1 Production process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162.1.2 Tolerances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162.1.3 Transport and erection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212.1.4 Fire protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232.2 Stability of precast concrete structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282.2.1 Arrangement of stability elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282.2.2 Loads on stability elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332.2.3 Distribution of horizontal loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452.2.4 Verification of building stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 582.2.5 Structural design of floor diaphragms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 622.2.6 Structural design of vertical stability elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 672.2.7 Design of perimeter ties to DIN 1045-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 722.3 Loadbearing elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 782.3.1 Suspended floor elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 782.3.2 Floor and roof beams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 852.3.3 Columns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 942.3.4 Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 972.3.5 Foundations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 992.4 Precast concrete facades . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1012.4.1 Environmental influences and the requirements of building physics . . . . . . . 1022.4.2 Facade design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1042.4.3 Joint design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1122.4.4 Facade fixings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1162.4.5 Architectural facades . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1252.5 Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1302.6 Current design issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1392.6.1 Additions to cross-sections, floors with concrete topping . . . . . . . . . . . . . . . . . . 139


2.6.2 Corbels and notched beam ends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1432.6.3 Lateral buckling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1562.6.4 Pad foundations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1632.6.5 Design for fire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167

3 Joints between precast concrete elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175

3.1 Compression joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1753.1.1 Butt joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1753.1.2 Zones of support to DIN 1045-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1803.1.3 Elastomeric bearings to DIN 4141 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1813.1.4 Elastomeric bearings to DIN EN 1337 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1883.2 Tension joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1903.2.1 Welded joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1903.2.2 Anchoring steel plates, dowels, studs and cast-in channels . . . . . . . . . . . . . . . . 1933.2.3 Shear dowels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1953.2.4 Screw couplers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1983.2.5 Transport fixings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1993.2.6 Retrofitted corbels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2013.3 Shear joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2033.3.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2033.3.2 Floor diaphragms and wall plates in-plane shear forces . . . . . . . . . . . . . . . . . . 2043.3.3 Joints in suspended floor slabs out-of-plane shear forces . . . . . . . . . . . . . . . . 209

4 Factory production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213

4.1 Production methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2134.2 Types of concrete in precast concrete construction . . . . . . . . . . . . . . . . . . . . . . . . 2194.2.1 Processing properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2204.2.2 Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2204.2.3 Self-compacting concrete (SCC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2234.2.4 Fibre-reinforced concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2244.2.5 Coloured and structured concrete surfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2254.3 Producing the concrete in the factory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2274.3.1 Heat treatment and curing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2274.3.2 Working hardened concrete surfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2294.3.3 Coating and cladding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2314.4 Installing the reinforcement in the factory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2334.4.1 Round bars and meshes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2334.4.2 Prestressing beds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2374.5 Quality control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259

XII Contents

Preliminary remarks

Chapter 1 contains general information about precast concrete construction, its historyand the status of the relevant Euronorms. Chapter 2 explains the design of structures basedon precast concrete elements and the design of the precast concrete elements themselves.Chapter 3 deals with joints. And to conclude this book, chapter 4 takes a look at the actualmanufacture of precast concrete elements so that the reader gains a full understanding ofthis form of construction and can take into account the needs and intricacies of production.

All this is seen from the viewpoint of the German construction industry. But with a view tothe European Single Market and the activities of German companies abroad, the status ofprecast concrete construction in other countries is also considered to a certain extent.

The authors have confined themselves in the main to structures in general. However, thefact that precast concrete construction has been able to secure sizeable market shares inmany other areas of construction through the development of economic bespoke solu-tions should not go unmentioned. The following are just some areas where precast con-crete construction has had considerable impact:

x Bridgesx Tunnelling (tunnel segments)x Pipes, pipe bridges, towers, masts, pilesx Detached housesx Prefabricated basements, retaining wallsx Room modules, prefabricated garagesx Noise barriersx Railway sleepers, slab tracks, guided bus tracksx Agricultural structuresx Cooling tower trickle fill structures

The reader is referred to the specialist literature dealing with these specialist areas. Thisbook also only describes structural or architectural precast concrete elements for build-ings and structures and not concrete products, i.e. small-format components manufac-tured and stocked in great numbers and available from trade outlets, e.g. sewage pipes,paving stones, etc.

The list of references has been extended since the previous edition. The references in thetext have been retained on the whole because they contain potential solutions to funda-mental problems that are still relevant today.

Earlier articles on the theme of precast concrete construction worth consulting are thosein the Beton-Kalender [13]. By the same token, reference to the general literature on re-inforced concrete construction has been omitted and the reader is referred to the corre-sponding articles in the Beton-Kalender, unless they concern areas that also touch on thespecific problems of precast concrete construction. Readers who wish to obtain a com-pressive overview of this subject are recommended to consult Konczs three-volumework dating from the 1960s [4] and the brochures published by the Fachvereinigung


Deutscher Betonfertigteilbau e.V. [58]. As well as covering small-format concrete pro-ducts, the Beton- und Fertigteil-Jahrbuch [9], which is published annually, also containsarticles on various structural and architectural aspects of precast concrete construction,different in each edition. Comprehensive information on mass-produced concrete pro-ducts can be found in [12], and a number of fundamental and general thoughts on indus-trialised building methods using precast concrete elements are to be found in [10, 11]. Thebooks [1316] are based on the lecture notes of a number of university professors. TheDIN standards most relevant to this subject, in the editions on which this publication isbased, are listed below. Also listed here are the directives of the Deutscher Ausschussfur Stahlbeton relevant to precast concrete construction and the leaflets published bythe Deutscher Beton- und Bautechnik-Verein e.V. and the Fachvereinigung DeutscherBetonfertigteilbau e.V. Section 1.3 deals in more detail with the status of the developmentof Euronorms. Directives or leaflets containing further information are referenced sepa-rately in the text.

Standards, leaflets and directives

2 Preliminary remarks

Table 1 DIN standards of NA 005 (NABau, Building & Civil Engineering Standards Committee)relevant to precast concrete construction (many available in English)

DIN Edition Parts/Title

488 2009 Parts 17 Reinforcing steels1045 2008 Parts 14 Concrete, reinforced and prestressed concrete structures1048 1991 Parts 15 Testing concrete1055 2002-2007 Parts 110 & 100 Actions on structures1164 2003-2005 Parts 1012 Special cementEN ISO 17660 2006-2007 Parts 1 & 2 Welding Welding of reinforcing steel4102 1977-2004 Parts 14 & 22 Fire behaviour of building materials and building

components4108 1981-2009 Parts 110 Thermal insulation in buildings4109 2003-2006 Parts 1 & 11 Sound insulation in buildings4141 1984-2008 Parts 13 & 13 Structural bearingsEN 1337 2005 Part 3 Structural bearings Elastomeric bearings4149 2005 Buildings in German earthquake areas Design loads, analysis and

structural design of buildings4212 1986 Reinforced concrete and prestressed concrete craneways; design

and construction4213 2003 Application in structures of prefabricated reinforced components of

lightweight aggregate concrete with open structure4223 2003 Parts 15 Prefabricated reinforced compliments of autoclaved aer-

ated concrete2008 Parts 100103 (draft) Application of prefabricated reinforced com-

ponents of autoclaved aerated concrete4226 2002 Part 100 Aggregates for concrete and mortar Recycled aggregatesEN ISO 9606 1999-2005 Parts 25 Approval testing of welders Fusion weldingEN 10088 2005-2009 Parts 15 Stainless steels18 057 2005 Concrete windows Dimensioning, requirements, tests18 065 2000 Stairs in buildings Terminology, measuring rules, main dimensions18 162 2000 Lightweight concrete wallboards unreinforced

3Preliminary remarks

DIN Edition Parts/Title

18 200 2000 Assessment of conformity for construction products Certification

of construction products by certification body18 202 2005 Tolerances in building construction Buildings18 203 1997 Part 1 Tolerances in building construction Prefabricated compo-

nents made of concrete, reinforced concrete and prestressed con-

crete18 230 1998-2002 Parts 13 Structural fire protection in industrial buildings18 500 2006 (pre-standard) Cast stones Terminology, requirements, testing, in-

spection18 515 1993-1998 Parts 1 & 2 Cladding for external walls18 516 1990-2009 Parts 1 & 35 Cladding for external walls, ventilated at rear18 540 2006 Sealing of exterior wall joints in buildings using joint sealings18 542 2009 Sealing of outside wall joints with impregnated sealing tapesmade of

cellular plastics Impregnated sealing tapes Requirements and

testing18 800 2008 Parts 14 Steel structures18 801 1983 Structural steel in building; design and construction

Table 2 DBV leaflets and status reports (Deutscher Beton- und Bautechnik-Verein e.V., GermanConcrete & Building Technology Association) (some available in English in the DBVs Concrete Best

Practice publication)

Edition Title

Building technology

2005 Multi-storey and basement car parks2006 Structural carcass/building services interfaces 2 parts2006 Limiting cracking in reinforced and prestressed concrete2002 Concrete cover and reinforcement

Concrete technology

2001 Steel fibre-reinforced concrete2002 High-strength concrete2004 Self-compacting concrete2004 Concrete surface concrete boundary zone1996 Unformed concrete surfaces2007 Special methods for testing wet concrete

Construction works

2004 Fair-face concrete

2004 Avoiding problems in placing concrete2006 Concrete formwork

Construction products

2002 Spacers and chairs for reinforcement2008 Bending back reinforcing bars and requirements for bar casings1996 Sealing materials for joints in buildings1997 Release agents for concrete part A: advice for selection and use1999 Release agents for concrete part B: tests

Construction works in existing buildings

2008 Guidelines2008 Fire protection2008 Concrete and reinforcing steel

4 Preliminary remarks

Table 3 FDB leaflets (Fachvereinigung Deutscher Betonfertigteilbau e.V., German Precast ConcreteConstruction Association) (No. 1 available in English, all others in German only)

No. Edition Title

1 2005 Fair-face concrete surfaces (surface appearance) of precast elements made

of concrete and reinforced concrete2 2005 Corrosion protection for inaccessible steel connecting elements (cast-in

parts) in precast concrete components3 2007 Design of precast concrete facades4 2006 Fixing methods for precast concrete facades5 2005 Checklist for precast concrete component drawings6 2006 Fit calculations and tolerances for cast-in parts and connecting elements7 2008 Fire protection requirements for precast concrete components

Table 4 DAfStb directives (Deutscher Ausschuss fur Stahlbeton, German Reinforced ConcreteCommittee) (available in German only)

Edition Title

1989 Heat treatment of concrete1995 Production of concrete using residual mixing water as well as concrete and mortar

residues2000 Loading tests on solid structures2001 Protection of and repairs to concrete components (parts 14)2003 Self-compacting concrete (SCC directive)2004 Concrete construction in connection with substances hazardous to water2004 Concrete to EN 206-1 and DIN 1045-2 with recycled aggregates to DIN 4226-1002006 Concrete with prolonged working time (retarded concrete)2006 Production and use of cement-bonded grouts2007 Measures to prevent damaging alkaline reactions in concrete (alkali directive), parts

13

1 General

1.1 The advantages of factory production

The corporate goal behind the use of a production method that is to establish itself in themarketplace must be: to produce a product better or cheaper or faster than the competition.The optimum situation would be if each or could be replaced by and. So what is thesituation with construction using precast concrete elements?

a) Improved quality

x Production in an indoor environment results in better working conditions with corre-spondingly better productivity than would be the case on a building site, and thathas an effect on quality, too.

x In the factory production situation, training makes it easier to compensate for the on-going severe shortage of skilled workers in the construction industry.

x Steel moulds can be used for standard elements or large batches, which enables a highdegree of dimensional accuracy to be attained.

x Factory production enables a specific concrete quality to be achieved.Only through factory production is it possible to produce concrete components witharchitectural textures and colours, especially for facade designs.As with other branches of industry outside the construction sector, factory productionresults in more efficient quality management.

b) Lower production costs

x The main purpose of precast concrete construction is to reduce the cost of the formwork.Several components can be produced in the same formwork, i.e. mould. And ofcourse, large batches are advantageous. Although mould types suited to the methodof production (e.g. rigid moulds with few fold-down parts) demand a design approachthat suits the production, this does lead to high mould reuses.

x Another reason for precast concrete construction was undoubtedly the reduction or to-tal elimination of scaffolding costs.

x Factory production enables the use of mechanisation and automation, which in turncan result in a substantial reduction in the numberof working hours necessary. However,if a factorys capacity is not fully exploited, this can be a disadvantage because of theensuing high proportion of fixed costs.

x Material savings arise from the possibility of using thin component cross-sections cor-responding to the structural requirements, i.e. double-Tor T-sections instead of rectan-gular sections. The advantage of the (possibly) lower weight of the concrete is in manycases only made possible through the higher quality of the concrete due to the factoryproduction methods. One typical example of saving material and weight is resolving asolid slab into a hollow-core slab. And this is only possible with precast concrete con-struction.

x Prestressing is easy to achieve in the form of pretensioning in the prestressing bed.


x One considerable cost factor for a precasting factory is of course the cost of transport,which limits the radius of activities and consequently the potential market for a pre-casting plant and hence its size. This does not represent a hindrance for the precastconcrete market as a whole because there are now proficient precasting works withineconomic reach of any location.

c) Faster construction

x One big advantage of precast concrete construction is the potential to shorten the con-struction time. For example, wall and suspended floor elements can be produced simul-taneously, even while the foundations are still being built. Production, and to a largeextent erection as well, can take place during the winter.

x No extensive, elaborate on-site facilities are required. The structural carcass is dry andready for immediate loading immediately after erection.

x The financial savings associated with a shorter construction time and the chance of gen-erating revenue at an earlier date are important, often underestimated, reasons for pre-cast concrete construction, particularly for industrial buildings.

x However, it should not be forgotten that structures made from precast concrete compo-nents often require a higher planning and design input. On the other hand, this input canbe substantially reduced by using a standardised precast component system. The firstCAD applications in reinforced concrete construction originated in precast concrete.

1.2 Historical development

Prefabrication, i.e. the building of components remote from their intended location in thestructure, followed by subsequent erection is a method of construction that is as old asbuilding with reinforced concrete itself. However, the development of modern construc-tion with precast reinforced concrete components from its origins to a form of industria-lised building only took place over the past 60 years. Ref. [20] contains a detailed descrip-tion of the development of prefabricated housing in Germany up to 1945.

Even though we might not be able to designate the first reinforced concrete flower tubs orboats of Joseph Monier or Joseph Louis Lambot in the mid-19th century as prefabricatedcomponents (Fig. 1.1), the first serious trials with structural precast reinforced concretecomponents did take place around 1900 (e.g. Coignets casino building in Biarritz,France, in 1891, and the prefabricated railway signalman and gatekeeper lodges of Hen-nebique and Zublin in 1896, Fig. 1.2) [17].

This development continued in the first half of the 20th century throughout Europe andthe USA, albeit only tentatively. The main reason for this was the lack of larger and flex-ible lifting equipment during this period.

The real breakthrough did not come until after the Second World War [18]. In a first phasefrom 1945 to 1960 it was the extraordinary demand for housing that presented the build-ing industry with a huge challenge. During this period it was the French (e.g. Camus, Es-tiot) and Scandinavian (e.g. Larsson, Nielsen) systems that provided decisive momentum

6 1 General

for construction with large-format panels. Their patents through licensees also domi-nated the German market.

In the second phase, about 1960 to 1973 (see also [18]), growing prosperity led to a rise indemand for owner-occupied housing with a higher standard of comfort. Inflationary ten-dencies resulted in a huge amount of investment in property, and the increasing shortageof skilled workers was another reason that forced production to be transferred to factories,which in turn helped precast concrete construction to achieve a breakthrough.

Alongside housebuilding, the increased need for more schools, colleges and universitiesled to the establishment of fully developed loadbearing skeletal frame systems with col-umns, beams and long-span floors (7.20 m/8.40 m). Buildings for industry and sportscentres resulted in standardised product ranges for single-storey sheds made from precastcolumns and prestressed rafters and purlins or sawtooth roofs.

The third phase, about 1973 to 1985, was marked by a serious crisis for the German con-struction sector, first and foremost housebuilding. This was compensated for to a certaindegree by increased demand in the oil-exporting countries. Housing, school, universityand office building construction projects were carried out in those countries, whichopened up completely new dimensions in the industrialisation of precast concrete struc-tures. However, the fall in the price of oil led to this compensatory business almost dryingup in the early 1980s.

In the years after 1985 a general economic upswing resulted in colossal improvements forthe construction sector as well. However, the high wage and social security costs forcedprecasting plants to switch to mechanised and automated methods of production.

Since late 1989 Germany has seen renewed demand for housing to meet the needs of im-migrants plus migrants from former East Germany. The opening of the border with theformer German Democratic Republic in 1990 resulted in major challenges for the build-ing industry in the ex-GDR.

71.2 Historical development

Fig. 1.1 Joseph Monier (c. 1850) [17]

Fig. 1.2 Prefabricated signalmans lodge (c. 1900) [17]

New noise abatement legislation is one of the results of the growing awareness of envir-onmental aspects, which has led to an increased demand for products such as noise bar-riers.

8 1 General

Fig. 1.3 Concrete products and prefabricated elements in Germany: concrete products in totalcompared to large-format precast concrete elements (top); large-format prefabricated elements for

structures (bottom)

But the increased demand for building work after German unification was short lived. Inthe period from about 1994 to 2004, the construction sector experienced almost 10 yearsof decline, coupled with a drastic reduction in the number of employees and a rise in thenumber of insolvencies, even of large companies. This fact is also revealed by the produc-tion statistics for concrete goods and precast components, which are shown in Fig. 1.3.Fortunately, we have seen a change in fortunes since 2005.

1.3 European standardisation

The creation of the European Single Market has been accompanied by the vigorous devel-opment of European codes of practice. Most important here is the adoption of the Con-struction Products Directive (CPD) by the European Commission. This has been in forcein Germany in the form of the Bauproduktengesetz (Construction Products Act) since 1992and is crucial to the building industry. In the meantime, the building regulations of Ger-manys federal states have been updated because the individual states will continue tobe responsible for building regulations. The CPD defines essential requirements to besatisfied by construction works (and not just the construction products) in a generalform.

These are:1. Mechanical resistance and stability2. Safety in case of fire3. Hygiene, health and the environment4. Safety in use5. Protection against noise6. Energy saving and heat insulation.

These requirements are concretised in six base documents, which are intended to formthe foundation for mandates for preparing harmonised European standards (or direc-tives for European approvals). These mandates must also include requirements for cate-gories and performance classes for individual products (e.g. for static loads only, firesafety rating, etc.). The Euronorms (EN) then have to be drafted by the European Com-mittee for Standardisation (CEN, based in Brussels). Products for which conformitywith these harmonised Euronorms can be verified will in future be labelled with the CEmarking (see also section 4.5). To date, the European Commission has issued the CENwith mandates for the standardisation of 30 product families.

The standardisation work is carried out in so-called Technical Committees (TC) or Sub-committees (SC) and their associated Working Groups (WG) or Task Groups (TG).Once a CEN standard has been adopted by the qualified majority of the EEC andEFTA member states, all member states are obliged to adopt this standard, even if itwas not mandated by the European Commission. In the case of mandated standar-dised Euronorms, no changes or additions are then possible when these are incorporatedinto the building legislation of Germanys federal states (a situation that is different fromthe DIN standards in the past) because that would lead to new trade barriers.


One key new development is that the supreme building authorities of the federal stateshave now published the Construction Products Lists A, B and C standardised docu-ments compiled by the Deutsches Institut fur Bautechnik (DIBt, German Institute ofBuilding Technology) [28].

Construction Products List A Part 1 contains construction products that have to complywith building authority requirements (e.g. suspended floor slabs, reinforcing steel, etc.).This corresponds to the building authority approval of the past.

10 1 General

Fig. 1.4 Systems for attestation of conformity procedures according to the Construction ProductsDirective (CPD) [29]

Construction Products List A Part 2 contains construction products that require only aNational Test Certificate (e.g. non-loadbearing lightweight partitions).

Construction Products List B contains all those construction products that may be placedon the market and traded according to EU regulations and which carry the CE marking.Every mandated product standard includes an annex ZA, which defines the requirementsregarding the CE marking and the procedure for the attestation of conformity [2931].Attestation of conformity procedure 2S applies to precast concrete products: initialtype-testing of the product, factory production control and certification by an approvedbody (see Fig. 1.4).

Construction Products List C contains those construction products that have only a minorsignificance (e.g. gutters, screeds, etc.). They may not carry the mark, the Germansymbol of conformity.

Annex ZA permits the use of a simplified label for the CE marking according to Fig. 1.5.The details of the product must be stated in an accompanying document according to Fig.1.6. The design documents mentioned in this are the drawing of the element and the struc-tural calculations.

At the time of preparing this chapter (late 2007), only two precast reinforced concretecomponents may be marketed with the CE marking:

Prefabricated reinforced components made from lightweight aggregate concrete ac-cording to DIN EN 1520

Prefabricated reinforced and prestressed concrete hollow-core slabs according to DINEN 1168

Consequently, only these currently appear in Construction Products List B Part 1 (edition2007/1), in section 1.1.6.

In addition, the German building authorities now require NABau (Building & Civil Engi-neering Standards Committee) to draw up a so-called National Application Document(NAD, DIN 20000-XXX) for every harmonised standard so that the respective Euronorm


Table 1.1 Application of the product standard for precast concrete floors

Level Generalregulations

Product standard Designstandard

Concrete Reinforce-ment

Europe DIN EN 13369

Common rules for

precast concrete

products

DIN EN 13747

Precast concrete

products Floor

plates for floor

systems

EN 1991-1-1

Eurocode 2

EN 206-1 EN 10080 Steel

for the reinfor-

cement of con-

crete

Germany DIN V 20 000-120

Application of

building products

in structures

Part 120: Applica-

tion rules for

DIN EN 13369

DIN V 20 000-126

Application of

building products

in structures

Part 126: Applica-

tion rules for

DIN EN 13747

DIN 1045-1 DIN 1045-2 DIN 488 Rein-

forcing steels/

National Tech-

nical Approvals

for lattice

beams

can be used with and is compatible with building regulations in Germany. When an ENstandard is introduced, a period of co-existence is defined during which both the DINstandard and the EN standard may be used.

A precast concrete floor, and its allocation to national and international design and mate-rials standards, is given here as an example of the practical application of a product stan-dard (see Table 1.1). The period of co-existence for this standard ended on 1 May 2008.Its incorporation in Construction Products List B is imminent [32].

On the national level, the work of the CEN is accompanied by so-called DIN mirror com-mittees, which in the main supervise the work of a TC. There are currently about 80 CEN/

12 1 General

Fig. 1.5 Example of a simplifiedlabel

Fig. 1.6 Example of the asso-ciated accompanying document,

see Fig. 1.5

TCs active for the construction sector. Those CEN/TCs currently active and relevant toprecast concrete construction are listed below together with the standards for whichthey are responsible.

CEN/TC 250 is working on the design standards (Eurocodes), with SC 2 playing the lead-ing role for concrete construction. Since late 2007 all Eurocodes have been available intrilingual editions. Ref. [26] reports on the current status of European standards for con-crete, and ref. [27] on the situation regarding reinforcing and prestressing steels. Accord-ing to the current state of knowledge (late 2008), it will first be possible to use EC 2 withthe corresponding German application rules in 2010.

CEN/BTS 1 Technical Sector Board for ConstructionCENTCs (Technical Committees) and the EN standards for which they are responsible andwhich are relevant to precast concrete construction


Standar-disationbody

TCNo.

Object Subcom.Working Gp.Task Group

Status EN No. Year Subject/designation

CEN TC 229 Precast

concrete

WG1 TG1 DIN EN 1168 09 Hollow-core slabs,

parts 1 & 2 (CE marking!)

components

relevant to

EC 2

TG2 DIN EN 12794 07 Foundation piles

TG3 DIN EN 12843 04 Masts and poles

TG4 DIN EN 13747 09 Floor plates for floor

systems

TG5 DIN EN 13224 07 Ribbed floor elements,

amend. 05

TG6 Ribbed slabs

TG7 DIN EN 13225 06 Linear structural

elements

TG8 DIN EN 14992 07 Wall elements

Products only

partly relevant

to EC 2

WG2 TG1 DIN EN 14843 07 Stairs

TG2 DIN EN 12737 07 Floor slats for livestock

TG3 DIN EN 12893 01 Elements for fences

TG4 Vehicle crash barriers

TG5 Noise barriers

TG6 Concrete window

frames

TG9 DIN EN 14258 09 Retaining wall elements

TG10 DIN EN 13693 09 Special roof elements

TG11 DIN EN 14844 Box culverts

TG12 DIN EN 13978-1 05 Precast concrete

garages, part 1

TG13 DIN EN 14991 07 Foundation elements

TG14 DIN EN 15050 07 Bridge elements

TG15 DIN EN Silos

Other concrete

products

WG3 TG1

TG2 DIN EN 1169 99 General rules for the

production control of

glass fibre-reinforced

cement

ECISS European Committee for Iron and Steel Standardisation

14 1 General


TCNo.


Status EN-No. Year Subject/designation

DIN EN 1170 9809 Test method for glass

fibre-reinforced ce-

ment, parts 1-8

Framework

guidelines

WG4 DIN EN 13369 07 Common rules for pre-

cast concrete products

CEN TC 250 Eurocodes for structural engineering

EC1 Safety DIN EN 1990 02 Basis of structural

design

SC 1 Actions DIN EN 1991 0295 Actions on structures,

parts 1-4

EC2 SC 2

Concrete

construction

DIN EN 1992 Design of concrete

structures

part 1-1 05 General rules and rules

for buildings

part 1-2 09 Structural fire design

part 2 04 Concrete bridges

part 3 07 Liquid retaining and

containment structures

EC3 SC 3 Steel

construction

ENV 1993

part 1-1 05 Design of steel

structures

part 1-2 05 General rules and rules

for buildings

Structural fire design

EC8 SC 8

Earthquakes

ENV 1998 0405 Design of structures for

earthquake resistance


TC-No.


Status EN-No. Year Subject/designation

ECISS TC 10 Structural

steels

TC1 DIN EN 10025 09 Hot-rolled products of

structural steels, parts 1-6

DIN EN 10210 06 Hot-finished structural hol-

low sections of non-alloy

and fine-grained steels,

parts 1 & 2

DIN EN 10219 06 Cold-formed welded struc-

tural hollow sections of non-

alloy and fine-grained

steels, parts 1 & 2

ECISS TC 19 Concrete re-

inforcing and

prestressing

steels

TC1 DIN EN 10080 05 Steel for the reinforcement

of concrete, parts 1-6

DIN EN 10088 05 Stainless steels, parts 1-3

TC2 DIN EN 10138 00 Prestressing steels, parts

1 & 2

2 Design of precast concrete structures

Designing a building made from industrially prefabricated parts calls for certain princi-ples to be adhered to during the planning work (see also [33, 34]).

It is important to be familiar with the particular features of precast concrete elements thatresult from their method of production. Modular dimensions should be defined for thestructure and the interior fitting-out and the building divided up into horizontal and ver-tical grids [35]. The transport dimensions and the loads to be lifted in the factory andon the building site are critical factors for precast concrete buildings. The fire protection,thermal performance and sound insulation requirements as well as the imposed loads forthe structural design are all governed by the use of the building.

The horizontal stability of multi-storey buildings calls for early coordination, not onlywith the structural engineer, but with the manufacturer as well. The provision of stiffeningcores or walls made from precast concrete components or in situ concrete has far-reachingconsequences for the design sequence and on-site construction times.

It is advisable to use standardised elements for the loadbearing structure, especially forsmaller buildings. Large construction projects tend to generate their own rules and alsopermit the use of their own systems, although it is then very important to consider the pro-duction engineering requirements if an economic design is to be realised.

The design of the interfaces between the individual elements is influenced by the struc-tural requirements, but also by the routing of building services. Sensible use of the stan-dard openings provided in the structural carcass or appropriate beam notches is usuallyonly achieved when the structural carcass and the interior fitting-out can be built by thesame contractor, i.e. in a turnkey project [10].

The design of the facade determines both the form and the architecture of the building as awhole. In addition, the facade, the external skin of the building, must satisfy all thebuilding physics requirements that the environment places upon it. One key design deci-sion is: To what extent does the facade contribute to the loadbearing function? Or is itonly a curtain wall?

In this book, all these points can only be dealt with in outline.

Early planning and coordination of all those involved in the construction project are cru-cial in order to achieve an optimum building design in terms of architecture, functionalityand economics. This begins with the architect and includes the building services andbuilding physics consultants, structural engineers and designers plus the fabrication anderection personnel.


2.1 Boundary conditions for precast concrete design

2.1.1 Production process

The production process for precast concrete components is in many ways fundamentallydifferent to the production process on the building site. For example, columns are mostlycast in horizontal moulds, which means that one side of the column is exposed to the air. Ifall sides are to have a fair-face finish, then this fourth side requires additional work.Where the column has corbels facing in different directions, then coordination with thefactory is required to establish from which side the column can or should be concreted.

Walls are mostly cast horizontally on tilt-up moulds, which means that one side is in con-tact with the mould, the other side is floated. Only in the case of walls produced verticallyin battery moulds are both sides in contact with the mould.

Facades are generally produced horizontally in a so-called negative mould, i.e. the facadesurface is on the underside in contact with the mould. Using this method it is easy to pro-duce textured and exposed-aggregate finishes. Please refer to section 2.4 for the produc-tion of sandwich panels (facade panels with integral thermal insulation).

As the side panels of moulds on the ground are moved or tilted clear upon demoulding,this joint must be properly sealed for concreting. This is generally achieved with triangu-lar plastic battens, which means that the bottom edges (bottom in the sense of the pro-duction process) of precast elements are chamfered. There must be a clear indication onthe drawings if the top edges are to be chamfered as well.

But in many cases beams or T-beams are produced in rigid moulds. In these cases thesides of rectangular beams or the webs of double-T sections are slightly inclined out-wards so that such elements can be lifted out of the mould once they have hardened with-out having to move the side panels. This is generally unimportant where the elements willlater be concealed behind a suspended ceiling, but where the elements remain exposed,these production-related characteristics of precast concrete elements will need to be con-sidered at the design stage.

2.1.2 Tolerances

The production process gives rise to dimensional deviations of the actual size from thenominal size [36, 37]. For example, dimensional deviations in precast concrete compo-nents ensue due to inaccurate transfer of the design dimensions to the mould, deformationof the mould during concreting, deterioration of or wear-related flaws in the mould.

However, the production process for a building also includes the erection work, which re-sults in additional positioning tolerances that essentially depend on the methods of mea-surement employed.

In addition, dimensional deviations occur as a result of the deformations of the individualcomponents or the entire structure. These deformations may be load- or time-related (e.g.as result of shrinkage and creep).

16 2 Design of precast concrete structures

DIN 18202 Tolerances in building construction Structures specifies permissible tol-erances that apply to the structural carcass and the interior fitting-out irrespective of thebuilding materials. The permissible limits of size for building materials are specified inthe materials standards, e.g. DIN 18203-1 Tolerances in building construction Part1: Prefabricated components made of concrete, reinforced concrete and prestressed con-crete, and these must be taken into account as well. According to these standards, thereare no longer any accuracy classes as in the past. It has been recognised that the only rea-son for specifying tolerances in standards should be to guarantee the proper assembly andfunctionality of components in the structural carcass and interior fitting-out without re-working, i.e. their fitness for purpose, and not, for example, aesthetic demands, e.g. theexact alignment of external wall joints. Fitness for purpose means satisfying, for exam-ple, the loadbearing function in the case of short bearing lengths for floor units, or thewaterproofing function of an external wall joint.

The tolerances laid down in the standards represent the accuracy achievable within thescope of normal diligence. Where greater accuracy is required, then this must be includedin the specification, possibly together with the necessary methods of testing and inspec-tion. Greater accuracy causes disproportionately higher costs (see [39, 40] and Fig. 2.1).

Tolerances specified in standards should only be understood as production tolerances dueto manufacture and assembly. The load- and time-related deformations, just like the fit-ness-for-purpose requirements (e.g. limit values for the permissible movement of a jointseal), must be limited in other specifications or related to the particular building and takeninto account in the structural calculations if necessary. Otherwise the tolerances wouldonly apply for very specific boundary conditions such as the time and date of handoverwith defined temperature and loading conditions.

The tolerance range is the difference between the maximum and minimum sizes. Permis-sible dimensional deviations of e10 mm therefore translate to a tolerance range of20 mm (Fig. 2.2). For example, DIN 18202 Table 2.1 specifies permissible limits ofsize for buildings on plan and elevation (e.g. lengths, widths, grid and storey dimensions)generally applicable to buildings and somewhat higher values for clear opening dimen-


Fig. 2.1 Costs of horizontal buildingtolerances [39]


Table 2.1 Tolerances for prefabricated components of plain, reinforced and prestressed concreteaccording to DIN 18203-1

a) Limits of size for lengths and widths

Line Component Limits of size in mm for nominal size in m

J 1.5 i 1.5

J 3i 3

J 6i 6

J 10i 10

J 15i 15

J 22i 22

J 30i 30

1 Lengths of linear-type

components (e.g. col-

umns, beams)

e6 e8 e10 e12 e14 e16 e18 e20

2 Lengths and widths of

floor slabs and wall

panels

e8 e8 e10 e12 e16 e20 e20 e20

3 Lengths of pre-

stressed components

e16 e16 e20 e25 e30

4 Lengths and widths of

facade panels

e5 e6 e8 e10

b) Limits of size for cross-sections

Line Component Limits of size in mm for nominal size in m

J 0.15 i 0.15

J 0.3i 0.3

J 0.6i 0.6

J 1.0i 1.0

J 1.5i 1.5

1 Thicknesses of floor

slabs

e6 e8 e10

2 Thicknesses of wall

and facade panels

e5 e6 e8

3 Cross-sectional

dimensions of linear-

type components

(e.g. columns, beams,

ribs)

e6 e6 e8 e12 e16 e20

c) Angular tolerances

Line Component Angular tolerances as perpendicular measurements in mm for length L

in m

J 0.4 i 0.4

J 1.0i 1.0

J 1.5i 1.5

J 3.0i 3.0

J 6.0i 6.0

1 Wall panels without

finished surface and

floor slabs

8 8 8 8 10 12

2 Wall and facade pa-

nels with finished sur-

face

5 5 5 6 8 10

3 Cross-sections of lin-

ear-type components

(e.g. columns, beams,

ribs)

4 6 8

sions (e.g. between columns) plus limits of size for window or door openings dependingon the nominal sizes.

Limit values are also specified for angular and flatness deviations and also out-of-plumbdeviations for columns, checked by way of permissible perpendicular measurements(DIN 18202; see Tables 2, 3 and 4). These may no longer be added to the limits of size.This corresponds to the box principle of ISO 4464 (now withdrawn), according to whichthe actual dimensions of a component or an opening must always lie within the limit di-mensions (Fig. 2.3).

The permissible flatness deviations do not include the flatness of the components with re-spect to each other, which must be considered additionally. For example, the steps be-


Fig. 2.2 Terminology of tolerances

Fig. 2.3 Illustration of the box principle using theexample of permissible dimensional deviations of

openings (permitted deviations and angular toler-

ances) [37]

tween adjacent prestressed concrete planks are often unavoidable and the admissibility ofsuch steps must be regulated separately.

By contrast, DIN 18203-1 (see Table 2.1) specifies the manufacturing tolerances for theprecast concrete components themselves, divided into limits for length, width andcross-sectional sizes of linear elements or floor, wall and facade panels. The angular tol-erances for planar panels and slabs and the cross-sections of linear components are alsoshown.

Ref. [36] is a commentary on DIN 18201 and DIN 18202. It contains advice for plannersconcerning tolerances and also proposes a method for checking the alignment of columnsin frame structures and single-storey sheds.

Structures with accuracy requirements according to DIN 18202 should always bechecked and monitored using surveying techniques. Conventional measurements by theforeman using a profile board, line and extending tape measure are by no means ade-quate! However, the German standards do not include any details about permissible de-viations for measurements.

According to ISO/DIS 4463, limits of size of e2K L

p[mm] (distance L in m) at inter-

vals of i 4 m are permissible (see also [37]),

whereK w 5 for earthworks, andK w 2 for structural works.

For many situations, defining minimum requirements for tolerances according to thestandard is adequate in practice. However, this does not necessarily mean that this is ade-quate for the fitting together. That can only be established following an appropriate fitcalculation which, however, presumes knowledge of the production accuracy achievable.And the tolerances specified form the foundation for this. Whether the manufacturer ofthe precast concrete components also erects and assembles these is also a crucial factor.Where this is not the case, all subcontractors would insist on the inaccuracies to whichthey are entitled and only the additive method remains if disputes are to be avoided.

Fit calculations taking into account the law of the propagation of uncertainties can cer-tainly yield savings, e.g. in jointing materials, for contractors who have the entire produc-tion process (measuring, production and erection of the precast concrete components) un-der control in terms of tolerances. Examples of such calculations can be found in [37, 41,42].

Furthermore, with structures built from precast concrete elements, the tolerances at thesupports are especially important. It must be guaranteed that the as-built tolerances matchthose on which the structural calculations were based. Permissible tolerances that influ-ence stability must therefore be specified on the working drawings. The tolerances ofbuilt-in items and connectors are specified in [38] together with a simple method for afit calculation.


2.1.3 Transport and erection

Dividing a structure into prefabricated elements is to a large extent governed by the trans-port restrictions and the erection weights of the individual components.

The aim should be to make the elements as large as possible because every subdivisiondoubles the handling activities necessary in the factory and on the building site. Thehigher the quality of an element, i.e. the more fitting-out components it contains (e.g.windows, doors or building services in a wall panel) or the more functions it has to per-form (e.g. a facade element providing loadbearing, thermal insulation and architecturalfunctions), the lower is the percentage cost of the transport.

It is the permissible road transport dimensions according to Germanys Road Traffic Act(StVZO, Straenverkehrs-Zulassungs-Ordnung) that have led to todays typical widths forfloor units of 2.40 or 2.50 m and wall panel heights ofI 3.60 m [43]. Where dimensionsor total weights exceed those given in Table 2.2, then a special permit according to StVZOcl. 29 must be applied for, and a police escort may even be necessary. Such permits can beissued by the respective authorities (e.g. local government departments) for each indivi-dual case or as a general permit valid for several years.

Individual permits will be necessary where the dimensions of the precast concrete com-ponents exceed the dimensions given in Table 2.2. In such situations it is essential to es-tablish the potential transport route at an early stage and also the duration and time of thedelivery (maybe only during the night). And when an oversize load has to travel throughmore than one federal state, then a travel permit must be applied for in each state and thevarious permits coordinated. This can prove to be extremely complicated in some cases,with negative repercussions for costs and delivery times. The vehicle types given in Table2.3 are generally used for road transport.

Transport by rail is relatively rare apart from projects for the railways themselves be-cause the transfer from road to rail and back again before the building site is reached isusually unavoidable. And the prerequisite in every case is that the factory itself has a di-rect railway link. Transport in containers, in which width and height are limited to approx.2.30 m and the length to 12.00 m, are hardly relevant for structural precast concrete ele-ments. The reader should refer to [48] for information on the problems of transport acrossnational and international frontiers.


Table 2.2 Maximum permissible dimensions and total weights for road transport (depends on par-ticular approving authority)

Without special permit(to StVZO cl. 32)

With annual permit(StVZO cl. 29)

Width 2.55 m 3.00 m

Height 4.00 m 4.00 m

Length 15.50 m 24.00 m

Total weight 40 t 48 t (tractor unit with self-steering trailer)

It is also vital to consider every detail of the erection sequence when designing the ele-ments.

The type of erection must be taken into account: horizontal, i.e. elements positionedstorey by storey with a tower crane, or vertical, i.e. bay by bay over the full height ofthe building with a mobile crane (Fig. 2.4).

Typically, tower cranes can handle only relatively light loads, albeit at a large radius andthrough a full 360h. However, the largest tower crane used in Germany to date was able tohandle a load of 30 t at a radius of 40 m.

Mobile cranes can lift heavy elements, but only from a position with a firm, stable base.And owing to their limited working radius and restrictions on the slewing circle with out-riggers extended, they often have to be repositioned during the work. These days, mobilecranes with a capacity of 400 t are relatively inexpensive. This is because it is the hire per-iod and not the actual cost of the crane itself that governs. For example, it takes almost awhole day to reposition a 500 t crane. Cranes mounted on crawler tracks are used whereeven greater lifting capacities are required. Although crawler-mounted cranes with liftingcapacities of up to 1300 t take approx. 12 weeks to set up, their crawler tracks mean that


Fig. 2.4 Types of erection and typical crane dimensions with loads

Table 2.3 Vehicle types for road transport

Type of component Type of transport

Columns and beams I 16 m long Tractor unit with (extending) semi-trailer

Columns and beams j 16 m long Tractor unit with trailing bogie

Facade panels Low-loader with frame for panels

Ground floor panels and ground beams Tractor unit with (low-bed) trailer

Bridge beams Tractor unit with trailing bogie

precast concrete elements are easily transported and positioned anywhere on the buildingsite, provided adequate manoeuvring space is available.

Of course, both types of erection can be combined on one building project, and adapted tosuit the conditions, with the tower crane remaining on site for the duration of the entireworks and mobile cranes being hired by the day as required.

One interesting example of such a detailed coordination of both forms of erection can beseen in Fig. 2.5, Zublin House. On this project, erection was divided into four phases (seealso Figs 2.125 and 2.149) [44].

Precast concrete components are being increasingly incorporated into composite precast/in situ concrete designs. In this approach it is possible to exploit the advantages of prefab-ricated production (complex geometry, surface finish, formwork savings for large series,etc.) and build the precast concrete elements into an in situ concrete structure. Attentionshould be given to making sure that the elements are not too heavy to be positionedwith a tower crane. If this is not possible, then the use of an additional mobile craneshould be concentrated into one period because otherwise the cost of having two craneson site will make itself felt.

2.1.4 Fire protection

Besides ensuring adequate stability, durability, thermal performance, moisture controlmeasures and sound insulation, it is also vital to verify the fire resistance, especially forthe loadbearing and enclosing components. This is carried out with DIN 4102 Fire beha-viour of building materials and building components, which is discussed in detail in[45]. The design rules are based on an internationally agreed standard temperature curveused in many countries.

DIN 4102-1 allocates building materials to classes according to their reaction to fire(Table 2.4). Building materials class A1 is for those materials that are incombustible inthe classical sense, e.g. concrete and steel. Class A2 covers newer building materialsthat contain combustible constituents to some extent, e.g. the majority of gypsum-basedboards or polymer concretes.


Table 2.4 Building materials classes to DIN 4102-1

Building materialsclass

Building authority designation

A

A1

A2

Incombustible building materials

B

B1

B2

B3

Combustible building materials

Not readily flammable building materials

Flammable building materials

Highly flammable building materials


(a)

(b)

(1a) (1b)

Fig. 2.5 An erection sequence divided into four phases using the example of Zublin House.Phase 1: Vertical erection of columns with mobile crane; (a) section through building, (b) positions of

tower cranes and slewing circles for horizontal erection. (1a) Erection of facade columns, (1b) erection

of internal columns.


(2a) (2b)

(2c) (2d)

Fig. 2.5Phase 2: Horizontal erection of perimeter beams, inverted channel section floor units and floor planks

with four tower cranes. (2a) Erection of L-shaped perimeter beams on facade columns, (2b) erection of

inverted channel section floor units on internal columns, (2c) positioning the floor planks, (2d) con-

creting the floor slabs.

Fig. 2.5Phase 3: Vertical erection of curtain

wall facade bay by bay.

Fig. 2.5Phase 4: Vertical erection of underground car

park, atrium lift/stairs tower, atrium walkways

and roof frame with two heavy-duty telescopic

cranes and one tower crane.

One typical example of a not readily flammable building material (class B1) is the light-weight wood-wool board. Certain testing regulations for furnace tests apply for the clas-sification of the building materials.

Joint sealing compounds or strips belong to class B1 or B2 depending on their composi-tion. They may be incorporated between concrete components in certain minimum depthsand maximum joint widths. Elastomeric bearings fall into class B2. Only class A1 mate-rials may be used for the sealing materials in expansion joints that must satisfy fire protec-tion requirements, e.g. mineral-fibre boards, asbestos foams or fibres and aluminium sili-cate fibres (see Fig. 2.13).

Components are classified according to their fire resistance; the fire resistance ratings aregiven in Table 2.5. The fire resistance of components is therefore specified according tofire resistance rating and building materials class. For example, the abbreviated formfor a fire resistance of 90 minutes is F 90.

Suffixes A, B, or AB are added to designate the combustibility:

F 90-B: general

F 90-AB: essential components incombustible (loadbearing structure and enclosingelements)

F 90-A: all components incombustible

The current regulations for multi-storey buildings generally specify an F 90 rating forloadbearing components. The commonest requirements for building components are F30-A and F 90-A. The loadbearing structure of a high-rise building must comply withF 120-A above a height of 60 m. And even F 180-A above a height of 200 m (see alsothe High-Rise Building Directive of the Hessen Ministry of the Interior).

DIN 4102-3 contains further requirements (e.g. additional impact loads) for fire wallsand non-loadbearing external walls, which include spandrel and fascia panels as well asroom-high, room-enclosing external walls.

Parts 5 to 8 of DIN 4102 mentioned here for completeness although they apply less toconcrete construction and more to building services and interior fitting-out deal with thefire protection of fire stops, lift enclosures, glazing and ventilation ducts and assign themappropriate fire resistance ratings (e.g. T 90, G 90, L 90, K 90, where T w door, G wglass, L w ventilation and K w flaps). The resistance of roof coverings to flying sparksis another aspect covered by these parts.

In Germany the fire protection requirements are generally defined in the building regula-tions of each federal state together with the provisions for their implementation. How-ever, the terms fire-retardant, fire-resistant, etc. are used here, which must be allocatedto the respective DIN 4102 terms in the introductory decrees, as listed in Table 2.5.

The federal state building regulations only cover standard buildings for standard uses(e.g. housing and offices) and therefore special facilities for special uses are dealt within special legislation. The following are just a few examples:


Geschaftshauserverordnung (GhVO, Business Premises Act), which covers, for in-stance, department stores, supermarkets, etc.

Versammlungsstattenverordnung (VStatt-VO, Places of Assembly Act), which covers,for instance, lecture theatres, sports halls, etc.

Garagenverordnung (GarVO, Garages Act), which covers, for instance, small garages,multi-storey car parks, etc.

Schulhaus-Richtlinien (SHR, School Buildings Directive)

Industriebaurichtlinie (IndBauR, Industrial Buildings Directive)

The last of these refers to DIN 18230 Structural fire protection in industrial buildings.Part 1 of this standard contains a method of calculation that allows industrial buildingswith definable fire loads to be designed with respect to the theoretically necessary fire re-sistance of their components if required a different approach from that in the IndustrialBuildings Directive. As precast concrete components by their very nature provide a highlevel of fire resistance, such verification is generally unnecessary.

Further information on fire protection for industrial buildings can be found in [46].

There are also special tall building and school building directives which, however, are notlegally binding in all Germanys federal states.

Where reinforced concrete components are subjected to compression, it is the concretesreaction to fire that is particularly relevant [49]. But where components are subjected tobending or tension, it is primarily the strength and deformation behaviour of the reinfor-cing steel. According to DIN 4102-4, the critical steel temperature critT is the tempera-ture at which the yield strength of the steel drops below the steel stress in the component;critT w 500 hC for reinforcing steel, and all the design rules are based on this. For pre-stressing steels (e.g. cold-drawn strands with critT w 350 hC), please refer to DIN4102-4 Table 1 (see also [47]). The compressive strength of the concrete is also depen-dent on the temperature: it drops to approx. 70% at 200 hC, and at 750 hC is only about20% of its strength at 20 hC.

However, knowledge of the temperature distribution within the cross-section is importantfor reinforced concrete components because the edge distances for the reinforcement arebased on this (Fig. 2.6 shows an example).


Table 2.5 Fire resistance rating F and building authority designations

Fire resistance ratingto DIN 4102-2

Duration of fireresistance in minutes

Building authority designation accordingto introductory decree

F 30

F 60

F 90

F 120

F 180

i 30

i 60

i 90

i 120

i 180

fire-retardant

fire-resistant

highly fire-resistant

Section 2.6.5 deals in more detail with the design of individual precast concrete elementsto meet fire protection requirements.

2.2 Stability of precast concrete structures

The fundamental considerations regarding the stability of frame building structures aredescribed in detail in [50]. A number of general thoughts on this subject are summarisedbelow and the problems specific to precast concrete construction examined in more de-tail.

2.2.1 Arrangement of stability elements

Stability in residential and office buildings is generally assured by stair shafts and/or en-closing shear walls. By contrast, in precast concrete single-storey sheds intended to houseproduction processes and some precast concrete frame structures with one or two storeys,the horizontal stability is provided by the columns. The columns of such buildingsusually extend over the full height of the building and are fixed at their foundations; thebeam-column connections in such buildings are pinned. Such systems are classed assway, or unbraced, frames and must be designed according to second-order theory takinginto account the deformed system (Fig. 2.7). Structures with more than two storeys re-quire additional shear walls, frames, girders or torsion-resistant service cores to ensuretheir horizontal stability. The connection of series of pinned-end beams and columns tothe stability components is achieved via the relatively rigid floor diaphragm.


Fig. 2.6 Isotherms in hC for a T-beamexposed to fire [45]

Fig. 2.7 Sway systems (design according to second-order theory)

When planning stabilising shear walls or cores, the aim should be to create a statically de-terminate arrangement on plan in order to prevent restraint forces in the floor diaphragmsas a result of shrinkage or temperature changes. In addition, it is essential to ensure thatthe stabilising cores or shear walls are positioned in a way that minimises the rotationof the building on plan in the case of a uniformly distributed horizontal load due towind and eccentricity. Shear walls must be positioned in at least two non-parallel direc-tions and on at least three axes (Fig. 2.8).

With statically determinate bracing systems, it is the deformation capacity of the columnsthat governs the maximum building size for a frame structure. According to [50], lengthsof 100 m and more are possible without expansion joints in a frame structure. The defor-mation capacity of the columns depends on the accuracy of the representation of the stiff-nesses in the cracked condition. Critical here are the cross-sectional values but, first andforemost, the magnitudes of the axial forces to be carried by the columns [52].

The deformation capacity of the columns can be increased by including pinned supportsfor the columns or sliding bearings for the first floor slab above the underside of the foun-dation, although such measures only need to be provided at the columns furthest from thecore (Fig. 2.9).

In the case of statically indeterminate bracing systems, non-uniform temperature changesresult in restraint forces between suspended floors and stability components (Fig. 2.10)(see section 2.2.2.5). Joints are usually the most appropriate means of avoiding restraintforces provided simple and clearly arranged joints are possible (Fig. 2.11). Fig. 2.12


Fig. 2.8 Arrangement of building stability elements on plan

shows possible joint arrangements, and Fig. 2.13 shows joints that satisfy fire protectionrequirements, where such are necessary. Expansion joints always represent a source ofpotential damage details that require substantial input to rectify. Their design shouldtherefore be carefully thought out and the appropriate drawings and installation instruc-tions must be prepared. Quality control on the building site is essential for guaranteeingproper construction. Damage often occurs as a result of unintentionally filling the entirejoint with concrete (constructional measures to prevent loss of grout) and incorrect instal-lation or the installation of the wrong bearings.


Fig. 2.9 Measures for increasing the deformability of columns and wallsfor horizontal floor expansion

Fig. 2.10 Restraints caused bythe prevention of horizontal floor

deformation


Fig. 2.11 The principles for positioning joints

Fig. 2.12 Building joints

Fig. 2.13 Joints complying with fire protectionrequirements [45]

Therefore, constructing buildings without joints is something that should always be con-sidered. Where a building is to be constructed without joints, then the following aspects inparticular must be considered:

The actual expansion due to temperature changes and shrinkage

The deformability of the stability components (including horizontal precast concretefloors), especially in the cracked state

The creep deformability of the concrete

The conditions during construction

A careful study of the problem using modern methods of calculation often leads to expan-sion joints being omitted.

At the very least a check should be carried out to ascertain whether the joints need to becontinued over the full height of the building or whether the upper floors of tall buildingscould be built without joints (Fig. 2.14) [53]. It is always only the lowest floors that areaffected most by restraint forces (if we neglect the fire loading case in the upper storeys).

In Zublin House (Fig. 2.15) each of the two 94 m long blocks is divided by one joint. Thispositioned the cores somewhat off centre and so these were strengthened by two cross-walls on the two central axes. The two floor diaphragms were connected together nearone of these two walls by means of a shear key (joggle or castellated) joint that is ableto move in the longitudinal direction of the building, which means that both floor dia-phragms can be supported on the cross-walls. The topmost floor of the building was builtwithout any joints. The ensuing restraint forces can be accommodated by this floor slaband the cores.

Stiffening shear walls can also be offset storey by storey, although in that case the shearforces in the walls will have to be transferred via the corresponding floor diaphragms(Fig. 2.16). The forces, and the floor deformations in particular, must be taken into ac-count in the structural calculations. It must be guaranteed that the forces can be trans-ferred between the vertical and horizontal stability elements. Openings in the floor arecommon at shear walls and service cores in particular, and these hinder the transfer offorces. The shear wall moment cannot be carried via the floor diaphragm acting as a mem-


Fig. 2.14 Expansion joint positioned in the lower storeysonly

brane, instead must be transferred to the foundations via the neighbouring columns in theform of a couple. Shear walls offset in different storeys must therefore match the struc-tural grid.

2.2.2 Loads on stability elements

2.2.2.1 Vertical loads

The vertical loading due to dead and imposed loads is carried by the columns, walls andservice cores.

The cores and stiffening walls should carry permanent vertical loads wherever possible inorder to do justice to their function (Fig. 2.17). Asymmetrical load transfers result in ver-tical loads acting eccentrically, which leads to moments being applied at the underside ofthe foundation. Eccentric loads on columns can also lead to horizontal loads being ex-erted on the core as a result of tie forces (Fig. 2.18). These can be avoided by cantileveringthe beams beyond the columns, as shown in Fig. 2.19.


Stiffening walls Building joint with shear key Horizontal forces from atrium roof beams in floor above 5th storey Post-tensioned prestressed concrete for walkways above 5th storey Service cores for stability

Fig. 2.15 Building stabilityand joint positions

for Zublin House [44]

Fig. 2.16 Offset positioning of shear walls

2.2.2.2 Wind loads

Wind loads are determined according to DIN 1055-4. In contrast to previous editions ofDIN 1055, the provisions now also apply to buildings susceptible to vibration up to aheight of 300 m. Almost all engineered structures (with the exception of bridges, but in-cluding chimneys) are now covered as well. The classification of wind speeds on the Eur-opean wind map also guarantees pan-European continuity with respect to the loading as-sumptions. Besides improved aerodynamic coefficients, there is now a distinction be-tween inland and coastal regions, and the influences of terrain roughness and turbu-lence-induced transverse vibrations are also dealt with.

Cyclic wind loads can induce vibrations in structures. Such vibrations lead to an increasein the loads due to wind pressure or suction. The susceptibility to vibration does not needto be considered when the increase in a deformation due to gust resonance does not ex-ceed 10%. DIN 1055-4 specifies simplified determination criteria for this. As a rule, re-sidential, office and industrial buildings up to 25 m high, and other buildings similar inform and type of construction, can be assumed to be not susceptible to vibration, and se-parate verification is unnecessary. However, buildings whose stability relies on fixed-base columns are relatively flexible and their susceptibility to vibration should bechecked even for building heights I 25 m.

The main calculation steps for these buildings are summarised below. The special provi-sions of the standard must be taken into account for buildings with a special form, tallerbuildings or buildings in exposed locations (e.g. coastal sites).


Fig. 2.17 Core wall, subjected to vertical andhorizontal loads

Fig. 2.18 Horizontal loads on core due torestraining forces caused by eccentric column

loads

Fig. 2.19 Centring eccentric column l

Precast Concrete Structures - Hubert Bachmann

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