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- Herausgeber: Wiley-VCH
- Kategorie: Wissenschaft und neue Technologien
- Serie: Beton-Kalender Series
- Sprache: Englisch
The European pre-standard CEN/TS 1992-4 for the design of fastenings by means of headed studs, anchor channels as well as post-installed mechanical and chemical anchors is ready for use. The background and interpretation of the provisions related to the determination of actions and resistances based on limit state design, durability, fire resistance, fatigue and earthquake actions as required by CEN/TS 1992 are described in detail.
Selected chapters from the German concrete yearbook are now being published in the new English "Beton-Kalender Series" for the benefit of an international audience.
Since it was founded in 1906, the Ernst & Sohn "Beton-Kalender" has been supporting developments in reinforced and prestressed concrete. The aim was to publish a yearbook to reflect progress in "ferro-concrete" structures until - as the book's first editor, Fritz von Emperger (1862-1942), expressed it - the "tempestuous development" in this form of construction came to an end. However, the "Beton-Kalender" quickly became the chosen work of reference for civil and structural engineers, and apart from the years 1945-1950 has been published annually ever since.
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Seitenzahl: 212
Veröffentlichungsjahr: 2013
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Contents
Cover
Related Titles
Title Page
Copyright
Editorial
Chapter 1: Introduction
Chapter 2: Fields of Application
Chapter 3: Basis of Design
3.1 General
3.2 Verifications
3.3 Partial Factors
Chapter 4: Derivation of Forces Acting on Fasteners
4.1 General
4.2 Tension Loads
4.3 Shear Loads
4.4 Tension Forces in a Supplementary Reinforcement
Chapter 5: Verification of Ultimate Limit State by Elastic Analysis for Post-Installed Fasteners (Mechanical Systems)
5.1 General
5.2 Tension Load
5.3 Shear Load
5.4 Combined Tension and Shear Load
Chapter 6: Verification of Post-Installed Fasteners (Chemical Systems) for the Ultimate Limit State Based on the Theory of Elasticity
6.1 General
6.2 Tension Load
6.3 Shear Load
6.4 Combined Tension and Shear
Chapter 7: Verification of Ultimate Limit State by Elastic Analysis for Headed Fasteners
7.1 General
7.2 Tension Forces in the Supplementary Reinforcement
7.3 Tension Load
7.4 Shear Load
7.5 Combined Tension and Shear Load
Chapter 8: Verification of Ultimate Limit State by Elastic Analysis for Anchor Channels
8.1 General
8.2 Tension Forces in the Supplementary Reinforcement
8.3 Tension Load
8.4 Shear Loads
8.5 Combined Tension and Shear Loads
Chapter 9: Plastic Design Approach, Fastenings with Headed Fasteners and Post-Installed Fasteners
9.1 General
9.2 Conditions of Application
9.3 Distribution of External Forces to the Fasteners of a Group
9.4 Design of Fastenings
Chapter 10: Durability
10.1 General
10.2 Fasteners in Dry, Internal Conditions
10.3 Fasteners in External Atmospheric or in Permanently Damp Internal Exposure and High Corrosion Exposure
Chapter 11: Exposure to Fire
11.1 General
11.2 Basis of Design
11.3 Resistances Under Tension and Shear Load
Chapter 12: Seismic Loading
12.1 General
12.2 Additions and Alterations to EN 1998-1:2004 (Eurocode 8)
12.3 Verification of Seismic Loading
Chapter 13: Outlook
References
Index
Related Titles
All books published by Ernst & Sohn are carefully produced. Nevertheless, authors, editors, and publisher do not warrant the information contained in these books, including this book, to be free of errors. Readers are advised to keep in mind that statements, data, illustrations, procedural details or other items may inadvertently be inaccurate.
Library of Congress Card No.: applied for
British Library Cataloguing-in-Publication Data
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The Deutsche Nationalbibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data are available on the Internet at <http://dnb.d-nb.de>.
© 2013 Wilhelm Ernst & Sohn, Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Rotherstraße 21, 10245 Berlin, Germany
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Print ISBN: 978-3-433-03044-8
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Editorial
The “Concrete Yearbook” is a very important source of information for engineers involved in design, analysis, planning and production of concrete structures. It is published on a yearly basis and offers chapters devoted to various subjects with high actuality. Any chapter gives extended information based on the latest state of the art, written by renowned experts in the areas considered. The subjects change every year and may return in later years for an updated treatment. This publication strategy guarantees, that not only the most recent knowledge is involved in the presentation of topics, but that the choice of the topics itself meets the demand of actuality as well.
For decades already the themes chosen are treated in such a way, that on the one hand the reader is informed about the backgrounds and on the other hand gets acquainted with practical experience, methods and rules to bring this knowledge into practice. For practicing engineers, this is an optimum combination. Engineering practice requires knowledge of rules and recommendations, as well as understanding of the theories or assumptions behind them, in order to find adequate solutions for the wide scope of problems of daily or special nature.
During the history of the “Concrete Yearbook” an interesting development was noted. In the early editions themes of interest were chosen on an incidental basis. Meanwhile, however, the building industry has gone through a remarkable development. Where in the past predominantly matters concerning structural safety and serviceability were in the centre of attention, nowadays an increasing awareness develops due to our responsibility with regard to society in a broader sense. This is reflected e.g. by the wish to avoid problems related to limited durability of structures. Expensive repair of structures has been, and unfortunately still is, necessary because of insufficient awareness of deterioration processes of concrete and reinforcing steel in the past. Therefore structural design should focus now on realizing structures with sufficient reliability and serviceability for a specified period of time, without substantial maintenance costs. Moreover we are confronted with a heritage of older structures that should be assessed with regard to their suitability to safely carry the often increased loads applied to them today. Here several aspects of structural engineering have to be considered in an interrelated way, like risk, functionality, serviceability, deterioration processes, strengthening techniques, monitoring, dismantlement, adaptability and recycling of structures and structural materials, and the introduction of modern high performance materials. Also the significance of sustainability is recognized. This added to the awareness that design should not focus only on individual structures and their service life, but as well on their function in a wider context, with regard to harmony with their environment, acceptance by society, the responsible use of resources, low energy consumption and economy. Moreover the construction processes should become cleaner, with less environmental nuisance and pollution.
The editors of the “Concrete Yearbook” have clearly recognized those and other trends and offer now a selection of coherent subjects which resort under a common “umbrella” of a broader societal development of high relevance. In order to be able to cope with the corresponding challenges the reader is informed about progress in technology, theoretical methods, new findings of research, new ideas on design and execution, development in production, assessment and conservation strategies. By the actual selection of topics and the way those are treated, the “Concrete Yearbook” offers a splendid opportunity to get and stay aware of the development of technical knowledge, practical experience and concepts in the field of design of concrete structures on an international level.
Prof. Dr. Ir. Dr.-Ing. h.c. Joost Walraven, TU DelftHonorary president of the international concrete federation fib
1
Introduction
With the publication of the European technical guideline for the anchorage of post-installed metal fasteners in concrete (European Organization for Technical Approvals (EOTA) (1997)) for the first time it was possible to release European approvals for post-installed fasteners. The practical application of these approvals requires detailed design rules. At this time no European design provisions existed for fastenings and the development of generally acknowledged European design rules was not to be expected at short notice. Therefore, the design of fastenings had also to be covered in this guideline. The design method for post-installed fasteners published in Appendix C is based to a high extent on a guideline of the Deutsches Institut für Bautechnik (DIBt, German Institute of Construction Technology) from 1993 (Deutsches Institut f ür Bautechnik (1993)). During the past years Annex C was updated several times to the actual state of knowledge (European Organization for Technical Approvals (EOTA) (2010a)) and supplemented by the Technical Report TR 029 (European Organization for Technical Approvals (EOTA), 2010b) for the design of post-installed chemical fasteners. The current versions date from September, 2010.
The first European technical approvals for headed bolts were released in 2003. The design procedure for headed bolts was essentially based on Annex C of the above mentioned guideline and extended by applications specific to headed fasteners. This design method was a component of the approval document. These approval documents were replaced in 2011 by new versions which refer to the design provisions of CEN/TS 1992-4 as design procedure.
European technical approvals for anchor channels exist since 2011. They contain the design provisions of CEN/TS 1992-4 with slight improvements.
From the beginning the persons in charge were aware that the consideration of the design within the scope of an approval guideline could be only an interim solution, because after the European Construction Products Directive, EOTA was assigned to provide only European technical approval guidelines (ETAGs) for building products. The publication of European regulations for the design of construction products is within the responsibility of CEN. Hence, ETAG 001, Annex C should be transferred in the medium term into a European design standard. Finally in 2000 under the responsibility of CEN/TC 250 “Structural Eurocodes” this work started and was finalized in 2009. In May 2009 CEN/TS 1992-4 was accepted by the European Committee for standardization (CEN) for the tentative use as a pre-standard. The German version was published in August, 2009 by DIN (German Institute for Standardization) titled DIN SPEC 1021-4 (Deutsches Institut für Normung (DIN), 2009).
The published set of rules CEN/TS 1992-4 is a European pre-standard (TS=Technical Specification, in the past named prEN). In this publication it is called CEN/TS. CEN/TS consists of the following five parts:
Part 1 is valid for all types of fasteners. Parts 2 to 5 contain special rules for the respective fasteners. These parts shall be applied only in connection with Part 1.
Although CEN/TS 1992-4 is a pre-standard, it may be already applied for the design of fastenings, provided that their suitability was verified for the intended application by a ETA. The respective ETA must refer to CEN/TS and contain all data necessary for the calculation. The ETA can be a so-called European Technical Approval (ETA), a European harmonized product standard (hEN) or a suitable national standard or regulation. The use of the post-installed fasteners, headed bolts and anchor channels covered by CEN/TS is regulated currently only by European Technical Approvals which are called in the following ETA (European Technical Approval). Other ETAs are not available currently. They are also not in the planning stage.
In the following CEN/TS provisions are explained. Detailed descriptions of the load bearing behaviour and procedures for the calculation of fastenings with mechanical and chemical post-installed fasteners, headed bolts and anchor channels can be found in Eligehausen and Mallée (2000) as well as Eligehausen, Mallée, and Silva (2006).
2
Fields of Application
CEN/TS covers the design of post-installed fastenings (fasteners) and cast in situ fasteners (headed fasteners and anchor channels) in concrete components. The following types of fasteners are considered:
In Figure 2.1 the different types of post-installed fasteners are shown schematically, Figures 2.2 and 2.3 show typical headed fasteners and anchor channels.
Fig. 2.1 Types of post-installed fasteners(a1) torque-controlled fastener (sleeve type)(a2) torque-controlled fastener (bolt type, also named or wedge type)(b) deformation-controlled fastener (drop-in fastener)(c1) undercut fastener (undercut in the direction to the bottom of the borehole enlarged)(c2) undercut fastener (undercut in the direction to the concrete surface enlarged)(d) concrete screw(e1) bonded fastener(e2) bonded expansion fastener
Fig. 2.2 Typical headed fasteners
Fig. 2.3 Typical anchor channel
Torque-controlled post-installed expansion fasteners are subdivided into sleeve type and bolt (wedge) type expansion fasteners. Post-installed fasteners of the sleeve type (Figure 2.1a1) consist of a screw or a threaded rod with nut, washer, distance sleeve, a part to prevent spinning of the fastener in the borehole as well as an expansion cone. Post-installed fasteners of the bolt type (Figure 2.1a2) consist of a bolt, the end of which is formed to one or two cones and shows at the other end a thread, expansion segments nested in the conical area of the bolt, as well as of a nut and a washer. The fasteners are anchored by applying a defined torque. During torqueing a prestressing force is generated in the bolt or in the screw, the cone or the cones at the end of the fastener is pulled into the expansion sleeve or segments. These are pressed against the borehole wall. The frictional forces caused thereby, fix the fasteners in the bore hole. The load-transfer mechanism employed by expansion anchors is called ‘friction’.
Displacement-controlled post-installed fasteners (Figure 2.1b) consist of an expansion sleeve and a conical expansion plug. The internally threaded steel sleeve allows to screw in a screw or a threaded rod. They are set via the expansion of the sleeve as controlled by the axial displacement of the expansion plug within the sleeve. This is achieved by driving the expansion plug into the sleeve with a setting tool and a hammer. Like torque-controlled expansion fasteners, displacement-controlled expansion fasteners transfer external tension loads into the base material via friction and, in the zone of the localised deformation to some degree via mechanical interlock.
Undercut fasteners develop a mechanical interlock between anchor and base material (working principle ‘mechanical interlock’). For this a cylindrically drilled hole is modified to create a notch, or undercut, of a specific dimension at a defined location either by means of a special drilling tool or by the undercutting action of the fastener itself (self-undercutting fastener). The Figures 2.1c1 and c2 show two typical undercut fasteners which differ for example in the direction of the undercut: Undercut that widens towards the bottom of the borehole (Figure 2.1c1) or towards the concrete surface (Figure 2.1c2). Undercut fasteners according to Figure 2.1c1 consist of a threaded stud with a conical end, expansion sleeve, nut, and washer. Internally threaded versions (not illustrated) accept bolts or threaded rods. This type of undercut fasteners is anchored by driving the expansion sleeve onto the conical end. Then the expansion sleeve fills the undercut area either produced with the help of a special tool or by cutting its undercut automatically by means of hammering or hammering/rotary action in the concrete. Undercut fasteners after Figure 2.1c2 consist of a threaded rod with hex nut and washer, a cylindrical nut, three curved bearing segments, cone, spacer sleeve, helical spring and a plastic ring which secures the bearing segments prior to installing the anchor. After drilling a cylindrical hole, the undercut is created with the help of a special undercutting tool. Afterwards the anchor is inserted into the borehole and the bearing elements are allowed to unfold into position at the level of the undercut. Defined torqueing of the fastener brings the bearing segments into contact with the supporting surfaces.
Concrete screws (Figure 2.1d) are screwed into pre-drilled holes with the help of a special impact power screwdriver, an electric power screwdriver, a hammer drill equipped with an adapter in rotary mode or a customary torque wrench. They show typically a hardened special thread to allow the process of cutting the threads into the concrete. The diameter of the drilled hole is matched to the geometry of the screw so that the thread cuts into the concrete and an external force can be transferred to the concrete by means of mechanical interlock.
Bonded fasteners (Figure 2.1e1) consist of a threaded rod, a hexagonal nut and a washer or an internally threaded sleeve to accept threaded parts as well as a chemical mortar as bonding material. The bonding materials may consist of polymer resins, cementitious materials, or a combination of the two. A distinction can be made between so-called capsule fasteners, in which the constituent bonding materials are contained in glass capsules or foil pouches, and injection systems. In case of capsule fasteners the mortar is mixed by driving (rotary/hammer mode of the drill) the threaded rod or internally threaded sleeve into the borehole. In case of injection systems the chemical mortar is pre-packaged in cartridges and und mixed via special mixing nozzles during injection into the borehole. The tension load is transferred to the base material by means of bond. This load-transfer mechanism is called ‘chemical interlock’.
Bonded expansion fasteners (Figure 2.2e2) employ a unique anchor rod geometry with multiple conical surfaces, nut and washer as well as an adhesive mortar as bonding agent. The mortar is delivered again in glass cartridges, foil pouches or cartridges. The anchor rod is either coated, or shows a smooth and hard surface to prevent adhesion between the anchor rod and the bonding material. After hardening of the mortar the bonded expansion anchor is pre-stressed by applying a defined installation torque. The hardened bonding material is thereby split into single mortar segments which work, in principle, like expansion sleeves of a post-installed expansion fastener. When a tensile force is applied to the anchor rod, the cones are displaced upward relative to the position of the hardened mortar and frictional forces originate between mortar sleeve and borehole wall (working principle ‘friction’).
Figure 2.2 shows typical headed fasteners. Headed fasteners after Figure 2.2a show a thread at the upper end for connecting with the attachment. The configurations of Figure 2.2b consist of a steel plate with headed studs butt-welded on. Headed studs are usually welded on using drawn arc stud welding. After retracting the formwork from the concrete component the attachment is welded or screwed to the embedded steel plate. Headed fasteners after Figure 2.2c show at the upper end an internal thread sleeve to accept screws or threaded rods. Headed fasteners derive their tensile resistance from mechanical interlock between the anchor head and the hardened concrete (working principle ‘mechanical interlock’).
Anchor channels (Figure 2.3) consist of a cold-formed or hot-rolled steel channel equipped with special anchor fittings. These channels, filled with rigid urethane foam to prevent concrete intrusion, are attached directly to the inside of the formwork. Following removal of the formwork and of the rigid foam, a variety of components can be attached with the aid of special T-headed bolts. Transfer of the load back into the concrete in case of anchor channels is generally achieved by way of T-, I-shaped or headed anchors welded or forged to the channel. However, there are also anchor channels available in which the load is transferred into the base material by way of loops of steel with tabs that are passed through the back of the channel and bent. This type of anchorage is not covered by CEN/TS since the anchor is not connected stiff to the channel and might become effective only after a certain degree of displacement of the channel. Anchor channels with serrated lips to transfer shear loads along the length of the channel are also not covered. At the time of the development of CEN/TS the state of the knowledge was not sufficient to allow for the standardisation of the design method.
CEN/TS applies to fasteners with a minimum diameter or a minimum thread size of 6 mm (M6) or a corresponding cross section and with a nominal steel tensile strength fuk ≤ 1000 N/mm2. In general, the minimum embedment depth should be hef ≥ 40 mm. The actual value for a particular fastener might be taken from the relevant ETA for example a European Technical Approval (ETA).
Furthermore CEN/TS applies to fasteners with established suitability for the specified application in concrete covered by provisions such as an ETA. CEN/TS is intended for applications in which the failure of fastenings will:
If the above conditions are given “safety related applications” exist and the employed fasteners must be prequalified demonstrated by an ETA and be designed accordingly. In all other cases the choice and the installation of the fasteners is performed directly by the user according to craftsmanship and knowledge, a detailed calculation of the fastening is not carried out, in general.
CEN/TS is valid for applications which fall within the scope of the series EN 1992. In applications where special considerations apply, for example nuclear power plants or civil defense structures, modifications may be necessary.
The support of the fixture may be either statically determinate or statically indeterminate, where each support may consist of one fastener or a group of fasteners. The design of the attachment for example the steel plate is not covered, requirements for stiffness and ductility of the attachment are given, however.
CEN/TS provides design methods for fasteners for structural purpose which are used to transmit actions locally into the concrete structure. They apply to single fasteners and groups of fasteners whereas it is assumed that a fastening group consists only of fasteners of the same type and size. Figure 2.4 shows possible configurations of post-installed fasteners and headed fasteners. Distinction is to be made between fastenings with and without hole clearance.
Fig. 2.4 Permissible configurations of fastenings according to CEN/TS 1992-4(a) fastenings without hole clearance, all edge distances(b) fastenings with hole clearance situated far from edges (c1 ≥ 10 hef and c1 ≥ 60 dnom, c2 ≥ 10 hef and c2 ≥ 60 dnom)(c) fastenings with hole clearance situated near to an edge (c1 < 10 hef or c1 < 60 dnom, c2 < 10 hef or c2 < 60 dnom)
In case of post-installed fasteners no hole clearance may be considered if any inevitable gap occurring between the fastener and the fixture due to installation is filled with mortar of sufficient compression strength or eliminated by other suitable means such as snap rings.
Headed fasteners without hole clearance shall be welded to the fixture or screwed into the fixture.
If no hole clearance exists, single fastenings as well as groups with two to nine fasteners may be accomplished independent of the edge distance (Figure 2.4a). For fastenings with hole clearance and more than two fasteners in a row the distribution of a shear load on the single post-installed fasteners or headed fasteners of the group is not predictable with certainty, because their positions within the holes of the attachment can be very different by chance. Fasteners, positioned not concentric in the hole of the fixture but in direct contact with the attachment in the direction of the shear load are engaged from the beginning. On the other hand fasteners which have no initial contact with the fixture after the installation due to the hole clearance participate in the shear load transfer only if the annular gap is overcome by a certain displacement of the fixture and after a suitable deformation of the loaded post-installed fasteners. This can lead to the fact that the single fasteners of a group participate clearly differently in the transfer of shear loads and in case of applications with fastenings under shear load close to the edge and the brittle failure mode concrete edge failure yield problems. Hence CEN/TS permits applications close to the edge (c < 10 · hef or c < 60 · dnom) (the greater of both values governs) only configurations with single fasteners or groups with two or four post-installed fasteners or headed fasteners (Figure 2.4c). Fastenings with three or six to nine post-installed fasteners or headed fasteners and hole clearance are only allowed, if the edge distance is large enough to preclude concrete edge failure. This is the case if all edge distances are c ≥ 10 · hef and c ≥ 60 · dnom (Figure 2.4b).
This regulation limits the range of application compared with ETAG 001, Annex C, third amendment dated August, 2010 (European Organization for Technical Approvals (EOTA) (2010)). After ETAG 001 configurations according to Figure 2.4b may be carried out also with small edge distances if no shear loads act. This clear enhancement of the field of application should be considered in the transfer from CEN/TS in a European Standard.
The loads acting on a fastening can be static, cyclic (causing fatigue failure) or seismic. The suitability of the fastener type to resist either cyclic or seismic loading is stated in the relevant ETA. Furthermore fasteners can be subjected to bending moments.
The loading on the fastener resulting from the actions on the fixture (e.g. tension, shear, combined tension and shear, bending moments in one or two directions or torsion moments or any combination thereof) will generally be axial tension and/or shear (Figures 2.5a to c). If a shear load with a lever arm acts (stand-off installation, Figure 2.5d), the fastener is loaded, in addition, by a bending moment.
Fig. 2.5 Forces acting on fastenings(a) tension load(b) shear load(c) combined tension load and shear load(d) shear load with lever arm (stand-off installation)
The loads acting on the concrete component serving as anchorage ground can be static, cyclic (causing fatigue failure) or seismic. However, if the concrete member is subjected to cyclic or seismic loading only certain types of fasteners may be allowed. This is stated in the corresponding ETA (ETA).
