SIST EN 1998-6:2005
(Main)Eurocode 8: Design of structures for earthquake resistance - Part 6: Towers, masts and chimneys
Eurocode 8: Design of structures for earthquake resistance - Part 6: Towers, masts and chimneys
Complementary to material related Eurocode parts dealing with towers, masts and chimneys. Design rules for the earthquake resistant design of tall, slender structures: towers, including bell-towers and intake towers, masts, industrial chimneys and lighthouses constructed in reinforced concrete or steel.
Eurocode 8: Auslegung von Bauwerken gegen Erdbeben - Teil 6: Türme, Maste und Schornsteine
Eurocode 8: Calcul des structures pour leur résistance aux séismes - Partie 6 : Tours, mâts et cheminées
(1) Le domaine d'application de l'Eurocode 8 est défini dans l'EN 1998-1:2004, 1.1.1 et le domaine d'application de la présente norme est défini en (2) a (4). Les autre parties de l'Eurocode 8 sont mentionnées dans l'EN 1998-1:2004, 1.1.3.
(2) L'EN 1998-6 établit des exigences, des criteres et des regles pour le dimensionnement de structures hautes et élancées : les tours, incluant les clochers, les tours d'aspiration, les pylônes de radio et de télévision, les mâts, les cheminées (incluant les cheminées industrielles auto-portantes) et les phares. Des dispositions additionnelles spécifiques aux cheminées en béton armé et en acier sont données aux articles 5 et 6, respectivement. Des dispositions additionnelles spécifiques aux pylônes en acier et aux pylônes haubanés en acier sont données aux articles 7 et 8, respectivement. La présente norme spécifie également des exigences pour les éléments non structuraux, tels que les antennes, le revetement des cheminées, et d'autres équipements.
NOTE 1 L'Annexe A informative donne des recommandations et des informations concernant l'analyse dynamique linéaire prenant en compte les composantes de rotation du mouvement du sol.
NOTE 2 L'Annexe B informative donne des recommandations et des informations concernant l'amortissement modal dans l'analyse modale avec réponse spectrale.
NOTE 3 L'Annexe C informative donne des informations concernant l'interaction sol-structure, ainsi que des recommandations visant a prendre en compte cette interaction dans l'analyse dynamique linéaire.
NOTE 4 L'Annexe D informative donne des informations et des recommandations supplémentaires concernant le nombre de degrés de liberté et le nombre de modes de vibration dont l'analyse doit tenir compte.
NOTE 5 L'Annexe E informative donne des informations et des recommandations concernant le dimensionnement sismique des cheminées en maçonnerie.
NOTE 6 L'Annexe F informative donne des informations supplémentaires concernant les performances et le di
Evrokod 8: Projektiranje potresnoodpornih konstrukcij – 6. del: Stolpi, jambori, dimniki
General Information
Standards Content (Sample)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Eurocode 8: Design of structures for earthquake resistance - Part 6: Towers, masts and chimneysEvrokod 8: Projektiranje potresnoodpornih konstrukcij – 6. del: Stolpi, jambori, dimnikiEurocode 8: Calcul des structures pour leur résistance aux séismes - Partie 6 : Tours, mâts et cheminéesEurocode 8: Auslegung von Bauwerken gegen Erdbeben - Teil 6: Türme, Maste und SchornsteineTa slovenski standard je istoveten z:EN 1998-6:2005SIST EN 1998-6:2005en91.120.25YLEUDFLMDPLSeismic and vibration protection91.060.40Dimniki, jaški, kanaliChimneys, shafts, ducts91.010.30Technical aspectsICS:SLOVENSKI
STANDARDSIST EN 1998-6:200501-oktober-2005
EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM
EN 1998-6
June 2005 ICS 91.120.25 Supersedes ENV 1998-3:1996 English version
Eurocode 8: Design of structures for earthquake resistance - Part 6: Towers, masts and chimneys
Eurocode 8: Calcul des structures pour leur résistance aux séismes - Partie 6 : Tours, mâts et cheminées
Eurocode 8: Auslegung von Bauwerken gegen Erdbeben - Teil 6: Türme, Maste und Schornsteine This European Standard was approved by CEN on 25 April 2005.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
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EN 1998-6:2005 (E) 2 Contents
1 GENERAL 8 1.1 SCOPE 8 1.2 REFERENCES 8 1.3 ASSUMPTIONS 9 1.4 DISTINCTION BETWEEN PRINCIPLES AND APPLICATION RULES 9 1.5 TERMS AND DEFINITIONS 10 1.5.1 Special terms used in EN 1998-6 10 1.6 SYMBOLS 10 1.6.1 General 10 1.6.2 Further symbols used in EN 1998-6 10 1.7 S.I. UNITS 11 2 PERFORMANCE REQUIREMENTS AND COMPLIANCE CRITERIA 12 2.1 FUNDAMENTAL REQUIREMENTS 12 2.2 COMPLIANCE CRITERIA 12 2.2.1 Foundation 12 2.2.2 Ultimate limit state 12 2.2.3 Damage limitation state 12 3 SEISMIC ACTION 13 3.1 DEFINITION OF THE SEISMIC INPUT 13 3.2 ELASTIC RESPONSE SPECTRUM 13 3.3 DESIGN RESPONSE SPECTRUM 13 3.4 TIME-HISTORY REPRESENTATION 13 3.5 LONG PERIOD COMPONENTS OF THE MOTION AT A POINT 13 3.6 GROUND MOTION COMPONENTS 14 4 DESIGN OF EARTHQUAKE RESISTANT TOWERS, MASTS AND CHIMNEYS 15 4.1 IMPORTANCE CLASSES AND IMPORTANCE FACTORS 15 4.2 MODELLING RULES AND ASSUMPTIONS 15 4.2.1 Number of degrees of freedom 15 4.2.2 Masses 16 4.2.3 Stiffness 16 4.2.4 Damping 17 4.2.5 Soil-structure interaction 17 4.3 METHODS OF ANALYSIS 18 4.3.1 Applicable methods 18 4.3.2 Lateral force method 18 4.3.2.1 General 18 4.3.2.2 Seismic forces 19 4.3.3 Modal response spectrum analysis 19 4.3.3.1 General 19 4.3.3.2 Number of modes 19 4.3.3.3 Combination of modes 19 4.4 COMBINATIONS OF THE EFFECTS OF THE COMPONENTS OF THE SEISMIC ACTION 20 4.5 COMBINATIONS OF THE SEISMIC ACTION WITH OTHER ACTIONS 20 4.6 DISPLACEMENTS 20 4.7 SAFETY VERIFICATIONS 20 4.7.1 Ultimate limit state 20 4.7.2 Resistance condition of the structural elements 20
EN 1998-6:2005 (E) 3 4.7.3 Second order effects 21 4.7.4 Resistance of connections 21 4.7.5 Stability 21 4.7.6 Ductility and energy dissipation condition 22 4.7.7 Foundations 22 4.7.8 Guys and fittings 22 4.8 THERMAL EFFECTS 22 4.9 DAMAGE LIMITATION STATE 22 4.10 BEHAVIOUR FACTOR 23 4.10.1 General 23 4.10.2 Values of modification factor kr 23 5 SPECIFIC RULES FOR REINFORCED CONCRETE CHIMNEYS 25 5.1 SCOPE 25 5.2 DESIGN FOR DISSIPATIVE BEHAVIOUR 25 5.3 DETAILING OF THE REINFORCEMENT 26 5.3.1 Minimum reinforcement (vertical and horizontal) 26 5.3.2 Minimum reinforcement around openings 27 5.4 SPECIAL RULES FOR ANALYSIS AND DESIGN 27 5.5 DAMAGE LIMITATION STATE 28 6 SPECIAL RULES FOR STEEL CHIMNEYS 29 6.1 DESIGN FOR DISSIPATIVE BEHAVIOUR 29 6.2 MATERIALS 29 6.2.1 General 29 6.2.2 Mechanical properties for structural carbon steels 30 6.2.3 Mechanical properties of stainless steels 30 6.2.4 Connections 30 6.3 DAMAGE LIMITATION STATE 30 6.4 ULTIMATE LIMIT STATE 30 7 SPECIAL RULES FOR STEEL TOWERS 31 7.1 SCOPE 31 7.2 DESIGN FOR DISSIPATIVE BEHAVIOUR 31 7.3 MATERIALS 31 7.4 DESIGN OF TOWERS WITH CONCENTRIC BRACINGS 31 7.5 SPECIAL RULES FOR THE DESIGN OF ELECTRICAL TRANSMISSION TOWERS 32 7.6 DAMAGE LIMITATION STATE 32 7.7 OTHER SPECIAL DESIGN RULES 34 8 SPECIAL RULES FOR GUYED MASTS 35 8.1 SCOPE 35 8.2 SPECIAL ANALYSIS AND DESIGN REQUIREMENTS 35 8.3 MATERIALS 35 8.4 DAMAGE LIMITATION STATE 36
EN 1998-6:2005 (E) 4 FOREWORD This European Standard EN 1998-6, Eurocode 8: Design of structures for earthquake resistance: Towers, masts and chimneys, has been prepared by Technical Committee CEN/TC 250 “Structural Eurocodes”, the secretariat of which is held by BSI. CEN/TC 250 is responsible for all Structural Eurocodes. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by December 2005 and conflicting national standards shall be withdrawn at latest by March 2010. This document supersedes ENV 1998-3:1996. According to the CEN-CENELEC Internal Regulations, the National Standard Organisations of the following countries are bound to implement this European Standard: Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom. Background of the Eurocode programme In 1975, the Commission of the European Community decided on an action programme in the field of construction, based on article 95 of the Treaty. The objective of the programme was the elimination of technical obstacles to trade and the harmonisation of technical specifications. Within this action programme, the Commission took the initiative to establish a set of harmonised technical rules for the design of construction works which, in a first stage, would serve as an alternative to the national rules in force in the Member States and, ultimately, would replace them.
For fifteen years, the Commission, with the help of a Steering Committee with Representatives of Member States, conducted the development of the Eurocodes programme, which led to the first generation of European codes in the 1980s.
In 1989, the Commission and the Member States of the EU and EFTA decided, on the basis of an agreement1 between the Commission and CEN, to transfer the preparation and the publication of the Eurocodes to CEN through a series of Mandates, in order to provide them with a future status of European Standard (EN). This links de facto the Eurocodes with the provisions of all the Council’s Directives and/or Commission’s Decisions dealing with European standards (e.g. the Council Directive 89/106/EEC on construction products - CPD - and Council Directives 93/37/EEC, 92/50/EEC and 89/440/EEC on public works and services and equivalent EFTA Directives initiated in pursuit of setting up the internal market). The Structural Eurocode programme comprises the following standards generally consisting of a number of Parts: EN 1990 Eurocode: Basis of structural design EN 1991 Eurocode 1: Actions on structures
1 Agreement between the Commission of the European Communities and the European Committee for Standardisation (CEN) concerning the work on EUROCODES for the design of building and civil engineering works (BC/CEN/03/89).
EN 1998-6:2005 (E) 5 EN 1992 Eurocode 2: Design of concrete structures EN 1993 Eurocode 3: Design of steel structures EN 1994 Eurocode 4: Design of composite steel and concrete structures EN 1995 Eurocode 5: Design of timber structures EN 1996 Eurocode 6: Design of masonry structures EN 1997 Eurocode 7: Geotechnical design EN 1998 Eurocode 8: Design of structures for earthquake resistance EN 1999 Eurocode 9: Design of aluminium structures Eurocode standards recognise the responsibility of regulatory authorities in each Member State and have safeguarded their right to determine values related to regulatory safety matters at national level where these continue to vary from State to State. Status and field of application of Eurocodes The Member States of the EU and EFTA recognise that Eurocodes serve as reference documents for the following purposes: – as a means to prove compliance of building and civil engineering works with the essential requirements of Council Directive 89/106/EEC, particularly Essential Requirement N°1 – Mechanical resistance and stability – and Essential Requirement N°2 – Safety in case of fire; – as a basis for specifying contracts for construction works and related engineering services; – as a framework for drawing up harmonised technical specifications for construction products (ENs and ETAs) The Eurocodes, as far as they concern the construction works themselves, have a direct relationship with the Interpretative Documents2 referred to in Article 12 of the CPD, although they are of a different nature from harmonised product standards3. Therefore, technical aspects arising from the Eurocodes work need to be adequately considered by CEN Technical Committees and/or EOTA Working Groups working on product standards with a view to achieving full compatibility of these technical specifications with the Eurocodes. The Eurocode standards provide common structural design rules for everyday use for the design of whole structures and component products of both a traditional and an innovative nature. Unusual forms of construction or design conditions are not specifically covered and additional expert consideration will be required by the designer in such cases.
2 According to Art. 3.3 of the CPD, the essential requirements (ERs) shall be given concrete form in interpretative documents for the creation of the necessary links between the essential requirements and the mandates for harmonised ENs and ETAGs/ETAs. 3 According to Art. 12 of the CPD the interpretative documents shall: a) give concrete form to the essential requirements by harmonising the terminology and the technical bases and indicating classes or levels for each requirement where necessary ; b) indicate methods of correlating these classes or levels of requirement with the technical specifications, e.g. methods of calculation and of proof, technical rules for project design, etc. ; c) serve as a reference for the establishment of harmonised standards and guidelines for European technical approvals. The Eurocodes, de facto, play a similar role in the field of the ER 1 and a part of ER 2.
EN 1998-6:2005 (E) 6 National Standards implementing Eurocodes The National Standards implementing Eurocodes will comprise the full text of the Eurocode (including any annexes), as published by CEN, which may be preceded by a National title page and National foreword, and may be followed by a National annex. The National annex may only contain information on those parameters which are left open in the Eurocode for national choice, known as Nationally Determined Parameters, to be used for the design of buildings and civil engineering works to be constructed in the country concerned, i.e: – values and/or classes where alternatives are given in the Eurocode, – values to be used where a symbol only is given in the Eurocode, – country specific data (geographical, climatic, etc.), e.g. snow map, – the procedure to be used where alternative procedures are given in the Eurocode. It may also contain
– decisions on the use of informative annexes, and
– references to non-contradictory complementary information to assist the user to apply the Eurocode. Links between Eurocodes and harmonised technical specifications (ENs and ETAs) for products There is a need for consistency between the harmonised technical specifications for construction products and the technical rules for works4. Furthermore, all the information accompanying the CE Marking of the construction products which refer to Eurocodes shall clearly mention which Nationally Determined Parameters have been taken into account. Additional information specific to EN 1998-6 For the design of structures in seismic regions the provisions of this standard are to be applied in addition to the provisions of the other relevant Eurocodes. In particular, the provisions of the present standard complement those of Eurocode 3, Part 3-1 " Towers and Masts " and Part 3-2 " Chimneys", which do not cover the special requirements for seismic design. National annex for EN 1998-6 Notes indicate where national choices have to be made. The National Standard implementing EN 1998-6 shall have a National annex containing values for all Nationally Determined Parameters to be used for the design in the country. National choice is required in the following sections.
4 see Art.3.3 and Art.12 of the CPD, as well as clauses 4.2, 4.3.1, 4.3.2 and 5.2 of ID 1.
EN 1998-6:2005 (E) 7 Reference section Item 1.1(2) Informative Annexes A, B, C, D, E and F. 3.1(1)
Conditions under which the rotational component of the ground motion should be taken into account. 3.5(2) The lower bound factor β=on design spectral values, if site-specific studies have been carried out with particular reference to the long-period content of the seismic action. 4.1(5)P Importance factors for masts, towers, and chimneys. 4.3.2.1(2) Detailed conditions, supplementing those in 4.3.2.1(2), for the lateral force method of analysis to be applied. 4.7.2(1)P Partial factors for materials 4.9(4) Reduction factor ν for displacements at damage limitation limit state
EN 1998-6:2005 (E) 8 1 GENERAL 1.1 Scope (1) The scope of Eurocode 8 is defined in EN 1998-1:2004, 1.1.1 and the scope of this Standard is defined in (2) to (4). Additional parts of Eurocode 8 are indicated in EN 1998-1:2004, 1.1.3. (2) EN 1998-6 establishes requirements, criteria, and rules for the design of tall slender structures: towers, including bell-towers, intake towers, radio and TV-towers, masts, chimneys (including free-standing industrial chimneys) and lighthouses. Additional provisions specific to reinforced concrete and to steel chimneys are given in Sections 5 and 6, respectively. Additional provisions specific to steel towers and to steel guyed masts are given in Sections 7 and 8, respectively. Requirements are also given for non-structural elements, such as antennae, the liner material of chimneys and other equipment. NOTE 1 Informative Annex A provides guidance and information for linear dynamic analysis accounting for rotational components of the ground motion. NOTE 2 Informative Annex B provides information and guidance on modal damping in modal response spectrum analysis. NOTE 3 Informative Annex C provides information on soil-structure interaction and guidance for accounting for it in linear dynamic analysis. NOTE 4 Informative Annex D provides supplementary information and guidance on the number of degrees of freedom and the number of modes of vibration to be taken into account in the analysis. NOTE 5 Informative Annex E gives information and guidance for the seismic design of Masonry chimneys. NOTE 6 Informative Annex F gives supplementary information for the seismic performance and design of electrical transmission towers. (3) The present provisions do not apply to cooling towers and offshore structures.
(4) For towers supporting tanks, EN 1998-4 applies.
1.2 Normative References 1.2.1 Use (1)P This European Standard incorporates by dated or undated reference, provisions from other publications. These normative references are cited at the appropriate places in the text and the publications are listed hereafter. For dated references, subsequent amendments to or revisions of any of these publications apply to this European Standard only when incorporated in it by amendment or revision. For undated references the latest edition of the publication referred to applies (including amendments).
1.2.2 General reference standards (1) EN 1998-1:2004, 1.2.1 applies.
EN 1998-6:2005 (E) 9 1.2.3 Additional reference standards for towers, masts and chimneys (1) EN 1998-6 incorporates other normative references cited at the appropriate places in the text. They are listed below: EN 1990 Basis of structural design – Annex A3: Application for towers and masts. EN 1992-1-1 Design of concrete structures – General rules and rules for buildings EN 1992-1-2 Design of concrete structures – Structural fire design EN 1993-1-1 Design of steel structures – General rules and rules for buildings EN 1993-1-2 Design of steel structures – Structural fire design EN 1993-1-4 Design of steel structures – Stainless steel EN 1993-1-5 Design of steel structures – Plated structural elements EN 1993-1-6 Design of steel structures – Strength and stability of shell structures EN 1993-1-8 Design of steel structures – Design of joints EN 1993-1-10 Design of steel structures – Selection of material for fracture toughness
and through thickness properties EN 1993-1-11 Design of steel structures – Design of structures with tension components made of steel EN 1993-3-1 Design of steel structures – Towers and masts EN 1993-3-2 Design of steel structures – Chimneys EN 1994-1-1 Design of composite steel and concrete structures – General rules and rules for buildings EN 1994-1-2 Design of composite steel and concrete structures – Structural fire design EN 1998-1 Design of structures for earthquake resistance – General rules, seismic actions and rules for buildings
EN 1998-5 Design of structures for earthquake resistance – Foundations, retaining structures and geotechnical aspects. EN 1998-2 Design of structures for earthquake resistance – Bridges. EN 13084-2 Free-standing chimneys – Concrete chimneys EN 13084-7 Free-standing chimneys – Product specification of cylindrical steel fabrications for use in single-wall steel chimneys and steel liners. 1.3 Assumptions (1)P The general assumptions of EN 1990:2002, 1.3 and EN 1998-1:2004, 1.3(2)P, apply. 1.4 Distinction between principles and application rules (1) EN 1990:2002, 1.4 applies.
EN 1998-6:2005 (E) 10 1.5 Terms and definitions 1.5.1 General terms and definitions (1) EN 1998-1:2004, 1.5.1 and 1.5.2 apply. (2) The definitions in EN 1993-3-1, 1.5 and EN 1993-3-2, 1.5 apply. 1.5.2 Further terms and definitions used in EN 1998-6 angle tower
transmission tower used where the line changes direction by more than 3o in plan. It supports the same kind of loads as the tangent tower dead-end towers (also called anchor towers) transmission tower able to support dead-end pulls from all the wires on one side, in addition to the vertical and transverse loads tangent tower transmission tower used where the cable line is straight or has an angle not exceeding 3o in plan. It supports vertical loads, a transverse load from the angular pull of the wires, a longitudinal load due to unequal spans, and forces resulting from the wire-stringing operation, or a broken wire telescope joint joint between tubular elements without a flange, the internal diameter of one being equal to the external diameter of the other transmission tower tower used to support low or high voltage electrical transmission cables trussed tower tower in which the joints are not designed to resist the plastic moment of the connected elements 1.6 Symbols 1.6.1 General (1) EN 1998-1:2004, 1.6.1 and 1.6.2 apply. (2) For ease of use, further symbols, used in connection with the seismic design of towers, masts and chimneys, are defined in the text where they occur. However, in addition, the most frequently occurring symbols used in EN 1998-6 are listed and defined in 1.6.2. 1.6.2 Further symbols used in EN1998-6 Eeq equivalent modulus of elasticity; Mi effective modal mass for the i-th mode of vibration;
EN 1998-6:2005 (E) 11 Rθ ratio between the maximum moment in the spring of an oscillator with rotation as its single-degree-of-freedom, and the rotational moment of inertia about the axis of rotation. The diagram of Rθ versus the natural period is the rotation response spectrum; Rx, Ry, Rz rotation response spectra around the x, y and z axes, in rad/s2;
unit weight of the cable; 1 tensile stress in the cable; j equivalent modal damping ratio of the j-th mode. 1.7 S.I. Units (1)P EN 1998-1:2004, 1.7(1)P applies. (2)
EN 1998-1:2004, 1.7(2) applies.
EN 1998-6:2005 (E) 12 2 PERFORMANCE REQUIREMENTS AND COMPLIANCE CRITERIA 2.1 Fundamental requirements (1)P For the types of structures addressed by this Eurocode, the no-collapse requirement in EN 1998-1:2004, 2.1(1)P applies, in order to protect the safety of people, nearby buildings and adjacent facilities. (2)P For the types of structures addressed by this Eurocode the damage limitation requirement in EN 1998-1:2004, 2.1(1)P applies, in order to maintain the continuity of the operation of plants, industries and communication systems, in the event of earthquakes. (3)P The damage limitation requirement refers to a seismic action having a probability of exceedance higher than that of the design seismic action. The structure shall be designed and constructed to withstand this action without damage and limitation of use, the cost of damage being measured with respect to the effects on the supported equipment and from the limitation of use due to disruption of operation of the facility.
(4) In cases of low seismicity, as defined in EN 1998-1:2004, 2.2.1(3) and 3.2.1(4), the fundamental requirements may be satisfied by designing the structure for the seismic design situation as non-dissipative, taking no account of any hysteretic energy dissipation and neglecting the rules of the present Eurocode that specifically refer to energy dissipation capacity. In that case, the behaviour factor should not be taken greater than the value of 1,5 considered to account for overstrengths (see EN 1998-1:2004, 2.2.2(2)). 2.2 Compliance criteria 2.2.1 Foundation (1)P Foundation design shall conform to EN 1998-5. 2.2.2 Ultimate limit state (1) EN 1998-1:2004, 2.2.2 applies.
2.2.3 Damage limitation state
(1) In the absence of any specific requirement of the owner, the rules specified in 4.9 apply, to ensure that damage considered unacceptable for this limit state will be prevented to the structure itself, to non-structural elements and to installed equipment. Deformation limits are established with reference to a seismic action having a probability of occurrence higher than that of the design seismic action, in accordance with EN 1998-1:2004, 2.1(1)P. (2) Unless special precautions are taken, provisions of this Eurocode do not specifically provide protection against damage to equipment and non-structural elements under the design seismic action, as this is defined in EN 1998-1:2004, 2.1(1)P.
EN 1998-6:2005 (E) 13 3 SEISMIC ACTION 3.1 Definition of the seismic input (1) In addition to the translational components of the earthquake motion, defined in EN 1998-1:2004, 3.2.2 and 3.2.3, the rotational component of the ground motion should be taken into account for tall structures in regions of high seismicity.
NOTE 1:
The conditions under which the rotational component of the ground motion should be taken into account in a country, will be found in the National Annex. The recommended conditions are structures taller than 80 m in regions where the product agS exceeds 0,25g.
NOTE 2:
Informative Annex A gives a possible method to define the rotational components of the motion and provides guidance for taking them into account in the analysis. 3.2 Elastic response spectrum
(1)P The elastic response spectrum in terms of acceleration is defined in EN 1998-1:2004, 3.2.2.2 for the horizontal translational components and in EN 1998-1:2004, 3.2.2.3 for the vertical translational component.
3.3 Design response spectrum (1) The design response spectrum is defined in EN 1998-1:2004, 3.2.2.5. The value of the behaviour factor, q, reflects, in addition to the hysteretic dissipation capacity of the structure, the influence of the viscous damping being different from 5%, including damping due the soil-structure interaction (see EN 1998-1:2004, 2.2.2(2), 3.2.2.5(2) and (3)). (2) For towers, masts and chimneys, depending on the cross section of the members, design for elastic behaviour until the Ultimate Limit State may be appropriate. In this case the q factor should not exceed q = 1,5.
(3) Alternatively to (2), design for elastic behaviour may be based on the elastic response spectrum with q = 1,0 and values of the damping which are chosen to be appropriate for the particular situation in accordance with 4.2.4.
3.4 Time-history representation (1) EN 1998-1:2004, 3.2.2.5 applies to the representation of the seismic action in terms of acceleration time-histories. In the case of the rotational components of the ground motion, rotational accelerations are simply used instead of translational ones. (2) Independent time-histories should be used for any two different components of the ground motion (including the translational and the rotational components). 3.5 Long period components of the motion at a point (1) Towers, masts and chimneys are often sensitive to the long-period content of the ground motion. Soft soils or peculiar topographic conditions might provide unusually large amplification of the long-period content of the ground motion. This amplification should be taken into account as appropriate. NOTE: Guidance on the assessment of soil type for the purpose of determining appropriate ground spectra is given in EN 1998-5:2004, 4.2.2 and in EN 1998-1:2004, 3.1.2. Guidance on cases where
EN 1998-6:2005 (E) 14 topographical amplification of motion may be significant is given in Informative Annex A of EN 1998-5:2004.
(2) Where site-specific studies have been carried out, with particular reference to the long period content of the motion, lower values of the factor β in expression (3.16) of EN 1998-1:2004 are appropriate. NOTE: The value to be ascribed to β for use in a country, in those cases where site-specific studies have been carried out with particular reference to the long-period content of the motion, can be found in its National Annex. The recommended value for β in such a case is 0,1. 3.6 Ground motion components (1) The two horizontal components and the vertical component of the seismic action should be taken as acting simultaneously.
(2) When taken into account, the rotational components of the ground motion should be taken as acting simultaneously with the translational components.
EN 1998-6:2005 (E) 15 4 DESIGN OF EARTHQUAKE RESISTANT TOWERS, MASTS AND CHIMNEYS 4.1 Importance classes and importance factors (1)P Towers, masts and chimneys are classified in four importance classes, depending on the consequences of collapse or damage, on their importance for public safety and civil protection in the immediate post-earthquake period, and on the social and economic consequences of collapse or damage. (2) The definitions of the importance classes are given in Table 4.1. Table 4.1 Importance classes for towers, masts and chimneys Importance class
I Tower, mast or chimney of minor importance for public safety
II Tower, mast or chimney not belonging in classes I, III or IV III Tower, mast or chimney whose collapse may affect surrounding buildings or areas likely to be crowded with people. IV Towers, masts or chimneys whose integrity is of vital importance to maintain operational civil protection services (water supply systems, an electrical power plants, telecommunications, hospitals). (3) The importance factor γI = 1,0 is associated with a seismic event having the reference return period indicated in EN 1998-1:2004, 3.2.1(3). (4)P The value of γI for importance class II shall be, by definition, equal to 1,0.
(5)P The importance classes are characterised by different importance factors γI, as described in EN 1998-1:2004, 2.1(3). NOTE The values to be ascribed to γI for use in a country may be found in its National Annex. The values of γI may be different for the various seismic zones of the country, depending on the seismic hazard conditions and on public safety considerations (see Note to EN 1998-1:2004, 2.1(4)). The recommended values of γI for importance classes I, III and IV are equal to 0,8, 1,2 and 1,4, respectively. 4.2 Modelling rules and assumptions 4.2.1 Number of degrees of freedom
(1) The mathematical model should: – take into account the rotational and translational stiffness of the foundation;
– include sufficient degrees of freedom (and the associated masses) to determine the response of any significant structural element, equipment or appendage; – include the stiffness of cables and guys; – take into account the relative displacements of the supports of equipment or machinery (for example, the interaction between an insulating layer and the exterior tube in a chimney);
EN 1998-6:2005 (E) 16 – take into account piping interactions, externally applied structural restraints, hydrodynamic loads (both mass
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