CEN/TC 250/SC2 N??? pren (2 nd draft)

Transcription

1 EUROPEAN STANDARD CEN/TC 2/SC2 N??? NORME EUROPÉENNE EUROPÄISCHE NORM July 2001 ICS Supersedes ENV Descriptors: Buildings, concrete structures, design, computation, fire resistance English version Eurocode 2: Design of concrete structures - Part 1.2: General rules Structural fire design Eurocode 2: Calcul des structures en béton - Partie 1-2 : Règles générales Calcul du comportement au feu Eurocode 2: Planung von Stahlbeton- und Spannbetontragwerken - Teil 1-2: Allgemeine Regeln Tragwerksbemessung für den Brandfall This European Standard was approved by CEN on 199?-??-??. 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. The European Standards exist 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, Czech Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom. CEN European Committee for Standardization Comité Européen de Normalisation Europäishes Komitee für Normung Central Secretariat: rue de Stassart, 36 B-10 Brussels

2 Page 2 FOREWORD This European Standard EN , Design of concrete structures - Part 1-2 General rules - Structural fire design", has been prepared on behalf of Technical Committee CEN/TC2 Structural Eurocodes, the Secretariat of which is held by BSI. CEN/TC2/SC 2 is responsible for Eurocode 2: Design of concrete structures. The text of the draft standard was submitted to the formal vote and was approved by CEN as EN 199x-1-2 on YYYY-MM-DD. [Reference to superseded ENV is made on the CEN cover page] Background of the Eurocode programme In 1975, the Commission of the European Community decided on an action programme in the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 19s. 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 the 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//EEC and 89/4/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 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 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). Ref. No. EN (July 2001)

3 Page 3 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 the designer in such cases will require additional expert consideration. 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, 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. Ref. No. pren (July 2000)

4 Page 4 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, decisions on the application of informative annexes, references to non-contradictory complementary information to assist the user to apply the Eurocode. LINKS BETWEEN EUROCODES AND PRODUCTS HARMONISED TECHNICAL SPECIFICATIONS (ENS AND ETAS) There is a need for consistency between the harmonised technical specifications for construction products and the technical rules for works 4. Furthermore, all the information accompanying the CE Marking of the construction products which refer to Eurocodes should clearly mention which Nationally Determined Parameters have been taken into account. ADDITIONAL INFORMATION SPECIFIC TO EN EN describes the Principles, requirements and rules) for the structural design of buildings exposed to fire, including the following aspects. Safety requirements EN is intended for clients (e.g. for the formulation of their specific requirements), designers, contractors and relevant authorities. The general objectives of fire protection are to limit risks with respect to the individual and society, neighbouring property, and where required, environment or directly exposed property, in the case of fire. Construction Products Directive 89/106/EEC gives the following essential requirement for the limitation of fire risks: "The construction works must be designed and build in such a way, that in the event of an outbreak of fire - the load bearing resistance of the construction can be assumed for a specified period of time - the generation and spread of fire and smoke within the works are limited - the spread of fire to neighbouring construction works is limited - the occupants can leave the works or can be rescued by other means - the safety of rescue teams is taken into consideration". According to the Interpretative Document N 2 "Safety in case of fire" the essential requirement may be observed by following various possible fire safety strategies prevailing in the Member States such as conventional fire scenarios (nominal fires) or natural (parametric) fire scenarios, including passive and active fire protection measures. The fire parts of Structural Eurocodes deal with specific aspects of passive fire protection in terms of designing structures and parts thereof for adequate load bearing resistance and for limiting fire spread as relevant. 4 see Art.3.3 and Art.12 of the CPD, as well as clauses 4.2, 4.3.1, and 5.2 of ID 1. Ref. No. EN (July 2001)

5 Page 5 Required functions and levels of performance can be specified either in terms of nominal (standard) fire resistance rating, generally given in National Fire Regulations or by referring to fire safety engineering for assessing passive and active measures. This Part 1-2, together with EN "Actions on structures exposed to fire" gives the supplements to EN 199x-1-1, which are necessary so that structures designed according to this set of Structural Eurocodes may also comply with structural fire resistance requirements. Supplementary requirements concerning, for example - the possible installation and maintenance of sprinkler systems, - conditions on occupancy of building or fire compartment, - the use of approved insulation and coating materials, including their maintenance, are not given in this document, because they are subject to specification by the competent authority. Numerical values for partial factors and other reliability elements are given as recommended values that provide an acceptable level of reliability. They have been selected assuming that an appropriate level of workmanship and of quality management applies. Design procedures A full analytical procedure for structural fire design would take into account the behaviour of the structural system at elevated temperatures, the potential heat exposure and the beneficial effects of active and passive fire protection systems, together with the uncertainties associated with these three features and the importance of the structure (consequences of failure). At the present time it is possible to undertake a procedure for determining adequate performance which incorporates some, if not all, of these parameters and to demonstrate that the structure, or its components, will give adequate performance in a real building fire. However, where the procedure is based on a nominal (standard) fire the classification system, which call for specific periods of fire resistance, takes into account (though not explicitly), the features and uncertainties described above. Application of this Part 1-2 is illustrated below. The prescriptive approach and the performancebased approach are identified. The prescriptive approach uses nominal fires to generate thermal actions. The performance-based approach, using fire safety engineering, refers to thermal actions based on physical and chemical parameters. For design according to this part, EN is required for the determination of thermal and mechanical actions to the structure. Design aids Where simple calculation models are not available, the Eurocode fire parts give design solutions in terms of tabular data (based on tests or advanced calculation models), which may be used within the specified limits of validity. Ref. No. pren (July 2000)

6 Page 6 It is expected, that design aids based on the calculation models given in EN 199x-1-2, will be prepared by interested external organisations. The main text of EN , together with informative Annexes A, B, C, and D, includes most of the principal concepts and rules necessary for structural fire design of concrete structures. NATIONAL ANNEX FOR EN This standard gives alternative procedures, values and recommendations for classes with notes indicating where national choices may have to be made. Therefore the National Standard implementing EN should have a National annex containing the Eurocode all Nationally Determined Parameters to be used for the design of buildings, and where required and applicable, for civil engineering works to be constructed in the relevant country. [To Project team: Do we delete civil engineering works or do we keep this?] National choice is allowed in EN through clauses: (2)P [list of clauses to be completed following later decisions] Figure from Model Clauses to be added [Figure from Model Clauses] Alternative proposal from Project Team for discussion: [Figures 1a, b and c from TH] Ref. No. EN (July 2001)

7 Page 7 Contents List 1 General 1.1 Scope 1.2 Normative references 1.3 Definitions 1.4 Symbols Supplementary symbols to EN Supplementary subscripts to EN Units 2 Basis principles and rules 2.1 Performance requirements General Nominal fire exposure Parametric fire exposure 2.2 Actions 2.3 Design values of material properties 2.4 Assessment methods General Member analysis Analysis of parts of the structure Global structural analysis 3 Material properties 3.1 General 3.2 Strength and deformation properties at elevated temperatures General Concrete Concrete under compression Tensile strength Reinforcing steel Prestressing steel 3.3 Residual mechanical properties Concrete Reinforcing and prestressing steel Thermal elongation Specific heat Thermal conductivity 3.4 Thermal properties Concrete with siliceous, calcareous and lightweight aggregates Thermal elongation Specific heat Thermal conductivity Reinforcing and prestressing steel Thermal elongation Specific heat Thermal conductivity Ref. No. pren (July 2000)

8 Page 8 4 Design methods 4.1 General 4.2 Simplified calculation method General Temperature profiles Reduced cross-section Strength reduction General Concrete Steel 4.3 General calculation methods General Thermal response Mechanical response 4.4 Shear and torsion 4.5 Anchorage 4.6 Spalling 4.7 Joints 4.8 Protective layers 5 Tabulated data 5.1 Scope 5.2 General design rules 5.3 Columns 5.4 Walls Non load-bearing walls (partitions) Load-bearing solid walls 5.5 Tensile members 5.6 Beams General Simply supported beams Continuous beams Beams exposed on all sides Slabs General Simply supported slabs Continuous slabs Flat slabs Ribbed slabs 6 High strength concrete 6.1 General 6.2 Spalling 6.3 Thermal properties Thermal conductivity Specific heat 6.4 Temperature field 6.5 Structural design Calculation of load-carrying capacity Structural systems Ref. No. EN (July 2001)

9 Page Simplified calculation method HSC columns and walls Beams and slabs Informative annexes A B C D Temperature profiles Simplified calculation methods Buckling of columns under fire conditions Simplified calculation method for beams and slabs Ref. No. pren (July 2000)

10 Page 10 SECTION 1 GENERAL 1.1 SCOPE P (2)P (3)P (4)P (5)P This Part 1.2 of EN 1992 deals with the design of concrete structures for the accidental situation of fire exposure and intended to be used in conjunction with EN and EN This part 1.2 only identifies differences from, or supplements to, normal temperature design. This Part 1.2 of EN 1992 deals only with passive methods of fire protection. Active methods are not covered. This Part 1.2 of EN 1992 applies to concrete structures that, for reasons of general fire safety, are required to fulfil certain functions when exposed to fire, in terms of: - avoiding premature collapse of the structure (load bearing function) - limiting fire spread (flame, hot gases, excessive heat) beyond designated areas (separating function) This Part 1.2 of EN 1992 gives principles and application rules (see EN ) for designing structures for specified requirements in respect of the aforementioned functions and the levels of performance. This Part 1.2 of EN 1992 applies to structures, or parts of structures, that are within the scope of EN and are designed accordingly. However, it does not cover: - structures with prestressing by external tendons - shell structures (6)P The methods given in this Part 1.2 of EN 1992 are applicable to concrete strength classes up to C90/105 and LC55/. Additional and alternative rules for strength classes above C/ are given in section Normative references The following normative documents contain provisions that, through reference in this text, constitute provisions of this European Standard. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. However, parties to agreements based on this European Standard are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest edition of the normative document referred to applies. EN Drafting note: to be checked later EN 1363 Fire resistance: General requirements; ENV Fire tests on elements of building construction: Ref. No. EN (July 2001)

11 Page 11 Part 1: Test method for determining the contribution to the fire resistance of structural members: by horizontal protective membranes; Part 2: Test method for determining the contribution to the fire resistance of structural members: by vertical protective membranes; Part 3: Test method for determining the contribution to the fire resistance of structural members: by applied protection to concrete structural elements; EN Fire classification of construction products and building elements Part 2 Classification using data from fire resistance tests, excluding ventilation services EN 1991 Eurocode 1. Basis of design and actions on structures: Part 1.2: Actions on structures exposed to fire; EN 1992 Eurocode 2. Design of concrete structures: Part 1.1: General rules : General rules and rules for buildings ISO 1000 SI units. 1.3 Assumptions Design which employs the Principles and Application Rules is deemed to meet the requirements provided the assumptions given in EN 1990 to EN 1999 are satisfied (see Section 2). (2) The general assumptions of this part 1.2 of EN 199x are : - The choice of the structural system and the design of the structure is made by appropriately qualified and experienced personnel. - The choice of the relevant fire design scenario is made by appropriate qualified and experienced personnel, or is given by the relevant national regulation, (new, compare to EN 1990) Execution is carried out by personnel having the appropriate skill and experience. Adequate supervision and quality control is provided during execution of the work, i.e. in design offices, factories, plants, and on site. The construction materials and products are used as specified in EN 1990 or in ENs 1991 and 199x or in the relevant execution standards, or reference material or product specifications. The structure will be adequately maintained. The structure will be used in accordance with the design assumptions. Note : There may be cases when the above assumptions need to be supplemented. Ref. No. pren (July 2000)

12 Page Distinction between principles and application rules Rules given in EN 1990 apply. 1.5 Definitions Drafting note: Horizontal Group Fire agreed that general definitions have to be put only in EN However, those used in this draft are given below, identified by a *, but should disappear in the final version. A reference number will be added for each definition For the purposes of this Part 1.2 of EN 1992, the definitions of EN 1990 and of EN apply with the additional definitions: Critical temperature of reinforcement : The temperature at which failure is expected to occur in reinforcement at a given load level. *Design fire: A specified fire development assumed for design purposes. Effective cross section: Cross section of the member in structure fire design used in the effective cross section method. It is obtained from the residual cross section by removing parts of the cross section with assumed zero strength and stiffness. *Fire compartment: A space within a building, extending over one or several floors, which is enclosed by separating elements such that fire spread beyond the compartment is prevented during the relevant fire exposure. Fire protection material: Any material or combination of materials applied to a structural member for the purpose of increasing its fire resistance. *Fire resistance: The ability of a structure, a part of a structure or a member to fulfil its required functions (load bearing function and/or separating function) for a specified fire exposure and for a specified period of time. *Global structural analysis (for fire): An analysis of the entire structure, when either the entire structure, or only parts of it, are exposed to fire. Indirect fire actions are considered throughout the structure. *Indirect fire actions: Internal forces and moments caused by thermal expansion. *integrity (E): The ability of a separating element of building construction, when exposed to fire on one side, to prevent the passage through it of flames and hot gases and to prevent the occurrence of flames on the unexposed side *insulation (I): The ability of a separating element of building construction when exposed to fire on one side, to restrict the temperature rise of the unexposed face to below specified levels. *Load bearing function (R): The ability of a structure or a member to sustain specified actions during the relevant fire, according to defined criteria. Maximum stress level: For a given temperature, the stress level at which the stressstrain relationship of steel is truncated to provide a yield plateau *Members analysis (for fire): The thermal and mechanical analysis of a structural member exposed to fire in which the member is assumed as isolated, with appropriate Ref. No. EN (July 2001)

13 Page 13 support and boundary conditions. Indirect fire actions are not considered, except those resulting from thermal gradients. Normal temperature design: Ultimate limite state design for ambient temperatures according to Part 1-1 of EN 1992 to 1996 or ENV 1999 Part of structure: isolated part of an entire structure with appropriate support and boundary conditions. Protected members: Members for which measures are taken to reduce the temperature rise in the member due to fire. *Separating function: The ability of a separating element to prevent fire spread (e.g. by passage of flames or hot gases - cf integrity) or ignition beyond the exposed surface (cf insulation) during the relevant fire. *Separating element: Load bearing or non-load bearing element (e.g. wall or floor) forming part of the enclosure of a fire compartment. *Standard fire resistance: The ability of a structure or part of it (usually only members) to fulfil required functions (load-bearing function and/or separating function), for the exposure to heating according to the standard temperature-time curve for a stated period of time. *Standard temperature-time curve: A nominal curve, defined in EN for representing a model of a fully developed fire in a compartment *Structural members: The load-bearing members of a structure including bracings. *Temperature analysis: The procedure of determining the temperature development in members on the basis of the thermal actions (net heat flux) and the thermal material properties of the members and of protective surfaces, where relevant. *Temperature-time curves: Gas temperature in the environment of member surfaces as a function of time. They may be: - nominal: Conventional curves, adopted for classification or verification of fire resistance, e.g. the standard temperature-time curve; - parametric: Determined on the basis of fire models and the specific physical parameters defining the conditions in the fire compartment. *Thermal actions: Actions on the structure described by the net heat flux to the members. 1.4 Symbols Supplementary symbols to EN P The following supplementary symbols are used: Drafting note: To be checked and completed later Latin upper case letters E d,fi design effect of actions in the fire situation Ref. No. pren (July 2000)

14 Page 14 E d design effect of actions for normal temperature design R d,fi design resistance in the fire situation; R d,fi (t) at a given time t. R or R,... fire resistance class for the load-bearing criterion for, or... minutes in standard fire exposure E or E,... fire resistance class for the integrity criterion for, or... minutes in standard fire exposure I or I,... fire resistance class for the thermal insulation criterion for, or... minutes in standard fire exposure T X k X d,fi temperature [K] (cf θ temperature [ o C]); characteristic value of a strength or deformation property for normal temperature design design strength or deformation property in the fire situation Latin lower case letters a axis distance of reinforcing or prestressing steel from the nearest exposed surface c f ck (θ) f pk (θ) f sk (θ) specific heat [J/kgK] characteristic value of compressive strength of concrete at temperature θ for a specified strain characteristic value of strength of prestressing steel at temperature θ for a specified strain characteristic strength of reinforcing steel at temperature θ for a specified strain k(θ)= X k (θ)/x k reduction factor for a strength or deformation property dependent on the material temperature θ t time of fire exposure (min) Greek lower case letters partial safety factor for a material in fire design γ M,fi η fi = ε s,fi λ E d,fi /E d reduction factor for design load level in the fire situation strain of the reinforcing or prestressing steel at temperature θ thermal conductivity [W/mK] Ref. No. EN (July 2001)

15 Page 15 σ c,fi σ s,fi compressive stress of concrete in fire situation steel stress in fire situation θ temperature [ o C] θ cr critical temperature [ 0 C] Supplementary to EN , the following subscripts are used: fi t θ value relevant for the fire situation dependent on the time dependent on the temperature 1.5 Units P SI units shall be used in conformity with ISO (2) Supplementary to EN , the following units are recommended : - temperature : C; - absolute temperature : K; - temperature difference : K; - specific heat : J/kgK; - coefficient of thermal conductivity : W/mK. Ref. No. pren (July 2000)

16 Page 16 SECTION 2 BASIC PRINCIPLES AND RULES 2.1 Performance requirements General P (2)P Where mechanical resistance in the case of fire is required, concrete structures shall be designed and constructed in such a way that they maintain their load bearing function during the relevant fire exposure - Criterion R. Where compartmentation is required, the elements forming the boundaries of the fire compartment, including joints, shall be designed and constructed in such a way that they maintain their separating function during the relevant fire exposure, i.e. when requested: - no integrity failure in order to prevent the passage through it of flames and hot gases and to prevent the occurrence of flames on the unexposed side - Criterion "E" - no insulation failure in order to restrict the temperature rise of the unexposed face to below specified levels - Criterion "I" - limitation of the thermal radiation from the unexposed side. Note: There is no need to consider the thermal radiation with an unexposed surface temperature below 0 C (see EN ) (3)P Deformation criteria shall be applied where the means of protection, or the design criteria for separating elements, require consideration of the deformation of the load bearing structure. (4) Consideration of the deformation of the load bearing structure is not necessary in the following cases, as relevant: - the efficiency of the means of protection has been evaluated according to 4.9, - the separating elements have to fulfil requirements according to nominal fire exposure Nominal fire exposure P With the standard fire exposure, members shall comply with criteria R, E and I as follows: - separating only: integrity (criterion E) and, when requested, insulation (criterion I) - load bearing only: mechanical resistance (criterion R) - separating and load bearing: criteria R, E and, when requested I (2) Criterion R is assumed to be satisfied where the load bearing function is maintained during the required time of fire exposure. (3) Criterion I may be assumed to be satisfied where the average temperature rise over the whole of the non-exposed surface is limited to 1 K, and the maximum temperature rise at any point of that surface does not exceed 1 K (4) With the external fire exposure curve the same criteria should apply, however the reference to this specific curve should be identified by the letters "ef". Ref. No. EN (July 2001)

17 Page 17 (5) With the hydrocarbon fire exposure curve the same criteria should apply, however the reference to this specific curve should be identified by the letters "HC" (6) Where a vertical separating element with or without load-bearing function have to comply with impact resistance requirement (criterion M), the element should resist a horizontal concentrated load as specified in EN 1363 Part 2. (rule to be incorporated only in EC2 and EC6) Parametric fire exposure The load-bearing function is ensured when collapse is prevented during the complete duration of the fire including the decay phase or during a required period of time. (2) The separating function with respect to insulation is ensured when: - the average temperature rise over the whole of the non-exposed surface is limited to 1 K, and the maximum temperature rise of that surface does not exceed 200 K at the time of the maximum gas temperature, - and the average temperature rise over the whole of the non-exposed surface is limited to 1 K, and the maximum temperature rise of that surface does not exceed 2 K during the decay phase of the fire or up to a required period of time. 2.2 Actions P The thermal and mechanical actions shall be taken from EN (2) In addition to EN , the emissivity related to the concrete surface should be equal to 0,8. Drafting note: Emissivity for concrete is 0,7 in pren Design values of material properties P Design values of mechanical (strength and deformation) material properties X d,fi are defined as follows: X d,fi = k θ X k / γ M,fi (2.1) where: X k is the characteristic value of a strength or deformation property (generally f k or E k ) for normal temperature design to EN 199x-1-1; k θ is the reduction factor for a strength or deformation property (X k,θ / X k ), dependent on the material temperature, see 3.2.1; γ M,fi is the partial safety factor for the relevant material property, for the fire situation. (2)P Design values of thermal material properties X d,fi are defined as follows: Ref. No. pren (July 2000)

18 Page 18 - if an increase of the property is favourable for safety: X d,fi = X k,θ /γ M,fi (2.2a) - if an increase of the property is unfavourable for safety: X d,fi = γ M,fi X k,θ where: X k,θ γ M,fi (2.2b) is the value of a material property in fire design, generally dependent on the material temperature, see section 3; is the partial safety factor for the relevant material property, for the fire situation. Note: For thermal properties of concrete and reinforcing and prestressing steel, the recommended value of partial safety factor for the fire situation is: γ M,fi = 1,0 For mechanical properties of concrete and reinforcing and prestressing steel, the recommended value of partial safety factor for the fire situation is: γ M,fi = 1,0 2.4 Assessment methods General P (2)P The model of the structural system adopted for design to this Part 1.2 of EN 1992 shall reflect the expected performance of the structure in fire. The structural analysis for the fire situation may be carried out using one of the following: - member analysis, see 2.4.2; - analysis of part of the structure, see 2.4.3; - global structural analysis, see Note 1: Thermal expansion may cause large action effect remote from the fire source. Note 2: For verifying standard fire resistance requirements, a member analysis is sufficient (3)P It shall be verified for the relevant duration of fire exposure that E d,fi R d,t,fi (2.2) where E d,fi is the design effect of actions for the fire situation, determined in accordance with EN , including effects of thermal expansions and deformations. R d,t,fi is the corresponding design resistance in fire situation. (4) Where application rules given in this Part 1.2 are valid only for the standard temperature-time curve, this is identified in the relevant clauses Ref. No. EN (July 2001)

19 Page 19 (5) Tabulated data given in Section 5 are based on the standard temperature-time curve. (6)P As an alternative to design by calculation, fire design may be based on the results of fire tests, or on fire tests in combination with calculations, see EN 1990 clause 5.2. Note: For further details see EN 1990 clause 5.2. (7) For direct application of fire resistance tests, EN applies. (8) Extended application of fire test results should be based on assessment of tests and calculations Member analysis Note: Standards for extended application are under preparation in CEN/TC 127. As an alternative to carrying out a structural analysis for the fire situation at time t = 0, the reactions at supports and internal forces and moments may be obtained from a structural analysis for normal temperature design by using: E d,fi = η fi E d (2.3) Where E d η fi is the design value of the corresponding force or moment for normal temperature design, for a fundamental combination of actions (see EN 1990); is the reduction factor for the design load level for the fire situation. (3) The reduction factor for the design load level for the fire situation η fi for load combination (6.10) in EN 1990 is given by: η fi = γ GA γ G Gk + ψ Gk + γ 1,1 Q,1 Q Q k,1 k,1 (2.4) or the smaller of the values given by the two following expressions for load combinations from Expressions (6.10 a) and (6.10b) of EN 1990: η fi = γgagk + ψ1,1q γ Gk + γ ψ Q G Q,1 0,1 k,1 k,1 (2.5a) γ GA Gk + ψ 1,1Qk,1 η fi = ξγ G Gk + γ Q,1Qk,1 where where is the principal variable load; Q k,1 (2.5b) Ref. No. pren (July 2000)

20 Page 20 γ GA is the partial factor for permanent actions in accidental design situations; ψ fi is the combination factor for frequent values given either by ψ 1,1 or ψ 2,1, see EN Drafting note: The choice of ψ 1,1 or ψ 2,1 is under discussion in SC 1. It will possibly be Nationally Determined Parameter. Note: Regarding equation (2.5), examples of the variation of the reduction factor η fi versus the load ratio Q k,1 /G k for Expression (2.4) and different values of the combination factor ψ 1,1 are shown in Figure 2.1 with the following assumptions: γ GA = 1,0, γ G = 1,35 and γ Q = 1,5. Expressions (2.5a) and (2.5b) give slightly higher values. Partial factors are specified in the relevant National Annexes of EN Note that Expressions (2.5 a) and (2.5b) below give slightly higher values. 0,81 ηfi 0,71 0,61 0,51 0, ψ1,1 = 0,9 ψ1,1 = 0,7 ψ1,1 = 0,5 0, ψ1,1 = 0,2 0,2 0 0,0 0 0,5 1 1,0 1 1,5 2 2, ,0 3 2,5 Qk,1/Gk Figure 2.1: Variation of the reduction factor η fi with the load ratio Q k,1 / G k (3) The reduction factor η fi for load combination (6.10a) and (6.10b) in EN 1990 is the smaller value given by the two following expressions: η fi = η fi = γ γ γ G GA G GA G k G k + ψ fi + γ Q,1 ψ Q 0,1 Gk + ψ Q ξγ Gk + γ fi Q,1 Q k,1 k,1 k,1 Q k,1 (2.5a) (2.5b) where ξ is a reduction factor for unfavourable permanent actions G. Note: As a simplification a recommended value of η fi = 0,7 may be used. Ref. No. EN (July 2001)

21 Page 21 (4) Only the effects of thermal deformations resulting from thermal gradients across the cross-section need be considered. The effects of axial or in-plain thermal expansions may be neglected. (5) The restraint conditions at supports and ends of member, applicable at time t = 0, are assumed to remain unchanged throughout the fire exposure. (6) Tabulated data, simplified or general calculation methods given in 4.2, 4.3 and 4.4 respectively are suitable for verifying members under fire conditions Analysis of parts of the structure As an alternative to carrying out a global structural analysis for the fire situation at time t = 0 the reactions at supports and internal forces and moments at boundaries of part of the structure may be obtained from structural analysis for normal temperature as given in (2) The part of the structure to be analysed should be specified on the basis of the potential thermal expansions and deformations such, that their interaction with other parts of the structure can be approximated by time-independent support and boundary conditions during fire exposure. (3) Within the part of the structure to be analysed, the relevant failure mode in fire exposure, the temperature-dependent material properties and member stiffnesses, effects of thermal expansions and deformations (indirect fire actions) shall be taken into account (3) The restraint conditions at supports and forces and moments at boundaries of part of the structure, applicable at time t = 0, are assumed to remain unchanged throughout the fire exposure Global structural analysis P When global structural analysis for the fire situation is carried out, the relevant failure mode in fire exposure, the temperature-dependent material properties and member stiffnesses, effects of thermal expansions and deformations (indirect fire actions) shall be taken into account. Ref. No. pren (July 2000)

22 Page 22 SECTION 3 MATERIAL PROPERTIES 3.1 General P The values of material properties given in this section shall be treated as characteristic values, see 2.3. (2) The values may be used with the simplified (see 4.3) and the general calculation method (see 4.4). Alternative formulations of material laws may be applied, provided the solutions are within the range of experimental evidence. (3)P The mechanical properties of concrete, reinforcing and prestressing steel at 20 C shall be taken as those given in EN for normal temperature design. 3.2 Strength and deformation properties at elevated temperatures General P Numerical values on strength and deformation properties given in this section are based on steady state as well as transient state tests and sometimes a combination of both. As creep effects are not explicitly considered, the material models have only been checked for heating rates between 2 and K/min. For heating rates outside the above range, the reliability of the strength and deformation properties shall be demonstrated explicitly Concrete Concrete under compression P The strength and deformation properties of uniaxially stressed concrete at elevated temperatures shall be obtained from the stress-strain relationships as presented in Figure 3.1. (2) The stress-strain relationships given in Figure 3.1 are defined by two parameters: - the compressive strength f c,θ - the strain ε c1,θ corresponding to f c,θ. (3) Values for each of these parameters are given in Table 3.1 as a function of concrete temperatures. For intermediate values of the temperature, linear interpolation may be used. (4) The parameters specified in Table 3.1 may be used for normal weight concrete with siliceous or calcareous (containing at least % calcareous aggregate by weight) aggregates and lightweight aggregate concrete with densities in the range of 10 to 2000 kg/m 3. (5) Values for ε cu,θ defining the range of the descending branch may be taken from Table 3.1, Column 4 for normal weight concrete with siliceous aggregates,

23 Page 23 Column 7 for normal weight concrete with calcareous aggregates and Column 10 for lightweight aggregate concrete. (6) For thermal actions in accordance with 4.3 of EN (natural fire simulation), particularly when considering the descending temperature branch, the mathematical model for stress-strain relationships of concrete specified in Figure 3.1 should be modified. (7) The tensile strength of concrete may be assumed to be zero, which is on safe side. If it is necessary to take account of the tensile strength, when using the simplified or general calculation method, may be used. σ f c,θ ε c1,θ ε cu,θ ε Range Stress σ(θ) ε ε c1(θ ) < ε ε c1, θ ε cu, θ ε c1,θ 3ε f c,θ ε 2 + ε c1,θ umerical purposes a descending branch should be adopted. Linear or non-linear models are permitted. 3 Figure 3.1: Mathematical model for stress-strain relationships of concrete under compression at elevated temperatures.

24 Page 24 Table 3.1: Values for the main parameters of the stress-strain relationships of normal weight concrete with siliceous or calcareous aggregates and lightweight aggregate concrete at elevated temperatures. Concrete Siliceous aggregates Calcareous aggregates Lightweight aggregates temp.θ f c,θ / f ck ε c1,θ ε cu,θ f c,θ / f ck ε c1,θ ε cu,θ f c,θ / f ck ε c1,θ ε cu,θ [ C] [-] [-] [-] [-] [-] [-] [-] [-] [-] ,00 0,0025 0,0200 1,00 0,0025 0,0200 1,00 0,0020 0, ,00 0,00 0,0225 1,00 0,00 0,0225 0,75 0,0025 0, ,95 0,0055 0,02 0,97 0,0055 0,02 0,73 0,00 0, ,85 0,00 0,0275 0,91 0,00 0,0275 0,73 0,00 0,01 0 0,75 0,0100 0,00 0,85 0,0100 0,00 0,72 0,0090 0,01 0 0, 0,01 0,0325 0,74 0,01 0,0325 0, 0,0125 0, ,45 0,02 0,03 0, 0,02 0,03 0,65 0,01 0,02 0 0, 0,02 0,0375 0,43 0,02 0,0375 0,55 0,0225 0,05 0 0,15 0,02 0,00 0,27 0,02 0,00 0,25 0,02 0, ,08 0,02 0,0425 0,15 0,02 0,0425 0,10 0,0295 0, ,04 0,02 0,04 0,06 0,02 0,04 0,05 0,05 0, ,01 0,02 0,0475 0,02 0,02 0,0475 0,02 0,0315 0, , , ,01 0,0320 0, Tensile strength The tensile strength of concrete may be assumed to be zero, which is on safe side. If it is necessary to take account of the tensile strength, when using the simplified or general calculation method, may be used. (2) The reduction of the characteristic tensile strength of concrete is allowed for by the coefficient k c,t,θ for which f ck,t (θ) = k ck,t (θ) f ck,t (3.1) (3) In absence of more accurate information the following k ck,t (θ) values should be used (see Figure 3.2): k ck,t (θ) = 1,0 for 20 C θ 100 C k ck,t (θ) = 1,0 1,0 (θ -100)/0 for 100 C < θ 0 C

25 Page 25 kck,t(θ) 1,0 1 0,8 1 0,6 1 0,4 0 0,2 0 0, Temperature θ [ C] Figure 3.2: Coefficient k ck,t (θ) allowing for decrease of tensile strength (f ck,t ) of concrete at elevated temperatures Reinforcing steel P The strength and deformation properties of reinforcing steel at elevated temperatures shall be obtained from the stress-strain relationships specified in Figure 3.3 and Table 3.2. (2) The stress-strain relationships given in Figure 3.3 are defined by three parameters: - the slope of the linear elastic range E s,θ - the proportional limit f sp,θ - the maximum stress level f sy,θ (3) Values for the parameters in (2) for hot rolled and cold worked reinforcing steel at elevated temperatures are given in Table 3.2. For intermediate values of the temperature, linear interpolation may be used. (4) The formulation of stress-strain relationships may also be applied for reinforcing steel in compression. (5) In case of thermal actions according to section 4.3 of EN (natural fire simulation), particularly when considering the decreasing temperature branch, the values specified in Table 3.2 for the stress-strain relationships of reinforcing steel may be used as a sufficiently precise approximation.

26 Page 26 σ fsy,θ f sp,θ α E = tan (α ) s,θ ε sp,θ ε sy,θ ε st,θ ε su,θ ε ε ε ε sp,θ Range Stress σ(θ) Tangent modulus ε < εsp,θ εe s,θ ε ε f sp,θ c + (b/a)[a 2 (ε sy,θ ε) 2 ] 0,5 sy,θ 2 2 ( ) ε ε a a b( ε Es,θ ε ε sy,θ < < f sy,θ 0 st,θ ε ε st,θ < f sy,θ [1 (ε ε t,θ )/(ε u,θ ε t,θ )] - su,θ ε ε = 0,00 - su,θ ε sy,θ ) Parameter * ) ε sp,f = f sp,θ / E s,θ ε sy,θ = 0,02 ε st,θ = 0,15 ε su,θ = 0,20 sp,θ 0,5 Functions a 2 = (ε sy,θ ε sp,θ )(ε sy,θ ε sp,θ +c/e s,θ ) c = b 2 = c (ε sy,θ ε sp,θ ) E s,θ + c 2 2 ( f sy,θ f sp,θ) ( ) 2( ) * ) Values for the parameters ε pt,θ and ε pu,θ for prestressing steel may be taken from Table 3.3 ε sy,θ Figure 3.3: Mathematical model for stress-strain relationships of reinforcing and prestressing steel at elevated temperatures (notations for prestressing steel p instead of s ) ε sp,θ E s,θ f sy,θ f sp,θ

27 Page 27 Table 3.2: Values for the parameters of the stress-strain relationship of hot rolled and cold worked reinforcing steel at elevated temperatures Steel Temperature f sy,θ / f yk f sp,θ / f yk E s,θ / E s θ [ C] hot rolled cold worked hot rolled cold worked hot rolled cold worked ,00 1,00 1,00 1,00 1,00 1, ,00 1,00 1,00 0,96 1,00 1, ,00 1,00 0,81 0,92 0,90 0,87 0 1,00 1,00 0,61 0,81 0, 0,72 0 1,00 0,94 0,42 0,63 0, 0,56 0 0,78 0,67 0,36 0,44 0, 0, 0 0,47 0, 0,18 0,26 0,31 0,24 0 0,23 0,12 0,07 0,08 0,13 0,08 0 0,11 0,11 0,05 0,06 0,09 0, ,06 0,08 0,04 0,05 0,07 0, ,04 0,05 0,02 0,03 0,04 0, ,02 0,03 0,01 0,02 0,02 0, ,00 0,00 0,00 0,00 0,00 0, Prestressing steel The strength and deformation properties of prestressing steel at elevated temperatures may be obtained by the same mathematical model as that presented in for reinforcing steel. (2) Values for the parameters in section (2) for cold worked (wires and strands) and quenched and tempered (bars) prestressing steel at elevated temperatures are given in Table 3.3. For intermediate values of the temperature, linear interpolation may be used. (3) In case of thermal actions according to section 4.3 of EN (natural fire simulation), particularly when considering the decreasing temperature branch, the values specified in Table 3.3 for the stress-strain relationships of prestressing steel may be used as a sufficiently precise approximation.

28 Page 28 Table 3.3: Values for the parameters of the stress-strain relationship of cold worked (cw) (wires and strands) and quenched and tempered (q & t) (bars) prestressing steel at elevated temperatures Steel temp. f py,θ / (0,9 f pk ) f pp,θ / (0,9 f pk ) E p,θ /E p ε pt,θ [-] ε pu,θ [-] θ [ C] cw q & t cw q & t cw q & t cw, q&t cw, q&t ,00 1,00 1,00 1,00 1,00 1,00 0,00 0, ,99 0,98 0,68 0,77 0,98 0,76 0,00 0, ,87 0,92 0,51 0,62 0,95 0,61 0,00 0, ,72 0,86 0,32 0,58 0,88 0,52 0,0055 0, ,46 0,69 0,13 0,52 0,81 0,41 0,00 0, ,22 0,26 0,07 0,14 0,54 0,20 0,0065 0, ,10 0,21 0,05 0,11 0,41 0,15 0,00 0, ,08 0,15 0,03 0,09 0,10 0,10 0,0075 0, ,05 0,09 0,02 0,06 0,07 0,06 0,00 0, ,03 0,04 0,01 0,03 0,03 0,03 0,0085 0, ,00 0,00 0,00 0,00 0,00 0,00 0,0090 0, ,00 0,00 0,00 0,00 0,00 0,00 0,0095 0, ,00 0,00 0,00 0,00 0,00 0,00 0,0100 0, Thermal properties Concrete with siliceous, calcareous and lightweight aggregates 3.3.1,1 Thermal elongation The thermal strain ε c (θ) of concrete may be determined from the following with reference to the length at 20 C : Siliceous aggregates: ε c (θ) = -1, θ + 2, θ 3 for 20 C θ 0 C ε c (θ) = for 0 C < θ 1200 C Calcareous aggregates: ε c (θ) = -1, θ + 1, θ 3 for 20 C θ 5 C ε c (θ) = for 5 C < θ 1200 C Lightweight aggregates: ε c (θ) = (θ 20) for 20 C θ 1200 C where θ is the concrete temperature ( C)

29 Page 29 (2) The variation of the thermal elongation with temperatures is illustrated in Figure ( l/l)c(10 ) Curve : Siliceous aggregate Curve (2): Calcareous aggregate Curve (3): Lightweight aggregate , ,200 Temperature θ [ C] Figure 3.5 Total thermal elongation of concrete Specific heat The specific heat c pθ of dry concrete may be determined from the following: Siliceous and calcareous aggregates: c pθ = 900 (J/kgK) for 20 C θ 100 C c pθ = (T - 100) (J/kgK) for 100 C < θ 200 C c pθ = (T - 200) (J/kgK) for 200 C < θ 0 C c pθ = 1100 (J/kgK) for 0 C < θ 1200 C where θ is the concrete temperature ( C). c pθ is illustrated in Figure 3.6a. (2) Where the moisture content is not considered explicitly the function given for the specific heat of concrete with siliceous or calcareous aggregates may be modelled by a peak value situated between 100 C and 115 C such as c p.peak = 14 J/kgK for moisture content of 1,5 % of concrete weight c p.peak = 2020 J/kgK for moisture content of 3,0 % of concrete weight The peaks of specific heat are illustrated in Figure 3.6a. (3) The variation of density with temperature is influenced by water loss and is defined as follows ρ θ = ρ 20 C for 20 C θ 115 C ρ θ = 0,98 ρ 20 C for 115 C < θ 200 C