Foreword This European Standard EN 1993-3-2, Eurocode 3: Design of steel structures: Part 3-2 Towers, masts and chimneys ~ Chimneys, has been prepared by Technical Committee CEN/TC250 «
Scope
Part 3.2 of EN 1993 pertains to the structural design of vertical steel chimneys, specifically those with circular or conical sections This section addresses chimneys that are either cantilevered, supported at intermediate levels, or guyed.
(2) The provisions in this Part supplement those given in Part 1.1 of EN 1993
(3) This PaIt 3.2 is concerned only with the requirement for resistance (strength, stability and fatigue) of steel chimneys
NOTE: In this context (i.e resistance) the term chimney refers to: a) chimney structures b) the steel cylindrical elements of towers c) the steel cylindrical shafts of guyed masts
(4) For provisions concerning aspects, such as chemical attack, thermo-dynamical performance or thermal insulation see EN 13084-1 For the design of Ii ners see EN 13084-6
(5) Foundations in reinforced concrete for steel chimneys are covered in EN 1992 and EN 1997 See also 4.7 and 5.4 of EN 13084-1
(6) Wind loads are specified in EN 1991-1-4
NOTE: Procedures for the wind response of guyed chimneys are given in annex B of EN 1993-3-1
(7) This Part does not cover special provisions for seismic design, which are given in EN 1998-6 See also 5.2.4.1 of EN 13084-1
(8) Provisions for the guys and their attachments are in EN 1993-3-1 and EN 1993-1 11
(9) For the execution of steel chimneys, reference should be made to EN 1090, Palt 2 and EN 13084-1
Execution is addressed to highlight the quality of construction materials and products required, as well as the standard of workmanship necessary on-site to meet the design rules' assumptions.
(10) The following subjects are dealt with in EN 1993-3-2:
Section 8: Design assisted by testing
This European standard incorporates provisions from various normative documents, which are referenced throughout the text For dated references, any amendments or revisions made after the publication date do not apply However, it is advisable for parties involved in agreements based on this standard to consider using the most recent editions of the referenced normative documents In the case of undated references, the latest edition of the cited normative document is applicable.
Execution (~lsteel structures and alllminillm structures Hot rolled prodllcts 0/ non-alloy structllral steels Technica/ delivel~v conditions Stain/e.)',)' steels
Free standing industrial chimneys Part I : General Requirements
Vvelding - Fllsion-welded joints in steel, nickel, titanillm alld their alloys (beam welding excluded) - Qllality levels/or impeJjections
1.4 Distinction between principles and application rules
(]) The terms and definitions that are defined in EN 1990 for common use in the Structural Eurocodes apply to this Part 3.2 of EN 1993
(2) Supplementary to Paft I of EN 1993, for the purposes of this Part 3.2, the following definitions apply Definitions used for chimney structures are shown in Figure 1.1
Vertical construction works or building components that conduct waste gases, or other flue gases, supply or exhaust air to the atmosphere
A chimney whose supporting shaft is not connected with any other construction above the base level
A chimney whose supporting shaft is held in place by guys at one or more height levels
A chimney whose structural shell also conducts the flue gases It may be fitted by thermal insulation and/or i nternall ini ng
A chimney consisting of an outer steel structural she1l and one inner liner which carries the flue gases
A group of two or more chimneys structurally interconnected or a group of two or more liners within a structural shell
The structural element (membrane) of the lining system, contained within the structural shell
The total system that separates flue gases from the structural shell includes a liner and its supports, as well as the space between the liner and the structural shell, along with any existing insulation.
The main load-bearing steel structure of the chimney, excluding any flanges
A device fitted to the chimney to reduce vOJ1ex excitation without increasing the structural damping
A device fitted to the chimney to reduce v0l1ex excited oscillations by increasing the structural damping
A device attached to the surface of a chimney with the objective of reducing cross wind response
1.5.13 helical strakes, shrouds or slats
Devices fitted to the outer surface of the chimney to reduce cross wind response
A horizontal plate fixed to the base of a chimney
A bolt for the connection of the chimney to the foundation
Horizontal members are essential for maintaining the round shape of the chimney shell during fabrication and transport, preventing ovalling They also serve as stiffeners at cutouts and openings, as well as at points where the slope of the structural shell changes.
Single wall chimney Double wall chimney
Figure 1.1 Definitions used for Chimneys
1.6 Symbols used in Part 3.2 of Eurocode 3
(l) In addition to those given in EN 1993-1-1 the following main symbols are used c corrosion allowance
N number of cycles b diameter d bolt diameter h height m slope time w wind pressure ref reference crit critical value ext external
F load f fatigue int internal lat lateral (cross wi nd) top top
1] factor to account for second order effects
(2) Further symbols are defined where they first occur
(2)P A chimney shall be designed so that provided it is properly constructed and maintained it is capable of satisfying the fundamental requirements specified in EN 1990 and in EN 13084-1
(3) The structural design of guyed chimneys should be in accordance with the relevant clauses of
EN 1993-3-1 as well as this Part
(1) Different levels of reliability may be adopted for the ultimate limit states verifications for chimneys, depending on the possible economic and social consequences of their collapse
NOTE: For the definition of different levels of reliability see Annex A
2.2 Principles of limit state design
(I)P The general requirements of section 4 of EN 1990 shall be satisfied
(2) The strength and stability of chimneys should be verified for the actions described in 2.3.2 and 2.3.3 2.3.2 Pennanent actions
(1) Tn calculating self-weight, the full thickness of steelwork should be considered, with no loss due to corrOSlon
Permanent actions must account for the estimated weight of all permanent structures and elements, including fittings, insulation, dust loads, clinging ash, coatings, and other loads The weight of the chimney and its lining should be assessed in accordance with EN 1991-1-1, considering the long-term effects of fluids or moisture on the density of linings when applicable.
(1) Imposed loads should be applied on platforms and railings
NOTE 1: The National Annex may give information on imposed loads on platforms and railings The following characteristic values of imposed loads are recommended:
Imposed loads on platforms: 2,0 kN/m2 (see also EN 13084-1)
Horizontal loads on railings: 0,5 kN/m
NOTE 2: These loads may be assumed to act in the absence of other climatic loads
(1) Wind action should be taken from EN 1991-1-4
Wind loads must be applied to the entire external surfaces of a chimney and its accessory components, such as ladders In addition to the drag forces from gusty winds acting in the wind direction, it is essential to account for forces resulting from vortex shedding, which can induce crosswind vibrations in the chimney.
NOTE: For guyed chimneys see also Annex B to EN ] 993-3-1
(3) Other wind actions, for instance due to uneven wind pressure distribution (ovalling) or interference effects, should be taken into account if the relevant criteria are exceeded, see 5.2.1
(4) Actions caused by interference galloping or classical galloping should be assessed according to
(5) If chimneys are predicted to be subject to excessive wind vibrations, measures may be taken to reduce these in the design, or by installation of damping devices, see Annex B
(1) If events are possible that may lead to abnormal under-pressure or to over-pressure, these cases should be treated as accidental loads
NOTE: The under-pressure may he determined, for from the gas flow velocilY, the gas density, the total resistance to now and the ambient conditions see EN 13084-1, Annex A
Thermal action on a structure can result from a uniformly distributed temperature as well as differential temperature effects caused by meteorological conditions and operational factors, including those stemming from imperfect gas flow.
(2) For meteorological thermal actions see EN 1991-1-5
(3) Temperatures from operational effects and due to imperfect gas flow, should also be taken into account, see EN 13084-1 and EN 13084-6
(1) For chimneys that are likely to be subject to ice loading, the appropriate ice thicknesses, densities and distributions should be determined
NOTE 1: The National Annex may further information on ice loading
(1) Seismic actions should be determined from EN 1998-6 See also EN 13084-1
(1) The risk of a fire inside a chimney should be considered
Chimney fires can occur due to several factors, including the ignition of unburned fuel from boilers or furnaces, hydrocarbon carryover after a furnace tube rupture, and the accumulation of soot and sulfur deposits Additionally, deposits from the textile industry, grease, or condensates can also contribute to the risk of chimney fires.
The load-bearing structure must remain intact during a fire, ensuring that surrounding components near the chimney do not reach their ignition temperature To mitigate fire risks, suitable fireproofing measures should be implemented, in accordance with EN 13084-6 and EN 13084-7 standards.
(1) For chemical actions see EN 13084-1
(I) For design values of actions and combination of actions see EN 1990
(2) In addition to ultimate limit state and to fatigue assessment limiting amplitudes in the serviceability limit state (see Section 7) may be relevant for design
NOTE: For partial factors for ultimate limit states see Annex A
(I) The stiffnesses and strengths of the structural parts should be determined with nominal geometrical data taking account of both corrosion allowances or temperature effects if relevant, see sections 3 and 5
Durability must be ensured by adhering to the fatigue assessment outlined in section 9 and selecting the appropriate calculated shell thickness as specified in section 4 of EN 1993-1-1, along with implementing suitable corrosion protection measures.
NOTE: The National Annex may give information on the design service life of the structure A service life of
(I) See EN 1993-1-], EN ]993-1-3 and EN 1993-1-4
(1) Due account should be taken of the variation of mechanical properties of the steels due to ambient and operational temperatures, see 3.2.2( 1)
(2) For temperatures exceeding 400°C the effects of temperature creep should be considered to avoid creep rupture
(3) For toughness requirements of structural steels see EN 1993-1-10
3.2.2 Mechanical properties for structural carbon steels
(I) For the mechanical properties of structural carbon steels S S 275, S 355, S 420, S 460 and for weathering steel S 235, S 275, S 355 see EN 1993-1-1 For properties at higher temperatures see
3.2.3 IVlechanical properties of stainless steels
(I) For the mechanical properties related to stainless steels see EN 1993-1-4 valid for temperature up to 400°C For propel1ies at higher temperatures see EN 10088 and EN 13084-7
When accounting for corrosion on exposed surfaces, resistance and fatigue calculations should utilize the corroded thickness of the steel, unless the uncorroded thickness results in more adverse stress conditions.
The total allowance for corrosion must include both external (cext) and internal allowances (Cilll) These allowances should be applied as necessary throughout each 10-year period.
(3) This total allowance should be added to the thickness needed to satisfy the requirements for strength and stabil ity of the members
(I) External corrosion allowance should be appropriate to the environmental conditions
NOTE: The National Annex may give values for the external allowance eext For normal environment lhe values in Table 4.1 are recommended
Table 4.1 External corrosion allowance (C ext)
Fi rst 10 years Each additional
Over a 10-year period, the corrosion rates for various types of steel are as follows: painted carbon steel without a repainting program shows a corrosion rate of 0.1 mm, while painted carbon steel with a repainting program exhibits no corrosion Painted carbon steel that is insulated and waterproofed also shows a corrosion rate of 0.1 mm In contrast, unprotected carbon steel experiences a corrosion rate of 1.5 mm, while unprotected weathering steel has a rate of 0.5 mm Unprotected stainless steel shows no corrosion, and the unprotected inner surface of the structural shell and outer surface of the liner in a double skin or multi-flue chimney made of carbon or weathering steel has corrosion rates of 0.2 mm and 0.1 mm, respectively.
The external corrosion allowances are applicable solely to the upper 517 of the chimney, where 17 represents the chimney's external diameter In environments with high aggression, such as those affected by industrial pollution, neighboring chimneys, or proximity to the sea, it is advisable to enhance these allowances or implement protective measures.
Distinction between principles and application rules
(]) The terms and definitions that are defined in EN 1990 for common use in the Structural Eurocodes apply to this Part 3.2 of EN 1993
(2) Supplementary to Paft I of EN 1993, for the purposes of this Part 3.2, the following definitions apply Definitions used for chimney structures are shown in Figure 1.1
Vertical construction works or building components that conduct waste gases, or other flue gases, supply or exhaust air to the atmosphere
A chimney whose supporting shaft is not connected with any other construction above the base level
A chimney whose supporting shaft is held in place by guys at one or more height levels
A chimney whose structural shell also conducts the flue gases It may be fitted by thermal insulation and/or i nternall ini ng
A chimney consisting of an outer steel structural she1l and one inner liner which carries the flue gases
A group of two or more chimneys structurally interconnected or a group of two or more liners within a structural shell
The structural element (membrane) of the lining system, contained within the structural shell
The total system includes a liner and its supports that separate the flue gases from the structural shell, along with the space between the liner and the structural shell, as well as any existing insulation.
The main load-bearing steel structure of the chimney, excluding any flanges
A device fitted to the chimney to reduce vOJ1ex excitation without increasing the structural damping
A device fitted to the chimney to reduce v0l1ex excited oscillations by increasing the structural damping
A device attached to the surface of a chimney with the objective of reducing cross wind response
1.5.13 helical strakes, shrouds or slats
Devices fitted to the outer surface of the chimney to reduce cross wind response
A horizontal plate fixed to the base of a chimney
A bolt for the connection of the chimney to the foundation
Horizontal members are essential for maintaining the round shape of the chimney shell during fabrication and transport, preventing ovalling They also serve as stiffeners at cutouts, openings, and areas where the structural shell changes slope.
Single wall chimney Double wall chimney
Figure 1.1 Definitions used for Chimneys
1.6 Symbols used in Part 3.2 of Eurocode 3
(l) In addition to those given in EN 1993-1-1 the following main symbols are used c corrosion allowance
N number of cycles b diameter d bolt diameter h height m slope time w wind pressure ref reference crit critical value ext external
F load f fatigue int internal lat lateral (cross wi nd) top top
1] factor to account for second order effects
(2) Further symbols are defined where they first occur
(2)P A chimney shall be designed so that provided it is properly constructed and maintained it is capable of satisfying the fundamental requirements specified in EN 1990 and in EN 13084-1
(3) The structural design of guyed chimneys should be in accordance with the relevant clauses of
EN 1993-3-1 as well as this Part
(1) Different levels of reliability may be adopted for the ultimate limit states verifications for chimneys, depending on the possible economic and social consequences of their collapse
NOTE: For the definition of different levels of reliability see Annex A
2.2 Principles of limit state design
(I)P The general requirements of section 4 of EN 1990 shall be satisfied
(2) The strength and stability of chimneys should be verified for the actions described in 2.3.2 and 2.3.3 2.3.2 Pennanent actions
(1) Tn calculating self-weight, the full thickness of steelwork should be considered, with no loss due to corrOSlon
Permanent actions must account for the estimated weight of all permanent structures and elements, including fittings, insulation, dust loads, clinging ash, coatings, and other loads The chimney and its lining weight should be assessed in accordance with EN 1991-1-1, considering the long-term effects of fluids or moisture on the density of linings when applicable.
(1) Imposed loads should be applied on platforms and railings
NOTE 1: The National Annex may give information on imposed loads on platforms and railings The following characteristic values of imposed loads are recommended:
Imposed loads on platforms: 2,0 kN/m2 (see also EN 13084-1)
Horizontal loads on railings: 0,5 kN/m
NOTE 2: These loads may be assumed to act in the absence of other climatic loads
(1) Wind action should be taken from EN 1991-1-4
Wind loads must be applied to the entire external surfaces of a chimney and its accessory components, such as ladders In addition to the drag forces from gusty winds acting in the wind direction, it is essential to account for forces resulting from vortex shedding, which can induce crosswind vibrations in the chimney.
NOTE: For guyed chimneys see also Annex B to EN ] 993-3-1
(3) Other wind actions, for instance due to uneven wind pressure distribution (ovalling) or interference effects, should be taken into account if the relevant criteria are exceeded, see 5.2.1
(4) Actions caused by interference galloping or classical galloping should be assessed according to
(5) If chimneys are predicted to be subject to excessive wind vibrations, measures may be taken to reduce these in the design, or by installation of damping devices, see Annex B
(1) If events are possible that may lead to abnormal under-pressure or to over-pressure, these cases should be treated as accidental loads
NOTE: The under-pressure may he determined, for from the gas flow velocilY, the gas density, the total resistance to now and the ambient conditions see EN 13084-1, Annex A
Thermal action on a structure can consist of a uniformly distributed temperature as well as differential temperature effects resulting from meteorological conditions and operational factors, including those due to imperfect gas flow.
(2) For meteorological thermal actions see EN 1991-1-5
(3) Temperatures from operational effects and due to imperfect gas flow, should also be taken into account, see EN 13084-1 and EN 13084-6
(1) For chimneys that are likely to be subject to ice loading, the appropriate ice thicknesses, densities and distributions should be determined
NOTE 1: The National Annex may further information on ice loading
(1) Seismic actions should be determined from EN 1998-6 See also EN 13084-1
(1) The risk of a fire inside a chimney should be considered
Chimney fires can occur due to several factors, including the ignition of unburned fuel from boilers or furnaces, hydrocarbon carryover after a furnace tube rupture, and the accumulation of soot and sulfur deposits Additionally, deposits from the textile industry, grease, or condensates can also contribute to the risk of chimney fires.
The load-bearing structure must remain intact under fire conditions, ensuring that adjacent components near the chimney do not reach their ignition temperature In the event of fire risk, suitable fireproofing measures should be implemented Refer to EN 13084-6 and EN 13084-7 for guidelines.
(1) For chemical actions see EN 13084-1
(I) For design values of actions and combination of actions see EN 1990
(2) In addition to ultimate limit state and to fatigue assessment limiting amplitudes in the serviceability limit state (see Section 7) may be relevant for design
NOTE: For partial factors for ultimate limit states see Annex A
(I) The stiffnesses and strengths of the structural parts should be determined with nominal geometrical data taking account of both corrosion allowances or temperature effects if relevant, see sections 3 and 5
Durability must be ensured by adhering to the fatigue assessment outlined in section 9 and selecting the appropriate calculated shell thickness as specified in section 4 of EN 1993-1-1, along with implementing suitable corrosion protection measures.
NOTE: The National Annex may give information on the design service life of the structure A service life of
(I) See EN 1993-1-], EN ]993-1-3 and EN 1993-1-4
(1) Due account should be taken of the variation of mechanical properties of the steels due to ambient and operational temperatures, see 3.2.2( 1)
(2) For temperatures exceeding 400°C the effects of temperature creep should be considered to avoid creep rupture
(3) For toughness requirements of structural steels see EN 1993-1-10
3.2.2 Mechanical properties for structural carbon steels
(I) For the mechanical properties of structural carbon steels S S 275, S 355, S 420, S 460 and for weathering steel S 235, S 275, S 355 see EN 1993-1-1 For properties at higher temperatures see
3.2.3 IVlechanical properties of stainless steels
(I) For the mechanical properties related to stainless steels see EN 1993-1-4 valid for temperature up to 400°C For propel1ies at higher temperatures see EN 10088 and EN 13084-7
When accounting for corrosion on exposed surfaces, resistance and fatigue calculations should utilize the corroded thickness of the steel, unless the uncorroded thickness results in more adverse stress conditions.
Allowance for corrosion must include both external (cext) and internal allowances (Cilll) These allowances should be applied as necessary throughout each 10-year period.
(3) This total allowance should be added to the thickness needed to satisfy the requirements for strength and stabil ity of the members
(I) External corrosion allowance should be appropriate to the environmental conditions
NOTE: The National Annex may give values for the external allowance eext For normal environment lhe values in Table 4.1 are recommended
Table 4.1 External corrosion allowance (C ext)
Fi rst 10 years Each additional
Over a 10-year period, the corrosion rates for various types of steel are as follows: painted carbon steel without a repainting program shows a corrosion rate of 0.1 mm, while painted carbon steel with a repainting program exhibits no corrosion Insulated and waterproof-clad painted carbon steel also has a corrosion rate of 0.1 mm In contrast, unprotected carbon steel experiences a corrosion rate of 1.5 mm, while unprotected weathering steel shows rates of 0.5 mm and 0.3 mm Unprotected stainless steel demonstrates no corrosion Additionally, the unprotected inner surface of the structural shell and the unprotected outer surface of the liner in a double skin or multi-flue chimney made of carbon or weathering steel have corrosion rates of 0.2 mm and 0.1 mm, respectively.
The external corrosion allowances are applicable solely to the upper 517 of the chimney, where 17 represents the chimney's external diameter In environments prone to aggressive corrosion, such as those affected by industrial pollution, neighboring chimneys, or proximity to the sea, it is essential to consider enhancing these allowances or implementing protective measures.
To prevent moisture retention in structural connections, it is essential to design them with careful consideration of member orientation, edge and pitch distances, and to provide detailed protection Additionally, maintaining clear vegetation at the ground line is crucial, and any direct embedments or foundation attachments should be coated to reduce the risk of corrosion from soil contact and constant moisture exposure.
(4) If weathering steel is used the measures set out in (3) should be adopted
5.1 Modelling of the chimney for determining action effects
For ultimate limit state verifications of chimneys, it is essential to disregard any potential composite action between the structural shell and the liner However, it is important to consider any restraints of the liner that could negatively impact the safety of the shell.
NOTE: Damping effects from interaction of the structural shell and the liner may be taken inlo account The National Annex may further information
(2) The strength and stability of the liner should then be assessed with due regard to the deformations imposed from the structural shell
(3) Due regard should be given to the temperature effects on the stiffness and strength of the steels used in the chimney structure
When determining the stiffness of a chimney, it is essential to use the corroded thickness of the shell, unless the uncorroded thickness results in greater stress conditions Both external and internal corrosion must be taken into account, as outlined in sections 4.2 and 4.3.
5.2 Calculation of internal stress resultants and stresses
5.2.1 Analysis of the structural shell
(1) For the calculation of stress resultants and stresses in the structural she]] see EN 1993-1-6
In general, linear shell analysis (LA), either by analytical tools or by finite elements, may be used
NOTE: Rules and formulae for LA analysis of cylindrical and conical shells are given in EN 1993-1-6