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The Eurocodes are a set of structural design standards, developed by [[#External links|CEN]] (European Committee for Standardisation) over the last 30 years, to cover the design of all types of structures in steel, concrete, timber, masonry and aluminium. In the UK, they are published by BSI under the designations BS&nbsp;EN&nbsp;1990 to BS&nbsp;EN&nbsp;1999; each of these ten Eurocodes is published in several Parts and each Part is accompanied by a National Annex that implements the [[#CEN documents|CEN document]]  and adds certain UK-specific provisions.

Although many previous national standards, including BS&nbsp;5950<ref name="BS5950">BS 5950 Structural use of steelwork in building:  Various parts, BSI</ref>, were withdrawn by BSI in 2010 they can still be used. This is likely to remain the case for some time.

This article introduces the [[Design codes and standards#Introduction to Eurocodes|Eurocode system]], sets out the format that is used and explains the relationship between the Eurocodes, their [[#National_Annexes|National Annexes]] and non-contradictory complementary information ([[#NCCI|NCCI]] ). It explains that the [[#BS EN 1990 Basis of structural design|basis of structural design]] is set out in BS&nbsp;EN&nbsp;1990<ref name="BSEN1990">BS EN 1990:2002+A1:2005. Eurocode: Basis of structural design. BSI</ref> and that this defines the common principles and specifies how design values are to be determined and verified. A brief summary of the various [[#Eurocode 1 - Actions|actions]] (loading) that are defined in EN&nbsp;1991 is given.

The article introduces the parts of EN&nbsp;1993 (Eurocode&nbsp;3) that are required when designing a steel framed building and briefly introduces EN&nbsp;1994 (Eurocode&nbsp;4), for [[#Composite structures|composite steel and concrete structures]], and EN&nbsp;1992 (Eurocode&nbsp;2), which covers the design of the concrete elements in composite structures.

Key issues from the relevant Eurocodes are identified. Much more detail is available in a wide range of [[#Resources|guides]] .

{|style="float: right; border: 0px"
|-
|{{#youtube:width=640px|id=9BazCswZrXI}}
|-
|'''An introduction to the Eurocodes'''
with contributions from:
*Dr Graham Couchman, CEO, Steel Construction Institute
*Professor Haig Gulvanessian, Chairman of the ICE Eurocode implementation committee
|}

==Building Regulations==
The Governments of the UK and its devolved regions publish documents which provide guidance on the means by which compliance with the Building Regulations in force in that region can be achieved. For structure safety these are: Approved Document A<ref name="ADA">[https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/429060/BR_PDF_AD_A_2013.pdf Approved Document A (Structure) 2004 Edition incorporating 2004, 2010, and 2013 amendments. Department for Communities and Local Government]</ref> 
(England); Approved Document A<ref name="ADAw">[http://wales.gov.uk/docs/desh/publications/130205building-regs-approved-document-a-structure-en.pdf Approved Document A (Structure) 2004 Edition incorporating 2010 amendments (Welsh Government)]</ref> (Wales); Scottish Technical Handbook <ref name="STH">[https://www.gov.scot/publications/building-standards-2017-non-domestic/ Building Standards Technical Handbook – Non-domestic buildings 2017, Section 1 – Structure, The Scottish Government]</ref> and Technical Booklet D<ref name="TBD">[https://www.finance-ni.gov.uk/sites/default/files/DFP%20Technical%20booklet%20D%20-%20Structure.pdf Technical Booklet D, Structure, Building Regulations (Northern Ireland) 2012, Department of Finance and Personnel of the Northern Ireland Government, 2012]</ref> in Northern Ireland. 
It should be noted that the English and Welsh Approved Documents have been separate only since 2013. Differences between them are small but one should be aware that they exist. When this article, or any other article on this site, refers to Approved Document A, by default it will be the English version<ref name="ADA"></ref>. 

Approved Document A<ref name="ADA"></ref> to the Building Regulations (England) currently references the [[Design_codes_and_standards#Introduction_to_Eurocodes|Eurocodes]]. It states that: ''British Standards for structural design based on the Eurocodes were.....implemented by the British Standards Institution on 1st April 2010 and it is these standards with their corresponding UK National Annexes which are now referenced in this Approved Document as practical guidance on meeting Part A requirements''.

It further states that: ''There may be alternative ways of achieving compliance with the requirements and there may be cases where it can be demonstrated that the use of withdrawn standards no longer maintained by the British Standards Institution continues to meet Part A requirements''.      

The Scottish Technical Handbook-Structures<ref name="STH"></ref>, has been updated in a similar way.

<gallery caption="Approved Documents" perrow=6 heights=180px widths=115px>
image:Approved_Document_A_2013.png
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image:Ad_b2_2006.gif
image:Ad_c_2006.gif
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</gallery>
<br>
It is important to recognise that the regulatory system in the UK is such that the Building Regulations themselves merely make high level demands, for example that a structure is safe. Use of the standards cited in Approved Document A<ref name="ADA"></ref> is only one way to demonstrate that requirement has been met.

==Introduction to Eurocodes==

===CEN documents===
There are ten separate Structural Eurocodes:
*EN&nbsp;1990 Eurocode: Basis of structural design<ref name="BSEN1990"></ref>
*EN&nbsp;1991 Eurocode&nbsp;1: Actions on structures<ref name="BSEN1991-1-1">BS EN 1991-1-1: 2002 Eurocode 1. Actions on structures. General actions. Densities, self-weight, imposed loads for buildings, BSI</ref> <ref name="NAtoBSEN1991-1-1">NA to BS EN 1991-1-1: 2002 UK National Annex to Eurocode 1. Actions on structures. General actions. Densities, self-weight, imposed loads for buildings, BSI</ref> <ref name="BSEN1991-1-2">BS EN 1991-1-2: 2002 Eurocode 1. Actions on structures. Actions on structures exposed to fire, BSI</ref> <ref name="NAtoBSEN1991-1-2">NA to BS EN 1991-1-2: 2002 UK National Annex to Eurocode 1. Actions on structures. General actions. Actions on structures exposed to fire, BSI</ref> <ref name="BSEN1991-1-3">BS EN 1991-1-3:2003+A1:2015, Eurocode 1. Actions on structures. General actions. Snow loads, BSI</ref> <ref name="NAtoBSEN1991-1-3">NA to BS EN 1991-1-3:2003+A1:2015, UK National Annex to Eurocode 1. Actions on structures. General actions. Snow loads, BSI</ref> <ref name="BSEN1991-1-4">BS EN 1991-1-4:2005+A1:2010 Eurocode 1. Actions on structures. General actions. Wind actions, BSI</ref> <ref name="NAtoBSEN1991-1-4">NA to BS EN 1991-1-4:2005+A1:2010, UK National Annex to Eurocode 1. Actions on structures. General actions. Wind actions, British BSI</ref> <ref name="BSEN1991-1-5">BS EN 1991-1-5:2003, Eurocode 1. Actions on structures. General actions. Thermal actions, BSI</ref> <ref name="BSEN1991-1-6">BS EN 1991-1-6: 2005, Eurocode 1. Actions on structures. General actions. Actions during execution, BSI</ref> <ref name="BSEN1991-1-7">BS EN 1991-1-7:2006+A1:2014. Eurocode 1: Actions on structures. General actions. Accidental actions. BSI</ref>
*EN&nbsp;1992 Eurocode&nbsp;2: Design of concrete structures <ref name="BSEN1992-1-1">BS EN 1992-1-1:2004+A1:2014. Eurocode 2: Design of concrete structures. General rules and rules for buildings. BSI</ref> <ref name="BSEN1992-1-2">BS EN 1992-1-2: 2004 Design of concrete structures. General rules. Structural fire design, BSI</ref>
*EN&nbsp;1993 Eurocode&nbsp;3: Design of steel structures<ref name="BSEN1993-1-1">BS EN 1993-1-1:2005+A1:2014, Eurocode 3: Design of steel structures. General rules and rules for buildings, BSI</ref> <ref name="NAtoBSEN1993-1-1">NA to BS EN 1993-1-1:2005+A1:2014, UK National Annex to Eurocode 3: Design of steel structures General rules and rules for buildings, BSI</ref> <ref name="BSEN1993-1-2">BS EN 1993-1-2: 2005 Eurocode 3. Design of steel structures. General rules. Structural fire design, BSI</ref> <ref name="BSEN1993-1-4">BS EN 1993-1-4:2006+A1:2015, Eurocode 3. Design of steel structures. General rules. Supplementary rules for stainless steels, BSI</ref> <ref name="BSEN1993-1-5">BS EN 1993-1-5:2006+A2:2019. Eurocode 3: Design of steel structures Plated structural elements. BSI</ref> <ref name="BSEN1993-1-8">BS EN 1993-1-8:2005. Eurocode 3:  Design of steel structures. Design of joints, BSI</ref> <ref name="BSEN1993-1-10">BS EN 1993-1-10:2005 Eurocode 3. Design of steel structures. Material toughness and through-thickness properties, BSI</ref> <ref name="BSEN1993-1-12">BS EN 1993-1-12: 2007, Eurocode 3. Design of steel structures. Additional rules for the extension of EN 1993 up to steel grades S 700, BSI</ref> <ref name="BSEN1993-2">BS EN 1993-2: 2006 Eurocode 3. Design of steel structures. Steel bridges, BSI</ref>
*EN&nbsp;1994 Eurocode&nbsp;4: Design of composite steel and concrete structures<ref name="BSEN1994-1-1">BS&nbsp;EN&nbsp;1994-1-1: 2004  Eurocode&nbsp;4. Design of composite steel and concrete structures. General rules and rules for buildings.  BSI</ref> <ref name="BSEN1994-1-2">BS EN 1994-1-2:2005+A1:2014, Eurocode 4. Design of composite steel and concrete structures. General rules. Structural fire design, BSI</ref>
*EN&nbsp;1995 Eurocode&nbsp;5: Design of timber structures
*EN&nbsp;1996 Eurocode&nbsp;6: Design of masonry structures
*EN&nbsp;1997 Eurocode&nbsp;7: Geotechnical design
*EN&nbsp;1998 Eurocode&nbsp;8: Design of structures for earthquake resistance
*EN&nbsp;1999 Eurocode&nbsp;9: Design of Aluminium Structures
<br>
Each Eurocode comprises a number of 'Parts', which are published as separate documents. Each Part consists of a main body of text, normative annexes, and informative annexes (the 'relevance' of which is decided on a national basis).

The full text of each Eurocode Part is issued initially by [[#External links|CEN]] (European Committee for Standardisation) in three languages with the above 'EN' designations; national standards bodies may translate the text into other languages but may not make any technical changes. The information given in this text is thus the same for each country in Europe.

The Eurocode text is then provided with a front cover and foreword by each national standards body and published within that country using a designation with the national prefix - for example EN&nbsp;1990 is published by BSI as BS&nbsp;EN&nbsp;1990<ref name="BSEN1990"></ref>. The text may be followed by a [[#National Annexes|National Annex]] or a National Annex may be published separately.

The Eurocode Parts contain two distinct types of statement - 'Principles' and 'Application Rules'. The former must be followed, to achieve compliance; the latter are rules that will achieve compliance with the Principles but it is permissible to use alternative design rules, provided that they accord with the Principles (see BS&nbsp;EN&nbsp;1990<ref name="BSEN1990"></ref> 1.4(5)).

The general principle that was adopted in drafting the Eurocodes was that there would be no duplication of Principles or Application Rules. Thus the design basis in BS&nbsp;EN&nbsp;1990<ref name="BSEN1990"></ref> applies irrespective of the construction material or the type of structure.

UK designers should be aware that the Eurocodes use terminology and notation that will be unfamiliar, resulting from the ambition to achieve consistency across Europe.

===National Annexes===
The National Annex (NA) is an essential document when using a [[#CEN documents|Eurocode Part]] . Where the opportunity is given in the text of the Eurocode, the National Annex will:
*Specify the value of a factor, to modify limiting values or a formula
*Specify which design method may be used
*State whether an informative annex may be used - such annexes are explicitly identified as being open to national acceptance (or otherwise), and may concern things such as test methods.
<br>
Although the NA may specify the value of partial factors to be applied to actions and resistances, in many cases it simply accepts the value recommended in the Eurocode text.

The guidance given in a National Annex applies to structures that are to be constructed within that country. National Annexes are likely to differ between countries within Europe. The National Annexes for the country where the structure is to be constructed should always be consulted in the design of a structure.<br clear=right>

<gallery widths=265px heights=370px>
Image:BS_EN_1991_Part_1.2.png|Typical cover page of a Eurocode part
Image:NAtoBSEN.PNG|Typical cover page of a National Annex <br>to a Eurocode part
</gallery>
<small>''Permission to reproduce extracts from British Standards is granted by the British Standards Institution (BSI). No other use of this material is permitted. British Standards can be obtained in PDF or hard copy formats from the BSI online shop: http://shop.bsigroup.com or by contacting BSI Customer Services for hard copies only: Tel: +44 (0)20 8996 9001, Email: cservices@bsigroup.com''</small>

===NCCI===
The National Annex may give references to publications that contain non-contradictory complementary information (NCCI) that will assist the designer when designing a structure to the Eurocodes. According to [[#External links|CEN]] rules, a [[#National Annexes|National Annex]] cannot contain NCCI, but references to NCCI may be given. As the name suggests, any guidance that is referenced in the National Annex must not contradict the principles of the Eurocode.

The Eurocodes omit some design guidance where it is considered to be readily available in text books or other established sources. Publications that contain such design guidance may be referenced in the National Annex as NCCI.

To assist designers, the steel construction sector collated a large amount of the NCCI required for steel design and made it available on a readily searchable website [http://www.steel-ncci.co.uk/ www.steel-ncci.co.uk]. Whilst this website is currently still live, and useful for identifying what NCCI is available, the documents themselves are now hosted on [https://portal.steel-sci.com/ SCI’s new ‘Portal’]. You do not need to be a member of SCI to access these NCCI documents, but non-members will need to register on that website, wait for a verification email, then login and click the 'STEELBIZ' tab before using the search box to locate the appropriate NCCI document and download it (by clicking the small green cloud alongside the description).

Additionally, BSI has published NCCI guidance in the form of several 'Published Documents' (PDs), e.g. PD 6695-1-10<ref name="PD6695-1-10">PD 6695-1-10:2009 Recommendations for the design of structures to BS EN 1993-1-10. BSI</ref>. These documents are only informative and do not have the status of a Standard.

==BS EN 1990 Basis of structural design==
BS&nbsp;EN&nbsp;1990<ref name="BSEN1990"></ref> can be considered as the 'core' document of the structural Eurocode system as it establishes the principles and requirements for the safety, serviceability and durability of structures. It also describes the basis for structural design and verification. The main sections of BS&nbsp;EN&nbsp;1990<ref name="BSEN1990"></ref> include:
*Requirements
*Principles of limit state design
*Basic variables
*Structural analysis and design assisted by testing
*Verification by the partial safety factor method.
<br>
===Limit state design===
The principles of limit state design (LSD) are set out briefly and the relevant design situations are classified as:
*Persistent - Conditions of normal use
*Transient - Temporary conditions, e.g. during repair
*Accidental - Exceptional conditions applicable to the structure or to its exposure, e.g. to fire, explosion or impact
*Seismic - Conditions applicable to the structure when subjected to seismic events.
<br>
Ultimate and serviceability limit states are defined and the requirement that verifications (checks) shall be carried out is stated.

====Ultimate limit state====
The following ultimate limit states (ULS) are required to be verified:

*EQU	- Loss of static equilibrium of the structure or a structural element
*STR	- Failure or excessive deformation of a structure or structural element
*GEO	- Failure or excessive deformation of the ground where the strengths of soil or rock are significant in providing resistance
*FAT	- Fatigue failure of the structure or structural elements.
<br>
BS&nbsp;EN&nbsp;1990<ref name="BSEN1990"></ref> gives expressions for the effects for three classes of combination of actions at the ultimate limit state:
*Fundamental combinations (for persistent and transient situations)
*Combinations for accidental situations
*Combinations for seismic situations.
<br>
For fundamental combinations, BS&nbsp;EN&nbsp;1990<ref name="BSEN1990"></ref> gives two alternative methods to determine the design value of the effects of combined actions.

The first method is to express the combination of actions as:
<br>
<br>
[[File:Eq_6.10.png|600px]]

The second method is to give two expressions for the combination of actions; the combination that gives the most onerous value should be used for the design verifications:
<br>
<br>
[[File:Eq_6.10a.png|600px]]

[[File:Eq_6.10b.png|600px]]

where:

"+"&nbsp;&nbsp;&nbsp;means "to be combined with"

''&Sigma;''&nbsp;&nbsp;&nbsp;implies "the combined effect of"

''G''<sub>k,j</sub>	represents the characteristic value of the j-th unfavourable permanent action

''P''&nbsp;&nbsp;&nbsp;is a prestressing action

Q<sub>k,1</sub>&nbsp;&nbsp;&nbsp;is the characteristic value of leading variable action ('main accompanying action' in 6.10a)

Q<sub>k,i</sub>&nbsp;&nbsp;&nbsp;represents the characteristic value of the i-th accompanying variable action (i >&nbsp;1)

''&gamma;''<sub>G</sub>,&nbsp;''&gamma;''<sub>P</sub>,&nbsp;''&gamma;''<sub>Q</sub>&nbsp;&nbsp;&nbsp;are representations of the factor ''&gamma;''<sub>F</sub> according to the type of action to which they relate

''&psi;''&nbsp;&nbsp;&nbsp;is a factor applied to an accompanying action

''&xi;''&nbsp;&nbsp;&nbsp;is a reduction factor applied to unfavourable permanent actions (in 6.10b)

For the majority of steel elements, the above expressions will simplify, as prestressing actions (''P'') will not be present. Typical values, from the UK National Annex, are given in the tables below.
{|class="wikitable" width=630px
|+'''Design values of actions (STR) taken from Table NA.A1.2(B) of the UK National Annex to BS EN 1990'''
|-
!rowspan=2|'''Combination'''
!colspan=2|'''Permanent actions'''
!rowspan=2|'''Leading variable action'''
!colspan=2|'''Accompanying variable actions'''
|-
!'''Unfavourable'''
!'''Favourable'''
!'''Main'''
!'''Others'''
|-
|align="center"|6.10||align="center"|1.35 ''G''<sub>kj</sub>||align="center"|1.00 ''G''<sub>kj</sub>||align="center"|1.5 ''Q''<sub>k,1</sub>|| ||align="center"|1.5''&psi;''<sub>0,1</sub>''Q''<sub>k,i</sub>
|-
|align="center"|6.10a||align="center"|1.35 ''G''<sub>kj</sub>||align="center"|1.00 ''G''<sub>kj</sub>|| ||align="center"|1.5''&psi;''<sub>0,1</sub>''Q''<sub>k,1</sub>||align="center"|1.5''&psi;''<sub>0,1</sub>''Q''<sub>k,i</sub>
|-
|align="center"|6.10b||align="center"|0.925''&times;''1.35 ''G''<sub>kj</sub>||align="center"|1.00 ''G''<sub>kj</sub>||align="center"|1.5 ''Q''<sub>k,1</sub>|| ||align="center"|1.5''&psi;''<sub>0,1</sub>''Q''<sub>k,i</sub>
|}

{|class="wikitable" width=630px
|+'''Values of ''&psi;'' factors for buildings, extracted from Table NA.A1.1 of the UK National Annex to BS EN 1990'''
|-
!'''Action'''!!'''''&psi;''<sub>0</sub>'''
|-
|Imposed loads in buildings, category (see BS EN 1991-1-1)	|| 
|-
|Category A: domestic, residential areas||align="center"|0.7
|-
|Category B: office areas||align="center"|0.7
|-
|Category E: storage areas||align="center"|1.0
|-
|Category H: Roofs||align="center"|0.7
|-
|Snow loads on buildings (see BS EN 1991-1-3)|| 	
|-
|For sites located at altitude H &le; 1000 m (above sea level)||align="center"|0.5
|-
|Wind loads on buildings (see BS EN 1991-1-4)||align="center"|0.5
|}

The National Annex<ref name="NAtoBSEN1990">NA to BS EN 1990:2002+A1:2005 UK National Annex for Eurocode. Basis of structural design. BSI</ref> must be consulted for guidance on which method to use. In the UK, the National Annex<ref name="NAtoBSEN1990"></ref> allows either approach to be used. However, in almost all persistent design situations the use of the second method (the use of expressions 6.10a and 6.10b) will produce lower design values of the effects of actions (and for buildings, 6.10b usually gives the governing value). For the transient design situation during execution, 6.10a is effectively the same as 6.10 (since ''&psi;''&nbsp;=&nbsp;1.0 - see BS EN 1991-1-6<ref name="BSEN1991-1-6"></ref> clauses A.1.1 and NA&nbsp;2.18) and thus governs rather than 6.10b.

For building design, Annex A of BS&nbsp;EN&nbsp;1990<ref name="BSEN1990"></ref> gives recommended values of the factors ''&gamma;'', ''&psi;'' and ''&xi;''; for buildings in the UK, the values are given in the National Annex to&nbsp;BS&nbsp;EN&nbsp;1990<ref name="NAtoBSEN1990"></ref> , clause NA.2.2.

====Serviceability limit state====
The serviceability limit state combinations of actions used are:

{|class="wikitable" width=600px
|'''Characteristic combination'''||Irreversible limit state which includes the functioning of the structure, damage to finishes or non structural elements
|-
|'''Frequent combination'''||Reversible limit state
|-
|'''Quasi permanent combination'''||Reversible limit states and long term effects
|}
The expression for the Characteristic combination of actions given in BS&nbsp;EN&nbsp;1990<ref name="BSEN1990"></ref> for serviceability limit state design is shown below.
<br>
<br>
[[File:Eq_6.14b.png|550px]]

The Frequent and Quasi-permanent combinations are not relevant to steel design in the UK.

The serviceability limits for vertical and horizontal deflections and dynamic effects may be given in the relevant material Eurocode. The UK National Annex to BS EN 1993-1-1<ref  name="NAtoBSEN1993-1-1"></ref> gives suggested limits for vertical (see table below) and horizontal deflections due to variable actions only, stating that deflections due to permanent actions need not be verified. With agreement from the Client, different limits may be used for a specific project.

{|class="wikitable" width=600px
|+'''Limiting vertical deflections'''
|-
|Cantilevers||Length/180
|-
|Beams carrying plaster of brittle finish||Span/360
|-
|Other beams (except purlins and sheeting rails)||Span/200
|-
|[[Building envelopes#Purlin and side rail options|Purlins and sheeting rails]]||To suit the characteristics of particular cladding
|}

==Eurocode 1 - Actions==
This section relates to BS&nbsp;EN&nbsp;1991 Part&nbsp;1 for buildings only. Alternative actions should be considered for the design of [[Bridges|bridges]] .

===Densities, self-weights and imposed loads for buildings===
BS EN 1991-1-1<ref name="BSEN1991-1-1">BS EN 1991-1-1: 2002 Eurocode 1. Actions on structures. General actions. Densities, self-weight, imposed loads for buildings, BSI</ref> gives design guidance and values of actions to be used when designing buildings and civil engineering works. It contains guidance on:

*Densities of construction and stored materials
*Self-weight of construction works
*Imposed loads for buildings.
<br>
The accompanying UK National Annex<ref name="NAtoBSEN1991-1-1">NA to BS EN 1991-1-1: 2002 UK National Annex to Eurocode 1. Actions on structures. General actions. Densities, self-weight, imposed loads for buildings, BSI</ref> presents tables containing significantly more occupancy sub-groups than given in the main text of the Eurocode. Some typical values are given in the tables below. The UK National Annex<ref name="NAtoBSEN1991-1-1">NA to BS EN 1991-1-1: 2002 UK National Annex to Eurocode 1. Actions on structures. General actions. Densities, self-weight, imposed loads for buildings, BSI</ref> also replaces the expression given for the reduction factor for imposed floor loads and accessible roofs (&alpha;<sub>A</sub>) and the reduction factor for imposed loads from several storeys (&alpha;<sub>n</sub>).

{|class="wikitable" width=600px
|+'''Typical self-weights for building elements'''
|-
!'''Element'''!!'''Typical weight'''
|-
|Precast units<br>(spanning 6 m, designed for a 5 kN/m&sup2; imposed load)||align="center"|3 to 4.5 kN/m&sup2;
|-
|Composite slab, normal concrete<br>(130 mm thick, 2400 kg/m&sup3;)||align="center"|2.4 to 3.0 kN/m&sup2;
|-
|Composite slab, lightweight concrete<br>(130 mm thick 1400 - 1800 kg/m&sup3;)||align="center"|1.9 to 2.3 kN/m&sup2;
|-
|Services||align="center"|0.25 kN/m&sup2;
|-
|Ceilings||align="center"|0.1 kN/m&sup2;
|-
|Steelwork (low rise 2 to 6 storeys)||align="center"|35 to 50 kg/m&sup2;
|-
|Steelwork (medium rise 7 to 12 storeys)||align="center"|40 to 70 kg/m&sup2;
|}

{|class="wikitable" width=600px
|+'''Minimum imposed load for office areas, from Table NA.2 and NA.3 of the National Annex to BS EN 1991-1-1'''
|-
!width=15%|'''Category of loaded area'''!!'''Specific use'''!!'''Sub-category'''!!'''Example'''!!width=10%|'''q<sub>k</sub><br>kN/m&sup2;'''!!width=10%|'''Q<sub>k</sub><br>kN'''
|-
|rowspan=2 align="center"|B||align="center" rowspan=2|Office areas||align="center"|B1||General use other than in B2	||align="center"|2.5||align="center"|2.7
|-
|align="center"|B2||At or below ground level||align="center"|3.0||align="center"|2.7
|}

===Actions on structures exposed to fire===
The methods given in BS EN 1991-1-2<ref name="BSEN1991-1-2">BS EN 1991-1-2: 2002 Eurocode 1. Actions on structures. Actions on structures exposed to fire, BSI</ref> should be used to determine the thermal and mechanical actions that act on structures exposed to fire. The values of actions determined should be used when carrying out [[Structural fire engineering|fire engineering design]] to Part&nbsp;1-2 of the relevant material Eurocode. The values of actions determined are considered to be accidental actions.

The UK NA<ref name="NAtoBSEN1991-1-2">NA to BS EN 1991-1-2: 2002 UK National Annex to Eurocode 1. Actions on structures. General actions. Actions on structures exposed to fire, BSI</ref> gives guidance for temperature analysis and fire models.

For the period of time within which to make the temperature analysis the UK NA<ref name="NAtoBSEN1991-1-2">NA to BS EN 1991-1-2: 2002 UK National Annex to Eurocode 1. Actions on structures. General actions. Actions on structures exposed to fire, BSI</ref> refers the designer to the:

*[[Structural fire resistance requirements#Approved Document B|Approved Documents]] for England and Wales
*[[Structural fire resistance requirements#Technical Handbook 2|Scottish Building Standards]] Technical Handbooks for Scotland
*[[Structural fire resistance requirements#Technical Booklet E|Technical Booklet E]] to the Building Regulations (Northern Ireland) for Northern Ireland.
<br>
The UK National Annex<ref name="NAtoBSEN1991-1-2">NA to BS EN 1991-1-2: 2002 UK National Annex to Eurocode 1. Actions on structures. General actions. Actions on structures exposed to fire, BSI</ref> specifies that no additional actions need be considered as acting simultaneously with the fire load and that the representative value of the variable action Q<sub>1</sub> should be taken as the frequent value (''&psi;''<sub>1,1</sub>, Q<sub>1</sub>).

===Snow loads===

BS&nbsp;EN 1991-1-3<ref name="BSEN1991-1-3"></ref> gives roof snow load coefficients that are to be used with the characteristic ground snow load maps given in Annex&nbsp;C of that Part of BS&nbsp;EN&nbsp;1991 to determine design roof snow loads for different roof shapes. The UK National Annex<ref name="NAtoBSEN1991-1-3"></ref> replaces the ground snow load map and some of the roof coefficients for buildings to be constructed in the UK.

===Wind actions===
The guidance given in BS&nbsp;EN 1991-1-4<ref name="BSEN1991-1-4"></ref> should be used to determine the wind actions to be considered during the structural design of buildings and civil engineering works. The information given is applicable to the whole or part of a structure, including elements attached to it such as [[Building envelopes|cladding]]. The values of wind actions are derived from a fundamental value of the basic wind velocity (which is given in the appropriate National Annex), from which a mean wind speed and peak velocity pressure are determined for the particular building; wind pressures and forces are determined using coefficients given in BS&nbsp;EN 1991-1-4<ref name="BSEN1991-1-4"></ref>. The UK National Annex<ref name="NAtoBSEN1991-1-4"></ref> provides numerous tables and figures for determining values for buildings in the UK.<br clear=right>

Guidance to assist structural engineers with the evaluation of wind actions for buildings in the UK is available in [[#Resources|SCI-P394]], and a [[Design software and tools#Wind loading calculator|Wind loading calculator]] is also available.

===Thermal actions===
Where structures are exposed to daily and seasonal climatic changes in temperature, the effects of thermal actions should be accounted for in the design. BS&nbsp;EN 1991-1-5<ref name="BSEN1991-1-5"></ref> gives principles and general rules that should be used to determine the characteristic values of thermal actions.

===Actions during execution of buildings===
The values of actions which should be taken into account during the [[Construction|construction]] of a building or civil engineering works should be obtained from the principles and general rules given in BS&nbsp;EN 1991-1-6<ref name="BSEN1991-1-6"></ref>.

The SCI advisory desk note [[#Resources|AD346]] gives guidance for determining the value of the actions present during the execution of a steel and concrete [[Composite construction#Composite slabs|composite floor]].

===Accidental actions===
{{#image_template:image=File:Accidental-action.PNG|wrap=true|align=right|caption=Accidental action on a structure|width=400}}
Strategies and rules for safeguarding buildings and other civil engineering works against accidental actions are given in BS&nbsp;EN&nbsp;1991-1-7<ref name="BSEN1991-1-7"></ref>. There are no rules for determining specific values of accidental actions caused by external explosions, warfare or terrorist activities, or for verifying the residual stability of structures damaged by seismic action or fire, etc.

Information regarding limiting the effects of a localised failure in buildings from an unspecified cause is given in Annex&nbsp;A of BS&nbsp;EN&nbsp;1991-1-7<ref name="BSEN1991-1-7"></ref>. The effects are limited in order to avoid [[Structural_robustness|disproportionate collapse]] of the structure. Annex&nbsp;A includes information relating to:
*Categorisation of [[Structural_robustness#Consequences_classes|consequence classes]] for buildings
*Provision of [[Structural_robustness#Horizontal tying|horizontal tying]] and [[Structural_robustness#Vertical ties|vertical ties]]
*Design of '[[Structural_robustness#Key elements|key elements]]'.<br clear=right>
<br>

==Eurocode 3 - Steel structures==
BS&nbsp;EN&nbsp;1993-1<ref name="BSEN1993">BS&nbsp;EN&nbsp;1993  Eurocode&nbsp;3: Design of steel structures. Various parts, BSI</ref> Eurocode&nbsp;3: Design of steel structures comprises a set of general rules in twelve parts (BS&nbsp;EN&nbsp;1993-1-1<ref name="BSEN1993-1-1"></ref> to BS&nbsp;EN&nbsp;1993-1-12<ref name="BSEN1993-1-12"></ref>) for all types of steel structure and additional rules in separate Parts for structures other than buildings, e.g. BS&nbsp;EN 1993-2<ref name="BSEN1993-2"></ref> for bridges. When designing a building structure of [[Steel construction products#Standard open sections|rolled sections]] and [[Steel construction products#Plate girders|plate girders]], the following parts of BS&nbsp;EN&nbsp;1993-1<ref name="BSEN1993">BS&nbsp;EN&nbsp;1993  Eurocode&nbsp;3: Design of steel structures. Various parts, BSI</ref> will be required.

*BS&nbsp;EN&nbsp;1993-1-1 General rules and rules for buildings<ref name="BSEN1993-1-1"></ref>
*BS&nbsp;EN&nbsp;1993-1-2 Structural fire design<ref name="BSEN1993-1-2"></ref>
*BS&nbsp;EN&nbsp;1993-1-5 Plated structural elements<ref name="BSEN1993-1-5"></ref>
*BS&nbsp;EN&nbsp;1993-1-8 Design of joints<ref name="BSEN1993-1-8">BS EN 1993-1-8:2005. Eurocode 3:  Design of steel structures. Design of joints, BSI</ref>
*BS&nbsp;EN&nbsp;1993-1-10 Material toughness and through-thickness properties.<ref name="BSEN1993-1-10"></ref>
<br>
For steel and concrete composite structures, Eurocode&nbsp;3 is referred to by Eurocode&nbsp;4<ref name="BSEN1994">BS&nbsp;EN&nbsp;1994 Eurocode&nbsp;4:  Design of composite steel and concrete structures. Various parts, BSI</ref> for the design of the steel elements.

SCI has produced a series of guides covering the application of Eurocode&nbsp;3, as well as an Introduction ([[#Resources|SCI P361]]) and a Concise Guide ([[#Resources|SCI P362]]). These cover all the essential rules for steel building design in accordance with the UK National Annexes.

===General rules and rules for buildings===
BS&nbsp;EN&nbsp;1993-1-1<ref name="BSEN1993-1-1"></ref> gives generic design rules for steel structures and specific guidance for structural steelwork used in buildings. The main aspects in BS&nbsp;EN&nbsp;1993-1-1<ref name="BSEN1993-1-1"></ref> are:

*[[#Material properties|Material properties]]
*[[#Structural analysis|Structural analysis]]
*[[#Section classification|Section classification]]
*[[#Cross section resistance|Section and member resistances]].
<br>
====Material properties====
The rules in BS&nbsp;EN&nbsp;1993-1-1<ref name="BSEN1993-1-1"></ref> relate to structural [[Steel_material_properties#Hot_rolled_steels|steel grades]] S235 to S460 in accordance with BS&nbsp;EN&nbsp;10025<ref name="BSEN10025>BS EN 10025-2: 2019, Hot rolled products of structural steels. Technical delivery conditions for non-alloy structural steels, BSI</ref>, BS&nbsp;EN&nbsp;10210<ref name="BSEN10210>BS EN 10210-1: 2006, Hot finished structural hollow sections of non-alloy and fine grain steels.  Technical delivery requirements, BSI</ref> or BS&nbsp;EN&nbsp;10219<ref name="BSEN10219>BS EN 10219-1: 2006, Cold formed welded structural hollow sections of non-alloy and fine grain steels.  Technical delivery requirements, BSI</ref> and thus cover all the structural steels likely to be used in buildings. In exceptional circumstances, components might use higher strength grades; BS&nbsp;EN&nbsp;1993-1-12<ref name="BSEN1993-1-12"></ref> gives guidance on the use of higher strength steels. For the design of stainless steel components and structures, reference should be made to BS&nbsp;EN&nbsp;1993-1-4<ref name="BSEN1993-1-4"></ref>. 

The UK National Annex<ref  name="NAtoBSEN1993-1-1"></ref> states that the nominal yield strength (<I>f</I><sub>y</sub>) and ultimate strength (<I>f</I><sub>u</sub>) of steel should be obtained from the minimum specified values according to the product standards.

Material requirements for fasteners (bolts) are given in BS&nbsp;EN&nbsp;1993-1-8<ref name="BSEN1993-1-8">BS EN 1993-1-8:2005. Eurocode 3:  Design of steel structures. Design of joints, BSI</ref>.<br clear=left>

====Structural analysis====
Section&nbsp;5.2 of BS&nbsp;EN&nbsp;1993-1-1<ref name="BSEN1993-1-1"></ref> gives guidance on [[Modelling and analysis|global analysis of structures]] and the structural stability of frames.

Generally, [[Modelling and analysis#First-order analysis|first order]] elastic global analysis may be used. In some circumstances (depending on member classification) [[Modelling and analysis#Plastic analysis|plastic global analysis]] may be used. Where the internal moments and forces are significantly increased due to deflections, [[Modelling and analysis#Second-order effects|second order effects]] need to be taken into account, either through magnification of first order effects or by a [[Modelling and analysis#Second-order analysis|second order analysis]].

====[[Member design#Classification of cross sections|Section classification]]====
{{#image_template:image=File:Tab5-2.PNG|wrap=true|align=right|caption=Extract from Table 5.2 concerning classification of outstanding flanges<br><small>''Permission to reproduce extracts from British Standards is granted by the British Standards Institution (BSI). No other use of this material is permitted. British Standards can be obtained in PDF or hard copy formats from the BSI online shop: http://shop.bsigroup.com or by contacting BSI Customer Services for hard copies only: Tel: +44 (0)20 8996 9001, Email: cservices@bsigroup.com''</small>|width=450}}
Four classes of cross section are defined in BS&nbsp;EN&nbsp;1993-1-1<ref name="BSEN1993-1-1"></ref> . Each part of a section that is in compression is classified and the class of the whole cross section is deemed to be the highest (least favourable) class of its compression parts. 

*Class 1 cross-sections are those which can form a plastic hinge with the rotation capacity required from plastic analysis without reduction of the resistance
*Class 2 cross-sections are those which can develop their plastic moment resistance, but have limited rotation capacity because of local buckling
*Class 3 cross-sections are those in which the stress in the extreme compression fibre of the steel member assuming an elastic distribution of stresses can reach the yield strength, but local buckling is liable to prevent development of the plastic moment resistance
*Class 4 cross-sections are those in which local buckling will occur before the attainment of yield stress in one or more parts of the cross-section.
<br>
Table&nbsp;5.2 of BS&nbsp;EN&nbsp;1993-1-1<ref name="BSEN1993-1-1"></ref> gives limits for the width to thickness ratios for the compression parts of a section for each classification.

====Cross section resistance====
Expressions for determining the [[Member_design#Resistance_of_cross_sections|cross section resistance]] in tension, compression, bending and shear for the four classes of sections are given in Section&nbsp;6.2 of BS&nbsp;EN&nbsp;1993-1-1<ref name="BSEN1993-1-1"></ref> . The design values of resistance are expressed as ''N''<sub>t,Rd</sub>, ''N''<sub>c,Rd</sub>, ''V''<sub>c,Rd</sub> and ''M''<sub>c,Rd</sub> respectively.

For slender webs, the shear resistance may be limited by shear buckling; for such situations, reference is made to BS&nbsp;EN&nbsp;1993-1-5<ref name="BSEN1993-1-5"></ref> Shear buckling is rarely a consideration with [[Steel construction products#Standard open sections|hot rolled sections]].

====Buckling resistance of members====
{{#image_template:image=File:Buckling curves Fig.6.1 from P362.png|width=360|wrap=true|caption=Buckling curves for members in compression (from SCI [[#References|P362]])}}The [[Member_design#Buckling_resistance_of_members|buckling  resistance]] of a member is determined by applying a reduction factor ''&chi;'' to the [[Steel material properties#Yield strength|yield strength]]. The value of ''&chi;'' varies depending on the buckling mode, with an appropriate subscript identifying which mode is being considered - for example ''&chi;''<sub>LT</sub> is the reduction factor for [[Member_design#Uniform_members_in_bending|lateral torsional buckling]].

The reduction factor ''&chi;'' is a function of the non-dimensional slenderness [[File:C13fig6.png|12px]], as shown in the figure left. The choice of curve depends on the type of cross-section, and the axis about which buckling will take place. Different curves are used for different buckling modes as explained in SCI&nbsp;[[#Resources|P362]].

Member resistances may be readily identified using SCI&nbsp;[[#Resources|P363]] .

=====Members in compression=====
BS&nbsp;EN&nbsp;1993-1-1<ref name="BSEN1993-1-1"></ref>  presents guidance for checking flexural, torsional and torsional-flexural buckling for [[Member_design#Uniform_members_in_compression|members in compression]]. The latter two modes will not be critical for doubly symmetric I or H&nbsp;sections, or [[Steel construction products#Structural hollow sections|hollow sections]]. <br clear=left>

=====Members in bending=====
Laterally unrestrained members in bending about their major axes need to be verified against [[Member_design#Uniform_members_in_bending|lateral torsional buckling]]. Rules are given in Clause&nbsp;6.3.2 of BS&nbsp;EN&nbsp;1993-1-1<ref name="BSEN1993-1-1"></ref>. 

For [[Member_design#Uniform_members_in_bending|uniform members in bending]], three approaches may be used:

*Lateral torsional buckling curves - general case 
*[[Member_design#Lateral_torsional_buckling_curves_for_rolled_sections|Lateral torsional buckling curves for rolled sections]] and equivalent welded sections - this is the recommended approach ([[#Resources|SCI P362]])
*A simplified assessment method for beams in buildings with discrete lateral restraints to the compression flange.
<br>
The guidance given for calculating the beam slenderness for the first two approaches requires the value of the elastic critical moment for lateral torsional buckling (''M''<sub>cr</sub>), but no expressions are given for determining this value. An NCCI method for calculating beam slenderness for rolled I, H and channel sections is given in [[#Resources|SCI P362]]. NCCI ([[#Resources|SN003b EN EU]]) for calculating ''M''<sub>cr</sub> is also available.

The third method treats the compression flange and part of the web as a simple compression member.

=====[[Member design#Uniform members in bending and axial compression|Members in bending and axial compression]]=====
For members subject to bending and axial compression, the criteria given in 6.3.3 of BS&nbsp;EN&nbsp;1993-1-1<ref name="BSEN1993-1-1"></ref> must be satisfied.

Interaction factors (k<sub>ij</sub>) used in the verifications may be calculated using either method&nbsp;1 or 2 given respectively in Annexes A or B of BS&nbsp;EN&nbsp;1993-1-1<ref name="BSEN1993-1-1"></ref>. Method&nbsp;2 is considered to be the simpler of the two methods.

=====General method for lateral and lateral torsional buckling=====
The general method given in 6.3.4 of BS&nbsp;EN&nbsp;1993-1-1<ref name="BSEN1993-1-1"></ref> should not be confused with the general case for lateral torsional buckling given in 6.3.2.2 of EN&nbsp;1993-1-1<ref name="BSEN1993-1-1"></ref>. The general method gives guidance for structural components that are not covered by the guidance given for compression, bending or bending and axial compression members, and is not likely to be used by most building designers.

====Serviceability limit states====
BS&nbsp;EN&nbsp;1993-1-1<ref name="BSEN1993-1-1"></ref>  does not give any serviceability limit state limits for dynamic effects, vertical deflections and horizontal deflections. The National Annex for the country where the building is to be constructed should be consulted for guidance. The UK National Annex<ref  name="NAtoBSEN1993-1-1"></ref> gives limits for deflections; limits for specific projects should be agreed with the client if they differ from the proposed limits.

====Additional guidance for buildings====
Informative Annex BB of EN&nbsp;1993-1-1<ref name="BSEN1993-1-1"></ref>  gives guidance for buckling of structural components in buildings. Guidance is given for:

*Flexural buckling of members in triangulated and lattice structures 
*Continuous restraints 
*Stable lengths of segments containing plastic hinges for out-of-plane buckling.
<br>

===Plated structures===
The provisions of BS&nbsp;EN&nbsp;1993-1-5<ref name="BSEN1993-1-5"></ref> are mainly appropriate to the design of [[Steel construction products#Plate girders|plate girders]], where the elements of the cross section are typically more slender. For building frames using [[Steel construction products#Standard open sections|hot rolled sections]], there is little need to refer to this Part, except for the design of webs subject to transverse forces due to concentrated local forces (commonly referred to as the determination of web bearing and buckling resistances).

Section&nbsp;6 of BS&nbsp;EN&nbsp;1993-1-5<ref name="BSEN1993-1-5"></ref> gives a method for determining the resistance of webs to transverse forces. This method should only be used for [[Steel construction products#Standard open sections|rolled I and H&nbsp;sections]] and [[Steel construction products#Plate girders|welded girders]]. Although not stated, the method should not be used for [[Steel construction products#Structural hollow sections|structural hollow sections]] as it gives a single check that combines the web bearing and buckling effects. For [[Steel construction products#Structural hollow sections|structural hollow sections]], the NCCI method given in [[#Resources|SCI P363]] and [[#Resources|SCI P374]] should be used.

BS&nbsp;EN&nbsp;1993-1-5<ref name="BSEN1993-1-5"></ref> also provides guidance on calculating the effective section properties of slender cross sections.

===Design of joints===
{{#image_template:image=File:SCI_P358.png|wrap=true|caption=Simple connections design guide ([[#Resources|SCI P358]])|width=250}}
BS&nbsp;EN&nbsp;1993-1-8<ref name="BSEN1993-1-8">BS EN 1993-1-8:2005. Eurocode 3:  Design of steel structures. Design of joints, BSI</ref> gives rules for the design of joints between structural members. Both bolted and welded connections are covered. 

Note that a joint is defined as a zone where two or more members are interconnected and a connection is the location where elements meet and is thus the means to transfer forces and moments. 

BS&nbsp;EN&nbsp;1993-1-8<ref name="BSEN1993-1-8">BS EN 1993-1-8:2005. Eurocode 3:  Design of steel structures. Design of joints, BSI</ref> gives guidance for the design of joints subject to predominantly static loading. The steel grades covered are S235, S275, S355 and S460. BS&nbsp;EN&nbsp;1993-1-8<ref name="BSEN1993-1-8">BS EN 1993-1-8:2005. Eurocode 3:  Design of steel structures. Design of joints, BSI</ref> uses the so-called component model to identify the resistance of each component making up a joint. Consideration of each of these resistances allows the joint resistance to be identified.

BS&nbsp;EN&nbsp;1993-1-8<ref name="BSEN1993-1-8">BS EN 1993-1-8:2005. Eurocode 3:  Design of steel structures. Design of joints, BSI</ref>  classifies joints according to their rotational stiffness as nominally pinned, rigid or semi-rigid and according to their strength as nominally pinned, full-strength or partial-strength. The appropriate type of joint model to be used in global analysis depends on this classification and the method of global analysis.

Although BS&nbsp;EN&nbsp;1993-1-8<ref name="BSEN1993-1-8">BS EN 1993-1-8:2005. Eurocode 3:  Design of steel structures. Design of joints, BSI</ref> provides a method of calculating connection stiffness, a connection may be classified on the basis of previous satisfactory experience. The UK National Annex states that connections designed in accordance with the principles of [[#Resources|SCI P358]] are nominally pinned; those in accordance with the principles of [[#Resources|SCI P398]] are rigid.

Detailed design guidance is provided for [[Simple_connections|simple connections]] in [[#Resources|SCI P358]] and for [[Moment_resisting_connections|moment resisting connections]], in [[#Resources|SCI P398]].<br clear=left>

===Material [[Steel material properties#Toughness|toughness]] and through-thickness properties===
{{#image_template:image=File:SCI-P419.jpg|caption=[[#Resources|SCI-P419]]|align=right|wrap=true|width=150}}
Maximum permissible element thicknesses, reference stresses and toughness qualities for different reference temperatures and [[Steel material properties#Yield strength|steel grades]] are given in Table&nbsp;2.1 of BS&nbsp;EN&nbsp;1993-1-10<ref name="BSEN1993-1-10"></ref>. These should all be considered as part of the [[Steelwork_specification|material specification]].

PD 6695-1-10<ref name="PD6695-1-10"></ref> gives NCCI tables that will enable the determination of maximum permissible thicknesses without considering the individual adjustments and without reference to Table&nbsp;2.1 in BS&nbsp;EN&nbsp;1993-1-10<ref name="BSEN1993-1-10"></ref>. It simplifies the use of BS&nbsp;EN&nbsp;1993-1-10<ref name="BSEN1993-1-10"></ref> and is recommended for buildings in the UK. Guidance on selection of an appropriate sub-grade is given in [[#Resources|ED007]].

However, it should be noted that these design rules were developed for structures subject to fatigue such as [[Bridges|bridges]] and crane supporting structures, and it is acknowledged that their use for buildings where [[Fatigue_design_of_bridges#The mechanism of fatigue|fatigue]] plays a minor role is extremely safe-sided. [[#Resources|SCI publication P419]] presents modified steel thickness limits which may be used in buildings where [[Fatigue_design_of_bridges#The mechanism of fatigue|fatigue]] is not a design consideration. These new limits have been derived using exactly the same approach behind the Eurocode design rules, but crucially reduce the crack growth due to [[Fatigue_design_of_bridges#The mechanism of fatigue|fatigue]]. Further background is available in a [http://www.newsteelconstruction.com/wp/wp-content/uploads/TechPaper/NSCTechSep17.pdf technical article in the September 2017 issue of NSC magazine].

Fracture toughness guidance given in BS&nbsp;EN&nbsp;ISO&nbsp;1461<ref name="BSEN1461">BS EN ISO 1461: 2009 Hot dip galvanized coatings on fabricated iron and steel articles. Specifications and  test methods, BSI</ref> should be used for [[Metallic coatings#Hot-dip galvanizing|hot dip galvanized]] elements.

==Composite structures==
{{#image_template:image=File:Comp-bm.PNG|wrap=true|align=right|caption=Composite beam|width=250}}
When designing a steel and concrete [[Composite_construction|composite]] building, the following parts of BS&nbsp;EN&nbsp;1994 Eurocode&nbsp;4: Design of composite steel and concrete structures will be required:

*BS&nbsp;EN&nbsp;1994-1-1<ref name="BSEN1994-1-1"></ref> General rules and rules for buildings
*BS&nbsp;EN&nbsp;1994-1-2<ref name="BSEN1994-1-2"></ref>  Structural fire design
<br>
Within these Parts, reference is made to BS&nbsp;EN&nbsp;1993 (Eurocode&nbsp;3) and to BS&nbsp;EN&nbsp;1992 Eurocode&nbsp;2: Design of concrete structures, notably to:

*BS&nbsp;EN&nbsp;1992-1-1<ref name="BSEN1992-1-1"></ref>  General rules and rules for buildings
*BS&nbsp;EN&nbsp;1992-1-2<ref name="BSEN1992-1-2"></ref>  Structural fire design
<br>
SCI has produced guidance on the design of composite floors in accordance with Eurocode&nbsp;4 ([[#Resources|SCI P359]]).

===Eurocode 4 - Composite steel and concrete structures===

====Material properties====
<u>Structural steel</u>

The guidance given in BS&nbsp;EN&nbsp;1994-1-1<ref name="BSEN1994-1-1"></ref>  relates to structural [[Steel material properties#Yield strength|steel grades]] up to S460. For [[Steel material properties|steel properties]] reference is made to BS&nbsp;EN&nbsp;1993-1-1<ref name="BSEN1993-1-1"></ref>.

<u>Concrete and reinforcement</u>

For structural concrete BS&nbsp;EN&nbsp;1994-1-1<ref name="BSEN1994-1-1"></ref>  refers to BS&nbsp;EN&nbsp;1992-1-1<ref name="BSEN1992-1-1"></ref>, although it omits the lowest and highest grades given in that code by only covering:

*Normal weight concrete between C20/25 and C60/75
*Lightweight concrete between LC20/22 and LC60/66.
<br>
It also refers to BS&nbsp;EN&nbsp;1992-1-1<ref name="BSEN1992-1-1"></ref> for the properties of reinforcing steel. However, it should be noted that BS&nbsp;EN&nbsp;1994-1-1<ref name="BSEN1994-1-1"></ref>  permits the design value of the modulus of elasticity for reinforcing steel to be taken as equal to that for structural steel given in BS&nbsp;EN&nbsp;1993-1-1<ref name="BSEN1993-1-1"></ref>, i.e.&nbsp;210&nbsp;kN/mm&sup2; rather than 200&nbsp;kN/mm&sup2;.
{{#image_template:image=File:Re-entrant-sheeting.PNG|wrap=true|align=right|caption=Example of re-entrant sheeting|width=250}}
The reinforcement industry in the UK has decided to standardise on grade 500C steel.

<u>Shear connectors</u>

BS&nbsp;EN&nbsp;1994-1-1<ref name="BSEN1994-1-1"></ref>  refers to BS&nbsp;EN&nbsp;ISO&nbsp;13918<ref name="BSENISO13918">BS EN ISO 13918: 2018, Welding. Studs and ceramic ferrules for arc stud welding, BSI</ref> , which covers a range of stud diameters from 10&nbsp;mm to 25&nbsp;mm and two materials - structural steel and stainless steel.

<u>[[Steel construction products#Decking for floors|Profiled steel sheeting (decking)]]</u>

BS&nbsp;EN&nbsp;1994-1-1<ref name="BSEN1994-1-1"></ref>  refers to Sections&nbsp;3.1 and 3.2 of BS EN&nbsp;1993-1-3<ref name="BSEN1993-1-3">BS&nbsp;EN&nbsp;1993-1-3:2006 Eurocode 3. Design of steel structures. General rules. Supplementary rules for cold-formed  members and sheeting, BSI</ref> for the material properties of [[Steel construction products#Decking for floors|profiled steel sheeting]].<br clear=right>

====Structural analysis and stability====
[[Modelling_and_analysis#First-order analysis|First order analysis]] can be used unless the [[Allowing_for_the_effects_of_deformed_frame_geometry|effects of the deformed geometry]] significantly modify the structural behaviour, in which case either modified first order effects should be determined or a [[Modelling_and_analysis#Second-order analysis|second order analysis]] carried out. BS&nbsp;EN&nbsp;1994-1-1<ref name="BSEN1994-1-1"></ref>  gives rules under four headings for the following types of global analysis:

*Linear [[Modelling_and_analysis#Elastic analysis|elastic analysis]], in which allowance is made for cracking of concrete, creep and shrinkage
*Non-linear global analysis, which generally follows the rules for plastic global analysis in BS&nbsp;EN&nbsp;1993-1-1<ref name="BSEN1993-1-1"></ref> and takes account of the behaviour of the [[#Shear connection|shear connection]]
*Linear elastic analysis with limited redistribution, which may be used where [[Modelling_and_analysis#Second-order effects|second order effects]] do not need to be considered
*Rigid plastic analysis, for which limitations at plastic hinge locations are given.
<br>
Generally, [[Modelling_and_analysis#Plastic analysis|plastic analysis]] is used as it enables more economic designs. For serviceability limit states, [[Modelling_and_analysis#Elastic analysis|elastic analysis]] should be used, but where necessary, consideration of concrete cracking should be made.

====[[#Section classification|Section classification]]====
The [[#Section classification|section classification]] in BS&nbsp;EN&nbsp;1993-1-1<ref name="BSEN1993-1-1"></ref> is adopted for composite sections. Where a steel element is attached to a reinforced concrete element, the classification of the element can, in some cases, be improved. Requirements for ductility of reinforcement in tension are given for Class&nbsp;1 and Class&nbsp;2 cross sections.

====Modular ratio====
For linear [[Modelling and analysis#Elastic analysis|elastic analysis]], the modular ratio for concrete is required. BS&nbsp;EN&nbsp;1994-1-1<ref name="BSEN1994-1-1"></ref>  gives an expression that depends on the creep coefficient, as defined in BS&nbsp;EN&nbsp;1992-1-1<ref name="BSEN1992-1-1"></ref>, and a factor that takes into account the type of loading.

====Cross sectional resistance====

=====Bending resistance=====
The design bending resistance of a composite section may be determined by [[Modelling and analysis#Elastic analysis|elastic analysis]] and non-linear theory for any class of cross section; for Class&nbsp;1 or Class&nbsp;2 cross sections, rigid-plastic theory may be used see [[#Resources|SCI P359]] .

Plastic resistance moments of composite sections may be determined either assuming full interaction between the steel and reinforced concrete or assuming [[#Partial shear connection|partial shear connection]] , i.e. when the force transferred to the concrete is limited by [[#Design resistance of shear connectors|resistance of the shear connectors]].

=====Resistance to vertical shear=====
The resistance of a composite section to vertical shear is generally taken simply as the shear resistance of the structural steel section. Where necessary, the resistance of uncased webs to shear buckling should be determined in accordance with BS&nbsp;EN&nbsp;1993-1-5<ref name="BSEN1993-1-5"></ref>.

====Shear Connection====
{{#image_template:image=File:Headed-shear-studs.PNG|wrap=true|align=right|caption=Detailing for headed shear studs (from [[#Resources|P359]])|width=400}}
Rules for the verification of the shear connection in [[Composite construction#Types of composite beam|composite beams]] are given in Section&nbsp;6.6 of BS&nbsp;EN&nbsp;1994-1-1<ref name="BSEN1994-1-1"></ref>. Detailed rules are only given for headed stud connectors. Dimension limits and rules for transverse reinforcement are given. Natural bond between the concrete and steel is ignored.

=====Design resistance of shear connectors=====
BS&nbsp;EN&nbsp;1994-1-1<ref name="BSEN1994-1-1"></ref>  gives the design shear resistance of a headed stud connector as the smaller of the shear resistance of the stud and the crushing strength of the concrete around it. When used with [[Steel construction products#Decking for floors|profiled steel sheeting]], a reduction factor, based on the geometry of the deck and the height of the stud, is used to reduce the resistance of the shear connectors. Stud connectors have sufficient ductility to develop plastic behaviour, provided that certain limits are observed if there is only partial shear connection.<br clear=right>

=====Partial shear connection=====
Limitations are given on the use of partial shear connection, i.e. for situations where the design shear resistance over a length of beam is insufficient to develop the full resistance of the [[Composite construction#Types of composite beam|composite beam]]. This will often be a critical design criterion for [[Long-span beams|long-span beams]].

=====Longitudinal shear resistance of concrete slabs=====
The longitudinal shear resistance of a slab is calculated using the procedure given in BS&nbsp;EN&nbsp;1992-1-1<ref name="BSEN1992-1-1"></ref>. However, the shear planes that may be critical and the contributions from the reinforcement or the [[Steel construction products#Decking for floors|profiled steel sheeting]] (if the shear connectors are through-deck welded) are defined in BS&nbsp;EN&nbsp;1994-1-1<ref name="BSEN1994-1-1"></ref>.

====Serviceability limit states====
No limits are given for vertical or horizontal deflections. However, Section&nbsp;7.4 of BS&nbsp;EN&nbsp;1994-1-1<ref name="BSEN1994-1-1"></ref>  does give details of the minimum reinforcement required to satisfy crack width limits.

====Connection design====
{{#image_template:image=File:P213 - cover.jpg|wrap=true|width=250|caption=Composite connection design guide ([[#Resources|SCI P213]])}}
For [[Composite construction#Composite connections|composite joints]], such as where there is a double-sided beam-to-column joint and the [[Composite construction#Composite slabs|composite slab]] is continuous, BS&nbsp;EN&nbsp;1994-1-1<ref name="BSEN1994-1-1"></ref>  provides supplementary rules to those in BS&nbsp;EN&nbsp;1993&#8209;1&#8209;8<ref name="BSEN1993-1-8"></ref> to verify the connections. Rules are also given for column web panels in shear or transverse compression when encased in concrete see [[#Resources|SCI P213]].

==CB/203 Design & Execution of Steel Structures==
CB/203 is the [https://www.bsigroup.com/en-GB/ BSI] committee responsible for the British Standards for the design and execution of steel structures, and for the UK input to CEN/TC 250/SC 3 Eurocode 1993 Design of steel structures and Eurocodes related documents. It also mirrors CEN/TC 135 Execution of steel and aluminium structures, and ISO/TC 167 Steel and aluminium structures.

Every 6 months CB/203 publishes a ‘Summary Report to Stakeholders’, which lists the design and execution standards under CB/203 responsibility, the standards due for Enquiry/Vote/Systematic Review, and provides an update on CEN and ISO Activities. The latest version is available below, along with a comments template for the Eurocodes Systematic Review and a more general template for those who use the standards that fall within the scope of CB/203 to comment on their good/bad experiences with the standards and to provide technical comments on them:
*[[Media:CB_203 Summary Report for Stakeholders 15 July 2017.pdf|CB/203 Summary Report to Stakeholders, 15 July 2017]]
*[[Media:Eurocode_Systematic_Review_Comments_Template.doc|Eurocode Systematic Review Comments Template]]
*[[Media:Stakeholder_Summary_Progress_Report_Template_for_CB_203.docx|Stakeholder Summary Progress Report Comment Template for CB/203]]
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==References==
<references responsive="0"/>

==Further reading==
*[https://www.wiley.com/en-gb/Steel+Designers%27+Manual%2C+7th+Edition-p-9781119249863 Steel Designers' Manual 7th Edition.] Editors B Davison & G W Owens. The Steel Construction Institute 2012, Chapters 1 and 3
*Eurocode guides to EN1993 and EN1994 from ICE publishing (Thomas Telford).

==Resources==
*[[Media:AD-346.pdf|SCI AD346, Design actions during concreting for beams and decking in composite floors, 2010]]
*[[Media:SN003b.pdf|NCCI: Elastic critical moment for lateral torsional buckling (SN003b EN EU) SCI]]
*[[Media:SCI_P359.pdf|SCI P359 Composite Design of Steel Framed Buildings, 2011]]
*[[Media:SCI_P361.pdf|SCI P361 Steel Building Design: Introduction to the Eurocodes, 2009]]
*[[Media:SCI_P362.pdf|SCI P362 Steel Building Design: Concise Eurocodes, 2009]]
*[[Media:SCI_P363.pdf|SCI P363 Steel Building Design: Design Data, 2013]]<br>A web-based interactive version of the '[[Design_software_and_tools#Interactive_.22Blue_Book.22|Blue Book]]', is also available.
*[[Media:SCI_P374.pdf|SCI P374 Steel Building Design: Worked Examples - Hollow Sections, 2009]]
*[[Media:SCI_P213.pdf|SCI P213 Joints in steel construction: Composite connections, 1998]]
*[[Media:SCI_P358.pdf|SCI P358 Joints in Steel Construction - Simple Joints to Eurocode 3, 2014]]
*[[Media:SCI_P398.pdf|SCI P398 Joints in Steel Construction - Moment-resisting Joints to Eurocode 3, 2013]]
*[[Media:SCI_P394.pdf|SCI P394 Wind Actions to BS EN 1991-1-4, SCI, 2013]]
*[[Media:ED007-D07.pdf|SCI ED007 Selection of steel sub-grade in accordance with the Eurocodes, 2012]]
*[[Media:SCI_P419.pdf|SCI P419 Brittle fracture: Selection of steel sub-grade to BS EN 1993-1-10, 2017]]
*[[Design software and tools#Wind loading calculator|Wind loading calculator]]

==See also==
*[[Steel_material_properties|Steel material properties]]
*[[Composite_construction|Composite construction]]
*[[Modelling_and_analysis|Modelling and analysis]]
*[[Allowing for the effects of deformed frame geometry|Allowing for the effects of deformed frame geometry]]
*[[Member_design|Member design]]
*[[Simple connections|Simple connections]]
*[[Moment_resisting_connections|Moment resisting connections]]
*[[Structural_fire_resistance_requirements|Structural fire resistance requirements]]
*[[Steelwork specification|Steelwork specification]]
*[[Structural_robustness|Structural robustness]]

==External links==
*[https://www.gov.uk/government/policies/building-regulation UK Building Regulations]
*[http://www.cen.eu/cen/Pages/default.aspx CEN]
*[http://www.steel-ncci.co.uk NCCI for steel design]
*[https://www.bsigroup.com/en-GB/ bsi]

==CPD==
*[[Continuing_Professional_Development#Introduction_to_EC3|An introduction to Eurocode 3]]

[[Category:Design]]
[[Category:Index of main articles]]