Bridges for Service Life Beyond 100 Years: Service Limit State Design (2014)

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269 A.1 Introduction A.1.1 General Information The Structural Eurocode program provides comprehensive information for the structural design and verification of build- ings and civil engineering works (including geotechnical aspects). The program comprises the following standards, each one consisting of a number of parts. [Often only a limited number of parts of each standard may be relevant to bridge structures.] EN 1990 Eurocode 0: 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 aluminum structures Following is a description of the serviceability limit state (SLS) requirements in sections relevant to bridges. A.1.2 Structural Eurocodes The Structural 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 innova- tive nature. Unusual forms of construction or design conditions are not specifically covered and additional expert consideration is required by the designer in such cases. The Eurocodes are being implemented by each member country of the European Union through National Standards which comprise the full text of each Eurocode (including any annexes) and may be followed by a National Annex. The National Annex only contains information on those parameters which are left open in the Eurocode for national choice, (known as Nationally Determined Parameters). They are to be used for the design of buildings and civil engineer- ing works to be constructed in the country concerned and are usually one or more of the following: • Values and/or classes where alternatives are given in the Eurocode; • Values to be used where a symbol only is given in the Eurocode. • Country specific data (geographical, climatic, etc.) e.g. snow map. • The procedure to be used where alternative procedures are given in the Eurocode. The National Annex may also contain the following: • Decisions on the application of informative annexes, and • References to non-contradictory complementary informa- tion to help the user apply the Eurocode. This summary does not include any numeric values pre- sented in any National Annex. The following sections address some of the Structural Euro- codes in turn and summarize the relevant articles relating to the serviceability limit state used in bridge design. A.2 EN 1990 Eurocode 0: Basis of Structural Design Eurocode 0 (Basis of structural design) is the lead document in the Eurocode suite. It describes the principles and require- ments for safety, serviceability, and durability of structures. It is based on the limit state concept used in conjunction A p p E N D I x A SLS Requirements in the Eurocode

270 with a partial factor method. It provides the basis and gen- eral principles for the structural design and verification of buildings and civil engineering works (including geotechni- cal aspects). EN 1990:2002 should be used in conjunction with all the other Eurocodes (EN 1991 to EN 1999) for design. NOTE: For the design of special construction works (e.g. nuclear installations, dams), other provisions than those in EN 1990 to EN 1999 might be necessary. EN 1990 also gives guidelines for the aspects of structural reliability relating to safety, serviceability, and durability: • For design cases not covered by EN 1991 to EN 1999 (other actions, structures not treated, other materials); • To serve as a reference document for other European Com- mittee for Standardization Technical Committees (CEN/TCs) concerning structural matters. EN 1990 is also applicable as a guidance document for the design of structures where other materials or other actions outside the scope of EN 1991 to EN 1999 are involved. EN 1990 is applicable for the structural appraisal of exist- ing construction, in developing the design of repairs and alterations, or in assessing changes of use. NOTE: Additional or amended provisions might be neces- sary where appropriate. EN 1990 is intended for use by • Committees drafting standards for structural design and related product, testing, and execution standards; • Clients (e.g., for the formulation of their specific require- ments on reliability levels and durability); • Designers and constructors; and • Relevant authorities. The general assumptions of EN 1990 are as follows: • The choice of the structural system and the design of the structure are made by appropriately qualified and expe- rienced personnel. • Execution is carried out by personnel having the appropriate skill and experience. • Adequate supervision and quality control are provided during execution of the work (i.e. in design offices, facto- ries, plants, and on site). • The construction materials and products are used as spec- ified in EN 1990 or in EN 1991 to EN 1999 or in the rele- vant execution standards, or reference material, or product specifications. • The structure will be adequately maintained; and • The structure will be used in accordance with the design assumptions. NOTE: There may be cases when these assumptions need to be supplemented. It should be noted that clauses are listed and enumerated within each article of the Eurocodes and that distinction is made between clauses that present principles and those that present Application Rules. This distinction is preserved in the summaries given in this report. The Principles comprise • General statements and definitions for which there is no alternative, as well as • Requirements and analytical models for which no alterna- tive is permitted unless specifically stated. The Principles are identified by the letter P following the paragraph number. [e.g. (2)P] The Application Rules [identified by a number in brackets, e.g. (2)] are generally recognized rules which comply with the principles and satisfy their requirements. It is permissible to use alternative design rules different from the Application Rules given in EN 1990 for works, pro- vided that it is shown that the alternative rules accord with the relevant principles and are at least equivalent with regard to the structural safety, serviceability, and durability which would be expected when using the Eurocodes. The clauses relating to serviceability limit state design pre- sented in Eurocode 0 are summarized in Table A.1. A.3 EN 1991 Eurocode 1: Actions on Structures Eurocode 1 (Actions on structures) provides information on all actions that should normally be considered in the design of buildings and civil engineering works. It is in four main parts. The first part is divided into seven sub-parts which cover densi- ties, self-weight, and imposed loads; actions due to fire; snow; wind; thermal actions; loads during execution; and accidental actions. The remaining three parts cover traffic loads on bridges, actions by cranes and machinery, and actions for silos and tanks. The second part (EN 1991-2:2003) concerns the design of bridges. Sections from this standard relating to the service- ability limit state are summarized in Table A.2. For the design of bridges, EN 1991-2 defines imposed loads (models and representative values) associated with road traf- fic, pedestrian actions, and rail traffic which include, when relevant, dynamic effects and centrifugal, braking, and accel- eration actions and actions for accidental design situations. For the design of new bridges, EN 1991-2 is intended to be used, for direct application, together with Eurocodes EN 1990 to EN 1999. The bases for combinations of traffic loads with non-traffic loads are given in EN 1990, A2. A summary of clauses relating to loads and actions in Eurocode EN 1991-2 is presented in Table A.2.

271 Table A.1. Summary of Clauses Relating to Serviceability Limit State Design in Eurocode 0 Eurocode Article Basic Provision Discussion Eurocode 0 3.4 Serviceability limit states (1)P The limit states that concern – the functioning of the structure or structural members under normal use; – the comfort of people; – the appearance of the construction works, shall be classified as serviceability limit states. NOTE 1: In the context of serviceability, the term “appearance” is concerned with such criteria as high deflection and extensive cracking, rather than aesthetics. NOTE 2: Usually the serviceability requirements are specific to each individual project. (2) P A distinction shall be made between reversible and irreversible serviceability limit states. NOTE: ‘Reversible’ = where no consequences of actions exceeding the specified service require- ment will remain when the actions are removed. ‘Irreversible’ = where some consequences of actions will remain when the actions are removed. (3) The verification of serviceability limit states should be based on criteria concerning the follow- ing aspects: a) deformations that affect – the appearance, – the comfort of users, or – the functioning of the structure (including the functioning of machines or services), or that cause damage to finishes or non-structural members; b) vibrations – that cause discomfort to people, or – that limit the functional effectiveness of the structure; c) damage that is likely to adversely affect – the appearance, – the durability, or – the functioning of the structure. NOTE: Additional provisions related to serviceability criteria are given in the relevant EN 1992 to EN 1999. Eurocode 0 6.5.1 Verifications (1)P It shall be verified that Ed ≤ Cd (6.13) where: Cd is the limiting design value of the relevant serviceability criterion. Ed is the design value of the effects of actions specified in the serviceability criterion, determined on the basis of the relevant combination. Eurocode 0 6.5.2 Serviceability criteria (1) The deformations to be taken into account in relation to serviceability requirements should be as detailed in the relevant Annex A according to the type of construction works, or agreed with the client or the National authority. NOTE: For other specific serviceability criteria such as crack width, stress or strain limitation, slip resistance, see EN 1991 to EN 1999. Eurocode 0 6.5.3 Combination of actions (1) The combinations of actions to be taken into account in the relevant design situations should be appropriate for the serviceability requirements and performance criteria being verified. (2) The combinations of actions for serviceability limit states are defined symbolically (see also 6.5.4): NOTE: It is assumed, in these expressions, that all partial factors are equal to 1. See Annex A and EN 1991 to EN 1999. a) Characteristic combination: (equation given at 6.14a) NOTE: The characteristic combination is normally used for irreversible limit states. b) Frequent combination: (equation given at 6.15a) NOTE: The frequent combination is normally used for reversible limit states. c) Quasi-permanent combination: (equation given at 6.16a) NOTE: The quasi-permanent combination is normally used for long-term effects and the appearance of the structure. (continued on next page)

272 Table A.1. Summary of Clauses Relating to Serviceability Limit State Design in Eurocode 0 Eurocode Article Basic Provision Discussion (3) For the representative value of the prestressing action (i.e. Pk or Pm), reference should be made to the relevant design Eurocode for the type of prestress under consideration. (4) P Effects of actions due to imposed deformations shall be considered where relevant. NOTE: In some cases expressions (6.14) to (6.16) require modification. Detailed rules are given in the relevant parts of EN 1991 to EN 1999. Eurocode 0 6.5.4 Partial factors for materials (1) For serviceability limit states the partial factors gM for the properties of materials should be taken as 1.0 except if differently specified in EN 1992 to EN 1999. Eurocode 0 Annex A2 A2.1 Field of application (1) This Annex A2 to EN 1990 gives rules and methods for establishing combinations of actions for serviceability and ultimate limit state verifications (except fatigue verifications) with the recommended design values of permanent, variable, and accidental actions and y factors (applied to actions) to be used in the design of road bridges, footbridges, and railway bridges. It also applies to actions during execution. Methods and rules for verifications relating to some material-independent serviceability limit states are also given. NOTE 1: Symbols, notations, Load Models, and groups of loads are those used or defined in the relevant section of EN 1991-2. NOTE 2: Symbols, notations, and models of construction loads are those defined in EN 1991-1-6. NOTE 3: Guidance may be given in the National Annex with regard to the use of Table 2.1 (design working life—for UK bridges this is normally 120 years). NOTE 4: Most of the combination rules defined in clauses A2.2.2 to A2.2.5 are simplifications intended to avoid needlessly complicated calculations. They may be changed in the National Annex or for the individual project as described in A2.2.1 to A2.2.5. NOTE 5: This Annex A2 to EN 1990 does not include rules for the determination of actions on structural bearings (forces and moments) and associated movements of bearings or give rules for the analysis of bridges involving ground-structure interaction that may depend on move- ments or deformations of structural bearings. (2) The rules given in this Annex A2 to EN 1990 may not be sufficient for – bridges that are not covered by EN 1991-2 (e.g. bridges under an airport runway, mechanically-moveable bridges, roofed bridges, bridges carrying water), – bridges carrying both road and rail traffic, and – other civil engineering structures carrying traffic loads (e.g. backfill behind a retaining wall). Eurocode 0 Annex A2 A2.2 Combination of actions A2.2.1 General (1) Effects of actions that cannot occur simultaneously due to physical or functional reasons need not be considered together in combinations of actions. (2) Combinations involving actions which are outside the scope of EN 1991 (e.g. due to mining subsidence, particular wind effects, water, floating debris, flooding, mud slides, avalanches, fire, and ice pressure) should be defined in accordance with EN 1990, 1.1(3). NOTE 1: Combinations involving actions that are outside the scope of EN 1991 may be defined either in the National Annex or for the individual project. NOTE 2: For seismic actions, see EN 1998. NOTE 3: For water actions exerted by currents and debris effects, see also EN 1991-1-6. (4) The combinations of actions given in expressions 6.14a to 6.16b should be used when verifying serviceability limit states. Additional rules are given in A2.4 for verifications regarding deformations and vibrations. (continued on next page) (continued)

273 Table A.1. Summary of Clauses Relating to Serviceability Limit State Design in Eurocode 0 Eurocode Article Basic Provision Discussion Eurocode 0 Annex A2 A2.2 Combination of actions A2.2.2 Combination rules for road bridges (1) The infrequent values of variable actions may be used for certain serviceability limit states of concrete bridges. NOTE: The National Annex may refer to the infrequent combination of actions. (6) Wind actions and thermal actions need not be taken into account simultaneously unless otherwise specified for local climatic conditions. NOTE: Depending upon the local climatic conditions, a different simultaneity rule for wind and thermal actions may be defined either in the National Annex or for the individual project. Eurocode 0 Annex A2 A2.4 Serviceability and other specific limit states A2.4.1 General (2) The serviceability criteria should be defined in relation to the serviceability requirements in accordance with 3.4 and EN 1992 to EN 1999. Deformations should be calculated in accor- dance with EN 1991 to EN 1999 by using the appropriate combinations of actions according to expressions (6.14a) to (6.16b) (see Table A2.6), taking into account the serviceability requirements and the distinction between reversible and irreversible limit states. NOTE: Serviceability requirements and criteria may be defined as appropriate in the National Annex or for the individual project. Eurocode 0 Annex A2 A2.4.2 Serviceability criteria regarding deformation and vibration for road bridges (1) Where relevant, requirements and criteria should be defined for road bridges concerning – uplift of the bridge deck at supports, and – damage to structural bearings. NOTE: Uplift at the end of a deck can jeopardize traffic safety and damage structural and non-structural elements. Uplift may be avoided by using a higher safety level than usually accepted for serviceability limit states. (2) Serviceability limit states during execution should be defined in accordance with EN 1990 to EN 1999. (3) Requirements and criteria should be defined for road bridges concerning deformations and vibrations, where relevant. NOTE 1: The verification of serviceability limit states concerning deformation and vibration needs to be considered only in exceptional cases for road bridges. The frequent combination of actions is recommended for the assessment of deformation. NOTE 2: Vibrations of road bridges may have various origins, in particular traffic actions and wind actions. For vibrations due to wind actions, see EN 1991-1-4. For vibrations due to traf- fic actions, comfort criteria may have to be considered. Fatigue may also have to be taken into account. Eurocode 0 Annex A2 A2.4.3.2 Pedestrian comfort criteria (for serviceability) (1) The comfort criteria should be defined in terms of maximum acceptable acceleration of any part of the deck. NOTE: The criteria may be defined as appropriate in the National Annex or for the individual project. The following accelerations (m/s2) are the recommended maximum values for any part of the deck: i) 0.7 for vertical vibrations, ii) 0.2 for horizontal vibrations due to normal use, and iii) 0.4 for exceptional crowd conditions. (2) A verification of the comfort criteria should be performed if the fundamental frequency of the deck is less than – 5 Hz for vertical vibrations, or – 2.5 Hz for horizontal (lateral) and torsional vibrations. NOTE: The data used in the calculations, and therefore the results, are subject to very high uncertainties. When the comfort criteria are not satisfied with a significant margin, it may be necessary to make provision in the design for the possible installation of dampers in the structure after its completion. In such cases the designer should consider and identify any requirements for commissioning tests. (continued on next page) (continued)

274 Table A.1. Summary of Clauses Relating to Serviceability Limit State Design in Eurocode 0 Eurocode Article Basic Provision Discussion Eurocode 0 Annex A2 A2.4.4.3 Limiting values for the maximum vertical deflection for passenger comfort A2.4.4.3.1 Comfort criteria (1) Passenger comfort depends on the vertical acceleration bv inside the coach during travel on the approach to, passage over, and departure from the bridge. (2) The levels of comfort and associated limiting values for the vertical acceleration should be specified. NOTE: These levels of comfort and associated limiting values may be defined for the individ- ual project. Recommended levels of comfort are given in Table A2.9. Eurocode 0 Annex A2 A2.4.4.3 Limiting values for the maximum vertical deflection for passenger comfort A2.4.4.3.3 Requirements for a dynamic vehicle/bridge interaction analysis for checking passenger comfort (1) Where a vehicle/bridge dynamic interaction analysis is required, the analysis should take account of the following behaviors: iv) a series of vehicle speeds up to the maximum speed specified, v) characteristic loading of the real trains specified for the individual project in accordance with EN 1991-2, 6.4.6.1.1, vi) dynamic mass interaction between vehicles in the real train and the structure, vii) the damping and stiffness characteristics of the vehicle suspension, viii) a sufficient number of vehicles to produce the maximum load effects in the longest span, ix) a sufficient number of spans in a structure with multiple spans to develop any resonance effects in the vehicle suspension. NOTE: Any requirements for taking track roughness into account in the vehicle/bridge dynamic interaction analysis may be defined for the individual project. (continued) Table A.2. Summary of Clauses Relating to Loads and Actions in Eurocode EN 1991-2 Eurocode Article Basic Provision Discussion Eurocode 1 1.3 Distinction between Principles and Applica- tion Rules (5) It is permissible to use alternative design rules different from the Application Rules given in EN 1991-2 for works, provided that it is shown that the alternative rules accord with the rele- vant principles and are at least equivalent with regard to the structural safety, serviceability, and durability which would be expected when using the Eurocodes. Eurocode 1 Section 2 Classification of actions 2.2 Variable actions (1) For normal conditions of use (i.e. excluding any accidental situation), the traffic and pedes- trian loads (dynamic amplification included where relevant) should be considered as variable actions. (2) The various representative values are – characteristic values, which are either statistical (i.e. corresponding to a limited probability of being exceeded on a bridge during its design working life) or nominal; see EN 1990, 4.1.2(7); – frequent values; and – quasi-permanent values. (3) For calculation of fatigue lives, separate models, associated values, and where relevant, specific requirements are given in 4.6 for road bridges, in 6.9 for railway bridges, and in the relevant annexes. Eurocode 1 Section 4 Road traffic actions and other actions specifically for road bridges 4.1 Field of application (1) Load models defined in this section should be used for the design of road bridges with loaded lengths less than 200 m. NOTE 1: 200 m corresponds to the maximum length taken into account for the calibration of Load Model 1 (see 4.3.2). In general, the use of Load Model 1 is safe-sided for loaded lengths over 200 m. NOTE 2: Load models for loaded lengths greater than 200 m may be defined in the National Annex or for the individual project. (2) The models and associated rules are intended to cover all normally foreseeable traffic situ- ations (i.e. traffic conditions in either direction on any lane due to the road traffic) to be taken into account for design [see however (3) and the notes in 4.2.1]. (3) The effects of loads on road construction sites (e.g. due to scrapers, lorries carrying earth) or of loads specifically for inspection and tests are not intended to be covered by the load mod- els and should be separately specified, where relevant. (continued on next page)

275 Table A.2. Summary of Clauses Relating to Loads and Actions in Eurocode EN 1991-2 Eurocode Article Basic Provision Discussion Eurocode 1 4.2 Representation of actions 4.2.1 Models of road traffic loads (1) Loads due to the road traffic, consisting of cars, lorries, and special vehicles (e.g. for indus- trial transport), give rise to vertical and horizontal, static and dynamic forces. NOTE 1: The load models defined in this section do not describe actual loads. They have been selected and calibrated so that their effects (with dynamic amplification included where indicated). NOTE 2: The National Annex may define complementary load models, with associated combi- nation rules where traffic outside the scope of the load models specified in this section needs to be considered. NOTE 3: The dynamic amplification included in the models (except for fatigue), although established for a medium pavement quality (see Annex B) and pneumatic vehicle suspension, depends on various parameters and on the action effect under consideration. Therefore, it cannot be represented by a unique factor. In some unfavorable cases, it may reach 1,7 (local effects), but still more unfavorable values can be reached for poorer pavement quality, or if there is a risk of resonance. These cases can be avoided by appropriate quality and design measures. Therefore, an additional dynamic amplification may have to be taken into account for particular calculations [see 4.6.1.(6)] or for the individual project. Eurocode 1 4.3 Vertical loads— Characteristic values 4.3.1 General and associated design situations (1) Characteristic loads are intended for the determination of road traffic effects associated with ultimate limit state verifications and with particular serviceability verifications (see EN 1990 to EN 1999). NOTE: There are 4 load models described in detail to cover most of the effects of the traffic of lorries and cars, special vehicles, and pedestrian crowd loading. They are used for general and local verifications. One of these models is used to represent dynamic effects on short structural members. Eurocode 1 4.6 Fatigue load models 4.6.1 General (1) Traffic running on bridges produces a stress spectrum which may cause fatigue. The stress spectrum depends on the geometry of the vehicles, the axle loads, the vehicle spacing, the composition of the traffic, and its dynamic effects. NOTE: There are 5 load models described in detail. The first two are intended to be used to check whether the fatigue life may be considered unlimited when a constant stress amplitude fatigue limit is given. Therefore, they are appropriate for steel constructions and may be inap- propriate for other materials. The remaining 3 load models are intended to be used for fatigue life assessment. Each of these last three models is more accurate than its predecessor, cul- minating in the last model which is based on actual traffic data. A.4 EN 1992 Eurocode 2: Design of Concrete Structures Eurocode 2 (Design of concrete structures) is concerned with the requirements for resistance, serviceability, durability, and fire resistance of concrete structures. (Other requirements, e.g. concerning thermal or sound insulation, are not consid- ered.) It applies to the design of buildings and civil engineer- ing works in plain, reinforced, and prestressed concrete. EN 1992 is presented in three main parts. The first part has two sub-parts covering buildings and structural fire design. The last two main parts cover concrete bridges and liquid retaining and containing structures, as in the following list. Those underlined have been reviewed in the compilation of this report. EN 1992-1.1:2004 Design of concrete structures. General rules and rules for buildings EN 1992-1.2:2004 Design of concrete structures. Fire design EN 1992-2:2005 Design of concrete structures. Concrete bridges. Design and detailing rules EN 1992-3:2006 Design of concrete structures. Liquid retaining and containing structures Note also PD 6687:2006 Background paper to the UK National Annexes to BS EN 1992-1 PD 6687-2:2008 Recommendations for the design of structures to BS EN 1992-2 The second part, EN 1992-2:2005 (Design of concrete struc- tures. Concrete bridges. Design and detailing rules) is relevant for the design of concrete bridges. Sections from this stan- dard relating to the serviceability limit state are summarized (continued)

276 Table A.3. Summary of Clauses Relating to the Serviceability Limit State Design of Concrete Bridges in Eurocode EN 1992-1 Eurocode Article Basic Provision Discussion Eurocode 2 Section 2 Basis of Design 2.1 Requirements 2.1.1 Basic requirements (3) The basic requirements of EN 1990, Section 2 are deemed to be satisfied for concrete struc- tures when the following are applied together: – limit state design in conjunction with the partial factor method in accordance with EN 1990, – actions in accordance with EN 1991, – combination of actions in accordance with EN 1990, and – resistances, durability and serviceability in accordance with this standard. NOTE: Requirements for fire resistance (see EN 1990 Section 5 and EN 1992-1.2) may dictate a greater size of member than that required for structural resistance at normal temperature. Eurocode 2 2.3.1.2 Thermal effects (1) Thermal effects should be taken into account when checking serviceability limit states. (2) Thermal effects should be considered for ultimate limit states only where they are significant (e.g. fatigue conditions, in the verification of stability where second order effects are of impor- tance). In other cases they need not be considered, provided that the ductility and rotation capacity of the elements are sufficient. (3) Where thermal effects are taken into account, they should be considered as variable actions and applied with a partial factor and y factor. NOTE: The y factor is defined in the relevant annex of EN 1990 and EN 1991-1.5. Eurocode 2 2.3.1.3 Differential settlements/movements (2) The effects of differential settlements should generally be taken into account for the verification of serviceability limit states. Eurocode 2 2.3.2 Material and product properties 2.3.2.1 General 2.3.2.2 Shrinkage and creep (1) Shrinkage and creep are time-dependent properties of concrete. Their effects should generally be taken into account for the verification of serviceability limit states. (3) When creep is taken into account, its design effects should be evaluated under the quasi- permanent combination of actions irrespective of the design situation considered (i.e. persistent, transient, or accidental). NOTE: In most cases the effects of creep may be evaluated under permanent loads and the mean value of prestress. Eurocode 2 2.4.2 Design values 2.4.2.4 Partial factors for materials (2) The values for partial factors for materials for serviceability limit state verification should be taken as those given in the particular clauses of this Eurocode. NOTE: The values of gC and gS in the serviceability limit state for use in a country may be found in its National Annex. The recommended value for situations not covered by particular clauses of this Eurocode is 1.0. Eurocode 2 Section 3 Materials 3.1 Concrete 3.1.1 General (1)P The following clauses give principles and rules for normal and high-strength concrete. (2) Rules for lightweight aggregate concrete are given in Section 11. Eurocode 2 3.3 Prestressing steel 3.3.1 General (1) P This clause applies to wires, bars, and strands used as prestressing tendons in concrete structures. (2) P Prestressing tendons shall have an acceptably low level of susceptibility to stress corrosion. (3) The level of susceptibility to stress corrosion may be assumed to be acceptably low if the prestressing tendons comply with the criteria specified in EN 10138 or given in an appropriate European Technical Approval. (continued on next page) in Table A.3. It should be noted that EN 1992-2 draws heavily from the general clauses presented in EN 1992-1.1 (Design of concrete structures. General rules and rules for buildings); where relevant, these clauses are also included in the summaries given in the table. EN 1992-2 describes the principles and requirements for safety, serviceability, and durability of concrete structures, together with specific provisions for bridges. For the design of new bridges, EN 1992-2 is intended to be used, for direct application, together with other parts of EN 1992 and Euro- codes EN 1990, 1991, 1997, and 1998. A summary of clauses relating to the serviceability limit state design of concrete bridges Eurocode EN 1992-1 is presented in Table A.3.

277 Table A.3. Summary of Clauses Relating to the Serviceability Limit State Design of Concrete Bridges in Eurocode EN 1992-1 Eurocode Article Basic Provision Discussion Eurocode 2 Section 4 Durability and cover to reinforcement 4.1 General (1)P A durable structure shall meet the requirements of serviceability, strength, and stability throughout its design working life, without significant loss of utility or excessive unforeseen maintenance (for general requirements see also EN 1990). (2) P The required protection of the structure shall be established by considering its intended use, design working life (see EN 1990), maintenance program, and actions. (3) P The possible significance of direct and indirect actions, environmental conditions (4.2), and consequential effects shall be considered. NOTE: Examples include deformations due to creep and shrinkage (see 2.3.2). Eurocode 2 Section 5 Structural analysis 5.2 Geometric imperfections (3) Imperfections need not be considered for serviceability limit states. Eurocode 2 5.4 Linear elastic analysis (1) Linear analysis of elements based on the theory of elasticity may be used for both the serviceability and ultimate limit states. (3) For thermal deformation, settlement, and shrinkage effects at the ultimate limit state (ULS), a reduced stiffness corresponding to the cracked sections, neglecting tension stiffening but including the effects of creep, may be assumed. For the serviceability limit state (SLS), a gradual evolution of cracking should be considered. Eurocode 2 5.6 Plastic analysis 5.6.4 Analysis with strut-and-tie models (2) Verifications in SLS may be carried out using strut-and-tie models (e.g. verification of steel stresses and crack width control) if approximate compatibility for strut-and-tie models is ensured (in particular the position and direction of important struts should be oriented according to linear elasticity theory). Eurocode 2 5.7 Non-linear analysis (1) Non-linear methods of analysis may be used for both ULS and SLS, provided that equilibrium and compatibility are satisfied and an adequate non-linear behavior for materials is assumed. The analysis may be first or second order. (105) Non-linear analysis may be used, provided that the model can appropriately cover all failure modes (e.g. bending, axial force, shear, compression failure affected by reduced effective con- crete strength) and that the concrete tensile strength is not utilized as a primary load resisting mechanism. If one analysis is not sufficient to verify all the failure mechanisms, separate addi- tional analyses should be carried out. The following design format should be used: – The resistance should be evaluated for different levels of appropriate actions which should be increased from their serviceability values by incremental steps, such that the value of gG.Gk and gQ.Qk are reached in the same step. The incrementing process should be contin- ued until one region of the structure attains the ultimate strength, evaluated taking account of aCC, or there is global failure of the structure. The corresponding load is referred to as qud. Further steps in the design format that should be used are given. Eurocode 2 5.10 Prestressed members and structures 5.10.9 Effects of prestress- ing at serviceability limit state and limit state of fatigue (1)P For serviceability and fatigue calculations, allowance shall be made for possible variations in prestress. Two characteristic values of the prestressing force at the serviceability limit state are estimated. These are based on the upper characteristic value and the lower characteristic value. Eurocode 2 Section 7 Serviceability limit states (SLS) 7.1 General (1)P This section covers the common serviceability limit states. These are – stress limitation (see 7.2), – crack control (see 7.3), and – deflection control (see 7.4). Other limit states (such as vibration) may be of importance in particular structures but are not covered in this standard. (continued on next page) (continued)

278 Table A.3. Summary of Clauses Relating to the Serviceability Limit State Design of Concrete Bridges in Eurocode EN 1992-1 Eurocode Article Basic Provision Discussion (2) In the calculation of stresses and deflections, cross sections should be assumed to be uncracked, provided that the flexural tensile stress does not exceed fct,eff. The value of fct,eff may be taken as fctm or fctm,n, provided that the calculation for minimum tension reinforcement is also based on the same value. For the purposes of calculating crack widths and tension stiffening, fctm should be used. Eurocode 2 7.2 Stress limitation (1) P The compressive stress in the concrete shall be limited to avoid longitudinal cracks, micro- cracks, or high levels of creep, where they could result in unacceptable effects on the func- tion of the structure. (102) Longitudinal cracks may occur if the stress level under the characteristic combination of loads exceeds a critical value. Such cracking may lead to a reduction of durability. In the absence of other measures, such as an increase in the cover to reinforcement in the com- pressive zone or confinement by transverse reinforcement, it may be appropriate to limit the compressive stress to the value k1fck in areas exposed to environments of exposure classes XD, XF, and XS (see Table 4.1 of EN 1992-1-1). NOTE: The value of k1 for use in a country may be found in its National Annex. The recom- mended value is 0.6. The maximum increase in the stress limit above k1fck in the presence of confinement may also be found in a country’s National Annex. The recommended maximum increase is 10%. NOTE: British National Document PD 6687:2006 (Background paper to the UK National Annexes to BS EN 1992-1) gives non-contradictory complimentary information for use with EN 1992-1. In particular, when considering stress limitation in serviceability it notes a) Stress checks in reinforced concrete members have not been required in the UK for the past 50 years or so, and there has been no known adverse effect. Provided that the design has been carried out properly for ultimate limit state, there will be no significant effect at serviceability in respect of longitudinal cracking. b) There has been no evidence either from research or practice that there is a correlation between high compressive stress and durability problems. (3) If the stress in the concrete under the quasi-permanent loads is less than k2fck, linear creep may be assumed. If the stress in concrete exceeds k2fck, non-linear creep should be consid- ered (see 3.1.4). NOTE: The value of k2 for use in a country may be found in its National Annex. The recom- mended value is 0.45. (4)P Tensile stresses in the reinforcement shall be limited to avoid inelastic strain, unacceptable cracking, or deformation. (5) When structural appearance is considered, unacceptable cracking or deformation may be assumed to be avoided if, under the characteristic combination of loads, the tensile strength in the reinforcement does not exceed k3fyk. Where the stress is caused by an imposed defor- mation, the tensile strength should not exceed k4fyk. The mean value of the stress in pre- stressing tendons should not exceed k5fyk. NOTE: The values of k3, k4, and k5 for use in a country may be found in its National Annex. The recommended values are 0.8, 1, and 0.75, respectively. Eurocode 2 7.3 Crack control 7.3.1 General considerations (1)P Cracking shall be limited to an extent that will not impair the proper functioning or durability of the structure or cause its appearance to be unacceptable. (2) Cracking is normal in reinforced concrete structures subject to bending, shear, torsion, or tension resulting from either direct loading or restraint or imposed deformations. (3) Cracks may also arise from other causes such as plastic shrinkage or expansive chemical reactions within the hardened concrete. Such cracks may be unacceptably large, but their avoidance and control lie outside the scope of this section. (4) Cracks may be permitted to form without any attempt to control their width, provided they do not impair the functioning of the structure. (continued) (continued on next page)

279 Table A.3. Summary of Clauses Relating to the Serviceability Limit State Design of Concrete Bridges in Eurocode EN 1992-1 Eurocode Article Basic Provision Discussion (105) A limiting calculated crack width wmax, taking account of the proposed function and nature of the structure and the costs of limiting cracking, should be established. Due to the random nature of the cracking phenomenon, actual crack widths cannot be predicted. However, if the crack widths calculated in accordance with the models given in this standard are limited to the values given in Table 7.101N, the performance of the structure is unlikely to be impaired. NOTE: The value of wmax and the definition of decompression and its application for use in a country may be found in its National Annex. The recommended value for wmax and the appli- cation of the decompression limit are given in Table 7.101N. The recommended definition of decompression is noted in the text under the table. NOTE: British National Document PD 6687-2:2008 (Recommendations for the design of structures to BS EN 1992-2:2005) gives non-contradictory complimentary information for use with EN 1992-2. In particular, it contains a Section 8, Serviceability limit states. Under 8.2.1 it makes recommendations for the values of wmax and notes a lack of clarity. Under 8.2.2 it offers a simplification in crack calculation methods. Under 8.2.3 it gives guidance on calculating crack widths due to early age restraint of imposed deformations, which can arise due to early thermal contraction and shrinkage. Such effects should be taken into account in design. (6) For members with only unbonded tendons, the requirements for reinforced concrete ele- ments apply. For members with a combination of bonded and unbonded tendons, require- ments for prestressed concrete members with bonded tendons apply. (7) Special measures may be necessary for members subjected to exposure class XD3. The choice of appropriate measures will depend upon the nature of the aggressive agent involved. (8) When using strut-and-tie models with the struts oriented according to the compressive stress trajectories in the uncracked state, it is possible to use the forces in the ties to obtain the corresponding steel stresses to estimate the crack width [see 5.6.4 (2)]. (9) Crack widths may be calculated according to 7.3.4. A simplified alternative is to limit the bar size or spacing according to 7.3.3. (110) In some cases it may be necessary to check and control shear cracking in webs. NOTE: Further information may be found in Annex QQ. Eurocode 2 7.3 Crack control 7.3.2 Minimum reinforce- ment areas (1) P If crack control is required, a minimum amount of bonded reinforcement is required to control cracking in areas where tension is expected. The amount may be estimated from equilibrium between the tensile force in concrete just before cracking and the tensile force in reinforcement at yielding or at a lower stress if necessary to limit the crack width. (102) Unless a more rigorous calculation shows lesser areas to be adequate, the required minimum areas of reinforcement may be calculated; a procedure is given. (3) Bonded tendons in the tension zone may be assumed to contribute to crack control within a distance 5 150 mm from the centre of the tendon. (4) In prestressed members, no minimum reinforcement is required in sections where, under the characteristic combination of loads and the characteristic value of prestress, the con- crete is compressed or the absolute value of the tensile stress in the concrete is below a given value. Eurocode 2 7.3 Crack control 7.3.3 Control of cracking without direct calculation (101) The control of cracking without direct calculation may be performed by means of simplified methods. A recommended method is given with several sub-clauses indicating where crack control is deemed to be adequate, provided relevant detailing rules have been followed. Eurocode 2 7.3 Crack control 7.3.4 Calculation of crack widths (101) The evaluation of crack width may be performed using recognized methods. NOTE: Details of recognized methods for crack width control may be found in a country’s National Annex. The recommended method is that in EN 1992-1-1, 7.3.4. (continued) (continued on next page)

280 Table A.3. Summary of Clauses Relating to the Serviceability Limit State Design of Concrete Bridges in Eurocode EN 1992-1 Eurocode Article Basic Provision Discussion Eurocode 2 7.4 Deflection control 7.4.1 General considerations (1) P The deformation of a member or structure shall not be such that it adversely affects its proper functioning or appearance. (2) Appropriate limiting values of deflection taking into account the nature of the structure, of the finishes, partitions and fixings and upon the function of the structure should be established. Eurocode 2 7.4 Deflection control 7.4.3 Checking deflections by calculation (1)P Where a calculation is deemed necessary, the deformations shall be calculated under load conditions which are appropriate to the purpose of the check. (2) P The calculation method adopted shall represent the true behavior of the structure under rel- evant actions to an accuracy appropriate to the objectives of the calculation. (3) Members which are not expected to be loaded above the level which would cause the tensile strength of the concrete to be exceeded anywhere within the member should be considered to be uncracked. Members which are expected to crack, but may not be fully cracked, will behave in a manner intermediate between the uncracked and fully cracked conditions. And for mem- bers subjected mainly to flexure, an adequate prediction of behavior is given by Expression (7.18) presented in EN 1992-1.1. (4) Deformations due to loading may be assessed using the tensile strength and modulus of elasticity of the concrete [see (5)]. (5) For loads with a duration causing creep, the total deformation including creep may be calcu- lated by using an effective modulus of elasticity for concrete according to Expression (7.20) presented in EN 1992-1.1. (6) Shrinkage curvatures may be assessed using Expression (7.21) presented in EN 1992-1.1. (7) The most rigorous method of assessing deflections using the method given in (3) above is to compute the curvatures at frequent sections along the member and then calculate the deflec- tion by numerical integration. In most cases it will be acceptable to compute the deflection twice, assuming the whole member to be in the uncracked and fully cracked condition in turn, and then interpolate using Expression (7.1 8). Eurocode 2 Section 8 Detailing of reinforcement and prestressing tendons— General No rules peculiar to the serviceability limit state are given. Eurocode 2 Section 9 Detailing of members and particular rules 9.1 General (103) Minimum areas of reinforcement are given to prevent a brittle failure and wide cracks and also to resist forces arising from restrained actions. NOTE: Additional rules concerning the minimum thickness of structural elements and the minimum reinforcement for all surfaces of members in bridges, with minimum bar diameter and maximum bar spacing for use in a country may be found in its National Annex. No addi- tional rules are recommended in this standard. Eurocode 2 Section 10 Additional rules for precast concrete elements and structures 10.3 Materials 10.3.1 Concrete 10.3.1.1 Strength (1) For precast products in continuous production, subjected to an appropriate quality control system according to the product standards, with the concrete tensile strength tested, a statistical analysis of test results may be used as a basis for the evaluation of the tensile strength that is used for serviceability limit states verifications, as an alternative to Table 3.1. (2) Intermediate strength classes within Table 3.1 may be used. Eurocode 2 Section 11 Lightweight aggregate concrete structures 11.7 Serviceability limit states (1) P The basic ratios of span/effective depth for reinforced concrete members without axial compression, given in 7.4.2, should be reduced by a factor when applied to LWAC [light- weight aggregate concrete]. (continued) (continued on next page)

281 Table A.3. Summary of Clauses Relating to the Serviceability Limit State Design of Concrete Bridges in Eurocode EN 1992-1 Eurocode Article Basic Provision Discussion Eurocode 2 Section 12 Plain and lightly reinforced concrete structures 12.1 General (4) Members using plain concrete do not preclude the provision of steel reinforcement needed to satisfy serviceability and/or durability requirements, nor reinforcement in certain parts of the members. This reinforcement may be taken into account for the verification of local ultimate limit states as well as for the checks of the serviceability limit states. Eurocode 2 12.5 Structural analysis: ultimate limit states (1) Since plain concrete members have limited ductility, linear analysis with redistri- bution or a plastic approach to analysis (e.g. methods without an explicit check of the deformation capacity) should not be used unless their application can be justified. (2) Structural analysis may be based on the non-linear or the linear elastic theory. In the case of a non-linear analysis (e.g. fracture mechanics) a check of the deformation capacity should be carried out. Eurocode 2 12.7 Serviceability limit states (1) Stresses should be checked where structural restraint is expected to occur. (2) The following measures to ensure adequate serviceability should be considered: a) with regard to crack formation, – limitation of concrete tensile stresses to acceptable values, – provision of subsidiary structural reinforcement (surface reinforcement, tying system where necessary), – provision of joints, – choice of concrete technology (e.g. appropriate concrete composition, curing), and – choice of appropriate method of construction. b) with regard to limitation of deformations, – a minimum section size, and – limitation of slenderness in the case of compression members. (3) Any reinforcement provided in plain concrete members, although not taken into account for load bearing purposes, should comply with 4.4.1. Eurocode 2 Section 113 Design for the execution stages 113.3 Verification criteria 113.3.2 Serviceability limit states (101) The verifications for the execution stage should be the same as those for the completed structure, with the following exceptions. (102) Serviceability criteria for the completed structure need not be applied to intermediate exe- cution stages, provided that durability and final appearance of the completed structure are not affected (e.g. deformations). (103) Even for bridges or elements of bridges in which the limit state of decompression is checked under the quasi-permanent or frequent combination of actions on the completed structure, tensile stresses less than k.fctm(t) under the quasi-permanent combination of actions during execution are permitted. NOTE: The value of k to be used in a country may be found in its National Annex. The recommended value of k is 1.0. (104) For bridges or elements of bridges in which the limit-state of cracking is checked under frequent combination on the completed structure, the limit state of cracking should be verified under the quasi-permanent combination of actions during execution. Eurocode 2 Annex B (informative) Creep and shrinkage strain B.100 General (101) This Annex may be used for calculating creep and shrinkage, including development with time. However, typical experimental values can exhibit a scatter of ±30% around the values of creep and shrinkage predicted in accordance with this Annex. Where greater accuracy is required due to the structural sensitivity to creep and/or shrinkage, an experimental assess- ment of these effects and of the development of delayed strains with time should be under- taken. Section B.104 includes guidelines for the experimental determination of creep and shrinkage coefficients. (continued) (continued on next page)

282 Table A.3. Summary of Clauses Relating to the Serviceability Limit State Design of Concrete Bridges in Eurocode EN 1992-1 Eurocode Article Basic Provision Discussion Eurocode 2 Annex E (informative) Indicative strength classes for durability E.1 General (1) The choice of adequately durable concrete for corrosion protection of reinforcement and pro- tection of concrete attack requires consideration of the composition of concrete. This may result in a higher compressive strength of the concrete than is required for structural design. The relationship between concrete strength classes and exposure classes (see Table 4.1) may be described by indicative strength classes. (2) When the chosen strength is higher than that required for structural design, the value of fctm should be associated with the higher strength in the calculation of minimum reinforcement according to 7.3.2 and 9.2.1.1 and crack width control according to 7.3.3 and 7.3.4. Eurocode 2 Annex F (informative) Tension reinforcement expressions for in-plane stress conditions F.1 General To avoid unacceptable cracks for the serviceability limit state, and to ensure the required deforma- tion capacity for the ultimate limit state, the reinforcement derived from Expressions (F.8) and (F.9) for each direction should not be more than twice and not less than half the reinforcement determined by Expressions (F.2) and (F.3) or (F.5) and (F.6). Eurocode 2 Annex G (informative) Soil structure interaction G.1 Shallow foundations G.1.1 General (1) The interaction between the ground, the foundation, and the superstructure should be con- sidered. The contact pressure distribution on the foundations and the column forces are both dependent on the relative settlements. More guidance is given in this annex. Eurocode 2 G.1.2 Levels of analysis (1) For design purposes, various levels of analysis are permitted, depending on conditions at both the serviceability and the ultimate limit states. More guidance is given. Eurocode 2 Annex KK (informative) Structural effects of time-dependent behavior of concrete KK.1 Introduction This Annex describes different methods of evaluating the time-dependent effects of concrete behavior. Eurocode 2 KK.2 General considerations (101) Structural effects of time-dependent behavior of concrete, such as variation of deformation and/or of internal actions, shall be considered, in general, in serviceability conditions. NOTE: In particular cases (e.g. structures or structural elements sensitive to second order effects or structures in which action effects cannot be redistributed), time-dependent effects may also have an influence at ULS. (102) It is noted that for higher compressive stresses, non-linear creep effects should be considered. (104) Different types of analysis and their typical applications are shown in a table. Brief outline details of some of the analysis methods are given in the sections that follow. Eurocode 2 Annex QQ (informative) Control of shear cracks within webs At present, the prediction of shear cracking in webs is accompanied by large model uncer- tainty. Where it is considered necessary to check shear cracking, particularly for prestressed members, the reinforcement required for crack control can be determined. Some detailed guidance is given. (continued)

283 A.5 EN 1993 Eurocode 3: Design of Steel Structures The scope of EN 1993 is wider than most of the other design Eurocodes due to the diversity of steel structures. This Euro- code covers both bolted and welded joints, and the possible slenderness of construction. The differences when compared with existing British standards are that the Eurocode brings new methods into the scope. For example, the design of semi-rigid joints in buildings is explained, and more advanced methods of design for cold-formed steelwork are included. The rules for shell structures and for the design of piles, sheet piling, and silos are new, and rules for stainless steel appear for the first time. EN 1993 has 20 parts covering common rules for fire design, bridges, buildings, tanks, silos, pipelined piling, crane supported structures, chimneys, towers and masts, and so on, as in the following list. Those underlined have been reviewed in the compilation of this report. EN 1993-1.1:2005 Design of steel structures. General rules and rules for buildings EN 1993-1.2:2005 Design of steel structures. General rules. Structural fire design EN 1993-1.3:2006 Design of steel structures. General rules. Supplementary rules for cold- formed members and sheeting EN 1993-1.4:2006 Design of steel structures. General rules. Supplementary rules for stainless steels EN 1993-1.5:2006 Design of steel structures. Plated struc- tural elements EN 1993-1.6:2007 Design of steel structures. General. Strength and stability of shell structures EN 1993-1.7:2007 Design of steel structures. General. Plated structures subject to out of plane loading EN 1993-1.8:2005 Design of steel structures. Design of joints EN 1993-1.9:2005 Design of steel structures. Fatigue strength EN 1993-1.10:2005 Design of steel structures. Material toughness and through-thickness properties EN 1993-1.11:2006 Design of steel structures. Design of structures with tension components EN 1993-1.12:2007 Design of steel structures. Additional rules for the extension of EN 1993 up to steel grades S 700 EN 1993-2:2006 Design of steel structures. Steel bridges EN 1993-3.1:2007 Design of steel structures. Towers, masts, and chimneys. Towers and masts EN 1993-3.2:2008 Design of steel structures. Towers, masts, and chimneys. Chimneys EN 1993-4.1:2007 Design of steel structures. Silos, tanks, and pipelines. Silos EN 1993-4.2:2007 Design of steel structures. Silos, tanks, and pipelines. Tanks EN 1993-4.3:2007 Design of steel structures. Silos, tanks, and pipelines. Pipelines EN 1993-5:2007 Design of steel structures. Piling EN 1993-6:2007 Design of steel structures. Crane sup- porting structures Note also EN 1090-2:2008 Execution of steel structures and aluminum structures. Technical requirements for the execution of steel structures PD 6695-1.9:2008 Recommendations for the design of structures to BS EN 1993-1.9 PD 6695-1.10:2009 Recommendations for the design of structures to BS EN 1993-1.10 PD 6695-2:2008 Recommendations for the design of bridges to BS EN 1993 EN 1993-2:2006 (Design of steel structures. Steel bridges) pro- vides a general basis for the structural design of steel bridges and steel parts of composite bridges. EN 1993-2 gives design rules which are supplementary to the generic rules in EN 1993-1-1. EN 1993-2 is intended to be used with Eurocodes EN 1990 (Basis of design), EN 1991 (Actions on structures), and the Parts 2 of EN 1992 to EN 1998 when steel structures or steel components for bridges are referred to. Matters that are already covered in those documents are not repeated within EN 1993-2. Sections from this standard (and, where noted, the other highlighted parts of EN 1993) relating to the serviceability limit state are summarized in Table A.4. A.6 EN 1994 Eurocode 4: Design of Composite Steel and Concrete Structures Eurocode 4 applies to the design of composite structures and members for buildings and civil engineering works. It com- plies with the principles and requirements for the safety and serviceability of structures, the basis of their design, and veri- fication that are given in EN 1990:2002 (Basis of structural design). Eurocode 4 is concerned only with requirements for resistance, serviceability, durability, and fire resistance of composite structures. Other requirements (e.g. concerning thermal or sound insulation) are not considered. Eurocode 4 is intended to be used in conjunction with EN 1990 Basis of structural design EN 1991 Actions on structures (text continues on page 289)

284 Table A.4. Summary of Clauses Relating to the Serviceability Limit State Design of Steel Bridges in Eurocode EN 1993-1 and 1993-2 Eurocode Article Basic Provision Discussion Eurocode 3 Section 2 Basis of design and modeling 2.1 General EN 1993-1.5 (Plated structural elements) stipulates (1) P The effects of shear lag and plate buckling shall be taken into account at the ultimate, service ability, or fatigue limit states. EN 1993-1.11 (Tension components) stipulates 2.2(1)P Due to the difficulties in modeling the excitation characteristics of tension elements, service- ability limit state checks should be carried out in addition to fatigue checks. 2.2(3) Any attachments to prefabricated tension components, such as saddles or clamps, should be designed for ultimate limit states and serviceability limit states using the breaking strength or proof strength of cables as actions; see Section 6. For fatigue see EN 1993-1-9. NOTE: Fatigue action on the ropes is governed by the radius in the saddle or anchorage area (see Figure 6.1 for minimum radius). Eurocode 3 2.3 Plate buckling effects on uniform members EN 1993-1.5 (Plated structural elements) stipulates (2) For the calculation of stresses at the serviceability and fatigue limit state the effective area may be used if the condition in 3.1 is fulfilled. For ultimate limit states the effective area according to 3.3 should be used with b replaced by bult. Eurocode 3 Section 3 Shear lag in member design 3.1 General EN 1993-1.5 (Plated structural elements) stipulates (1) Shear lag in flanges may be neglected if b0 < Le/50 where b0 is taken as the flange outstand or half the width of an internal element and Le is the length between points of zero bending moment; see 3.2.1(2). (2) Where the above limit for b0 is exceeded, the effects due to shear lag in flanges should be considered at serviceability and fatigue limit state verifications by the use of an effective width according to 3.2.1 and a stress distribution according to 3.2.2. For the ultimate limit state verification an effective area according to 3.3 may be used. Eurocode 3 3.2 Effective width for elastic shear lag 3.2.1 Effective width EN 1993-1.5 (Plated structural elements) stipulates (1) The effective width beff for shear lag under elastic conditions should be determined from beff = b b0 (3.1) where the effective factor b is given in Table 3.1. This effective width may be relevant for serviceability and fatigue limit states. EN 1993-1.5 Annex E gives alternative methods for determining effective cross sections. It gives a calculation for the serviceability limit slenderness to give effective area for stiffness. It also gives that (3) The effective second moment of area Ieff may be taken as variable along the span according to the most severe locations. Alternatively a uniform value may be used based on the maxi- mum absolute sagging moment under serviceability loading. Eurocode 3 Section 4 Durability (6) Components that cannot be designed with sufficient reliability to achieve the total design working life of the bridge should be replaceable. These may include – stays, cables, hangers; – bearings; – expansion joints; – drainage devices; – guardrails, parapets; – asphalt layer and other surface protection; – wind shields; and – noise barriers. EN 1993-1.11 (Tension components) contains a section (4) devoted to durability of wires, ropes, and strands. This gives details of corrosion protection for the three classes of tension components defined at the beginning of this standard. EN 1993-1.11 (Tension components) covers transport, storage, and handling of tension components in its Annex B (informative). (continued on next page)

285 (continued) Table A.4. Summary of Clauses Relating to the Serviceability Limit State Design of Steel Bridges in Eurocode EN 1993-1 and 1993-2 Eurocode Article Basic Provision Discussion Eurocode 3 Section 7 Serviceability limit states 7.1 General (1) A steel structure should be designed and constructed such that all relevant serviceability cri- teria are satisfied. (2) The basic requirements for serviceability limit states are given in 3.4 of EN 1990. (3) Any serviceability limit state and the associated loading and analysis model should be speci- fied for a project. (4) The following serviceability criteria should be met: a) Restriction to elastic behavior to limit – excessive yielding, see 7.3(1); – deviations from the intended geometry by residual deflections, see 7.3(1); and – excessive deformations, see 7.3(4). b) Limitation of deflections and curvature to prevent – unwanted dynamic impacts due to traffic (combination of deflection and natural fre- quency limitations), see 7.7 and 7.8; – infringement of required clearances, see 7.5 or 7.6; – cracking of surfacing layers, see 7.8; and – damage of drainage, see 7.12. c) Limitation of natural frequencies (see 7.8 and 7.9) to – exclude vibrations due to traffic or wind which are unacceptable to pedestrians or pas- sengers in cars using the bridge; – limit fatigue damages caused by resonance; and – limit excessive noise emission. d) Restriction of plate slenderness (see 7.4) to limit – excessive rippling of plates; – breathing of plates; and – reduction of stiffness due to plate buckling, resulting in an increase of deflection, see EN 1993-1-5. e) Improved durability by appropriate detailing to reduce corrosion and excessive wear; see 7.11. f) Ease of maintenance and repair (see 7.11) to ensure – accessibility of structural parts for maintenance and inspection, renewal of corrosion protection and asphaltic pavements; and – replacement of bearings, anchors, cables, expansion joints with minimum disruption to the use of the structure. (5) In most situations serviceability aspects should be dealt with in the conceptual design of the bridge, or by suitable detailing. However, in appropriate cases, serviceability limit states may be verified by numerical assessment (e.g. for calculating deflections or Eigen frequencies). NOTE: The National Annex may give guidance on serviceability requirements for specific types of bridges. EN 1993-1.11 (Tension components) stipulates 7.1(1) The following serviceability criteria should be considered: 1. Deformations or vibrations, and 2. Elastic service conditions. NOTE 1: Limits for deformations or vibrations may result in a stiffness requirement governed by the structural system, the dimensions and the preloading of high-strength tension compo- nents, and by the slipping resistance of attachments. NOTE 2: Limits to retain elastic behavior and durability are related to maximum and minimum values of stresses for serviceability load combinations. 7.1(2) Bending stresses in the anchorage zone may be reduced by suitable measures (e.g. neoprene pads for transverse loading). Eurocode 3 7.2 Calculation models (1) Stresses at serviceability limit states should be determined from a linear elastic analysis, using the appropriate section properties; see EN 1993-1-5. (2) In modeling the structure, the non-uniform distribution of loads and stiffness resulting from the changes in plate thickness, stiffening, etc. should be taken into account. (3) Deflections should be determined by linear elastic analysis using the appropriate section properties; see EN 1993-1-5. NOTE: Simplified calculation models may be used for stress calculations, provided that the effects of the simplification are conservative. (continued on next page)

286 Table A.4. Summary of Clauses Relating to the Serviceability Limit State Design of Steel Bridges in Eurocode EN 1993-1 and 1993-2 Eurocode Article Basic Provision Discussion Eurocode 3 7.3 Limitations for stress (1) The nominal stresses sEd.ser and tEd.ser resulting from the characteristic load combinations, cal- culated making due allowance for the effects of shear lag in flanges and the secondary effects caused by deflections (e.g. secondary moments in trusses), should be limited. The standard gives equations for maximum allowable stresses. NOTE 1: Where relevant, the above checks should include stresses sz from transverse loads; see EN 1993-1-5. NOTE 2: The National Annex may give the value for gMser. gMser = 1,00 is recommended. NOTE 3: Plate buckling effects may be ignored as specified in EN 1993-1-5, 2.2(5). (2) The nominal stress range Dsfre, due to the frequent load combination, should be limited to 1.5 fy/gMser; see EN 1993-1-9. (3) For non-preloaded bolted connections subject to shear, the bolt forces due to the character- istic load combination should be limited to Fb.Rd.ser ≤ 0.7 Fb.Rd (7.4) where Fb.Rd is the bearing resistance for ultimate limit states verifications. (4) For slip-resistant preloaded bolted connections category B (slip-resistant at serviceability, see EN 1993-1-8), the assessment for serviceability should be carried out using the charac- teristic load combination. EN 1993-1.11 (Tension components) stipulates 7.2(1) Limiting stress may be specified for the characteristic load combination for the following purposes: – to keep stresses in the elastic range for the relevant design situations during construc- tion and in the service phase; – to limit strains such that corrosion control measures are not affected (i.e., cracking of sheaths, hard fillers, opening of joints) and also to cater for uncertainty in the fatigue design; – ULS verifications for linear and sub-linear structural response to actions. Numeric values of limiting stress in the serviceability limit state are given. Eurocode 3 7.4 Limitation of web breathing (1) The slenderness of web plates should be limited to avoid excessive breathing that might result in fatigue at or adjacent to the web-to-flange connections. NOTE: The National Annex may define cases where web breathing checks are not necessary. (2) Web breathing may be neglected for web panels without longitudinal stiffeners or for subpan- els of stiffened webs, where certain criteria are met. (Criteria for road bridges and for rail bridges are given in the standard. If the criteria are not met, a method for checking web breathing is given.) NOTE also EN 1993-1.7 (Plated structures subject to out of plane loading) gives a note (8.2) on the out of plane deflection limit as the condition in which the effective use of a plate segment is ended. Eurocode 3 7.6 Limits for visual impression (1) To achieve a satisfactory appearance of the bridge, consideration should be given to precambering. (2) In calculating camber, the effects of shear deformation and slip in riveted or bolted connec- tions should be considered. (3) For connections with rivets or fitted bolts, a fastener slip of 0.2 mm should be assumed. For preloaded bolts, slip does not need to be considered. Eurocode 3 7.8 Performance criteria for road bridges 7.8.1 General (1) Excessive deformation should be avoided where it could – endanger traffic by excessive transverse slope when the surface is iced; – affect the dynamic load on the bridge by impact from wheels; – affect the dynamic behavior causing discomfort to users; – lead to cracks in asphaltic surfacing; – adversely affect the drainage of water from the bridge deck. NOTE: For durability requirements, see Annex C. (continued) (continued on next page)

287 Table A.4. Summary of Clauses Relating to the Serviceability Limit State Design of Steel Bridges in Eurocode EN 1993-1 and 1993-2 Eurocode Article Basic Provision Discussion (2) Deformations should be calculated using the frequent load combination. (3) The natural frequency of vibrations and deflections of the bridge should be limited to avoid discomfort to users. NOTE also EN 1993-1.7 (Plated structures subject to out of plane loading) gives guid- ance on excessive vibration limits: 8.3(1) Excessive vibrations should be defined as the limit condition in which either the failure of a plated structure occurs by fatigue caused by excessive vibrations of the plate or serviceability limits apply. EN 1993-1.11 (Tension components) contains a section (8) devoted to vibration of cables. A general section is followed by a section on measures to limit vibration of cables and a section giving estimation of risks. Eurocode 3 7.8.2 Deflection limits to avoid excessive impact from traffic (1) The deck structure should be designed to ensure that its deflection along the length is uni- form and that there is no abrupt change in cross section giving rise to impact. Sudden changes in the slope of the deck and changes of level at the expansion joints should be elimi- nated. Any transverse girders at the end of the bridge should be designed to ensure that the deflection does not exceed – the limit specified for the proper functioning of the expansion joint; – 5 mm under frequent loads unless other limits are specified for the particular type of expansion joint. NOTE: Guidance on the deflection limit of expansion joints is given in Annex B. (2) Where the deck structure is irregularly supported (e.g. by additional bracings at intermediate bridge piers), the deck area adjacent to these additional deck supports should be designed for the enhanced impact factors given in EN 1991-2 for the area close to the expansion joints. Eurocode 3 7.8.3 Resonance effects (1) Mechanical resonance should be taken into account when relevant. Where light bracing members, cable stays, or similar components have natural frequencies that are close to the frequency of any mechanical excitation due to regular passage of vehicles over deck joints, consideration should be given to either increasing the stiffness or providing artificial dampers (i.e. oscillation dampers). NOTE: Guidance on members supporting expansion joints is given in Annex B. Eurocode 3 7.12 Drainage (1) All decks should be waterproofed, and the surfaces of carriageways and footpaths should be sealed to prevent the ingress of water. (2) The layout of the drainage should take into account the slope of the bridge deck as well as the location, diameter, and slope of the pipes. (3) Free fall drains should carry water to a point clear of the underside of the structure to prevent water entering into the structure. (4) Drainage pipes should be designed so that they can be cleaned easily. The distance between centers of the cleaning openings should be shown on drawings. (5) Where drainage pipes are used inside box girder bridges, provisions should be made to pre- vent accumulation of water during leaks or breakage of pipes. (6) For road bridges, drains should be provided at expansion joints on both sides where [it] is appropriate. (7) Provision should be made for the drainage of all closed cross sections, unless these are fully sealed by welding. Eurocode 3 Section 8 Fasteners, welds, connections, and joints 8.1 Connections made of bolts, rivets, and pins 8.1.1 Categories of bolted connections EN 1993-1.8 (Design of joints) stipulates 3.4 Categories of bolted connections 3.4.1 Shear connections (1) Bolted connections loaded in shear should be designed as one of the following: a) Category A: Bearing type In this category, bolts from Class 4.6 up to and including Class 10.9 should be used. No preloading and special provisions for contact surfaces are required. The design ultimate shear load should not exceed the design shear resistance, obtained from 3.6, nor the design bearing resistance, obtained from 3.6 and 3.7. (continued) (continued on next page)

288 Table A.4. Summary of Clauses Relating to the Serviceability Limit State Design of Steel Bridges in Eurocode EN 1993-1 and 1993-2 Eurocode Article Basic Provision Discussion b) Category B: Slip-resistant at serviceability limit state In this category, preloaded bolts in accordance with 3.1.2(1) should be used. Slip should not occur at the serviceability limit state. The design serviceability shear load should not exceed the design slip resistance, obtained from 3.9. The design ultimate shear load should not exceed the design shear resistance, obtained from 3.6, nor the design bearing resistance, obtained from 3.6 and 3.7. c) Category C: Slip-resistant at ultimate limit state In this category, preloaded bolts in accordance with 3.1.2(1) should be used. Slip should not occur at the ultimate limit state. The design ultimate shear load should not exceed the design slip resistance, obtained from 3.9, nor the design bearing resistance, obtained from 3.6 and 3.7. In addition, for a connection in tension, the design plastic resistance of the net cross section at bolt holes Nnet.Rd , (see 6.2 of EN 1993-1-1), should be checked, at the ultimate limit state. 3.4.2 Tension connections (1) Bolted connection loaded in tension should be designed as one of the following: a) Category D: Non-preloaded In this category, bolts from Class 4.6 up to and including Class 10.9 should be used. No preloading is required. This category should not be used where the connections are fre- quently subjected to variations of tensile loading. However, they may be used in connec- tions designed to resist normal wind loads. b) Category E: Preloaded In this category, preloaded 8.8 and 10.9 bolts with controlled tightening in conformity with 1.2.7 Reference Standards: Group 7 should be used. The design checks for these connections are summarized in Table 3.2. Eurocode 3 Section 9 Fatigue assessment 9.1 General 9.1.1 Requirements for fatigue assessment (1) Fatigue assessments should be carried out for all critical areas in accordance with EN 1993-1.9. (2) Fatigue assessment is not applicable to – pedestrian bridges, bridges carrying canals, or other bridges that are predominantly stati- cally loaded, unless such bridges or parts of them are likely to be excited by wind loads or pedestrians; – parts of railway or road bridges that are neither stressed by traffic loads nor likely to be excited by wind loads. NOTE that EN 1993-1.9 (Fatigue) specifies that the actions applied for a fatigue limit state verification are different from those used for ultimate limit state or for serviceability state. However, the stresses should be calculated at the serviceability state [Clause 5(1)]. NOTE that EN 1993-1.11 (Tension components) comments [2.2(1)P] that, due to the diffi- culties in modeling the excitation characteristics of tension elements, serviceability limit state checks should be carried out in addition to fatigue checks. Eurocode 3 9.1.2 Design of road bridges for fatigue (1) Fatigue assessments should be carried out for all bridge components unless the structural detailing complies with standard requirements for durable structures established through testing. NOTE: The National Annex may give guidance on the conditions where no fatigue assess- ment is necessary. (2) Fatigue assessment should be carried out using the procedure given in this section and EN 1993-1-9. Eurocode 3 Section 10 Design assisted by testing 10.1 General (1) Design can be assisted by testing. If so, it should be in accordance with EN 1990, supple- mented by the additional provisions given in 10.2 and 10.3. (continued)

289 European Standards (ENs), Harmonized European Standards (hENs), Guidelines for European Technical Approval (ETAGs), and European Technical Approvals (ETAs) for construction products relevant for composite structures EN 1090 Execution of steel structures and aluminum structures EN 13670 Execution of concrete structures EN 1992 Design of concrete structures EN 1993 Design of steel structures EN 1997 Geotechnical design EN 1998 Design of structures for earthquake resistance EN 1994 has three parts covering common rules and rules for buildings, structural fire design, and bridges, as in the fol- lowing list. Those underlined have been reviewed in the com- pilation of this report. EN 1994-1.1:2004 Design of composite steel and concrete structures. General rules and rules for buildings EN 1994-1.2:2005 Design of composite steel and concrete structures. General rules. Structural fire design EN 1994-2:2005 Design of composite steel and concrete structures. General rules and rules for bridges Note also PD 6696-2:2007 Recommendations for the design of structures to BS EN 1994-2:2005 EN 1994-2 describes the principles and requirements for safety, serviceability, and durability of composite steel and con- crete structures, together with specific provisions for bridges. It is based on the limit state concept used in conjunction with a partial factor method. It gives design rules for steel-concrete composite bridges or members of bridges, additional to the general rules in EN 1994-1-1. Cable stayed bridges are not fully covered by this part. EN 1994-2 contains the general rules from EN 1994-1-1 as well as the specific rules for the design of composite steel and concrete bridges or composite members of bridges. EN 1994-2 is intended to be used with EN 1990, the relevant parts of EN 1991, EN 1992 for the design of concrete structures, and EN 1993 for the design of steel structures. Sections from this standard (and, where noted, the other highlighted recommendations) relating to the serviceability limit state are summarized in Table A.5. Table A.5. Summary of Clauses Relating to Serviceability Limit State Design of Composite Steel and Concrete Bridges in Eurocode EN 1994-2 Eurocode Article Basic Provision Discussion Eurocode 4 Section 2 Basis of design 2.1 Requirements (3) The basic requirements of EN 1990:2002, Section 2 are deemed to be satisfied for composite structures when the following are applied together: – limit state design in conjunction with the partial factor method in accordance with EN 1990:2002; – actions in accordance with EN 1991; – combination of actions in accordance with EN 1990:2002; and – resistances, durability, and serviceability in accordance with this standard. Eurocode 4 2.3.3 Classification of actions (1) P The effects of shrinkage and creep of concrete and non-uniform changes of temperature result in internal forces in cross sections, and curvatures and longitudi- nal strains in members; the effects that occur in statically determinate structures, and in statically indeterminate structures when compatibility of the deformations is not considered, shall be classified as primary effects. (2) P In statically indeterminate structures the primary effects of shrinkage, creep, and temperature are associated with additional action effects, such that the total effects are compatible; these shall be classified as secondary effects and shall be consid- ered as indirect actions. Eurocode 4 4.2 Corrosion protection at the steel-concrete interface in bridges (1) The corrosion protection of the steel flange should extend into the steel-concrete interface at least 50 mm. For additional rules for bridges with precast deck slabs, see Section 8. Eurocode 4 Section 7 Serviceability limit states 7.2 Stresses 7.2.1 General (1) P Calculation of stresses for beams at the serviceability limit state shall take into account the following effects, where relevant: – shear lag; – creep and shrinkage of concrete; – cracking of concrete and tension stiffening of concrete; – sequence of construction; (continued on next page) (continued from page 283)

290 Table A.5. Summary of Clauses Relating to Serviceability Limit State Design of Composite Steel and Concrete Bridges in Eurocode EN 1994-2 Eurocode Article Basic Provision Discussion – increased flexibility resulting from significant incomplete interaction due to slip of shear connection; – inelastic behavior of steel and reinforcement, if any; – torsional and distorsional warping, if any. (2) Shear lag may be taken into account according to 5.4.1.2. (3) Unless a more accurate method is used, effects of creep and shrinkage may be taken into account by use of modular ratios according to 5.4.2.2. (4) In cracked sections, the primary effects of shrinkage may be neglected when verify- ing stresses. (5)P In section analysis, the tensile strength of concrete shall be neglected. (6) The influence of tension stiffening of concrete between cracks on stresses in rein- forcement and prestressing steel should be taken into account. Unless more accu- rate methods are used, the stresses in reinforcement should be determined according to 7.4.3. (7) The influences of tension stiffening on stresses in structural steel may be neglected. (8) Stresses in the concrete slab and its reinforcement caused by simultaneous global and local actions should be added. Eurocode 4 7.2 Stresses 7.2.2 Stress limitation for bridges (1) P Excessive creep and microcracking shall be avoided by limiting the compressive stress in concrete. (2) Stress limitation for concrete to the value k1 fck should be in accordance with EN 1991-1-1:2002, 7.2, as modified by EN 1992-2. (3) P The stress in reinforcing steel and in prestressing tendons shall be such that inelastic strains in the steel are avoided. (4) Under the characteristic combination of actions, the stresses should be limited to k1 fsk in reinforcing steel and to k5 fpk in tendons, where the values k1 and k5 are given in EN 1992-1-1:2004, 7.2(5). (5) The stresses in structural steel should be in accordance with EN 1993-2, 7.3. (6) For serviceability limit states, the longitudinal shear force per connector should be limited according to 6.8.1 (3). Eurocode 4 7.2.3 Web breathing (1) The slenderness of unstiffened or stiffened web plates of composite girders should be limited according to 7.4 of EN 1993-2. Eurocode 4 7.3 Deformations in bridges 7.3.1 Deflections (1) For the limit state of deformation, EN 1990:2002; A2.4 of Annex A2; and EN 1993-2, 7.5 to 7.8 and 7.12 apply where relevant. (2) Deflections should be calculated using elastic analysis in accordance with Section 5. (3) Deformations during construction should be controlled such that the concrete is not impaired during its placing and setting by uncontrolled displacements and the required long-term geometry is achieved. Eurocode 4 7.3.2 Vibrations (1) For the limit state of vibration, EN 1990:2002; A2.4 of Annex A2; EN 1991-2:2003, 5.7 and 6.4; and EN 1993-2, 7.7 to 7.10 apply where relevant. Eurocode 4 7.4 Cracking of concrete 7.4.1 General (1) For the limitation of crack width in bridges, the general considerations of EN 1992-1- 1:2004, 7.3.1 as modified in EN 1992-2 apply to composite structures. The limitation of crack width depends on the exposure classes according to EN 1992-2, 4. (2) An estimation of crack width can be obtained from EN 1992-1-1:2004, 7.3.4, where the stress ss should be calculated by taking into account the effects of tension stiffening. Unless a more precise method is used, ss may be determined according to 7.4.3(3). (3) As a simplified and conservative alternative, crack width limitation to acceptable width can be achieved by ensuring a minimum reinforcement defined in 7.4.2, and bar spacing or diameters not exceeding the limits defined in 7.4.3. (4) Application rules for the limitation of crack widths to wk are given in 7.4.2 and 7.4.3. NOTE: The values of wk and the combination of actions may be found in the National Annex. The recommended values for relevant exposure classes are as given (as wmax) in the note to EN 1992-2, 7.3.1(105). (continued) (continued on next page)

291 Table A.5. Summary of Clauses Relating to Serviceability Limit State Design of Composite Steel and Concrete Bridges in Eurocode EN 1994-2 Eurocode Article Basic Provision Discussion (5) Where composite action becomes effective as concrete hardens, effects of heat of hydration of cement and corresponding thermal shrinkage should be taken into account only during the construction stage for the serviceability limit state to define areas where tension is expected. (6) Unless specific measures are taken to limit the effects of heat of hydration of cement, for simplification a constant temperature difference between the concrete section and the steel section (concrete cooler) should be assumed for the determi- nation of the cracked regions according to 7.4.2 (5) and for limitation of crack width according to 7.4.2 and 7.4.3. For the determination of stresses in concrete, the short-term modulus should be used. NOTE: The National Annex may give specific measures and a temperature differ- ence. The recommended value for the temperature difference is 20K. Eurocode 4 7.4.2 Minimum reinforcement (1) Unless a more accurate method is used in accordance with EN 1992-1-1:2004, 7.3.2(1), in all sections without prestressing by tendons and subjected to significant tension due to restraint of imposed deformations (e.g. primary and secondary effects of shrinkage), in combination or not with effects of direct loading, the required mini- mum reinforcement area As for the slabs of composite beams is given in this section together with rules on its placement. Eurocode 4 7.4.3 Control of cracking due to direct loading (1) Where at least the minimum reinforcement given by 7.4.2 is provided, the limitation of crack widths to acceptable values may generally be achieved by limiting bar spacing or bar diameters. Maximum bar diameter and maximum bar spacing depend on the stress ss in the reinforcement and the design crack width are given in tables. (2) The internal forces should be determined by elastic analysis in accordance with Sec- tion 5, taking into account the effects of cracking of concrete. The stresses in the reinforcement should be determined taking into account effects of tension stiffening of concrete between cracks. Unless a more precise method is used, the stresses may be calculated according to the method given in (3). Eurocode 4 7.5 Filler beam decks (a deck consisting of a rein- forced concrete slab and partially concrete-encased rolled or welded steel beams, having their bot- tom flange on the level of the slab bottom) 7.5.1 General (1) The action effects for the serviceability limit states should be determined according to paragraphs given earlier in the standard (5.4.2.9). Rules for cracking of concrete, minimum reinforcement, and control of cracking due to direct loading are also given for filler beam decks in this section. Guidance for transverse filler beams is given in PD 6696-2:2007. It indicates that for the determination of stresses in the concrete slab and steel beams, the concrete slab and steel beams should be considered to be • non-composite at ultimate limit state (ULS) • composite and to have equal deflections at serviceability limit state (SLS). Eurocode 4 Section 9 Composite plates in bridges 9.1 General 9.4 Design of shear connectors (1)P Resistance to fatigue and requirements for serviceability limit states shall be verified for the combined local and simultaneous global effect. (continued)