1、PD 6687-2:2008 Recommendations for the design of structures to BS EN 1992-2:2005 ICS 91.010.30; 91.080.40; 93.040 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW PUBLISHED DOCUMENTPublishing and copyright information The BSI copyright notice displayed in this document indicate
2、s when the document was last issued. BSI 2008 ISBN 978 0 580 58681 1 The following BSI references relate to the work on this standard: Committee reference B/525/2 Publication history First published July 2008 Amendments issued since publication Amd. no. Date Text affected PD 6687-2:2008 BSI 2008 i P
3、D 6687-2:2008 Contents Foreword ii Introduction 1 1 Scope 1 2 General 2 3 Basis of design 2 4 Materials 3 5 Durability and cover to reinforcement 4 6 Structural analysis 4 7 Ultimate limit states 9 8 Serviceability limit states 19 9 Detailing of reinforcement and prestressing tendons General 20 10 D
4、etailing of members and particular rules 24 11 Additional rules for precast concrete elements and structures 27 12 Additional rules for external prestressing 28 Bibliography 29 List of figures Figure 1 Imperfections for pier built in at both ends 5 Figure 2 Limiting strain distributions 10 Figure 3
5、Illustration of increment size for shear reinforcement design 13 Figure 4 Reinforcement A swto include in punching check 16 Figure 5 Illustration of quadruply staggered laps 21 Figure 6 Corner pile within 2d of a column base 26 List of tables Table 1 Effective height, l 0 , for columns 8 Table 2A Li
6、miting stress ranges Longitudinal bending for unwelded reinforcing bars in road bridges 18 Table 2B Limiting stress ranges Transverse bending for unwelded reinforcing bars in road bridges 18 Table 3 Minimum spacing of post-tension ducts 23 Table 4 Minimum radius of curvature of tendons in the deviat
7、ors 24 Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 30, an inside back cover and a back cover.PD 6687-2:2008 ii BSI 2008 Foreword Publishing information This Published Document is published by BSI and came into effect on 31 July 2008. It w
8、as prepared by Subcommittee B/525/10, Bridges, under the authority of Subcommittee B/525/2, Structural use of concrete and Technical Committee B/525, Building and civil engineering. A list of organizations represented on this committee can be obtained on request to its secretary. Relationship with o
9、ther publications This Published Document gives non-contradictory complementary information for use in the UK with the Eurocode for concrete bridges, BS EN 1992-2 and its UK National Annex. Background is provided to some of the National Annex provisions where these differ from recommended values. Pr
10、esentational conventions The provisions in this standard are presented in roman (i.e. upright) type. Its recommendations are expressed in sentences in which the principal auxiliary verb is “should”. Commentary, explanation and general informative material is presented in smaller italic type, and doe
11、s not constitute a normative element. The word “should” is used to express recommendations of this standard. The word “may” is used in the text to express permissibility, e.g. as an alternative to the primary recommendation of the clause. The word “can” is used to express possibility, e.g. a consequ
12、ence of an action or an event. Notes and commentaries are provided throughout the text of this standard. Notes give references and additional information that are important but do not form part of the recommendations. Commentaries give background information. Contractual and legal considerations Thi
13、s publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. This Published Document is not to be regarded as a British Standard. BSI 2008 1 PD 6687-2:2008 Introduction When there is a need for guidance on a subject that is
14、not covered by the Eurocode, a country can choose to publish documents that contain non-contradictory complementary information that supports the Eurocode. This Published Document provides such information and has been cited as a reference in the UK National Annex to BS EN 1992-2. It is recommended
15、that reference also be made to PD 6687:2006 1)which contains non-contradictory complementary information that supports BS EN 1992-1. Parts of PD 6687:2006 are relevant to the design of structures to BS EN 1992-2. NOTE 1 Many of the clauses in BS EN 1992-1-1 are called up in BS EN 1992-2. Although th
16、e information provided in this Published Document relates to designs undertaken to BS EN 1992-2, for clarity, clause references are generally provided to the Eurocode part in which the relevant clause is given. NOTE 2 References are also included to papers and publications that provide additional ba
17、ckground or more detailed information associated with a specific issue. It should be noted that these papers and publications might also include material that is not fully in accordance with Eurocode requirements. 1 Scope This Published Document contains non-contradictory complementary information f
18、or use with BS EN 1992-2 and its UK National Annex for the design of concrete structures. It does not cover assessment. This Published Document gives: a) background to the decisions made in the National Annex to BS EN 1992-2 for some of the Nationally Determined Parameters; b) commentary on some spe
19、cific subclauses from BS EN 1992-2; c) commentary on the application to bridge structures of some specific subclauses of BS EN 1992-1-1 that are called up in BS EN 1992-2; d) guidance on subjects not covered by BS EN 1992-2, but previously included in British Standards and other standards and codes
20、of practice. 1) PD 6687:2006 is being revised and is to be renumbered PD 6687-1. PD 6687-2:2008 2 BSI 2008 2G e n e r a l 2.1 Definition of National Authority BS EN 1992-2:2005, Foreword Several clauses in BS EN 1992-2:2005 make reference to the “National Authority”. In UK there is no single such bo
21、dy and, therefore, the NA to BS EN 1992-2:2005 defines the National Authority as “the body with a statutory responsibility for the safety of the structure”. Such bodies will not necessarily have “national” coverage, for example in the case of a local Highway Authority. This definition aims to draw t
22、hose aspects of the design for which reference has to be made to the “National Authority” within established processes of technical approval. 3B a s i s o f d e s i g n 3.1 Actions and environmental influences BS EN 1992-1-1:2004, 2.3.1 BS EN 1992-1-1:2004, 2.3.1 allows thermal effects, settlements,
23、 and creep and shrinkage to be neglected at ultimate limit state provided they are not significant or because the ductility and rotation capacity of the elements affected are sufficient. In assessing whether the ductility and rotation capacity of elements are sufficient it should be noted that there
24、 will be additional demand on the rotation capacity: a) when moment redistribution is carried out; and, b) to cater for differences between the stiffnesses assumed in an elastic design and the true element stiffnesses as the ultimate limit state is approached. In the absence of a rigorous analysis,
25、for solid sections of constant width, b, it may be assumed that the rotation capacity required to accommodate the differences between the stiffnesses assumed in an elastic design and the true element stiffnesses will not exceed 50% of the allowable plastic rotation capacity determined in accordance
26、with BS EN 1992-1-1:2004, 5.6.3 (4) for sections where the area of main reinforcement exceeds 0.005bd. Generally, it will be reasonable to neglect thermal effects, settlements, and creep and shrinkage at ultimate limit state when moment redistribution is not carried out. 3.2 Partial factors for mate
27、rials BS EN 1992-1-1:2004, 2.4.2.4 (3) and Annex A BS EN 1992-1-1:2004, Annex A should only be used in conjunction with an execution specification that aligns fully with the special control and testing processes required by BS EN 1992-1-1:2004, Annex A and any additional special requirements of the
28、National Authority. BSI 2008 3 PD 6687-2:2008 4 Materials 4.1 Creep and shrinkage BS EN 1992-1-1:2004, 3.1.4 In the absence of more specific data, the relative humidity may be taken as 70% for the design of bridge structures in the UK. 4.2 Design compressive and tensile strengths BS EN 1992-2:2005,
29、3.1.6 (101)P The value of ccin BS EN 1992-2:2005, Expression (3.15) is recommended to be 0.85 for bridges. This value is appropriate for calculations on bending and axial force in BS EN 1992-2:2005, 6.1. However, there are other cases where a value of 1.0 is reasonable, such as for shear calculation
30、s, as the empirical model for shear is deemed to account for cc . Similarly, the membrane rules in BS EN 1992-2:2005, 6.109 already incorporate a 0.85 factor in the formula for direct compressive strength and, therefore, a value of 1.0 for ccis clearly justified. The NA to BS EN 1992-2:2005, therefo
31、re, identifies the clauses for which the value of ccshould be taken as 0.85. For other clauses the value should be taken as 1.0. The clauses for which the value of ccshould be taken as 0.85 were determined to achieve consistency with the use of 0.85 for bending and axial force and 1.0 for shear. For
32、 example, ccis taken equal to 1.0 in the compression strut limit in BS EN 1992-1-1:2004, Expression (6.56), as this compression limit corresponds to that used in the variable angle shear truss model given in BS EN 1992-2:2005, 6.2 where ccis also taken as 1.0. Conversely, in BS EN 1992-1-1:2004, Exp
33、ression (6.63), ccis given the value of 0.85 in the partially loaded area rules in order to give parity between these rules and those used for calculations of bending and axial force in BS EN 1992-2:2005, 6.1 when the entire cross-sectional area is loaded. 4.3 Confined concrete BS EN 1992-1-1:2004,
34、3.1.9 The general detailing requirements given in BS EN 1992-2:2005 should not be assumed to provide sufficient confinement for the model for increased concrete strength and strain capacity given in BS EN 1992-1-1:2004, 3.1.9 (2) to be used in the general design of elements for bending, axial force,
35、 shear and torsion. The expressions provided for confined concrete may be used in checking triaxially confined nodes, in accordance with BS EN 1992-1-1:2004, 6.5.4 (6). 4.4 Ductility characteristic BS EN 1992-2:2005, 3.2.4 BS EN 1992-2:2005, 3.2.4 (101)P allows the classes of reinforcement that may
36、be used in bridges to be defined. The recommended classes are Class B and Class C. The NA to BS EN 1992-2:2005 relaxes this requirement and allows the use of Class A fabric reinforcement provided it is not taken into account in the evaluation of the ultimate resistance.PD 6687-2:2008 4 BSI 2008 The
37、restriction on taking account of Class A fabric reinforcement in the evaluation of the ultimate resistance stems from the fact that the ultimate limit state deformation capacity of structures with Class A reinforcement can be very low compared with structures with Class B or Class C reinforcement 1,
38、 particularly for lightly reinforced elements. Therefore, its use as primary reinforcement for bridges is not allowed, including its use as shear reinforcement. Class A fabric reinforcement may be used in the verification of serviceability criteria given in BS EN 1992-2:2005, Section 7 and the minim
39、um reinforcement requirements given in BS EN 1992-2:2005, Section 9. 5 Durability and cover to reinforcement 5.1 Requirements for durability BS EN 1992-1-1:2004, 4.3 Half-joints should not be used in bridges unless there are adequate provisions for inspection and maintenance. 6 Structural analysis 6
40、1 Second order effects BS EN 1992-1-1:2004, 5.1.4 (1)P For externally prestressed members, second order effects between deviators, or other points where the tendon position in the section is fixed, need not be considered when the spacing between these points does not exceed 10 times section depth i
41、f the tendon force at the ultimate limit state is determined using BS EN 1992-1-1:2004, 5.10.8 (2). If non-linear analysis is used to determine the tendon force, second order effects should be considered. 6.2 Geometrical imperfections BS EN 1992-1-1:2004, 5.2 The disposition of imperfections used in
42、 analysis should reflect the behaviour and function of the structure and its elements. The shape of imperfection should be based on the anticipated mode of buckling of the member. For example, in the case of bridge piers, an overall lean imperfection should be used where buckling will be in a sway m
43、ode (“unbraced” conditions), while a local eccentricity within the member should be used where both ends of the member are held in position (“braced” conditions). BSI 2008 5 PD 6687-2:2008 In using BS EN 1992-1-1:2004, Expression (5.2) the eccentricity, e i , derived should be taken as the amplitude
44、 of imperfection over the half wavelength of buckling; Figure 1 shows the imperfection suitable for a pier rigidly built in for moment at each end. A lean imperfection should however be considered in the design of the positional restraints for braced members. Further guidance and background are give
45、n in Hendy and Smith 2. 6.3 Linear elastic analysis BS EN 1992-1-1:2004, 5.4 The use of fully cracked section properties to derive internal effects in members from indirect actions at the serviceability limit state is not permissible, as the formation of wide cracks implicit in this assumption canno
46、t be accepted at the serviceability limit state. If cracking is considered in global analysis, the member stiffness used should be commensurate with the degree of cracking permitted at the serviceability limit state. This leads to the requirement in BS EN 1992-1-1:2004, 5.4 (3) that a “gradual evolu
47、tion of cracking should be considered”, which requires a non-linear analysis allowing for the effects of cracking and tension stiffening. Un-cracked global analysis in accordance with BS EN 1992-1-1:2004, 5.4 (2) may always be used as a conservative alternative to such considerations. Figure 1 Imper
48、fections for pier built in at both ends l 0= l/2 e = 2e i= l /2 a) Sinusoidal imperfection b) Angular imperfection l 0 e i e i l ePD 6687-2:2008 6 BSI 2008 6.4 Linear elastic analysis with limited redistribution BS EN 1992-1-1:2004, 5.5 If a linear elastic analysis with limited redistribution is und
49、ertaken, shears and reactions used in the design should be taken as those either prior to redistribution or after redistribution, whichever is greater. 6.5 Plastic analysis BS EN 1992-1-1:2004, 5.6 BS EN 1992-2:2005, 5.6.1 (101)P allows the use of plastic analysis when permitted by National Authorities. Permission for the use of plastic analysis should therefore be sought from the relevant body on a project-specific basis, see 2.1 of this document. Typically this will be part of the tec
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