U.K. FOREWORD

INTRODUCTION

SCI has a history going back over 25 years of producing design guides aimed at structural engineers. These have typically been of a 'how to do' nature, aimed at designers with a certain level of experience and within the context of a given design standard.

This publication represents a departure from that tradition. It is the first in an envisaged series of joint ECCS-SCI publications, a series we hope will be extremely helpful to U.K. designers given the step change that the move to Eurocodes represents. We believe its format complements other SCI guidance. This joint publication is the 1st Edition, revised second impression of the ECCS Eurocode Design Manual to EN 1993-1-1, which was published in 2013, supplemented by a U.K. Foreword.

The content includes much useful background to the code rules (pointers to reasoning and research work that should help ensure correct application of the rules), and a reminder of some engineering principles. Helpfully, this information is presented in the context of Eurocode terminology and notation, and with reference to clause numbers etc, to aid the reader's familiarity with EN 1993-1-1. A significant number of SCI publications and other work are cited in the references.

Within this so-called U.K. Foreword the reader will find information that is either of a general nature, or relevant to specific sections of the publication. In both cases this information is presented to facilitate application of the rest of the publication in a U.K. context.

It is noted and should be accepted that there will inevitably be some differences of interpretation between the recommendations of ECCS and those previously published by SCI.

GENERAL COMMENTS

The Eurocodes contain so-called Nationally Determined Parameters (NDPs), which permit specific parts of the codes to be subject to national variations. The base ECCS publication uses either the default (recommended) Eurocode values, or in some cases Portuguese values for these NDPs. For a given design the NDPs must be in accordance with the rules for the country in which the structure is to be constructed. Some uses of specific NDPs in the U.K. are noted below.

The examples are described as being 'realistic', but it must be recognised that practice varies between nations so they do not necessarily reflect typical U.K. practice. Some specific exceptions are noted in this U.K. Foreword. Similarly, some references to 'common practice' may not reflect common U.K. practice, and these are highlighted.

Some units may be unfamiliar to U.K. designers, in particular 1 GPa = 1 N/mm2

The following comments are also included in the specific sections throughout the book.

SECTION SPECIFIC COMMENTS

Section 1.2

Reference is made to the need for integration between standards, to ensure that design rules are compatible with execution tolerances. When complementary material is used, which it invariably will be because even a set of standards as comprehensive as the Eurocodes cannot cover every need, the designer should take care to ensure it is appropriate.

Section 1.3.2

At the time of writing (Autumn 2014) an amendment is about to be published that moves the decision regarding Execution Class from EN 1090 to EN 1993-1-1.

Section 1.3.3.3

Reference is made to material partial safety factors (?m), which are NDPs. Both recommended and U.K. values are based on extensive analysis of European steel production. When steel from other sources is used these values may not be appropriate.

Section 1.3.5

Reference is made to rules of thumb that may be used to assure satisfactory dynamic performance. SCI has produced guidance on this subject (SCI, 2009a) and suggests rules of thumb are only used with care, as they can be misleading.

Section 1.4.1

Its U.K. National Annex states that Table 3.1 of EN 1993-1-1 should not be used, moreover that when a range of ultimate strengths is quoted in a product standard the lowest value should be taken.

Section 1.5

The National Structural Steelwork Specification 5th edition (CE Marking Version) was configured to complement EN 1090-2 (BCSA, 2010).

Section 2.2.2

The Eurocodes use a different convention for axis notation than has traditionally been used in the U.K. Also, the Eurocodes are not entirely consistent within themselves concerning axis definition. Care is therefore needed!

Section 2.2.3

Common U.K. practice is to determine forces and moments at centreline intersections, not to use rigid links and to determine forces and moments at (for example) the face of a column.

Section 2.2.5

Although non-linear springs may be used to model joint behaviour, it is very difficult to model the complex behaviour of a joint (connection) - its stiffness, strength, rotation capacity, and indeed different behaviour in loading and unloading. This is mentioned in Section 5.2 of the guide. Traditional U.K. practice is to predict joint behaviour on the basis of past experience.

Section 2.2.7 - Example 2.1

It should be noted that European sections are not commonly used in the U.K. (although they are the subject of growing interest). S 235 steel is not used in the U.K., where S 355 is the current (2014) common grade.

Normal U.K. practice is to assume joint classification (generally 'rigid' or 'nominally pinned') and subsequently to ensure that the joint details satisfy the assumptions made.

Figures 2.29 and 2.30 show a joint with a stiffener that appears to prevent fitting of bolts/nuts. A Morris Stiffener could be used to avoid this problem.

Section 2.3.2.1

Reference is made to amplifying internal forces and displacements to model second order effects. In the U.K. an alternative approach is to reduce resistance rather than increasing forces, by use of effective lengths. However this can be laborious and for that reason is not recommended.

For certain frame geometries the U.K. National Annex to EN 1993-1-1 permits second order effects to be ignored at acr > 5 for the so-called gravity load combination.

Section 2.3.3

The definition of m as the 'number of columns in a row' is not strictly correct. It should be defined as the 'number of columns having an effect on the stability system'. An amendment to EN 1993-1-1 is anticipated.

Section 2.4

All UB sections are Class 1 in bending alone.

Section 3.1.1

The U.K. National Annex to EN 1993-1-1 defines values of ?M0 = 1.0, ?M1 = 1.0, and ?M2 = 1.1. Note these values may vary between Eurocodes, and indeed Eurocode Parts.

Section 3.2.2

Since EN 1993 does not cover what is, in the U.K. at least, a common situation of more than one bolt in the width of an angle leg, it is common practice to use complementary guidance from BS5950 when calculating members resistances.

Section 3.3.5 - Example 3.5

The example assumes that the restraint provided by the composite floor is sufficient. SCI has provided guidance on how a designer can ensure it is sufficient (SCI, 2009b), as in practice it should never be simply assumed.

Section 3.6.2.2

The omission of rules on how to calculate Mcr is one of the gaps in EN 1993 that many U.K. designers are aware of. Some useful complementary information is given here.

Section 3.7.2.2

Reference is made to the two alternative methods for beam-column design given in EN 1993-1-1. It is anticipated that only one method will be given in future editions of the code, although this publication highlights that economy of design effort and economy of design result can sometimes vary depending on the method chosen.

Section 4.1

It should not be assumed that most U.K. design offices use 3D analysis. Reference is also made to the so-called wind moment method having been popular in the past in the U.K. - with modern computing power and knowledge it is not recommended, as its use beyond specific (empirical) limits has no justification.

Reference is made to braced and unbraced frames, and it is worth noting that this does not mean the same thing as non-sway sensitive and sway sensitive. It is not uncommon for a frame that is braced to be sway sensitive - it depends how stiff the bracing mechanism is.

Section 4.2.4 - Example 4.1

The example considers column bases that are fully restrained. These should be avoided if possible - more because of the cost and practicalities of the foundations than the steelwork - and in any case correctly modelled.

Section 4.4.3.4

It should be noted that the calculation of wind actions should follow the U.K. National Annex, which differs significantly from the Eurocode.

Section 4.4.3.6

The definition of m as the 'number of columns in a row' should be changed to the 'number of columns having an effect on the stability system'. In U.K. practice it would generally be assumed that the floor diaphragm constrains all columns to have the same imperfection.

Section 4.4.3.7

For economy, U.K. designers are likely to favour the use of expressions 6.10a and 6.10b of EN 1990 to determine ultimate loads. The combination factors should be taken from the U.K. National Annex to EN 1990.

At the Serviceability Limit State (SLS) the...