Chapter 1
INTRODUCTION

1.1. GENERAL OBSERVATIONS

Steel construction combines a number of unique features that make it an ideal solution for many applications in the construction industry. Steel provides unbeatable speed of construction and off-site fabrication, thereby reducing the financial risks associated with site-dependent delays. The inherent properties of steel allow much greater freedom at the conceptual design phase, thereby helping to achieve greater flexibility and quality. In particular, steel construction, with its high strength to weight ratio, maximizes the useable area of a structure and minimizes self-weight, again resulting in cost savings. Recycling and reuse of steel also mean that steel construction is well-placed to contribute towards reduction of the environmental impacts of the construction sector (Simões da Silva, 2005).

The construction industry is currently facing its biggest transformation as a direct result of the accelerated changes that society is experiencing. Globalisation and increasing competition are forcing the construction industry to abandon its traditional practices and intensive labour characteristics and to adopt industrial practices typical of manufacturing. This further enhances the attractiveness of steel construction.

All these advantages can only be achieved with sound technical knowledge of all the stages in the life-cycle of the construction process (from design, construction and operation to final dismantling). The objective of the ECCS Eurocode Design Manuals is to provide design guidance on the use of the Eurocodes through a "light" overview of the theoretical background together with an explanation of the code's provisions, supported by detailed, practical design examples based on real structures. Each volume addresses a specific part of the Eurocodes relevant for steel construction.

This inaugural volume of the ECCS Eurocode Design Manuals addresses the Design of Steel Structures in terms of the General Rules and Rules for Buildings, covering all the topics of Part 1-1 of Eurocode 3 (CEN, 2005a), abbreviated in this book to EC3-1-1. These range from structural analysis of skeletal structures to design of members and components. More specifically, chapter 1 of this manual introduces general aspects such as the basis of design, material properties and geometric characteristics and tolerances, corresponding to chapters 1 to 4 and chapter 7 of EN 1993-1-1. It highlights the important topics that are required in the design of steel structures. Structural analysis is discussed in chapter 2, including structural modelling, global analysis and classification of cross sections, covering chapter 5 of EN 1993-1-1. The design of steel members subjected to various types of internal force (tension, bending and shear, compression and torsion) and their combinations is described in chapter 3, corresponding to chapter 6 of EN 1993-1-1. chapter 4 presents the design of steel structures using 3D elastic analysis based on the case study of a real building. Finally, chapter 5 discusses plastic design, using a pitched-roof industrial building to exemplify all relevant aspects.

The design examples are chosen from real design cases. Two complete design examples are presented: i) a braced steel-framed building and ii) a pitched-roof industrial building. The chosen design approach tries to reproduce, as much as possible, real design practice instead of more academic approaches that often only deal with parts of the design process. This means that the design examples start by quantifying the actions. They then progress in a detailed step-by-step manner to global analysis and individual member verifications. The design tools currently available and adopted in most design offices are based on software for 3D analysis. Consequently, the design example for multi-storey buildings is analysed as a 3D structure, all subsequent checks being consistent with this approach. This is by no means a straightforward implementation, since most global stability verifications were developed and validated for 2D structures.

The scope of this manual is limited to those issues covered by Part 1-1 of EC3. Issues such as fire design and the design of joints, which are covered by Parts 1.2 and 1.8 of EN 1993, are not included in this manual. Other companion publications on fire design (Franssen and Vila Real, 2015) and joint design (Jaspart and Weynand, 2016) address these. Seismic action is also not considered in this manual. This is because the many different options that could be adopted in the conceptual design phase would lead to completely different structures for the same architectural brief. A forthcoming manual dealing specifically with seismic design issues for buildings is planned (Landolfo et al, 2016).

This manual follows the code prescriptions of the Structural Eurocodes. This is done without loss of generality since the theoretical background, the design philosophy and the design examples are code independent, except when it comes to the specific design procedures.

1.2. CODES OF PRACTICE AND NORMALIZATION

1.2.1. Introduction

The European Union has spent several decades (since 1975) developing and unifying the rules for the design of structures. This work has culminated in a set of European standards called the Eurocodes which have recently been approved by member states. The foreword to each part of the set of Eurocodes contains the following statement:" In 1975, the Commission of the European Community decided on an action programme in the field of construction, based on article 95 of the Treaty. The objective of the programme was the elimination of technical obstacles to trade and the harmonization of technical specifications. Within this action programme, the Commission took the initiative to establish a set of harmonized technical rules for the design of construction works which, in a first stage, would serve as an alternative to the national rules in force in the Member States and, ultimately, would replace them. For fifteen years, the Commission, with the help of a Steering Committee with Representatives of Member States, conducted the development of the Eurocodes programme, which led to the first generation of European codes in the 1980's. In 1989, the Commission and the Member States of the EU and EFTA decided, on the basis of an agreement between the Commission and CEN, to transfer the preparation and the publication of the Eurocodes to CEN through a series of Mandates, in order to provide them with a future status of European Standard (EN). This links de facto the Eurocodes with the provisions of all the Council's Directives and/or Commission's Decisions dealing with European standards (e.g. the Council Directive 89/106/EEC on construction products - CPD - and Council Directives 93/37/EEC, 92/50/EEC and 89/440/EEC on public works and services and equivalent EFTA Directives initiated in pursuit of setting up the internal market)."

The publication of the Construction Products Directive in 1989 (OJ L 040, 1989) established the essential requirements that all construction works must fulfil, namely: i) mechanical resistance and stability; ii) fire resistance; iii) hygiene, health and environment; iv) safety in use; v) protection against noise and vi) energy economy and heat retention.

The first two requirements are addressed by the following nine Structural Eurocodes. These have been produced by CEN (European Committee for Standardization) under the responsibility of its Technical Committee CEN/TC 250:

1. - EN 1990 Eurocode: Basis of Structural Design
2. - EN 1991 Eurocode 1: Actions on Structures
3. - EN 1992 Eurocode 2: Design of Concrete Structures
4. - EN 1993 Eurocode 3: Design of Steel Structures
5. - EN 1994 Eurocode 4: Design of Composite Steel and Concrete Structures
6. - EN 1995 Eurocode 5: Design of Timber Structures
7. - EN 1996 Eurocode 6: Design of Masonry Structures
8. - EN 1997 Eurocode 7: Geotechnical Design
9. - EN 1998 Eurocode 8: Design of Structures for Earthquake Resistance
10. - EN 1999 Eurocode 9: Design of Aluminium Structures

Each Eurocode contains provisions that are open for national determination. Such provisions include weather aspects, seismic zones, safety issues etc. These are collectively called Nationally Determined Parameters (NDP). It is the responsibility of each member state to specify each NDP in a National Annex that accompanies each Eurocode.

More recently (July 2013) the Construction Products Directive was replaced by the Construction Products Regulation (OJ L 088, 2013). This document adds an additional basic requirement: sustainability. This seventh basic requirement must follow the standards prepared by CEN/TC 350 and should be incorpared in future revisions of the Eurocodes.

The Structural Eurocodes are not, by themselves, sufficient for the construction of structures. Complementary information is required on: the products used in construction ("Product Standards", of which there are products used in construction ("Product Standards", of which there are currently about 500);

1. - the tests used to establish behaviour ("Testing Standards", of which there are currently around 900);
2. - the execution standards used to fabricate and erect structures ("Execution Standards").

The flowchart in Figure 1.1 illustrates the full range of information...