Composite Structures of Steel and Concrete

Beams, Slabs, Columns and Frames for Buildings

Roger P. Johnson

• Publisher: Wiley-Blackwell
• Year: 2018
• ISBN:
  9781119401384
• Edition: 4
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

This book provides an introduction to the theory and design of composite structures of steel and concrete. Material applicable to both buildings and bridges is included, with more detailed information relating to structures for buildings. Throughout, the design methods are illustrated by calculations in accordance with the Eurocode for composite structures, EN 1994, Part 1-1, 'General rules and rules for buildings' and Part 1-2, 'Structural fire design', and their cross-references to ENs 1990 to 1993. The methods are stated and explained, so that no reference to Eurocodes is needed.

The use of Eurocodes has been required in the UK since 2010 for building and bridge structures that are publicly funded. Their first major revision began in 2015, with the new versions due in the early 2020s. Both authors are involved in the work on Eurocode 4. They explain the expected additions and changes, and their effect in the worked examples for a multi-storey framed structure for a building, including resistance to fire.

The book will be of interest to undergraduate and postgraduate students, their lecturers and supervisors, and to practising engineers seeking familiarity with composite structures, the Eurocodes, and their ongoing revision.

1
Introduction

1.1 Composite beams and slabs

The design of structures for buildings and bridges is mainly concerned with the provision and support of load‐bearing horizontal surfaces. Except in some long‐span structures, these floors or decks are usually made of reinforced concrete, for no other material provides a better combination of low cost, high strength, and resistance to corrosion, abrasion and fire.

The economic span for a uniform reinforced concrete slab is little more than that at which its thickness becomes sufficient to resist the point loads to which it may be subjected or, in buildings, to provide the sound insulation required. For spans of more than a few metres it is cheaper to support the slab on beams, ribs or walls than to thicken it. Where the beams or ribs are also of concrete, the monolithic nature of the construction makes it possible for a substantial breadth of slab to act as the top flange of the beam that supports it.

At spans of more than about 10 m, and especially where the susceptibility of steel to loss of strength from fire is not a problem, as in most bridges, steel beams often become cheaper than concrete beams. It was at first customary to design the steelwork to carry the whole weight of the concrete slab and its loading; but by about 1950 the development of shear connectors had made it practicable to connect the slab to the beam, and so to obtain the T‐beam action that had long been used in concrete construction. The term ‘composite beam’ as used in this book refers to this type of structure.

The same term is in use for beams in which prestressed and in situ concrete act together; and there are many other examples of composite action in structures, such as between brick walls and beams supporting them, or between a steel‐framed shed and its cladding; but these are outside the scope of this book.

No income is received from money invested in construction of a multistorey building such as a large office block until the building is occupied. The construction time is strongly influenced by the time taken to construct a typical floor of the building, and here structural steel has an advantage over in situ concrete.

Even more time can be saved if the floor slabs are cast on permanent steel formwork that acts first as a working platform, and then as bottom reinforcement for the slab. The use of this formwork, known as profiled steel sheeting, began in North America (Fisher, 1970) and is now standard practice in Europe and elsewhere. These floors span in one direction only, and are known as composite slabs. Where the steel sheet is flat, so that two‐way spanning occurs, the structure is known as a composite plate. These occur in box‐girder bridges.

Steel profiled sheeting and partial‐thickness precast concrete slabs are known as structurally participating formwork. Cement or plastic profiled sheeting reinforced by fibres is sometimes used. Its contribution to the strength of the finished slab is normally ignored in design.

The degree of fire protection that must be provided is another factor that influences the choice between concrete, composite and steel structures, and here concrete has an advantage. Little or no fire protection is required for open multistorey car parks, a moderate amount for office blocks, and most of all for public buildings and warehouses. Many methods have been developed for providing steelwork with fire protection.

Design against fire and the prediction of fire resistance is known as fire engineering (Wang et al., 2012). Several of the Eurocodes have a Part 1.2 devoted to it. Full encasement of steel beams, once common, is now more expensive than the use of lightweight non‐structural materials. Concrete encasement of the web only, done before the beam is erected, is more common in continental Europe than in the UK, and is covered in EN 1994‐1‐1 (BSI, 2004). It enhances the buckling resistance of the member (Section 4.2.4) as well as provi...

Table of contents

• Cover
• Table of Contents
• Preface
• Symbols, Terminology and Units
• Chapter 1: Introduction
• Chapter 2: Shear Connection
• Chapter 3: Simply‐supported Composite Slabs and Beams
• Chapter 4: Continuous Beams and Slabs, and Beams in Frames
• Chapter 5: Composite Columns and Frames
• Chapter 6: Fire Resistance
• Appendix A: Partial‐interaction theory
• References
• Index
• End User License Agreement