Design of structural elements

 The task of the structural engineer is to design a
 structure which satisfies the needs of the client and
 the user. Specifically the structure should be safe,
 economical to build and maintain, and aesthetic
ally pleasing. But what does the design process
 involve?
 Design is a word that means different things to
 different people. In dictionaries the word is de
scribed as a mental plan, preliminary sketch, pat
tern, construction, plot or invention. Even among
 those closely involved with the built environment
 there are considerable differences in interpretation.
 Architects, for example, may interpret design as
 being the production of drawings and models to
 show what a new building will actually look like.
 To civil and structural engineers, however, design is
 taken to mean the entire planning process for a new
 building structure, bridge, tunnel, road, etc., from
 outline concepts and feasibility studies through
 mathematical calculations to working drawings
 which could show every last nut and bolt in the
 project. Together with the drawings there will be
 bills of quantities, a specification and a contract,
 which will form the necessary legal and organiza
tional framework within which a contractor, under the supervision of engineers and architects, can con
struct the scheme.
 There are many inputs into the engineering
 design process as illustrated by Fig. 1.1 including:
 1. client brief
 2. experience
 3. imagination
 4. a site investigation
 5. model and laboratory tests
 6. economic factors
 7. environmental factors.
 1.1 Introduction
 The task of the structural engineer is to design a
 structure which satisfies the needs of the client and
 the user. Specifically the structure should be safe,
 economical to build and maintain, and aesthetic
ally pleasing. But what does the design process
 involve?
 Design is a word that means different things to
 different people. In dictionaries the word is de
scribed as a mental plan, preliminary sketch, pat
tern, construction, plot or invention. Even among
 those closely involved with the built environment
 there are considerable differences in interpretation.
 Architects, for example, may interpret design as
 being the production of drawings and models to
 show what a new building will actually look like.
 To civil and structural engineers, however, design is
 taken to mean the entire planning process for a new
 building structure, bridge, tunnel, road, etc., from
 outline concepts and feasibility studies through
 mathematical calculations to working drawings
 which could show every last nut and bolt in the
 project. Together with the drawings there will be
 bills of quantities, a specification and a contract,
 which will form the necessary legal and organiza
tional framework within which a contractor, under
 The starting-point for the designer is normally
 a conceptual brief from the client, who may be a
 private developer or perhaps a government body.
 The conceptual brief may simply consist of some
 sketches prepared by the client or perhaps a detailed
 set of architect’s drawings. Experience is crucially
 important, and a client will always demand that
 the firm he is employing to do the design has pre
vious experience designing similar structures.
 Although imagination is thought by some to
 be entirely the domain of the architect, this is not
 so. For engineers and technicians an imagination
 of how elements of structure interrelate in three
 dimensions is essential, as is an appreciation of
 the loadings to which structures might be subject
 in certain circumstances. In addition, imaginative
 solutions to engineering problems are often required
 to save money, time, or to improve safety or quality.
 A site investigation is essential to determine the
 strength and other characteristics of the ground
 on which the structure will be founded. If the struc
ture is unusual in any way, or subject to abnormal
 loadings, model or laboratory tests may also be used
 to help determine how the structure will behave.
 In today’s economic climate a structural designer
 must be constantly aware of the cost implications
 of his or her design. On the one hand design should
 aim to achieve economy of materials in the struc
ture, but over-refinement can lead to an excessive
  number of different sizes and components in the
 structure, and labour costs will rise. In addition
 the actual cost of the designer’s time should not be
 excessive, or this will undermine the employer’s
 competitiveness. The idea is to produce a workable
 design achieving reasonable economy of materials,
 while keeping manufacturing and construction costs
 down, and avoiding unnecessary design and research
 expenditure. Attention to detailing and buildability
 of structures cannot be overemphasized in design.
 Most failures are as a result of poor detailing rather
 than incorrect analysis.
 Designers must also understand how the struc
ture will fit into the environment for which it is
 designed. Today many proposals for engineering
 structures stand or fall on this basis, so it is part of
 the designer’s job to try to anticipate and recon
cile the environmental priorities of the public and
 government.
 The engineering design process can often be
 divided into two stages: (1) a feasibility study in
volving a comparison of the alternative forms of
 structure and selection of the most suitable type and
 (2) a detailed design of the chosen structure. The
 success of stage 1, the conceptual design, relies
 to a large extent on engineering judgement and
 instinct, both of which are the outcome of many
 years’ experience of designing structures. Stage 2,
 the detailed design, also requires these attributes
 but is usually more dependent upon a thorough
 understanding of the codes of practice for struc
tural design, e.g. BS 8110 and BS 5950. These many generations of engineers, and the results of
 research. They help to ensure safety and economy
 of construction, and that mistakes are not repeated.
 For instance, after the infamous disaster at the
 Ronan Point block of flats in Newham, London,
 when a gas explosion caused a serious partial col
lapse, research work was carried out, and codes of
 practice were amended so that such structures could
 survive a gas explosion, with damage being con
f
 ined to one level.
 The aim of this book is to look at the procedures
 associated with the detailed design of structural
 elements such as beams, columns and slabs. Chap
ter 2 will help the reader to revise some basic the
ories of structural behaviour. Chapters 3–6 deal with
 design to British Standard (BS) codes of practice
 for the structural use of concrete (BS 8110), struc
tural steelwork (BS 5950), masonry (BS 5628) and
 timber (BS 5268). Chapter 7 introduces the new
 Eurocodes (EC) for structural design and Chapters
 8–11 then describe the layout and design principles
 in EC2, EC3, EC6 and EC5 for concrete, steel
work, masonry and timber respectively
 documents are based on the amassed experience of