F. K. Kong MA, MSc, PhD, CEng, FICE, FIStructE, R. H. Evans CBE, DSc, D ès Sc, DTech, PhD, CEng, FICE, FIMechE, FIStructE (auth.)-Reinforced and Prestressed Concrete-Springer US (1987)

Chapter 1
Limit state design concepts
Preliminary note: Readers interested only in structural design to BS 8110
may concentrate on the following sections:
(a) Section 1.2: Limit state design philosophy.
(b) Section 1.4: Characteristic strengths and loads.
(c) Section 1.5: Partial safety factors.
1.1 The aims of structural design
This book is concerned with reinforced and prestressed concrete, and since
structural engineering is dominated by design, it is appropriate to begin by
stating the aims of structural design and briefly describing the processes by
which the structural engineer seeks to achieve them [ 1].
There are three main aims in structural design. First, the structure must
be safe, for society demands security in the structures it inhabits. Second,
the structure must fulfil its intended purpose during its intended life span.
Third, the structure must be economical with regard to first cost and to
maintenance costs; indeed, most design decisions are, implicitly or
explicitly, economic decisions.
A structural project is initiated by the client, who states his requirements
of the structure. His requirements are usually vague, because he is not
aware of the possibilities and limitations of structural engineering. In fact,
his most important requirements are often not explicitly stated. For
example, he will assume that the structure will be safe and that it will
remain serviceable during its intended life. The process of structural design
begins with the engineer's appreciation of the client's requirements. After
collecting and assimilating relevant facts, he develops concepts of general
structural schemes, appraises them, and then, having considered the use of
materials and the erection methods, he makes the important decision of
choosing the final structural scheme-after consultations with the client if
necessary. This is followed by a full structural analysis and detailed design,
which are often collectively referred to as structural design and which form
the subject matter of this book. Having checked, through such analysis and
design, that the final structure is adequate under service conditions and
during erection, the engineer then issues the specifications and detail