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)

ChapterS
Reinforced concrete beamsthe
serviceability limit states
Preliminary note: Readers interested only in structural design to BS 8110
may concentrate on the following sections:
(a) Section 5.3: Deflection control in design (BS 8110).
(b) Section 5.4: Crack control in design (BS 8110).
5.1 The serviceability limit states of deflection and
cracking
The deflection of a structure or any part of a structure must not adversely
affect the appearance or efficiency of the structure; similarly, any cracking
of the concrete must not adversely affect its appearance or durability.
Lately the serviceability of concrete structures has become a much more
important design consideration than in the past, mainly because more
efficient design procedures have enabled engineers to satisfy the ultimate
limit state requirements with lighter but more highly stressed structural
members. For example, during the past few decades, successive British
codes have allowed the maximum service stress in the reinforcement to be
approximately doubled in design.
Of the serviceability limit states, those of excessive flexural deflection
and of excessive flexural cracking are currently the two that normally
must be considered in design [1-4]. In day-to-day practical design, the
serviceability limit state requirements are met by the following straightforward
procedures:
(a)
(b)
Deflections are controlled by simply limiting the span/depth ratios, as
explained in Section 5.3.
Crack widths are controlled by simply limiting the maximum spacings
of the tension reinforcement, as explained in Section 5.4.
However, an engineer's work is not confined to the simple task of
complying with code requirements. There are times when he needs to
estimate how a particular structure will behave; there are times when he
needs to predict the deflections of a structure, for comparison with site
measurements, for example. Therefore, in this chapter we shall also
explain the analytical methods for calculating the magnitudes of deflections