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 slabs and
yield-line analysis
Preliminary note: Readers interested only in structural design to BS 8110
may concentrate on the following sections:
(a) Section 8.1: Flexural strength (BS 8110).
(b) Section 8.7: Shear strength (BS 8110).
(c) Section 8.8: Design of slabs (BS 8110).
8.1 Flexural strength of slabs (BS 8110)
For practical purposes, the ultimate moment of resistance (1] of reinforced
concrete slabs may be determined by the methods explained in Chapter 4
for beams. The beam design chart in Fig. 4.5-2 may of course be used for
slab design, but since practical slabs are almost always under-reinforced,
only the initial portion of the lowest curve in the chart is really relevant.
Designers generally prefer to use the formulae given by the I.Struct.E.
Manual [1]. These formulae are of course the same as those explained in
Section 4.6(c) for beams:
A = M (8.1-1)
s 0.87fyz
M = K'f. bd 2
u cu (8.1-2)
where the lever-arm distance z is obtained from Table 4.6-1 and K' is
taken as 0.156. (Note: Where there is moment redistribution, use Table
4. 7-2 for z and Table 4. 7-1 for K'.) Of course, the symbols in eqns
(8.1-1) and (8.1-2) have the same meanings as in the corresponding
equations in Section 4.6(c), except that A 8 , M and Mu here all refer to a
width b of the slab (b is normally taken as 1 m).
One-way slabs, which as the name implies, span in one direction, are in
principle analysed and designed as beams and present no special problems.
The design of two-way slabs presents varying degrees of difficulty
depending on the boundary conditions. The simpler cases of rectangular
slabs may be designed by using the moment coefficients in BS 8110:
Clause 3.5.3. For irregular cases, the yield-line theory provides a powerful
design tool as we shall see in the following sections of this chapter.