Civil Engineering Reference
In-Depth Information
Figure 16.3
Column and middle strips.
The part of the moments assigned to the column and middle strips may be assumed
to be uniformly spread over the strips. As will be described later in this chapter, the per-
centage of the moment assigned to a column strip depends on the effective stiffness of
that strip and on its
aspect ratio
1
is the length of span, center to center, of
supports in the direction in which moments are being determined and
2
/
1
(where
2
is the span
length, center to center, of supports in the direction transverse to
1
).
16.5
SHEAR RESISTANCE OF SLABS
For two-way slabs supported by beams or walls, shears are calculated a
t a
distance
d
from
the faces of the walls or beams. The value of
c
b
w
d
.
V
c
is, as for beams,
2
f
Shear is not
usually a problem for these types of slabs.
For flat slabs and flat plates supported directly by columns, shear may be the critical
factor in design. In almost all tests of such structures, failures have been due to shear or
perhaps shear and torsion. These conditions are particularly serious around exterior
columns.
Two kinds of shear must be considered in the design of flat slabs and flat plates.
These are the same two that were considered in column footings—one-way and two-way
shears (that is, beam shear and punching shear). For beam shear analysis, the slab is con-
sidered to act as a wide beam running between the supports. The critical sections are
taken at a distance
d
from the face of the column or capital. For punching shear, the criti-
