Page 181 - Civil Engineering Formulas

118 CHAPTER FIVE

Negative moment at face of all supports for
(a) slabs with spans not exceeding 10 ft (3 m)
and (b) beams and girders where the ratio of
sum of column stiffness to beam stiffness
2
exceeds 8 at each end of the span wl n 12
Negative moment at interior faces of exterior
supports, for members built integrally with
their supports
Where the support is a spandrel beam or girder wl n 24
2
2
Where the support is a column wl n 16
Shear Forces

Shear in end members at first interior support 1.15 wl n 2
Shear at all other supports wl n 2

End Reactions
Reactions to a supporting beam, column, or wall are obtained as the sum of shear
forces acting on both sides of the support.

DESIGN METHODS FOR BEAMS,
COLUMNS, AND OTHER MEMBERS

A number of different design methods have been used for reinforced concrete con-
struction. The three most common are working-stress design, ultimate-strength
design, and strength design method. Each method has its backers and supporters.
For actual designs the latest edition of the ACI Code should be consulted.

Beams
Concrete beams may be considered to be of three principal types: (1) rectangu-
lar beams with tensile reinforcing only, (2) T-beams with tensile reinforcing
only, and (3) beams with tensile and compressive reinforcing.

Rectangular Beams with Tensile Reinforcing Only This type of beam includes
slabs, for which the beam width b equals 12 in (305 mm) when the moment and
shear are expressed per foot (m) of width. The stresses in the concrete and steel
are, using working-stress design formulas,

2M M M
f c f s (5.6)
kjbd 2 A s jd pjbd 2