Building Design and Construction Handbook - Merritt - Ventech!

FIGURE 9.55 Reinforcement for deep beams.
When the beam thickness exceeds 10 in, a layer
of vertical rebars should be provided near each
face of the beam.
CONCRETE CONSTRUCTION 9.131
FIGURE 9.56 Shear and normal forces acting on a longitudinal
section through a shear wall.
A � 0.0025b s (9.108)
vh w 2
When b w � 10 in. shear reinforcement
should be placed in each face of the
beam. If the beam has a face exposed to
the weather, between one-half and twothirds
of the total shear reinforcement
should be placed in the exterior face.
Bars should not be smaller than No. 3.
Bending. The area of steel provided
for positive bending moment in a deep
beam should be at least
200bwd A � (9.109)
where ƒ y � yield strength of flexural reinforcement, psi. This minimum amount can
be reduced to one-third more than that required by analysis.
A safe assumption for preliminary design is that the extreme top surface in
compression is 0.25 of the overall depth h below the top of very deep beams for
computation of a reduced effective depth d for flexure (Fig. 9.55).
(J. G. MacGregor, ‘‘Reinforced Concrete Mechanics and Design,’’ 2d ed., Prentice-Hall,
Englewood Cliffs, NJ.)
9.89 SHEAR WALLS
Cantilevered shear walls used for bracing structures against lateral displacement
(sidesway) are a special case of deep beams. They may be used as the only lateral
bracing, or in conjunction with beam-column frames. In the latter case, the lateral
displacement of the combination can be calculated with the assumption that lateral
forces resisted by each element can be distributed to walls and frames in proportion
to stiffness. For tall structures, the effect of axial shortening of the frames and the
contribution of shear to lateral deformation of the shear wall should not be neglected.
Figure 9.56 indicates the forces assumed to be acting on a horizontal cross
section of a shear wall.
s
ƒ y