Civil Engineering Reference
In-Depth Information
structural behaviour of deep beams. In this chapter consideration is given to
one specific implication of the depth of these elements, which is the
additional action of vertical direct tensile forces arising from substantial
loads applied at the soffit and lower levels of the beam. Research in this
field has been limited and it is therefore reviewed within the scope of the
chapter. It will be shown on the basis of comparison with laboratory tests
that CIRIA design recommendations (1977) are safe and conservative in
their recommendations for shear walls with combined top and bottom
loadings. ACI procedures for deep beams 1983 are applicable only to top
loading and these are also conservative.
6.2
Early tests on deep beams under top and bottom loading
Graf and colleagues (1943) appear to have been the first to test a deep beam
under bottom loads. The beam had a height/span ratio of 2.2 and is shown in
Figure 6.1. Load was applied through horizontal nibs built into the soffit and
initial cracks were observed above the nibs. These cracks were horizontal but
as the load was increased additional sloping cracks appeared at higher levels
in the beam. Failure occurred due to yielding of the main reinforcement and
deterioration of the section immediately above the line of the horizontal nibs.
Figure 6.1
Details of specimens tested by Graf.
