Stresses Near SupportNear TopMax. tensile stresses a few degrees
clockwisexyMid-heightMax tensile stress 45Near bottomxyxyMax.
tensile stressesa few degrees ccw
Shear Failure PathVertical reinforcing steel, shear stirrups,
are added to resist the portion of the shear force not resisted by
the concrete.
Shear Strength of ConcreteThe shear strength of a reinforced
concrete beam is a result of the dowel force, aggregate interlock,
and shear compression force.
fc in psi
Shear Strength of Steel Stirrupswhere, s = stirrup spacingAv =
total cross-sectional area of the vertical legs of one stirrupFor
equilibrium:For design:where, = 0.75
ACI Limitations on Stirrup Spacings d if , fc in psi. And for
beams and girders if
s d if (upper limit on Vs)
,fy in ksi and Av in in2
s < 3 in. to allow placement of concrete
Shear AnalysisCoefficients for shear given on p. 19 of notes or
Part 5 of Manual of Steel ConstructionIf a beam or girder is
supported in such a way that vertical compression is induced in the
bottom, as will be the case if support is provided by a column or a
considerably deeper member, the shear force a distance d from the
support is used for design.
Design of Shear Reinforcementfor Previous Example p. 21 notesThe
partial office building floor plan shown had beams spanning 30 ft
and girders spanning 24 ft. Design the slab, beams, and girders to
support a live load of 80 psf and a dead weight of 15 psf in
addition to the self weight of the structure. Use grade 60
reinforcing steel and 4000 psi concrete. 30 ft30 ft30 ft30 ft24
ft24 ft24 ft
