Structural Concrete - Hassoun

570 Chapter 16 Continuous Beams and Frames
Figure 16.15 (a) Considère hinge, (b) Mesnager hinges for a series of portal frames,
and (c) Considère hinge.
16.6.2 Considère Hinge
The difference between the Considère hinge and the Mesnager one is that the normal force P u is
assumed to be transmitted to the footing by one or more short, spirally reinforced columns extending
deep into the footing, whereas the horizontal force H is assumed to be resisted by the inclined bars
A and B (Fig. 16.15). The load capacity of the spirally reinforced short column may be calculated
using Eq. 10.7, neglecting the factor 0.85 for minimum eccentricity:
P u = φP n = 0.75[0.85f ′ c(A g − A st )+A st f y ] (16.7)
where A g is the area of concrete hinge section, or bh ′ ,andA st is the area of longitudinal bars within
the spirals. Ties should be provided in the column up to a distance equal to the long side of the
column section h.
16.6.3 Lead Hinges
Lead hinges are sometimes used in reinforced concrete frames. In this type of hinge, a lead plate,
usually 0.75 to 1.0 in. thick, is used to transmit the normal force, P u , to the footing. The horizontal
force H is resisted by vertical bars placed at the center of the column and extended to the footing
(Fig. 16.16). At the base of the column, the axial load P u should not exceed the bearing strength
specified by the ACI Code, Section 22.8.3, of φ(0.85f ′ cA 1 ),whereφ = 0.65 and A 1 = bh ′ . The area
of the vertical bars is A s . = H/0.6f y ,whereH = factored horizontal force.