Civil Engineering Reference
In-Depth Information
Figure 2.20
Steel arrangement for shear and torsion
The advantages and deficiencies of the equilibrium (plasticity) truss model are summa-
rized below:
Advantages
1. The equilibrium truss model theory satisfies completely the equilibrium condition. It pro-
vides three equilibrium equations which are conceptionally identical in element shear, beam
shear and torsion.
2. From a design point of view, the three equilibrium equations can be used directly to design
the three components of the truss model, namely, the transverse steel, the longitudinal steel
and the diagonal concrete struts.
3. The three equilibrium equations satisfy the Mohr circle.
4. The model provides a very clear concept of the interaction of bending, shear, torsion and
axial load.
5. Equilibrium (plasticity) truss model is applied to the analysis of beams in Section 8.1
(Chapter 8). The model provides a rational explanation of the 'shift rule' as described in
Section 8.1.1.3.
Deficiencies
1. The equilibrium truss model does not take into account the strain compatibility condition.
As a result, it can not predict the shear or torsional deformations of a RC member.
2. The model can not predict the strains in the steel or concrete. Consequently, the yielding of
steel or the crushing of concrete can not be rationally determined, and the modes of failure
can not be discerned.
