Achievements of Truss Models for Reinforced Concrete Structures: Advanced Study

Achievements are presented for truss models of RC structures developed in previous years: 1. Two
constitutive models, biaxial and triaxial, are based on regular trusses, with bars obeying nonlinear
uniaxial σ-ε laws of material under simulation; both models have been compared with test results and
show a dependence of Poisson ratio on curvature of σ-ε law. 2. A truss finite element has been used
in the nonlinear static and dynamic analysis of plane RC frames; it has been compared with test
results and describes, in a simple way, the formation of plastic hinges. 3. Thanks to the very simple
geometry of a truss, the equilibrium equations can be easily written and the stiffness matrix can be
easily updated, both with respect to the deformed truss, within each step of a static incremental
loading or within each time step of a dynamic analysis, so that to take into account geometric
nonlinearities. So the confinement of a RC column is interpreted as a structural stability effect of
concrete. And a significant role of the transverse reinforcement is revealed, that of preventing, by its
close spacing and sufficient amount, the buckling of inner longitudinal concrete struts, which would
lead to a global instability of the RC column. 4. The proposed truss model is statically indeterminate,
so it exhibits some features, which are not met by the “strut-and-tie” model.