Achievements of Truss Models for Reinforced Concrete Structures: Advanced Study

P. G. Papadopoulos; H. Xenidis; P. Lazaridis; A. Diamantopoulos; P. Lambrou; Y. Arethas

P. G. Papadopoulos Department of Civil Engineering, Aristotle University of Thessaloniki, Greece.
H. Xenidis Department of Civil Engineering, Aristotle University of Thessaloniki, Greece.
P. Lazaridis Department of Civil Engineering, Aristotle University of Thessaloniki, Greece.
A. Diamantopoulos Department of Civil Engineering, Aristotle University of Thessaloniki, Greece.
P. Lambrou Department of Civil Engineering, Aristotle University of Thessaloniki, Greece.
Y. Arethas Department of Civil Engineering, Aristotle University of Thessaloniki, Greece.

Keywords: Reinforced concrete structure, truss model, constitutive law, material and geometric nonlinearities, concrete cracking, reinforcement yield, concrete ultimate compressive strength, plastic hinge, RC column confinement, buckling of inner concrete struts, global instability

Abstract

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 ?-? laws of material under simulation; both models have been compared with test results and show a dependence of Poisson ratio on curvature of ?-? 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.