ULTIMATE AND NOMINAL STRENGTH ANALYSIS OF COMPOSITE SECTIONS WITH ARBITRARY SHAPE
Cosmin G. Chiorean 1*, Stefan M. Buru1
1 Department of Structural Mechanics, Technical University of Cluj-Napoca, Cluj-Napoca, Romania
This paper presents a new computational method for ultimate strength analysis of composite steel-concrete cross-sections with arbitrary shape. The ultimate (maximum) strength capacity is formulated as a problem of unconstrained mathematical optimization by applying the method of Lagrange multipliers. The optimized function is defined as a total internal bending moment and two constrains are defined by enforcing the constant axial force and bending moment ratio. Hence, the ultimate bending moment capacities are directly obtained by solving three coupled nonlinear equations. This procedure adopts a tangent stiffness strategy for the solution of the nonlinear system of equations thus resulting in a high rate of convergence. The developed procedure has been used to predict the bending moment capacity diagrams of several cross-sections and the differences between the ultimate and nominal strength capacities of cross-sections are highlighted. The strain-softening effect exhibited by the concrete in compression is discussed in this respect and the comparisons made prove the effectiveness and the reliability of the proposed method of analysis.
Ultimate strength capacity; Nominal strength capacity; Composite steel-concrete cross-section; Bi-axial bending; Strain-Softening.