Ultimate strength analysis of composite sections under biaxial bending and axial load

A new generic fiber model algorithm is presented that allows for the efficient analysis of arbitrary composite sections under biaxial bending and axial load. The geometry of the cross section is described by multi-nested curvilinear polygons i.e. closed polygons with edges that are straight lines or circular arcs. The polygons may be convex or concave and may contain openings. The stress–strain diagrams of materials consist of any number and any combination of consecutive polynomials, which allows for consideration of various effects such as concrete confinement and tensile strength, strain hardening of the reinforcement etc. The integration of the stress field is performed analytically. The algorithm focuses on the construction of moment–curvature diagrams, interaction curves and failure surfaces. It can also be used for calculating the deformed state of a cross section under given external loads. Several examples are presented to demonstrate the versatility and the advantages of the proposed algorithm in comparison to existing methods.