Steel encased polymer concrete under axial compressive loading: Analytical formulations

Composite structures and in particular steel encased concrete structures, are rapidly emerging as one of the inevitable structural systems for earthquake resistance, as they have been known to exploit the best attributes of steel and concrete, resulting in higher stiffness, strength and ductility. However, limitations imposed by the encased cement concrete, e.g., its brittleness, low tensile strength and diminished durability, further compounded by mounting environmental concerns since the 1997 Kyoto protocol and the need for sustainable development, dictate that novel ecologically benign construction materials be sought for the 21st century. In this context, experimental and analytical studies have been conducted on polymer-based materials (latex cement mortar and epoxy concrete) as supplementary and/or complementary materials to ordinary cement concrete in composite tubular systems. Results from experimental work on the compressive behaviour of steel encased polymeric materials reveal significant increase in strength and/or ductility of polymer and polymer concrete filled steel stub columns. In addition, polymer formulations were found to present an array of basic properties, which could be tailored to meet specific design requirements. In conjunction with the experimental results, existing models by several researchers are evaluated and found to generally underestimate the confined strength of the fill materials. A proposed model, taking into consideration key material properties such as shear and bulk moduli, is found to depict the confined strengths satisfactorily. Finally, force–strain models are developed for the composite stub columns that adequately capture the elastic stiffness and ultimate state, unlike existing models.