Examining mechanical behavior of steel-bamboo composite I-section column under long-term loading

The steel-bamboo composite structure is a novel composite structure, which is characterized by light weight and high bearing capacity of structural components, as well as excellent seismic performance and good thermal performance of fabricated buildings. To facilitate its engineering application and better understanding the deformation law of composite column during design reference period, mechanical properties of steel-bamboo composite column under long-term loads are investigated in this paper. 27 composite I-section columns were designed and fabricated, among which 18 specimens were first investigated in static loading test with steel ratio and slenderness ratio as main parameters, failure modes and effect of each parameter on the axial compression performance was observed and analyzed. Then, a self-balanced loading device was designed to perform long-term loading test on 6 specimens with loading level and steel ratio as main parameters, and the other 3 specimens were adopted to monitor the temperature effect on creep. The creep process of specimens was observed and the nonlinear fitting analysis of creep data was carried out using Burger model. Once the predetermined long-term loading duration was reached, the secondary static loading test were carried out to study the influencing factors of bearing capacity and deformation, as well as their variation laws. Further, calculation formula of yield bearing capacity was derived by analyzing yield conditions of composite column, as two calculation methods of ultimate bearing capacity were proposed based on superposition principle and limit equilibrium theory. Results show that the composite columns have good integrity, high deformation capacity and bearing capacity, which improves significantly with the increase of steel ratio and decreases with the increase of slenderness ratio. Creep deformation become basically stable after 90 days of loading, which can be accurately described by Burger model. After the long-term loading, ductility and ultimate strain of the specimens were obviously increased, while the bearing capacity was not significantly affected. The average error between the theoretical and experimental results of yield and ultimate bearing capacity is smaller than 7%, which indicates that the established calculation methods have high accuracy and are suitable for predicting the bearing capacity of steel-bamboo composite I-section columns. It is proved that scientifically designed steel-bamboo composite columns have reliable bearing capacities and controllable deformations, and can be safely applied to practical projects.