Comparison of steady-state and transient thermo-mechanical responses of unprotected aluminum columns at elevated temperatures

摘要

In modern construction, aluminum is often used as a structural material due to its relatively high strength-to-weight ratio, resistance to corrosion, and architecturally pleasing finish. For instance, aluminum has been an important component for the development of skyscrapers atriums and exterior facades, as aluminum structures can weigh up to sixty percent less than similar steel structures with comparable strength. However, the thermo-mechanical behavior of aluminum makes design against building fires challenging, mainly because aluminum has a low melting point, and experimental data and analysis-based models for fire design are limited. Generally, steady-state and transient tests are used to determine material properties at high temperatures. In a steady-state test, a tensile specimen is heated up to a target temperature, and then subjected to axial load under constant temperature. Alternatively, a transient tensile test is completed by applying static axial load to the specimen, and then gradually heating the material to realistically simulate fire conditions. Results from steady-state tests are easier to obtain and, therefore, more commonly used in computational models. This project investigates the accuracy of numerical results obtained through "transient" models that adopt steady-state mechanical properties to study the effects of fire on aluminum structures. Thin-walled columns were analyzed using nonlinear finite element models with mechanical properties from steady-state and transient tests. Results from Abaqus collapse analyses are used to compare the load-carrying capacities and critical temperatures of slender and non-slender hollow members. Parametric studies were completed to characterize the impact of member slenderness and geometric imperfections on the stability of hollow aluminum columns at elevated temperatures.