Equivalent load of reinforced concrete columns under fire

Purpose: The fire response of structural reinforced concrete columns is usually justified by the reduction in ultimate load bearing capacity. This is due to the decrease in mechanical strength of steel and concrete upon exposure to a fire. In structural design, it is more desirable to consider the action of load directly. The concept of equivalent accidental load due to a fire might give more convenient structural design data. This paper aims to focus on these issues. Design/methodology/approach: A theoretical analysis for the equivalent accidental load imposed on reinforced concrete columns (axially loaded columns, uniaxially loaded columns and biaxially loaded columns) exposed to four-side fires is carried out. The test results of previous research are used as examples and for checking computations. After determining its temperature field, the equivalent accidental load due to fire is calculated using simplified methods. The fire resistance period of reinforced concrete columns can also be determined. Findings: If the response of a structural element to a fire can be converted into an accidental load, it can be combined with other components such as wind load and earthquake action to give a total design load. With this method, the equivalent accidental load due to a fire and fire resistance of reinforced concrete columns at elevated temperature can be derived directly, and the process is very simple. The equivalent accidental load and fire resistance of reinforced concrete columns exposed to fire on one, two or three sides can also be derived by the same method. However, the thermal performance of steel and concrete cannot be considered during the calculation. Originality/value: A simplified approach of equivalent accidental load due to fire is proposed. Much simpler guides can be drafted in structural fire design.