Thermal bowing on steel columns embedded on walls under fire conditions

• Geometrical material non-linear analysis on steel columns embedded in walls.
• Fire behaviour of H steel columns subjected to differential heating.
• Contact of columns with walls leads to a reduction on the steel temperatures.
• Interaction axial force–bending moment diagrams for non-uniformly heated columns.
• Eurocode 3, considering uniform temperature, leads to very conservative curves.

The contact of steel columns with building walls is responsible for huge thermal gradients within its cross-section during fire. Current regulatory codes for fire design of steel members provide a formulation to assess the load-bearing capacity of these members assuming uniform temperature through the cross-section; however, this is not what happens in the major part of the cases in real structures where the columns are embedded on walls. The walls on one hand will provide a temperature reduction on the columns, which is somehow favourable in terms of its fire resistance, on the other hand the differential heating on the columns cross-section may lead to unfavourable stresses (bending moments) responsible for instability (thermal bowing). Considering that the structural behaviour of columns is strongly dependent of the second order effects this is an important phenomenon which may lead to a significant reduction on its fire resistance. This paper presents the results of a numerical study to assess the influence of the differential heating on the fire design of steel columns. New interaction axial force–bending moment diagrams for non-uniformly heated H steel columns are proposed.