Axiale Verschiebung als Funktion der Versuchszeit in den vier Versuchsphasen
Source: BAM, Division Fire Engineering
In the past, the two events earthquake and fire were always - although not in accordance with reality - regarded as non-simultaneous catastrophes. However, in the recent past activities on the analysis of the consequences of an earthquake in the event of fire are increasingly growing. The present study, which was funded by the Alexander von Humboldt Foundation as part of a postdoctoral fellowship, focuses on the behavior of concrete filled tubes (CFT) columns. Their resistance to both earthquakes and fire exposure as a single event has been demonstrated in many studies. This article is particularly concerned with the consequences of combined loads from earthquakes and subsequent fire.
To this end, a nonlinear three-dimensional finite element model (FE) was first developed and validated to investigate the effects of the position of the seismic damage on the response of CFT columns in fires after earthquake. Cyclic, thermal and structural FE analyzes were carried out successively. The accuracy of the proposed FE model was tested by comparing the numerical results with available fire resistance tests and experiments at room temperature with cyclic loading. Based on the validated model, the behavior of previously damaged CFT columns subjected to fire after an earthquake was investigated. As a seismic pretreatment it was assumed within a high damage level that the CFT column reached 50% of its load-bearing capacity against transverse loading, while nevertheless retaining its overall stability after the earthquake. The axial deformation behavior can be divided into four phases as a function of the duration of the fire after the earthquake: After cyclic loading, a pure thermal expansion against the applied load takes place until in the second phase due to a thermally induced strength reduction, a rearrangement of the load from the steel tube on the concrete takes place, which is accompanied by a sharp decrease in the axial displacement. After a relatively long resistance phase of the concrete the column enters the fourth phase, in which the load bearing capacity of the concrete is finally exceeded and the column fails.
The performance of concrete filled steel tube columns under postearthquake fires
Elnaz Talebi, Manfred Korzen, Sascha Hothan
Journal of Constructional Steel Research, 2018, Volume 150, Pages 115-128
BAM Department Safety of Structures, Division Fire Engineering