Post‐fire Residual Strength and Ductility of Structural Steels from Hollow Sections

Abstract

Steel structures are severely affected by the extreme temperatures reached during a fire. After this, if the structure has not collapsed, the remaining elements can be reused if they are not excessively distorted or the material is still fit for service. In the last case, residual properties of steel must be adequate and fulfil the requirements of the current standards. On this matter, it is hypothesized that residual behaviour of steel not only depends on the highest temperature reached during the fire episode, but also on the load it was simultaneously bearing. This work is focused on an experimental study on the post‐fire behaviour of structural steels. Specimens were cut from structural steel (S355) cold‐formed circular hollow sections (CHS) and subjected to a combination of tensile stress and high temperature. Afterwards, the specimens were cooled in air back to room temperature and, finally, load was increased until specimen failure. The obtained results allowed discussing on the residual yield strength, ultimate strength and stiffness of the steel, and a special focus was put on the residual ductility. The results of this work can provide a basis to the appraisal of steel structures after fire, supporting the further decision on its reinstatement or subsequent demolition.

Influence of load and high temperature on the post‐fire behaviour of high‐strength structural steels

“…From Figures 7-8, the values shown in Tables 7-8 can be determined: There are some combinations of target temperature and degree of utilisation in which the ductility requirement (mainly that on ε f ) is not fulfilled after cooling down. This result was also found in previous works on mild steels [7][8].…”

“…The experimental setup is depicted in Figure 1 and it was used in previous works of the authors [7][8]. It consisted of a hydraulic universal testing machine equipped with a 200 kN load cell, controlled by a closed-loop system.…”

“…The combined influence of load and temperature in the post-fire behaviour of steel has been studied in a few works on mild steel [7][8] but there are no works concerning HSS.…”