Condition Evaluation of Fire Exposed Concrete Foundation

Ashok Kakade (P.E., F. ASCE, F. ICRI, F.ICI)

This article provides some basic information on effects of fire on concrete, various condition evaluation methods, and show findings from a case study of a fire exposed concrete foundation in California, and informs construction professionals that fire exposed concrete structures can be repaired without destroying and re-building the structure.

Photograph 1: A square steel column supporting a car parking slab was distorted in a fire that lasted less than one hour. The hot air within the hollow square steel columns caused the column to become round and the metal roof had buckled. All steel members had to be discarded.

After a devastating fire in a building, concrete and masonry members are most likely to be the only surviving structural members. Fire consumes wood rapidly and distorts exposed steel structures within minutes. Although steel structures regain strength upon cooling, it remains structurally distorted, which makes the strength gain useless. History has shown that concrete structures possess excellent fire resistance and can retain its structural integrity even in severe building fires. The cast-in-place reinforced concrete columns, slabs, and walls are likely to remain in place longer than their expected code compliant duration and thus provide occupants valuable time to escape the building. Wood and exposed steel frame structures do not offer this level of fire resistance and advantage. Concrete’s inherent low thermal conductivity and high specific heat allows it to provide good protection for reinforcing steel against fire, though it may sustain extensive damage in the process.

Under certain conditions, however, concrete may suffer significant distress. One such condition is when fire is caused by long term burning due to a fuel source in direct contact with concrete. However, in contrast to other construction materials such as timber and steel, concrete’s superior fire resistance allows it to repair in-situ or with partial replacement as compared to complete demolition and reconstruction. However, thorough investigation and testing is required to assess the concrete’s structural damage to determine its condition as well as that of the reinforcing steel before it is considered for repair or reuse.

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