The Case of the Burning Steel Building

Discolored Structural Steel MembersThe Problem:

After a fire inside a steel building, structural evaluations were conducted in accessible regions of building.  Structural steel columns, beams, crane girders were examined in the field and tested in the metallurgical laboratory.  The fire started in a corner and may have been arson.  The owner insisted that the columns, beams and girders were structurally worthless after the fire and that the building must be demolished.  

In-Situ Brinell HardnessMy Assessment: 

Conditions were observed of the post fire building members - columns, beams, crane girders.  Mechanical tests were conducted on the columns, beams, supports and girders. Brinell hardness readings were obtained in-situ at 48 locations on the steel members.   Hardness test results were indications of each steel member’s tensile strength rating.  The hardness of steel is measured by pressing a tungsten-carbide ball against the smooth steel surface under standardized test conditions. The hardness is expressed in Brinell Hardness Number (BHN) computed by dividing the by the area of indentation made by the ball.   

Three 1” diameter plugs were removed from column webs with a hole saw for preparation and evaluations in the metallurgical laboratory.  Alloy analyses and grain structure  were evaluated.  The micrographs did not reveal grain structures subjected to deleterious, elevated temperatures from the fire.  The structural members were evaluated for load capacity in both the pre-fire and post-fire conditions.

Cross-Section, Steel Metallurgical SpecimenThe Consequences: 

The owner’s engineer wrote a report stating that the columns and beams were structurally deficient after the fire and that the building was unsafe.  There was no evidence of degraded capacity of structural building members and girders.  There was no evidence of degraded mechanical properties, metallurgical damage or annealed steel members.  Building replacement costs were staggering.

The Lessons Learned: 

The results of engineering assessments were that the load capacity of the steel members was not degraded by the fire.  The steel building columns, beams and girders were fit for the intended service.   The building was not demolished.  Cosmetic renovations were undertaken in areas affected by the fire.