Evaluation of preserved materials reveals cause of column collapse

December 30, 2007
Publication: Forensic Engineering - Proceedings of the Fourth Forensic Engineering Congress, ASCE p 516-530

Abstract: This paper describes an investigation of the partial collapse of a structural steel frame during construction of a shopping mall in December 1999. The accident occurred when an assembly of a 36 ft tall steel column and an 80 ft long girder overturned in high winds and fell to the ground. Two ironworkers attempting to make a girder-to-column connection at the top of the column died in the accident. The investigation, as well as observations by others, showed substantial deviations in the failed column's base connection to the footing from the requirements of the structural design drawings. As fabricated, the column's baseplate was a different shape with a different configuration and fewer number of anchor bolts than shown on the design drawings. A setting grout pad, placed before erection of the column, was undersized for both the as-designed baseplate and the as-fabricated baseplate. Most significantly, the cast-in column anchor bolts were installed in the wrong configuration for the as-fabricated baseplate, and the contractor cut off these bolts and replaced them with adhesive-set remedial anchors. A unique aspect of the investigation involved testing and inspection of the anchor bolts from the base of the failed columns as well as concrete cores, which had been removed from the footing, containing the holes in which the adhesive-set anchors had been placed. We performed laboratory tests using CAT scans, materials analysis, and microscopy to examine the anchor-bolt-to-concrete bond interface. Due to several errors in installing the anchors, the anchors had no adhesive bonding to the concrete. The deviations in the column base connection from the requirements of the structural drawings grossly reduced the overturning capacity of the column. The accident would not have occurred if the column base had been constructed as required by the design drawings.