Rebar Straightening Evaluation After Cage Collapse
Consulting Services Lab Services
A bridge pier (two reinforced concrete columns supported by a reinforced concrete footing), designed to support the superstructure of an Interstate highway, was under construction near Richmond, Virginia. In bridge pier construction, vertical rebar (dowels) project upward from the pier footing into each column and are spliced to longitudinal bars within the reinforcing bar cage, prior to concrete placement.
All of these vertical dowels were severely bent from their initial vertical configurations when a massive reinforcing bar cage collapsed during construction. In order to resume construction of the pier column, the bent dowels would either need to be straightened (re-bent) to near vertical or a significant portion of the massive foundation had to be demolished and rebuilt. The contractor responsible for pier construction opted to try straightening the dowels without applying heat, possibly impairing the strength and ductility of the steel. Moreover, straightened bars were expected to exhibit some irregularity in straightness that could affect the completed pier's performance.
CTLGroup was retained to evaluate the bar straightening procedure. When field engineers initially visited the site, the rebar cage remained collapsed. Samples of both curved and straight dowels were selected for removal and laboratory testing. Three months later, when about half of the dowels had been straightened, a second site inspection was conducted. Magnetic particle examinations were performed on 30 randomly selected dowels (both bent and straightened) in order to identify the presence of fracturing. No indications of fractures were found. Engineers selected a field-straightened portion and a straight portion from each of five dowels for subsequent tests.
Laboratory testing showed that specimens retained the physical and chemical properties needed for satisfactory performance. Structural calculations led to designated limits on the acceptable variance from straightness and guidelines on installing supplemental reinforcement where necessary. CTLGroup's work allowed the contractor to continue construction with confidence, once all straightness irregularities were addressed and all supplemental dowels were provided.