PROJECT DESCRIPTION:

A coal-loading facility with three towering cast-in-place concrete silos that are 50’-0” in diameter and 133’-3” tall. A mechanical failure caused a fire in one of the silos causing structural damage. Because of extensive damage, the silo was shut dow

ADDITIONAL PROJECT FACTS:

  • Petrographic analysis and concrete cylinder testing utilized to assess extent of material damage.
  • Testing determined extensive micro cracking in slab and columns.
  • Underside of slab reinforced with 6-inch reinforced shotcrete layer.
  • Columns reinforced with fiber-reinforced polymer wraps.

Norfolk Southern Corporation operates a modern coal-loading and transshipping facility on Lake Erie. Three towering cast-in-place concrete silos (50’-0” in diameter and 133’-3” tall) serve as transload points for coal. The perimeter concrete walls are 12” thick with a 36”-thick cast-in-place hopper slab. The perimeter concrete walls and six interior columns support the slab. The slab supports up to 5,000 tons of coal. A mechanical failure caused a fire in one of the silos. The fire caused structural damage to the bottom of the hopper slab, several of the concrete columns, and portions of the perimeter walls. Due to the extensive damage, the silo was shut down and emergency repairs were required. To better assess the structural damage, concrete cylinders from the damaged slab were obtained in order to perform petrographic analysis and compression tests. In addition, several samples of the damaged reinforcing bars were collected to perform tensile tests. The petrographic analysis revealed that the intense heat generated by the fire caused micro cracking in a large portion to the underside of the slab and in the upper portion of the concrete columns. Additionally, the tensile tests of the reinforcing bars indicated the tensile strength for some reinforcement had been reduced by as much as 33%. Based on the testing results, it became apparent restoring the structural integrity and load-carrying capacity of the slab and the columns was required. Deteriorated/spalled concrete was removed along with two additional inches of concrete from the underside of the slab where micro cracking was detected in the petrographic analysis. A 6” reinforced shotcrete layer with the proper reinforcing bars was added to the underside of the damaged concrete slab. The new layer was anchored to the existing slab with dowels for proper load transfer between layers. The concrete was installed in multiple layers using shotcrete techniques. The restoration of the columns was more challenging due to the presence of equipment around the columns. Clearances around the columns were limited. To facilitate the repairs, fiber-reinforced polymer (frp) strengthening systems were utilized.

Damaged Silo FRP Wrap Column Repairs Fire Damage

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