What anchor bolt restoration strategies are available?
Several strategies are available to reestablish anchor bolt integrity. Anchor bolts restoration strategies can be as follows:
Repair existing anchor bolts
Near surface separated anchor bolts can be repaired using mechanical couplings or welding stud extensions. Both techniques remove and replace anchor bolt threaded regions damaged by corrosion, lateral shear, or vertical ‘cup and cone’ failures. Property installed and incorporating appropriate metallurgical detailing, repairs as described can add significant service life to the existing anchor bolt system, once the ‘root cause’ of the failure has been determined.
|Repair of corroded anchor bolts using coupling and welding techniques.
Relocation of anchor bolts
Anchor bolt chairs are welded or bolted/riveted assemblies that are solidly affixed to the foundation support member/skirt just above the concrete foundation interface. (images) One of the major disadvantages in anchor bolt relocation is the probable obstructions caused by cast in place rebar that may be present at the new location. Use pachometers or GPR to locate steel up to 19 in. in depth below the concrete’s top surface.
|Excavation and inspection of corroded anchor bolts and anchor bolt chairs covered by a mason brick and mortar veneer.
|Corroded anchor bolt chair assemblies with bearing plates were only visible after insulation was removed.
Full depth anchor bolt extraction and reinstallation
The best alternative in many situations is the complete removal and replacement of the anchor bolts. In elevated structures, large equipment vessels can have anchor bolts extend through the entire reinforced concrete member thickness. (image) The existing corroded anchor bolts were forced through the grout sleeve annulus using modified jack hammers fitted with drill steel tips, and the existing anchor bolts were drilled/hammered out of position. The resulting anchor bolt annulus was grouted ‘tight’ for corrosion protection with a flowable, cementitious grout incorporating corrosion inhibiting admixtures.
Many times, the anchor bolts terminate within the structural section. In these situations, ‘over-coring’ employed. This process placed new anchor bolts at the same location as the original anchor bolts, but the anchorages can be longer with a larger diameter. This allows them to have a tighter ‘hold down’ capacity than the original anchorage system.
|Full depth corroded anchor bolts removed and new anchor bolts installed extending through a thick reinforced concrete structural slab.