Trouble Shooting Anchors
Troubleshooting Anchors Secure Strand During Post Tensioning Repair
When post tensioning strands fail, the result can be serious. Depending on the extent of the damage and the age of the strand, damaged strand can cause sudden structural failure. The cable may even erupt out of the slab and threaten anything or anyone nearby.
Fortunately, instances like these are rare, especially when post tensioning crews are called in to repair the damage before it reaches critical levels. And when they are called in, part of the job includes isolating the damaged strand and replacing it without disturbing the rest of the cable. This is where troubleshooting anchors come in.
Troubleshooting anchors are used with unbonded single strands, which are in widespread use in residential and commercial slabs. Unbonded strands can be accessed individually and secured with troubleshooting anchors. Bonded tendons, which are typically found in bridges and girders, are not compatible with troubleshooting anchors and require specialized equipment to repair.
How Do Troubleshooting Anchors Work?
A troubleshooting anchor looks like a typical tendon anchor, only it has a removable piece that borders the anchor’s wedge cavity. This piece can be removed and secured with a bolt. When removed, the anchor can be fitted around the strand, so it can be used to “lock off” or maintain tension forces while other parts of the strand are repaired. This is what the process looks like:
- An access hole is cut in the slab to expose the damaged stretch of cable.
- A steel bearing plate is installed at the strand’s up side. The up side is the end where tension forces must be preserved.
- The bearing plate is leveled using grout, so that it can match the horizontal and vertical positioning of other anchors on the strand.
- The troubleshooting anchor is placed adjacent to the bearing plate and fitted around the strand.
- A multi-piece wedge is placed on the strand and seated into the troubleshooting anchor.
- Once the wedges are in place, the damaged part of the strand can be cut away and replaced.
During this process, it’s the troubleshooting anchor that maintains the tension load on the strand. You’ll hear these anchors referred to as lock-off devices because they isolate the tension forces to the intact part of the strand. This allows crews to detension the damaged part of the strand and safely remove it without recoil.
Although troubleshooting anchors are built like permanent anchors, they aren’t always used as a permanent replacement. If needed, a troubleshooting anchor can remain on the strand until new strand is laid down and spliced with the intact strand. A new anchorage set can then be installed at the slab’s edge and used to anchor this spliced strand in place. The troubleshooting anchor can then be removed without risk.
When is a Troubleshooting Anchor Needed
Troubleshooting anchors are strictly for strand repair or replacement, so you’ll only see them when there’s damage to an existing slab. Some of the most common causes behind this damage include:
- Corrosion. Corrosion is a primary threat to post tensioning strand, especially in older slabs where there’s minimal protection in place. In fact, strand that’s decades old may only be wrapped in paper. Corrosion is caused by exposure to water or chemicals, and eventually saps the strand’s strength.
- Errors during stressing. Poor core drilling or saw cutting techniques can inadvertently damage the strand. Improper anchor installation can cause failures at the end of strands.
In all of these cases, a troubleshooting anchor is needed for its ability to lock off the damaged strand.
Durability and Compatibility with Strand are Priorities in Troubleshooting Anchors
Given the role a troubleshooting anchor plays in post tensioning repair, it’s critical that crews have durable anchors to work with. Troubleshooting anchors must be reliable and durable enough to withstand intense force application, much like any anchorage set. As such, troubleshooting anchors are typically manufactured from high-strength steel, including carbon steel.
In addition to durability, your troubleshooting anchor must be fitted for the strand it will be used with. This means matching the anchor to the right strand diameter, whether that’s .5 or .6 strand.
Flickinger Machine Can Help Maintain Troubleshooting Anchors
When tensioning crews are called in for repair, they may need a collection of troubleshooting anchors to fully restore the strand’s function. If your crew frequently handles post tensioning repairs for its clients, then you’ll need an inventory of anchorage sets to ensure project efficiency.
The Flickinger Machine team can provide those anchorage sets, including troubleshooting anchors for varying strand diameters. Our troubleshooting anchors are manufactured by leading brands and are field proven for their reliability.