Steel anchors are central connecting elements in structural engineering, geotechnical engineering, and plant construction. They transfer tensile and transverse forces into concrete, masonry, or rock and secure components, machine foundations, façades, column bases, or temporary shoring. In deconstruction and during repair works, the construction type, embedment depth, and pre-tension of steel anchors influence the choice of method and tool. Especially when working with concrete pulverizers as well as hydraulic rock and concrete splitters from Darda GmbH, understanding the anchor geometry, the load transfer, and the boundary conditions is crucial to work in a controlled, material-friendly, and safe manner.
Definition: What is meant by steel anchor
Steel anchors are steel anchorages that introduce loads into a load-bearing substrate. They often consist of threaded rods or strands with an anchor head and an anchor plate, are fixed mechanically (for example by expansion or undercut) or adhesively (for example with injection mortar) in the borehole, and transfer forces via friction, positive fit, and bond. In rock and tunnel construction, pre-tensioned rock bolts and permanent anchors are also used to secure excavations, adits, or cavities. In existing structures, steel anchors appear as bonded anchors, dowels, through-anchors, headed studs, or as part of anchor plate assemblies and must be treated in deconstruction as local reinforcements and potential restraint points.
Design and types of steel anchors
Steel anchors can be differentiated by their working principle and installation. Mechanical anchors generate an expansion effect in the borehole or engage positively in an undercut geometry. Chemical anchors utilize the bond between mortar and substrate; they are often suitable for cracked and older concrete. Through-anchors and installation anchors are set through the attached parts and can be identified in existing structures by visible nuts and washers. Rock bolts and strand anchors are usually pre-tensioned; their end anchorage with an anchor plate is accessible, while the free anchor length is grouted in the borehole. In refurbishment works, grouted dowels, headed studs, and bonded anchors are also encountered; when cutting, these can produce different failure behaviors.
Planning and investigation: identifying steel anchors in existing structures
Careful investigation reduces surprises in deconstruction. Clues are provided by existing drawings, anchor logs, reinforcement and formwork drawings, as well as a visual inspection of anchor heads, plates, or supports. For concealed anchors, trial openings, magnetic location, and endoscopic drillings help. Decisive parameters are embedment depth, diameter, edge distances, and any pre-tension. These determine whether controlled exposing with concrete pulverizers, splitting with stone and concrete splitters, or cutting with steel shear and Multi Cutters from Darda GmbH is appropriate. For pre-tensioned systems, safe releasing before severing must be planned; the procedure follows project-specific requirements and should always be chosen to minimize risk.
Deconstruction concept: expose, split, cut, extract
Exposing with concrete pulverizers
Concrete pulverizers locally crush the concrete cover to make anchor heads, nuts, washers, and anchor plates accessible. Targeted nibbling reduces vibrations and enables successive exposing even in sensitive areas. Controlled force application via hydraulic power units from Darda allows finely metered work that minimizes spalling at edges and corners.
Splitting with stone and concrete splitters
Stone and concrete splitters as well as stone splitting cylinders create defined fracture planes along the desired separation line. Around anchor zones, this allows the concrete to be broken into manageable pieces without introducing extensive impacts or vibrations. This is particularly advantageous in concrete demolition and special demolition when neighboring components or installations must be protected.
Cutting with steel shears, Multi Cutters, and combination shears
After exposing, anchor rods, anchor plates, or tension members are separated with steel shears or Multi Cutters. For mixed-material cross-sections—such as residual concrete with embedded steel parts—combination shears help cut through both materials in a single pass. The choice of cutting jaws depends on diameter, material strength, and accessibility. For thick anchor plates, step-by-step removal combined with splitting of the surrounding concrete can be more process-safe.
Releasing pre-tensioned anchors
Pre-tensioned rock bolts or strand anchors may contain stored energy. Before any cut, a safe release must be ensured, for example by controlled loosening of the anchor plate, incremental backing off of the nut, or by pre-removing surrounding concrete to reduce clamping and bond forces. The specific procedure should follow recognized rules and be performed only by trained personnel.
Load transfer, edge distances, and failure modes
Steel anchors transfer tensile forces into the substrate through bond and positive-fit mechanisms. Typical failure modes are steel failure, pull-out of the concrete tension cone, bond failure in the mortar, or a combination thereof. Edge distances and spacing influence the size of the tension cone and thus both the load-bearing capacity and the controlled removal in deconstruction. Sufficient exposing with concrete pulverizers facilitates the targeted placement of splitting wedges and reduces uncontrolled spalling. With tight edge distances, splitting in multiple, staggered placements is recommended to steer crack propagation.
Application areas: practical use
Concrete demolition and special demolition
In heavily anchored foundations or machine substructures, steel anchors are often large in size. The coordinated interaction of exposing, splitting, and cutting—concrete pulverizers, stone and concrete splitters, and steel shears—enables sequential removal that accounts for residual load-bearing capacity and increases occupational safety.
Strip-out and cutting
When dismantling façade anchors, brackets, and attachments, accessibility is crucial. After opening the connection zone with concrete pulverizers, anchor rods are separated with Multi Cutters. The low vibration levels preserve adjacent fit-out and installations.
Rock demolition and tunnel construction
Temporary rock bolts and securing elements are removed or destressed depending on the project. Splitting techniques help remove anchor heads and anchor plates without destabilizing the surroundings. Where full extraction is not required, flush cutting and the safe sealing of core drill holes is often sufficient.
Natural stone extraction
In quarries, anchored safety and temporary fixings are used. Stone and concrete splitters enable precise opening along split cracks, while steel shears separate steel anchorings. Blocks can thus be released in a controlled manner and sized for transport.
Special operation
In special situations—such as severely corroded or oversized anchor heads—a combined approach may be necessary: segmental nibbling of the plate, splitting the anchor surroundings, and final separation of the remaining tension members. Hydraulic power packs from Darda GmbH provide the finely metered power needed for a controlled approach.
Material, corrosion, and durability
Material properties influence cutting behavior. High-strength steels are more notch-sensitive; cutting surfaces should therefore be produced with minimal burrs. Corrosion can reduce bond or create nonuniform load paths, changing the failure pattern. Injection mortars and fillers encountered during exposing can vary—from mineral to polymeric. The appropriate tool and cutting sequence are therefore matched to material, moisture, and substrate strength.
Procedural principles for controlled deconstruction
Sequence and pacing
First expose, then split, and finally cut—this sequence provides clarity, reduces restraint, and facilitates safe extraction. For plate anchors, a star-shaped approach with alternating contact points has proven effective.
Achieving load-free states
Before tension members are cut, the component should be brought as close as possible to a load-free state, for example by temporary shoring or relief via additional cuts. This avoids uncontrolled movements.
Cleanliness in the borehole and at the contact zone
Dust and loose particles affect bond and crack propagation. Careful cleaning of the contact zones improves the predictability of splitting and failure behavior.
Quality assurance and documentation
Ongoing documentation of the work steps—such as photos of exposing, cut interfaces, and removed anchor parts—increases traceability. Cut edges, remaining lengths, and the treatment of boreholes are recorded. Removed steel must be separated according to applicable rules and directed to recycling. Where project-specific requirements for noise emission, dust exposure, or vibrations apply, working with hydraulic concrete pulverizers and splitters offers advantages, as these methods can be precisely and low-emission metered.
Occupational safety and environmental protection
When dealing with steel anchors, personnel safety and protection of the surroundings come first. Potential risks include stored pre-tension forces, uncontrolled component movements, cutting and crushing hazards, as well as dust and noise emissions. Protective measures include exclusion zones, load release, spark and debris protection, appropriate personal protective equipment, and a clear communication structure within the team. Procedures must always be planned project-specifically and executed with due care.