Anchorages are a fundamental element for safe and predictable load transfer in structures and rock. They connect components permanently or temporarily to the competent substrate and ensure that tensile, compressive, and shear forces are introduced in a controlled manner into concrete, masonry, or rock. In concrete demolition, special demolition, gutting works, rock breakout, and tunnel construction, an appropriate anchorage strategy enables precise work with hydraulic tools—such as concrete demolition shears or rock and concrete splitters from Darda GmbH—and reduces risks to people, the structure, and the surroundings.
Definition: What is meant by anchorage
Anchorage refers to the structural fastening of a component or system to the load-bearing substrate to safely resist service and self-weight, installation forces, or dynamic actions. This includes mechanical anchors (e.g., expansion and undercut anchors), bonded systems (injection or adhesive anchors), rock bolts and threaded rods set in mortar, as well as anchor channels and temporary tie-backs. The design considers material condition (cracked/uncracked concrete, rock category), embedment depth, edge distance and spacing, type of action (tension, shear, combined), as well as corrosion and environmental influences.
Anchorage in concrete and rock: systems, load transfer, and boundary conditions
The selection of a suitable anchoring system depends on the substrate, load level, and construction sequence. Mechanical anchors transfer loads into the member via expansion or positive locking, while bonded anchors transfer forces through an adhesive bond along the borehole wall. In rock, rock bolts, strand or bar anchors, and nailing are also used, often combined with cement or resin injection.
For reliable load transfer, the following parameters are decisive:
- Substrate: Concrete strength (compressive strength, crack state), rock quality (jointing, shear planes, water ingress), masonry structure.
- Embedment: Embedment depth, borehole geometry, borehole cleaning, and bond quality.
- Edge distance and spacing: Avoidance of edge spalling, breakout cones, and overlapping stress fields.
- Actions: Static, cyclic, and impact loads; temperature and humidity; chemical influences.
- Corrosion protection: Material selection (e.g., stainless steels), coatings, sealing in exterior and tunnel environments.
In practice this means: The higher the tensile components and the smaller the edge distances, the more likely undercut or bonded systems with sufficient embedment depth should be chosen. For rock anchors, assessing jointing and the quality of injection is crucial to transfer loads into intact rock.
Types of anchorage at a glance
Mechanical anchorages
Expansion anchors and undercut anchors offer fast installation, are preassembly-friendly, and can be loaded immediately. They are suitable for dense substrates with sufficient edge clearance and defined concrete quality.
Bonded and injection anchors
Bonded systems transfer loads through the adhesive bond along the borehole wall. They are advantageous at small edge distances, larger embedment depths, in cracked concrete, and in heterogeneous substrates. Curing times and borehole cleanliness are critical.
Rock anchors, nailing, and rock bolts
In rock breakout and tunnel construction, these systems stabilize break edges, tunnel face, and crown. They are often prestressed and grouted with cement or resin to limit displacements.
Anchor channels and temporary fixing points
Anchor channels allow sliding attachment of add-on components. Temporary fixing points are used for tie-back, slinging of lifting devices, or guiding separation cuts during deconstruction.
Design and verification of anchors
Design follows recognized engineering practice. The basis is load assumptions, substrate assessment, detailing, setting method, and verifications against steel failure, concrete/rock breakout, and combined actions.
- Subsoil investigation: visual inspection, rebound hammer, core drilling, rock logging; jointing and moisture determine the system choice.
- Load model: characteristic loads and partial safety factors; consider installation, lifting, and cutting loads during deconstruction.
- Geometry: minimum distances, member thicknesses, embedment depth; avoidance of reinforcement hits.
- Detailing: corrosion protection, fire protection, sealing; accessibility for installation and inspection.
- Testing concept: suitability and setting tests, if necessary on-site anchor pull-out test to confirm input values.
Anchorage in concrete demolition and special demolition
In controlled deconstruction, anchorage is used to secure components, guide separation cuts, and stabilize lifting operations. The interaction with hydraulic tools is central.
Working with concrete demolition shears
When separating wall and slab elements with concrete demolition shears, temporary anchors take the segment loads, limit rotation, and prevent uncontrolled edge breakout. Load paths are defined before the shear cut; corresponding edge distances and embedment depths must be planned.
Rock and concrete splitters
During hydraulic splitting, the fracture line can be guided by targeted pre-anchorage and tie-backs. Anchors provide retaining force until the splitting process is complete and secure adjacent components against secondary fall.
Segmentation suited to disposal
Anchorages serve as attachment points for lifting gear and enable controlled lowering of detached components. This minimizes consequential damage and accelerates workflows.
Anchorage in rock breakout and tunnel construction
In rock, anchors are used to stabilize break edges, disturbed zones, and crown areas. In combination with rock wedge splitters, defined predetermined breaking lines can be created, while rock bolts ensure the stability of the remaining structures.
Pre-support and stabilization
Prestressed anchors reduce movements and secure areas against spalling. In water-bearing joints, bonded systems with suitable injection and sealing are advantageous.
Gutting and cutting
For separation cuts with wire or wall saws and during core drilling, precise fixing points are required. Anchorages hold guide rails, saw stands, and drill stands. Load-bearing capacity and edge distances must be verified for thin elements and ribs; dust and slurry management affect borehole quality and thus the bond.
Natural stone extraction
In natural stone extraction, rock and concrete splitters are used to create separation joints. Anchorages are used to brace the blocks, guide the fracture line, and serve as attachment points when flipping and transporting. Substrate variability (bedding, joints) requires adapted embedment depths and setting tests.
Installation, setting technique, and quality assurance
Execution determines load-bearing capacity. Errors in borehole creation and cleaning are the most common causes of reduced capacity, especially with bonded anchors.
- Drilling technique: diameter and depth per system specification; low-vibration methods to preserve existing structures.
- Borehole cleaning: blow out and brush until clean; only then does a load-bearing bond develop.
- Setting and tightening: torque control for mechanical anchors; observe curing times for bonded anchors.
- Documentation: records of drilling and setting data, batch numbers, temperatures, and results of setting and anchor pull-out tests.
Safety and legal notes
Anchorages are safety-relevant components. Planning, installation, and testing should be performed by competent personnel. The applicable standards, recognized rules of practice, and approvals must be observed. Stated capacities and limits of use must be verified for the specific project; legally binding assessments cannot be provided here.
Common sources of error and how to avoid them
- Insufficient substrate investigation leads to incorrect system selection.
- Failure to maintain edge distances promotes edge spalling.
- Incomplete borehole cleaning reduces bond performance.
- Lack of torque control for mechanical anchors reduces clamping action.
- Underestimated installation and lever-arm effects during deconstruction overload fixing points.
Tools and methods in the context of anchorage
Hydraulic tools such as concrete demolition shears, rock and concrete splitters, rock wedge splitters, combination shears, Multi Cutters, steel shears, and tank cutters from Darda GmbH are often integrated into workflows that rely on reliable anchorages. Hydraulic power units supply the required energy for controlled cutting and splitting processes, while the anchorage ensures the position, load transfer, and safety of the components during processing.
Practical guide: Choosing the right anchorage
- Assess the substrate: concrete strength, crack pattern, rock category, moisture.
- Define the load case: tensile, transverse, or combined loads; installation and dynamic components.
- Select the system: mechanical for immediate loadability, bonded for small edge distances, rock bolts for jointed substrates.
- Set geometry: embedment depth, edge distances, member thickness.
- Secure execution: borehole cleaning, setting and torque control, curing times; implement the testing concept.