The anchoring force describes the ability of a fastener to reliably transfer loads into a substrate such as concrete, natural stone, or rock. In concrete demolition and special deconstruction, during strip-out and cutting, as well as in rock demolition and tunnel construction, a correctly dimensioned anchoring force determines stability and safety—for example when fastening work platforms, guide rails, anchor points, or reaction supports. It also plays a central role when hydraulic tools such as hydraulic concrete crushers or hydraulic rock and concrete splitters from Darda GmbH transmit forces into components that serve as abutments or are diverted via temporary anchors.
Definition: What is meant by anchoring force
Anchoring force refers to the maximum permissible force that an anchor, dowel, or bonded system can transfer into the substrate in tension and/or shear without failure due to pull-out, concrete breakout, edge failures, or steel failure. It results from interlock (e.g., expansion action), friction, and bond between the fastening and the substrate. Decisive factors include the cracked condition of the concrete, concrete strength, embedment depth, edge distances, group effects, the type of loading (static, predominantly static, cyclic), and installation quality. In practice, a distinction is made between characteristic resistances and design capacities, with safety factors and partial safety factors to be applied. Anchoring force is therefore not a fixed material value, but the outcome of the system, the installation situation, and the load case.
Basics and influencing factors of anchoring force
The anchoring force is determined by the interaction of the fastening element and the substrate. For the substrate, homogeneity, density, crack pattern, moisture, and temperature are decisive; for the fastening element, geometry, steel grade, surface condition, and corrosion protection. In hydraulic applications—for example when using concrete crushers or rock and concrete splitters—additional dynamic and fluctuating components from start-up torques, impact loads, and vibrations can influence the allowable anchoring forces.
- Substrate: concrete strength (e.g., C20/25 vs. C40/50), cracked/uncracked, carbonation, edge distances, member thickness, reinforcement ratio.
- Anchor type: expansion anchors, undercut anchors, adhesive/bonded anchors, threaded rods with injection mortar, heavy-duty anchors; respective geometry and embedment length.
- Load case: tension, shear, combined loading, eccentricity, moments, fatigue; impact-type and cyclic loads from hydraulic duty cycles.
- Installation quality: drill hole diameter and depth, drill hole cleaning, curing times for mortars, tightening torque, installation in wet or cold conditions.
- Environment: temperature range, moisture, chemical action, corrosion, fire exposure, and UV influence on resin systems.
Types of loads and combinations
Anchors must resist tensile and shear forces, often in combination with bending moments. With concrete crushers, load peaks can arise from gripping and crushing; with rock and concrete splitters, reactive tensile forces in supports or abutments are relevant. Eccentric loading reduces the effective anchoring force through additional moments. Group effects in anchor arrays reduce capacities when the concrete cones overlap.
Substrates: concrete, rock, masonry
Concrete generally behaves isotropically, while masonry and natural stone/rock are often anisotropic. In rock, joint sets, foliations, and bedding interfaces influence pull-out resistance; the anchoring force must be considered along the dominant discontinuities. In masonry, hollow block zones, bed joints, and unit formats are critical. For tunnel construction and natural stone extraction, the orientation of the anchors relative to bedding and jointing is a decisive design parameter.
Design and verification of anchoring force
Design is based on approval-related parameters and application-specific safety concepts. In practice, realistic load assumptions, sufficient edge distances, embedment depths, and proper installation are essential. Where uncertainties exist, on-site anchor pull-out tests can determine the available anchoring force in the specific substrate. Normative and approval requirements are project-specific and require a well-founded, non-generic assessment.
- Determine loads: self-weight of fixtures, reaction forces of hydraulic tools, additional loads (hoses, adapters), dynamic components.
- Check the substrate: strength, crack condition, member thickness, edge distances, reinforcement position (locating).
- Select the system: expansion or undercut anchors for fast installation, bonded anchors for small edge distances or cracked substrates.
- Define embedment depth and arrangement: embedment length, spacings, edge distances, check slab thicknesses; consider group effects.
- Define installation: drilling method, cleaning, curing times, tightening torque, and installation checks.
- Provide verification: capacities in tension/shear, combined loads, interaction checks, and deformations.
- Testing/monitoring: suitability and spot checks, documentation, and, where applicable, recurring inspections for long service durations.
Example load sources when using concrete crushers and rock and concrete splitters
- Reactive forces from closing/opening concrete crushers as well as from splitting processes in concrete and rock.
- Impact loads when loosening residual components, breaking webs, or preloading splitting wedges.
- Vibrations from the hydraulic system (hydraulic Power Units), pressure surges, and intermittent operation.
- Eccentric loads due to asymmetric arrangement of auxiliary structures, guide rails, or supports.
Anchoring force in typical applications
Requirements vary by application. The key is that the anchoring force matches the actual loads and boundary conditions at the site and includes adequate reserves for operational and environmental influences.
Concrete demolition and special deconstruction
When opening, separating, and dismantling components, temporary anchors are used for anchor points, support frames, or reaction struts. Edge distances are often limited; bonded anchors with sufficient embedment length can offer advantages. With concrete crushers, combined shear/tension loads are common, so anchor plates with a larger hole pattern improve load distribution.
Strip-out and cutting
Reproducible anchoring forces are important for guide rails and machine mounts. Drill hole cleaning, defined curing times, and controlled tightening torques ensure load-capable installation. In damp and cool environments, the processing conditions of injection mortars are decisive.
Rock demolition and tunnel construction
In rocky substrates, joint orientations and shear planes influence the effective anchoring force. Rock splitting cylinders generate considerable splitting forces that can be introduced into anchors via supports or auxiliary structures. Short anchors with undercut geometry or deeply embedded bonded anchors are options, provided the rock quality allows it.
Natural stone extraction
During extraction and pre-cutting, temporary anchors stabilize rails, stops, or supports. The anchoring force must be dimensioned to account for uneven grain structure and possible voids. Test drillings and local pull-out tests increase planning reliability.
Special applications
In potentially explosive, chemically aggressive, or fire-exposed environments, material selection and system type significantly influence anchoring force. Stainless steel or coated systems can reduce corrosion risks; under temperature exposure, reductions in the load-bearing capacity of bonded systems must be considered.
Anchoring force and equipment concept
The selection and design of the anchorage depend on the tool used and its force introduction. Systems from Darda GmbH cover various load patterns from selective concrete demolition to rock removal:
- Concrete crushers: Predominantly shear and combined tension/shear loads in anchor plates or brackets; significant influence of impact loads.
- Rock and concrete splitters: Dominant tensile components at abutments and supports; high demands on edge distances and embedment lengths.
- Combination shears, multi cutters, steel shears: A stable substrate and form-fit fixtures reduce anchor loads; anchoring force primarily for fixings and anchor points.
- Tank cutters: Often thin-walled structures; when auxiliary frames are anchored to concrete, vibrations and shear components are in focus.
- Hydraulic power packs: Indirect influence through pressure and cycling behavior; vibration-isolated setups reduce dynamic load components on fastenings.
Installation quality and test methods
The best design is of little use without proper installation. The anchoring force only reaches the assumed values if drill hole diameter, depth, and cleaning are correct and anchors are installed as specified. For bonded anchors, mixing quality, temperature, and curing times are critical; for mechanical anchors, the correct tightening torque is essential.
- Create the drill hole: suitable diameter, sufficient depth, gentle method.
- Clean the drill hole: blow out, brush, blow out again—until dust-free.
- Install the system: mix and dispense bonded mortar correctly; rotate/press the anchor in centrally.
- Cure/tighten: observe specified times; apply tightening torque in a controlled manner.
- Acceptance/inspection: visual check, dimensional check, document spot pull-out testing.
Site-specific risks
Hitting reinforcement, insufficient edge distances, wet drill holes, or dust in the hole reduce the usable anchoring force. Overhead installations increase the requirements for cleaning and occupational safety. Shock loads from demolition operations require additional reserves.
Durability, corrosion, and environmental influences
The anchoring force changes over the service life: corrosion can reduce cross-sections, freeze-thaw cycles and chemical attack can impair bond. Temperature peaks—e.g., due to friction, solar radiation, or fire—particularly affect bonded systems. In crack-prone concrete, crack openings reduce capacity reserves. For cyclic loads from hydraulic work cycles, fatigue strength is decisive.
Practical guidance for estimating the required anchoring force
The required anchoring force results from the sum of all governing loads including dynamic allowances, divided by the number of effectively arranged anchors and reduced by interaction effects. A load-path assessment is sensible: forces from concrete crushers, rock and concrete splitters, or auxiliary structures should be introduced into the substrate as straight as possible and with minimal eccentricities. Larger anchor plates, increased embedment length, and sufficient edge distances increase the usable anchoring force. Where uncertainties exist, on-site tests are a suitable means to verify capacity reserves under real conditions.
Documentation and responsibilities
For the safe use of temporary and permanent anchors, complete documentation for design, installation, and testing is required. Binding verifications are governed by project-specific regulations; the design requires knowledgeable assessment of loads, substrates, and systems. Responsibility for selection, installation, and control lies with the executing specialist personnel and site management; the information in this article is general in nature and does not replace project-specific design.