Anchor bolts are central components of fastening technology in deconstruction, rock processing, and structural engineering. They reliably transfer tensile and shear forces into concrete and rock, secure equipment and temporary installations, and create defined load paths. In combination with devices from Darda GmbH – such as Darda concrete crushers, hydraulic rock and concrete splitters, rock splitting cylinders, combi shears, steel shears, multi cutters, tank cutters, and associated hydraulic power packs – they enable predictable and controlled workflows in concrete demolition and special deconstruction, gutting and cutting, rock demolition and tunneling, natural stone extraction, as well as special operations.
Definition: What is meant by anchor bolts
The term anchor bolt generally refers to steel threaded studs or anchors, sometimes stainless and sometimes galvanized, that are installed in a drilled hole and secured there by frictional or positive interlock. They serve to connect components, load-bearing systems, bearings, shoring or guides to concrete or rock. Depending on the principle, a distinction is made between mechanical heavy-duty anchors (expansion and undercut anchors) and chemical or injected anchors (bonded anchors). In practice, anchor bolts are used temporarily for assembly and safety tasks or permanently for structural connections, often under cracked concrete conditions, in edge zones, at elevated temperatures, or under dynamic loads.
Design, operating principle, and types
The selection of an anchor bolt is based on load capacity, base material (concrete strength, crack state), edge and spacing distances, environmental conditions, as well as installation and testing concept. Three basic principles are widespread:
Mechanical expansion and bolt anchors
Expansion anchors create a frictional bond in the drilled hole via cones and expansion sleeves. They are set with a defined tightening torque and carry load immediately. Advantages include immediate loadability and a well-controllable installation. Typical applications are bracing points, lifting/attachment points and brackets to absorb reaction forces that occur when working with concrete crushers or during cutting and separating operations.
Bonded anchors (injection and bonded mortar)
Bonded anchors transfer forces via adhesion between the threaded rod, mortar, and substrate. They are particularly suitable in cracked concrete, for small edge distances, and in rock. Load transfer occurs through bond stresses; the mortar curing defines the waiting time until loadability. In gutting and special deconstruction, bonded anchors are preferred when borehole quality, edge distances, or thermal effects impose special requirements.
Undercut anchors
Undercut systems create a positive interlock in a back-milled zone of the drilled hole. They offer high security against setting losses and are suitable for highly loaded, permanent fixings with minimal displacements, for example for load-bearing structures, guide rails, or reaction frames.
Materials, corrosion protection, and durability
Anchor bolts are manufactured from unalloyed steels (hot-dip galvanized), from stainless steels (e.g., austenitic grades), or from highly corrosion-resistant materials. The choice depends on moisture, chlorides, temperature, and service life. In areas with wet cutting, coolant/lubricants, or in tunnel situations, an appropriate corrosion protection is crucial. For temporary applications, galvanized versions may suffice; for permanent anchorage points in exposed locations, stainless variants are often used.
Design, load capacity, and boundary conditions
Design covers the tensile and shear capacity of the steel, the bond to the substrate, and concrete structural failure (e.g., concrete spalling, concrete tension cone, edge breakout). Group effects, reduced edge and spacing distances, crack widths, temperature, and fire exposure must also be considered. In dynamic applications – such as demolition with pulsating load peaks – load spectra, fatigue, and setting behavior must be evaluated. Verification is usually based on building authority–assessed values and conservative partial safety factors.
Relevant failure modes
- Steel failure of the bolt under tension or shear
- Pull-out due to insufficient embedment depth or borehole cleaning
- Concrete tension cone and edge breakout with unfavorable edge distances
- Setting and creep behavior (especially with bonded anchors and elevated temperatures)
Drilled hole creation, installation, and setting procedures
The load capacity of an anchor bolt stands and falls with the quality of the drilled hole. Accurate drilling, correct cleaning, and adherence to the setting process are mandatory.
Installation sequence for mechanical bolt anchors
- Create the drilled hole with the correct diameter and depth (hammer drilling or core drilling as specified).
- Remove drilling dust completely (blow out and brush until clean).
- Insert the anchor and apply the specified tightening torque to activate expansion.
- Attach the fixture, check torque, and document.
Installation sequence for bonded anchors
- Create the drilled hole to exact dimensions; pay particular attention to edge distances and hole depth.
- Cleaning in defined cycles: blow out, brush, blow out – until the hole is clean and dry (unless otherwise approved).
- Inject mortar with a static mixer (fill free of air, discard initial extrudate).
- Insert the threaded rod with a rotary motion up to the mark; wait for curing time.
- Install the component, apply tightening torque, perform inspection.
Quality assurance and testing
- Torque checks for mechanical anchors
- Pull-out tests (spot checks) for bonded anchors
- Documentation of borehole cleaning, mortar batch, and curing times
Applications in concrete demolition and special deconstruction
In controlled deconstruction, anchor bolts serve as temporary attachment points, for bracing components, and for fastening reaction frames. When using concrete crushers from Darda GmbH, anchors can, for example, support capture and guide assemblies, load distribution plates, or safety ropes. Loads are often combined (tension and shear), partly dynamic and alternating, which is why a safety-oriented design and testing concept is required.
Relation to concrete crushers
When biting off slabs and beams, load peaks and vibrations occur. Anchor bolts can fix mounting brackets, catch beams, or protective barriers. Adequate edge distances are important to avoid edge breakout on thin slabs, as well as verification for cracked concrete – especially in existing structures.
Use with rock and concrete splitters and rock splitting cylinders
Splitting operations require controlled boundary conditions and clear load paths. Anchor bolts, for example, secure guide rails, guards, or braces when blocks or walls are separated in a targeted manner. In combination with rock splitting cylinders from Darda GmbH, anchors can also serve as temporary abutments, provided the substrate is sufficiently load-bearing and the load case has been verified.
Combi shears, steel shears, multi cutters, and tank cutters
Cutting work on steel beams, tanks, or pipelines often requires mounting frames, rail guides, and holding points. Anchor bolts connect these safely to concrete foundations or rock. For tank cutters, spark formation and media contact must be given special consideration; systems with clean borehole preparation and clearly documented setting procedures are suitable here.
Rock demolition, tunneling, and natural stone extraction
In geological substrates, anchor bolts – often as bonded anchors in drilled holes with resins or injection mortars – are used to secure blocks, to fasten nets, and to create tension points for non-explosive splitting techniques. In rock demolition and tunneling, borehole cleanliness, shaft friction, and embedment length are influenced by the rock class. In natural stone extraction, anchors can temporarily serve as tie-back points or to guide splitting operations when large blocks are released.
Temporary vs. permanent anchorages
Temporary anchors are designed for the construction phase and are removed afterward or cut flush and properly sealed. Permanent anchorages require higher demands on corrosion protection, setting security, and verification. The respective concept must be defined early, especially if the anchors will no longer be accessible later. If removability is required, detachable systems or defined predetermined breaking points must be considered.
Safety, occupational safety, and general notes
Work with anchor bolts is subject to the usual safety rules for drilling, lifting, cutting, and hydraulic processes. The decisive factors are the manufacturer’s specifications for the anchors used, the installation instructions, and the structural verifications. For applications involving personal loads, net and capture systems, or anchors in potentially explosive atmospheres, increased requirements apply. The statements in this article are general and do not replace project-specific planning or verification.
Planning, selection, and coordination
A reliable anchoring solution arises from the interplay of design, installation, and testing. The following criteria are crucial in practice:
- Substrate: concrete strength, crack state, rock quality, moisture
- Load case: tension, shear, combined loading, dynamics, fatigue
- Geometry: edge and spacing distances, embedment depth, group spacing
- Installation: drilling method, dust extraction, borehole cleaning, setting tools
- Environment: temperature, corrosion, fire exposure, media contact
- Process: curing times, intermediate inspections, documentation, deconstruction
Common sources of error and practical remedies
- Insufficient borehole cleaning for bonded anchors – leads to reduced bond; perform cleaning cyclically and in accordance with standards.
- Incorrect drill diameter or embedment depth – loss of load capacity; verify dimensional accuracy before installation.
- Failure to observe curing times – setting and creep issues; consider ambient and component temperature.
- Edge distances too small – concrete edge breakout; adjust anchor type or geometry.
- Missing or incorrect tightening torque – setting errors with expansion anchors; use calibrated tools.
- Underestimated corrosion environment – premature damage; reconsider material selection and protection concept.
Sustainability, deconstruction, and repair
Where possible, removable anchoring solutions are advisable: remove temporary anchorages or cut them flush, close drilled holes, and properly repair surfaces. Complete documentation facilitates later deconstruction and proof to the client and authorities.