Anchoring bolts are central connecting elements in industrial and construction environments: they carry loads, position components, and enable detachable or permanently anchored connections in concrete, steel, and natural stone. In practice, they appear in machine foundations, flange joints, anchor plates, guardrails, equipment mountings, and temporary auxiliary structures. In deconstruction and when working on existing structures, anchoring bolts play an important role—for example, during controlled exposure, separation, and removal in the course of concrete demolition and deconstruction, during building gutting and concrete cutting, or in rock demolition and tunnel construction. Expert handling of anchoring bolts increases safety, accelerates workflows, and minimizes damage to the load-bearing system—especially when precise, hydraulic tools such as concrete pulverizers or hydraulic wedge splitters are used.
Definition: What is meant by anchoring bolts
An anchoring bolt is a headless, bolt-shaped connecting element that is fully or partially provided with an external thread and sits firmly and permanently in a base material (e.g., concrete, natural stone, or steel)—it effectively “stands” as a threaded bolt. Using nuts, washers, or mounted components, the anchoring bolt creates a detachable connection. Anchoring bolts are implemented as screwed-in elements, grouted elements (grouted anchor), cast-in elements (cast-in anchor rods), or welded-on elements (weld studs). In day-to-day project work, anchoring bolts are often also referred to as anchor rods, threaded studs, or anchor bolts. They differ from screws primarily by the absence of a screw head and by the type of anchorage in the base material.
Design variants, materials, and standards
Anchoring bolts exist in numerous versions, tailored to load, environmental conditions, and installation method. Common designs include double-ended or single-ended threaded studs, bolts with centering or fitted sections, weld studs with an ignition tip, and fully threaded anchor rods for bonded systems. Materials include non-alloy steels by strength classes (e.g., 5.6, 8.8, 10.9), stainless steels (e.g., A2, A4), and corrosion-resistant special alloys for aggressive media. Selection is based on mechanical loading (tension, shear, combined actions), temperature, corrosivity category, and required durability. Terminology, dimensions, and quality requirements are aligned with recognized standards and specifications (e.g., DIN standard and ISO standards for thread dimensions, strength classes, weld studs, and threaded rods) as well as technical regulations and building authority/performance-specific requirements. Project work also draws on manufacturer-specific approvals and test reports, for example for grouted anchor systems in concrete.
Load behavior and design fundamentals
The load behavior of anchoring bolts is determined by steel strength, embedment depth, edge distance and spacing, the condition of the substrate, and the load type. In concrete, characteristic failure modes include pull-out (steel/bond failure), concrete breakout at edges, splitting failure (at small edge distance), steel failure in tension/shear, or combined loading with bending. Design and verification follow recognized engineering practice using partial safety factors and interaction relationships; governing parameters include concrete strength, anchorage substrate, borehole geometry, embedment depth, and installation quality. In natural stone or masonry, material homogeneity, joints, and anisotropy require special consideration. In steel assemblies (e.g., flange joints), shear and tensile stresses in the thread dominate, as do friction in preloaded connections and contact pressure under the bearing surface.
Influencing factors on load capacity
- Edge distance and spacing, concrete compression zone, and existing reinforcement
- Embedment depth, borehole quality, and drilling method
- Installation parameters (torque/preload, curing times for grouted anchors)
- Environmental conditions (temperature, humidity, chloride contamination, chemical attack)
- Material selection and corrosion protection system
- Installation tolerances and component fit
Installation: methods and quality assurance
The choice of installation method depends on the substrate, required load capacity, and site constraints. For grouted anchors (bonded anchoring bolts), clean, dimensionally accurate boreholes, standardized cleaning (brushing and blowing), and correct dosing of the grout are critical. Embedment depth is verified, curing time observed, and tightening torque documented. For cast-in placement, bolts are fixed using drilling templates or anchor cages to ensure position, alignment, and thread protection during concreting. Weld studs require clean surfaces, defined welding parameters, and subsequent visual or, if necessary, non-destructive testing. Screwed-in anchoring bolts require sound internal threads and a coordinated tightening method, often with torque or turn-of-nut control.
Tools and aids
- Drilling and cleaning equipment (rotary hammer, brushes, blow-out devices), setting tools
- Torque tools and instruments for preload measurement
- Welding equipment for weld studs with test instruments
- Assembly gauges, templates, thread protection
Anchoring bolts in existing structures: exposure, separation, and deconstruction
In deconstruction, anchoring bolts are often exposed, cut to length, or completely removed without unnecessarily weakening the load-bearing structure. In concrete demolition and special demolition, localized removal of the surrounding concrete allows subsequent loosening or shearing. Concrete pulverizers are suitable for fragmenting concrete precisely and with low vibration levels until the threaded sections become accessible. For massive foundations, hydraulic wedge splitters can be used to split the concrete in a controlled manner and selectively relieve anchor zones—an emissions-low alternative to impact-intensive methods. Protruding anchoring bolts on steel components or flanges can be separated using suitable cutting or shearing tools (e.g., steel shears or multi-cutters). In confined areas, as typically encountered during building gutting and concrete cutting, compact hydraulic solutions with a matching hydraulic power pack are advantageous to optimize precision, occupational safety, and cycle times.
Procedure by substrate
- Concrete: Local exposure with a concrete pulverizer; supplementary core drilling to reduce stresses; then shearing/cutting off or unscrewing, where possible.
- Steel: Separation by shearing, sawing, or thermal cutting; protect threads and bearing surfaces if components are to be reused.
- Natural stone: Gentle splitting with rock wedge splitters to prevent uncontrolled crack formation; localized exposure enables low-damage disassembly.
- Tunnel construction/shotcrete: Observe edge distances and reinforcement layers; low-vibration methods reduce impacts on the shotcrete bond.
Safety, emissions, and occupational safety
When exposing and separating anchoring bolts, dust, noise emission, vibration, and sparks must be minimized. Personal protective equipment, controlled work areas, and coordinated cutting or splitting strategies are essential. Low vibration levels methods such as splitting or targeted fragmentation with concrete pulverizers can protect sensitive environments, utilities, and adjacent components.
Corrosion protection and durability
To ensure reliable service life, anchoring bolts are protected by suitable coatings (e.g., galvanic or hot-dip galvanizing), by stainless steel, or by duplex systems. In chloride contamination environments, splash zone areas, or tunnel sections with varying humidity, material selection and sealing of contact surfaces are particularly important. Insulating layers, suitable washers, and properly sealed penetrations prevent contact corrosion and moisture ingress. Maintenance plans with visual inspections, retightening of nuts, and spot checks increase operational safety.
Testing, acceptance, and documentation
Quality assurance includes visual inspections, dimensional checks, torque and preload checks, and random tensile or pull-out tests, especially for grouted anchors in concrete. For weld studs, visual and, if required, non-destructive testing are used. Documentation of installation parameters, batches, grout systems, and curing times facilitates later verification during operation or modifications. In existing structures, suitability tests and pull-off tests provide reliable indicators of the load capacity of existing anchoring bolts, including targeted anchor pull-out test campaigns where appropriate.
Typical sources of error and practical tips
- Insufficient borehole cleaning with grouted anchors leads to reduced bond capacity.
- Incorrect tightening torque alters preload and can impair shear capacity.
- Failure to observe curing time reduces initial strength.
- Edge distances that are too small promote concrete breakout; consider boundary conditions early.
- Material mix-ups (e.g., wrong strength class or stainless grade) cause unwanted failure modes or corrosion.
- In deconstruction: Cutting without stress relief can promote cracking; controlled exposure with a concrete pulverizer or splitting technique improves safety.
Relevance across application areas
Anchoring bolts are a cross-cutting topic in numerous projects: In concrete demolition and special demolition, machine foundations with cast-in anchor rods are dismantled; precise exposure using concrete pulverizers reduces consequential damage. During building gutting and concrete cutting, anchoring bolts on equipment, brackets, and cable tray supports must be systematically released, marked, and documented. In rock excavation and tunnel construction, anchoring bolts appear on anchor plates, equipment, and temporary fixings; edge distances in shotcrete and reinforcement layout call for low-vibration procedures where hydraulic wedge splitters offer advantages. In natural stone extraction, anchoring bolts often secure machines and lifting devices to foundations; robust and well-protected connections are essential. In special demolition (e.g., industrial deconstruction), flange joints and steelwork connections with anchoring bolts are frequently handled under confined, safety-critical conditions where low-noise, precise cutting and splitting methods are required.
Reference to selected tools
Concrete pulverizers enable selective removal of concrete to expose anchoring bolts in a controlled manner without excessively loading adjacent structure. Hydraulic wedge splitters are ideal for opening massive sections, relieving stresses, and accessing anchor zones. Additionally, suitable cutting and shearing tools (e.g., steel shears, multi-cutters) can efficiently sever protruding threaded studs. A matching hydraulic power pack is used to operate hydraulic devices.
Survey, locating, and planning
Thorough surveying reduces risks and rework. This includes plan review, exploratory openings, and locating reinforcement, embedded items, and anchor zones, e.g., with ground-penetrating radar (GPR). Inspection openings, markings, and sampling provide information on embedment depths, material condition, and corrosion patterns. Based on these data, the method selection, work sequence, and protection measures are defined—particularly where sensitive utilities, machines, or historical components are adjacent.
Terminology and differentiation
In project practice, it is useful to distinguish between anchoring bolts, through-bolts, threaded rods, and mechanical anchors. Anchoring bolts are fixed in the substrate and provide the mating part for nut connections; through-elements clamp components with a head and nut. Grouted anchors transfer load through a curing grout, while mechanical anchors work via expansion or undercut mechanisms. This classification helps to select installation, testing, and deconstruction methods precisely and to clearly define interfaces between trades.