The term reinforcing steel resistance value describes the set of parameters used to capture the load-bearing and section behavior of reinforcement steel in structures. For planning, deconstruction, and selective demolition this value is decisive: it influences how concrete and reinforcement fail together, what cutting forces tools must deliver, and how reliably components can be separated into controlled sections. In conjunction with concrete pulverizers and hydraulic rock and concrete splitters from Darda GmbH, the resistance of reinforcing steel shapes the technical approach—from exposing the reinforcement to safely severing the bars.
Definition: What is meant by reinforcing steel resistance value
In the narrower sense, the reinforcing steel resistance value refers to the governing mechanical material properties (e.g., yield strength, tensile strength, shear resistance) that describe a reinforcing bar’s resistance to plastic deformation and separation. In design, characteristic and design resistances are derived from these (e.g., from the characteristic yield strength fyk of grade B500). In a broader sense, this also includes electrical resistivity, which can be used for assessments of corrosion processes or for non-destructive testing. For deconstruction, concrete demolition, and rebar cutting, however, the primary concern is mechanical resistance, as it determines the required cutting force and the procedure with concrete pulverizers, combination shears, or steel shears.
Parameters and design quantities of reinforcing steel
Reinforcing steel (rebar) is used in standardized grades with characteristic strengths. Steels of strength class B500 are common, with a characteristic yield strength of about 500 N/mm². The tensile strength lies above that; ductility (elongation and strain hardening behavior) matters for the fracture pattern and for cutting work. For cutting operations in deconstruction, the effective shear resistance is decisive; in practice it results from yield strength, bar diameter, cutting geometry, and friction effects. The electrical resistivity of unalloyed structural steels typically ranges around 0.1 to 0.2 Ω·mm²/m; it is useful for corrosion assessment and NDT, but not for sizing cutting operations.
Importance in concrete demolition and special deconstruction
In selective deconstruction, concrete and reinforcement form a composite system. The mechanical resistance of the reinforcing bars influences the demolition concept in several steps:
- Exposing with concrete pulverizers: The higher the bars’ resistance, the more strongly the reinforcement holds fragments together. Concrete pulverizers are used to selectively break the concrete, reduce the cover, and make bars accessible.
- Cutting with steel shears or multi cutters: The cutting force must match bar diameter and steel grade. Higher resistance values require greater reserves and adapted cutting geometries.
- Splitting with stone and concrete splitters: Rebar acts like a “clamp.” The resistance of the bars can limit crack opening. With dense reinforcement, the drilling and splitting pattern is adjusted, or bars are severed beforehand.
In strip-out and cutting, tunnel construction, or special deployments, the reinforcing steel resistance value determines whether to cut first or to crush/split first. The goal is controlled failure with minimal edge effects, low vibration, and clean separation between concrete and steel.
Estimating the required cutting force
For selecting concrete pulverizer combinations and for cutting reinforcement, a rough estimate of the cutting force is helpful. It is guided by bar diameter, steel grade, and cutting geometry:
- Determine the diameter: Identify the nominal size (e.g., 12, 16, 20, 25 mm). The cross-section A follows from the diameter (circular area).
- Assume the steel grade: If no documentation is available, conservatively assume at least B500 for newer structures.
- Account for a cutting factor: The effective shear resistance is typically below the tensile yield strength. A practical approach applies a factor that represents cutting geometry, friction, material hardening, and edge wear.
- Safety margins: Aging, work hardening, corrosion, or irregularities call for reserves, especially for large diameters.
Illustrative guidance
For a Ø 20 mm bar (A about 314 mm²) of grade B500, depending on cutting geometry and condition, forces well above 100 kN may be necessary. Larger diameters and work-hardened or older steels increase the demands. For consistent performance, reliable hydraulic power units must deliver the required pressure and flow steadily so the cutter proceeds uniformly.
Influence of bar diameter, ductility, and surface
Beyond strength, additional features govern resistance to separation and the interaction with the concrete:
- Diameter: Cutting work increases more than proportionally with cross-section; small diameters are usually cut flush, large diameters often require positioning in the cutting notch.
- Ductility: Tough steels flow more before the separating cut, increasing cutting work but reducing the risk of brittle fracture.
- Rib geometry: Ribbed bars anchor better in concrete; during exposing, “hook effects” can occur, necessitating additional crushing with concrete pulverizers.
- Concrete cover: Larger cover increases the effort to expose; insufficient cover promotes corrosion and can locally affect mechanical properties.
Electrical resistance and corrosion: relevance in deconstruction
The electrical resistance of reinforcing steel plays a role in material diagnostics. A higher specific resistivity of the concrete (not the steel) damps corrosion currents; the steel itself has relatively low specific resistivity. For deconstruction this is indirectly relevant: corroded bars often have cross-sectional losses and roughened surfaces, which can change cutting work. Visual inspections, tapping off rust layers, and proper exposing are therefore advisable before cutting with shears.
Interaction of concrete pulverizers and stone and concrete splitters
In practice, a sequential workflow has proven effective:
- Local crushing with concrete pulverizers to reduce concrete cover, open cracks, and make reinforcement visible.
- Targeted splitting with stone and concrete splitters in predrilled holes, when components must be separated without vibrations or with low noise. Dense reinforcement can limit crack propagation; in such cases, bars are relieved beforehand.
- Final severing of the bars with precision steel shears for rebar or multi cutters. Cutting under tensile load is avoided; where possible, bars are relaxed in advance.
Adapt drilling and splitting pattern
For heavily reinforced components, drilling spacings are reduced and lines are aligned with reinforcement layers. The reinforcing steel resistance value dictates whether additional separating cuts are needed to avoid “bridges” formed by bars.
On-site practical assessment
In deconstruction, metallurgical data are rarely available. The following pragmatic steps help with assessment:
- Measure the diameter (caliper) and check bar type (plain or ribbed).
- Consider the construction date: More recent structures often contain B500; older ones may include lower grades, sometimes with different ductility.
- Assess condition: Corrosion, accretions, layers, and coatings influence cutting work and positioning in the cutter jaw.
- Plan conservatively: If in doubt, assume the higher grade and divide the cutting task into smaller sections.
Influence of aging, work hardening, and temperature
Repeated loading, bending, straightening, or old cold-forming often increase flow stress locally. As a result, the effective resistance to separation can rise. Low temperatures favor brittle behavior, while elevated temperatures can reduce strengths. Deconstruction is therefore carried out where possible at moderate temperatures, and bars with visible bends or hooked zones receive special attention.
Safety and work organization
Cutting reinforcement requires accurate positioning control, sufficient exposing, and suitable tool selection. Principles:
- No cuts under tension: Bars still supporting components are only severed after unloading to prevent unexpected movement or whiplash.
- Seat the cutter correctly: Position bars centrally in the notch, avoid skewing, ensure sufficient reach.
- Hydraulic power packs are operated with stable pressure and flow; lines and couplings are checked before use.
- Personal protective equipment and barricading are mandatory; risks of splinters and crushing must be considered.
Legal and normative requirements may vary by country and project. Requirements must be observed; project-specific evaluations are performed by competent personnel.
Special cases: high-strength steels and prestressing steel
Some structures contain high-strength reinforcement or prestressing steel. Their resistance values are significantly above those of conventional reinforcing steels; additionally, prestressed systems store substantial energy. Severing such elements requires special procedures and careful unloading plans. Without clear identification and release, such steels are not cut. If tendon ducts or anchorage heads are suspected in the component, the workflow is adapted accordingly.
Material separation and recycling
A clean separating cut facilitates the sorted collection of reinforcing steel. If the concrete is crushed with concrete pulverizers and the reinforcement is cut appropriately, steel portions can be removed efficiently. Knowing the resistance values helps sequence cuts to minimize rework and to divide components into manageable segments.
Planning notes for typical areas of application
Concrete demolition and special deconstruction
For slabs, beams, and walls with reinforcement on both faces, concrete pulverizers are first used to reduce tight cover. Bars are then cut in accessible positions. High resistance values and large diameters are addressed with additional pre-openings.
Strip-out and cutting
Indoors, controlled work with low emissions is paramount. Stone and concrete splitters are advantageous where vibrations must be avoided; reinforcement is severed in accessible areas.
Rock demolition and tunnel construction
Concrete and shotcrete structures in tunnel construction often feature dense reinforcement meshes. The resistance of the bars influences the crack pattern during splitting; drilling patterns and force paths are adjusted accordingly.
Natural stone extraction and special operations
Natural stone contains no reinforcement; the reinforcing steel resistance value is relevant here only when deconstruction is combined (e.g., dismantling foundations with steel content). In special operations with mixed constructions, the workflow is designed for the toughest resistances.
Tool care and tool life
High resistance values and large bar diameters load cutting edges and bearings. Regular inspection of cutting edges, reversing or replacing worn inserts, and proper lubrication of moving parts increase tool life. Clean hydraulics (filter condition, tightness) ensures consistent performance, which is critical for tough steels and near-limit diameters.
Conclusion for planning cutting and splitting tasks
The reinforcing steel resistance value brings together the decisive parameters for reinforcement behavior in demolition: strength, ductility, diameter, and condition. Combining concrete pulverizers for exposing and crushing with stone and concrete splitters for low-vibration separations, the right assessment of resistances leads to controlled workflows and calculable cutting forces. Hydraulic power units provide the necessary energy, while steel shears and multi cutters precisely sever the reinforcement. This enables efficient, safe, and cleanly separated deconstruction—from the first crack formation to the final cut.