Tearing force

Tearing force describes the force required to destroy or separate a material, component, or joint by tensile loading. In concrete demolition and rock excavation as well as when cutting and separating steel, knowing the tearing force is crucial to deploy methods in a planned, safe, and material-appropriate way. It is closely related to forces generated by hydraulic tools, such as concrete demolition shears, hydraulic splitter, hydraulic wedge splitter, combination shears, steel shear, Multi Cutters, or tank cutter. In the application areas of concrete demolition and special demolition, building gutting and cutting, rock excavation and tunnel construction, natural stone extraction, and special demolition, the tearing force largely determines which tool principle and which hydraulic parameters are effective. In technical communication, the term is also used pragmatically for pull-out or splitting actions where tensile stresses govern failure, typically expressed in kN.

Definition: What is meant by tearing force?

Tearing force is the minimum force needed to bring a material or component to failure under tensile or pull-off loading. It is a load quantity (force F in newtons or kilonewtons) and must be distinguished from tensile strength (a stress quantity in MPa). Both quantities are related via the cross-section A: approximately F_R ≈ σ_R · A. While tensile strength is a material-specific characteristic value, tearing force additionally accounts for geometry, notches, cracks, support conditions, and loading rate. In brittle materials such as concrete or natural stone, tensile strength is significantly lower than compressive strength; the failure mode is crack-driven. In ductile steel, necking and elongation up to fracture contribute to tearing force varying strongly with cross-sectional area and material grade. Practical tearing-force values therefore reflect not only the material but also the detail of the component and the load introduction.

Mechanical fundamentals and relationships

Stress is force per area (σ = F / A). Tearing force comes into play where tensile stresses become critical: at notches, drill holes, cracks, edges, or under eccentric loading. In practice, mixed states often occur: compression at the tool attack point (shear, wedge, blade) induces bending tension and splitting tension in the component – this is where crack initiation starts. Where stress concentrations are high, the effective resistance can be far below the nominal cross-sectional estimate; stress raisers and restraint conditions dominate.

Hydraulics: from pressure to force

Hydraulic tools convert operating pressure into force. For cylinders, the idealized relation is F = p · A (operating pressure p, piston area A). hydraulic power units supply the required pressure and flow rate to transmit force to concrete demolition shears or hydraulic splitter. The tearing force in the component arises from how the tool force is transformed into tensile stresses through geometry and contact conditions. In splitting, wedges and spreaders generate radial stresses that produce splitting tension; with shears, compressing and bending induce tension on the opposite side. Real systems show losses from friction, seal drag, and kinematics – field calibration via pressure readings and known piston areas improves the force estimate.

Lever arms and kinematics in shears and cutters

The force at the cylinder is translated into jaw force through lever arms and joint kinematics. Depending on jaw position, the effective lever varies; the local stress peak in the component results from contact area, edge radius, and friction. With concrete demolition shears, crack initiation in concrete is the focus; with steel shears and Multi Cutters it is the severing of sections or reinforcement. Where components are additionally torn out (e.g., fixings or plates), direct tearing force is active. The opening angle typically trades off force for speed – near closed-jaw positions, higher forces with smaller travel are available.

Tearing force in concrete demolition, rock excavation and natural stone extraction

In concrete demolition, components are opened in a controlled manner: concrete demolition shears generate targeted cracking and progressively release concrete segments, while reinforcement is selectively cut or pulled. Hydraulic splitters introduce splitting forces into the component or rock via drill holes that exceed tensile resistance and create a defined separation plane – at low vibration levels and without percussive action, using hydraulic rock and concrete splitters. In natural stone extraction and rock excavation, tearing force can be steered by the drilling pattern, hole depth, and spreading direction so that crack propagation follows the structure (bedding, joint systems). Orientation to fabric and jointing minimizes overbreak and improves block quality.

Building gutting and cutting

In building gutting, attachments, installations, and composite systems are released. Relevant tearing-force phenomena include pulling out anchors and fasteners, removing service penetrations, and opening composite layers. Concrete demolition shears and Multi Cutters can position, score, and bend components to generate tensile stresses up to failure. Tank cutters and steel shears sever plates and sections; where material composites, welds, or corrosion zones fail, local tearing force governs the opening of the joint zone. Adhesive layers, coatings, and embedded inserts often alter the failure path and should be assessed before cutting sequences are defined.

Influencing factors on the required tearing force

• Material: Concrete tensile strength (f_ct), aggregate, fines content; steel grade and ductility; rock type (granite, limestone, sandstone) and anisotropy.
• Geometry: Cross-section, hole spacings and diameters, edge distances, eccentricities.
• Pre-damage: Hairline cracks, notches, openings, corrosion, fatigue.
• Boundary conditions: Support, restraints, temperature, moisture, aging (carbonation), freeze-thaw cycles.
• Loading rate: Dynamic or impact loading often increases the apparent tensile strength of brittle materials but changes the fracture mechanism.
• Reinforcement and bond: Degree of reinforcement, bond behavior, development lengths, anchor design; in composite components, bond tensile strength often dominates.
• Rock fabric: Jointing, bedding, water fill, and in-situ stresses in tunnel or rock works.
• Tool contact and confinement: Contact area, edge radii, surface condition, and local confinement influence stress concentration and crack initiation.

Calculation and practical estimation

For a first estimate, the tearing force can be calculated from a representative tensile strength and the effective cross-section: F_R ≈ σ_R · A. Typical tensile strengths are about 2–4 MPa for normal concrete (splitting tension); for natural stone they vary widely (e.g., limestone approx. 3–10 MPa, granites significantly higher); for structural steel they are on the order of several hundred MPa. In practice, notches, holes, and edge distance largely govern the required tool force. For planning, conservative ranges and partial allowances for imperfections, friction, and restraint are recommended.

Example 1: Crack initiation in a concrete slab

A 30 cm wide and 15 cm thick slab zone (A = 0.045 m²) with an average splitting tensile strength of 3 MPa yields a rough tearing force of F ≈ 3·10⁶ N/m² · 0.045 m² = 135 kN. Under direct shear loading, locally lower forces are sufficient to initiate the first crack due to notch and bending effects; for complete separation, however, allowances for crack propagation, friction, and reinforcement load contributions must be included. The estimate is sensitive to actual restraint and to the presence of near-surface defects.

Example 2: Pulling out an anchor

For an M16 bar (A ≈ 157 mm²) and a steel tensile strength of 500 MPa, the theoretical result is F ≈ 78.5 kN. In practice, however, the bond tensile strength in concrete often governs failure. If a bond area of 2,000 mm² with 2 MPa bond tensile strength is assumed, F ≈ 4 kN is already sufficient to release the bond – the steel remains undamaged. The estimate must therefore always consider bond and boundary conditions.

Common pitfalls and safety factors

• Neglecting stress concentrations: Holes and edges reduce the effective capacity compared with a uniform cross-section.
• Rate and temperature effects: Brittle materials can show higher apparent strength at high rates; cold or moisture can change crack paths.
• Overlooking restraint: Supports and attachments introduce secondary bending that alters the required tearing force.
• Use verified values: Prefer measured or code-based characteristic strengths with suitable partial factors for safe planning.

Measurement and testing methods

1. Tensile test on specimens: Determination of tensile strength (tearing strength) of steel, fiber composites, or plastic components.
2. Splitting tensile test (Brazilian test): Indirect determination of the tensile strength of brittle materials such as concrete and natural stone.
3. Pull-off tests: Determination of the bond tensile strength of coatings, composite layers, and anchor connections.
4. Field measurement via hydraulic pressure and load cells: Derivation of tool force on concrete demolition shears or hydraulic splitter from operating pressure, piston area, and kinematics.
5. Optical or acoustic monitoring: Digital image correlation or acoustic emission helps track crack initiation and propagation during trials.

Tearing force and tool principles

The tool selection is based on the mechanism by which tearing force is generated in the component:

• Concrete demolition shears: Crack initiation by compressing and bending tension, followed by separation; tearing force manifests in crack propagation and when extracting partial areas.
• Hydraulic splitter with hydraulic wedge splitter: Generate splitting tension around the drill hole; tearing force depends on drilling pattern, spreading travel, friction, and material anisotropy.
• Combination shears and Multi Cutters: Switch between cutting, compressing, and pulling; the resulting tearing force is highly dependent on position and edges.
• Steel shears and tank cutters: Primarily shearing and cutting; tearing force becomes relevant when seams, bonds, or corroded areas open or when sections are pulled.
• Hydraulic power pack: Dimension the available pressure and flow; via piston area and leverage the force acting on the workpiece arises, which is converted into tearing force.

Application in concrete demolition and special demolition

In special demolition, tearing force is used to separate components in a controlled manner: beam bearings are exposed and opened with concrete demolition shears, slab panels are split along drill patterns with hydraulic splitter, and reinforcement is then cut with steel shears. In areas with strict vibration and noise requirements (special demolition), splitting permits a progressive exceedance of local tensile strength with minimized collateral influence. In tunnel construction and rock excavation, tearing-force-guided splitting supports progression along jointed zones; tool design follows the desired crack line. Sequencing of cuts and splits, controlled debris management, and pre-weakening of secondary load paths reduce unexpected crack branching.

Planning: from tearing force to tool selection

For reliable planning, tearing-force requirements are translated into simple, verifiable quantities. A step-by-step approach helps:

• Component survey: Material, geometry, reinforcement, bonds, edge distances, drill patterns.
• Determine or assume characteristic values: Splitting tensile strength, bond tensile strength, steel grades; choose conservative ranges.
• Estimate the required tearing force per cut or splitting segment; include allowances for friction, crack branching, and imbalances.
• Define tool principle: Shears for crack initiation and demolition edges, splitter for calm, linear separations, shears/cutters for reinforcement and steel.
• Derive hydraulic parameters: Minimum operating pressure, required piston areas or jaw forces, cycle times.
• Conduct a field trial/test: Verify crack behavior, adjust drilling pattern or attack points.
• Monitoring: Pressure/force levels, crack growth, spalling; adapt if deviations occur.
• Check reaction forces: Provide supports and shoring for counterforces from spreaders, shears, and lifting aids.
• Documentation: Record parameters and observations to refine subsequent steps and improve repeatability.

Safety and general notes

Tearing processes are crack-driven and can be brittle. Protective zones, shoring, and retention systems should be designed to cover unforeseen crack paths and sudden fractures. For composite systems (anchors, layers, sandwich builds), a cautious load increase regime with continuous observation is advisable. Applicable standards, guidelines, and regulatory requirements must be observed; the values and estimates are general in nature and do not replace project-specific design. Remote operation, controlled access, and PPE mitigate risks from sudden release, flying fragments, and unplanned component displacement.

Practical know-how: levers for targeted tearing force

The following control variables help use tearing force effectively and safely:

• Vary the point of application: Edges, notches, and existing cracks favor crack initiation.
• Control the contact area: Smaller contact produces higher local stress peaks (use judgment regarding spalling).
• Optimize the drilling pattern: Adapt hole spacing and depth for hydraulic splitter to the material and the desired crack line.
• Steer the load path: Pre-cut with shears/cutters reduces secondary load shares (e.g., reinforcement), letting tearing force act specifically in the concrete.
• Ramp the pressure regime: Increase operating pressure step by step, observe crack progression, reset contact.
• Pre-score where appropriate: Shallow cuts or scoring lines provide a path for controlled crack propagation.
• Consider environment: Moisture, temperature, and debris in joints influence friction and crack initiation – keep interfaces clean and adjust parameters.