Shear force

Shear force is a fundamental internal action in structural analysis and materials science. It describes forces that act transverse to the longitudinal axis of a member or rock body and generate shear stress. In professional deconstruction, in rock excavation or in dimension-stone extraction, mastering shear force determines whether components separate in a controlled manner, cracks propagate as intended, and loads are safely transferred. Tools and systems from Darda GmbH—from concrete demolition shears and rock and concrete splitters to steel shears, combi shears, multi cutters, tank cutters, hydraulic power units and stone splitting cylinders—always operate in practice within the interaction of compression, tension, bending and shear force. Those who understand shear force control processes more precisely, reduce unintended failures, and increase construction site safety.

Definition: What is meant by shear force

Shear force refers to external or internal forces that act transverse to the member axis and induce shear stress in cross-sections. In beams, slabs and panel elements, shear force typically causes diagonally oriented crack patterns (often around 30–45 degrees to the axis), slip planes, or local spalling at supports. Shear force rarely acts in isolation: it acts together with bending moments, axial forces and torsion and, depending on the material (concrete, steel, natural stone), changes both stiffness and load and failure behavior. In deconstruction, shear force is critical when components could shear uncontrollably along weak planes. In targeted demolition, by contrast, shear force is intentionally generated or purposefully reduced to make separation cuts, split lines, and load redistributions predictable.

Mechanics of shear force in concrete and natural stone

Concrete, masonry and natural stone exhibit strongly material-dependent behavior under shear force. Concrete transfers shear through a combination of aggregate interlock, compression struts in the web region and—where present—shear reinforcement; natural stone, by contrast, fails predominantly along existing jointing and foliation planes or at notches. Thin-walled steel and sheet-metal components (e.g., tank walls) respond more ductilely, but form local shear folds when cutting or shearing forces are introduced without sufficient support.

• Geometry and support: Shear-force peaks arise at supports, notches, openings, recesses and drill holes, as well as at transitions with stiff connection details.
• Material condition: Strength, fabric, moisture, temperature and crack history determine whether shear forces are transferred by interlock or along weakness zones.
• Type of loading: Static, cyclic and impact actions lead to different crack patterns and residual load-bearing capacities.
• Pre-treatments: Pre-sawn separation cuts, core drilling or defined notches steer shear cracks in a controlled way and reduce unintended slip planes.

Shear stress, compression struts and crack patterns

In concrete bodies under shear force, compression struts form and, transverse to them, tension or shear cracks. Without sufficient reinforcement or pre-separation, brittle shear failure with wedge-shaped spalls occurs. In natural stone, sliding and splitting along anisotropic fabrics dominate. For deconstruction this means: identify shear paths early, secure potential sliding planes, and concentrate shear force on defined, controllable regions by means of targeted cutting or splitting measures.

Shear force in concrete demolition and special demolition

In controlled demolition, shear-force processes act in virtually every step: from load redistribution to cutting out wall and slab segments to lifting heavy components. The goal is to guide shear-force introductions so that no uncontrolled shear cracks form, adjacent areas are protected, and load paths remain predictable.

Concrete demolition shears: cutting and crushing under controlled shear force

Concrete demolition shears from Darda GmbH generate local compressive and shear stresses at the cutting and crushing jaws. The shear force concentrates in the contact area and is distributed through the member. Skilled handling reduces unwanted prying and lever effects.

• Choose the initial bite: Start with small bites and progressive advance to smooth shear-force peaks.
• Mind the direction: Position the shears so potential shear cracks run into safe areas and reinforcement is separated step by step.
• Support and bear: Provide support points and intermediate shoring to limit free spans and lower shear-force levels.
• Pre-separate: Core drilling or saw cuts guide crack propagation and minimize sudden shear failures.

Stone and concrete splitters: reduce shear force, exploit tensile cracking

Stone and concrete splitters from Darda GmbH work with wedge or expansion mechanics. They primarily induce tensile stresses along defined split lines. This markedly lowers the shear force required for member separation. The method protects adjacent structures, reduces vibrations, and guides the fracture line in desired directions—useful wherever shear failures could cause collateral damage.

Rock excavation and tunnel construction: understanding shear force in rock

In rock excavation, shear-force processes concentrate on joint systems, bedding planes and foliations. Stone splitting cylinders, supplied by Darda’s hydraulic power packs, apply controlled expansion forces that preferentially activate tensile cracks along exploitable discontinuities. This avoids large shear-force transfers that could otherwise trigger sudden sliding events.

Joint control and notch effect

Preparatory notches or short saw cuts define starter edges and shorten shear paths. In layered or jointed rocks, the splitting direction is chosen so that potential shear planes are either mitigated or deliberately used. The result is predictable block sizes with a lower tendency to uncontrolled shearing.

Strip-out and cutting: shear force at shears and cutting tools

Combi shears, multi cutters, steel shears and tank cutters from Darda GmbH create cuts through concentrated shearing action at the blade. Local shear-force peaks arise that—depending on support and member thickness—can lead to folding, edge tearing or sliding. With the right cutting strategy, the shear-force share remains manageable.

Cutting strategy and support

• Secure the component: Before cutting, add support points, suspend or catch components so that shear cracks do not propagate uncontrollably.
• Stage the work: Several short cuts instead of one long cut reduce peaks in shear force and improve control.
• Avoid edges: Do not start shearing directly at sharp-edged recesses; small pilot holes mitigate notch stresses.
• Plan the direction: Choose the cut path so the remaining residual cross-sections can safely carry shear force until the section is released.

Reinforcement, bond and dowel bars

Reinforcing bars transfer shear force through dowel action and bond. In deconstruction, it is sensible to release these shear-force paths step by step—e.g., by selectively cutting the bars with concrete demolition shears or suitable cutting tools—before making large-area cuts. This prevents brittle shear failure in the concrete body.

Planning, assessment and verification in deconstruction

Competent planning examines shear-force paths just as carefully as bending moments and axial forces. Load-bearing mechanisms, support reactions and possible crack paths are recorded. The rules and verifications to be applied are based on the technical standards and regulations in force; they must be selected by qualified persons and interpreted for the specific project. In practice, structured procedures have proven effective:

1. Survey: Record material, member thicknesses, reinforcement layout, joints, notches and joint systems.
2. Load paths and support: Shore, catch, pre-relieve; limit shear-force peaks at supports.
3. Separation strategy: Choose the combination of sawing, splitting and shearing so that shear force is purposefully created or avoided.
4. Sequencing: Work in logical stages, keep residual cross-sections controlled and release them only at the end.
5. Control: Monitor crack formation, inspect cut edges, adjust forces; remain responsive to changes in boundary conditions.

Occupational safety and environmental influences

Shear-force-related failures can occur suddenly. Therefore, safe distances, shoring and redundant safeguards are essential. Methods that reduce shear-force peaks—such as targeted splitting—can mitigate vibrations, noise emission and dust generation. The specific choice of method must take local requirements, the surroundings and protection objectives into account.

Practical guide: procedure for controlling shear force

1. Identify weak points: Identify supports, openings, notches, anchorage points and crack lines.
2. Prepare: Install temporary supports and catch systems to shorten shear-force paths.
3. Pre-separate: Make core drill holes or short saw cuts to prescribe crack directions.
4. Tool selection: Concrete demolition shears for combined shearing/crushing operations, stone and concrete splitters for controlled tensile cracking, shears for metallic inserts.
5. Stage the work: Small steps, controlled bites and defined residual cross-sections.
6. Monitor: Observe crack patterns, displacements and noises; adjust hydraulic pressure and cutting sequence.
7. Release: Separate residual cross-sections in a safe sequence and size them for transport.

Typical mistakes when handling shear force in deconstruction

• Missing shoring: Unsupported edge fields lead to uncontrolled shear cracks.
• Steps too large: Long cuts or big bites generate shear-force peaks and sliding planes.
• Ignored notches and openings: The notch effect increases local shear stress.
• Unknown reinforcement: Unrecognized dowel action of reinforcement keeps shear-force paths active.
• Wrong cutting sequence: Residual cross-sections no longer carry shear force sufficiently and fail in a brittle manner.

Distinction and interaction: shear force, bending, axial force, torsion

Shear force never acts alone. Bending creates tension and compression zones where shear cracks preferentially initiate. Axial forces can improve (compression) or impair (tension) shear load-bearing behavior. Torsion induces shear across the entire cross-section. In practice it becomes clear: Clean guidance of shear force is the key to keeping other internal actions manageable.

Material-dependent behavior under shear force

Concrete tends toward brittle shear failure if there is insufficient interlock or reinforcement. Masonry follows mortar and bed joints; natural stone shears along joints. Steel and tank plates show ductile behavior but require stable counter-supports when cutting so that shear force results in separation cuts rather than deformations. Tools from Darda GmbH are selected accordingly: concrete demolition shears for mineral composites, stone and concrete splitters for targeted tensile cracking in concrete and natural stone, steel shears and tank cutters for metallic cross-sections, combi shears and multi cutters for mixed assemblies. Hydraulic power packs provide the precisely controllable energy to introduce shear-force effects in a metered and reproducible manner.