{"id":19772,"date":"2025-12-16T10:38:42","date_gmt":"2025-12-16T09:38:42","guid":{"rendered":"https:\/\/www.darda.de\/?page_id=19772"},"modified":"2025-12-16T10:38:42","modified_gmt":"2025-12-16T09:38:42","slug":"shear-stress","status":"publish","type":"page","link":"https:\/\/www.darda.de\/en\/knowledge\/shear-stress","title":{"rendered":"Shear stress"},"content":{"rendered":"
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Shear stress<\/em> is a central concept in materials and rock mechanics and determines how concrete, steel, and natural stone deform or fail under transverse actions. In practical deconstruction it governs crack formation, slip joints, and controlled fracture surfaces\u2014such as when using concrete demolition shear, stone and concrete splitters<\/a>, combination shears, or steel shear<\/a>. Those who understand and control shear stresses reduce collateral damage, master fracture paths, and increase execution safety in fields such as concrete demolition, strip-out, rock excavation, tunnel construction, and natural stone extraction.<\/p>\n

Definition: What is meant by shear stress<\/h2>\n

Shear stress<\/strong> \u03c4 denotes the stress components acting tangentially to the considered surface. It arises when a shear force F acts across a cross-section or along a separation plane and has the same dimension as compressive and tensile stresses (N\/mm\u00b2 or MPa). Idealized, \u03c4 = F\/A applies for uniformly distributed shear forces over the shear area A. In real components and rocks, however, the distribution is usually non-constant; geometry, notches, joints, reinforcement, and friction significantly influence local peak values. Material behavior in shear is governed by the shear modulus<\/em> G (\u03c4 = G \u00b7 \u03b3 with the shear strain \u03b3) as well as by friction and cohesion at contact surfaces.<\/p>\n

Significance in deconstruction and rock mechanics<\/h2>\n

Shear stresses control where concrete elements slip, where rock yields along joint systems, and how steel is sheared when cutting. In concrete demolition with concrete demolition shear, compressive, tensile, and shear components superimpose at the crushing jaws; with stone and concrete splitters, radial expansion pressure initiates tensile cracks that subsequently propagate along shear planes<\/em> or weakness zones. In natural stone extraction and tunnel construction, the orientation and shear strength of discontinuities (joints, bedding, fractures) determine fracture geometry and stability. For strip-out and cutting works, shear stresses in sheets and sections govern cut quality, for example when using steel shear, Multi Cutters, or tank cutters.<\/p>\n

Physical fundamentals and key parameters<\/h2>\n

Shear stresses occur in torsion, in shear-force regions of beams, and at contact interfaces. Important relations include: \u03c4 = G \u00b7 \u03b3 (linear-elastic), in beam segments approximately \u03c4 \u2248 1.5 \u00b7 V\/A for rectangular cross-sections (V = shear force), and in torsion \u03c4 = T \u00b7 r \/ J (T = torsional moment, r = radius, J = polar moment of inertia). In heterogeneous materials such as concrete, aggregates, matrix, moisture, and crack density affect shear stiffness; in rock, anisotropy and joint surface roughness are decisive. At contact limits the Mohr\u2013Coulomb criterion is frequently used: \u03c4 = c + \u03c3n<\/sub> \u00b7 tan \u03c6 (cohesion c, normal stress \u03c3n<\/sub>, friction angle \u03c6), which illustrates the dependence of shear strength on normal load.<\/p>\n

Shear distribution in concrete, steel, and natural stone<\/h3>\n

Concrete transfers shear through its matrix, aggregates, and\u2014once cracked\u2014through interlock at crack faces and reinforcement engagement. Steel behaves linearly in the elastic range and shows ductile shearing once the yield strength is exceeded. Natural stone and rock exhibit brittle behavior; along rough joints, interlock increases shear capacity, while smooth or lubricated joints reduce it markedly. Temperature, loading rate, and moisture change shear strength, which is why ongoing observation and adaptation of the approach<\/strong> are important.<\/p>\n

Shear stress in concrete demolition and special deconstruction<\/h2>\n

During deconstruction, shear stresses arise primarily at notches, openings, bearing regions, and along cracks. Concrete demolition shear produces controlled fracture zones; the combination of localized compression and lever action leads to pronounced shear and tensile components at crack tips. The aim is to orient fracture surfaces so that members fail along planned planes without triggering undesired slip mechanisms in adjacent areas. Hydraulic power unit settings<\/a> influence the rate of force build-up through flow rate and pressure and thus shear-governed crack propagation; smooth, reproducible load steps improve control.<\/p>\n

Practical guide: Steering shear stresses deliberately<\/h3>\n