Steel Fracture in Demolition

Steel fracture describes the failure of steel components due to crack initiation and crack propagation up to complete separation. In deconstruction, during building gutting, in rock demolition and tunnel construction, or when cutting tanks and plant equipment, understanding fracture mechanisms determines safety, precision, and efficiency. For controlled separation of steel and reinforced concrete, practical methods include, among others, concrete pulverizers, stone and concrete splitters, steel shears, combi shears, multi cutters, and tank cutters, all driven by hydraulic power packs. The aim is to avoid uncontrolled fractures, safely reroute loads, and create defined cut or split lines.

Definition: What is meant by steel fracture

Steel fracture is the materials science term for the severing of a steel cross-section as a result of mechanical or corrosive loading. A distinction is primarily made between brittle fracture (sudden fracture with almost no deformation) and ductile fracture (with pronounced deformation). In addition, fatigue fractures due to alternating loads and corrosion-assisted cracks occur. Characteristic features are crack initiation (often at notches, weld seams, or corrosion sites), crack propagation, and the final failure event. In deconstruction, steel fracture is desirable when it is a controlled separation process, and undesirable when forces are released unexpectedly or components break uncontrollably.

Metallurgical fundamentals and fracture types

The fracture behavior of steel is determined by microstructure (e.g., ferrite, pearlite, bainite, martensite), toughness, strength, cleanliness, wall thickness, temperature, and type of loading. The following fracture types are relevant in practice:

Common fracture types at a glance

Brittle fracture: Sudden, crystallographic fracture with a smooth fracture surface and little deformation. Favored by low temperatures, high strain rates, notches, thick cross-sections, hydrogen embrittlement, or cold areas adjacent to weld seams.
Ductile fracture: Tough failure with necking and pronounced plastic deformation. Desired in dismantling because it is more predictable and shows warning signs.
Fatigue fracture: Crack growth due to cyclic loading (e.g., vibrations in beams, pipelines). Typical are concentric “beach marks.” Often followed by a final brittle fracture after long-term pre-damage.
Stress corrosion cracking and hydrogen embrittlement: Crack formation under simultaneous mechanical stress and corrosive environment or hydrogen ingress. Relevant for tanks, pipelines, plant components, and high-strength steels.
Mixed-mode fracture: Combination of ductile and brittle portions, e.g., in thick plates or in weld-adjacent areas.

Notch effect and crack propagation

Notches, edges, holes, corrosion pits, and weld seam irregularities increase local stress. Such geometries act as crack starters. Crack propagation depends on toughness, temperature, and loading rate. For deconstruction this means: the more precisely the separation line is defined (e.g., by pre-scoring or targeted notching), the more controlled the fracture; the more uncontrolled the notches and residual stresses, the higher the risk of sudden steel fracture.

Steel fracture in deconstruction: relevance for concrete pulverizers and stone and concrete splitters

In selective deconstruction of reinforced concrete components, steel fracture and concrete brittle fracture occur in parallel. Concrete pulverizers create controlled concrete break-up and expose reinforcing steel. These are then separated with steel shears or multi cutters. Stone and concrete splitters as well as stone splitting cylinders generate defined crack lines in massive members; it must be considered how the steel anchored in concrete reroutes forces. Uncontrolled steel fractures in overloaded reinforcement can be avoided if load paths are relieved in advance and steels are cut in a targeted manner instead of being “torn off.”

Structural dependencies in reinforced concrete

Identify load paths: tension members, support reinforcement, stirrups, and shear studs.
Define sequence: first locally weaken/remove concrete (concrete pulverizers), then define and cut exposed steels (steel shears, multi cutters).
Secure interfaces: avoid prying and peeling stresses to prevent brittle fracture in work-hardened steels.
Set up temporary shoring, hangers, and exclusion zones to prevent uncontrolled fracture events.

Tools and methods for controlled steel separation

Hydraulically operated steel shears, combi shears, and multi cutters enable defined cutting operations on sections, beams, reinforcement, plates, and pipes. Tank cutters are designed for low-spark cold cutting of thin- to medium-walled vessels and tanks. In composite members, concrete pulverizers are used for exposure; stone and concrete splitters create controlled separation cracks in massive components. Hydraulic power packs (mobile hydraulic power units) provide the required drive power and enable mobile, low-emission work in interior and tunnel areas.

Selection criteria for the appropriate separation method

Material and condition: structural steel, high-strength steel, corroded or coated surfaces, weld seam zones.
Geometry: wall thickness, cross-section shape (H-/I-sections, pipes, plates), space constraints.
Loading: existing prestress, load transfer, vibrations, residual stresses.
Environment: explosion-hazard areas (ATEX zones), indoor spaces, proximity to sensitive infrastructure.
Process objective: longitudinal cut, cross-cut, segmental separation, preparation for single-grade sorting.

Parameters for clean cuts instead of uncontrolled steel fracture

Blade condition and geometry: Sharp, intact cutting edges reduce notch effects and cutting forces.
Cutting clearance and support: Support the component to guide the cut, avoid tipping moments, control the cutting gap.
Sequence: Separate secondary members or attachments first, main load-bearing members last and under safeguarding.
Preparation: Pre-scoring/center-punching can define the separation line; remove corrosion layers if necessary.
Temperature: Very low temperatures promote brittle fracture; where possible, work at moderate temperatures.

Influencing factors: temperature, material condition and weld seams

Many structural steels show a transition from ductile to brittle behavior with decreasing temperature. Thick cross-sections, high strain rates, and notches shift this transition unfavorably. Weld seams and heat-affected zones can exhibit hardening, embrittlement, or hydrogen ingress. Corrosion reduces cross-section and toughness, coatings can conceal cracks. In practice, a conservative assessment is recommended: assume situations prone to brittle fracture and secure accordingly.

Weld seam zones in focus

Irregularities such as lack of fusion, undercut, or hardened zones in weld seams promote crack initiation. When separating near the seam, a defined cut path is advantageous. If necessary, pre-relief and a segmental approach are useful to prevent sudden crack advance.

Corrosion and coatings

Corrosion pits increase local stresses, under-rusting changes load-bearing behavior. Thick coatings, bitumen, or multilayer paints can influence the cutting process. Preparatory work (e.g., localized cleaning) improves cut quality and reduces uncontrolled spalling.

Crack diagnostics and condition assessment before separation

Before using concrete pulverizers, steel shears, combi shears, multi cutters, or tank cutters, a condition assessment is advisable. Depending on the circumstances, non-destructive testing can help identify risks.

Visual inspection for notches, corrosion, deformations, indications of cracking (e.g., rust streaks).
Magnetic particle or dye penetrant testing for near-surface crack detection.
Ultrasonic measurements for wall thickness and internal flaws in accessible components.
Assessment of weld seams and adjacent zones, especially in load-bearing elements.
Documentation of cut sequence, safeguarding measures, and exclusion zones.

Occupational safety: avoiding uncontrolled steel fracture

Occupational safety takes precedence. Establish exclusion zones, pick up loads, install shoring, and provide suspensions to reduce risk. Cold-cutting methods such as hydraulic cutting and splitting avoid sparks and reduce thermal stresses. When cutting tanks and pipelines, residual media, gases, and coatings must be considered; proper preparation is essential. Legal requirements and recognized rules of technology must generally be observed; individual assessments depend on the specific project.

Analyze hazards: fall direction, residual stresses, springback, vibrations.
Create access: secure components, define supports, plan emergency egress.
Communication: define cut sequence and signals, ensure line of sight.
Equipment use: hydraulic power packs function-tested, cutting tools maintained and properly sized.

Practice in concrete demolition and special deconstruction

Through the interplay of concrete pulverizers, steel shears, combi shears, multi cutters, tank cutters, and stone and concrete splitters, controlled deconstruction of complex components succeeds. The following procedures have proven effective:

Sequence when separating reinforced concrete

Relieve and secure the component (shoring, suspensions, load redistribution).
Use concrete pulverizers to remove concrete in a controlled manner and expose reinforcement.
Cut exposed steels with steel shears or multi cutters; segmental cutting for thick cross-sections if necessary.
Remove remaining concrete or selectively split it with stone and concrete splitters.
Lower, pick up, and remove sections in an organized manner.

Tanks, silos and pipelines

In deconstruction of vessels, the tank cutter enables low-spark cold cutting, which is advantageous in sensitive areas. Preparatory steps include removing residual substances and safely venting gases in accordance with applicable regulations. Segmental cutting reduces distortion and minimizes the risk of sudden steel fractures at local notches.

Rock excavation and tunnel construction

In tunnel construction, steel arches, lattice girders, and anchors are coupled with the rock mass. Stone splitting cylinders or stone and concrete splitters generate controlled cracks in the rock; in parallel, steel components are separated with steel shears or combi shears. A coordinated approach is essential to ensure load redistribution without uncontrolled brittle fracture.

Material and process parameters helpful for planning

Toughness: Measure of energy absorption up to fracture; highly desirable to avoid brittle failure modes.
Impact toughness: Characteristic value for behavior under impact loading; relevant for work at low temperatures.
Strain-rate sensitivity: Rapid loading promotes brittle fracture; calm, controlled cutting operations are preferable.
Residual stresses: Arise during rolling, welding, or cold forming; influence crack initiation and propagation.
Work hardening: Cold-worked zones (e.g., at edges) may respond more brittle; adjust cut path accordingly.

Typical failure patterns and their causes

Sudden brittle fracture in cold weather: Preheating the component is usually not planned; better to change cut sequence, reduce load, and avoid notches.
Tearing instead of cutting: When components are under tension, prying leads to uncontrolled cracks; better to make defined cuts under reduced load.
Cracking at weld seams: Separation too close to notches/porosity; shift the cut position or pre-relieve the seam area.
Distortion and binding during segmentation: Provide intermediate cuts and temporary support to control tipping moments.

Follow-up and documentation

Fracture and cut surfaces provide insight into component behavior. A brief documentation of the cut sequence, the tools used (e.g., concrete pulverizers, steel shears, combi shears, multi cutters, tank cutters), and the safeguarding measures facilitates evaluation for subsequent work steps. Single-grade separation of steel and mineral fractions supports recycling; clean cut edges improve recycling quality.