Pipe structural analysis describes the load-bearing and deformation capacity of pipes under internal and external actions. It links soil mechanics, materials science, and structural design. It is crucial for concrete demolition and special deconstruction, strip-out and cutting, as well as rock excavation and tunnel construction: anyone who cuts, exposes, or removes pipes in sections affects ring forces, support conditions, and stability. Sound understanding helps to produce controlled fracture patterns, avoid damage to neighboring structures, and increase occupational safety. In practice, this particularly concerns the removal of concrete and reinforced concrete pipes with concrete pulverizers and the controlled splitting of pipe and manhole components with rock and concrete splitters. Steel shears, multi cutters, and tank cutters are also used—depending on cross-section, material, and installation situation; hydraulic power units provide the energy required for precise and metered workflows.
Definition: What Is Meant by Pipe Structural Analysis
Pipe structural analysis is the mechanical assessment of pipes under load: internal pressure, external pressure, soil cover, traffic loads, temperature, and imposed deformations act on the annular cross-section. The pipe responds with ring stiffness, bending and membrane stresses; the surrounding soil provides support and bedding reactions. A distinction is generally made between rigid (e.g., concrete, cast iron) and flexible (e.g., PE, PP, GRP) systems. Verifications address load-bearing capacity (safety against fracture, buckling, flotation) and serviceability (allowable deflection, ovalization, crack widths). Pipe structural analysis thus forms the basis for design, construction, inspection, and proper deconstruction of pipelines and manhole structures.
Fundamentals of Loads and Design in Pipe Structural Analysis
Design follows the interaction of actions and resistances, supplemented by boundary conditions such as installation depth, bedding, and groundwater. The goal is a safe, economical, and as low-deformation as possible solution—in both new construction and deconstruction.
Actions
- Permanent loads: self-weight of the pipe and its contents (medium), soil cover, water pressure from outside or inside.
- Variable loads: traffic loads, construction stages (excavation, exposure, shoring), thermal and shrinkage deformations, vibrations.
- Special cases: vacuum/suction, hydraulic shocks, settlement-induced restraint, buoyancy at high groundwater levels.
Resistances and Verifications
- Ring stiffness and bedding: resistance against ovalization; governing for flexible pipes.
- Sectional load-bearing capacity: compressive and bending stresses, shear, cracking; typical for concrete and reinforced concrete pipes.
- Stability: buckling/local buckling under external pressure, especially for thin-walled steel or GRP pipes.
- Watertightness and serviceability: deformations, joint openings at sockets, longitudinal displacements.
Rigid Versus Flexible Pipes
Rigid pipes carry loads primarily through cross-sectional strength, with the soil acting as a support. Flexible pipes mobilize the soil to a greater extent: bedding stiffness limits ovalization. For deconstruction, this means: if bedding is removed or the ring is weakened by cuts, load paths change. Staged unloading and controlled segmentation reduce the risk of sudden redistributions.
Bedding, Installation Methods, and Soil Influence
The bedding largely governs the pipe response. Degree of compaction, grain gradation, and density of the soil control the bedding modulus and thus the deformations. When exposing or partially undermining, lateral support diminishes; ovalization can increase. Careful shoring, intermediate ribs, and a defined cutting sequence keep the system stable.
Open Trench Construction and Trenchless Methods
In open trench work, trench width, layer build-up, and construction stages shape load behavior. In trenchless methods (pipe jacking, microtunneling) the soil acts through ring pressure; segmental or jacking pipes must resist external pressure and shocks. For the deconstruction of jacking pipes in tunnel construction, preloads, friction, and bond to the surrounding ground must be considered before opening cross-sections and purposefully shedding loads using concrete pulverizers, rock and concrete splitters, or steel shears.
Material Behavior and Typical Pipe Types
Material and wall thickness determine load-bearing mechanisms, cut layout, and tool selection.
Concrete and Reinforced Concrete
High compressive strength, limited tensile strength, cracking under bending. Steel reinforcement carries tension; concrete pulverizers can crush concrete in a targeted manner, with the reinforcement then cut (e.g., with combination shears or steel shears). Rock and concrete splitters create controlled split lines along the ring zone.
Steel and Ductile Materials
High toughness and ductility, risk of local buckling and buckling under external pressure. Steel shears or multi cutters are suitable for separations; for large diameters and wall thicknesses, tank cutters can be used. Stability reserves should be checked before making cuts; segmental removal limits deformations.
GRP and Thermoplastic Pipes
Pronounced deformability, ring stiffness depends on wall build-up. Consider long-term behavior (creep) and notch sensitivity; cuts often create local stress concentrations. Soft support and low point loads are important during deconstruction.
Long-Term Behavior and Creep
In polymer pipes, creep leads to increased deformation under sustained load. In deconstruction, unloading and redistribution can cause short-term spring-back. Cutting sequences should account for this to avoid uncontrolled openings.
Corrosion and Aging
Corrosion, sulfate attack, alkali-silica reaction, or fatigue weaken wall cross-sections. Pre-damage reduces reserves against local buckling or crack propagation. A condition assessment before intervention is therefore essential.
Pipe Structural Analysis in Concrete Demolition and Special Deconstruction
The deconstruction-induced change of support and load conditions requires a procedure with clearly defined construction stages. In pipe trenches, shafts, and tunnel bores, earth pressure, groundwater, and traffic loads must be considered. Tools such as concrete pulverizers and rock and concrete splitters enable controlled breaking of the ring zone without provoking shock-like load redistributions. Hydraulic power units allow finely metered force transmission.
Planning the Deconstruction
- Investigation: contents, material, wall thickness, joints, bedding, groundwater level, adjacent structures.
- Relief: draining, flushing, degassing; if necessary, temporary shoring and anti-buoyancy measures.
- Cutting and splitting concept: define windows, segment sizes, sequence, emergency shoring.
- Protective measures: cordon off, ventilate, measurements (gases), vibration and settlement monitoring.
- Deconstruction: sectional opening, removal, sorting, transport.
Cutting and Removing Concrete and Steel Pipes
For concrete and reinforced concrete pipes, a combination has proven effective: first weaken the ring zone with concrete pulverizers, then perform targeted splitting with rock and concrete splitters. Reinforcement is cut with steel shears or combination shears. For steel pipelines, circumferential cuts are made segment by segment; multi cutters or tank cutters separate thick-walled sections. A structurally sound sequence is crucial: reduce loads first, then open cross-sections, and finally remove segments.
Cutting Layout from a Structural Perspective
- Window and segment technique: small segments limit ring relaxation and prevent tipping or flapping movements.
- Asymmetric openings: targeted cutting at the crown or invert prevents uncontrolled ovalization.
- Socket and connection areas: increased stiffness can cause crack deflections; adapt the cut layout.
Special Situations from the Perspective of Pipe Structural Analysis
Groundwater and Buoyancy
Buoyancy forces can govern when draining pipelines or shafts. Temporary ballasting or anchoring prevents flotation. When opening the cross-section, flow and pressure conditions change; controlled lowering of the water level reduces risks.
Under-Crossings and Traffic Areas
For pipes beneath roads, dynamic traffic loads act. Before exposure, check clearances, cover, and bedding condition. If necessary, ensure temporary load transfer before making cuts.
Connection Areas, Sockets, and Special Components
Transitions between materials, fittings, shafts, and linings have altered stiffness. Crack tips and local buckles often occur here. A tailored tool and segmentation concept avoids secondary damage.
Testing, Monitoring, and Documentation
For demanding special operations, simple measuring and control means are helpful: deformation measurements (ovalization), crack maps, settlement markers, groundwater level, vibration monitoring. Ongoing documentation supports assessing construction stages and selecting suitable work steps.
Occupational Safety and Protective Measures
Work on pipes often takes place in confined spaces: oxygen deficiency, explosion hazard, residual media, and pressurized systems are risks. Applicable technical rules and operational permits apply. These include atmospheric clearance testing, ventilation, pressure relief, isolation, PPE, secure supports, and lifting points. The procedure with concrete pulverizers, rock and concrete splitters, and shears must be planned so that operators remain outside the danger zone and load redistributions are predictable.