The load spectrum describes the totality of all load reversals, peak loads, and idle phases that a component or system experiences during a defined duty profile. In concrete demolition, in building gutting, as well as in rock excavation and tunnel construction, this spectrum of loads decisively determines the operational durability of tools and hydraulic components. For the products of Darda GmbH—particularly concrete demolition shears as well as hydraulic rock and concrete splitters—understanding the load spectrum is central to assess stresses on cylinders, shear arms, pin bearings, blades, and splitting wedges and to reliably predict service life.
Definition: What is meant by load spectrum
A load spectrum is the statistical condensation of time-dependent loads into classes that represent the number and magnitude of load cycles as well as the distribution of mean value and amplitude. It is often formed from measured force-, torque-, or pressure–time series and presented as a load or stress spectrum. Characteristic are cyclic portions (fully reversing and pulsating loading), impact portions, idle phases, and partial-load phases. The load spectrum serves as a basis for operational fatigue assessment (e.g., via life concepts) and for the sizing design of structural components and hydraulic systems. In the context of hydraulic tools, it includes both the mechanical spectrum at the points of action (e.g., the mouth of a concrete demolition shear, splitting wedge in the borehole) and the pressure spectrum in the hydraulic system (pressure spikes, pulsations, load reversals).
Structure and key parameters of a load spectrum
A practical load spectrum describes not only maxima, but also the frequency and sequence of loading scenarios. Key parameters are amplitude, mean value, range, R-ratio, number of cycles, event density, peak loads, and rest times. Common counting methods such as rainflow or peak–valley are used to form the spectrum, which classify load cycles and enable cumulative damage considerations (e.g., via linear damage summation). In application to concrete demolition shears and hydraulic wedge splitters, the spectrum typically appears as a sequence of approach load, gripping or spreading phase, peak load at fracture, and unloading and positioning movement; in doing so, pressure spikes from the hydraulics are superimposed with mechanical resonances of the structure.
Application relevance in concrete demolition, rock excavation and special demolition
In practice, load spectra differ significantly depending on the construction task. Reinforced concrete often generates higher, impact-like peak loads and larger ranges in concrete demolition shears; massive natural stone formations lead in hydraulic wedge splitters to long phases of increasing pressure load up to brittle failure. In tunnel construction, repetitive load sequences and elevated event density can be expected, whereas in building gutting more varying, short-cyclic loadings occur. These differences shape the local stress histories in shear arms, splitting cylinders, pin bearings, and in the sealing systems of the hydraulics.
Design and fatigue strength of hydraulic components
The design of structure and hydraulics is oriented toward the relevant load spectrum. Load-bearing components such as shear arms, jaws, blade holders, bearing pins, cylinder eyes, and weld seams are dimensioned against cyclic loading, with material properties, notch effects, friction conditions, and contact pressures being decisive. On the hydraulic side, pressure spectra determine the stresses of cylinders, power packs, valves, lines, and seals. Pressure spikes at sudden fracture events, valve switching, and flow-rate steps can superimpose to high load cycles. Proper damping, suitable switching logic, and adequate hose routing reduce harmful peaks.
Hydraulic pressure load spectrum and system dynamics
The hydraulic spectrum comprises basic operating states (ramp-up, hold, release), pulsating portions from pump and valves, and transient events. Crucial are rise times, pressure gradients, internal leakage flow, and the interaction of structural stiffness and oil compressibility. Short, steep pressure rises can be mechanically very effective even when the mean load is moderate.
In-service influencing factors
Rock type, reinforcement ratio, component geometry, temperature, tool condition (e.g., blade sharpness, wedge surface), operating strategy, and positioning accuracy strongly influence the actual load spectrum. Repeated partial-load cycles with occasional overload peaks stress components differently than many uniform cycles without peaks. For service life, not only the highest loads but especially the frequently occurring mid-load ranges are relevant.
Determination and description in practice
To determine the load spectrum, measurements are taken with pressure sensors, displacement or force transducers, and data loggers. The time series are filtered, segmented, and transformed into classes using counting methods. From these classes, frequency spectra and mission-type profiles can be derived. For tools from Darda GmbH, a separate consideration of the mechanical spectrum at the point of action and the hydraulic pressure spectrum has proven effective, supplemented by a qualitative description of the sequence of use (positioning, applying, loading, breakthrough, unloading).
Typical class groupings
- Low-load range: positioning, engagement, minor corrections
- Mid-load range: continuous gripping/spreading, controlled material build-up
- High-load range: breakthrough, heavily reinforced zones, hard rock veins
- Peak events: impact and rebound, sudden crack, valve switching
Load patterns for concrete demolition shears
For concrete demolition shears, a typical cycle evolves through closing the jaws, building up cutting and crushing forces, crack propagation, and release. The load spectra show:
- Interactions between edge pressure at the blade areas and global bending of the arms
- Load asymmetries due to eccentric gripping or uneven reinforcement
- Cyclic loading of bearing pins and cylinder eyes through close/open sequences
- Hydraulic pressure spikes at breakthrough and during rapid opening
For service life, the frequently occurring medium cutting loads are often more dominant than rare peaks. Smooth operation reduces the number of harmful high-load events and thus cumulative damage.
Load patterns for stone and concrete splitting devices
Hydraulic wedge splitters generate very high, rather monotonically increasing forces via the splitting cylinder and wedge systems until the crack propagates abruptly. The load spectrum is therefore characterized by long pulsating phases with a high mean value, followed by short relief. Influencing factors are borehole alignment, splitting wedge friction, rock anisotropy, and temperature. Pressure spikes in the hydraulic system can occur during detachment after breakthrough; these spikes are short but effective and should not be neglected in the spectrum.
Examples of typical load spectra in the application areas
- Concrete demolition and special demolition: frequent medium- to high-load cycles, irregular peaks due to reinforcement, increased event density with tight takt
- Building gutting and cutting: varying short cycles with moderate loads, occasional peaks at load-bearing nodes
- Rock excavation and tunnel construction: longer hold and rise phases, distinct peaks during crack propagation, repetitive mission profiles
- Natural stone extraction: plannable load increases, relatively constant mission cycles, load spectra with low scatter
- Special operation: highly scattering spectra with unpredictable peaks, stronger focus on damping and monitoring
Planning, assessment, and selection based on load spectra
For technical planning, a clearly defined mission description is recommended: number of cycles per shift, expected load ranges, share of peak events, environmental conditions. This information supports the selection of suitable tools from Darda GmbH and the coordinated design of the hydraulic power pack and suitable hydraulic power units. Important are compatible pressure and flow-rate ranges, sufficient hose sizing, and a control that limits harmful transient effects.
Operating strategy
- Position with a minimal load level
- Build load evenly and without unnecessary switching
- Anticipate breakthrough, initiate opening movement in a controlled manner
- Regularly inspect bearings and sealing points after high-load phases
Maintenance, inspection, and service-life prediction
Maintenance intervals can be derived from load spectra to match actual stresses. Relevant are inspection intervals for pins and bearings, visual checks on blade and jaw areas, seal conditions on cylinders, and hose and fitting inspections. Simple, cycle-based documentation (cycle counters, pressure-spike counters) increases the quality of predictions. Preventive measures such as timely blade replacement or maintaining wedge surfaces on splitters reduce harmful peaks and improve the service-life balance.
Edge cases and special operations
For atypical deployments with highly scattering loads, a cautious ramp strategy, a monitoring phase if necessary, and a conservative assessment of the load spectrum are recommended. Temperature and environmental conditions (dust, moisture) act indirectly via friction values and sealing properties on the load spectrum and should be documented in the deployment description.
Documentation and communication in the project
A concise description of the load spectrum includes the duty profile, relevant parameters (amplitude, mean value, number of cycles, peak events), hydraulic limit values, as well as observations on material behavior and operating sequence. This documentation facilitates coordination between construction site, planning, and technical support at Darda GmbH and forms the basis for robust decisions in design, deployment, and maintenance.