Strengthening measures secure and increase the load-bearing capacity of structures, structural elements, and geotechnical systems. They are used when uses change, loads increase, or damage reduces performance. In practice, planners and contractors rely on a coordinated interplay of structural analysis and design, suitable materials, and precise preparation of the existing structure. This also includes selective deconstruction and separation works, for example with concrete demolition shears or hydraulic rock and concrete splitters from Darda GmbH, to gently remove damaged zones or create bearing surfaces for the upgrade. In this way, quality, safety, and the integrity of the remaining load-bearing system are ensured—whether in building construction, civil engineering structures, or in rock and tunnel construction.
Definition: What is meant by a strengthening measure
A strengthening measure encompasses all deliberate interventions for structural reinforcement or retrofit of existing structures. The goal is to improve load-bearing and serviceability performance, increase durability, or enhance safety against exceptional actions (e.g., earthquakes or impact). Typical approaches include cross-section enlargements with concrete or shotcrete, bonding CFRP laminates or steel plates, shear and torsion strengthening, local underpinning, as well as adding or replacing reinforcement and steel components. Proper substrate preparation—often by concrete demolition with concrete demolition shears or by controlled splitting with hydraulic splitters—is an integral component, especially in sensitive environments with strict requirements for low vibration, noise, and dust.
Fields of application and typical triggers
Strengthening is planned and executed on a project-specific basis. Depending on the structure and use, it relates to different causes and touches various application areas of Darda GmbH—from concrete demolition and special demolition to building gutting and cutting through to rock excavation and tunnel construction or special applications.
- Increasing loads: Change of use, vertical extensions, heavy equipment, or increased traffic on bridges require higher safety margins.
- Damage and ageing: Concrete carbonation, chloride contamination, cracks, spalling, or fire damage necessitate targeted repair and rebuilding of cross-sections.
- Seismic retrofit: Increasing ductility and energy dissipation via additional reinforcement, jacketing, CFRP systems, or steel sections.
- Heritage protection and preservation of existing structures: Minimally invasive measures with low intervention in the fabric and low-vibration procedures.
- Tunnel and rock construction: Stabilization by rock bolts, netting, and shotcrete—often after selectively removing loose material, for example by splitting instead of blasting.
- Operational and occupational safety: Upgrading bearing areas, punching and shear strengthening of slabs, brackets, and columns.
Methods of structural strengthening
The choice of method depends on material, geometry, load transfer, environment, and construction stages. Multiple methods are often combined, which places high demands on planning, execution, and quality assurance.
- Cross-section strengthening with concrete/shotcrete: Overlays, column and beam jacketing, local build-ups for higher bending and shear capacities.
- Fiber-reinforced systems (CFRP/AFRP): External reinforcement for bending and shear strengthening, as laminates or fabrics, with defined surface preparation.
- Steel plate or section strengthening: Bonded/bolted plates, bolted-on sections, and jackets for ductility and load redistribution.
- Prestressing and reinforcement retrofit: External prestressing, post-installed reinforcement connections, anchor bars, and shear dowels.
- Underpinning and local foundation repair: Increasing foundation safety, e.g., for vertical extensions or changed loading.
- Crack and void treatment: Injections (cementitious or resin-based) to restore composite action and watertightness.
Preparation of the existing structure: selective removal and exposure
Before installing strengthening systems, damaged concrete layers, loose rock, and contaminated zones must be removed, reinforcement exposed, and bonding surfaces created. In practice, concrete demolition shears are often used to break concrete in a controlled manner and expose the reinforcement. In vibration-sensitive areas or with massive components, hydraulic splitters enable low-vibration separation to protect adjacent elements. Steel shears and Multi Cutters support cutting or trimming reinforcing bars and sections. Hydraulic power units from Darda GmbH provide the required energy for powerful yet precise operation.
Procedure in practice
A systematic approach ensures strengthening measures remain technically effective and economical without causing secondary damage.
- Condition survey and diagnosis: Visual inspection, non-destructive testing, material properties, chloride and carbonation depths, crack analysis.
- Structural analysis and planning: Modeling, design, definition of construction stages, load redistribution, and temporary shoring.
- Exposure and selective deconstruction: Removing damaged areas, creating defined edges, exposing reinforcement with concrete demolition shears; splitting with low vibration where necessary.
- Substrate preparation: Abrasive blasting, milling, cleaning, pull-off adhesion tests; ensuring concrete cover and adequate surface tensile strength.
- Installation of the strengthening: Bonding CFRP laminates, installing steel components, applying concrete/shotcrete, setting anchors, applying prestress.
- Protection and sealing systems: Corrosion protection, surface protection systems, and fire protection claddings as required.
- Quality assurance and documentation: Test records, evidence, measurements, photo documentation, monitoring during operation.
Special aspects in sensitive environments
In hospitals, historic buildings, laboratories, or ongoing production facilities, vibration, noise, and dust must be minimized. Hydraulic splitters enable controlled separation without impact energy, concrete demolition shears reduce vibration compared to impact tools. In addition, dust extraction, water spray systems, enclosures, and a coordinated disposal and logistics concept are required. In tunnels and caverns, site ventilation plays a central role; fire safety and evacuation routes must be kept clear at all times.
Material selection and design criteria
The choice of strengthening follows the actions and exposure environment. Relevant criteria are load-bearing capacity, stiffness, ductility, durability, fire protection, and construction stages.
- Mechanics: Bending and shear reserves, torsion, punching verification, fatigue under cyclic loads.
- Environment and durability: Concrete carbonation, moisture cycling, freeze–thaw, alkali–silica reaction; select suitable protection systems.
- Bond: Surface tensile strength, residual moisture, pull-off tests; controlled roughness for CFRP/steel plates.
- Fire protection: Temperature resistance, claddings or reactive coatings; consider building authority–approved solutions.
- Compatibility: Thermal expansion, stiffness ratios, corrosion protection at interfaces.
Interface with concrete demolition and special demolition
Strengthening and deconstruction are often two sides of the same coin. The existing structure must be prepared precisely before new systems can perform. In concrete demolition and special demolition, concrete demolition shears ensure controlled removal of weakened material without unnecessarily stressing the structure. Hydraulic splitters are helpful where impact energy or blasting are not options. For building gutting and cutting, depending on boundary conditions, concrete saws, core drills, or Multi Cutters with hydraulic drive from Darda GmbH are also used.
Quality assurance, testing, and monitoring
The effectiveness of a strengthening is demonstrated by tests and traceable documentation. Not mandatory, but proven:
- Pre-tests: Pull-off adhesion on the substrate, trial areas, material approvals.
- Accompanying controls: Installation logs, temperature and humidity monitoring during curing.
- Acceptance: Spot checks, load tests within permissible limits, visual inspection of critical details.
- Monitoring: Crack widths, settlements, vibrations; sensors for long-term observation as needed.
Occupational safety and environmental protection
Hydraulic tools are powerful and require clear work instructions, personal protective equipment, and cordoned-off hazard zones. The hydraulic hose lines of the hydraulic power packs must be laid with pressure-rated components, and leaks must be avoided. Dust protection and noise control, clean construction waste separation of removed materials, and orderly disposal are integral parts of the concept. For work in tunnels, ventilation, limitation of fire load, and rescue routes are particularly important.
Schedule and cost control
Cost-effectiveness arises from the interplay of the right method, short construction stages, and minimal disruption to operations. Selective methods—such as crushing with concrete demolition shears or low-vibration splitting—often save follow-on costs because they protect adjacent structures, minimize rework, and simplify permitting. Early contractor involvement, trial sections, and realistic drying and curing schedules prevent delays.
Limits and alternatives
Not every structure can be strengthened economically or technically sensibly. With severely damaged core concrete, insufficient bond capacity, or inadequate geometry, partial deconstruction and new construction are options. Temporary shoring, load redistribution measures, or replacing individual elements can be interim solutions. Here, too, hydraulic splitters and concrete demolition shears support controlled deconstruction without endangering the surroundings.
Strengthening in rock and tunnel construction
In underground construction, the focus is on stabilizing the rock mass and protecting the lining. Measures include rock bolts, anchors, netting, and shotcrete. Loose or overhanging material is removed beforehand. Where blasting is not possible or not desired, hydraulic splitters offer a controlled alternative to open joints or free blocks. Shotcrete then creates a homogeneous surface before strengthening is added and waterproofing is completed. In special applications—for example with confined cross-sections or night work—compact, high-performance hydraulic tools are advantageous.
Common error sources and how to avoid them
- Insufficient diagnosis: Missing material values or undetected damage lead to incorrect design.
- Inadequate substrate preparation: Smooth, contaminated, or wet surfaces jeopardize bond.
- Unplanned construction stages: Missing shoring and load redistribution risk secondary damage.
- Failure to control environmental impact: Vibration, dust, and noise impair operations and the existing structure.
- Unclear interfaces: Gaps between planning, deconstruction, strengthening, and corrosion protection cause defects.
- Underestimated fire protection and durability requirements: Later retrofits become expensive.