Girder bearing

Girder bearings are the interface where a beam transfers its loads into a support element such as piers, walls, abutments, or rock. This zone decisively influences the load-bearing capacity, serviceability, and durability of a structure. In existing structures, it also directly affects workflows in concrete demolition, in special demolition, and during building gutting. Tools such as concrete pulverizers or rock and concrete splitters from Darda GmbH make it possible to expose, separate, or deconstruct bearing areas in a controlled, low-vibration, and highly precise manner-from the bearing plinth to the anchor plate, without promotional intent, but as a factual classification within the work sequence. In technical language, the bearing zone is also referred to as the bearing seat or bearing area, highlighting its role as the contact and transfer region between superstructure and substructure.

Definition: What is meant by a girder bearing?

A girder bearing is the structural support and contact zone between a beam (e.g., reinforced concrete, prestressed concrete, or steel girder) and its supporting component. It can be formed as a direct bearing (beam on a mortar or grout joint) or via a mechanical bearing (e.g., elastomeric, pot, spherical, or sliding bearings). Tasks include the safe transfer of vertical and, where applicable, horizontal forces, allowing required deformations (rotations, longitudinal displacements), and protecting the contact surfaces against excessive pressures, edge spalling, and corrosion. In bridges, halls, industrial plants, and tunnel construction, the configuration of the girder bearing governs the deformation and restraint behavior of the overall system. In addition, constructability, replaceability, and inspection access in the bearing zone are integral to a durable, low-maintenance design over the life cycle.

Construction, types, and functional principles of girder bearings

The configuration depends on material, load level, boundary conditions (temperature, settlements, earthquakes), and the maintenance strategy. Common types are:

• Direct bearing on a bearing plinth with grout or leveling mortar: common in building construction; load distribution via compression struts, stirrups, and anchors. Flatness, defined joint thickness, and sufficient bearing length are important.
• Elastomeric bearings (laminated or solid rubber): accommodate rotation, allow limited displacements; suitable for standard applications in bridges and frame halls.
• Pot and spherical bearings: for high loads with defined displacement/rotation capacities; common in civil engineering structures.
• Sliding bearings (e.g., PTFE/stainless steel): low friction for large length changes; executed as fixed and free bearings.
• Steel bearings with bearing plates, brackets, saddle bearings: especially for steel girders; often anchored into the bearing plinth with dowels/anchors.
• Seismic isolation bearings (e.g., lead-rubber or pendulum principles): decouple horizontal actions under earthquakes while permitting service displacements.

Functionally, a distinction is made between fixed bearings (transfer of horizontal forces) and free bearings (allow longitudinal displacements). Uplift restraints, shear keys, or shear dowels prevent uncontrolled lifting or sliding. The bearing zone is to be designed as a load- and restraint-friendly transition with clearly defined force paths and coordinated tolerances.

Design and detailing in the bearing zone

Design covers local compressive stresses, shear capacity, anchorage and punching verifications, as well as deformations and fatigue. A robust detail avoids restraint, reduces stress concentrations, and protects against moisture and chloride ingress. Equally relevant are accessibility for inspection, drainage of the bearing seat, and the replaceability of mechanical bearings without major interventions in the superstructure.

Bearing pressures and the bearing joint

The bearing joint compensates tolerances and distributes pressures. Critical are flatness, a sufficiently stiff bearing plinth, and a grout with high early and final strength. Edge distance and chamfers reduce spalling risk; at high loads, inclined stresses, strut effects, and local transverse compression reinforcement must be considered. Specify joint thickness and evenness tolerances, ensure proper substrate preparation (clean, saturated surface-dry if required), and observe curing to limit shrinkage-induced gaps.

Fixed and free bearings, restraint and temperature

Fixed bearings introduce horizontal actions (wind, braking loads). Free bearings allow longitudinal displacements due to temperature, shrinkage, and creep. The bearing arrangement determines restraint distribution-blocked bearings lead to cracking and increased bearing forces. Rotational compatibility, friction coefficients, and sliding surfaces must be coordinated so that temperature movements and imposed deformations can occur without constraint.

Reinforcement, anchors, and dowels

Stirrups at the bearing, headed studs, and anchor plates ensure shear and tension load paths. Adequate lap and anchorage lengths (e.g., rebar lap splice) as well as contact corrosion and fire protection must be planned. Anchorage detailing is to consider edge distances, concrete cone failure, and redundancy for temporary conditions during bearing replacement.

Typical damage, causes, and assessment

In practice, girder bearings often show locally confined but safety-relevant findings:

• Spalling and transverse compression cracks due to excessive bearing pressures or insufficient joint quality.
• Blocked bearings (deformation-inactive due to corrosion, contamination, adhesion) with restraint cracking in the superstructure.
• Settlements and tilting of the bearing plinth with uneven load distribution.
• Corrosion on bearing plates, anchors, and bearing housings; damaged sliding or elastomer components.
• Missing or insufficient uplift restraints, inadequate edge distances.
• Aging of elastomer layers (ozone cracks, hardening) with reduced rotation/displacement capacity.
• Water ingress and insufficient drainage at the bearing seat leading to freeze-thaw damage and chloride transport.

Assessment is visual, metrological (rotation/displacement capacity, settlements), and structural (re-analysis). Non-destructive testing, targeted opening of inspection windows, and monitoring (e.g., displacement gauges) improve the basis for decisions. Results guide repair, bearing replacement, or deconstruction, including prioritization by urgency and impact on operations.

Refurbishment, replacement, and deconstruction of girder bearings

During repair or replacement, loads are temporarily rerouted, bearings are dismantled, and bearing surfaces are upgraded. Especially in concrete demolition and special demolition, a low-vibration, controlled approach is essential to avoid impairing the superstructure and operations (e.g., traffic, plants). Sequencing, traffic and plant coordination, and quality checkpoints (survey, flatness, joint thickness) are to be defined in the method statement.

Work sequence in deconstruction

1. Investigation and planning: exposure, documentation, and surveying of bearing position and elevation; definition of load transfer, lifting, and securing points.
2. Temporary load rerouting: auxiliary shoring and lifting operations with suitable hydraulics; continuous monitoring of deformations.
3. Selective surface removal: use concrete pulverizers from Darda GmbH to remove the cover concrete without protective casings, expose reinforcement, and selectively open interference points on the bearing plinth.
4. Controlled release of massive areas: deploy concrete splitter via boreholes to split core zones of the bearing plinth with low stress and define removal edges.
5. Separating steel components: cut anchors, bearing plates, and brackets with steel shear or Multi Cutters; for thick-walled parts, a cutting torch can be appropriate.
6. Removal of the bearing: dismantle the old bearing, clean and level the contact surfaces, produce the new bearing joint.
7. Rebearing and testing: install the new bearing, controlled lowering, functional testing (displaceability, bearing pressures), final documentation.
8. Shielding and protection: install spark and debris protection, dust suppression, and drip trays for oils and grout where necessary.
9. Quality control: verify flatness and joint thickness, record torque/tensioning values where applicable, and document as-built geometry.

Tools and methods in the context of girder bearings

The choice of technique depends on component thickness, reinforcement, accessibility, and vibration sensitivity. Additional criteria include emission control (noise, dust), permissible loads on the surroundings, and the precision required at interfaces between steel and concrete.

Concrete pulverizers in the bearing zone

Concrete pulverizers enable precise, low-vibration removal of edge concrete. Typical tasks include exposing bearing stirrups, removing defective concrete on the bearing plinth, and producing clean working edges in confined areas of building gutting and concrete cutting. They help minimize collateral damage to adjacent components and keep reinforcement intact for subsequent work steps.

Concrete splitters for low-noise removal

Concrete splitters act linearly in the borehole and create defined crack surfaces. This allows massive bearing blocks or brackets to be separated into transportable pieces-particularly suitable near sensitive infrastructure, for night work, or during ongoing operations. By controlling splitting pressure and wedge geometry, crack propagation can be directed to preserve adjacent structures.

Professional separation of steel components

For anchor rods, bearing plates, base plates, or brackets, steel shear and Multi Cutters are used. For large-format, thick-walled steel parts, a cutting torch can accelerate the cut. Combined tasks (cutting and gripping) can be covered with combination shears. Preparatory load relief and sequencing reduce the risk of jamming and uncontrolled part movement.

Hydraulic power packs and accessibility

Compact hydraulic power units provide the required energy for pulverizers, splitting cylinders, and shears, even in niches, shafts, or under superstructures. The ability to tune pressure and flow supports a material-friendly approach. Hose routing, quick-couplers, and remote control options facilitate safe operation in restricted spaces.

Applications: From concrete demolition to tunnel construction

• Concrete demolition and special demolition: bearing replacement on bridges, deconstruction of bearing brackets, lowering and partial demolitions with reduced vibrations.
• Building gutting and concrete cutting: exposing bearing details in existing buildings, staged removal of edge beams and brackets.
• Rock breakout and tunnel construction: bearings of steel frames on rock benches, bearing plates at crown and column heads; precise separation in confined space.
• Special operations: work under traffic, in vibration-sensitive plants, or with increased requirements for dust suppression and noise reduction measures.
• Seismic retrofits and upgrades: staged exchange of bearings and introduction of isolation elements while maintaining partial operation.

Safety, environment, and quality assurance

Work on the girder bearing directly affects load transfer. Planning, shoring, measurement, and safeguarding measures must be coordinated with the responsible specialist planners. Notes on occupational safety, hazardous substances, and disposal (e.g., when removing bearings with sliding or elastomer components) must be observed in general; case-specific binding statements are not made here. Separate collection of concrete, steel, and bearing components facilitates recycling and proper disposal. Environmental protection includes dust and noise management, water handling, and spill prevention; quality assurance encompasses defined hold points, acceptance criteria for bearings and joints, and traceable documentation.

Practice-oriented execution notes

• Prepare bearing surfaces dry, clean, and flat before surveying; select joint material according to the required compressive strength.
• Provide edge distances, chamfers, and transverse compression reinforcement against spalling; favor structurally robust details.
• For deconstruction: choose the sequence so that restraint and residual load-bearing behavior remain controlled; start with “soft” exposure using concrete pulverizers, then separate core areas with concrete splitter.
• Relieve steel parts in time before separating them with steel shear or Multi Cutters; consider sparks and fire load, use wet methods or shielding if necessary.
• Set measurement points for settlements/rotations and monitor them during lifting and lowering operations.
• Mark fixed and free bearings, rotation directions, and displacement axes clearly before lifting operations.
• Plan curing and protection of grout/mortar to achieve specified early strength before reloading; record temperatures and times.
• Document as-built geometry, bearing identification, and testing results for future inspections and maintenance planning.

Applications in bridges, building construction, and industry

In bridge construction, bearing arrangement and bearing details influence overall behavior under traffic loads. In building construction, bearing lengths, bracket details, and shear paths determine the load reserves of edge beams and girders. In industry, anchors, bearing plates, and steel brackets are often part of secondary load-bearing and the machine foundation, whose deconstruction or adaptation requires precise cuts and controlled removal-a field of application for concrete pulverizers, concrete splitter, and complementary shear tools from Darda GmbH. Across all applications, coordinated design, execution, and inspection ensure durable, serviceable bearing zones with predictable maintenance throughout the service life.