Seismic Bearing Installation and Replacement: Temporary Works and Sequencing

Engineering Assessment and Temporary Works Planning

Before commencing any seismic isolation bearing installation or replacement project, engineers must conduct a thorough structural assessment of the existing superstructure and substructure conditions. Temporary jacking schemes and temporary support towers must be engineered to safely transfer dead loads and any permitted construction live loads during bearing removal. Detailed calculation notes should account for potential load eccentricity, differential vertical deflections, and site-specific geometric constraints. All temporary works designs must be reviewed and approved by the engineer of record alongside the governing project specifications and approved construction drawings before mobilizing heavy equipment to the bridge site.

Jacking Operations and Superstructure Elevation Control

Executing controlled jacking operations requires synchronized hydraulic systems equipped with pressure transducers and displacement feedback sensors to monitor real-time bridge deck elevation. Lifting forces must be applied gradually across designated hard points on the substructure pier cap or abutment seat, strictly adhering to limiting lift heights specified in the approved methodology. Excessive differential lifting can induce unintended torsional stresses or cracking in concrete box girders and steel superstructures. Continuous optical leveling or digital sensor networks must track minute movements throughout the jacking cycle, ensuring the structure remains within specified vertical and horizontal tolerances while old bearings are unloaded.

For a related project route, review Seismic Isolation Bearings or Spherical Bearings in the context of Seismic Retrofit.

Removal of Existing Bearings and Substructure Preparation

Once the superstructure is safely supported on temporary works and hydraulic holds, extraction of legacy bridge bearings can proceed systematically. Anchor bolts, shear keys, and grout pads are inspected and removed in accordance with environmental and structural protocols. Concrete bearing seats must undergo rigorous surface preparation, including abrasive blasting and repair of any spalled or honeycombed mortar using approved non-shrink structural grouts. Elevations and flatness of the prepared concrete or steel mounting surfaces must be surveyed meticulously against benchmark levels defined in the installation drawings. Proper surface preparation guarantees uniform load distribution across the base plate of the newly installed seismic isolation device.

Placement, Alignment, and Final Grouting Procedures

The positioning of new seismic isolation bearings demands precise horizontal alignment relative to global bridge coordinates and thermal movement axes. Anchorage assemblies, dowel connections, and base plate orientations are secured without inducing premature shear or rotational restraint. Following mechanical fastening, precision dry-pack mortar or flowable high-strength epoxy grouts are placed beneath bearing base plates to eliminate voids and ensure complete bearing-to-seat contact. Final inspection protocols verify anchor torque values, clearance gaps, and movement capacity before releasing temporary hydraulic jacks. Final acceptance is contingent upon compliance with approved project design actions, drawings, and specifications.