AGOM Italia

AGOM International SrlVia Mesero, 12 – 20010 OSSONA (MI)www.agom.it

POT BEARINGS

H A N D L I N G - S T O R A G EINSTALLATION AND MAINTENANCE


INTRODUCTION

This manual gives the main list of the mostimportant operations to correctly install theAGOM bridge bearings.

Under control of the Engineer who designedthe bridge, bearings must be installed byexpert workers, with precision to meet thebridge and bearing design criteria.

Inappropriate handling, storage andinstallation will have an adverse effect onthe bearing life, usually exstimated in morethan 50 years (for more details about thismatter, read the final chapter of this guide).

AGOM structural bearings are manufacturedto close tolerances by skilled techniciansworking in clean conditions.

To obtain the requisite performance frombearings it is imperative that they are properlyhandled at the work site and installed with thesame care as when they were assembled inthe factory.

AGOM bearings are clearly identified andmarked on the top plate to ensure correctinstallation. The typeface on the cover orsliding plate gives information on the type,size and number of the bearing.Moreover, arrows indicate the movement axisand the presetting direction (if applicable).

Every bearing is provided with a steelidentification label with all the most importantbearing information


HANDLING AND STORAGE

Care should be taken in storage to preventcontamination and damage to the workingsurfaces. AGOM bearings should be stored ina controlled environment where they areprotected from contamination, misuse andexcessive moisture.

Robust transportation devices are fitted to allbearings to ensure that the components aremaintained in they correct relative positionsbefore and during installation.

The devices are normally finished in red paint.

Unless special devices have been specified,they should not be used for slinging orsuspending the bearings beneath beams.

Due to unpredictable conditions, which mayoccur during transportation or handling on site,the alignment and presetting (if applicable) ofthe assembled bearing should be checkedagainst the drawing.

Do not try to rectify any discrepancies on site.

Bearing too heavy to be lifted by hand shouldbe properly slung using lifting equipment.

PRESETTING

If bearing are required to preset eg. whereonce only large movements may occur duringstressing operations, this should be specifiedas a requirement and should only be carriedout in AGOM prior to despatch.Do not attempt this operation on site.


BEDDING

Bearings must be supported on a flat rigidbed. Steel spreader plates must be machinedflat and smooth to mate exactly with thebearings’ upper and lower faces. Bearingsmay also be bedded on epoxy or cementmortar or by dry packing. Grout or mortarshould be applied in accordance with themanufacturers instructions, to a minimumthickness of 25 mm (unless agreedotherwise).Whichever system is preferred for theparticular structure it is of extreme importancethat the final bedding is free from high or hardspot, shrinkage, voids, etc..

Before casting the bearing in concrete, itshould be adjusted to the correct position bythe means of for wedges placed under thebearing bottom plate at four points. Thebearing should be level and stable with 30-40mm distance to the substructure.Unless there is a specific design requirement,the planar surfaces must be installed inhorizontal plane. The correct installation ofthe bearings is vital for the bearingsperformance. Costly repairs becomenecessary all too often due to inadequatespecification or poor site supervision. Thebearings should not be loaded until thebedding mortar has cured.

Special care must be taken to ensure thatguided bearings are correctly oriented.


FIXING POT BEARINGBearings are normally bedded in acementitious or chemical resin mortar. Cast-inanchors can be prefixed but it is generallyfound simpler to leave pockets in theabutment shelf or column top. The bearingcomplete with anchors can then be loweredonto a correctly levelled timber jig and theanchors grouted in position.When the mortar in the anchors has set, thetimber can be removed and the bearinggrouted up.The red temporary fixings must be removedbefore the bearing is allowed to rotate or slide.

Alternatively bearing must be fixed directly tometal bedding plates that may be cast-in orbedded on top of the supporting structure tothe correct level and location. Only a thin layerof bedding mortar should be use and thenother than synthetic resin mortar is used forthis purpose it should be housed in a recesssuitably reinforced on all sides.If the substructure is of steel, the bearing maybe bolted directly to it. In such cases theremay be difficulties in achieving location to lineand level within the tolerances unless otherprovision is made. Before providing foradjustment, the need for such accuratelocation should be assessed.

The bearing should be installed within atolerance of ± 0,0025 radians of the intendedinclination of the contact surfaces of thestructure.

FIXING BEARINGS SUPPORTINGCAST-IN-SITU STRUCTURECare must be taken to ensure that thebearings are not damaged by the formwork orcontaminated by concrete seepage. Theinterface between the top plate and theformwork should be protected and sealed.Owing to the loading effect of a wet concretemass, the top plate should be propped toprevent rotation and plate distortion. Bearingto plate of PFTE sliding bearings areespecially vulnerable in this respect.


FIXING BEARINGS SUPPORTINGPRECAST CONCRETE OR STEELELEMENTSA thin layer of synthetic mortar should be usedbetween bearing and precrast concretebeams. Alternatively, bearings with outerbearings plates may be bolted to anchorplates or anchors embedded in precastelements, or to machined sole plates on steelelements.

BEARING REMOVABILITYWhere possible, bearings should be fixed insuch a manner as to facilitate removal.AGOM bearing are generally been designedwith this mind.

REMOVAL OF TRANSPORTDEVICESThe transport devices, normally painted redshould only be removed when the bearing isproperly installed and ready for operation.

Any tapped holes exposed after removal oftransportation brackets etc (coloured red)should be sealed with self-vulcanizing siliconsealant.

SITE COATINGCare should be taken to ensure that workingsurfaces are not damaged in any site coatingoperation. After installation damaged coatingmust be repaired irrespective of any call forsite coating. Exposed fixing bolts should beprotected after final tightening.


MAINTENANCE OF BEARINGS

The service life of a pot bearing is usually exstimated in more than 50 years.The most important thing to assure such a long life time is a correct and carefulmaintenance of the bearing, that is usually installed in a severe environment.

What follows is a general bearing inspection and maintenance program that must beadapted by the bridge designer to the specific service conditions of the bridge.

Immediately following the installation, bearingsshall be inspected to ensure that all aspects ofinstallation of bearings have been adhered to.

Bearings shall subsequently be re-inspected not less frequently than everyfive years after their installation.

The period between two subsequentmaintenance inspections is dependent onsuch factors as the severity of theenvironment in which the bearings arelocated, loading and access.On structures utilising bearing with PTFEwhere the movement is generally the result ofthermal movements a five year inspectionshould be enough.For bearings subject to consistent high loadingfluctuation a reduced period of inspection maybe considered relevant. (the position of thebearing plates relative to the PTFE disc willvary with the season of the year).For bearings installed in a particular severeenvironment (sea zones for example) it mustbe considered as recommendable an annualinspection.

A typical complete routine check of the bearing installed should be comprehensive ofthe following activities.

1. Paint and other specified protective coatings must be maintained in good andefficient condition and free from scratches or chips. Any areas of the protectivecoating showing damage or distress must be rectified as soon as it is seen.

2. Area surrounding the bearings must be kept clean and dry and free from theadverse effects of external influences such as airborne debris or water/salt (forexample emanating from leaking joints).

3. The wearing surfaces of the bearing must be checked to ensure that they arecontinuing to operate efficiently

4. Where possible seals should be checked to ensure that they are intact.5. Fixing bolts must be checked for tightness.


6. Any bedding material showing signs of distress or ineffectiveness must bereplaced and the reason for its failure investigated and corrected.

7. Routine inspections shall include a check that translational and rotationalcapacities of the bearing have not been exceeded and show no sign of beinglikely to exceeded the requirements specified at the design stage.

8. PTFE discs should be within limits of their design movement and have at least 1mm thickness of material visible. Excess movement will be evident if the PTFEdisc have travelled outside the limits of the stainless steel slider plate.

If from a routine check it is pointed out any unusual damage, it could be decided bythe bridge responsible to make some deepest investigations or, as a final solution, itcan be decided to remove and substitute the bearing.

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