Method of placing Neoprene bearings in position

yogendra borse

(A) For solid slab super structure.

Preparing Seating.

Strip in concrete cap

During concreting of the pier/abutment caps, a continuous strip of width 'B' (slightly more than width of bearing) and depth of 10 to 15 mm. shall be kept in concrete this can be done by removing concrete carefully when green.

Bearings in position: 

Levelling & Placing the Bearings 

A few days before placing of superstructure: 

i) Concrete the strip as formed in above image shall be completely filled in by stiff cement mortar 1:1 proportion with water cement ratio not exceeding that of parent concrete of pier cap. Very fine sand with size between 3 mm. shall be used for preparing this mortar. The top surface shall be perfectly levelled.

ii) Centre line positions of the bearings shall be marked accurately on pier and abutment caps in both the directions. The plan dimensions of the bearings shall then be marked. 

iii) The bearings shall be placed on the green martar by light tamping if necessary. The mortar shall be cured for atleast 7 days.

Erection of centering and casting the slab

a) Casting in situ deck.

The area around the bearings shall be filled with well rammed, selected fine damp sand. The thickness being equal to that of the bearing. The sand shall be covered with polythene layer. The side gap between soffit and pier cap may be sealed off by timber packing pieces.

The rest of the centering shall be erected as standard practice. The reinforcement for the solid slab shall be fixed in position as usual. During concreting great care shall be taken to avoid puncturing of the polythene membrane and displacement of the bearings.

Draining out Sand.

After 14 days from casting of the solid slab, the side timber parkings shall be removed and the sand shall be drained out by water jets.

(B)  For T Beam and slab superstructure. 

Preparing Seating. 

Same as above.

Levelling and placing the bearings in position. 

same as above.

iii) In case where M. S. plate is to be placed below the bearings, the plate shall be placed in position on the green mortar by light tamping. The position of bearing shall then be marked on these plates. The bearings shall then be placed in position. Epoxy arout shall be applied to the top and bottom surfaces of the bearing, wherever specified. The mortar shall be cured for minimum 7 days.

Erection of centering and casting superstructure.

i) For cast in situ decks. The procedure will be same as for solid slab. The sand packing will be required only under the main girders and not all over pier cap.

ii) For Precast Decks. Precast beam shall be placed on these bearings after a minimum period of 7 days from placement of the mortar, to allow mortar to develop adequate strength.