Project Description : Roller Rehab Bridge Bearing Service , 19th – 22nd June, 2018. Bearing rust removal, cleaning, painting, greasing and oiling. Report on service and any defects identified. Rust remove and protect with Action Corrosion.
Slide Plate Bearings and Pot Bearings.
The slide plate bearings on this 27 span structure are in generally good condition. Curiously the bottom plate of all slide bearings and the large pot bearings either side of span across the river (piers 21 and 22) were never painted or primed. They have now been coated in Carboline Miox Grey.
There appears to have been many guide bolts on the bearings which have been replaced with stainless steel ones. Pier 13 has a snapped guide bolt which requires replacement. The reason the original bolts snapped is evident on a number of bearings are shown below. The guide bolts were tightened too low not allowing enough clearance between the head of the bolt and and the slotted top plate. The guide bolts are often tapped and screwed in at an angle, meaning when there is longitudinal movement in the girder, the head of the bolt digs into the bottom plate and is eventually sheared off. The stainless replacement bolts fitted have excellent clearance as shown below to prevent this from occurring in the future.
Many of the bearings beds have been replaced with a white resin. This resin seems to be providing a good solid base for the bearings. No cracks in these repairs were evident.
The most urgent repair is a FULL bearing bed replacement on the bearing at the Grace Street abutment. Measurements were taken from the underside of the bearing anchoring bolt to the top of the bearing bed plate. From these measurements we estimate the bearing has dropped at least 10mm as a result of the disintegrating bed on which it sits.
Bearing Defects
Bottom plates on all slide plate bearings and the larger slide plate bearings and pot bearings on piers 21 and 22 were never painted. The surface rust was removed and the untreated areas painted.
Snapped bolt requires a replacement on pier 13.
Some of the original bolts provide evidence of why many snapped and required replacement. The guide bolts were tightened down too far meaning that if the bolts were not tapped perfectly square, longitudinal movement in the the girder would result in one side of the bolt head digging in and eventually shearing off.
The replacement bolts give ample clearance to prevent the reoccurrence of bolt damage.
The bearing pad on the Abutment at the Grace Street end has totally disintegrated. Measurements taken from the under side of the anchoring both to the top of the bottom plate indicate the bearing has dropped approximately 10mm.
Serviced oiled and greased pot bearings left and slide plate bearings right. Slide plate bearings marked to gauge future movement.
Recommendations
Bed on the abutment to be replaced.
Bolt on Pier 13 to be replaced.
Bearings to be cleaned, ballast removed and greased every 5 years.
