A bridge bearing pad under a bridge provide the flexibility to the structure and bear the load of upper structure including the traffic load. Live load of traffic creates different types of load in different directions of bridge structure. Each bearing pad has capacity to bear load of bridge structure including the movement in all directions and designed as per the live and dead loads of a bridge. Different types of bearing pads used as per load calculation of bridge. Some types consist of steel plates sandwiched into Rubber layers and some types have little mechanical system to bear heavy load and large movement. They are called Rubber bearing pads since they have steel plates sandwiched between rubber layers and can bear heavy loads. The other type consists of metals and PTFE plates to bear heavy load and also the large movements.

It is observed bearing pads performance on many bridges and thoroughly examined the bulging and impact of point load on bearing pads of bridge. During girder launching when girder slips from one side it moves the bearing pad under the girder and creates point load on the bearing pad.

We would like to share our observations with photographs as follows:

In a bridge we observed girders. We found that one side of the bearing is overloaded while the other 3 sides are behaving normal. There are two types of slopes: one of 0,48 m and one horizontal of 2 %.  The pedestal is not so straight as you can see in below picture.

Supabizz Bearing size: 660 x 250 x 68 mm

In this bridge we observe in girder that on front side two ends of the bearing are bulged while the middle part of the bearing is straight. In the attached picture you will see that steel scale goes between bearing and pedestal in the middle part.

The pedestal’s outer surface may have been level, but the girder was not evenly loaded on the bearing pad, resulting in deformation on both sides. Broken pedestal on this girder causes uneven load distribution.

Our overall comments for this bridge is that issue is minor so traffic is open.

Bearing size: 660 x 250 x 68 mm

In picture girder there is no contact in the left down side between the pedestal and the bearing.   

In girder 4 level is all right in y sense but not in the x sense. Right side does not lean properly; it is possible to pass the metallic scale beneath.

 Insufficient cleaning of the girder bottom caused uneven concrete to press on the bearing pad and bulge. 

It is very important to clean the girder properly in order that it does not affect the bearings behavior.We checked the level just after placing the bearing and in the long direction of the bearing was not right.

In above picture there is a level issue on the top but the bearing is behaving normal. The metallic scale can pass in the upper side of the bearing.

In the below picture there is a bearing pad.There is only one bulge on the lateral sides, approximately 4 mm thick. Bearing seems completely deformed. Rubber and steel reinforcement may not adhere well, causing this bulge. 

In this picture level is not all right and it produces a deformation in the length and short side of the bearing.

In below picture pedestal has slope and it provoques a bubble on the right. Girder will produce a deformation in the bearing.

In below picture 1 Pedestal with a bad level. In the short side of the bearing is possible to pass the metallic scale.

Uplifted bearing pad. Bearing is not working.

In the picture the short external side does not lean on the pedestal completely, but its working all right

CONCLUSIONS

We have thoroughly checked many Projects and we appreciate efforts of the consultants who arranged our detailed survey and share their point of view with us.

We have visited more than a hundred sites worldwide.Your problem is a normal change in bearing pad behavior over time after applying loads.

In order to prevent slipping during girder launching, use planks or some other solution to stop lateral load. This is the best way to get rid of point load with wood planks.

Bulging

Observed is a normal deformation in rubber because it does not overpass the European criteria.

Rubber behaves according to its rigidity, much lower than the Steel. This characteristic allows rubber to accommodate small girder and pedestal defaults that could appear. It can also absorb small slopes. The rubber underwent too much deformation in the bridge test for our bearings. The bearings deform during settlement and during the normal operation of the bridge as part of the rubber’s job.