Differences in the installation of pot bearings and sliding elastomeric bearing pads for highway bridges

Installation method of pot bearings on bridges:

1. Adopting welding connection method: When the construction unit constructs the upper and lower parts of the bridge during construction, the installation position of the basin type rubber bearing should be pre embedded with steel plates larger than the top and bottom plates of this series of bearings, and reliable anchoring measures should be taken. After the pot bearing is in place, use intermittent welding to weld the top and bottom plates of the support together with the embedded steel plates.

2. Using anchor bolt connection method: connect the support with the upper and lower structures of the bridge using anchor nuts. The above two methods can also be mixed, such as using anchor bolts to connect the support and the main beam, and using welding to connect the pier and abutment. When using pre embedded anchor bolt holes for connection, it is recommended to use epoxy resin mortar instead of grouted concrete, with a mix ratio (by weight) of epoxy resin (6101) 100, dibutyl resin 17,8, and sand 250. Pot type rubber bearings, also known as "highway bridge pot bearings", are a new type of bridge rubber bearing product that combines steel components and rubber. Compared with ordinary plate type rubber bearings, they have the characteristics of large bearing capacity, large horizontal displacement, flexible rotation, and are lightweight, compact in structure, simple in structure, low in building height, convenient in processing and manufacturing, steel saving, and cost reduction.

Replacement plan for PTFE sliding bearing pad

1、 Disease and Cause Analysis of Bridge Bearings

1. The pressure on rubber bearings is uneven, with some bearings partially or even completely detached and not participating in structural stress, resulting in increased pressure on other bearings and significant deformation.

2. The rubber bearing  is cracked. There are many reasons for cracking of rubber bearings, which can be mainly divided into two categories: one is the quality problem of the rubber bearings themselves. The second is the issue of construction and installation.

The quality issues of the rubber bearing itself mainly include: the rubber quality does not meet the requirements, such as using recycled rubber; There are inclusions and low content of micropores in the rubber material; The thickness of the adhesive layer is uneven, and the thickness of the protective adhesive layer cannot meet the requirements. In addition, the rubber bearing is contaminated and damaged during transportation and storage, which affects the quality of the bearing.

The main problems during construction and installation include: 1. The height of the bearing pad stone does not meet the requirements, and the deviation between the pad stone and the beam bottom bearing surface is too large, causing some bearings to become empty and the support to be under excessive pressure. 2. The surface of the upper bearing pad stone and the beam bottom bearing surface are not flat, causing the support to be biased. 3. The position and size deviation of the bearing pad stone and the beam bottom bearing surface are too large. 4. The position deviation of the bearing installation is too large

3. The rubber bearing undergoes shear deformation, with excessive shear deformation and even cracks. The main reason for this phenomenon is that the initial shear deformation during the installation of the bearing is too large.

4. The height of the bearing pad stone is not enough, and it is leveled with ordinary mortar, causing the mortar to crush. The upper support on it does not bear the upper load, and some of the upper supports become empty, even sealing the gaps with mortar

5. There are debris on the cushion stones of the piers and abutments, such as concrete formwork and soil. The reasons for this phenomenon include: slurry leakage during pouring of wet joints, debris falling into the expansion joints before installation not being cleaned, temporary fixing facilities not being removed, and debris on the piers and abutments may contaminate the rubber bearings, while others may surround the bearings, affecting their normal functioning.

6. The elevation of the top surface of the pier and abutment where the support is placed exceeds the standard. In order to maintain the elevation of the beam bottom, grooves are left at the support to make up for it.

7. The PTFE sliding rubber bearing is deformed and cracked due to shearing. The main reason for this phenomenon is incorrect installation methods, such as: the rubber sliding bearing is not cleaned thoroughly, sediment enters the contact surface between the PTFE sliding bearing and the stainless steel plate, the surface protective film of the stainless steel plate is not removed, silicone oil is not injected or replaced with lubricating oil on the PTFE slidingbearing, the installation deviation of the support is too large, and some PTFE bearing supports are even installed upside down, and the stainless steel plate is set on the pad stone.

2、 Steps for replacing bridge bearings

Erect supports and construction platforms

 1. The replacement of bridge abutment bearings utilizes the bridge abutment as the construction platform, and measures are taken for areas with insufficient space to ensure the safe implementation of construction.

 2. For the replacement of bridge pier bearings, special steel hangers are used to fix them on the pier body or bridge as a construction platform.

Cleaning of the top surface of the abutment cap and cap beam

1. Clean the soil and concrete blocks on the top area of the platform cap or cover beam, and if necessary, use steel needles to clean the concrete waste.

 2. Use a wire brush or clean the top surface of the abutment cap or cover beam to ensure that the operation is clean and tidy when replacing the support.

 Clean up the garbage and debris deposited in the expansion joint to prevent mutual compression between the lifting inner beams.