Laminated Rubber Bearing construction scheme

Laminated Rubber Bearing preparation for installation1.

1. Laminated Rubber Beam Mobilization Inspection

(1) When using the laminated rubber beam, check the bearing for the manufacturer’s mark. Next, make sure the size, model, appearance, and other details match the design and specs.

Notch the steel plate under the bearing with 5 mm deep grooves where the bearing sits. This notch helps boost the bearing’s anti-sliding capacity. Make a groove in the stainless steel plate. This will stop the PTFE sliding plate support from slipping out. Then, anchor the stainless steel plate in this groove. This will boost the seismic performance. The part of the stainless steel plate that touches the PTFE plate must remain undamaged. This prevents higher friction and protects the PTFE plate.

Send the samples to a qualified testing unit. Do this based on the mobilization batch, quantity, and model.

2. Technical Preparation

(1) Review the installation drawings for the lagged rubber beam. Prepare the construction plan. Organize technical staff and workers for training after approval.

(2) Inspect the bearing pad stone and accept it based on the requirements.

The allowable error for the bearing pad stone is:

• Axis offset: 5 mm

• Top surface elevation: 2 mm

• Height difference of the four corners: 1 mm

We must handle those who are not meeting the requirements until they qualify.

(3) We need to accept the bridge’s substructure, upper beam, and slab in three stages. Also, we must prepare for these acceptances ahead of time.

(4) Surveying and setting out: Mark the center lines on the bearing pad stone and the bearing positions. Do this according to the design drawings. This ensures that we position the bearing with precision.

(5) Carry out a sampling test of various raw materials and design the mix proportions of epoxy mortar.

3. Material preparation

Laminated rubber bearing: We’ll include a packing list, product certificate, and installation guidelines for mobilization. Specifications, quality, and technical performance must meet current highway bridge bearing standards. They should also meet design requirements.

Prepare epoxy mortar using these materials:

• Dibutyl ester

• Ethylene diamine

• Epoxy resin

• Xylene

• Fine sand

All materials, except for fine sand, must include certificates and operating instructions. The variety and quality of fine sand must follow relevant standards.

The site must provide a quality certificate for the welding electrode upon entry. Choose a welding electrode that matches the strength of the base metal. The type, specification, and quality must meet current national standards and design needs.

Other materials: acetone or alcohol, silicone, etc.

4. Preparation of machines, tools, and equipment

(1) Main machinery includes:

• Transport truck

• Generator

• Electric welding machine

• Truck crane

• Water truck

• Water pump

• And more.

(2) Tools:

• Wrench

• Spirit level

• Iron chisel

• Small spade

• Iron pot

• Spade

• Iron trowel

• Wood float

• Rubber hammer

• Wire brush

• Steel wedge

• Fine screen

• Broom

• Small line

• Plumb bob

(3) Measuring equipment: total station, level, steel ruler, etc.

(4) Test equipment: universal testing machine and press machine.

5. Site preparation

The concrete on the pier and abutment must be flat, clean, and dry. It should also be free of floating sand. This ensures even pressure across the entire area.

Examine all pad stone surfaces for any imperfections. Look at the top surface elevation, pier, and abutment axis. Make sure they meet the design requirements.

Workers have erected ladders for the upper and lower piers and abutments to be in place.

Installation and construction of an animated rubber beam.

1. Construction process flow:

• Check the bearing.

• Measure and set out.

• Place the bearing.

• Install the beam and slab.

• Check the bearing again.

2. Installation of ordinary lagged rubber beam

Move the rubber bearing to the pier top. Then, set it on the pad stone, following the lofted cross center line. It is only required to overlap the bearing center with the pad stone center line. Check if the bearing’s cross center matches the pad stone’s cross center. Also, ensure that the elevation at all four corners meets the required specifications. Install the C steel plate at the middle cross beam’s bottom support after inspection. You must weld the door reinforcement on the C steel plate in advance. And install the C steel plate with precision. You can use a straight steel ruler to measure any changes. Each support on the beam must sit on the same plane. This avoids eccentric compression, uneven support, and separation between supports.

3. Installation of PTFE Rubber Bearing Pad

First, mix epoxy resin mortar. The site lab must provide the mix proportion. We must prepare the epoxy resin mortar exactly as stated. First, dry the fine sand. Then, put the fine sand, epoxy resin, dibutyl ester, and xylene into the iron pot. Heat and mix them well. Before bonding the steel plate, mix ethylenediamine with the mortar for a uniform blend. Ethylenediamine is a curing agent. Don’t add too much or too early. This can harm bonding quality because the mortar may solidify too soon. Use triethylenetetramine in summer because ethylenediamine solidifies in a short time then. In spring and winter, stick with ethylenediamine. Transport the epoxy resin mortar and PTFE rubber bearing pad to the pier and abutment top.

First, smear a layer of epoxy resin mortar on the treated pad stone top. The thickness of the epoxy resin mortar must be uniform. Then, place the lower steel plate of the support on the PTFE rubber bearing pad stone. The epoxy resin mortar bonds the lower steel plate. The cross centerline of the lower steel plate overlaps with the pier and abutment top pad stone. This follows the cross center extension line that is already set out.

Then, install the PTFE rubber bearing pad. Before you install, clean the sliding surfaces well with acetone or alcohol. You must also clean other parts of the support. After cleaning, fill the PTFE plate’s oil storage tank with silicone lubricant. Keep it clean to lower the friction coefficient. The installation of the PTFE rubber bearing pad requires precision. Put the support in the notch. Then, place it on the lower steel plate, aligning it with the marked cross centerline.

Only overlap the cross center of the support with the cross centerline of the lower steel plate. Check if the center of the support matches the center of the pad stone. Also, measure if the height of the four corners meets the specification requirements. Install the upper steel plate on the support after passing the inspection. Make sure to place the upper steel plate in the correct position. Use a straight steel ruler to measure and adjust its position. Coat the exposed steel plates of the PTFE rubber bearing pad with anti-rust paint.

4. Installation of Beam and Slab

For precast beam slab installation:

• The design at the beam slab’s end must align with the bearing centerline.

• The beam slab’s long axis should run parallel to the bearing centerline.

When the beam arrives at the site, first check for cement paste on the embedded steel plate at the bottom. Then, ensure that the edges of the steel plate are flat and properly treated. When the beam falls, use wooden triangle blocks. They will stop sliding between the beam and the PTFE rubber pad. Place these blocks on both sides of the beam. After the beam has fallen, you can remove it. To lower the beam, first mark the center lines of the two supports on the end beam with an ink marker.

Then, draw straight lines along these center lines on the beam’s elevation. Finally, align the beam with the centerline of the pier and abutment. For the following several spans, the construction team can drop the beam based on the first span beam. Lower the beam in a controlled manner. This helps avoid uneven compression or initial shear deformation on the support.

If the precast beam slab isn’t placed right or isn’t snug against the support, lift and reposition it to close the gap. Do not use crowbars to move the beam slab. The rubber bearing’s top surface should stay horizontal after installing the beam. To make it easier to replace the PTFE rubber beam pad, weld the steel plate at the bottom of the beam to the steel plate on the support in sections. Each weld should be 8mm thick and 5cm long. When welding, the welder should clear debris from the support. They must also cover the rubber block with flame-retardant materials.

This stops fire from damaging the support. It also keeps the steel body cool, protecting the concrete. If the beam body slopes, we can shape the steel plate into a wedge. This keeps the surface between the PTFE rubber beam pad and the stainless steel plate flat. The beam plant must install the leveling wedge steel plate. The construction team must use epoxy resin. This will bond the wedge steel plate to the embedded steel plate at the bottom of the beam. Weld the embedded steel plate to the beam bottom in sections after 24 hours. The weld joint must be 8mm thick and each weld joint must be 5cm long. When welding the connecting steel plate, pay attention not to burn the concrete. The workers need to change the cross slope of the hollow slab. They will use a wedge-shaped steel plate in the same way.

5. Installation of dust cover:

Install the dust cover. You must provide a dust cover for a PTFE rubber bearing pad. They use a 5 mm thick rubber sheet or nylon fiber cloth for the dust cover. Then, they glue the four sides to the upper steel plate with epoxy resin.

6. Completely check the bearing

After finishing the beam-slab system conversion, check the PTFE rubber bearing pad for issues. If some supports pull away, show big shear deformation, or face high pressure, we need to find the causes. We should make adjustments without delay. A jack can lift the beam end. Then, apply a layer of epoxy resin mortar on both surfaces of the bearing. After that, lower the beam again. Gravity will keep the upper and lower surfaces of the bearing parallel. They should maintain contact with both the bottom of the beam and the top surface of the pier. The supports at both ends of a beam must be in the same plane. Control the beam’s angle to prevent noticeable shear deformation at the support.

Quality Control and Inspection

1. PTFE rubber bearing pads must not have exposed rebar, cavities, honeycomb, pitted surfaces, or cracks.

2. Check the raw materials before construction, and keep the certificate records.

3. When the bearing arrives at the site, examine it with thorough attention. Make sure the specifications and quality match the design requirements. Also, ensure the product qualification certificate is complete. Inspect the bearing for any damage resulting from transportation. Do not use the bearing if you have not qualified it.

4. Check if someone has filled the PTFE rubber bearing pad with silicone oil. You must not replace silicone oil with lubricating oil.

5. Check if the bearing shows too much compression deformation. Check the rubber plates between the stiff steel plates. Make sure they have a uniform curve and are in good condition.

6. The warehouse for storing PTFE rubber bearing pads must be dry and ventilated. Stack the supports in order and keep them clean. You must not mix them with acid, alkali, or oil. Organic solvents must be in contact with the ground and must be at least 1 m away from the heat source.