Special bearings for India’s first lift bridge

Pamban, India. After over 100 years of service, the Pamban railway bridge in India has been replaced with a modern lift bridge that is now also protected against earthquakes. Special sliding isolation pendulums were developed and installed instead of the initially planned elastomeric bearings, as these were better suited to the task. What makes these earthquake bearings special is the way that they open and close with the lift bridge, while also always returning to the correct position automatically. They also resist corrosion and are optimised for monsoon conditions. MAURER India and MAURER Munich worked together hand in hand on the project.

Measuring around 2.06 km in length, the Pamban bridge in southern India connects the island of Pamban (Rameshwaram Island) with the mainland. There are actually three separate bridges on the site. The original railway bridge is over 100 years old and has been closed since 2022. It sits alongside the roadway bridge opened in 1988 and the “New Pamban Bridge” – a two-track railway bridge. This new bridge aims to improve transport connections and support the local economy, as the town of Rameshwaram on Pamban is an important destination for pilgrims.

The new bridge is a girder bridge with spans of 100 m. The technical challenge in this project was the central span of 72.5 m under which ships can pass. It was designed as India’s first lifting bridge at sea, with a lifting range of 17 m. This design ensures unimpeded shipping traffic and minimises stopping times for trains passing on the bridge. It was also designed to meet the new earthquake protection requirements.

Load + displacement + realignment

The initial plans for the Pamban bridge called for elastomeric bearings. As planning moved into greater detail, however, it became clear that the bridge’s location in a windy area at risk of earthquakes required a more capable bearing system. This needed to be able to absorb large movements while also having low elastic horizontal resistance.

“The challenge here was not just transferring the high loads and movements, but also realigning the bearing components under highly dynamic service and earthquake conditions. On top of all this, the environment is highly corrosive”, explain project managers Jitendra Rathore and Rohit Kumar.

The initial approach to this challenge was to use MSM® spherical bearings. These are sliding bearings with a service life of at least 50 years. They absorb rotations in any direction via an internal spherical joint without significant resistance, while also transferring very high loads on an extremely compact installation surface.

The key to the system is the high-performance sliding material MSM® (MAURER Sliding Material) in combination with a special rotating culotte. The culottes are made from the corrosion-resistant sliding alloy MSA® (MAURER Sliding Alloy).

Alongside the need for high earthquake resistance, the frequent opening (raising) of the Pamban bridge presented an additional challenge. This called for bearings that could be opened and realigned when the bridge was lowered, returning it precisely into position regardless of any movements occurring during the process due to temperature fluctuations, storms and rain, for example. As conventional spherical bearings have a flat sliding surface, they were incapable of realigning. That is why the project used sliding isolation pendulums instead.

SIP® bearings with integrated spring reset
MAURER’s bridge planners and experts developed the SIP®-FZ bearing as a special solution. These bearings are based on SIP® bearings (sliding isolation pendulums). Instead of a flat culotte, they have a concave curved sliding plate that ensures that the bearing realigns itself like a pendulum in the event of horizontal displacement. Due to the construction conditions, the four bearings were installed rotated by 180° with the sliding plate facing downwards.

The SIP® bearings in the Pamban bridge have four tasks:

• They realign the bridge in the correct position after it is raised or in the event of an earthquake.

• They transfer vertical loads.

• They isolate or separate the bridge deck from the piers in the event of an earthquake, so that only a small portion of the seismic energy is transferred to the bridge itself.

• They minimise the seismic energy from friction and movement by a factor of 2-5.

The letters F and Z in the name SIP®-FZ stand for Federn and Zug, the German words for springs and pull respectively. When the bridge is raised to allow a ship to pass underneath, the upper part of the bearing with the top half of the culotte is pulled up with it.

The bottom half of the culotte and the concave sliding plate remain on the substructure. When the bridge deck is lowered again, the upper half of the culotte automatically sits back into the lower half with the help of horizontal springs and a tray-like shape. The culotte also compensates rotations between the bridge superstructure and substructure.

Drainage and corrosion protection
But this function is not the only thing that makes the SIP®-FZ bearings special.

Water can collect in the tray-like bottom halves of the culottes when the bridge is raised or when it is raining. Drainage channels on the sides prevent this. The bearings also feature corrosion protection that meets class C5 very high as per ISO 12944-5, in order to reliably protect against the highly corrosive atmosphere at sea. They measure 1,205 x 845 mm and are designed for a load of 9,300 kN. They can displace by up to ±125 mm in the event of temperature fluctuations and earthquakes.

The cutting edge SIP®-FZ bearings allow the bridge to be raised and lowered frequently, while also protecting it against earthquakes. Thanks to the innovative combination of MSM® and MSA® sliding materials, the bridge can function without wear even under extremely dynamic load situations. The bearings have a service life of at least 50 years, making them an incredibly sustainable solution too.

The bearings were produced and inspected by TÜV Rheinland in Munich, before being installed in August 2024. Following the Kattwyk bridge in Hamburg and the Botlek bridge in Rotterdam, this represented another major international lift bridge project for MAURER, making it one of the leading companies in this area. The first track direction of the Pamban bridge was opened in April, with the superstructure for the second track due to follow. The bridge is owned by Indian Railway and the general contractor was RVNL.