Wall sleeper: Most innovative web joint for extreme demands

Munich, Montreal. Wall sleepers are an innovative component that has only been used a few times on railroad bridges worldwide. The new Champlain Bridge over the St. Lawrence River received one of the largest ever built. The earthquake-resistant wall sleepers were also equipped with a newly developed derailment protection system. The 3.4-kilometer "New Samuel de Champlain Bridge" over the Saint Lawrence River replaces the Champlain Bridge built in 1962 and is already considered an icon. With its white color, the 170m high pair of pylons and the asymmetrical cable harps, it is a landmark for Montreal. The main span is 240m and with a width of 60m it is the widest cable-stayed bridge in the world. Up to 60 million vehicles cross the St. Lawrence River here every year. Road traffic has been flowing on the two outer bridge decks, each with four lanes, since 2019. The northern deck also has a multi-use lane for cyclists and pedestrians. Construction is still underway on the middle bridge, which passes between the pair of pylons. The new Réseau Express Métropolitain (REM) automated light rail system is scheduled to operate here from fall 2022. Large movements plus twisting The expansion joints on the central bridge were a particular challenge. This is a very slim design, which results in relatively large longitudinal movements during train crossings, braking and acceleration. Added to this are strong winds, severe winters and possible earthquakes. "The relatively large vertical movements in combination with twisting from torsion and bending effects plus horizontal displacements were a challenge that could only be met with our new wall sleepers," reports Dipl.-Ing. Stefan Vollert, development engineer at MAURER. But there was a whole package of further requirements for the transition:

• Completely watertight across the entire width of the bridge deck (also in combination with the trailing plate joint, called SP Expansion Joint) due to patented sealing profile.
• Can be inspected from below without interrupting traffic
• Suitable for the installation space of the slab track
• Perfectly uniform opening and closing behavior of the gaps
• Temperature range from -35 to +40° C

The Canadian railroad authority knew about the technical possibilities of the Wall Sleeper because representatives had visited the MAURER plant in Munich two years ago. At that time, the world's first earthquake-resistant wall sleepers for the Toluca-Mexico City railroad line were manufactured there. In fact, the wall sleeper is able to fulfill the whole package of requirements of the new Champlain Bridge.

Expansion joints for railroad bridges

Wall sleepers are expansion joints for railroad bridges. They bridge the structural gap at bridge ends or between bridge sections, in Montreal, for example, in front of and behind the main spans at the pair of pylons, and allow movement and twisting in all directions. The wall sleeper is based on the principle of the slewing beam expansion joint used in road construction, only much more stable, because large axle loads act on the structure with each train crossing. The sleeper absorbs these rapid vertical passing impulses and the associated movements without fatigue. Horizontal expansions are distributed evenly over the sleeper spacing by a geometrically guided control system. In contrast to an elastically guided control system, this provides greater stability and thus a longer service life. In addition, the movable bearings in the design allow the sleepers to "wander" or twist in or around the longitudinal, transverse and even vertical axes. During a train crossing, no significant elastic deformations occur within the wall sleeper. Even earthquake movements are compensated without damage within the expansion joint, so that trains can run again directly after a strong earthquake. The moving sleeper is currently the only railroad expansion joint capable of transmitting and absorbing fast, impulsive and large seismic movements without damage to the component or the structure. Customized

The special challenge in Canada was that the calculated movements were larger than foreseen by German codes and also larger than the standard wall sleepers previously developed by MAURER. "Since all bridge movements are outside the normed standard, we had to perform special verifications for the rails and rail support points," Vollert explains. In addition, it was required that the derailment protection systems commonly used on rail bridges be implemented across the expansion joints. These systems are mainly used to protect the bridge in case of derailment of individual train axles, which is actually not that rare in railroad operations. MAURER therefore developed a derailment protection system for the wall sleeper for the first time. High-performance sliding material MSM®

Small, laterally guided MSM® plain bearings ensure low-wear, virtually frictionless and controlled sliding of the sleepers with minimum resistance. MSM® stands for "MAURER Sliding Material" and is a sliding material developed and patented by MAURER. Compared to conventional Teflon (PTFE), it can absorb twice as much pressure, perform 5 times the sliding travel without wear and withstand 7.5 times the sliding speed. For this reason, MSM® is also installed as a durable, low-friction plain bearing at all bearing points. The New Champlain Bridge is supposed to have a service life of 125 years, for the wall sleeper at least 30 years were required. In fact, the MAURER Wall Sleepers are designed for at least 60 years. The durability of the control system and the load-bearing components was proven in a 10-km sliding distance test. The test was carried out with an original sized CT4 (CT4 = Guided Cross Tie with 4 joint gaps): according to the requirements of RIL804 in an independent laboratory of the Munich University of Applied Sciences, which is certified as a third-party inspector. There was no wear or fatigue in the moving components. A total of 16 wall sleepers with derailment protection for Montreal were manufactured in Munich, 4 of them as the large "CT4" variant with a movement of up to 1,030 mm. Transport and installation equipment

The wall sleepers are supplied with a specially designed transport frame. The sleepers can be moved longitudinally within the frame. During installation, this allows the sleepers to be adjusted to the respective displacement condition of the bridge. For fast and accurate placement of the wall sleepers, six mounting feet per expansion joint are measured into the structure and fixed before installation. This procedure saves the use of heavy lifting equipment. The 16 wall sleepers were installed from November 2020 to April 2021. For fastening, the rails were equipped with special rail support points (BSP FF-B-2-RE from Schwihag), which were converted for the American RE115 rail. These rail support points are used in the fixed guideway and meet increased requirements for vertical forces and transverse deformability. Scheduled to open in fall 2022, the rail bridge is being built and operated by Signature on the Saint Laurent Group G.P (SSLG). The bridge was designed by T.Y.Lin International and built by SSLC (Signature on the Saint Laurent Construction GC).