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With a population of almost six million people living on a land area of little more than 700 km2, Singapore is one of the most densely populated countries in the world. It also has one of the world’s highest GDPs per capita, and is thus well positioned to build and maintain the bridges that make it possible for so many people to travel safely and easily throughout the garden city.
Taking an interesting approach to bridge maintenance with the focus on key components rather than on individual structures as a whole, a programme of works was launched three years ago to replace the bearings of 36 bridges and viaducts across the country’s main island. The contracts were awarded to Gim Tian Civil Engineering Pte Ltd, who employed VSL Singapore Pte Ltd and Utracon Structural Systems Pte Ltd as installation contractors, and mageba as bearing supplier and specialist consultant.
Since the project required the new bearings to be installed to replace existing ones, rather than simply to be installed in new structures, the installation process for each structure required a great deal of planning and precision – not only because the bridges generally had to remain in service while the bridge bearings were replaced, but also because the new bearings had to be designed, fabricated and installed to exactly suit the layout, construction and dimensions of the existing bridge structures. This work can be especially challenging where the positioning of connection bolts and the height of the bearing must precisely match the position and level of every connecting surface and dowel. mageba is happy to have provide the required specialist knowledge and experience in structural bearing installation, assisting in developing and approving detailed plans for the widely varying circumstances arising in the numerous structures.
While a number of the bridges required simple elastomeric bearings, many of them needed mechanical bearings of the pot type – a kind of bearing that mageba has supplied to countless bridges around the world for decades already. mageba’s local Singapore subsidiary met this need by supplying 273 RESTON® POT bearings, designed for loads of up to 15,500 kN, the last of which was installed earlier this year. The project specification required the use of pot bearings of the same pot diameter, designed in accordance with BS5400, but this presented a problem: at numerous locations, superstructure movements since the time of the bridge construction resulted in an irreversible offset between the existing connection points to the superstructure and the substructure. Fortunately for the project, mageba was able to provide a solution, proposing the use of the HP (“High Performance”) version of the pot bearing, designed in accordance with EN 1337 and mageba’s European Technical Assessment for this bearing type. The RESTON® POT HP bearing offers several advantages over the standard RESTON® POT bearing – most notably the much higher characteristic strength of the elastomeric pad, with vulcanised POM sealing chain, at its core (120 N/mm2, double the value defined by EN 1337-5). This results in a much more compact bearing design, which as well as reducing weight and making easier to install, also enabled the pot bearings to be designed to suit the existing upper and lower connections in spite of the offset.
In order to ensure the overall quality of the planning and implementation work, a mageba structural bearing expert was appointed in the role of Bearing Specialist for the project. Working together with the similarly appointed professional engineer, he co-chaired technical meetings, verified that bearing designs were suitable for all aspects of the installation including jacking operations etc, and certified bearing installation and measurements. With all bearings properly installed and the work now completed, we are glad to have been able to contribute to this special citywide bearing replacement programme – and to have been able to overcome one of the biggest challenges faced by the diligent project team during its execution thanks to the extra-high bearing capacity of our high-performance “HP” pot bearing.
Main contractor: Gim Tian Civil Engineering Pte Ltd
Installation contractors: VSL Singapore Pte Ltd / Utracon Structural Systems Pte Ltd
Owner: LTA Singapore
Design and production of the RESTON® POT bearings – the key parts of which are shown in this design representation of a bearing of the guided-sliding type – required great accuracy to help ensure that all bearings would precisely match the connection details and dimensions of the existing bearings they replace