Inventing on the job

In supplying seismic protection bearings for a major new expressway in South Korea, mageba’s local and regional teams worked together to develop a new innovation – now patented – to meet the project’s needs which enables a single pendulum-type isolator bearing to support separate superstructures from both sides with uneven loading during the construction stage.

In the early stages of a project to construct the Pohang-Yeongdeok Expressway in eastern South Korea, a challenge was identified in the way the construction of one of the multi-span bridges was being planned – with the concrete superstructure being prefabricated in lengths corresponding to each span, and then stitched together with reinforcement and concrete at each pier. Unusual about the approach taken was that the continuous superstructure formed by the concreting together of the individual spans required to be supported, at each side of the superstructure, by a single bearing. This presented a particular challenge for the design of the bearings, which consequently had to support the uneven loading arising throughout the construction process. Most drastically, each bearing would be required to carry a load of 1600 kN at one side of the bearing before any load was applied at the other side, but a state of consistent even loading would only be achieved several months – or up to a year in some cases – after the first elements of superstructure were installed. This was particularly challenging because the bridge’s design called for the use of seismic isolators to support the superstructure, protecting it in case of an earthquake, and isolators of the curved surface slider (pendulum) type were specified – a type of isolator that offers no resistance to rotation in normal circumstances.

mageba RESTON®PENDULUM isolator bearings were selected for use on three of the project’s multi-span highway bridges – Bangseok No. 1, Bangseok No. 2 and Seojeongri Cheon. These were to be of the Duplo type, with two curved surfaces facilitating translation and simultaneous lifting of the supported structure during an earthquake. To address the specific challenge of the proposed bridge construction method for Seojeongri Cheon Bridge, a solution had to be developed and validated at short notice. Our local engineers in South Korea, working closely together with their colleagues in mageba’s Shanghai design and manufacturing facility and with the client, came up with the solution that is illustrated in the attached pictures. The bearings were designed with additional support elements between the upper and lower connection plates, one at each corner, to keep the connection plates parallel in spite of any uneven loading that might arise. These were designed with inclined sliding surfaces as shown to facilitate their easy removal when they are no longer needed – an elegant solution that has since been patented. Congratulations to our teams in South Korea and China for developing and validating this solution so quickly to meet the project’s special needs – always willing to go the extra mile for their clients!  

Main contractor: DL E&C CO., LTD.
Owner: Korea Expressway Corporation

The three new bridges for which the bearings are being supplied are part of the Pohang-Yeongdeok Expressway in eastern South Korea, scheduled to be completed by late 2023

The construction method of Seojeongri Cheon Bridge requires a single bearing at each side of the superstructure to support uneven loading on each pier until the prefabricated elements of all spans are lifted into position and concreted together to act as a truly continuous beam

Cross-section illustration of a standard RESTON®PENDULUM seismic isolator bearing of the Duplo type – with two curved surfaces facilitating translation and simultaneous lifting of the supported structure during an earthquake

Illustration of the solution developed to prevent rotation of the bearing due to uneven loading during construction of the bridge

The support elements inserted at each corner are designed for easy removal when no longer needed, with greased ROBO®SLIDE sliding material

When unscrewed, the support elements between the bearing’s upper and lower connection plates can simply slide outwards to be removed

A specially fabricated scale model of a pendulum isolator bearing helps to understand its concept. It shows the support elements at each corner that are also designed to prevent superstructure movements due to thermal expansion

Independent testing of a standard RESTON®PENDULUM isolator bearing at a Korea Certification & Testing laboratory, to confirm its proper functioning before installation

Preparation of some of the project’s 86 bearings (standard bearings for the first bridge) for transport to site