현수교의 터널식 앵커리지 설계・시공 안전성 평가에 대한 고찰

Abstract

The Ulsan Bridge is a suspension bridge with a main span of 1,150m and it connects Maeam-dong and Ilsan-dong in Ulsan. The PPWS(Prefabricated Parallel Wire Strand) cables with a tensile strength of 1960Mpa were adopted as main cables in south Korea for the first time. The 203m high pylon was filled with concrete using the ACS(Auto Climbing System) form. The anchorages that bear the load of the suspension bridge are a gravity anchorage on the starting side and a tunnel-type anchorage at the end. The tunnel-type anchorage adopted for the Ulsan Bridge is a steel concrete structure that has 70 meters average length and 9.7m in diameter and it used 1,750 tons of tensile members and 14,141㎥ of concrete for filling it. The tunnel-type anchorage is constructed to bore a tunnel through rocks to install the steel frames as a tension member and the tunnel is to be filled with concrete. The tension members are connected with the main cables of suspension bridge. The tension of main cables is supported by the weight of in-filled concrete and the friction at the interface of the concrete and the surrounding rocks. This study is based on the review for securing the safety of the tunnel anchorage for the suspension bridge, which was designed and constructed by referring to overseas construction cases due to the lack of relevant guidelines and data. In the design stage, the safety evaluation has been considered by dividing into self-weight resistance, frictional resistance and anchoring resistance of tunnel-type anchorage. The sum of them satisfied the required resistances which include the safety factors. In the construction stage, ground investigation and sampling have been conducted to check the ground constants predicted at the design stage. The ground constants adopted for the design were checked through mock-up tests. The tension effect of tension members against the tensile load of main cables was managed not to produce any crack in the in-filled concrete. In addition, the surface treatment method was decided through mock-up tests. Changes in the tensile force during the construction phase of tunnel-type anchorage have been monitored by using the monitoring system installed in the suspension bridge for maintenance purposes. The safety of the anchorage system was confirmed through the whole process of stress changes.