This study investigated structural behavior of long-span partially earth-anchored cable-stayed bridges with a main span length of 810 m that use a new key segment closing method based on a thermal prestressing technique. A detailed construction sequence analysis matched with the free cantilever method (FCM) was performed using a three-dimensional finite element (FE) model of a partially earth-anchored cable-stayed bridge. The new method offers an effective way of connecting key segments by

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... ing large movements resulting from the removal of the longitudinal restraint owing to the asymmetry of axial forces in the girders near the pylons. The new method develops new member forces through the process of heating the cantilever system before installing the key segment and cooling the system continuously after installing key segments. The resulting forces developed by the thermal process enhance the structural behavior of partially earth-anchored cable-stayed bridges owing to decreased axial forces in the girders. Appl. Sci. 2016, 6, 231 2 of 21 the installation of the key segment, and the bridge geometry should match in both the vertical and transverse directions. The process of a set back and reset back is widely used in ensuring sufficient space between the key segment and adjacent segments in a cantilever state. However, in this process, tremendous forces for key segment closure are required because partially earth-anchored cable-stayed bridges show relatively large reactions at longitudinal restraints prior to the process of set back and reset back. The restraints are installed between the girders and the pylons to guarantee the stability of a bridge at the start of the FCM. Owing to the difference of axial forces between the left and right side girders of the restraint devices, which are caused by earth-anchored cables, the release of the reaction forces just before the process of set back causes large movements (see the latter chapter 4.1). Thus, application of the general set back and reset back processes is not valid for long-span partially earth-anchored cable-stayed bridges. However, in case of general self-anchored cable-stayed bridge where all of the cables are anchored to the pylon and the girder, there is little difference of axial forces between the left and right side girders of restraint devices. Owing to the small reactions at longitudinal restraints, the set back and reset back can be done easily by hydraulic jacks controlling the space between the key segment and adjacent segments. This study focuses on the application of a partially earth-anchored cable system to a long-main-span cable-stayed bridge constructed by the FCM where the application of set back and reset back process is not possible. A new type of key segment closing method is applied based on the thermal prestressing technique [6] , which provides an effective way of closing key segments by means of thermal expansion. To investigate structural behavior in the new closing method, a detailed construction sequence analysis was performed using a three-dimensional FE model of a partially earth-anchored cable-stayed bridge. The influence of the new method on the structural members was examined after construction was completed, and the variation of the member forces was checked according to the specific construction stage during the thermal prestressing process. Key Segment Closing Method Partially Earth-Anchored Cable-Stayed Bridge The stiffening girders of cable-stayed bridges can transmit tensile as well as compressive forces. Figure 1 shows the axial force distributions of a partially earth-anchored cable-stayed bridge. The combination of supporting conditions and anchoring locations alters the axial force distributions of the girders. Most cable-stayed bridges are constructed with a self-anchored cable system in which all of the cables are anchored to the pylon and the girder. Thus, a self-anchored cable system experiences compression throughout the girders. In contrast, the partially earth-anchored cable system anchors some cables to the ground outside of the girders and supports the girders by allowing longitudinal movement at the pylons and the abutments or anchor piers. A partially earth-anchored cable system undergoes compression in the girders near the pylons and tension at the mid-span.