## 1 Introduction  
A partially earth-anchored cable system was developed by [PERSON] to reduce peak compressive forces in the girders of cable-stayed bridges [1]. In this type of bridge, tensile forces are developed in the main span, while the peak compressive forces in the girders near the pylons are decreased [1]. Reducing the peak compressive forces in the girders facilitates construction of cable-stayed bridges with ultra-long main spans of over 1000 m [2; 3; 4]. However, in this bridge type, a special erection method for the central parts of the girders in the main span is needed since a considerable tensile force at mid-span is required [5].  
It should be noted that the partially earth-anchored cable system can also be applied to cable-stayed bridges with long main span lengths of between 600 m and 1000 m constructed by the free cantilever construction method (FCM). The FCM is a preferred construction method in cable-stayed bridges where the deck is cantilevered from each pylon towards the center of the main span. In the FCM, construction is completed by connecting both ends of the deck in a cantilever state. The connection is made by installing and closing the final segment, which is called a key segment. Closure of the key segment is performed carefully since sufficient space should be provided for 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.