# Investigation of Load Environment and Bending Load Capacities of Aged Prestressed Concrete Sleepers
## 1 Introduction  
Sleepers are important track components that support rails, maintain the distance between the left and right rails, and distribute the load transmitted from the rails to the ballast. Prestressed concrete (PC) sleepers, the subject of this study, were installed for the first time in European countries, such as England and Germany, in the latter half of the 1940s. PC sleepers are widely used worldwide and are an indispensable track component for comfortable, safe, and stable high-speed railway transportation [1]. Japan's PC sleepers were first installed on a trial basis in 1951. Since then, over 40 million sleepers have been built by Japanese National Railways and the Japan Railway Group alone (excluding private railway companies).  
PC sleepers are generally expected to last approximately 50 years [1], but in recent years, a large number of PC sleepers have exceeded this life span. Therefore, various studies have been conducted on the evaluation of the service lives and remaining lives of aged PC sleepers [2]. The static and impact loads acting on PC sleepers should be considered in evaluating their service lives and remaining lives. Various studies have been vigorously performed worldwide on related topics, such as the examination of design methods [3; 4; 5] and the evaluation of impact loads [6; 7; 8; 9]. In addition, studies have been conducted on the damage to PC sleepers [10], their fatigue lives considering abrasion [11], fatigue lifeevaluation methods based on wheel loads acting on PC sleepers [12], and fatigue life based on the bending moments generated in PC sleepers [13]. The support conditions of PC sleepers, which considerably affect the bending moments generated in PC sleepers, have likewise been studied [14; 15; 16]. Altogether, valuable information has been obtained for evaluating the service lives of PC sleepers.  
In summary, researchers worldwide are exploring PC sleepers using various approaches. However, except for a few examples [2], researchers have not evaluated the load-bearing capacities of aged PC sleepers installed on commercial lines. Therefore, in the current study, we investigate the load environment of aged PC sleepers installed on commercial lines and evaluate their bending load capacities. Although the target PC sleepers in this study are limited to those in Japan, the actual load-bearing capacities of PC sleepers that have been used for nearly 50 years are evaluated. These results will be valuable for the literature on PC sleepers. In addition, the load environment evaluated in this study targets the straight section. Naturally, it is thought that the load environment will be different in curved sections and turnout sections, but we would like to address these issues in the future.  
In Japan, maintenance vehicles run every day before the first Shinkansen trains run, and detailed track inspections are conducted. However, the soundness assessments of PC sleepers remain based on visual inspections, and this evaluation method is not necessarily linked to the load-bearing performances of the PC sleepers [17]. Contrary to the large number of installed PC sleepers, the number of sleepers that can be replaced in one night's work is limited. Thus, if existing PC sleepers fail to meet their load-bearing capacities at a certain time, replacement work may fail to resolve the issue, and safety will be affected. To avoid this situation, Japan plans to set a quantitative service life and conduct systematic maintenance.  
In this study, we address the following objectives to establish a new maintenance management system for PC sleepers:  
1. To investigate the actual load environment of PC sleepers installed on commercial lines by measuring their bending moments.
2. To verify the effects of various parameters on the bending moments of PC sleepers via numerical analyses.
3. To collect a wide range of aged PC sleepers on commercial lines and evaluate their bending load capacities by conducting bending tests specified by the Japanese Industrial Standard (JIS) E 1201 [18].