# Fatigue Behavior of Prestressed Concrete Beam for Straddle-Type Monorail Tracks
## 1 Introduction  
With the fast expansion of modern cities, different types of urban rail transit systems have been developed to address the increasing challenge of traffic congestion [1]. Monorail transportation systems have been widely used in medium and small cities as well as hilly cities [2; 3] owing to their excellent climbing ability, lower noise, and shorter construction period [4]. Monorail transportation systems can be classified into two categories: (1) straddle types, and (2) suspension types [5], according to how the monorail vehicle is operated. The track beam of a suspension type system is mainly made of steel, which is costly and requires frequent maintenance.  
As a critical component of straddle-type monorail systems [6], prestressed concrete (PC) track beams serve as the load-bearing structure and guideway subjected to repeated traffic load, influencing the safety of transportation infrastructure. Under such circumstances, the fatigue effect on mechanical behavior generally results in the degradation of stiffness and load-bearing capacity, having adverse effects in the comfort of passengers [7]. This consideration is particularly important for monorail track beams due to the large proportion of live load (more than 50%). Fatigue behavior must be considered in design to satisfy the safety and serviceability requirements [8; 9].  
During the last decade, a large amount of theoretical and experimental research has been proposed to investigate the fatigue behavior and mechanism of the PC beam in detail [10; 11; 12]. [PERSON] and [PERSON] [13] found that the fatigue life of PC beams is related to the degree of prestressing, the longitudinal reinforcement ratio, and the strength of concrete. [PERSON] et al. [14] found that cracking and deflection changed rapidly in the initial stage of fatigue, and changed stably afterwards until failure. [PERSON] [15] carried out an experimental investigation of the fatigue strength of post-tensioned concrete girders, finding that fatigue failure occurred in the vicinity of cracks. [PERSON] et al. [16] analyzed the evolution of the fatigue failure pattern of PC beams and regularities of midspan deflection and strain of concrete of PC beams. However, most of the studies focused on the fatigue behavior of partially-prestressed concrete beams [17] and beams strengthened with carbon fiber-reinforced plastics sheets [18; 19; 20; 21]. However, there is no research on fatigue behavior of fully prestressed concrete beams. The primary reason is that fully prestressed concrete beams are considered not susceptible to fatigue damage due to the applied full prestressing force. However, fully prestressed concrete beams can be turned into partially prestressed concrete beams under the effects of overloading or other extreme events. Moreover, cracks are not allowed in fully prestressed concrete beams under service loads, which is different from partially prestressed concrete beams.  
Model tests and in situ tests have been considered as effective approaches to investigate mechanical performances of structures [22; 23; 24; 25; 26; 27; 28; 29; 30]. In this study, a full-scale fatigue test of a prestressed concrete beam was carried out. Displacement, rotation, strain of concrete, and reinforcement were examined under post-fatigue static loading condition. A three-dimensional finite element model was established to understand stress distributions.