###### Abstract  
The modular structure has a discontinuity owing to the joint between the modules; thus, structural behavior verification is required. In this study, the tensile behavior of a steel reinforcement at the discontinuity interface was evaluated in the joint of a modular flexural member. The modular specimen was fabricated with a 400 mm joint, and an integral specimen was fabricated with the same specifications as the modular specimen, without a joint. The largest crack width of the integral specimen was measured at the center of the beam, and that of the modular specimen was measured at the discontinuity interface. The maximum crack width of the modular specimen was greater than that of the integral specimen. The strain of the steel reinforcement was estimated using the measured crack width and six formulas for evaluating the crack width. The estimated strain of the modular specimen was higher than that of the integral specimen, and the deformation of the steel reinforcement at the discontinuity interface was accelerated with the increasing load. Therefore, the tensile load was concentrated at the discontinuity interface in the modular specimen, and the steel reinforcement at the discontinuity interface was likely to yield earlier than the integral specimen.  
prefabricated structure; joint discontinuity; tensile reinforcement; strain estimation; crack width +
Footnote †: journal: Applied Physics Letters  
15 October 2019201915 November 20191  
[PERSON] et al. [15], [PERSON] et al. [16], [PERSON] et al. [17], and [PERSON] et al. [18] verified the structural performance according to the shape of the joint and conducted analytical studies. [PERSON] et al. [19] and [PERSON] et al. [20] proposed a new connection method. However, the experiments in these studies were performed to verify the structural performance according to the joint shape and connection method between precast modules and involved various variables and site conditions; thus, there were limitations for the general prediction of the joint behavior.  
POSCO [9] conducted design and structural performance verification studies on girder and slab-type precast modular bridges. On the basis of their results, various studies were conducted. The behavior of a modular bridge was analyzed according to the cyclic load, and a joint design procedure was proposed [12]. Lap splices were redesigned from ultimate strength design to limit state design in order to improve the stability and moment strength of the joint [21]. The difference in the crack progress was reported, and the characteristics of the joint in the modular member on the cyclic load were analyzed in terms of the moment of inertia [22]. Additionally, a calculation method for the deflection of the modular member considering the strength of the precast module and the joint was proposed [23], and the mean steel reinforcement strain of the modular member was evaluated using the compressive strength of the concrete and the ratio of reinforcement [24]. However, these studies compared the load and deflection of the modular member with those of the integral member and evaluated the performance without analyzing the joint behavior. Thus, the theoretical approach to characterizing the joint behavior was insufficient. Hence, the objective of the present study was to evaluate the behavior of modular members quantitatively through estimation of the steel reinforcement tensile strain using crack width [25].