## 1 Introduction  
With the acceleration of urbanization, the demand for the construction pace of rail transit systems is increasing rapidly. Among the various structural configurations of transportation systems, the straddle monorail, as a significant representative of medium-capacity rail transit, serves as an economically viable alternative to subways. It helps reduce infrastructure investment and operational costs while catering to the passenger transportation needs of small- and medium-sized cities, and it demonstrates broad prospects for application within urban rail transit networks [1, 2]. In a straddle monorail system, the track beam is a critical structural component that not only bears structural loads but also serves as the guiding path for vehicle operation, with its performance directly influencing the safety and operational stability of the straddle monorail system. Compared to traditional concrete beams, steel-concrete composite beams can effectively reduce structural weight, shorten construction periods, and significantly enhance seismic performance. Additionally, in contrast to pure steel beams, steel-concrete composite beams can effectively mitigate vibrations and noise during operation, thereby improving the overall ride comfort of the straddle monorail system [3, 4, 5, 6]. However, the effective application of this structural form largely depends on the design and performance of its shear connectors, particularly the use of group stud connectors, which is essential to ensure the synergy between steel beams and concrete slabs [7; 8; 9; 10]. Unlike the single stud connection, the force distribution in the group stud connectors is more complex. Due to the mechanical interaction between studs, referred to as \"group stud effect\", the shear force distribution is often uneven, which affects the overall bearing capacity and deformation performance [11; 12; 13]. In recent years, international researchers have carried out extensive research on the mechanical properties of pile group connectors, highlighting the significant influence of pile group effect on the shear capacity. [PERSON] et al. [14] employed the three-dimensional finite element model to explore the mechanical behavior of different types of stud connectors, and found that the group stud effect significantly reduced the shear capacity, especially when the studs were densely arranged. [PERSON] et al. [15] conducted a study on the load-bearing behavior of grouped studs embedded in prefabricated UHPC panels under combined loading conditions. Through push-out experiments, they developed predictive models for the shear-tension interaction strength and the shear resistance of UHPC stud connectors under such loading scenarios. Similarly, [PERSON] et al. [16] found that the group stud effect leads to serious local stress concentration under large loads, thus affecting the durability of the structure, especially under high-frequency loads. [PERSON] et al. [17] developed an improved finite element (FE) model to simulate the push-out behavior of shear stud group connectors (SSGCs). Based on this model, they conducted a parametric analysis considering factors such as concrete properties, stud diameter, and the number of studs, and proposed a theoretical formula for calculating the stiffness of SSGCs. Despite extensive theoretical analyses, numerical simulations, and experimental studies conducted by scholars on the mechanical performance of \"group stud connectors, most research has primarily focused on the mechanical behavior of uniform-distributed studs (as shown in Figure 1a) [18]. In order to realize the assembly construction of straddle monorail, cluster-distributed studs (as shown in Figure 1b) are commonly adopted to reduce on-site casting work and shorten the construction period, thereby avoiding the drawbacks of uniform-distributed studs. This arrangement not only facilitates efficient prefabrication and assembly of monorail panels but also minimizes concrete shrinkage and creep effects.