## 1 Introduction  
Fiber-reinforced polymer (FRP), with its excellent mechanical properties, is widely applied in the repair and reinforcement of bridges and various civil and industrial building projects [1, 2]. In the early days, externally bonded FRP strengthening was widely used [3]. However, in practical applications, FRP materials have poor fire resistance, and organic adhesives such as epoxy resin used for external bonding are susceptible to high temperatures, prone to aging, have poor bonding effects with the concrete interface, and are likely to cause peeling failure, resulting in high maintenance costs. To overcome the above drawbacks, scholars have used inorganic materials to replace organic adhesives [4], thus giving birth to Fiber-Reinforced Cemertitious Matrix Composite (FRCM). FRCM is a new type of reinforcement material for reinforced concrete structures, which is composed of a fiber fabric grid and a cementitious matrix. It is externally bonded to existing structural members to play roles such as flexural resistance and shear resistance, so as to improve their performance [5]. Among them, the commonly used cement-based matrix is polymer cement mortar (PCM), which is more effective in improving shear strength compared with traditional cement mortar [6]. Shear failure has brittle characteristics and occurs without obvious signs, which needs to be strongly avoided in structural design. The research on the shear behavior of RC beams strengthened with the FRP grid-PCM composite system is still in the development stage in both domestic and international academic circles, and some achievements have been made. [PERSON] et al. [7] conducted an experimental investigation and found that increasing the cross-section area of the FRP grid or reducing its spacing can increase the ultimate load of the beam, but this strengthening effect is not linearly related to the cross-section area or spacing. Then, based on the effective strain of the CFRP grid, a formula for the shear behavior capacity of the strengthened beam was proposed; subsequent research [8] further analyzed and presented a calculation formula that comprehensively considers the shear contributions of the horizontal and vertical grids. The experimental investigation by [PERSON] et al. [9] found that embedding a CFRP in the mortar can effectively improve the shear behavior capacity of the beam. But it will increase the slope of the shear diagonal cracks and fewer stirrups can be crossed by the cracks, reducing the shear contribution of the stirrups. With a sufficient mortar layer covering the grid, the failure mode of the strengthening layer can be transformed into grid fracture. [PERSON] et al. [10] conducted an experimental investigation on the shear reinforcement of reinforced concrete deep beams using FRCM of different grid types and found that the shear behavior capacities of beams strengthened with different fabric grids are different, decreasing in the order of carbon fiber, PBO fiber, and glass fiber. The peeling of the composite layer was significantly observed in the first two types of strengthened beams. The investigation by [PERSON] et al. [11] found that the stress characteristics of the horizontal and vertical CFRP grids are similar to those of longitudinal reinforcement and stirrups, respectively, and there is a synergistic effect among them. The experimental investigation by [PERSON] et al. [12] found that the FRP/ECC composite layer can effectively suppress the formation and development of diagonal cracks in concrete, and as the thickness of the FRP grid increases, both the shear behavior capacity of the strengthened beam and the strain of the FRP grid increase, while as the shear span ratio increases, both the shear behavior capacity and the grid strain decrease. The experimental investigation by [PERSON] et al.