## 1 Introduction  
Recently, composites have become popular as a new type of structural material used in civil engineering because they are light weight, strong, corrosion resistant, and have good designability in section shapes. However, there is still a lack of an effective connecting method in composite structures. In general, similar to steel joints, there are three schemes for composite structure joints [1]: (1) bolted, (2) adhesively bonded, and (3) combined (bolted and bonded) connections. Bolted and adhesively bonded connections each present unique benefits and characteristics. Bolted connections can be installed easily but induce severe stress concentrations. Adhesive bonds achieve good load distribution in composite connections, however, they remain vulnerable to the service temperature, humidity, and other environmental conditions. In combination joints, both adhesives and bolted connections are used, which can provide greater reliability and shear resistance but also increases the difficulty of construction. Unlike slip-critical connections, none of the connections mentioned above can provide with high strength, stiffness, good load distribution and construction convenience simultaneously. [PERSON] et al. [2] examined bolted connections and joints in pultruded fiber reinforced polymers and concluded that further research was necessary to improve the design of composite mechanically fastened joints. Unlike metal, the inherently brittle behavior (linear elasticity) of pultruded composite materials compromises its ability to yield and deform to redistribute loads, thus increasing the sensitivity to stress concentrations [3]. As a result, a large portion of current composite structural connections were inadequate because they were created by simply duplicating steel structural connections. [PERSON] et al. [3] introduced four typologies of connections for composite structures and selected a slip-critical connection to conduct shear tests. This connection has a somewhat complicated layout, with two steel connecting plates, double pultruded fiber reinforced plastic (PFRP) cover plates, and double steel cover plates. They found that the slip factor for this type of connection can surpass 0.37. To date, no type of effective slip-critical connection for composite structures has been proposed. [PERSON] et al. [4] proved that the slip factor for slip-critical connections with all composite components is relatively low, ranging from 0.14 to 0.27, which fails to meet the application standard in civil engineering. Additionally, simple bolted assemblies for PFRP plates would lose more than 40% of the bearing capacity during their service life-time. To address these issues, [PERSON] et al. [5] added stainless-steel cover plates with a girth-blasting treatment to (glass fiber reinforced plastic) GFRP-GFRP slip-critical connections and concluded that the slip factor for this type of connection can reach 0.4, and 86% of its strength would remain after one year under the bolt pre-tension. [PERSON] et al. [6] also examined the influence of different surface treatments in combination with austenitic stainless-steel bolting assemblies in slip-critical connections. The results demonstrated that the influence of surface treatments on the slip-resistant behavior of preloaded bolted connections with all steel elements is significant. However, little research has been dedicated to induced girth-blasting treatments for composite plates within a slip-critical connection or to the influence of cover plates. [PERSON] et al. [3] found that applying the tightening procedure to assemblies including PFRP plates with the torque method recommended by EN1090-2 (which is for steel structural connections) led to a similar accuracy. However, insufficient data are available regarding the influence of various prevailing torques on the slip factor.