###### Abstract  
The rotational stiffness of the pocket-type connection used in system scaffolding to join horizontal members and vertical members was evaluated. To investigate the rotational stiffness of connections when subjected to bending moments in the downward, upward, and lateral rotation directions, load tests were performed on 30 specimens with cantilever specimens for each rotational direction. Results showed that failure shapes of pocket-type connections were different depending on the rotation direction. Owing to the differences in the failure phenomena, the maximum moment capacity of the upwardly rotated specimens was the largest, followed by that of the downwardly rotated specimens and the laterally rotated specimens in that order. Compared to the Eurocode 3 connection classification, the pocket-type connections correspond to semi-rigid connections when the rotation direction is downward or upward, and they can be considered nominal pin connections when the rotation direction is lateral. From the moment-rotation curves, it was concluded that the rotational stiffness of the pocket-type connections could be estimated as a bilinear model. rotational stiffness; pocket-type connection; system scaffolding; rotational direction; bilinear model +
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demonstrated that the estimated strength of the scaffolding varies with the consideration of the rotational stiffness of connections [10; 11]. Notably, the assumption of connections as hinges allow for conservative designs of scaffolding structures in terms of safety; however, it is difficult to estimate the accurate structural behavior of scaffoldings. The connections of system scaffoldings could distribute the moment of vertical members to horizontal members; therefore, considering the rotational stiffness of the connections is important to predict the structural behavior of scaffoldings accurately. As such, accurately evaluating the rotational stiffness of connections is essential for ensuring the quantitative safety of scaffolding structures. Researchers are continually conducting studies to evaluate the performance and stiffness of connections in temporary structures such as system scaffolding. Based on reviews of studies on scaffolding connections, researchers have presented models of the rotational stiffness of scaffolding connections with a variety of forms according to experiments and analysis. [PERSON] et al. [12] analyzed the rotational stiffness of right-angle clamps used in coupler scaffolding, considering the bolt tightening torque, product condition (new or old), various clamp combinations, and load direction. [PERSON] and [PERSON] [13] performed experiments on cuplock-type connections, considering the composition of the connections, and they presented a connection rotational stiffness for modeling system scaffolding. In addition, studies have been performed on wedge-type connections, which are among the forms used for system scaffolding connections, and results include the development of connection rotational stiffness models for the structural analysis of system scaffolding considering a variety of influencing factors such as product condition and load direction [14; 15; 16]. The results of previous studies [2; 12; 13; 14; 15; 16] have revealed that the rotational stiffness of various connection shapes can influence the structural behavior of scaffolding, and significant differences can be observed in the rotation-resisting behavior according to the shape of the connection. The scaffolding used in Korea generally features a pocket-type connection or wedge-type connection form. However, compared with wedge-type connections, limited studies have focused on the rotational stiffness of pocket-type connections. [PERSON] et al. [17] performed experiments on pocket-type connections that applied loads in the downward direction to horizontal members connected to other horizontal members, and they proposed a bilinear rotational stiffness model.