## 1 Introduction  
Bolted top-seat angle connections without (TSAC) or with web angles (TSACW) have been extensively used in steel and composite structures, because of their relatively high moment capacity and easy construction. These types of connections are mainly designed to resist gravity loads of determinate steel beams. A schematic layout is proposed in Figure 1. Based on the AISC standard [1], a given TSACW is classified as a semi-grid beam-to-column connection, in which the moment-rotation (\(M\)-\(\theta\)) behavior needs to be considered in the overall force distribution and structural analysis. Accordingly, there are no doubts on the necessity to accurately predict the (\(M\)-\(\theta\)) behavior of TSACW joints. The (\(M\)-\(\theta\)) behavioral trends of steel connections represent essential features of their response, and in particular with regard to the initial stiffness \(S_{j,ini}\), maximum moment capacity \(M_{n}\), and maximum rotation \(\theta_{n}\). Once these features are correctly estimated, a reliable simulation of the actual behavior toward the optimum design of structures would be possible. The behavior of TSACs and TSACWs has been investigated and equivalent equations have been proposed to simulate their mechanical behavior for applicationsto steel frames [2; 3; 4; 5; 6]. In parallel to TSACWs, a similar solution has a key role also for \"modular buildings\", namely, off-site prefabricated building modules in which the primary structure consists of steel frames, whose construction has become increasingly popular due to the advantages, including reduced resource wastage and improved quality [7; 8; 9; 10]. The typical connection takes the form of a bolted connection with a plug-in device or a bolted connection with a rocket-shaped tenon. Being classified as \"bolted\", these connections have the advantages of reduced site work and demountability. In both the cases, the mechanical properties of connections have a great influence on the strength and stability of the structural system to which they belong. An unrealistic design of connections may negatively affect the serviceability of the structure as a whole, due to the occurrence of large deflections. Deformations in connection components as a result of local buckling phenomena is also a common reason for the failure of these connections. The key role of connections for modular buildings has been recognized to affect the overall structural performance of modular systems. Despite this importance, the design of reliable connections is still identified as a major challenge, and prevalent knowledge of their structural performance is still limited [11; 12]. In this paper, an original study is presented for TSACWs. An artificial neural network (ANN) model able to capture the underlying mechanism and to accurately estimate both the initial stiffness \(S_{j,ini}\) and the ultimate moment capacity \(M_{n}\) for TSACWs is proposed. To this aim, two reference calculation approaches are taken into account from the literature, and investigated in detail, namely, (i) the mechanical component-based model approach  
Figure 1: Reference configurations for (**a**) top-seat angle connections without (TSAC) or (**b**) with web angles (TSACW). proposed by Eurocode 3 (\"EC3\" [13]) and (ii) the analytical formulation proposed by [PERSON] and [PERSON] in [14] (\"KK\"). Since the \(S_{j,ini}\) and \(M_{n}\) features for a given TSACW are the most influential parameters that affect the overall mechanical characterization of a given bolted beam-to-column connection, these two selected properties are preliminarily calculated based on the selected \"EC3\" and \"KK\" formulations, and compared against each other, with the support of experimental data from the literature (77 specimens in total). Successively, a comprehensive ANN approach, combined with a metaheuristic artificial bee colony (ABC) algorithm, is developed in this paper to extract an informational model for TSACWs.