RT Journal Article T1 Nonlinear Analysis of Rotational Springs to Model Semi-Rigid Frames A1 Rodríguez González, César Antonio A1 Caparrós Mancera, Julio José A1 Hernández Torres, José Antonio A1 Rodríguez Pérez, Ángel Mariano AB This paper explains the mathematical foundations of a method for modelling semi-rigid unions. The unions are modelled using rotational rather than linear springs. A nonlinear secondorder analysis is required, which includes both the effects of the flexibility of the connections as well as the geometrical nonlinearity of the elements. The first task in the implementation of a 2D Beam element with semi-rigid unions in a nonlinear finite element method (FEM) is to define the vector of internal forces and the tangent stiffness matrix. After defining the formula for this vector and matrix in the context of a semi-rigid steel frame, an iterative adjustment of the springs is proposed. This setting allows a moment–rotation relationship for some given load parameters, dimensions, and unions. Modelling semi-rigid connections is performed using Frye and Morris’ polynomial model. The polynomial model has been used for type-4 semi-rigid joints (end plates without column stiffeners), which are typically semi-rigid with moderate structural complexity and intermediate stiffness characteristics. For each step in a non-linear analysis required to adjust the matrix of tangent stiffness, an additional adjustment of the springs with their own iterative process subsumed in the overall process is required. Loops are used in the proposed computational technique. Other types of connections, dimensions, and other parameters can be used with this method. Several examples are shown in a correlated analysis to demonstrate the efficacy of the design process for semirigid joints, and this is the work’s application content. It is demonstrated that using the mathematical method presented in this paper, semi-rigid connections may be implemented in the designs while the stiffness of the connection is verified PB MDPI SN 1099-4300 (electrónico) YR 2022 FD 2022-07 LK http://hdl.handle.net/10272/21071 UL http://hdl.handle.net/10272/21071 LA eng NO Rodríguez González, C. A. R., Caparrós-Mancera, J. J., Hernández-Torres, J. A., & Rodríguez-Pérez, Á. M. (2022). Nonlinear Analysis of Rotational Springs to Model Semi-Rigid Frames. In Entropy (Vol. 24, Issue 7, p. 953). MDPI AG. https://doi.org/10.3390/e24070953 DS Repositorio Institucional de la Universidad de Huelva RD 1 jun 2026