A Layer-Based CAD-to-FEM Workflow for Seismic Assessment of Existing Reinforced Concrete Bridges

The numerical modelling of existing reinforced concrete (RC) bridges represents one of the most time-consuming and operator-dependent phases of seismic vulnerability assessment. Although advanced nonlinear analysis procedures are widely available, the generation of finite element (FE) models is still commonly performed through manual operations, limiting modelling efficiency, repeatability, and interoperability between design and analysis environments. This paper presents a layer-based CAD-to-FEM workflow for the structured generation of simplified FE models of existing RC bridges. The proposed methodology uses a standardized layer-based CAD organization and direct DXF interoperability with MIDAS Civil to transfer a centroidal representation of the bridge into a simplified beam-based finite element model. The centroidal axes of the bridge components are extracted from the original engineering drawings and classified into dedicated structural layers, providing a structured basis for subsequent FE model generation. The proposed workflow is designed to reduce manual preprocessing operations and improve modelling consistency by organizing the structural geometry through standardized CAD layers, thereby facilitating the generation of analysis-ready models for seismic assessment. The workflow is integrated with a Multi-Modal Pushover Analysis (MPA) procedure to evaluate the seismic vulnerability of bridges characterized by multiple significant vibration modes. A case study involving an existing Italian RC bridge demonstrates the feasibility of using the proposed simplified modelling strategy within a multi-modal nonlinear seismic assessment, including the evaluation of both ductile and brittle collapse mechanisms through seismic risk indices. The proposed workflow provides a structured framework for integrating conventional engineering drawings with nonlinear seismic assessment procedures.