This conference paper was submitted for presentation at the NAFEMS World Congress 2025, held in Salzburg, Austria from May 19–22, 2025.

Abstract

This study addresses the structural analysis of the wagon gate of one Petrobras dam, which is a critical structure for water intake by the upstream refinery. Built in 1967, the dam and its accessory structures have undergone corrective maintenance over the years. Following the accidents in Mariana and Brumadinho, the National Water Agency (ANA) revised inspection procedures, classifying this dam as low immediate risk but with high potential for associated damage in case of failure. The main objective of this study is to evaluate the current structural conditions of the wagon gate, which ensures the tightness of the pipeline by blocking about 22 meters of water column. The methodology used is based on elastoplastic stress analysis according to the API 579-1/ASME FFS-1 (2016) code, with the construction of an "as-built" model of the structure and thickness measurements. The structural analysis was performed using the Finite Element Method (FEM), which allows a detailed assessment of stresses and deformations in the structure. The model was built based on drawings provided by the refinery and thickness measurements taken on the plates and beams that make up the gate. The mechanical properties of the material were obtained from the ASME II Part D code, and the stress analysis followed the API 579-1 methodology. The results indicate that the wagon gate, despite the natural deterioration process, does not present an immediate risk of structural failure. The numerical analysis considered hydrostatic pressure loads and the structure's own weight. Boundary conditions were defined to prevent rigid body movements, and soil stiffness was modeled based on the Vertical Reaction Module. The API 579-1 methodology allows the extrapolation of design codes, which was essential for the evaluation of the wagon gate, since the ABNT NBR 8883 standard, used as a design reference, was canceled in 2019. Elastoplastic stress analysis requires the multiplication of load combinations by load factors, as described in table 2D.4 of API 579-11. The safety coefficient was obtained from NBR 8883 and applied in the evaluation of the risk of plastic collapse failure. In addition to the analysis with the safety coefficient, additional simulations were performed to verify the actual state of stresses and deformations in the structure, considering different thickness conditions in the gate components1. The thicknesses were measured by refinery on 29/5/2020, and additional hypotheses were considered for regions without direct measurements. This study was essential to ensure the safety of workers during the maintenance of downstream components of the gate and to ensure the structural integrity of the dam. The detailed analysis of the current structural conditions of the wagon gate provides essential information for decision-making on future maintenance and risk mitigation measures.