Structural evaluation of the steel girder deck of the bridge over the Bulubulu River, Guayas province

Abstract

Introduction: Bridges are fundamental structures for socioeconomic development worldwide, they are essential elements for roadways and Ecuador has important bridges in its road network. On the other hand, our country, being a territory with a high seismic hazard, requires for bridges not only an analysis of gravity loads, but also under lateral loads coming from seismic action. This case study will address the structural behavior of the BuluBulu bridge deck, specifically the flexural and shear analysis of the longitudinal structural steel beams, and the axial load analysis of the support and interior diaphragms. Objective: To determine the structural behavior of the longitudinal beams and diaphragms of the Bulubulu Bridge deck under gravity loads and seismic loads by means of a spectral modal analysis of a mathematical model of the structure developed in the CSI Bridge program. Methodology: Review the structural drawings of the original project, evaluate the acting loads, develop a mathematical model of the structure in the CSI BRIDGE program, perform a spectral modal analysis of the mathematical model of the structure, obtain the maximum demands on the longitudinal beams and diaphragms, verify the demand-capacity ratios (D/C) in bending and shear of the longitudinal beams, as well as the D/C ratios in compression and axial tension of the diaphragms. Results: From the maximum demands obtained from the structural analysis and the evaluation of the capacity of the elements, the following results were obtained. The steel beam "VIGA I (1.360x0.020x0.40x0.03) m" has sufficient capacity for the stresses to which it will be subjected, working at 79% for negative bending, 67% for positive bending and 25% for shear. The diaphragms satisfactorily meet the requirements and design philosophy of remaining in the elastic range in the event of an earthquake. For the end diaphragm, compression predominates in the diagonal, working at 91% of its capacity, while for the interior diaphragm, tension predominates in the horizontal, working at 49% of its capacity. Conclusion: Through structural analysis using the mathematical model developed at CSI Bridge, the maximum and most critical stresses in the longitudinal beam and diaphragm elements were determined. The longitudinal steel girders and the interior and support diaphragms satisfactorily meet the design requirements according to AASHTO LRFD 2020, and the diaphragms comply with the design philosophy of keeping these elements in the elastic range. For this study, the design of the longitudinal beams is governed by Limit State Strength I, the supporting diaphragms are governed by Extreme Event L.S. and the interior diaphragms are governed by Strength I L.S.