Experimental stress-strain state research of damaged railway bridge trusses

   The article presents the results of surveys and tests on a railway bridge with spans of through main trusses, with an estimated length of 66 meters, after replacing a failed element in the upper belt. The survivability of the superstructure, due to the spatial redistribution of forces between the intact elements and the excess strength of the components in relation to the applied loads, has made it possible to prevent a progressive collapse of the structure and even allow trains to continue operating on the Trans-Siberian railway for a period of time. The article experimentally investigates the factors that influence the stress-strain state of truss structures. The preliminary examination was conducted using the laser scanning technique, which resulted in the generation of a point cloud that covered all the structures of the supports and superstructure. The tests were conducted under passing loads. During the tests, the deflections of the trusses, the vertical displacement of the support parts, and the fiber stresses of certain elements of the superstructure were monitored. It was found that the superstructure had geometric deviations in the form of tilts of vertical elements up to 110 mm and misalignments of support points up to 18 mm in height. The tests revealed a complex stress-strain state of the structure and an uneven distribution of stress across the truss elements, which deviated from the traditionally assumed design assumptions. Many truss elements were working in compression with bending, with bending stresses exceeding axial stresses. While the overall deflections of both trusses were similar, the fiber stresses in the elements of extreme panels consisted of bending deformations up to 70 %, more typical of truss belts. Uneven settlement of the supporting structures under load was observed, with a difference in settlement of more than two times. Based on this observation, the article draws conclusions about the factors that may have caused the failure of the load-bearing components.

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