Results of the checking calculation of the structures of pedestrian bridge over the military descent in Odessa

Анотація

Problem. The highest pedestrian bridge in Odessa is stretched over the Military Descent between Primorsky Boulevard and M. Zhvanetsky Boulevard in Odessa. During the whole life of pedestrian bridge, the research and testing [3] of bridge structure in 1969, and inspection [6] in 2000 and 2005 were carried out. Unfortunately, not all recommendations of the work [6] have been implemented. This fact doesn’t contribute to the satisfactory operation of pedestrian bridge structure, especially near the shore anchor No. 0. The above-mentioned recommendations included: vertical planning of the slope and the area under the bridge deflection near the shore anchors; fixing a block-divided limestone-shell rock massif; fixing the retaining walls, which support the slope, in the area of inclined supports foundations and near the shore anchors No. 0 and No. 3. The technical condition of the bridge is generally classified as partially serviceable (state 4) according to standard [9]. According to inspections [3], the operating conditions of the bridge structure and the surrounding area are extremely unsatisfactory. Goal. The goal of the work is estimating the technical condition of pedestrian bridge structure over the Military Descent between Primorsky Boulevard and M. Zhvanetsky Boulevard in Odessa, to ensure the further reliable operation of the pedestrian bridge and  development of the project of high-priority measures for bridge major overhaul. Methodology. On the basis of provided materials, a three-dimensional computer model of pedestrian bridge was developed. Computer model calculations were performed using the LIRA software package. The design scheme of the bridge is adopted in the form of a spatial system consisting of shell elements that simulate the behavior of steel sheet structures, as well as bar elements that simulate the behavior of struts on shore anchors, anchor bars and auxiliary elements in modeling the hinged support of inclined racks. Results. Analysis of the results of steel structures calculation showed that: the maximum load on foundation pier 1a from the design load combination (DLC) No. 6 is 289.1 t;  the first and third oscillation modes are translational vertical oscillations, the second oscillation mode is horizontal oscillations; the maximum vertical deflection in the central span from DLC No. 16 is 193 mm, which exceeds the limit deflection of 130 mm; the vertical deflection in the end spans doesn’t exceed the limit value, which is 105 mm; the maximum horizontal deformation on the shore anchor No. 0 is 51.8 mm, and on the anchor No. 3 it is 23.6 mm; the natural oscillation periods of  unloaded bridge are: for the 1^st  mode (vertical) – 0.892 s, for the 2^nd mode (horizontal) – 0.576 s. They don’t fall into the forbidden range [10] – from 0.45 to 0.60 s in vertical plane and from 0.9 to 1.2 s in horizontal plane; the main stresses in the steel bridge structures from DLC No. 2, 3, 4, 6, 7, 9, 10, 12, 13, 15, 16, 28, 31 exceed the yield strength of steel. At the same time, the places of stress concentration and their distribution pattern are identical for all DLC, except DLC No. 3, where an excess of the yield strength of steel occurs in the lower zones of inclined racks and in the support tables of cantilever beams; stress concentrators in computational model, to some extent, can be caused by peculiarities of mathematical algorithm of  finite element method, and assumptions that were adopted in computational model. Practical value. Making final decisions about strengthening the bridge structural elements in places of stress concentration, it is necessary to perform a duplicate calculation in another software package; if the result is confirmed, it is necessary to strengthen the bridge elements according to the specially developed project and consider reducing the load (mobile and pedestrian); to reduce the temperature load on the steel bridge structures, it is urgent to overhaul the moving rollers of shore anchors No. 0 and No. 3 in accordance with the project [4]; engineering and geodetic observations should be continued for vertical displacements of bridge elements and horizontal displacements of pedestrian part of the bridge.