SPbGASU scientists are working on increasing the endurance of bridges

At the SPbGASU Department of Roads, Bridges and Tunnels, research in the field of reliability of structures, determination of their resource and endurance, analysis of dynamic characteristics is historically strong. Assistant Professor of the department Nikolai Kozak, under the guidance of Professor Vladimir Bystrov, is engaged in calculations on the endurance of the nodes of the union of steel-reinforced concrete spans. We asked the young scientist to talk about his research.

– The objects in my research are the nodes for joining steel-reinforced concrete spans. These are anchors that combine a steel beam and a reinforced concrete slab into a single structure. Inspections of existing steel-reinforced concrete bridges showed that sagging of spans is observed at many objects, usually caused by the loss of their rigidity. The reason for this is often insufficient endurance of the combination elements, which is explained by inaccuracies in the calculations.

– What is meant by the term "endurance"?

– This is the ability of an element to withstand fatigue, that is, destruction under the impact of cyclic loads, which is essential for bridges, where traffic loads are dynamic both in size and position. As the analysis of existing calculation practices has shown, according to domestic bridge standards, the endurance of the unification elements is not taken into account at all, and the simplified assessment model with empirical endurance thresholds used abroad raises questions at the level of theoretical justification. Actually, the purpose of my research is to develop a methodology for determining the fatigue strength of the union elements, the use of which in practice will allow avoiding premature fatigue failures.

– Have such studies been conducted at the university before?

– Research in this area at our department has been carried out since the 1980s. Professor Natalia Novozhilova, Dr. of Engineering, at that time the head of the department, dealt with the issues of metal fatigue in bridge structures and Vladimir Bystrov investigated the reliability of structures. My work is based on this research. The latest published studies of the St. Petersburg University of Railways, Moscow Automobile and Road Institute, the Central Research Institute of Architecture and Construction, Tomsk University of Architecture and Civil Engineering, as well as foreign publishers often touched on related areas; some of the hypotheses were used in my models. The analysis of foreign studies was particularly difficult: our engineering methods for assessing endurance were too far apart, we had to deeply study the theoretical justifications of the proposed methods.

– What have you and your colleagues established during the work? What are your main findings?

– We experienced the greatest scientific surprise when we carried out mathematical modeling of the shear forces at the nodes of the bridge under construction from arbitrary vehicles and then compared the results of calculating the endurance of stops using four methods: domestic, ones used in the European Union, the U.S. and Ukraine. The latter technique is particularly interesting precisely by the synthesis of domestic and European methods.

According to the results of the calculation, it turned out that according to domestic standards, the calculated values are 60% of the limiting normalized values of the controlled quantities, and by all the other standards considered they reach 115-150%!

We found ourselves at a paradigm crossroads and decided to conduct an experiment. It is needed to determine which method is nevertheless closer to the actual state. Further, work began on the preparation of the experiment: it was necessary to find strain-gauge equipment, make components for it, develop a method of protecting the strain gages glued to the stops and then concreted from external influences... To date, we have coped with this task, the equipment is on the bridge and waiting for the concrete slab.
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– Where, when and how will the experiment be conducted?

– The experiment will be carried out on the reconstructed bridge over the Vuoksa river in the Vyborg district of the Leningrad region, located on the federal highway A-181 Scandinavia at the entrance to the multi-sided Svetogorsk automobile checkpoint, not far away from the border with Finland and the city of Svetogorsk. The experiment will involve a mobile complex for dynamic monitoring of voltages; at the moment, the issue of a specific model is still being resolved. I pasted primary elements on the structure, i.e., strain gauges, to which the transducers will then be connected.

– Who do you work with, who helps you in your work?

– On the topic of my research, I work with the widest circle of colleagues. Of course, first of all, this is my scientific advisor, Professor Vladimir A. Bystrov, who corrects the path of my research and helps in global issues. I often seek advice from other senior staff members of our department, and not only. After an internship at the University of Sofia (Bulgaria) under the Erasmus + program in the spring, I established contacts with Bulgarian researchers and now we regularly correspond and share our ideas.

✔ Well, in solving particular research problems, you have to organize true teamwork! Nikolay Dalyaev, a senior lecturer of our department, helped me a lot in organizing an experiment in-situ, and it is impossible to imagine launching a monitoring system without a senior lecturer Dmitry Yaroshutin. We have very close topics of dissertation research with Dmitry and now we have a good symbiosis. This is exactly the advantage of a unified scientific school.

When carrying out mathematical modeling, I also turn to employees of other departments for advice: for example, we are building in Abaqus a finite element model of a node together with Nina Puchkova, an assistant professor at the Department of Reinforced Concrete Structures, whom I have known since my student days. On some issues, it is helpful to talk to postgraduate students who have a very fresh perspective on many issues. In terms of questions, I turn for advice to my colleagues outside the university to solve my problems, it is necessary to process large amounts of data, and here we can do nothing without programmers.

– Please share with us your future plans.

– So far, the main plans are related to this topic but I do not let my mind be away from other interests: perhaps, in the future, they will be of paramount importance. Rather slowly, with the students, we develop the topic of assessing and regulating the aesthetic qualities of bridge structures: as the recent IABSE symposium in Poland showed, this topic is quite important and widely discussed abroad. I do not put down the topic of information modeling of structures, albeit in smaller volumes than during my student days. But in general, of course, first of all, the dissertation task of determining endurance is now essential: it is necessary to focus on a narrow range of tasks.

Text: Tatyana Petrova

✔ Learn more about the Department of Motor Roads, Bridges, and Tunnels, its teachers and research projects