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<article article-type="research-article" dtd-version="1.3" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xml:lang="ru"><front><journal-meta><journal-id journal-id-type="publisher-id">mgssuvest</journal-id><journal-title-group><journal-title xml:lang="ru">Вестник МГСУ</journal-title><trans-title-group xml:lang="en"><trans-title>Vestnik MGSU</trans-title></trans-title-group></journal-title-group><issn pub-type="ppub">1997-0935</issn><issn pub-type="epub">2304-6600</issn><publisher><publisher-name>Moscow State University of Civil Engineering (National Research University) (MGSU)</publisher-name></publisher></journal-meta><article-meta><article-id pub-id-type="doi">10.22227/1997-0935.2025.12.1839-1852</article-id><article-id custom-type="elpub" pub-id-type="custom">mgssuvest-808</article-id><article-categories><subj-group subj-group-type="heading"><subject>Research Article</subject></subj-group><subj-group subj-group-type="section-heading" xml:lang="ru"><subject>Проектирование и конструирование строительных систем. Строительная механика. Основания и фундаменты, подземные сооружения</subject></subj-group><subj-group subj-group-type="section-heading" xml:lang="en"><subject>Construction system design and layout planning. Construction mechanics. Bases and foundations, underground structures</subject></subj-group></article-categories><title-group><article-title>Изгибно-крутильная и плоская формы потери устойчивости двутаврового стержня с переменной высотой стенки</article-title><trans-title-group xml:lang="en"><trans-title>Bending-torsional and flat forms of instability of an I-beam with variable wall height</trans-title></trans-title-group></title-group><contrib-group><contrib contrib-type="author" corresp="yes"><name-alternatives><name name-style="eastern" xml:lang="ru"><surname>Ильюшенков</surname><given-names>А. О.</given-names></name><name name-style="western" xml:lang="en"><surname>Ilyushenkov</surname><given-names>A. O.</given-names></name></name-alternatives><bio xml:lang="ru"><p>Александр Олегович Ильюшенков — инженер промышленного и гражданского строительства</p><p>680000, г. Хабаровск, ул. Уссурийский бульвар, д. 2</p></bio><bio xml:lang="en"><p>Alexander O. Ilyushenkov — civil and industrial engineer</p><p>2 Ussuriysky Boulevard, Khabarovsk, 680000</p></bio><email xlink:type="simple">revivaltree@gmail.com</email><xref ref-type="aff" rid="aff-1"/></contrib></contrib-group><aff-alternatives id="aff-1"><aff xml:lang="ru"><institution>Территориальный проектный институт «Хабаровскпромпроект»</institution><country>Россия</country></aff><aff xml:lang="en"><institution>Territorial Design Institute “Khabarovskpromproekt”</institution><country>Russian Federation</country></aff></aff-alternatives><pub-date pub-type="collection"><year>2025</year></pub-date><pub-date pub-type="epub"><day>30</day><month>12</month><year>2025</year></pub-date><volume>20</volume><issue>12</issue><fpage>1839</fpage><lpage>1852</lpage><permissions><copyright-statement>Copyright &amp;#x00A9; Ильюшенков А.О., 2025</copyright-statement><copyright-year>2025</copyright-year><copyright-holder xml:lang="ru">Ильюшенков А.О.</copyright-holder><copyright-holder xml:lang="en">Ilyushenkov A.O.</copyright-holder><license xml:lang="ru" license-type="creative-commons-attribution" xlink:href="https://creativecommons.org/licenses/by/4.0/" xlink:type="simple"><license-p>Данная работа распространяется под лицензией Creative Commons Attribution 4.0.</license-p></license><license xml:lang="en" license-type="creative-commons-attribution" xlink:href="https://creativecommons.org/licenses/by/4.0/" xlink:type="simple"><license-p>This work is licensed under a Creative Commons Attribution 4.0 License.</license-p></license></permissions><self-uri xlink:href="https://www.vestnikmgsu.ru/jour/article/view/808">https://www.vestnikmgsu.ru/jour/article/view/808</self-uri><abstract><sec><title>Введение</title><p>Введение. Цель исследования — изучение задачи изгибно-крутильной и плоской формы потери устойчивости тонкостенного элемента открытого сечения. Приводится уточнение технической теории В.З. Власова для тонкостенных стержней. Полученные уточненные дифференциальные уравнения описывают условия устойчивости двутаврового стержня с переменной высотой стенки. Представлены замкнутые решения на основе уточняющих дифференциальных уравнений с помощью аналитического метода Бубнова – Галёркина. В статье приводятся сравнительные графики, позволяющие оценить различия между аналитическими решениями и конечно-элементным анализом.</p></sec><sec><title>Материалы и методы</title><p>Материалы и методы. Использована техническая теория В.З. Власова и метод Бубнова – Галёркина.</p></sec><sec><title>Результаты</title><p>Результаты. На основе сделанных уточнений получено замкнутое решение задачи упругой потери устойчивости стержня с линейно изменяющейся высотой стенки. Предложен аналитический метод расчета изгибно-крутильной и плоской формы потери устойчивости тонкостенного элемента открытого сечения.</p></sec><sec><title>Выводы</title><p>Выводы. Продемонстрированная теоретическая работа показывает, что решение задачи плоской формы и изгибно-крутильной потери устойчивости балки-колонны с линейно изменяющейся высотой стенки открытого сечения может быть достигнуто путем уточнения дифференциальных уравнений и представлено в замкнутой форме, аналогичной для балок-колонн постоянного сечения, но с дополнительными поправками в виде формульных коэффициентов.</p></sec></abstract><trans-abstract xml:lang="en"><sec><title>Introduction</title><p>Introduction. The aim of the study is to investigate the problem of bending-torsion and flat-form loss of stability of a thin-walled open-section element. A refinement of V.Z. Vlasov’s technical theory for thin-walled rods is presented. The refined differential equations obtained describe the stability conditions of an I-beam with variable wall height. Closed solutions based on refined differential equations are presented using the Bubnov–Galerkin analytical method. The paper provides comparative graphs that allow the differences between analytical solutions and finite element analysis to be assessed.</p></sec><sec><title>Materials and methods</title><p>Materials and methods. The technical theory of V.Z. Vlasov and the Bubnov–Galerkin method were used.</p></sec><sec><title>Results</title><p>Results. Based on the clarifications made, a closed-form solution was obtained for the problem of elastic buckling of a rod with a linearly varying wall height. An analytical method was proposed for calculating the bending-torsional and flat forms of buckling of a thin-walled open-section element.</p></sec><sec><title>Conclusions</title><p>Conclusions. The theoretical work presented demonstrates that the solution to the problem of the plane shape and bending-torsional instability of a beam-column with a linearly varying wall height of an open section can be achieved by refining the differential equations and presented in a closed form similar to that for beams-columns of constant section, but with additional corrections in the form of formula coefficients.</p></sec></trans-abstract><kwd-group xml:lang="ru"><kwd>плоская форма потери устойчивости</kwd><kwd>изгибно-крутильная потеря устойчивости</kwd><kwd>упругая потеря устойчивости</kwd><kwd>коэффициент градиента момента</kwd><kwd>редукция</kwd><kwd>переменное сечение</kwd><kwd>стальные балки</kwd><kwd>стальные колонны</kwd><kwd>тонкостенные стержни</kwd><kwd>теория секториальных характеристик</kwd><kwd>дифференциальные уравнения</kwd><kwd>упругий критический изгибающий момент</kwd></kwd-group><kwd-group xml:lang="en"><kwd>flat form of instability</kwd><kwd>bending-torsional instability</kwd><kwd>elastic instability</kwd><kwd>moment gradient coefficient</kwd><kwd>reduction</kwd><kwd>variable cross-section</kwd><kwd>steel beams</kwd><kwd>steel columns</kwd><kwd>thin-walled rods</kwd><kwd>theory of sectorial characteristics</kwd><kwd>differential equations</kwd><kwd>elastic critical bending moment</kwd></kwd-group></article-meta></front><back><ref-list><title>References</title><ref id="cit1"><label>1</label><citation-alternatives><mixed-citation xml:lang="ru">Cywinski Z. 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