The article presents the developed rationalization technique of composite steel reinforced concrete sections with steel open section beams based on the criterion of equal strength of the section elements that are extremely distant from the neutral line. Algorithms for search for geometric parameters of a composite section limited to a certain range of values are implemented to achieve the equal strength condition. The dimensions of the individual elements which are parts of the cross-section are obtained from the condition of the constant ratio of the distances from the neutral axis to the extreme concrete and steel fibers. The numerical methods were used for calculation of continuous three-span composite reinforce concrete bridge. The technique implements the steps of bridge construction, taking into account the contact yield of the composite section, the redistribution of forces between the elements, and the effect of elastic-plastic and rheological properties of materials. The generalized kinetic curve was utilized for evaluation of concrete creep together with the phenomenological equations for the development of deformations based on a colloid-chemical representation of the mechanism for long-term concrete deformation. The proposed methodology is implemented in the LIRA-SAPR software package based on the Building Information Model Technology (BIM) and the Finite Element Method (FEM).

Abstract. The development of transport infrastructure, reconstruction of roads and railways, together with growing urban traffic necessitate the construction of new bridges and/or the reconstruction of existing ones. The primary objective of design is obtaining a reasonable system in compliance with the requirements for stress-strain state: equal strength or equal torque, maximum rigidity or minimum weight of the structure. In the paper, the object of optimization is the design of a three-span girder bridge of a specified length under the constant load. The sets of both statically determinate and statically indeterminate systems are considered, namely: three-span hinged girders in which the hinge joints are located in the end spans or middle span, and three-span continuous girders on unilateral supports or on resilient supports. Two variable design parameters are taken into account: the length of each end span z1 and the position of the hinges x for the statically determinate systems, and the displacement of support assemblies joints Δ or the value that affects the displacement, i.e. flexibility of yielding supports c for the statically indeterminate ones. The authors proved that there are optimal solutions in the set of statically indeterminate systems both with unilateral and with elastic constraints.

дослідження комбінованих рівноміцнісних перерізів, що базуються на властивостях приведених перерізів, складових матеріалів і результатах експериментальних даних різних авторів. Результати. На підставі сортаменту стальних двотаврів був виконаний розрахунок і підбір комбінованого двотаврового перерізу, у якого верхня полиця замінена на тонкостінне стальне «корито», заповнене бетоном, і його порівняння з двотавровим перерізом, посиленого бетонною плитою. Щоб досягти умову рівноміцності, підбираються висота і ширина бетонної плити. Показано, що найбільш вигідне з точки зору вартості є тавровий стальний переріз з верхньою полицею у вигляді тонкостінного стального «корита» з бетонною плитою. Наукова новизна. У результаті виконаних розрахунків, на підставі умови рівноміцності, вибрані оптимальні вид і розміри сталебетонного перерізу, що забезпечують найменшу вартість. Практична значимість. У наш час сталезалізобетонні конструкції все частіше використовуються у будівництві. Це пов'язано з тим, що вони мають меншу у порівнянні з залізобетоном власну вагу, в також їх сталева частина може виступати у якості незнімної опалубки. Удосконалення таких конструкцій призводить до підвищення міцнісних характеристик і зниженню вартості.

The development of modern construction is closely related to the efficient use problemof building materials in terms of rational use materials’ strength properties. The search of rationalstructure in terms of geometric parameters, the materials use and providing the same bearingcapacity is important question in the modern building. The purpose of article is to carry out acomparative analysis of the geometric and strength characteristics of different reinforced concretecross-sections, and consideration of existing methods for calculating the bearing capacity andassessment of the stress-strain state of reinforced concrete beams.The steel-concrete structures using in different building structures is paid much attention in theworld practice. The steel-concrete structures widespread using leads to the economy of materials,reducing the complexity of manufacture, reducing time erection. The using of reinforced concreteleads to significant economy of steel, and set the new tasks for the engineers in the same time: ownweight and geometric parameters reducing of the cross-section without reducing of bearing capacityin whole. With the search for new structures that would meet the building requirements and usage ofdifferent building, nowadays significant attention pays to the improvement and development of thesteel-concrete elements. During the development and improvement of steel-concrete structures,significant changes have been made in terms of ensuring the joint operation of reinforced concreteand steel. Such structures require constant research and improvement in order to reduce their ownweight, financial costs, etc. The question of finding a rational structure in terms of geometricparameters, the materials using, as well as ensuring the same bearing capacity is currently important