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The paper provides a brief overview of domestic and foreign guidelines (manuals) for the design of composite steel and concrete structures: steel-concrete slabs on profiled flooring, combined beams, and columns with rigid reinforcement. The necessity of creation of the actual manual corresponding to the modernlevel of development of construction science, normative documents and design practiceslinked to the new formulary SP 266.1325800.2016 is proved. It will facilitate the design, reduce labor expenditures and improve the reliability of composite steel and concrete structures. The new guidance provides general recommendations for the design of composite steel and concrete structures and the basic regulations for the calculations. The new guidance describes recommendations for modeling of composite steel and concrete structures and elements in the calculated complexes, the recommendations for calculation of combined beams fully concreting rectangular and T-section, partially concreting along with support slab on the lower flange of the beam, columns with rigid reinforcement, shear a connection of composite beams. Recommendations on the registration of creep, shrinkage and crack formation in the appointment of the modulus of elasticity are given. Recommendations on the use of diagrams of the state of concrete, reinforcement, and steel in the calculation of steel-concrete elements on a nonlinear deformation model are given. Recommendations on the use of the range of sheet flooring for steel-reinforced concrete slabs, as well as metal profiles as steel beams and rigid reinforcement in the cross sections of columns and combined beams, are presented. Recommendations on a design of units and details of composite steel and concrete structures are given, refined recommendations on buffer are presented. The examples of connection of steel beams with columns with rigid reinforcement are given. The examples of calculation of composite steel and concrete structures taking subject to the recommendations given in the Manual are presented.

Introduction. At present, creep is the main parameter determined in the long-term loading tests of concrete samples. However, creep appears to be only one of the deformation properties of a concrete sample during operation under the action of long-term loading. Another important property involves stress relaxation. Moreover, in individual problems (temperature problems, force redistribution problems, etc.), stress relaxation plays a more important role than creep. The introduction of a new test procedure can improve the accuracy of the obtained results (in standard creep tests, concrete relaxation is determined only mathematically), which in turn will increase the accuracy of calculations.Aim. To develop a procedure for testing concrete samples with the determination of their stress relaxation.Materials and methods. The article describes a methodology for conducting an experiment to study the relaxation of concrete samples in compression and bending modes, as well as the parameters of test benches, samples and the principles of load transfer.Results. The main results of experimental studies are presented graphically. An analysis of the results obtained was carried out; the convenience of conducting tests was evaluated.Conclusion. The prospects of the proposed approach for testing concrete samples are demonstrated, and recommendations for amending GOST 24544 are prepared.

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