A new building structure is proposed - a welded steel I-beam with a prestressed perforated wall. The prestress in the beam is created by stretching the web and subsequent welding with chords. Before prestressing, holes are cut in the wall. Using the LIRA-SAPR software package, a model is proposed that can be used to study the operation of a prestressed perforated beam (PNPB) structure. The influence of various forms of voids in the wall on the change in the stress-strain state of steel I-beams prestressed by the wall drawing is studied. A preliminary assessment was made of the favorable effect of prestressing in a conventional perforated beam on the stress-strain state of beams with different forms of perforations in the web.

Keywords: steel structures, prestressing, numerical experiment, normal and shear stresses, bearing capacity

In this article, the stress state of a wooden beam reinforced with polymer composite reinforcement made of carbon tape of various lengths is investigated. The minimum required length of a carbon fabric-based reinforcing tape is determined in the most loaded lower stretched zone of a single-span solid-wood beam.

Keywords: solid-wood beam, polymer composite construction, carbon fabric tape, physical and mechanical characteristics of the composite, design load, place of breakage of the reinforcing tape, stress state of the beam, stress concentration zone

The main elements of the system of external reinforcement of bent reinforced concrete structures are fabrics and lamellas. Fabrics and lamellas are glued to the surface of building structures in a polymer matrix. The matrix provides adhesion of the reinforcing filler with the reinforced structure. The price of reinforcement with carbon lamellas is several times higher than for reinforcement with carbon fabric. The article shows a comparison of proposals on the market of building materials for the reinforcement of reinforced concrete structures with lamellas based on carbon fibers. On the example of a reinforced concrete beam of four types of cross-section, a comparative analysis of the selected reinforcement systems under different temperature conditions was carried out, a conditional utility coefficient was identified, showing the ratio of price to the percentage reinforcement of the structure. The results obtained can be used to select the most cost-effective composite reinforcement system.

Keywords: reinforced concrete beams; strengthening; composite material; carbon lamellas; external reinforcement; operating temperature

This article attempts to consider some of the features of the calculation and operation of light trusses from rolling corners. Is given brief information about the history of the use of trusses from single corners, their advantages and some disadvantages, as well as the prospects for the use of structures of this type in modern construction practice. Based on the analysis of the design documentation for a number of industrial facilities built over the past two decades in the Khabarovsk Territory, are analyzed the most common mistakes that designers make when developing roof structures using trusses from single rolling angles.

Keywords: farm from single rolling corners; corrosion resistance of elements; eccentricity of the acting effort; loading nodal moment; the value of the coefficient of working conditions; farm support node; additional forces in compressed rods

The article deals with the case when a concentrated force is applied to the web of a prestressed beam. The preliminary shear stresses do not affect the stress state in the middle of the beam span. However, preliminary normal stresses will act over the entire height of the wall and affect the distribution of the zone of local stresses and the stress state of the web. Determination of stresses in a beam is based on the beam theory of S.P. Timoshenko. The article presents a system of equivalent forces on the edges of the wall and the equation of normal stresses in the cross section of a prestressed beam. Compared to a conventional beam, prestressing reduces normal stresses from concentrated forces.

Keywords: thin-walled structure, steel beam, I-beam cross-section, prestressing, local stresses, local effect, Saint-Venant principle, Timoshenko SP beam theory, Karman's solution, Fourier integral, stress function

The article provides an assessment of the economic efficiency of a prestressed bistal beam, prestressed stretching of web. The comparison is made with a conventional bistal girder without prestressing with the same cross-section. The costs of material, design, production, transportation and installation are considered. It is taken into account that to create pre-stress, more labor costs are always needed, therefore, the manufacture of pre-stressed structures is more expensive than conventional structures. The purpose of prestressing is to reduce the consumption of steel in the fabrication of the structure. The structure of labor costs for the manufacture of structures is given. A comparative analysis of the cost "in business" of a running meter of a beam, prestressed by wall stretching, and a beam without prestressing, depending on the complexity of their manufacture, is carried out.

Keywords: thin-walled structure, bistal girder, I-beam, prestressing, stretching of web, structure weight, overhead costs, labor intensity of manufacture, cost-effectiveness, custom design, value in action

The article analyzes the results of experimental studies of prestressed steel I-beams. Presented specific features of the stressed and deformed states of welded steel beams, prestressed by wall stretching and bending of the initial T-element. In the first method, the prestressing in the beam was created by mechanical stretching of the wall on a special stand. In the second method, the T-piece is loaded by external forces applied to the T-bar plate until normal stresses appear at the bottom point of the wall, equal to the design resistance of low-carbon steel, then the second belt plate is welded to the T-piece element. The results of a numerical experiment with these beams, carried out in the SP LIRA, are considered. Presented a comparative assessment of the results of numerical and full-scale tests of prestressed I-beams a similar section with bimetallic beams without prestressing.

Keywords: web stretching, T-beam bending, section asymmetry, numerical experiment, test stand, stress, bearing capacity, beam rigidity, bending deformation, local stability

Blasting operations are often the only way to prepare the material for the recess for laying roads and railways in the rocks. Explosive loosening is also used to extract stone as a building material. Field testing is costly and often dangerous. Therefore, it is necessary to first conduct a series of experiments on the model and find out the conditions for ensuring good quality loosening of rocks. In order for the results of model tests to be transferred to nature, a similarity between model and specimen is required. The approximate similarity is achieved by the equality of the similarity criteria for the model and specimen. The characteristic similarity criteria are obtained by analyzing the physical quantities inherent in a mechanical system using the theory of dimension and similarity. The received criteria are presented in the classical form. These are the criteria of Strouhal, Froude, Cauchy and Newton.

Keywords: explosive loosening, rock material, deceleration interval, similarity criterion, modeling, rock density, model, specimen, expansion height, dimensionality, physical quantity