Main Tensile Stress Research Articles

Optimized Design of Anchor Plates for 2200 MPa-Class Prestressing Anchorage Zones

The strength of prestressed steel strands has developed towards high strength, increasing from 1860 MPa to over 2200 MPa. The stress in the prestressed anchorage zone is more concentrated and complex, and the anchor plates for dispersed loads need to be optimized in design. This article proposes a design scheme for adding a middle pressure-bearing step based on the existing anchor plate and then establishes a 1/4 model of the concrete anchoring area of the anchor plate for finite element analysis. Based on the theory of the strut-and-tie model, the position of the middle pressure-bearing step is determined according to the maximum angle of the strut-and-tie model. Then, carry out force transfer tests in the anchorage zone for verification. The research results indicate that after adding a middle pressure bearing step to the anchor plate, the angle between the strut-and-tie model in the anchorage zone increases, and the bearing capacity improves. The position of the middle pressure-bearing step in the anchor plate is different, and the angle between the strut-and-tie models is different. According to the middle step position parameter, λ (the ratio of the effective width of the middle step to the distance from the middle step to the end face of the anchor plate) is 0.533 to optimize the anchor plate, and the bearing capacity of its anchorage zone is relatively high. The main tensile and main compressive stresses of the anchor plate after optimization increased by 6.2% and 5.74%, respectively, compared to the anchor plate before optimization. The main tensile stress of the spiral reinforcement under the anchor plate decreased by 0.59%, the main compressive stress decreased by 2.89%, and the von-Mises stress decreased by 2.32%. The side surface tensile stress of concrete under the anchor plate was reduced by 4.3 percent. Finally, three concrete specimens were poured for force transfer testing in the anchorage zone, verifying the safety and reliability of the optimized anchor plate in the 2200 MPa-level prestressed anchorage zone.

FEATURES OF THE CALCULATION OF REINFORCED CONCRETE ELEMENTS UNDER THE ACTION OF TRANSVERSE FORCE ACCORDING TO DIFFERENT STANDARDS

Shear force action is probably themost studied type of damage to reinforced concretestructures with conventional or pre-stressedreinforcement. However, some issues remainunclear or controversial. In contrast to the resistanceto bending, there is not even a universally acceptedcalculation model that would describe the behaviorof structures under the action of a transverse force.In beams, the transverse force mostly actstogether with the bending moment. The stressedstate at any point of the beam is characterized bytotal stresses - a set of normal and tangentialstresses.At points where the tangential stresses are equalto zero, the main tensile and main compressivestresses act.The main platforms are inclined at an angle of45 and 135 to the longitudinal axis of the beam.On the neutral axis of the beam, where the normalstresses are equal to zero, the principal stresses areequal in value to the tangential (rocking) stresses.The principal compressive stresses can mostlybe absorbed by the concrete and are not, as a rule,decisive. The main tensile stresses are the mostdangerous. Since concrete does not resist tensionwell, the principal tensile stresses cause obliquecracks to form. The criterion for their occurrence isthe excess of the tensile strength of concrete by themain tensile stresses. If inclined cracks are formed,it is necessary to place appropriate reinforcement inthe wall of the beam, which perceives tension. Suchreinforcement can be either vertical or inclined bars.One of the main questions in various methods ofcalculating elements for the action of transverseforce is the question of what perceives it - onlyconcrete, only reinforcement, or both concrete andreinforcement?Despite some degree of uncertainty, the designof inclined sections can be carried out withconfidence, since the accepted methods ofcalculation in various norms have been checked andadjusted on the basis of a large amount ofexperimental data.

Structures of Wooden Beams of Increased Load-Bearing Capacity

The article suggests the use of glued reinforced wooden beams with increased load-bearing capacity. The beam is provided with reinforcing elements in the grooves, namely, in the lower zone – prestressed flexible bundles made of composite, and in the upper zone – steel rods. The analysis of structural behaviour of the beam and the location of the reinforcing elements, the calculation of the bearing capacity of beams and evaluation of the effectiveness decision on material and Flexural rigidity. Composite rods can be prestressed to increase the efficiency of the reinforcement and increase the beam stiffness and load-bearing capacity. Installation of reinforcing elements along the line of action of the main tensile stresses in a wooden beam creates tension in them, which allows the use of flexible bundles and leads to a decrease in the complexity of their installation in the lower grooves, and, therefore, reduces the complexity of manufacturing a wooden beam as a whole.

МЕТОД ПІДТВЕРДЖЕННЯ РЕСУРСНИХ ХАРАКТЕРИСТИК МЕТАЛЕВОЇ ЛОПАТІ НЕСУЧОГО ГВИНТА ВЕРТОЛЬОТА ЗА РЕЗУЛЬТАТАМИ ВИПРОБУВАНЬ

The helicopter main rotor blade is the basic product that determines the reliability and service life of the helicopter as a whole. The problem of predicting and ensuring the specified blade life is an urgent problem considered at the stage of its design. The analysis of the design, structural materials and design and technological solutions of the main rotor blade (RB) of the Mi-8 helicopter has been carried out. A brief description of the main rotor blade of the Mi-8 helicopter is presented. The analysis was carried out and a standard flight cycle (SFC) of the helicopter was developed. The type of bench equipment for carrying out bench fatigue tests of the blade has been selected and justified. The loads on the main rotor blade for the SFC are determined. To determine the fatigue life of a blade, it is necessary to know the characteristics of the stress-strain state. The calculation of the stress-strain state (SSS) of a blade by the finite element method (FEM) using the ANSYS system is presented. The characteristics of the stress-strain state of the spar of the regular and irregular parts of the rotor blade of a helicopter are determined using the ANSYS system. The use of numerical methods for calculating the characteristics of the stress-strain state can significantly reduce the time and cost of designing a blade. The paper presents the results of calculating the regular part of the main rotor blade of the Mi-8 helicopter in the hover mode in the case of its loading with aerodynamic and inertial load from rotation, as well as the force from its own weight. With the help of the ANSYS system, a finite element model of the regular part of the blade was developed, consisting of a set of beam elements of variable section, a calculation was carried out taking into account the geometric nonlinearity of the structure's behavior, and an analysis of the results obtained was carried out. To describe the response of materials to an external action, a model of an elastically deformable isotropic body was used with the assignment of the corresponding elastic constants of the material. The analysis of the calculation results includes the determination of reactions at the attachment points, the values of the maximum displacements of structural elements and stresses in dangerous sections. Dangerous sections are determined and the values of the longitudinal force and bending moment in these sections are calculated. The assessment of the static strength of the blade by the safety factor was carried out. When evaluating the static strength, the equivalent stresses according to Mises were considered as the maximum design stresses. To assess the fatigue strength, we analyzed the distribution of the main tensile stresses in the power elements over typical stress concentrators. The maximum level of the main tensile stresses in the dangerous section indicates that the blade material operates in the zone of high-cycle fatigue. A technique for calibrating strain gauge channels has been developed. The calculation of the characteristics of the rotor blade of a helicopter is based on the requirements set forth in the technical literature, regulatory documents. When performing work, the requirements of the Aviation Rules, Part 29 (AP - 29) were taken into account. These studies were the basis for the development of a method for confirming the resource characteristics of a helicopter main rotor blade based on the results of flight and bench tests.

Experimental and finite element investigations on hydration heat and early cracks in massive concrete piers

The concrete hydration heat and different construction methods directly affects the early crack resistance of massive concrete structures and may lead to concrete cracks. In this work, the hydration heat test and finite element simulation were conducted to investigate the early cracking resistance and the main influencing factors of the massive concrete bridge pier. The size of the bridge pier was 8 m (length) × 4 m (width) × 22.5 m (height), and the pier was poured in two layers (8.5 m/14 m) with an interval of 37 h. The internal temperature of the pier was tested 16 days after the concrete pouring using pre-buried temperature sensors, and the crack expansion on the surface of the pier was continuously observed during the test period. The test obtained a maximum concrete temperature of 64.25 °C after 100 h after the concrete pouring, and 3 cracks were found on the surface of the pier. The pier simulation model is established according to the actual situation in the test, The maximum temperature inside the bridge pier obtained from the simulation is 61.73 ℃, and the temperature field development pattern and the crack expansion on the pier surface were basically consistent with the test, which confirmed the reliability of the simulation method. Besides, the simulation process found that the maximum main tensile stress on the surface of the bridge pier was 2.77 MPa, which was mainly distributed near the interface of the 2 layers, indicating that the layered pouring scheme adopted in the test was improper. The effect of layered casting schemes on the early cracking resistance of massive concrete has rarely been discussed, and further simulations revealed that: the maximum main tensile stress can be reduced by gradually improving the number of layers, layer height and interval between each layer. By changing the original layered pouring scheme to 3 layers with an interval of 3 days between each layer, the maximum principal tensile stress is reduced to 1.50 MPa, and early cracking of the bridge pier can be avoided. This work provides a general numerical analysis method with high accuracy, parameterization and quantification for early crack control of massive concrete structures in a multi-factor complex environment.

Full-scale model fatigue test of orthotropic steel deck

In order to study the fatigue failure behaviour and fatigue strength of orthotropic steel deck in an urban rail transit steel bridge, a full-scale test model of the orthotropic steel deck was established based on the main span beam of a cable-stayed bridge for urban rail transit. During the test, the stress values and the cracking condition of the structure were observed to evaluate the fatigue strength. The results show that there is no cracking during 2 million external load cycles; the main tensile stress values of each key test point before and after each cycle exhibit little difference. This shows that there is no obvious redistribution of stress, and the fatigue performance of the model under 2 million external load cycles meets requirements, and has a certain safety reserve. The load amplitude was increased and another 1.5 million cycles were carried out. When the external load cycles to 3.25 million times, cracks appear at the joint of the plate and U-rib. When the external load cycles to 3.5 million times, cracks are found at the symmetrical position of the first crack, and the test is terminated. The paper provides a theoretical and an experimental basis for the same type of bridge.

Stress recovery behaviour of a large-diameter Fe-SMA stranded wire developed for structural prestressing loss compensation

A new type of large-diameter iron-based shape memory alloy (Fe-SMA) stranded wire was developed, and its stress recovery behaviour was experimentally investigated in this study. The produced Fe-SMA stranded wires had a diameter of 15.2 mm, which were the same as the most commonly used steel-stranded wires. This kind of large-diameter Fe-SMA stranded wire matched the existing prestressed anchorage system to reduce application cost and accelerate the field application of the Fe-SMA in civil engineering. The effects of prestrain levels (4%, 6%, 8%, 10%), activation temperatures (200°C, 300°C, 400°C, 500°C), and secondary activation effect on the recovery stress of Fe-SMA stranded wires were analysed. Test results showed that the recovery stresses of the Fe-SMA stranded wire were 223–357 MPa. The maximum recovery stress was measured for the specimen with a prestrain of 8% and an activation temperature of 500°C. With increasing activation temperature, the recovery stress increased, but the increment decreased gradually. An increased prestrain level resulted in a first increase and a second decrease in the recovery stress, which was highest at the 8% prestrain level. If the shape memory effect (SME) was not fully used during the first activation, then the remaining martensitic phase changed on the second activation. The recovery stress generated by the first activation was essentially the same as those generated by the second activation at the same activation temperature. Taking the Nanshao River concrete box girder bridge in China as an example, the effect of using Fe-SMA stranded wires to compensate the prestressing loss was calculated. The results showed that the Fe-SMA stranded wire developed was able to compensate the vertical prestress loss of the prestressed box girder bridge web well and maintain the main tensile stresses at a low level during the service life of the bridge.

FRACTURED TECTONICS OF CHROMITITES OF THE MAIN SARANOVSKOYE DEPOSIT (PERM KRAI)

The Main Saranovskoe deposit is one of the largest chrome deposits in Russia. The chrome ore bodies are localized in the ultramafites of the Northern Saranovsky massif which has been studied since 1907. The research revealed that the massif is similar to the Bushveld stratiform complex. Unlike other layered plutons, the Northern Saranovsky massif has a large amount of chrome ore bodies as compared to ultramafic host rocks. As many studies have shown, the chromitites of the Main Saranovskoe deposit are severely tectonized. The strike and dip of the ore bodies is complicated by numerous faults. These observations imply that the massif is a fragment of a large stratified pluton intruded into the Proterozoic metasedimentary unit. The fracturing reflects the massif intrusion conditions and provides new petrogenetic information on the relevance of our study of the tectonic fractures of the Saranovsky massif. Studies have been made on the fracture and furrow displacement orientations along the planes in the main ore bodies: western, central and eastern, within the two parts of the deposit. The local stress tensor has been reconstructed using the Angelier method in the Win-Tensor program. It has been stated that the chromitites studied contain 3–4 main fracture systems whose orientation varies together with the orientation of the ore bodies. The main compressive stress axis is oriented subvertically both in the central and southern parts of the deposit, and the main tensile stress axis forms an acute angle with the ore body contacts in the center of the deposit and is oriented subperpendicular to them in the southern part. It has been concluded that fracturing of the chrome ore bodies in the Main Saranskoe deposit took place during the massif motion into the upper crustal horizons with the subvertical orientation of the ore bodies remained unchanged. This casts doubts on the probability of formation of the Northern Saransky massif as a result of gravity differentiation of magmatic melt, since in this case the ore bodies should have undergone a vertical turn which is not exhibited by their fracturing.

Causes of cracks in the plaster of unheated stone buildings

Introduction. The objects of the study are unheated stone buildings. Most of them are historical, including cultural heritage sites. The subject of the study is the analysis of the causes of cracks in the inner plaster layer. Damage of the internal plaster coating has a strong influence on the condition of wall paintings and artistic decoration of the exterior walls of preserved historical objects of cultural heritage. There is a lack of systematic studies of the causes of the damage on the walls. The scientific novelty of the work is the development of a finite element model. In this model, a fragment of masonry is considered together with a plaster coating. The practical significance of the study is to establish causal relationships between damage to load-bearing stone walls and internal plaster coatings. The study is aimed at identifying the most significant factors and impacts that influence the appearance of damage in the inner plaster layer of unheated stone buildings and religious buildings.
 
 Materials and methods. A detailed analysis of the stress state of the plaster layer during the course of shrinkage deformations in it was performed. Numerical research methods based on a finite element model of a fragment of masonry with a plaster layer were used.
 
 Results. The paper provides a graph of the dependence of the main tensile stresses on the ratio of the modulus of elasticity of the plaster mortar to the modulus of deformation of the masonry. With an increase in this ratio, the values of the main tensile stresses increase linearly. When they reach a value of 1.0 MPa, they become comparable to the limiting stresses at which a crack is formed. The obtained results are of great practical importance in the development of programs for the inspection, repair and restoration of historical cultural heritage sites.
 
 Conclusions. It is established that the values of the main tensile stresses practically do not depend on the thickness of the plaster layer. Humidity deformations of the plaster layer significantly exceed temperature ones and are the most significant factors for the appearance of cracks on the internal plaster coating of external walls in the absence of force cracks in the walls.

Flexural strength of fibre reinforced concrete in relation to the angle of magnetically orientated fibres

This paper focuses on high-performance fibre-reinforced concrete and its flexural strength concerning fibre orientation. The orientation is provided by a fully controlled special device. This device can align the fibres in fresh concrete using a magnetic field. The specimens are inserted into the device at different angles to ensure different fibre orientations concerning the longer side of the sample, which corresponds to the direction of the main tensile stresses. Specifically, angles of 0 °, 30 #x00B0;, 60 ° and 90 ° are tested and compared with each other and with reference specimens that are not exposed to a magnetic field. All samples are measured by a non-destructive method. This method was developed in our previous research and is based on measuring the quality factor Q of a measuring coil using an impedance meter. The samples are inserted into a measuring coil connected to an impedance meter. Flexural strength is obtained from the results of a three-point bending test. All samples are tested until complete failure.

Quantitative analysis of diaphragm plate caused by pedestal void of assembled box girder

In this paper, ANSYS finite element software is used to study the influence of pedestal void on the diaphragm force of prestressed prefabricated box girder bridge. Three different working conditions of no support void, side span support void and middle span support void were simulated respectively, and then the principal tensile stress and vertical deflection of each diaphragm key point were studied under different working conditions. The results show that the support void has almost no effect on the main tensile stress and vertical deformation of the diaphragm in the mid-span, but has a significant effect on the diaphragm at the end of the beam. The influence of the middle span support void on the main tensile stress of the diaphragm is larger than the opposite span support void. The effect of side-span bearing void on the vertical deflection of diaphragm is greater than that of mid-span bearing void. The void of the support will lead to the uneven force of the whole structure and finally affect the stability of the whole structure.

АНАЛИЗ ХАРАКТЕРИСТИК НАПРЯЖЕННО-ДЕФОРМИРОВАННОГО СОСТОЯНИЯ КОМЛЕВОЙ ЧАСТИ ЛОПАСТИ НЕСУЩЕГО ВИНТА ВЕРТОЛЕТА

The butt part of the main rotor blade (RB) of the helicopter is presented. A geometric model of the calculated connection was developed using the CATIA V5 system. With the help of the ANSYS system, a finite element model of the butt part of the main rotor blade was developed, and the calculation and analysis of the characteristics of the results obtained were carried out. To describe the response of materials to an external action, a model of an elastically deformable isotropic body was used with the assignment of the corresponding elastic constants of the material. The case of loading a bolted joint by a centrifugal force arising during the rotation of a blade is considered. To model the contact interaction, a generalized surface-to-surface contact interaction model was adopted. The analysis of the calculation results includes the determination of reactions at the attachment points, the values of the maximum displacements of structural elements and stresses in the stress concentration zones. In the course of the calculation, reactions were determined at the points of attachment of the tip along the holes in the lugs. The nature of the deformation of the bolted joint as a whole and of its individual elements is analyzed. The assessment of total displacements and displacement components is carried out. To assess the static and fatigue strength of the elements of the bolted connection of the tip with the blade spar, the stresses in the load-bearing elements were analyzed for typical concentrators. When assessing the static strength, the distribution of equivalent stresses according to Mises was analyzed. The distribution of stresses in the zone of holes along the rows is analyzed, starting from the root section in the direction of increasing the Y coordinate. The maximum von Mises stresses for typical stress concentration zones were compared with the ultimate strength of the structural element material. To assess the fatigue strength, we analyzed the distribution of the main tensile stresses in the load-bearing elements by typical stress concentrators. The maximum values of these stresses were compared with the fatigue limit of the structural element material.

Stretch-induced structural transition of linear low-density polyethylene during uniaxial stretching under different strain rates

The structural evolutions of linear low-density polyethylene (LLDPE) are investigated by in-situ synchrotron radiation wide-angle X-ray diffraction (WAXD) during tensile deformation over a wide strain rates range from 0.005 to 250 s−1. The phase transition mechanism is discussed by combining the phase diagram in 2D true stress (σtrue)-strain rate (ε˙) space with the evolutions of several micro-structural parameters, such as the crystallinity (χc), crystal sizes (L110, L200) and lattice parameters (aO, bO). The true stress space can be roughly divided into three regions by two critical true stresses at the onset formation of the monoclinic (σM-onset) and the hexagonal (σH-onset) crystals. In region I where only orthorhombic crystals exist, lattice distortion under the effects of stress plays a dominant role. In region II, the martensitic transformation from orthorhombic to monoclinic crystals occurs and monoclinic crystals load the main tensile stress. In region III, stress-induced melt recrystallization occurs and hexagonal crystals appear. In addition, the effects of strain rate on the stress-induced melt crystallization and lattice deformation are also discussed. This study on LLDPE films might aid to deepen the understanding of structural evolutions during real post-stretching process.

Design and Calculation of PC Composite Rigid Frame Bridge with Variable Section Steel Truss Webs

Steel truss web prestressed concrete composite bridge has many advantages, such as light weight, clear stress, beautiful structure, convenient construction, etc., but it is still in its infancy in China. Taking Shuinianbao bridge of Yanchong high speed as an example, this paper introduces the design method of PC composite rigid frame bridge with variable cross-section continuous steel truss web, and analyzes the static calculation of the whole bridge in combination with the code, so as to provide design reference for the construction and development of PC composite bridge with variable cross-section steel truss web. The analysis results show that: the calculation results obtained after modeling according to the design size meet the design requirements. Under the condition of ultimate bearing capacity, the top plate obtains a more uniform maximum resistance, and the arch curve makes the internal force of the bottom plate relatively small. Under the combination of short-term load effect, the main tensile stress of the inclined section appears at the position close to the support and the middle span section of the top plate. The main tensile stress of the steel truss web member is the most different under the unfavorable load combination, the maximum tensile stress is greater than the compressive stress, and the maximum tensile stress occurs at 1/4 of the mid-span.

Study on Mechanical Properties of Main Girder of Continuous Box Girder Bridge Strengthened By A Cable-Stayed System

The local stress concentration of the main girder during the tensioning construction of the continuous box girder bridge strengthened by the cable-stayed system is more prominent, which may lead to the sudden damage of the structure. Therefore, this paper studies the key section stress and deformation of the main girder in combination with the real bridge test. The results show that the maximum tensile and compressive stress increase of the main girder appears at the root floor and midspan floor; The tensile action strengthens the compressive stress between the anchorage point of the long cable and the anchorage point of the short cable to the top of the pier, which releases some of the compressive stress across the mid-slab, improves the stress state of the main girder, and improves the shear load of the main girder ability; With the increase of the cable force, the main tensile stress of the web in the anchoring area first increases and then decreases. The lifting amount of the midspan section of the main girder accounts for 20.06% of the total deflection, and the effect of the cable-stayed system on improving the deflection of the main girder is obvious.

Effect of forged substrate geometry on temperature and stress field in additive manufacturing

The forming technology compounding forging and additive manufacturing (AM) is a new approach to fabricate partial structures by AM based on forged substrates. Such technology has great potential for improving material utilization and manufacturing efficiency. Using this technology, three three-dimensional transient-coupled thermomechanical finite element models were developed in this study. The models comprised single-pass multilayer walls deposited on three different types of forged substrates, i.e., with a groove, platform, and boss. The temperature and residual stress of the components were measured by an infrared camera and X-ray diffraction, respectively, and the simulated results were found to be consistent with the experimental results. Based on this, the effects of forged substrate geometry on the temperature field and stress field in the laser solid forming process of a Ti-6Al-4 V alloy were investigated. It was found that during the AM process, there was little difference in the molten pool maximum temperature and range of high temperature region for the components fabricated using AM based on forged substrates with different geometries. In addition, the temperature gradient decreased with an increasing number of deposited layers. The component fabricated with a groove had the largest temperature gradient in the early depositional stage, whereas the component with a platform had the lowest residual tensile stress. The higher the bonding zone between the forged substrate and AM part, the higher the longitudinal and transverse main tensile stress zone, and the normal tensile stress was concentrated at the wall corners. The residual stress of the components using reciprocating scanning was much lower than that using single-direction scanning.

Study on Dynamic Response Laws and Shock Absorption Measures of Mountain Tunnel under Strong Earthquake

Based on the longitudinal and transverse seismic and shock absorption theory of tunnel structure, relying on the actual engineering, a finite element analysis model of a typical mountain tunnel was established. Four calculation conditions including the presence or absence of shock absorption layers and seismic joints are defined. The principal tensile (compressive) stress and displacement response of the vault, arch waist, foot of side wall, and middle of invert are studied. The results show that the shock absorption layer and the seismic joint have great influence on the dynamic response of the tunnel structure, which can reduce the main tensile (pressure) stress of different parts of the lining and change the way of stress distribution. The peak principal tensile (pressure) stress of the lining is reduced more obviously when the shock absorption layer and seismic joint are set. However, the presence of the shock absorption layer and the seismic joint will increase the peak displacement of each monitoring point of lining. The displacement of each monitoring point of lining is increased more obviously by the single shock absorption layer. Therefore, when the seismic design of the tunnel structure is carried out, the maximum seismic demand of the tunnel structure should be determined according to the specific calculation content in order to guide the design.

The distribution of the main stresses in the section of the ceramsite concrete fixed formwork block with four cells

One of the main issues in block design is the prediction of possible areas of crack formation and their further spread. In structural elements, one of the possible places of crack formation is stress concentrators, because, under an external load, significant local stresses arise in the cross-sections of such parts, which can lead to their destruction. This article discusses possible ways to refine the section to reduce the stress concentration in places of a sharp change in the section of the block. After modeling the distribution of the main stresses in the section in the Abaqus program, it was revealed that with a radius of rounding at the inner corners of the block cells, the maximum values of the main tensile stresses decrease significantly, as does their distribution zone. At the same time, the maximum values of the main compressive stresses increase slightly, and their distribution area increases significantly.

To the determination of the actual stress state of the elements of flat precast-monolithic slabs

Problem statement. Recently, a constructive system with the use of frame and frame-bced frameworks with precast reinforced concrete elements (flat precast-monolithic slabs) has been widely spread. The design of the frame uses monolithic or prefabricated columns and prefabricated monolithic flat slabs. A constructive solution is a flat floor slab consisting of precast hollow-core slabs adjacent in one level to monolithic bearing girders (conditional girders), using concrete dowels located in round cavities open at the plate ends and made monolithically with bearing girders. The work of the joints of the ends of the plates with bearing girders is of great interest. It appears that below in the above mentioned joints there are deformations of compression, as a result of the work of hollow-core slabs as the part of the floor slab for bending with an emphasis on bearing crossbars according to the hypothesis of flat sections that should affect the stressed state of the slab elements. It is established that the distribution of the main tensile and compressive stresses in the longitudinal central section of the multi-tensile plates clamping through the apertures in the linear and physically nonlinear problem, based on the performed studies, is not the same. In the linear and physically nonlinear formulation of the problem one can see that the distribution of the main compressive stresses is different by nature. Thus, in the case of a linear problem in the quarter of the slab, there is a zone of zero stresses, which is the boundary between the distribution of the main compressive stresses in the lower edge and the upper passage of the section of the element. In the nonlinear formulation of the problem, the zero-voltage zone is absent. Under the influence of the arched effect, the initial bending moment in the middle bores under the action of the distributed load is partially reduced.

Testing steelfibroconcrete centrifuged specimens of pipes used in drainage and water disposal systems at places of automobile and railway transport heavy traffic

Ferroconcrete pipes, used in drainage and water disposal systems of roads, works in conditions, in which the direction of the main tensile stresses is either unknown, or can change during exploitation. One of the ways of solving this problem is using of steel fibrous concrete, i.e. concrete on hydraulic tenacious substances with addition of reinforcing elements in the form of short lengths (fibers). Using of steel fibrous concrete allows to get the construction of low pressure centrifuged pipe for drainage and water disposal systems at places of automobile and railway transport heavy traffic with higher tensile and bending strength, crack resistance for the work under conditions when the direction of the main tensile stresses is unknown.