Search

Beams of a trapezoidal cross-section with a wide upper edge with prestressed reinforcement combine positive qualities in terms of strength, crack resistance, deformability and resource saving, which allows them to cover significant spans of multi-storey buildings. To develop a method for calculating the moment of cracking in these structures, a nonlinear deformation model was adopted, which includes equilibrium equations, conditions for the linear distribution of relative deformations along the height of the element section, and refined deformation diagrams of concrete and reinforcement. Concrete state diagrams are assumed to be nonlinear without a falling branch. To describe the deformation diagrams of high-strength and conventional reinforcement, a universal dependence is adopted, consisting of one linear and two nonlinear equations, in which the calculation of individual parameters is performed using different formulas. For the initial stage of the crack formation process, a design scheme is presented, in accordance with which the necessary equations and ratios are drawn up in relation to the considered prestressed reinforced concrete beam of a trapezoidal cross-section. The purpose of the study, in addition to developing a calculation methodology, was also the development of an algorithm and a computer calculation program. To obtain and analyze the results, a numerical experiment was carried out, the results of which are presented in tabular form. Due to the fact that the calculation method was built without involving empirical dependencies, the possibility of its application to determine the crack resistance of prestressed reinforced concrete beams of trapezoidal cross-section for any class of concrete and reinforcement was confirmed.

This paper presents an analytical method for calculating the cracking moment of concrete beams reinforced with fiber reinforced polymer (FRP) bars, which considers the non-linear behavior of concrete in the tension zone and the contribution of FRP reinforcement. Theoretical cracking moments obtained by the proposed method were verified with the experimental results and the theoretical results calculated according to ACI 440.1R-15. The comparison results show good agreement between theoretical and experimental data. A parametric study on the effect of longitudinal FRP reinforcement ratio and elastic modulus of FRP on the cracking moment of FRP reinforced concrete beams also were done by using the proposed method. The parametric study results show that both longitudinal reinforcement and modulus of elasticity of FRP significantly affect the cracking moment of FRP reinforced concrete beams. Moreover, parametric study results also clarify the weakness of ACI 440.1R-15 in determining the cracking moment of concrete beams reinforced with a large amount of FRP reinforcement ratio and with high modulus of elasticity of FRP.

This paper aims to study the temperature control of mass concrete, and to understand concrete pouring of hydration heat temperature field and temperature stress distribution. The influence of relevant parameters on reducing the temperature difference between inside and outside and the concrete temperature control and crack resistance measures are put forward. Taking Fuma Yangtze River Bridge as the engineering background, the combining of engineering measurement, theoretical calculation, and ANSYS numerical simulation is adopted. Results show that the use of ANSYS simulation for the mass concrete casting process is feasible. Furthermore, it is concluded that the cracks of mass concrete are prone to appear at the corner of the surface, and the influences of t input temperature, mixing ratio on reducing the internal and external temperature difference are also studied.

The correlation dependences between the safety factors of the yield stress and the safety factors of the crack resistance characteristics (fracture viscosity, crack resistance diagram, critical J integral, and crack-tip opening displacement) are provided. It is proposed to calculate the probabilistic safety factors at preset failure probabilities by means of the probabilistic safety factors of the yield stress, taking into account their correlation, as well as the independence of the static mechanical performance variation coefficients from the type of limit state. The results of calculating the probabilistic safety factors applied to fracture viscosity and the crack resistance diagram are provided.

The results of experimental and theoretical researches of crack resistance, development and growth of cracks of a fragment of a reinforced concrete multi-storey frame of a monolithic building with prestressed beams for a special emergency impact caused by a sudden removal of one of the load-bearing elements are presented. Removal of the middle column of the frame was considered as an emergency impact. Analysis of the pattern cracking in the frames with a prestressed beam before and after a special impact is carried out against the pattern cracking in an unstressed frame structure. Based on the increments of cracks width in the beam, the coefficient of dynamic additional loading in prestressed frame structures from a special impact was calculated. The obtained results of experimental and theoretical researches of the crack resistance of frame structures in considered influences can be used in the development of methods for protecting the frames of monolithic multi-storey buildings against progressive collapse.

Introduction . The paper is devoted to the analytical determination of general criteria for predicting the wear resistance of heavily loaded friction couples, in particular, stamping tools, operating under various loading conditions. The proposed system of criteria is based on physical dependencies that link the basic wear index, i.e. the number of loading cycles NF with crack resistance parameters n and C. The work objectives were the development and analytical foundation of the calculation technique that provides for predicting the wear resistance of the stamping tool for various loading conditions, as well as the predetermination of experimental verification of the efficiency of the developed methodology. Materials and Methods . Mathematical models that link the key criterion of wear-resistance, the number of loading cycles NF with crack resistance parameters nand C, are proposed. An analytical verification of the proposed models is carried out. Results . Mathematical models are developed for predicting the wear resistance of a stamping tool operating under various loading conditions. In particular, for the following cases: under sliding and rolling friction of the tool on a plastically deformable metal, for conditions of thermo-mechanical contact fatigue, for high-cycle brittle contact damaging, for pulsating contact on a plastically deformable metal, as well as for combined types of frictional contact. Discussion and Conclusions . The results obtained can be used in the design and structural optimization of the stamping tool operating under various loading conditions, as well as in predicting its life cycle.

In this paper, the effectiveness of the group method of data handling (GMDH) and the adaptive neuro-fuzzy inference system (ANFIS) methods in modelling the fracture parameters of asphalt mixtures w...

The article discusses the methodology for the reinforced concrete structures’ probabilistic deformation calculation. The uniform deformation criteria for assessing the reliability of reinforced concrete structures in the operation stage for strength, stiffness and crack opening are proposed. Taking into consideration the relatively high degree of heterogeneity of reinforced concrete as a building material, each criterion is determined with a predetermined provision.

This paper proposes a lightweight low-profile steel plate-reinforced ultrahigh-performance concrete (UHPC) deck panel with only longitudinal ribs as an alternative to traditional bridge de...

In this paper, the novel gradient concrete is innovatively applied to the bridge towers of Chizhou Yangtze River Bridge to solve the cracking and insufficient durability problems of concrete towers. Fiber-reinforced concrete is used in the outer functional area of the bridge tower, to significantly improve its crack resistance during construction and service. Moreover, the integrated design of anti-cracking and mechanical properties of tower materials is achieved. To study the performance of the novel functional gradient concrete (FGC) tower, the mechanical properties of the FGC tower material are tested, and the overall finite element stress is analyzed. Based on the material properties, the mechanical behavior of the cable-stayed bridge tower is studied. The temperature and stress of the FGC tower during the generation of the hydration heat are compared with that of the ordinary concrete tower. The crack resistance of the FGC tower is analyzed by the finite element method. The results show that the FGC tower has good mechanical properties and durability for the cable-stayed bridge towers.

The behaviour of square stainless steel tubular (SSST) stub columns after elevated temperatures under axial compression is presented in this paper. A total of sixty specimens were tested, including forty-eight SSST stub columns at elevated temperatures cooled in air, nine SSST stub columns at elevated temperatures cooled in water and three SSST stub columns at ambient temperature. A total of twelve square CFSST stub columns were carried out load-strain tests. The main parameters explored in the test include thickness (1.0 mm, 1.2 mm, 1.5 mm), high temperature duration (30 min, 60 min, 90 min, 120 min), temperature ranging from 400 °C to 1000 °C and cooling methods. This paper presents the failure modes, ultimate load-bearing capacity, load-strain curves, load versus displacement curves, initial stiffness at the elastic stage and ductility of the specimens. It was found that high temperature has the greatest influence on the ultimate load-bearing capacity of the columns, and the cooling methods also have some effect on it. As the elevated temperature specimens subjected increased, the percentage decrease in load-bearing capacity had an obvious increase, the ductility became worse and the initial compressive stiffness slightly decreased. The crack resistance of the specimens improved after elevated temperature. The axial deformation versus load curves had an obvious elastic-plastic stage as the elevated temperature duration increased to 120 min. Based on the experimental results, a formula was proposed to calculate the ultimate load-bearing capacity of SSST stub columns after elevated temperatures.

Main parameters, which characterize shear strength, are crack distribution, width of diagonal crack opening and angle of inclined crack. There are in this article, comparison crack resistant of testing reinforced concrete (RC) beams on the shear with such variable parameters like presence or absence internal reinforcement, different shear span, and presence or absence external composite reinforcement. Shear span (relative span to effective depth ratio) was acquired the following values: a/d=2, 1.5, 1. For internal reinforcement, rebar’s A240C with diameter 8 mm and steps 100 mm was chosen. The composite FRCM system was like external reinforcement with three stripe of composite fabric with width 70 mm and step 100 mm. Eight RC beams were tested. After testing, we discovered that the most influenced on the serviceability capacity was shear span. Internal transverse reinforcing increased shear strength on the same level and it was independent from shear span and other factors. Only quantity of reinforcing determine level of increasing shear capacity. FRCM system is efficient strengthening system, which significant increase shear crack resistant for RC beams. External FRCM reinforcing increase shear crack resistance on the same percentage and independent from presence or absence internal reinforcement.

The paper presents results of the study for samples of concrete beams reinforced with fiberglass rebar produced by LLC “KomAR”. The aim of the study is to determine strength, stiffness and crack resistance of beams with fiberglass rebar, various reinforcement schemes and their comparison with calculated data. Tests have been carried out in accordance with the regulatory requirements for a design scheme with two points of load application P1 = P2. The adopted scheme of pure bending is used in the laboratory for informativeness of the obtained results and getting maximum efforts in a stretched zone of bent elements. A comparison has been made of the data obtained as a result of tests with the ones which have been calculated according to the document SP (Construction Rules) 295.1325800.2017 “Concrete structures reinforced with polymer composite reinforcement. Design rules”, this document is based on the design principle of concrete structures reinforced with metal reinforcement. Due to the fact that composite fittings significantly differ from metal fittings in a number of indicators, comparative tests of concrete beams reinforced with metal and composite fittings have been carried out earlier. Data of the investigations are necessary for understanding behavior of structures and possibility of their application in the objects of capital construction. An excess of inclined section strength on the action of transverse forces over an actual one has been revealed when calculating concrete beams according to the I group of limiting states. While making calculations for the II group of limiting states, the need has been revealed to make changes in the procedure for calculating width of crack opening in order to approximate the calculated data to the data obtained as a result of tests and a procedure for calculating deflections.

In article features of influence of heat exchange of the hardening concrete of designs and environment taking into account ensuring crack resistance of concrete are considered. Features of the accounting of own thermotension of concrete as the major factor providing the demanded consumer properties of a design are shown. On the example of a real design it is shown how at the expense of own thermotension it is possible to increase admissible difference of temperatures on the section of a design and to provide its crack resistance.

The results of comprehensive studies of multifactor processes, mechanisms and criteria for fracture at a variation of the crack-like defect state, loading conditions and mechanical properties of structural materials carried out in the 20th - 21st centuries are presented on the basis of monographic publications and articles published in the journal “Zavodskaya Laboratoriya. Diagnostika Materialov.” Crack resistance of materials and structures has become a key problem of the material science, technology, design, manufacture and service of structures. Fracture mechanics including estimation of the stress-strain and limiting states in a cracks tip formed a scientific basis of the crack resistance analysis Stress intensity factors (linear fracture mechanics) and strain intensity factors (nonlinear fracture mechanics) are accepted as the basic criteria of those states. The basic computational relations for construction of the fracture diagrammes which link the cracks growth with conditions of a static, cyclic, long-term, dynamic loading are presented. Parameters of computational relations are put into correspondence with the features of fracture processes on nano-, micro-, meso- and macrolevels. Prospects of the research and guidelines of further studing crack resistance are discussed.

ObjectivesThe aim of the studyis to develop ways to increase the crack resistance and durability of prestressed wall panels made of cellular concrete.MethodA complex study was carried out at the stage of factory manufacturing of two-module, aerated concrete wall panels with prestressed rods of class A-III reinforcing steel, 10 mm in diameter, located in the middle of the panel in the longitudinal and transverse directions.ResultsIt was found that the total stress losses in straining rods prior to casting of the aerated concrete mix, connected with stress relaxation in the reinforce and with deformations of the headings of the straining rods in the gripping jaws, the steel mould deformations, as well as the losses after the panel exit from the autoclave during the transfer of force to the concrete, are 15-20% of the initial level. At the same time, depending on the dimensions of the straining rods, the length of the strain transfer zone was in the range of 150 to 250 mm. A study of the effect of pre-compression on the closure of possible technological cracks in concrete test panels showed that, due to biaxial compression of concrete, new cracks do not appear when they work on bending and stretching (during the decking and transportation). Moreover, initial cracks that sometimes can appear during the autoclave processing become closed.ConclusionComparative tests of prestressed and typical panels for short-term load in accordance with GOST 8829-94 requirements indicate a significant increase in their rigidity and crack resistance, as well as the shear strength of their bridge part. The design of straining reinforcing rods with the end transverse anchor in the form of a horseshoe, together with attached flat welded frameworks made of Vr-I wire with a diameter of 5 mm, which are installed along the contour of the window openings of the test panels, ensure its reliable adhesion to cellular concrete and effective anchoring in the panel's body until the end of its useful life. Biaxial prestressed reinforcement by single rods in combination with conventional frame reinforcement opens up possibilities for the production of external wall panels from non-autoclaved cellular concrete with ordinary heat treatment, instead of ceramsite concrete panels.

In this research, high strength fiber reinforced concrete (HSFRC) was used to replace the normal strength concrete (NSC) in steel-concrete composite beams to improve their working performance, which might change the static performance of stud connectors. Firstly, push-out tests were conducted to investigation on the static performance of stud connectors in steel-HSFRC composite beams and compared with steel-NSC composite beams. Studs of 8 sizes, 13 mm, 16 mm, 19 mm and 22 mm in diameter and 80 mm and 120 mm in height were adopted to study the influence of stud dimension. The test phenomenon shown that the crack resistance of HSFRC was better than that of NSC, and there were some splitting cracks on NSC slabs whereas no visible cracks on HSFRC slabs when specimens failed. Next, the load-slip curves of studs were analyzed and a typical load-slip curve was proposed which was divided into four stages. In addition, the effects of test parameters were analyzed according to the characteristic points of load-slip curve. Compared with NSC slab, HSFRC slab could provide greater restraining force to the studs, which improved the shear capacity and stiffness of studs while suppressed the ductility of studs. The shear capacity, stiffness and ductility of studs would significantly increase with the increasement of stud diameter and the studs with large diameter were more suitable for steel-HSFRC composite beams. The stud height had no obvious influence on the static performance of studs. Finally, based on the test results, the empirical formulas for load-slip curve and shear capacity of stud connectors embedded in HSFRC were developed which considered the influence factors more comprehensively and had better accuracy and applicability than previous formulas.

Cracking in non-load-bearing internal partition walls is a serious problem that frequently occurs in new buildings within the short term after putting them into service or even before completion of construction. Sometimes, it is so considerable that it cannot be accepted by the occupiers. The article presents tests of cracking in ceramic walls with a door opening connected in a rigid and flexible way along vertical edges. The first analyzes were conducted using the finite element method (FEM), and afterward, the measurements of deformations and stresses in walls on deflecting floors were performed on a full scale in the actual building structure. The measurements enabled to determine floor deformations leading to cracking of walls and to establish a dependency between the values of tensile stresses within the area of the door opening corners and their location along the length of walls and type of vertical connection with the structure.

The issue of concrete modification of railway sleepers remains relevant in connection with the growing demand for this product and increased requirements for the operational characteristics of one of the basic materials of the track superstructure. The problem is a partial early failure of sleepers, loss of load-bearing capacity in the early periods of operation (in the first years or after ten years). A lot of work has been done in this direction, most of them are aimed at concrete modification, but it is also worth considering the design features of the sleepers, and in order to increase the bearing capacity it is necessary to consider other ways to solve the problem. The aim of the researching was to modify the properties of concrete by polycarboxylate-based superplasticizers as concrete modifiers, determines their optimal dosages (from 0.8 to 1.1% by weight of cement) in accordance with the physical and mechanical properties of the raw materials and the required concrete workability. The sleepers considered in this article are reinforced with a wire with a diameter of 7 mm (one of the options for enlarged reinforcement). An option for additional reinforcement of sleepers in the area of the rail seat is proposed. Tests were carried out to determine the physical and mechanical properties of raw materials, the strength of concrete, and full-scale tests of the spars for crack resistance in bending were also carried out. The tests were carried out on certified equipment. According to the research results, it was concluded that for the production of sleepers that meet the requirements, it is necessary to use high-quality cements, polycarboxylate- based superplasticizers and additional reinforcement.

The article analyzes regulatory and technical documents and research results that apply to the design of road pavements, identifies the main simplifications allowed in the calculations of structural layers of road pavements, such as incomplete correspondence of design schemes to real operating conditions of structures, inconsistency of standard strength characteristics with actual loads, lack of accounting indicators of weather conditions, changes in the temperature of asphalt concrete during its operation. These errors, according to the authors, lead to the premature destruction of road pavements. In the course of experimental studies, tests were carried out to determine the Poisson’s ratio for asphalt concrete. During the tests, the deformation and strength characteristics of asphalt concrete were clarified through the Poisson ratio. In the course of laboratory experiments, the assumption was confirmed that Poisson’s ratio for various types and compositions of asphalt concrete depends on the temperature and load level, as well as the loading rate. To carry out the experiment, a research methodology was proposed to determine Poisson’s ratio at various temperatures and load levels. The recommended design features of the operation of road pavements in conditions of temperature differences have been substantiated.

This article presents a critical development analysis of the general deformation theory and models of reinforced concrete elements and structures resistance to force effects. Their relationship with the defining provisions of the mechanics of reinforced concrete elements and structures deformation is estimated. The main disadvantages of the considered models are established. General provisions of the mechanics of reinforced concrete elements and structures deformation are proposed to be developed on the basis of a universal deformation-force model. It is noted that the latter is devoid of most of the shortcomings characteristic to other models. The main advantage of the deformation-force model is indicated, associated with the expansion of the well-known system of static, geometric and physical relationships to the level of statically definable. It becomes especially noticeable when calculating reinforced concrete elements and structures for deflections and crack resistance. One of the main features of the deformation-force model is emphasized, which makes it possible to quite simply «embed» or integrate the technical theory of reinforcement to concrete adhesion into the general theory of reinforced concrete deformation. Through the averaged design section and average deformations of materials in the block between adjacent cracks, all parameters of the normal cracks formation and opening in the deformation-force model are directly related to the parameters of reinforcement to concrete adhesion.The effectiveness of using the deformation-force model of reinforced concrete to force effects resistance was evaluated by a statistical comparison of theoretical calculations with the reinforced concrete elements experimental studies results tested by different authors. Similar comparisons were made for the methods of the current standards. It was confirmed that the priority in the accuracy of assessing the reinforced concrete elements stress-strain state parameters belongs to the calculation method, which is based on the deformation-force model of reinforced concrete resistance.

The fact that high-strength concrete is easily to crack has a significant negative impact on its durability and strength. This paper gives an optimum design method of high-strength concrete for improving crack resistance based on orthogonal test artificial neural networks (ANN) and genetic algorithm. First, orthogonal test is operated to determine the influence of the concrete mix proportion to the slump, compressive strength, tensile strength, and elastic modulus, followed by calculating and predicting the concrete performance using ANN. Based on results from orthogonal test and ANN, a functional relationship among slump, compressive strength, tensile strength, elastic modulus, and mix proportion has been built. On this basis, using the widely used shrinkage and creep models, the functional relationship between the concrete cracking risk coefficient and the mix proportion is derived, and finally genetic algorithm is used to optimize the concrete mix proportion to improve its crack resistance. The research results showed that, compared with the control concrete, the cracking risk coefficient of the optimized concrete was reduced by 25%, and its crack resistance was significantly improved.

A novel lightweight prestressed ultrahigh-performance concrete (UHPC) bent cap is proposed, consisting of a large cantilevered thin-walled box girder weighing approximately 40% less than n...

Experimental data of strength, deformability, and crack resistance of 2,000×200×100mm reinforced concrete and basalt-concrete beams are given. Longitudinal reinforcement consisted of 2 Ø14 A500C for reinforced concrete beams and 2 Ø14 BFRP (AKB800) for basalt-concrete beams. Transverse reinforcement consisted of 2 Ø3,4,5 ВрI for reinforced concrete beams and 2 Ø4,6,8 BFRP (АКБ800) for basalt-concrete beams. Beams were made of heavy concrete of C16/20, C30/35, and C40/50 classes. The experimental beam specimens were tested according to a four-point scheme as loosely supported beams loaded with two concentrated forces. Loading in the series of tests was stepwise increasing, static and low-cycle repeated at high levels of 0.50, 0.65, and 0.80Fult. Distance from supports to concentrated forces (shear span), a/h0, varied within 1, 2, 3. Experimental beam specimens were made and tested according to the theory of experimental design according to the Box B4, optimal plan D. Comparative analysis of main performance parameters of reinforced concrete and basalt-concrete beams under the action of abovementioned loads was performed. The necessity of these studies was determined by the unsatisfactory convergence of experimental and calculated values of bearing capacity of oblique sections of basalt-concrete beams determined according to existing standard methods. The studies have established the influence of design factors and loading nature on basic parameters of the working capacity of basalt-concrete beam elements in a form of experimental-statistical dependences. These results will form a basis for a physical model of resistance of oblique sections in such structures to external loads. The presented results will significantly supplement the existing database of the operation of beam basalt-concrete structures and will be used in the development of an analytical method for calculating strength, deformability, and crack resistance

In recent decades, steel-reinforced concrete (SRC) members under eccentrical tension have been adopted more frequently in modern buildings due to the constraints of more complex structural design/detailing that accompanying contemporary architectural creations. Crack resistance of this type of structures has become a critical design consideration but received insufficient research attention in the past. In this context, the anti-cracking performance of prestressed SRC columns reinforced with CFRP tendons under eccentric tensile loads is investigated experimentally and analytically with the following first-hand experimental validations: 1) prestressed CFRP tendons can well strengthen SRC columns under eccentric tensile load and restrain the crack propagation; 2) an increase in the load eccentricity progressively weakened the influence of prestressing tension level on the cracking load; 3) specimens with the higher prestressed tension level, larger longitudinal reinforcement diameter, and flange thickness exhibited greater crack resistance capacity. Furthermore, the plane-section assumption was also validated in this study. A test data-enhanced analytical method was proposed for determining the cracking load of PSRC columns.

The investigations carried out in the field of creation of large-size crack-resistant structures and cellular concrete products have shown that this problem is multifaceted and it must be solved in a complex manner, and one of the ways to increase the crack resistance and durability of such structures and products is prestressed reinforcement.

The presents the strength analysis of reinforced concrete elements under combined action of the axial load, flexure moment and torque using the strength ratio between strength and crack resistance. The limit values for these parameters are detected. Experimental results describe the propagation of deformations in the concrete and reinforcement, crack formation, fracture, bearing capacity and deformability of test specimens. The algorithm and the structural analysis technique are proposed for the conditions of the joint effect of the axial load, flexure moment and torque. The diagrams are suggested for the calculation results

The analysis of the use of modern high-strength concrete in world practice is carried out. The advantages and disadvantages of highstrength concrete have been analyzed. The existing examples of the implementation of high-strength concrete in the world and their types and areas of application are considered. The prospects for using high-strength concrete in the construction industry of Ukraine are determined.Use of qualitative materials for the construction of supporting structures of high-rise building, and the construction of bridges, tunnels and other highly responsible buildings and structures. High-strength concrete with high durability, waterproof and gas tightness, corrosion resistance due to its homogeneous structure is efficient and promising for maintenance of all needs. In this work, samples of cubes, prisms, beams were developed and tested experimentally to determine and consider the efficiency of using high strength concrete in bending elements. In this article there are presented experimental results of tests, data on the selection of the effective composition of concrete mixture, and provided experimental samples with characteristic fractures. On the samples of the cubes that were presented, it can be seen the principles of destruction − the class C20 with normal destruction, and in the classes C60 and C80 there is a fragile nature of destruction. Also, the results of tests of prism fractures of classes C20, C60 and C80 were presented, where examples of fracture are also provided and elastic moduli of the samples were determined. The combined table showed cubic and prism strength, which shows the effectiveness of applying high-strength concrete in comparison with traditional concrete, since in concrete increase the compressive strength and the relative tensile strength, density, decreases the porosity and the structure is generally improved. The results of experimental studies of durability and crack resistance of reinforced concrete beams made of high-strength concrete are presented and compared with beams of ordinary concrete.

A framework for characterising the static and fatigue crack resistance of a fully supported beam on an elastic foundation is presented. The crack resistance is given as a function of the resisting ...

The work is focused on the analysis of the crack resistance of the TEKKEN-specimen during its cooling after welding. The TEKKEN-specimen is manufactured according to GOST 26388–84 type IX and is designed for estimation of propensity of the weld joint's metal to formation of the cold cracks. It was necessary to establish the margin of technological safety of the welded joint and to reveal the critical places of possible cracks. The basis is the principle of assessing the welding stresses with yield stress, obtained by cooling of samples with a high speed typical for a welded joint. A numerical estimation of a stress level in various points of a welded joint with allowance for a welding mode, conditions of fastening is made in ESI SYSWELD. Dependency graphs of the first main stresses on temperature were built. With a reduction of a crack resistance below one, it is probably the formation of cracks, because in this case the acting stresses exceed the yield stress. It is shown the most dangerous things are the transition zones from the weld joint to the base metal at a temperature of 1020 Celsius, and the root of the weld joint after full cooling. The developed analysis method of crack resistance can be used to evaluate other typical welded joints and samples.

An approaches to the study of the fatigue strength of a freight car 18-100 bogie’s side frame are under consideration in this article. There is a decline of the quality of the manufacture side frames and increase of the number of defects, which leads to an increase the number of accidents. The relationship of the stress intensity factor and crack length for different types of fatigue cracks (surface crack and full perforation) was introduced. The algorithm of a bogie with a crack fa-tigue calculation was introduced. The inhibition of crack growth under overloading was taking into account during cal-culation. The additional numerical calculation of fatigue strength was performed by the specialized software package. Some defects of bogie larger than 1 mm is unacceptable as it dramatically reduces the fatigue strength.

The results of experimental studies of reinforced concrete constructions at complex resistance to torsion with bending are shown in the article. The main purposes of the researches are detection of regularities and determination of deformation and cracking parameters. The most important of the studding parameters are cracking load, destructive load, the coordinates of spatial cracks formation, the width of crack's opening at the axis of the longitudinal and transverse tensile reinforcement and along the entire profile of cracks; changing the distance be- tween the cracks and crack length according to increasing the deformation load; deformation of compressed concrete and reinforcement in a complex stress-strain state. The test results are presented in the form of relationships of structure's deflections, deformations of compressed concrete and reinforcement, including results which were determined by the indications of electrotensometric sockets. The obtained relationships allow us to assess the reliability of the calculating methods reinforced concrete constructions subjected the action torsion and bend- ing.

The article represents crack control research results of horseshoe-shaped fibre reinforced concrete tunnel linings which are constructed by conventional tunneling method on a full cross-section in rocks. Based on linear fracture mechanics an alternative method for estimation of the crack resistance for such kind of linings is proposed. The research was carried out by using the finite element method supported with experiment planning method.

Six large Ultra-High-Performance Fiber-Reinforced Concrete (UHPFRC) slabs were fabricated and tested to investigate the restrained shrinkage and cracking behaviors. The use of expanded polystyrene and Teflon sheets with two different slab thicknesses was considered to improve the shrinkage crack resistance. Free shrinkage was simultaneously measured to evaluate the degree of restraint according to the above test parameters. The test results showed that free shrinkage strains of -689 μe to -723 μe were obtained after 9 days, and prismatic specimens with a higher exposed surface area-to-volume ratio (S/V) had slightly higher free shrinkage strains than those with a lower S/V. Increasing the concrete slab thickness and using expanded polystyrene and Teflon sheets were effective at reducing the degree of restraint and improving the shrinkage crack resistance of the UHPFRC slabs. Among the various specimens, the slabs with the expanded polystyrene exhibited the lowest degree of restraint by 0.45 after 9 days.

A method is proposed for predicting the critical stress-intensity coefficient K 1c of structural steels (their crack resistance) on the basis of uniaxial tensile tests of standard samples. The derivation of this method relies on the concepts of mechanical stability and embrittlement when nonuniform force fields act on a metal. The strain-hardening index n of the metal at the critical transition temperatures from the plastic state to the quasi-brittle state (T c or T 0) and from the quasi-brittle state to the brittle state (T k2) plays a key role here. The proposed method may prove effective in monitoring the crack resistance of steels certified in scientific and plant laboratories.

The article presents geoecoprotective technology of property improvement. The technology of silica sol absorption used with transport concrete articles is an as example of such a technology. The point of the technology is increasing properties of concrete by forming new calcium silicate hydrates in the pores and capillaries of a concrete stone. This new method was named lithosynthesis. It starts from the surface of a concrete article used in road construction. Technical properties and durability of road construction articles were improved. Low temperature resistance, crack resistance and constructive quality coefficient were studied. As a result of property improvement it is possible to reduce raw material consumption.

The results of an experimental study on crack-resistance of large scale compressed-bent reinforced concrete columns strengthened under initial load are represented in this paper. Structural performance of unstrengthened reference samples and jacketed samples under initial load of 30%, 50%, 70% and 90% of the bearing capacity of the reference samples was investigated. During the tests of the columns cracks pattern along the length of the columns, cracks length and width development were observed and recorded. Crack width vs Load graphs were plotted for the analysis of cracks development. Crack width at each loading stage was recorded to determine the critical crack. The load Nw when the critical crack reached the width of wmax = 0.3 mm (according to Eurocode-2: Design of Concrete Structures) was considered as a loss of serviceability of the column. Analyzing the increase of columns serviceability after reinforced concrete jacketing the conclusion was made that higher load level during strengthening results in the lover strengthening effect. The maximum increase in serviceability of the columns considering the ultimate crack width was achieved when the sample was jacketed without any initial loading and the minimum - for the samples jacketed under the load of 90% of their bearing capacity.

This paper proposes a novel fully prefabricated composite deck system to achieve green and accelerated construction in bridge engineering. Ultra-high-performance concrete (UHPC), which has ...

Rebar fixators of various types (plastic and concrete) became widespread with manufacturing of building structures of precast and monolithic reinforced concrete in order to fix steel reinforcement cage in strictly design position and to exclude the probability of its displacement during concreting. Such sufficiently rigid fixing is necessary for the following reliable operation of the structure in the building, as well as for the preservation of steel reinforcement which protected by a necessary layer of concrete from corrosion. Information available in the literature does not allow us to judge about the effects that different types of fixators apply to exploitative properties (such as strength and crack resistance) of reinforced concrete. The experiments, according to the accepted method, showed that these characteristics are slightly worse for the samples with plastic fixators and fixators made of low grade concrete than for the samples without fixators or fixators made of high grade concrete. On the base on the research results it becomes possible to substantiate the distinction between the areas of application of plastic and concrete fixatives

A new installation for testing concrete samples has been developed. The methodology for testing concrete samples with a crack has been clarified. Tested. Strength and energy characteristics of crack resistance of concrete samples are obtained. The results are presented in the form of graphs and tables. The results of experimental studies are compared with the theoretical characteristics of concrete obtained by modeling the behavior of concrete samples by the finite element method. The research results showed the possibility of using the proposed installation and test methodology in further studies.

Monolithic construction in winter faces problems of concrete strength set at negative ambient temperature. In order to ensure the necessary temperature conditions for hardening concrete use different methods of heating structures. One of the most effective ways is to warm up using a heating wire. The tasks of stood concrete in winter conditions are multifactorial, and computer modeling can significantly improve the efficiency of work. The ELCUT software complex is a tool in solving such problems, based on the method of the final elements. On the example of a monolithic foundation slab, the process of hardening of concrete at the temperature of the coldest five-day and medium-winter in Bratsk was simulated. The calculation of the concrete strength set and the analysis of temperature fields, taking into account the requirements for crack resistance, has been made. Computer simulations allowed to pick up the parameters of laying the heating wire in the concrete.

Aiming at the high internal and external water pressure tunnels built in unfavorable geological bodies, this study proposes a novel type of composite support structure in which steel plates are poured inside concrete linings. Compared with traditional structures, it has the advantages of higher tensile strength, better crack resistance, and impermeability. Taking the diversion tunnel of a hydropower station as an example, based on linear and non-linear finite element simulations, mechanical properties of the steelconcrete composite lining structure for a hydraulic tunnel in soft surrounding rocks are analyzed. On this basis, the concrete crack control under this supporting condition is verified. Research results can provide a reference for the selection of reasonable steel plate thicknesses and reinforcement types in design.

The article presents the main results of complex experimental and theoretical research into the crack resistance and the limit state of reinforced-concrete sleepers with elastic rail fastening systems without base-plate. The objective of this study is to uncover reasons for the cracks and other breakages during operation, demonstrate their importance, and produce a set of recommendations for prevention of the most serious defects. The research also involved statistical analysis of the defect factor for sleepers, and determined the number of defects by type according to track layout, traffic density, tonnage transported, concrete grade and other characteristics based on the results of full-scale research of track sections and surveys from maintenance specialists. The full-scale research was made on rail sections under standard operational modes and on a test track section of straight and curved elements with sleepers of concrete grades C32/40, C35/45 and C40/50.The study was based on numerical methods, modelling of the stress-strain behaviour of the track, and estimation of the performance of sleepers with cracks.The method used incremental-iterative algorithms to consider the elastic plastic properties of materials, solve contact problems in operation of rail fastening systems, and also reveal the structural nonlinearity of joint action for track elements. The method was realized in LIRA-SAPR software on the basis of Building Information Modelling (BIM) and the Finite Element Method (FEM).The results were verifiedby experimental research into the sleepers under static and dynamic loads with estimation of crack development in terms of concrete grades, deformation modulus, rigidities of the ballast layer and the sub-grade, position of the reinforcement and other characteristics.

High-grade (API 5L X80) and large-diameter (OD 1422 mm) line pipes are used in the Sino–Russian eastern route gas pipeline project for high pressure (12 MPa) transmission, and this can significantly increase the transmission capacity and meet China's energy strategic demand. With the increase of steel grade, transmission pressure, pipe diameter and design coefficient, however, ductile crack of line pipes becomes the dominant crack mode, so it is necessary to focus on crack arrest and control study. In this paper, therefore, an intensive study was performed on the Battelle Two-Curve (BTC) method which is the major solution to the calculation of arrest toughness, as well as the crack resistance curve and decompression curve. Based on the study, the principle and application range of the BTC method were confirmed. In addition, a series of analysis were conducted on the issues which occurred when the BTC method was applied to high-strength, high-toughness line pipe steel, and the commonly used modified approaches to BTC calculation results were also provided. After the crack control scheme of the X80 large OD 1422 mm line pipes for the Russian Bovanenkovo–Ukhta was reviewed, the BTC calculation results were corrected on the basis of the design parameters of the Sino–Russian eastern routine gas pipeline project, the Charpy V-notched (CVN) impact energy which meets the project requirement was finally worked out to be 245 J.

The practice of the determination of cyclic crack resistance, i.e., the rate of fatigue crack growth depending on the range of the stress intensity factor, has existed for more than a decade. However, a number of problems related to the use of these data for the quantitative assessment of the service life for deep-sea equipment remain poorly understood. They are description of crack kinetics under alternating and mainly compressive loading cycles and taking into account the possible impact of differences in loading frequency for a sample and for a structure in corrosive media. The investigation of the impact of these factors is performed using a technique for monitoring the changes in the compliance of a sample, which allows one to register the loads of crack opening and complete closing and crack propagation at small temporal bases under testing with reduction of the frequency to 0.01 Hz.

Slow crack growth behavior in polyethylene pipe grade resins were studied using both static fatigue (stress-rupture) and cyclic fatigue tests. This was done to better understand the applicability of cyclic fatigue in the prediction of slow crack growth ranking determined from the static fatigue test. In all polyethylene pipe grade resins tested at 80 °C, reduced crack growth failure times were exhibited when the cyclic fatigue test was employed. However, when applied to rank the resins through their slow crack failure times, the cyclic fatigue results did not always confirm those obtained from the static fatigue test. That is, in some cases, a resin with higher slow crack resistance ranking (longer failure times) than another resin in static fatigue exhibited lower ranking (shorter failure times) in the cyclic fatigue test. This abnormality of reversal in ranking is not a general observation but does occur. Based on the data obtained so far, when resins with smaller differences between static fatigue and cyclic fatigue slow crack growth failure times are compared with those resins having larger differences, the chances of correctly predicting the ranking obtained from static fatigue using cyclic fatigue tend to decrease. Hence, it is suggested that one needs to practice caution when using cyclic fatigue to predict the static fatigue ranking of resins for slow cracking resistance. Some insight into the cause of such abnormality is discussed with reference to creep-fatigue interactions.