Strengthening of reinforced concrete structures by composite materials taking into consideration the carbonization of concrete

One of the main causes for deterioration of reinforced concrete structures in modern construction is corrosion of reinforcement. Corrosion leads to decrease of adhesion between reinforcement and concrete, formation of cracks and destruction of the protective layer of concrete. All this reduces the load-bearing capacity of reinforced concrete structures. The structures of sludge reservoirs exposed to carbon dioxide were used as an object of the study. The characteristic defects and damages revealed by visual inspection were described. The verification calculation of the considered construction depending on the pH of the medium was performed on the basis of the results of technical inspection and study. The degree of carbon dioxide impact on the considered structures was determined by the phenolphthalein test method, which is based on the color change of acid-base indicator solution on the surface of concrete and reinforced concrete depending on the pH value of its medium. The phenolphthalein test revealed that pH of the medium is less than 8 for the depth more than the thickness of the concrete protective layer. A verification calculation of the considered structure was performed on the basis of the technical inspection results and the conducted research. According to the calculation results, a variant of beam reconstruction and strengthening using external reinforcement based on carbon fibers FibARM 230/150 was proposed. The reconstruction was carried out with account of the carbonized concrete layer

A method for assessing the stress-strain state of reinforced concrete structures

The article analyses the modern methods of estimation of stress-strain state of reinforced concrete structures. The result of the analysis is a new method for estimating the stress-strain state of reinforced concrete structures. The method is based on extracting a small sample of concrete from the array. The article describes the method of execution of works, the method of calculating the stresses. Previously, the method was investigated under laboratory conditions. The results are presented in graphs and tables. The research was conducted to assess the stress state of existing concrete structures. As the objects of research, two industrial buildings of 1933 and 1941 construction years were taken. An assessment of a stress state of a panel residential building was held. The measurement results were analyzed. The method for determining the stresses in reinforced concrete buildings and structures is recommended

Engineering structures stability against progressive collapse

The calculating stability of an engineering structure against progressive collapse is considered in this article. The calculations results are analyzed. A dangerous emergency scenario was developed and measures were developed to prevent the progressive building collapse in the structures local destruction in accordance with the regulatory documents requirements for such an object. The most dangerous design schemes are considered to assess the structure stability against progressive collapse. A scenario for calculating stability against progressive collapse in the case of local failure has been selected, and a consistent action algorithm has been obtained that makes it possible to perform a calculation for resistance to progressive collapse., The kinematic method of the limit equilibrium theory for structures with elastic-plastic materials properties is used to calculate the resistance to progressive collapse. It corresponds to the turning the system into a plastic kinematic chain, the links movement is carried out due to the plastic flow of the system's links. Two types of undamaged structures were identified to assess the building resistance to progressive collapse: neighbouring beams and columns, in which local destruction impact does not cause a qualitative change in the stress state, but leads to an increase in stresses and forces (neighboring beams, columns); pavement slabs resting on a beam and welded through embedded parts to a beam that has lost its original support, and located above a local fracture, the stress state changes. The conclusion is made about the requirements that should be met in order to conclude the calculation justification so it can be said that resistance to progressive collapse is ensured. It has been established that the calculations performed confirm the object stability - the drainage chamber to progressive collapse in the local destruction as an emergency situations result

Самозаклинивающиеся элементы в трубобетонных колоннах

Выполнено исследование образцов трубобетонных колонн круглого сечения (ТБК) при местном сжатии с начальным эксцентриситетом. Для повышения прочности внецентренно сжатых ТБК в бетонном ядре размещались стальные самозаклинивающиеся элементы. Они укладывались в три ряда в пространстве между верхним торцом свежеуложенного бетона и внутренней поверхностью стальной трубы. Причём, нижний и верхний слои самозаклинивающихся элементов выполнялись в форме частично усечённых тетраэдров, полученных разрезанием кубов плоскостями, проходящими через середины их рёбер, на две равные части. Между слоями усечённых тетраэдров размещался слой кубов таким образом, чтобы все элементы плотно соприкасались между собой своими гранями. Выполненные эксперименты подтвердили способность самозаклинивающихся структур за счёт высокой жёсткости более равномерно перераспределять передающиеся через них сосредоточенные нагрузки. Показано, что подбор рациональной геометрии элементов структуры самозаклинивающихся элементов и условий их взаимодействия друг с другом может являться эффективным методом повышения жёсткости определённых участков конструкций. Использование структуры из трёх слоев самозаклинивающихся элементов заметно изменило характер деформирования и разрушения образцов ТБК, что привело к увеличению прочности исследованных образцов в среднем на 11%

Compressed Concrete Filled Steel Tube Elements of Annular Cross-Section

The problem of determining the strength of a short centrally compressed concrete-filled steel tube element of annular cross-section is considered. The corresponding calculation procedure is proposed. The procedure is based on the theoretical positions of the mechanics of solids and it implements the method of limiting forces. It considers the complex stress state of the concrete core and steel shell as well as nonuniform distribution of transversal stresses over the cross-section of the calculated element. If there is high-strength reinforcement in the concrete, the stress in it is calculated considering the increased deformability of the concrete. The dependences for determining the initial modulus of elasticity of concrete as well as ultimate relative strains of uniaxially compressed and volumetrically compressed concrete are presented. The proposed procedure is applicable to structures made of different concrete types and steel classes

Experimental and calculated evaluation of carbon fiber reinforcing for increasing concrete columns carrying capacity

The article presents the concrete columns tests results reinforced with canvases based on carbon fibers FibARM Tape 530/300 and FibARM Lamel 14/100 slats, the calculation of the use effectiveness for strengthening the compressed reinforced concrete elements. Three groups of columns were tested: unreinforced columns, columns reinforced with FibARM Tape 530/300 canvases in one layer, reinforced with FibARM Lamel 14/100 lamella (width is 100 mm), while one of the samples was reinforced with lamella only, and the other was reinforced both lamella and clamps. In addition, it was proposed calibration calculation of concrete columns reinforced with canvases based on carbon fibers FibARM Tape 530/300, the calculation purpose was to determine the bearing capacity for evaluating the suitability in the further structure operation after columns strengthening. According to the experiment results, data were obtained on the carrying capacity of centrally compressed concrete columns reinforced with carbon fiber both with a discrete arrangement of bands (strips) made of composite material along the height of the structures, as well as with their continuous wrapping (analogue of reinforced concrete holder). According to the experiment results, data were obtained on the carrying capacity of centrally compressed concrete columns reinforced with carbon fiber, both with a discrete arrangement of bands (strips) made of composite material along the height of structures, and with their continuous wrapping (analogue of reinforced concrete holder)

Sustainable regeneration of urban areas (using the example of Moscow renovation program)

The paper discusses advantages and disadvantages of the renovation program in the city of Moscow (Russia). This program of the Moscow government is aimed at demolishing low-rise housing built in the 1960s and new construction in the vacated territory. On the basis of the analysis of this program’s disadvantages, seven major problems were identified - a flaw in the socio-spatial model of the city, a threat to small and medium businesses, a mortgage crisis, an economic issue, a low level of apartment comfort, an environmental problem, and increase in population density. Various methods for the reconstruction of the five-story buildings of the first mass series with superstructure floors are considered

An integrated approach to the use of composite materials for the restoration of reinforced concrete structures

The article presents the results of a technical inspection of the state of the structures of the object. To conduct the study, horizontal structures of the sludge pool that were exposed to the carbonization reaction were taken for the objects under investigation. Defects and damages of the considered structures revealed during visual inspection are described. The degree of carbonization of reinforced concrete structures was determined by the phenolphthalein sample method. According to the results of the technical inspection, a verification calculation of the beam was carried out in order to determine its bearing capacity for assessing the suitability for further operation after restoration and strengthening. The calculation was performed using software. Based on the calculation results, data on the bearing capacity of the beam reinforced with composite materials were determined. The option of restoring and strengthening the beam using external reinforcement based on carbon fibers FibArm 230/150 is presented. The restoration was carried out taking into account the carbonized concrete layer. Based on the results of the study, an assessment is given of the application of an integrated approach to the restoration and strengthening of structures with composite materials, taking into account the carbonized concrete layer

Application of composite reinforcement for modernization of buildings and structures

Properties of new reinforcing element — composite reinforcement, are considered. Feasibility study of using this material for modernization of buildings, namely for vertical extension with additional storey, is carried out. Comparative analysis of performance is conducted for metal and composite reinforcement, as well as calculations are performed which results will be used for determination of advantages and disadvantages of this innovative reinforcing method. An important factor for development of projects of building vertical extension after quite a long operation period is a proper selection of construction materials and strength analysis considering the structures to be erected. Calculation of a floor slab erected with using composite fiberglass reinforcement is represented. Results obtained in the calculation and the analysis of the data prove high efficiency of this reinforcing method through the decrease of loads on lower storeys of the building, economic feasibility and other factors

Mathematical modeling of groundwaters pressure distribution in the underground structures by cylindrical form zone

A mathematical model is developed for studying the distribution of groundwater pressure and its variation in the zone of underground structures of a cylindrical shape. Based on the created model, the influence of the thickness of the aquifer, the soil porosity, the filtration coefficient, the viscosity coefficient and the piezoelectric conductivity coefficient on the pressure that groundwater exerts on the lower part of the underground structure is investigated. The analysis of the possibility of pushing the structure and breaking the foundation under the influence of pressure caused by groundwater is analyzed. Analytical formulas are obtained for estimating the stresses in the foundation and predicting the possibility of its destruction