Thin-walled Concrete Structure Research Articles

Experimental and analytical study of flexural creep of impregnated woven fabric-reinforced concrete

Textile-reinforced concrete (TRC) is a promising composite material that has growing demands in the construction industry. The time-dependent behavior of TRC is a less-studied characteristic of these materials. Since the wide use of TRC in constructing thin-walled concrete structures, the present study performed an experimental and analytical study on the flexural creep of concrete reinforced with resin-impregnated woven fabrics. An analytical viscoelastic model is developed based on multi-scale micromechanics, classical lamination theory, and Alfrey’s correspondence principle to predict the upper and lower limits of creep deformation of TRC. Due to uncertainty observed in the cracking force of TRC, this parameter is considered a random variable with normal distribution. Probabilistic intervals are calculated for TRC midspan creep deflections. Short-term and long-term creep tests are conducted to evaluate the proposed model. The results showed that a probabilistic model is more appropriate to predict the creep behavior of TRC rather than a deterministic model.

Influence of temperature rising inhibitor on temperature and stress field of mass concrete

As a new type of concrete admixture, concrete temperature rising inhibitor (TRI) can slow down the heat release rate of the initial hydration reaction of concrete. However, due to the lack of a clear feasibility analysis, its application in engineering is limited. In this paper, the thermodynamic parameters of concrete with different TRI are obtained by fitting the experimental data. At the same time, taking the sluice as an example, the influence of TRI on the temperature and stress field of mass concrete is studied by numerical simulation. The results show that when the content of TRI reaches 0.6% of the cementitious material, the temperature and stress peak value are obviously reduced, and the temperature control effect is obvious. Furthermore, the effect of TRI is inversely proportional to structure thickness, and its temperature control effect is more noticeable for mass thin-walled concrete structures. Compared with other temperature control measures, such as lowering the peak value of adiabatic temperature rise and the pouring temperature, the effect of TRI is more effective. It can be used as a means of temperature control in engineering and combined with other measures to put forward a more reasonable and economical temperature control scheme.

Estimation of creep and damage accumulation in thin-walled concrete structures

Long-term strength investigations of construction elements made of reinforced concrete (RC) under creep conditions are considered. A calculation method that allows determination of the load-bearing capacity and long-term strength of RC thin-walled elements under short- and long-term loading is proposed. The method is based on a combination of the finite-element method for solving boundary value problems at each time step and the finite-difference method for integrating the initial value problems. The numerical results are compared with experimental data obtained in the loading–unloading mode during long-term deformation. An example of creep and damage calculations in the RC coating and recommendations for parameter selections are given.

The influence of pretensioning on the load-bearing behaviour of concrete beams reinforced with carbon fibre reinforced polymers

High performance concrete (HPC) and carbon fibre reinforced polymers (CFRP) are promising materials with advantageous properties. The authors’ approach is to combine these materials to build light and thin-walled concrete structures. A significant drawback of these filigree constructions is the lower stiffness of the cross section and the relatively low Young’s modulus of the CFRP compared to its high tensile strength. In case of steel reinforced structures, a common practice to optimise the deflection behaviour is by prestressing of the reinforcement. Based on this insight the presented research concentrates on the investigation of the influence of pretensioning on the load-bearing behaviour of concrete beams reinforced with CFRP. A total of 18 beams with four varying parameters were tested. Apart from the influence of the pretensioning force, the influences of the CFRP bar (especially the surface properties), the concrete compressive strength, and the end anchorage were investigated in four-point bending tests.

Durability of fine-grained limestone concrete

Production of effective building materials of high-density and high-durability is connected with the development of methods of modification of such materials on macro-, micro- and nanostructural levels. Presently the application of finest ingredients in admixture compositions such as limestone filler produced from local quarries is viewed as a primary task of cost reduction in limestone concrete manufacturing. The efficiency of limestone filler to enhance the durability of fine-grained limestone concrete is shown in tests performed. Limestone half inert filler conjointly with superplasticizer are found to enhance crack-resistance and reduces creep strains, which makes fine-grained limestone concrete the most effective and long-standing material. Knowledge of the stress-strain distribution in concrete with limestone fines under compression is important for the design of certain kinds of reinforced thin-walled concrete structures, such as shells, membranes and domes. These structures are manufactured with addition of both limestone filler and superplasticizer performing synergetic effect which leads to increasing a level of crack causing stresses.

Mineral-impregnated carbon fibre reinforcement for high temperature resistance of thin-walled concrete structures

For a wide application of carbon-reinforced concrete, the sufficiency of the bond between concrete matrix and reinforcing elements must be ensured, even at high temperatures such as in the case of fire. Mineral-impregnated carbon fibre reinforcement offers a promising alternative to conventional polymer-impregnated carbon yarns or bars, whose performance deteriorates markedly with increasing temperature. One of the challenges in the production of mineral-impregnated carbon fibre reinforcement is the selection of a processing technology and adequate raw materials. The work at hand addresses this challenge while focusing on the influence of the particle-size distribution of mineral fines on the impregnating behaviour of suspensions. Subsequently, the concentration shifts to the mechanical performance of thin reinforcement bars made of mineral-impregnated carbon fibre, as observed in three-point bending and pull-out tests. In comparison to polymer-impregnated reference materials, the new reinforcement demonstrates significantly enhanced mechanical properties at elevated temperatures of 100 °C and 200 °C.

Experience of Concrete Works Execution by the Means of Air-Placed Concreting

This article is devoted to the generalization of production experience of concrete works by means of pneumatic concrete casting, which extends to the production of concrete works on the construction of residential, industrial buildings and other structures, their reconstruction and repair, as well as the manufacture of concrete structures in the factory. The paper considers the technology of production of works in concreting monolithic thin-walled concrete structures by means of pneumatic concrete casting. It is proved the advantages of the method of pneumatic concrete casting. The materials used and the selection of the concrete mix composition are described in detail. The methods of calculation for composition of the concrete mixture, the selection of equipment for the transportation of fine concrete mixtures and mortars, injection, primary and control injection are shown. The differences between pneumatic concrete casting and other methods of guniting are considered. All stages of the production process are described in detail. The article presents the operational characteristics of the installation “pneumatic concrete” for pneumatic concrete casting, in particular, the required amount of compressed air. The description of stages of pneumatic concrete casting is of interest. The issues of the work organization are considered, the service personnel and its duties are given. It is formulated the requirements of safety compliance at work. A detailed description of work technology opens up new opportunities for its improvement. This article will be useful for specialists engaged in the production of concrete works by means of pneumatic concrete casting. The article provides a detailed bibliography on the issue of pneumatic concrete casting, mechanization of production, technology of production of works. The normative documents used in the production of concrete works by the method of pneumatic concrete casting are given.

Cylindrical thin-walled concrete structures under lateral loading

Thin-walled reinforced concrete structures are widely used for water tanks, silos and hydro-power generator buildings. Twenty-two model specimens were tested and then analysed using non-linear finite-element analysis. After reasonable validation with the experimental test results of companion specimens, the analysis was expanded to provide a parametric study correlating the ultimate strength behaviour of modelled specimens to the height-to-diameter ratio and steel reinforcement percentage. Good agreement was observed between the experimental and analysis results. The specimens were analysed to determine the effect of changing the height-to-diameter ratio and the percentage of steel reinforcement and the absence or presence of an opening. The investigation revealed that a reduction in the height-to-diameter ratio and the reinforcement ratio reduced the ultimate moment capacity, ductility, and shear and flexural crack development and also increased the ultimate shear capacity. The formation and propagation of cracks for specimens with and without openings are also explained.

Temperature Control and Anti-Cracking Measures for a High-Performance Concrete Aqueduct

To solve the problem of cracks developing on thin-walled concrete structures during construction, the authors expound on the causes of cracks and the crack mechanism. The difference between external and internal temperatures, basic temperature difference and constraints are the main reasons of crack development on thin-walled concrete structures. Measures such as optimizing concrete mixing ratio, improving construction technology, and reducing temperature difference can prevent thin-walled concrete structures from cracking. Moreover, water-pipe cooling technology commonly used in mass concrete can be applied to thin-walled concrete structures to reduce temperature difference. This method is undoubtedly a breakthrough in anti-cracking technology for thin-walled concrete structures, particularly for thin-walled high-performance concrete structures. In addition, a three-dimensional finite element method is adopted to simulate the calculation of temperature control and anti-cracking effects f. Results show the apparent temperature controlling effect of water-pipe cooling for thin-walled concrete structures.

The Impact of Temperature Difference between Day and Night on Thin-Walled Concrete Structure

When temperature difference between day and night is considered, there are worse effects on thin-walled concrete structure than its on mass concrete structure during construction. In the view of this problem, the 3-D FEM is adopted to simulate the thermal field and stresses field of thin-walled concrete launder during construction when temperature difference between day and night is considered. The simulation results show that the fluctuation of stress will appear not only in the surface but also in the inner of thin-walled concrete structure, so it brings a lot of difficulties for temperature control and crack prevention. In order to reduce the impact degree of temperature difference between day and night, some effective measures should be taken, including enhancing the level of external heat preservation and prolonging the form removal time and so on. If the variation of daily temperature is used to the simulation computation of thin-walled concrete structure during construction, the results should be very reasonable and effective. This research is of practical reference value for the construction of the concrete structure which is built in the area where large temperature difference between day and night easily occurs.

Effect of Cooling Pipe in Thin-Walled Hydraulic Structure during Construction

In view of the problem of concrete crack in the period of construction, this paper introduces the cause and the forming mechanism of crack in thin-walled concrete structure and points out that the difference between the inside and outside temperature at early stage and the basic difference of the temperature at later stage are considered as the main factors influencing the phenomena. This paper puts forward the application of pipe cooling which is used in the mass concrete to the thin-walled concrete structure. In doing so, the difference of the internal and surface temperature is reduced and the appearance of cracking is avoided. Under the basic theories of temperature field and stress field of concrete, the 3-D FEM with the numerical algorithm of pipe cooling is adopted to simulate the thermal field and stresses field of concrete aqueduct during construction and the result shows that good effect of temperature control and crack prevention is achieved in thin-walled concrete structure. At the same time, water cooling pipe has many merits including simple operation, easy adjustment, high adaptability, and low cost

The Impact of Cold Wave Strike on Thin-Walled Concrete Structure

When the cold wave comes, there are worse effects on thin-walled concrete structure than its on mass concrete structure during construction. In the view of this problem, the 3-D FEM is adopted to simulate the thermal field and stresses field of thin-walled concrete launder during construction when it is struck by cold wave. The simulation results show that shrinkage stress in the surface and inner of thin-walled concrete structure will appear and bring a lot of difficulties for temperature control and crack prevention. In order to reduce the impact degree of cold wave strike, some effective measures should be taken, including enhancing the level of external heat preservation and prolonging the form removal time and so on. This research is of practical reference value for the construction of the concrete structure which is built in the area where cold wave easily occurs.

Study on the Application of Cooling Pipe in Thin-Walled Concrete Structure

Cracks of concrete structure easily appear in the period of construction and the difference between the inside and outside temperature at early stage and the basic difference of the temperature at later stage are considered as the main factors causing cracks, so the temperature control becomes the key of problem. In view of this problem, this paper puts forward the pipe cooling technology which is usually used in the mass concrete to the thin-walled concrete structure. Under the basic theories of concrete temperature field and numerical algorithm of pipe cooling, the 3-D FEM is adopted to simulate the thermal field of concrete sluice with and without cooling pipe during construction. The results of comparison show that cooling pipe in thin-walled concrete structure can achieve better effect on temperature control, so it should have great reference signification to similar concrete projects in the future.

Creep buckling of imperfect thin-walled shallow concrete domes

The sensitivity of the nonlinear long-term creep behaviour of shallow concrete domes to geometric and material imperfections is investigated in this paper. A nonlinear incremental theoretical model is developed, which accounts for the effects of creep and shrinkage, considers the aging of the concrete material and the variation of the internal stresses and geometry in time, and is applicable for different and nonaxisymmetric imperfection scenarios and loading schemes. The model focuses only on shallow concrete domes, but the modelling concepts and solution techniques can be generated for the creep buckling analysis of different types of thin-walled concrete structures. The field equations are derived using the variational principles of virtual work and using integral-history-type constitutive relations that are based on the principle of superposition. A step-by-step procedure is used for the solution of the governing equations in time, while the solution of the incremental partial differential equations in space is achieved by a separation of variables and expansion into truncated Fourier series in the circumferential direction, along with the use of the multiple shooting method in the meridional direction. Numerical and parametric studies, which highlight the capabilities of the model and which provide insight into the nonlinear long-term behaviour of imperfect shallow concrete domes, are presented. The results show that the structural behaviour and the critical time to cause creep buckling are very sensitive to geometric and material imperfections.

Use of epoxy compounds in structural elements and insulation in the Kislogubsk tidal power station

1. Epoxy foam heat-and-water insulation and epoxy-pitch waterproofing have been found to be suitable for structures in regions with a severe climate, and in particular for tidal power stations built by the floating method. 2. Industrial experience in the construction of the Kislogubsk tidal power station has shown the advantages of using epoxy plastic solutions for constructing waterproofing seams and repairing defects in the concreting of thin-walled concrete structures. 3. The coating technology is simple and requires no special equipment. 4. Subsequent service experience of the concrete structures of the Kislogubsk tidal power station and insulating coatings in the Barents Sea confirms the long life of the compositions used, and the results can be taken into consideration when devising new types of sheathing.