Bearing Capacity Of Concrete Structures Research Articles

Prediction Model for Fracture Toughness of Waterborne Polyurethane Modified Concrete at Different Temperatures

In certain extreme environments, the bearing capacity of concrete structures diminishes significantly as temperatures soar, simultaneously exposing them to a heightened risk of brittle cracking. The paper aims to elucidate the fracture toughness of waterborne polyurethane modified concrete (WPMC) at different temperatures. Furthermore, a predictive model for the fracture toughness of WPMC, which incorporates both temperature and the waterborne polyurethane (WP) content, is proposed. The flexural strength and fracture toughness of WPMC were tested separately at 20℃, 40℃, 60℃, and 80℃. Utilizing digital image correlation (DIC) technology, the bottom longitudinal strain of WPMC under flexural loading was analyzed. The impact of temperature and WP content on the energy absorption capacity and deformation behavior of WPMC exposed to extreme environment was also investigated. By introducing the microstructural parameters C and Cw to characterize the elastic and plastic deformations of WPMC before and after cracking, a fitting model between the microstructural parameters and temperature, WP content was established. This model enables the prediction of the fracture toughness KIC of WPMC at different temperatures by measuring Fmax.

Numerical simulation on the load-bearing capacity of CFRP-strengthened concrete arches

To investigate the bearing capacity of concrete structures strengthened by carbon fiber reinforced composite (CFRP), this study conducted numerical simulation research on seven CFRP-strengthened concrete arch structures with five different strengthening schemes. The finite element model was established by HYPERMESH, the simulation results were compared with the experimental results to verify the accuracy of the model. Based on this, the interfacial bonding performance of concrete and CFRP under different strengthening schemes was analyzed, and the static damage mode of the reinforced concrete arch structure was revealed. The results indicate that the application of CFRP to the surface of a concrete arch will increase the linear segmental stiffness, cracking load, and ultimate load of the structure. The five strengthening schemes in this paper provide enhancements ranging from 2.9 % to 57.6 % for concrete arch cracking loads, from 3.3 % to 14.7 % for ultimate loads, and from 1.1 % to 17.6 % for stiffness. If both the inner and outer sides are strengthened with CFRP, the ultimate bearing capacity of the arch structure can be significantly enhanced. Circumferential wrapping of CFRP can delay the concrete cracking and further enhance the bearing capacity of the arch, and the strengthening effect can be maximized. This study can provide a valuable reference for the strengthening of old concrete arch structures and the construction of newly assembled arch tunnels.

Experimental Analysis of Bearing Capacity of Basalt Fiber Reinforced Concrete Short Columns under Axial Compression

Adding basalt fiber to concrete can improve the mechanical properties of concrete, and it is also one of the best ways to enhance the ultimate bearing capacity of concrete structure. In this paper, the construction performance and the compressive strength of basalt-fiber-reinforced concrete (BFRC) with five kinds of fiber lengths and eight kinds of fiber volume content subjected to an axial load are systematically investigated. The optimum fiber length and fiber volume content are obtained by comprehensively considering the construction performance and compressive strength. Moreover, the prediction model and finite element analysis method of the ultimate bearing capacity of basalt-fiber-reinforced concrete are developed. The results show that the optimum fiber length is about 12–24 mm and the fiber volume content is 0.15%. Adding an appropriate amount of basalt fiber can effectively improve the ultimate bearing capacity of concrete short columns, with maximum and average increases of 28% and 24%, respectively. In addition, the comparison with the experimental results shows that both the proposed prediction method and the finite element modeling method have good applicability, and they can be used to predict the ultimate bearing capacity of the BRFC short columns in practical engineering.

Simulation analysis of the influence of Carbon Fiber Reinforced Polymer (CFRP) on the load bearing capacity of reinforced concrete beams by finite element method using ANSYS APDL software

In recent years, the need to upgrade and increase the load bearing capacity of concrete structures has become popular due to the deterioration of constructions after long use; or due to the demand of owners. One among popular reinforcement methods today is to use Carbon Fiber Reinforced Polymer (CFRP) to strengthen the tensile zone of the concrete structure. The installation of this method is rapid and convenient. However, the technical instructions for installation is still limited in Vietnam due to the time-consuming and high cost of experiments. This research presents a numerical simulation study on the load bearing capacity of reinforced concrete beams strengthened with CFRP via the finite element method (using ANSYS APDL software) and compares the findings with experimental result afterwardss. The results show that ANSYS APDL software can accurately analyze the mechanical behavior of RC beams strengthened with CFRP. The research results can be expand to further analyze stress, deformation, and simultaneously investigate other factors that may influence RC beams strengthened with CFRP.

Residual fracture energy of concrete suffering from fatigue loading

To investigate the degradation of the residual fracture energy of concrete suffering from fatigue loading, 150 three-point bending (TPB) beams were first subjected to a fatigue load until the preset number of fatigue cycles was reached, and then the static load was applied to these specimens until failure occurred. Based on the equilibrium relationship between the energy dissipated by the fatigue fracture process zone (FPZ) under static loading and the external work, a calculation method for the residual fracture energy of concrete suffering from fatigue loading was proposed. The effects of the number of fatigue cycles, the fatigue crack opening displacement, and the fatigue load level on the residual fracture energy of concrete were evaluated, and an empirical model for predicting the residual fracture energy was proposed. The results showed that in the initial stage of fatigue loading, there was a rapid drop of the residual fracture energy with a decelerated degradation rate. With the increases of the number of fatigue cycles and the fatigue crack opening displacement, a stable degradation stage of the residual fracture energy with an approximately constant degradation rate was observed. Furthermore, with the decreasing fatigue load level, the residual fracture energy increased for the same fatigue cycles, while the residual fracture energy decreased for the same fatigue crack opening displacement. The residual fracture energy obtained in this study is essential for the numerical calculation of the residual bearing capacity of concrete structures.

Damage evaluation method based on ultrasound technique for gangue concrete under freezing-thawing cycles

As a major industrial waste, gangue has significant environmental, economic, and social benefits when used in the preparation of concrete. The durability and bearing capacity of concrete structures in cold regions are affected by freeze-thaw damage. Therefore, the damage evolution behavior and degree of gangue concrete damage under a freeze–thaw environment should be accurately evaluated. In this paper, rapid freeze-thaw tests were carried out on gangue concrete with volume replacement ratios of 0%, 20%, 40%, and 60% coarse aggregate. The compressive strength and water absorption properties of gangue concrete were tested, and the changing rules of them were analyzed. In addition, the damaged layer thickness of gangue concrete was tested by ultrasonic nondestructive testing technology. The eigenvalue of the damage layer and the residual strength of the material in the damaged area were considered. The correction coefficient was introduced to modify the measured damaged layer thickness. A method for evaluating freeze–thaw damage in gangue concrete on the basis of damaged layer thickness was proposed. Results showed that the compressive strength and damage layer characteristic value of gangue concrete decreased gradually with the increase of freeze–thaw cycles, whereas the water absorption depth, damage layer thickness, and damage degree increased gradually; change rate increased with the replacement rate of gangue. With the increase of the replacement rate of gangue, the frost resistance of gangue concrete decreased obviously, whereas the damage deterioration rate increased. After introducing the damage layer correction coefficient, the accuracy of the evaluated degree of freeze–thaw damage increased significantly. Correction coefficient increased gradually with freeze–thaw time, indicating that the evolution of the residual strength of materials in the damage area decreased continuously and the actual degree of damage increased gradually.

Structural safety reliability of concrete buildings of HTR-PM in accidental double-ended break of hot gas ducts

Abstract Safety analysis of nuclear power plant (NPP) especially in accident conditions is a basic and necessary issue for applications and commercialization of reactors. Many previous researches and development works have been conducted. However, most achievements focused on the safety reliability of primary pressure system vessels. Few literatures studied the structural safety of huge concrete structures surrounding primary pressure system, especially for the fourth generation NPP which allows existing of through cracks. In this paper, structural safety reliability of concrete structures of HTR-PM in accidental double-ended break of hot gas ducts was studied by Exceedance Probability Method. It was calculated by Monte Carlo approaches applying numerical simulations by Abaqus. Damage parameters were proposed and used to define the property of concrete, which can perfectly describe the crack state of concrete structures. Calculation results indicated that functional failure determined by deterministic safety analysis was decided by the crack resistance capability of containment buildings, whereas the bearing capacity of concrete structures possess a high safety margin. The failure probability of concrete structures during an accident of double-ended break of hot gas ducts will be 31.18%. Adding the consideration the contingency occurrence probability of the accident, probability of functional failure is sufficiently low.

Determination of mechanical properties of normal strength limestone concrete after exposure to elevated temperatures

Fire resistance is one of the essential requirements that has to be considered in the design process of any structure. Methods for ensuring fire resistance of new structures are therefore, relatively well developed. Thus, loss of bearing capacity of a concrete structure during fire is relatively well known and documented, while determination of remaining bearing capacity of concrete structure after fire is less known. This can mainly be attributed to the lack of adequate knowledge of mechanical properties of concrete after fire, duration of fire exposure, heating rate, and maximum temperatures reached in the structure during fire. These factors have to be taken into account when making a decision on the rationality of the structure’s restoration. Estimation of bearing capacity of concrete structures after fire depends on precise but difficult determination of temperature dependent changes in material. Bearing capacity of structures after fire is in general, often assessed with simplified procedures and experimental investigation. These mainly covers visual inspection of the damaged structure and the execution of some standard, mostly destructive tests. Such tests are precise, but often difficult to implement, expensive, time-consuming, limited to certain pre-selected locations and can somehow weaken the individual structural element. Therefore, in order to determine bearing capacity of concrete structure after fire, various non-destructive methods are being developed. Among these, different ultrasonic (US) tests are frequently used and well described in the literature. These results indicate good connection between US pulse velocity and concrete compressive strength after exposure to elevated temperatures.This article presents the first part of the ongoing research. Main goal of the research is to develop a numerical method based on artificial neural network approach to estimate concrete properties after fire using non-destructive tests. In this paper, results of destructive and non-destructive tests are presented and analyzed to determine changes in basic mechanical properties of standard concrete mixture after exposure to elevated temperatures, namely 200 °C, 400 °C, 600 °C, or 800 °C. With the aim of separating ‘material’ and ‘structural’ effects, temperature gradients within the concrete specimens, were minimized, as possible. Prior experimental testing, the damage to the concrete was roughly detected by observing the specimen’s surface. Compressive strength, tensile strength, surface hardness, dynamic elastic modulus, and shear modulus are determined. It is noticed that crack formation at 400 °C has an influence on reduction of the US pulse velocity, tensile strength, dynamic elastic, and shear modulus. Analysis of variance is used for assessing the experimental results sensitivity on temperature elevation. It is noticed that US method detects statistically significant impact of elevated temperatures on US pulse velocity. On the other hand, rebound hammer technique indicates statistically significant impact of elevated temperatures on concrete surface hardness between 400 °C and 600 °C.

An Engineering Heat and Mass Transport Model Utilized for Concrete at Fire

Mathematical models which can sufficiently describe processes proceeding in concrete during fire play an important role when assessing a load bearing capacity of concrete structures. In this paper a coupled heat and mass transport model based on principles of conservation of mass and energy is presented. A 2D computational solver using FEM was created to find three unknowns – a temperature, an amount of free water and a magnitude of pore pressure in concrete cross section during rapid heating. These variables, mutually connected through state equation, are necessary not only for determination the load bearing capacity of concrete element but also for prediction of concrete spalling. A parametric study of numerical results influenced by material properties of concrete (e.g. permeability, thermal conductivity) and initial conditions (e.g. relative humidity, temperature) is introduced and discussed in the end.

Monitoring of Grouting Compactness in a Post-Tensioning Tendon Duct Using Piezoceramic Transducers.

A post-tensioning tendon duct filled with grout can effectively prevent corrosion of the reinforcement, maintain bonding behavior between the reinforcement and concrete, and enhance the load bearing capacity of concrete structures. In practice, grouting of the post-tensioning tendon ducts always causes quality problems, which may reduce structural integrity and service life, and even cause accidents. However, monitoring of the grouting compactness is still a challenge due to the invisibility of the grout in the duct during the grouting process. This paper presents a stress wave-based active sensing approach using piezoceramic transducers to monitor the grouting compactness in real time. A segment of a commercial tendon duct was used as research object in this study. One lead zirconate titanate (PZT) piezoceramic transducer with marble protection, called a smart aggregate (SA), was bonded on the tendon and installed in the tendon duct. Two PZT patch sensors were mounted on the top outside surface of the duct, and one PZT patch sensor was bonded on the bottom outside surface of the tendon duct. In the active sensing approach, the SA was used as an actuator to generate a stress wave and the PZT sensors were utilized to detect the wave response. Cement or grout in the duct functions as a wave conduit, which can propagate the stress wave. If the cement or grout is not fully filled in the tendon duct, the top PZT sensors cannot receive much stress wave energy. The experimental procedures simulated four stages during the grout pouring process, which includes empty status, half grouting, 90% grouting, and full grouting of the duct. Experimental results show that the bottom PZT sensor can detect the signal when the grout level increases towards 50%, when a conduit between the SA and PZT sensor is formed. The top PZT sensors cannot receive any signal until the grout process is completely finished. The wavelet packet-based energy analysis was adopted in this research to compute the total signal energy received by PZT sensors. Experimental results show that the energy levels of the PZT sensors can reflect the degree of grouting compactness in the duct. The proposed method has the potential to be implemented to monitor the tendon duct grouting compactness of the reinforced concrete structures with post tensioning.

Application FRP-rebar in the Manufacture of Reinforced Concrete Structures

Reinforced concrete is one of the first places in terms of use in various areas of construction. This is primarily determined by its relative cheapness and durability. Concrete Durability significantly associated with metal reinforcement durability. Durability depends upon the metal reinforcement corrosion that occurs under the influence of an aggressive environment. As a result, corrosion of the metallic reinforcement and, to some extent, of the concrete, there is a loss of bearing capacity of concrete structures in general and buildings. To ensure the durability of concrete structures is necessary to take measures against the development of concrete and reinforcement corrosion. The object of the study are reinforced concrete constructions basalt reinforcement. Restore the bearing capacity of reinforced concrete structures with corroded reinforcement is possible using known design techniques.However, essentially no use of technology in the construction field and specific data on the bearing capacity of concrete structures with basalt reinforcement. No complete information on the value of its adhesion to concrete and its dependence: the composition of concrete and its method of compression; treatment of the outer surface of basalt reinforcement in various ways to increase its adhesion to concrete; destruction of the nature of such structures from the effects of external loads.The search for alternative ways of replacement of the metal reinforcement in concrete structures bearing on the composite, not subject to corrosion and, at the same time having a high load-bearing capacity, is the actual research task. It is known that composite materials to minimize corrosion and other security and environmental impact. At the same time, they must be extremely reliable to manufacture environmentally friendly and does not emit harmful substances polluting the environment.Currently, intensive research to find ways to replace metal in structures of the other valves. An example of such research is to create different types of plastics, which are gradually replacing it. Work is underway in the field of replacement of the metal reinforcement in the non-metallic fittings on the basis of modern composite materials.A major breakthrough in this direction in recent years was the opening of “basaltic technology” that allowed the “update” the base of building materials for new building designs types of valves.

El Eurocódigo 2 y la evaluación de estructuras de hormigón armado con armaduras corroídas

The reinforcement corrosion is one of the major problems with relevant economic impact in the life cycle of concrete structures and that is why it is necessary to optimize the repair strategies in corroded structures. However, almost no international codes are available for structural evaluation and some criteria will be included in the revision of Eurocode 2 to evaluate existing deteriorated structures. A summary of Contecvet project funded EC is presented in this paper as well as some more recent developments. A first step in the evaluation of existing structures is to identify if the aggressive has reached the reinforcement and how much has affected to the structural performance. As soon as the corrosion rate has been calculated from the data taken in the structure, it is possible to estimate the rate of the structural deterioration process through the developed models and the remaining service life. Some models and expressions are summarized to estimate the residual bearing capacity of concrete structures with corroded reinforcement to be considered when drafting the new Eurocode 2.

Research on Bearing Capacity of Prestressed Concrete T-Beam at High Temperature in Fire

The bearing capacity of bridge structure would decrease under high temperature in fire, and there is a risk of structural collapse when the bearing capacity decreased to a certain degree. The estimate of bearing capacity of concrete structure at high temperature in fire will directly influence the scheme of disaster relief. Recently, there are a few researches on evaluating the bearing capacity of concrete structure at high temperature in fire, even fewer on bearing capacity of prestressed structure. Surface temperature and temperature of internal specific position of prestressed concrete T-beam are put forward in this paper by making use of ISO 834 international standard heating curve and distribution rules of temperature field of ASCE. The degradation of mechanical properties of concrete, steel bar, steel strand and other materials at high temperature are worked out according to relationships between material mechanical properties and high temperature, and on this basis, the bearing capacity of 3 prestressed concrete T-beams are calculated and evaluated at high temperature in fire. The results show that after being under 3-hour's high temperature in fire, the bearing capacity in high temperature of prestressed concrete T-beam would decreased to it’s 25% in normal; the stronger the concrete is or the thinner the concrete cover is, the greater decrease of bearing capacity of prestressed concrete T-beam would be. Based on calculations and evaluations, a statistics regression equation of bearing capacity of prestressed concrete T-beam at high temperature in fire is obtained.

Chemoporoplasticity of Calcium Leaching in Concrete

This paper presents a macroscopic material model for calcium leaching in concrete, for the quantitative assessment, in time and space, of the aging kinetics and load bearing capacity of concrete structures subjected to severe chemical degradation (such as radioactive waste disposal applications). Set within the framework of chemically reactive porous continua, the model accounts explicitly for the leaching of calcium of portlandite crystals and C-S-H, and its cross-effects with the elastic deformation (chemical damage) and irreversible skeleton deformations (chemical softening) treated within the theory of chemoplasticity. In the first part of this paper the governing equations are derived focusing on the chemomechanical couplings between calcium dissolution, increase in porosity, and deformation and (micro-) cracking of concrete. Without any a priori assumption concerning local equilibrium between the solid calcium concentration s and the interstitial calcium concentration c the well-known calcium leachi...