A Theoretical Model for Debonding Prediction in the RC Beams Externally Strengthened with Steel Strip and Inorganic Matrix

This paper shows a theoretical model for predicting the moment–curvature/load–deflection relationships and debonding failure of reinforced concrete (RC) beams externally strengthened with steel reinforced geopolymeric matrix (SRGM) or steel reinforced grout (SRG) systems. Force equilibrium and strain compatibility equations for a beam section divided into several segments are numerically solved using non-linear behaviour of concrete and internal steel bars. The deflection is then obtained from the flexural stiffness at a mid-span section. Considering the appropriate SRGM-concrete bond–slip law, calibrated on single-lap shear bond tests, both end and intermediate debonding failures are analysed. To predict the end debonding, an anchorage strength model is adopted. To predict intermediate debonding, at each pair of flexural cracks a shear stress limitation is placed at concrete–matrix interface and the differential problem is solved at steel strip–matrix interface. Based on the theoretical predictions, the comparisons with experimental data show that the proposed model can accurately predict the structural response of SRGM/SRG strengthened RC beams. It can be a useful tool for evaluating the behaviour of externally strengthened RC beams, avoiding experimental tests.

New Multistrain Bacterial Consortium for Feed Probiotics

Introduction. Multistrain probiotics often include biocompatible strains, which leads to suppression of microbial viability and, as a result, decreases their efficacy. Therefore, new probiotics should be based on well-matched strains with no antagonism. Study objects and methods. The research featured strains of lactic and propionic acid bacteria from the VNIIPBT collection. The method of direct co-cultivation on dense medium (drop technique) was used to assess the biocompatibility of lactic acid bacteria. Antagonism was detected visually based on signs of suppression after 24 and 48 h after the onset of incubation. Antagonism of the consortia was assessed by the Romanovich method. Results and discussion. The screening resulted in seven promising strains with the specific growth rate of 0.32–0.84 h–1 and the maximum population density ≤ 2.2 billion CFU/cm3. A set of experiments on the strain adaptation mechanisms revealed combinations of strains with the lowest antagonism and competition for the substrate. The research resulted in a four-component consortium of Lactobacillus plantarum 314/8, Lactobacillus helveticus R0052/6, Enterococcus faecium B-2240D, and Propionibacterium freudenreichii subsp. shermanii 103/27. The optimal ratio was the one where the cultures were present in equal proportions. The study also described the biosynthetic properties of the consortium and the ratio of the strains in its composition. The consortium demonstrated a balanced growth, good strain compatibility, and absence of antagonism. The cultivation mode was tested anaerobically on milk whey at 37°C for 24 h (strain ratio = 1:1:1:1). Conclusion. The new consortium proved suitable for industrial production of feed probiotics.

Bond Degradation and Residual Flexural Capacity of Corroded RC Beams

An analytical model is developed to predict the residual flexural capacity of corroded RC members. This was established by first developing an analytical model to calculate the residual bond strength at steel-concrete interface. The bond model is then implemented within the framework of the moment resistance method, and a new strain compatibility analysis was developed: to account the analysis of a corroded reinforced concrete beam, to incorporate dependence of the bond response on the stress strain and damage state of the concrete and steel. Method for calculating flexural capacity of corroded RC beams is then proposed, which is based on flexural analysis of RC beams that considers the effect of bond degradation. The predicted results of these models correlated very well with results observed in various experimental studies. This indicates that those developed analytical models tend to estimate conservatively the residual bond strength and flexural capacity of corroded RC beams. .

Flexural (Moment) Capacity of Ultra-high Performance Fiber Reinforced Concrete Beams

Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) is a relatively new generation of cementitious material exhibiting exceptional mechanical characteristics. One of the main applications of this new material is strengthening existing bridges and the construction of new Igirders during the rehabilitation process. Previous research on (UHPFRC) beam girders and prestressed girders found the analytical moment capacity to be 76% of the experimental (test) results. A method based on strain compatibility, equilibrium and the stress-strain relationships is developed to determine the flexural capacity of UHPFRC beams with about 90% accuracy between experimental and numerical capacities. A testing program of five beam specimens is conducted at Ryerson University Structural Laboratory to verify the experimental results. Furthermore, the results of the finite element numerical simulation of ABAQUS software using concrete damage plasticity (CDP) constitutive model predict the flexural capacity of the tested UHPFRC beams reasonably well.

Bond Degradation and Residual Flexural Capacity of Corroded RC Beams

An analytical model is developed to predict the residual flexural capacity of corroded RC members. This was established by first developing an analytical model to calculate the residual bond strength at steel-concrete interface. The bond model is then implemented within the framework of the moment resistance method, and a new strain compatibility analysis was developed: to account the analysis of a corroded reinforced concrete beam, to incorporate dependence of the bond response on the stress strain and damage state of the concrete and steel. Method for calculating flexural capacity of corroded RC beams is then proposed, which is based on flexural analysis of RC beams that considers the effect of bond degradation. The predicted results of these models correlated very well with results observed in various experimental studies. This indicates that those developed analytical models tend to estimate conservatively the residual bond strength and flexural capacity of corroded RC beams. .

Flexural (Moment) Capacity of Ultra-high Performance Fiber Reinforced Concrete Beams

Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) is a relatively new generation of cementitious material exhibiting exceptional mechanical characteristics. One of the main applications of this new material is strengthening existing bridges and the construction of new Igirders during the rehabilitation process. Previous research on (UHPFRC) beam girders and prestressed girders found the analytical moment capacity to be 76% of the experimental (test) results. A method based on strain compatibility, equilibrium and the stress-strain relationships is developed to determine the flexural capacity of UHPFRC beams with about 90% accuracy between experimental and numerical capacities. A testing program of five beam specimens is conducted at Ryerson University Structural Laboratory to verify the experimental results. Furthermore, the results of the finite element numerical simulation of ABAQUS software using concrete damage plasticity (CDP) constitutive model predict the flexural capacity of the tested UHPFRC beams reasonably well.

Strain Field Development of a Rectangular Dislocation Loop in a Semi-Infinite Medium with Verification

This paper considers a rectangular Volterra dislocation loop lying beneath and parallel to a free surface in a semi-infinite material. The paper utilizes the displacement field of an infinitesimal dislocation loop to obtain the strain field and then integrate over a finite rectangular area. For the loop, it can have three non-zero Burgers vector components. The stress field is also obtained from Hooke’s law for isotropic materials. Analytical and numerical verifications of the strain and stress fields are performed. In addition, the effect of the free surface on stresses is displayed versus depth from the surface. Verification includes satisfaction of the zero-traction boundary condition, the stress equilibrium equations and the strain compatibility equations.

Design and verification of reinforced concrete shell elements

abstract: Reinforced concrete shell elements are relevant in several civil and industrial structures. It is important to know the methods for designing and verifying such elements. In this context, the present paper aims at describing the iterative three-layer method proposed by Colombo et al. This method is based on the Model Code/1990, and it can be applied in the design of shell elements. An additional method for verifying reinforced concrete shell elements is also proposed and discussed. This one is based on the multilayer method proposed by Kollegger et al. Formulations as well as numerical examples are presented for both methods. The design proposed by Colombo et al. is verified by using the methodology based on the multilayer method. Although both methods lead to the equilibrium between applied and resistance loads using approximately the same amount of reinforcement, especially for small neutral axes in relation to the element thickness, one may conclude that the three-layer design method has limitations due to not considering strain compatibility along the thickness of the element and due to the impossibility to calculate the compression reinforcement. Although the multilayer method overcomes such limitations, it is a verification method, and more studies about its use in the design of reinforced concrete shell elements are necessary.