Strain Compatibility Research Articles

Time for change? A systematic review with meta-analysis of leptospires infecting dogs to assess vaccine compatibility in Brazil.

Dogs are thought to be highly exposed to environmental pathogenic leptospires, possibly acting as potential sources of infection for zoonotic transmission. Vaccination stands as the cornerstone strategy to prevent disease and urinary shedding in dogs, yet the success of vaccination is highly dependent on the correspondence of leptospires circulating locally with those used in vaccine compositions. To provide evidence for vaccine compatibility, and to assess whether there are regional differences on serogroup distribution, we conducted a systematic review with meta-analysis on serological data, characterization of leptospiral isolates and risk factors for seropositivity in dogs from Brazil. Studies reporting canine leptospirosis within the Brazilian territory were eligible for inclusion, and methodology was validated by PROSPERO under registration CRD42020204187. Six electronic databases were searched, and data regarding population, methods, and outcomes were extracted. Sixty-one studies were included to access serogroup distribution and risk factors, with a pooled positivity rate of 19.7% in dog population. Serological evidence indicates that Canicola, Icterohaemorrhagiae and Autumnalis are the most frequently found serogroups. Twenty-eight records were included to access leptospiral strains isolated in Brazil, with n=56 strains characterized as serogroups Canicola, n=37 as Icterohaemorrhagiae, n=2 as Pomona, and n=1 strain as Australis and Sejroe each. Risk factor analysis revealed that stray dogs, puppies or elderly dogs, male dogs and dogs kept by tutors with poor social and economic conditions are at high risk for infection. The present study revealed overall good compatibility of leptospiral strains circulating locally with those used in vaccines against canine leptospirosis in Brazil. The circulation of serovars Pomona and Grippotyphosa has not been consistently demonstrated, and the inclusion of these serovars in local vaccines cannot be supported by our results. The results also provided serological evidence for the circulation of Serogroup Autumnalis among the studied populations.

A new approach to numerical simulation of boundary value problems of the theory of elasticity in stresses and strains

The main parameters characterizing the process of deformation of solids are displacements, strain and stress tensors. From the point of view of the strength and reliability of the structure and its elements, researchers and engineers are mainly interested in the distribution of stresses in the objects under study. Unfortunately, all boundary value problems are formulated and solved in solid mechanics mainly with respect to displacements, or an additional stress functions. And the required stresses are calculated from known displacements or stress functions. In this case, the accuracy of stress calculation is strongly affected by the error of numerical differentiation, as well as the approximation order of the boundary conditions. The formulation of boundary value problems directly with respect to stresses or strains allows to increase the accuracy of stress calculation by bypassing the process of numerical differentiation.
 Therefore, the present work is devoted to the formulation and numerical solution of boundary value problems directly with respect to stresses and strains. Using the well-known Beltrami-Miеchell equation, and considering the equilibrium equation as ah additional boundary condition, a boundary value problem(BVP) is formulated directly with respect to stresses. In a similar way, using the strain compatibility condition, the Beltrami-Mitchell type equations for strains are written.
 The finite difference equations for two-dimensional BVP are constructed and written in convenient a form for the use of iterative method. A number of problems on the equilibrium of a rectangular plate under the action of various loads applied on opposite sides are numerically solved. The reliability of the results is ensured by comparing the numerical results of the 2D elasticity problems in stresses and strains, and with the exact solution, as well as with the known solutions of the plate tension problem under parabolic and uniformly distributed loads

Experimental and Numerical Investigation of the Behavior of Steel Beams Strengthened by Bolted Hybrid FRP Composites

The strengthening of steel beams using hybrid fiber-reinforced polymers (HFRPs) has gained enormous attention over the last decades. Few researchers have investigated the effectiveness of the fastening techniques without a bonding agent to overcome the undesirable debonding failure of the bonded FRP–steel system. This paper reports the outcomes of experimental and numerical investigations conducted on steel beams strengthened by HFRP using steel bolts. Twenty-two steel beams were tested in four-point loading to investigate the effect of the HFRP length and the bolt arrangement on the flexural behavior of the strengthened systems. The observed failure modes, load-deflection relations, deflection profiles, and strain measurements were also studied. The tested beams showed a ductile behavior, with 15.1 and 22.2% enhancements in the yield and ultimate flexural capacities, respectively. Simplified empirical equations were developed to predict the ultimate load of the bolted HFRP–steel beams. ANSYS software was used to model the beams’ behavior and investigate the effects of the HFRP thickness, bolt spacing, steel grade, loading scheme, and beam length on the effectiveness of the adopted fastening technique. Increasing the HFRP length enhanced the utilization of HFRPs as well as the beam’s ductility, with a reduction of up to 51.2% in the mid-span deflection. Moreover, the strain compatibility of the HFRP–steel beams was improved with an 87.2% reduction in the interfacial slippage. The bolt arrangement showed an insignificant effect on the overall performance of the beams. The numerical results verified the effectiveness of the fastening technique in enhancing the flexural performance of the steel beams, with gains of up to 16.7% and 34.5% in the yield and ultimate load-carrying capacities, respectively.

Roles of cooling rate of undercooled austenite on isothermal transformation kinetics, microstructure, and impact toughness of bainitic steel

At present, the application of extra thick super bainite steel has attracted considerable attention. In this paper, medium carbon bainite steel is taken as the research object, and the effects of the cooling rate of undercooled austenite on the transformation kinetics, microstructure and mechanical properties of bainite steel are studied systematically. The results show that the incubation period of bainite shortens and the transformation kinetics accelerates with the decrease of the cooling rate of undercooled austenite. The segregation of solute atoms at a slow cooling rate shortens the incubation period. When bainite nucleates and grows by an autocatalytic method, the size of the untransformed austenite is large and the strain compatibility is strong, leading to low activation energy of its autocatalytic nucleation and accelerating the kinetics of bainite transformation. The size of block structure and the length of bainite sheaves decrease with the increase of cooling rate. The impact toughness of the sample with a cooling rate of 30 °C/s is twice as high as that of the sample with a cooling rate of 0.3 °C/s. As the smallest unit to control the toughness of bainite steel, block structure affects the impact toughness. The impact toughness of bainite increases with the decrease of its block size. The content of film-like retained austenite increases with the increase of cooling rate, which is also one of the factors of excellent impact toughness of bainite at high cooling rate.

Effect of ECC layer thickness and reinforcement ratio on the load carrying capacity of steel‐reinforced composite beams

AbstractThe present study investigates the effect of Engineered Cementitious Composites (ECC) layer thickness against various reinforcement ratios on the flexural performance of reinforced ECC–concrete composite beams. In total, 20 reinforced composite beams are selected from the literature to predict their flexural response using Finite Element (FE) analysis. In addition to the FE analyses, a detailed analytical study is performed using the strain compatibility procedure to predict the flexural strength of ECC–concrete composite beams. The results from the FE analyses are compared against the experimental results and are found to show a close agreement. Using the validated FE models, detailed parametric studies are conducted to determine the effectiveness of different design parameters such as (a) ECC height replacement for a reinforcement ratio, (b) reinforcement ratio for an ECC height replacement, and (c) adequate reinforcement ratio for effective strengthening. The results of the parametric study show that the use of 0.4 ECC height replacement ratio and 1.70% steel reinforcement ratio exhibit better load‐carrying capacity in ECC–concrete composite beams. The effective tensile reinforcement ratio for the ECC–concrete composite beams from minimum to maximum varies in the range of 0.92%–1.85%, respectively. The moment capacities predicted from the section analysis is in good agreement with the experimental and numerical moment capacities.

Management of take-all disease caused by Gaeumannomyces graminis var. tritici in wheat through Bacillus subtilis strains.

Wheat (Triticum aestivum) is the second largest grain crop worldwide, and one of the three major grain crops produced in China. Take-all disease, caused by Gaeumannomyces graminis var. tritici (Ggt) infection, is a widespread and devastating soil-borne disease that harms wheat production. At present, the prevention and control of wheat take-all depend largely on the application of chemical pesticides. Chemical pesticides, however, not only lead to increased drug resistance of pathogens but also leave significant residues in the soil, causing serious environmental pollution. In this study, we investigated the application of Bacillus subtilis to achieve take-all disease control in wheat while reducing pesticide application. Antagonistic bacteria were screened by plate test, species identification of strains was performed by Gram staining and sequencing of 16s rDNA, secondary metabolite activity of strains was detected by clear circle method, strain compatibility and effect of compounding on Ggt were detected by plate, and the application prospects of specific strains were analyzed by greenhouse and field experiments. We found that five B. subtilis strains, JY122, JY214, ZY133, NW03, Z-14, had significant antagonistic effects against Ggt, and could secrete antimicrobial proteins including amylase, protease, and cellulase. Furthermore, Z-14 and JY214 cultures have also been shown to change the morphology of Ggt mycelium. These results also showed that Z-14, JY214, and their combination can control take-all disease in wheat at a reduced level of pesticide use. In summary, we screened two Bacillus spp. strains, Z-14 and JY214, that could act as antagonists that contribute to the biological control of wheat take-all disease. These findings provide resources and ideas for controlling crop diseases in an environmentally friendly manner.

Halophilic soil microbial strains improve the moisture stress tolerance in oilseed crop by sustaining Photosystem II functionality

The sunflower (Helianthus annus L.) is a vital oilseed crop exposed to drought globally. A vast proportion of research is devoted to the naturally occurring microbes and their interaction with plants to alleviate stress consequences. Halophilic bacterial strains, i.e., Bacillus cereus KUB-15 (accession number NR 074540.1), KUB-27 (accession number NR 074540.1), and Bacillus licheniformis strain AAB9 (accession number MW362506), were isolated. Later, isolated strains were used for sunflower through inoculation. Plants were allowed to grow, and thirty-days-old plants were exposed to fixed moisture stress (40–45%). The functionality of photosystem II, light-harvesting ability, and physiological tolerance of cultivars were examined. Bacterial strains B. licheniformis sustained substantial electron flow in between photosystem II (PS II) and photosystem I (PS 1) that not only favored the passable photosynthetic performance but also enhanced antioxidant enzyme activity under stress condition. Compared to other halophilic strains, Bacillus licheniformis did manage reasonable relative water content (RWC), chlorophyll content index (CCI) and biomass production under stress condition. In comparison to both sunflower cultivars, bacterial inoculation was greatly restored growth and photosynthetic performance in Agsun-5264 than S-278 under moisture stress environment. Hence, it is suggested that that bacterial strain and plants cultivar compatibility are essential aspect for sustainable agriculture production.

Fractional and fractal derivative-based creep models for concrete under constant and time-varying loading

In this paper, fractional and fractal derivative-based viscoelastic laws are adopted to develop linear creep models for reinforced and prestressed concrete under constant and time-varying loading. The model parameters are determined by curve-fitting the creep compliances of the spingpot and Kelvin-Voigt viscoelastic models to experimental data of basic creep in plain concrete specimens. Equilibrium and strain compatibility equations are formulated for reinforced and prestressed concrete under concentric loading which are solved simultaneously with the constitutive stress–strain equation of the selected viscoelastic model. For the case of a constant load, adoption of the fractal viscoelastic models lead to first-order differential equations that, when solved, yield analytical expressions for basic creep in reinforced and prestressed concrete. A semi-analytical solution is derived when adopting the fractional viscoelastic laws, obtained using the Laplace transform technique. Both models ensure strain compatibility and consider stress redistribution from concrete to the steel reinforcement bars. A high-level of agreement is made between the derived fractional and fractal-derivative based models and existing experimental data of creep in reinforced and pre-stressed concrete members under constant load. When the applied loading varies with time, numerical procedures are employed to approximate the fractional and fractal derivatives. It is found that creep in plain concrete members subjected to time-varying loads is accurately predicted when using the fractional derivative models. Comparisons are then made to other methods of modelling creep under time-varying stress. The primary advantage of the derived models is that only up to three parameters require calibration using basic creep tests for an accurate representation of creep and that closed-form expressions for creep can be obtained for the case of constant, sustained loading.

Creep anisotropy behavior, deformation mechanism, and its efficient suppression method in Inconel 625 superalloy

Mill products, such as sheets, usually show obvious anisotropy in their mechanical properties, which greatly affects both their applications and workability. In this study, the orientation-dependent tensile and creep behaviors of Inconel 625 alloy sheets with weak local textures were systematically investigated at 650℃. The results showed that Inconel 625 superalloy exhibits nearly isotropic tensile properties; however, obvious creep anisotropy appears when loading along different directions. Creep life in the rolling direction (150 ± 5 h) was approximately 4.5 times longer than in the transverse direction (33 ± 1 h). Severe creep anisotropy was found to be determined by two aspects: (i) the change in deformation mechanisms along the rolling direction (a combination of boundary sliding, dislocation slipping, and twinning) and the transverse direction (dislocation slipping). Stronger impingement of slip bands on grain boundaries accelerated intergranular crack initiation and propagation during loading along the transverse direction, which resulted in a short creep life. (ii) The differences in strain compatibility at grain boundaries (i.e., creep loading along the transverse direction resulted in the initial grains forming strong Brass, Cu, and S textures). Creep cracks preferentially nucleated at the junctions between Cu/Brass texture grains, as these interfaces exhibit the worst strain compatibility (Luster–Morris parameter m′ ≤ 0.22). Furthermore, pre-stress aging (PSA) treatment is proposed as an efficient method to suppress creep anisotropy. The discrepancy rate of creep life was found to be reduced by nearly 50% after PSA treatment.

Heterogeneous-structured Ti-6Al-4V with enhanced mechanical properties in monotonic and cyclic deformation modes

This study aimed to develop heterogeneous-structured (HS) Ti-6Al-4V composed of coarse and fine grains to enhance the alloy's mechanical properties. This microstructure was induced by selective activation of dynamic globularization by using water-quenching and subsequent rolling below the β-transus temperature. Microstructures and mechanical properties of the HS alloy in monotonic and cyclic deformation modes were compared with those of coarse-grained (CG) and ultrafine-grained (UFG) counterparts. HS Ti-6Al-4V had a higher mechanical strength and better resistance to low-cycle fatigue (LCF) fracture without the loss of ductility compared with commercial mill-annealed CG alloy, and HS alloy had an engineering advantage of low-cost mass production in contrast to UFG counterpart, despite their similar mechanical properties under both monotonic and cyclic deformations. The enhanced mechanical properties of HS alloy were attributed to the presence of UFG region and the partial transformation of transverse to basal texture with a high intensity. Such conditions gave rise to an active slip transfer, low internal stress, and high strain compatibility, thereby leading to the high LCF resistance.

Efficacy of Single and Multi-Strain Probiotics on In Vitro Strain Compatibility, Pathogen Inhibition, Biofilm Formation Capability, and Stress Tolerance.

Compatibility of each strain in a multi-strain probiotic (MSP), along with its properties, becomes a strong base for its formulation. In this study, single-strain probiotics (SSPs) and multi-strain probiotics (MSPs) were evaluated in vitro for strain compatibility, microbial antagonism, biofilm formation capacity, and stress tolerance. Bacillus amyloliquefaciens L11, Enterococcus hirae LAB3, and Lysinibacillus fusiformis SPS11 were chosen as MSP1 candidates because they showed much stronger antagonism to Aeromonas hydrophila and Streptococcus agalactiae than a single probiotic. MSP 2 candidates were Lysinibacillus fusiformis strains SPS11, A1, and Lysinibacillus sphaericus strain NAS32 because the inhibition zone produced by MSP 2 against Vibrio harveyi and Vibrio parahaemolyticus was much higher than that produced by its constituent SSPs. MSP1 in the co-culture assay reduced (p < 0.05) A. hydrophila count from 9.89 ± 0.1 CFU mL-1 to 2.14 ± 0.2 CFU mL-1. The biofilm formation of both MSPs were significantly higher (p < 0.05) than its constituent SSPs and the pathogens. The SSPs in both MSPs generally showed resistance to high temperatures (80, 90, and 100 °C) and a wide range of pH (2 to 9). This in vitro assessment study demonstrates that MSP1 and 2 have the potential to be further explored as multi-strain probiotics on selected aquatic species.

Use of Lactiplantibacillus plantarum for dairy and non-dairy fermented products

In this study, two strains of Lactiplantibacillus plantarum 299v and CCDM 181 were tested for their ability to grow in milk and soy beverage, for stability during cold storage of fermented beverages, compatibility with yoghurt culture and activity against yeasts. Both strains grew better in soy drink compared to milk. During co-culturing with the yoghurt culture, sufficient acidification of milk and soy beverage necessary for the production of fermented products was achieved. The stability of tested strains in media at pH 4.5 for 28 days at 5 °C was good. L. plantarum was effective in the inhibition of undesirable yeast growth, but the ability was strain-specific. Tested strains demonstrated also a strain-specific ability to suppress the growth of yoghurt culture bacteria. For a possible application of co-culturing L. plantarum with the yoghurt culture, verification of the mutual compatibility of specific strains is necessary.

Detecting the Deformation Behavior of Bimodal Ti-6Al-4V Using a Digital Image Correlation Technique.

The evolution of a local strain of the Ti-6Al-4V alloy subjected to tensile loading was investigated in situ by using the digital image correlation technique. The results show that some local strain concentration areas have already appeared in the elastic deformation stage, which then connected and became concentrated in the gauge region when the specimen yielded. The strain compatibility of grains in the macroscopic region is kept constant. The deformation process is further divided into six parts based on the development of the maximum strain gradient, and the strain compatibility of each stage of the alloy is summarized and analyzed. The quasi-in situ experiment reveals that the primary α(αp) grains undertake the main deformation at the micro-scale.

Calculating local geomembrane strains from gravel particle indentations with thin plate theory

A new general method is presented to calculate local strains in geomembranes from the deformed shape imposed by overlying coarse gravel particles under vertical pressure. Past methods assume that the geomembrane attains its deformed shape by only deforming vertically and hence neglect the effect of lateral displacements on strain. The new method treats the geomembrane as a thin plate with mid surface components of displacements in three directions (x, y and z). Lateral components of displacements (those in the x and y directions) are related to vertical displacements (z direction) by large-strain-displacement relationships and compatibility of strains. Normal and shear strains in the lateral directions are calculated using Airy's stress function and a linear elastic constitutive law. Bending and torsional strains calculated from curvature and are added to the mid surface strains to find strains on the top and bottom surfaces. The method was validated against data sets with known three-dimensional displacements and strain generated by finite element analysis. The application of the new method to calculate local strains in a geomembrane from the deformed shape obtained from a protection-layer-assessment physical test is illustrated.

Selection behavior of {10−12} tensile twin variants and its contribution during plastic processing of magnesium alloy

{10−12} tensile twins are successfully prefabricated in the magnesium alloy sheet by bending and straightening. The relationship between twin morphologies and twin variants is established and the effects of the Schmidt factor, geometric compatibility parameter, and local strain field on the twin variant selection are comprehensively explored. The results show that the twin plates in the parallel relationship in the same matrix grains belong to the same variant usually with a high Schmidt factor, while the twin plates that orientate at a certain angle are the parasite variants usually corresponding to low Schmidt factor with respect to the applied stress. Whether the selection behavior of twin variants conforms to Schmidt's law is determined by the local strain field at the position of the twins rather than the matrix grains. The degree of strain compatibility between twins will change the result of the twin variants selection caused by the strain field. Compared to the local strain field, the geometric compatibility parameter between transgranular twins has a greater impact on the choice of twin variants. The twins are preferentially nucleated and have a positive effect on activating the Pyramidal II<a+c> slip of the matrix grains. • A comprehensive analysis of the factors influencing the twin variants selection. • In-grain misorientation quantified local stress field. • Tensile twinning activates the pyramidal II<a+c> slip of the matrix.

Seismological Evidence for Girdled Olivine Lattice‐Preferred Orientation in Oceanic Lithosphere and Implications for Mantle Deformation Processes During Seafloor Spreading

AbstractSeismic anisotropy produced by aligned olivine in oceanic lithosphere offers a window into mid‐ocean ridge (MOR) dynamics. Yet, interpreting anisotropy in the context of grain‐scale deformation processes and strain observed in laboratory experiments and natural olivine samples has proven challenging due to incomplete seismological constraints and length scale differences spanning orders of magnitude. To bridge this observational gap, we estimate an in situ elastic tensor for oceanic lithosphere using co‐located compressional‐ and shear‐wavespeed anisotropy observations at the NoMelt experiment located on ∼70 Ma seafloor. The elastic model for the upper 7 km of the mantle, NoMelt_SPani7, is characterized by a fast azimuth parallel to the fossil‐spreading direction, consistent with corner‐flow deformation fabric. We compare this model with a database of 123 petrofabrics from the literature to infer olivine crystallographic orientations and shear strain accumulated within the lithosphere. Direct comparison to olivine deformation experiments indicates strain accumulation of 250%–400% in the shallow mantle. We find evidence for D‐type olivine lattice‐preferred orientation (LPO) with fast [100] parallel to the shear direction and girdled [010] and [001] crystallographic axes perpendicular to shear. D‐type LPO implies similar amounts of slip on the (010)[100] and (001)[100] easy slip systems during MOR spreading; we hypothesize that grain‐boundary sliding during dislocation creep relaxes strain compatibility, allowing D‐type LPO to develop in the shallow lithosphere. Deformation dominated by dislocation‐accommodated grain‐boundary sliding (disGBS) has implications for in situ stress and grain size during MOR spreading and implies grain‐size dependent deformation, in contrast to pure dislocation creep.

Flexural performance of CFRP strengthened beams - comparison with analytical model

ABSTRACT In recent years, strengthening methods for reinforced concrete structures using fibre-reinforced polymer (FRP) composites have been gaining widespread interest and growing acceptance in civil engineering industry. Near surface mounted (NSM) reinforcement as well as externally bonded reinforcement (EBR) sheets have emerged as new strengthening methods in which external reinforcement (in the form of bars or sheets) is embedded into grooves or adhered to the section with epoxy adhesive. This paper proposes a simplified analytical approach to predict flexural behaviour of simply supported reinforced-concrete (RC) beams strengthened with carbon fibre-reinforced polymer (CFRP) using the above-mentioned methods. The flexural capacity and deformational behaviour of FRP strengthened beams are analysed using trilinear moment curvature relationship at three critical points namely (i) crack initiation point (ii) steel yield initiation point and (iii) ultimate capacity point, based on strain compatibility and principles of equilibrium. A good predictive performance of analytical model is appraised by simulating force-deflection response registered in the experimental program composed of RC beams strengthened with NSM as well as EBR methods. The analytical solutions have also given accurate prediction of experimental results in the literature regardless of the arrangement of CFRP reinforcement.

Experimental Investigation into the Capacity of Concentrically Loaded Steel Connections with Pretensioned High-Strength Bolts and Longitudinal Fillet Welds in Combination

This paper presents the results of an experimental study aiming to investigate the behavior of steel connections that combine pretensioned high-strength bolts and longitudinal fillet welds on a common faying surface. A total of 75 double-shear tension splices were tested under direct tension loading to quantify the effect of various connection variables on the load-deformation behavior of the connection. These variables include the (1) bolt pattern (2×2 and 2×3), (2) bolt size (3/4 in. and 1 in.), (3) bolt grade (ASTM F3125 Grade A325, A490, and F1852), (4) bolt pretensioning method (turn-of-nut and tension control bolts), (5) faying surface class (Class A and B), and (6) weld/bolt strength ratio. The variation in the connection characteristics covered a wide range of weld/bolt strength ratios from 0.50 to 2.00. The bolts were installed in oversized holes, and the specimens were assembled in a negative bearing condition to allow for a maximum slip distance. The load-deformation behavior of the combination connections was recorded and compared to that of the bolted- and welded-only control specimens. In all tests, the addition of welds increased the capacity of the connection. The investigation shows that the capacity of the combination connection with pretensioned high-strength bolts and longitudinal fillet welds can be computed by adding the capacities of the individual connecting elements while considering the strain compatibility.

Nonlinear steel strains in cracked RC beams based on bond-stress profiles

Steel–concrete bond is instrumental in transferring tensile forces to the concrete via the bond stresses, whose values and distribution along a steel bar vary with the level of the load applied to the reinforcement. To study the profile of the strains in the reinforcement, the variation of the bond-stress distribution is considered and the bond stresses are introduced according to Model Code 2010. The transfer length where the bond stresses are active is shown to be a function of the slip in the cracked sections. This slip can be evaluated from the concrete strains based on the plane-section hypothesis to take care of the strain compatibility between the concrete and the reinforcement. The equilibrium of the internal forces, the constitutive laws of the materials and the bond stress-slip law make it possible to model the kinematic interaction between the concrete and the reinforcement. An iterative algorithm is proposed to calculate the steel strains, and the effectiveness of the numerical procedure is checked against the test data coming from simply-supported RC beams tested in this research project or available in the literature. The results show that the nonlinear evolution of steel–concrete slip close to the cracks may increase the transfer length of the bond stresses by 50% under increasing loads, and the steel strains by up to 90% along the bonded length. As a result, the steel-strain profile becomes a slightly-nonlinear function of the load, which is also markedly affected by the crack pattern.

A Complete Assessment of the Moment‐Curvature Relationship of Compressed Steel‐concrete Composite Cross‐sections

AbstractIn the non‐linear evaluation of the behavior of steel, concrete and steel‐concrete composite cross‐sections, increment and iteration strategies are necessary for the complete construction of the moment‐curvature relationship (M‐Φ). For the correct simulation of sections composed of strain‐softening materials, a numerical strategy based on constant force increments does not capture the downward branch of the M‐Φ relationship. Therefore, the present study aims to couple the strain compatibility method to the path‐following strategies to go beyond the critical bending moment points in the construction of the relations that describe the complete cross‐section mechanical behavior. In this context, the generalized displacement technique, which depends on a generalized stiffness parameter, and the minimum residual displacement method, are adapted to the cross‐sectional non‐linear problem. To validate the proposed numerical formulation, the results obtained here are compared with the numerical data available in the literature. Additionally, the softening effect on the concrete was increased to induce descending stretches in the moment‐curvature relationship, and this condition was correctly evaluated.