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A beam's Neutral Axis (NA) is a parameter that has been utilized to detect damage. Its position depends on the geometry of the cross-section and also a member's axial loads. Shifts in its position can indicate changes in either load distribution or geometric characteristics. When considering structures such as cable-stayed bridges where the inclined cables induce significant axial forces, the effect of axial loads on NA position is significant. In this research, a simplified analytical model was developed consisting of the key elements of a cable-stayed bridge (beam, cable, and bearing). The model was loaded with a vertical point load representing a vehicle load. The NA position was calculated beneath the load as it moves over the length of the beam. By changing element properties, one can observe how the NA position behaves in different locations of the beam, due to simulated damage in the beam, cable, or bearing. It was found that changes in NA position can capture not only whether damage has occurred, but also in which component of the structure the damage is located (beam, cable, or bearing). This ability to use NA position for damage identification renders it an excellent parameter for monitoring cable-stayed bridges. [ABSTRACT FROM AUTHOR]

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Damage to girders threaten a bridge's safety. They can be effectively detected by the neutral axis (NA) position of a girder. However, the NA position is inevitably affected by the nonlinear temperature gradient of girders, which could mask the damage-induced abnormality. Aiming at the practicality of the NA position, an improved thermal-varying NA model was scientifically derived by accommodating vertically distributed measurements of a nonlinear temperature gradient, followed by several simplified models. By eliminating the effect of the nonlinear temperature gradient on the NA position to the maximum, an abnormality alarming framework was then established for damage detection of girders. Finally, a girder model imposed by an actual nonlinear temperature gradient was developed to validate the advantages of the improved model and the effectiveness of the alarming framework. The proposed models are an improvement over the existing model in terms of prediction accuracy and stability. Additionally, the NA-based alarming method can effectively detect minor damage to the girder subjected to varying nonlinear temperature gradients. The optimal strain measurement is recommended at the lowest turning point of the temperature difference characteristic above the NA position, and the optimal temperature measurement should effectively represent the statistical outline feature of the temperature difference. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation revealing the effects of key design parameters on the behavior of disconnected piled raft (DPR) system. Large-scale model tests are conducted on instrumented foundations by varying the pile spacing, pile length, and the cushion thickness. From the test results, the load capacity improvement (LCI) factor of 3 × 3 DPR is found to increase with increasing pile spacing and length and decreasing cushion thickness. Interestingly, this factor is found to be higher at lower settlement of the raft irrespective of the length and spacing of the piles. The maximum axial load in a pile is found to occur 0.25 m below the pile head due to the generation of negative skin friction in the shallow depth. A significant downward shift of the neutral axis of the pile is observed with increasing cushion thickness resulting a higher difference between the pile head load and maximum axial load. The average load proportions of the piles and the raft in a DPR system are found 31% and 69%, respectively, when the raft settlement reaches 10% of its width. Based on the quantitative impact of these design parameters, recommendations are also provided regarding the design of the DPR system. [ABSTRACT FROM AUTHOR]

To investigate the development mechanism of sectional plastic stress and biaxial bending moments of H-section steel members prior to local buckling subjected to monotonic and cyclic loading, extensive parametric analysis models were established in ABAQUS. These models explicitly accounted for different axial force ratios, plate width-thickness ratios under different loading angles, verifying the applicability against existing experimental data. Based on the results of finite element analysis, the effects of various factors on the development of normal stresses in the cross-section were thoroughly investigated. A semi-empirical semi-theoretical calculation model was established to address biaxial loading in H-section steel members, considering bidirectional displacement, the form of normal stress distribution, and the relationship between the biaxial bending moments. By comparing the model with finite element results, it was observed that the model effectively predicted the progression of biaxial bending moments development subjected to biaxial loading in H-section steel members. This model provides a more convenient design approach for considering the partial plastic development of the cross-section in bidirectional flexural design. [ABSTRACT FROM AUTHOR]

Due to the high cost of laboratory testing, many researchers are considering developing methods to predict the behavior of unreinforced and reinforced wood beams. This work aims to create either numerical or analytical models useful for extrapolating already conducted tests to other schemes/materials used as reinforcement. In the case of timber structures, due to the complexity of timber, this task is difficult. The first part of the article presents an analysis of the suitability of using a simplified mathematical model based on the equivalent cross-section method to describe the behavior of unreinforced and reinforced with carbon-fibre-reinforced polymer (CFRP) composite full-size laminated veneer lumber (LVL) beams. The theoretical results were compared with the results of conducted experimental tests. The scope of the analysis includes the estimation of modulus of rupture, bending stiffness, and determination of the neutral axis position. The equivalent cross-section method showed good agreement in determining the bending stiffness and neutral axis position of the strengthened sections. However, the suitability of using the equivalent cross-section method to estimate the load-carrying capacity of a cross-section reinforced with fiber composites still needs to be confirmed, which, according to the authors, is due to the differences between the assumed (linear) and actual (nonlinear) strain distribution in the compression zone. The second part uses the equivalent cross-section method to estimate the predicted bending stiffness of LVL beams strengthened with aramid-fibre-reinforced polymer (AFRP), glass-fibre-reinforced polymer (GFRP), and ultra-high modulus carbon-fibre-reinforced polymer (CFRP UHM) sheets. The proposed method can be used for preliminary evaluation of strengthening effectiveness of LVL beams. [ABSTRACT FROM AUTHOR]

The traditional objective function (TOF) of bridge model updating is usually defined on the basis of the structural response residuals between numerically calculated and experimentally measured values. However, this model finds it difficult to determine the weighting factors, and the updated model lacks accuracy. To offset these disadvantages, this study proposes a novel objective function (NOF) for finite-element model updating of a long-span cable-stayed bridge using in situ static and dynamic measurements. The proposed NOF comprises the residual functions of the displacement assurance criterion, the position of the neutral axis, and the natural frequency. The global sensitivity analysis–based model updating uses the Kriging model as the surrogate model to save computational costs. The nondominated sorting genetic algorithm II is employed to find the Pareto solutions. The updating results with the TOF defined directly using displacement, stress, and frequency are listed for the purposes of comparison. The results show that the NOF avoids determining the weighting factors and provides more accurate results than the TOF. The updated displacement curves, the position of the neutral axis, and the frequencies obtained from the NOF are all closer to the experimentally measured ones than those obtained from the TOF. After model updating, the displacement's relative errors are around 5% without considering the displacement values under 10 mm. The relative errors of the first four frequencies are all less than 10%. The updated model can serve as the baseline finite-element model of the bridge. [ABSTRACT FROM AUTHOR]

Avian eggs represent a striking evolutionary adaptation for which shell thickness is crucial. An understudied eggshell property includes the neutral axis, a line that is drawn through any bent structure and whose precise location is characterized by the k‐factor. Previous studies have established that, for chicken eggs, mean k corresponds to the golden ratio (Φ = 1.618, or 0.618 in its reciprocal form). We hypothesized whether such an arrangement of the neutral axis conforms to the eggshell of any bird or only to eggshells with a certain set of geometric parameters. Implementing a suite of innovative methodological approaches, we investigated variations in k of 435 avian species, exploring which correspond to Φ. We found that mean k is highly variable among birds and does not always conform to Φ, being much lower in spherical and ellipsoid eggs and higher in pyriform eggs. While 21 species had k values within 0.618 ± 0.02 (including four falcon species) and the Falconinae subfamily (six species) revealed a mean of 0.618, it is predominantly domesticated species (chicken, ducks, and geese) that lay eggs whose neutral axis corresponds to the golden ratio. Thus, the study of the mathematical secrets of the eggshell related to the golden ratio of its neutral axis suggests its species‐specific signatures in birds. [ABSTRACT FROM AUTHOR]

In order to investigate the influence of modulus of the base layer on the strain distribution for asphalt pavement, the modulus ratio of the base layer and the AC layer (Rm) is introduced as a controlled variable when keeping modulus of the AC layer as a constant in this paper. Then, a three-layered pavement structure is selected as an analytical model, which consists of an AC layer with the constant modulus and a base layer with the variable modulus covering the subgrade. A three dimensional (3D) finite element model was established to estimate the strains along the horizontal and vertical direction in the AC layer under different Rm. The results show that Rm will change the distribution of the horizontal strains along the depth in the AC layer; the increase of Rm could reduce the maximum tensile strain in the AC layer, but its effect is limited; the maximum tensile strain in the AC layer does not necessarily occur at the bottom, but gradually rises to the middle with the increase of Rm. Rm could significantly decline the bottom strain in the AC layer, and there is a certain difference between the bottom and the maximum strain when Rm is greater than or equal to one, which will enlarge with increasing Rm. Rm could change the depth of the neutral axis in the AC layer, and the second neutral axis will appear at the bottom of the AC layer under a sufficiently large Rm. The average vertical compressive strain in the AC layer will significantly enlarge with the increase of Rm.

A novel subdiscipline of bionics is emerging in the form of ‘egg-inspired engineering’ through the use of egg-shaped ovoids as thin-walled tanks and building structures. Hügelschäffer’s and Narushin’s models of egg geometry are highly applicable within this proposed subdiscipline. Here we conducted a comparative analysis between the two models with respect to some of the most important egg parameters. These included contents volume, shell volume, and the location of the neutral axis along the shell thickness. As a first step, theoretical studies using the Narushin’s model were carried out due to the lack (or limited amount) of data on the geometric relationships of parameters and available calculation formulae. Considering experimental data accumulated in the engineering and construction industries, we postulate a hypothesis that there is a correlation between location of the neutral axis and the strength of the walls in the egg-shaped structure. We suggest that the use of Narushin’s model is preferable to Hügelschäffer’s model for designing thin-walled shelled vessels and egg-shaped building structures. This is due to its relative simplicity (because of the requirement for only two initial parameters in the basic equation), optimal geometry in terms of material costs per unit of internal capacity, and effective prerequisites for shell strength characteristics.

The loads in the deep beams are transmitted diagonally from the load area to the support area by means of the strut and the tie. It is characterized by having a small span to depth ratio. which causes the distribution of stresses to be non-linear within the beam, which motivates researchers to study the effect of the placing of longitudinal hollows and the extent to which these holes affect the behavior and distribution of stresses for these types of beams. In addition to the advantages added by longitudinal hollow to the beam such as reducing weight and passing various electrical and mechanical services...etc. This study investigated the effect of making longitudinal circular holes (with a diameter of 50mm) with a slope on the structural behavior of three deep beams with a solid sample as a reference where the slope used was 0%, 4.3%, and 7.8%. The results showed that making holes reduces the load capacity of the deep beam, a decrease in the failure load was observed by 7.56%, 8.96%, and 11.2% for hollow beams with a slope of 0%, 4.3%, and 7.8%, respectively. Also, the appearance of flexural cracking increased by 2.66%, 2.66%, and 6.66%.and 2.14%, 3.52%, and 7.14%, respectively, for shear cracks. While the effect was small for the neutral axis location as well as for the vertical deflection.

A surface nanocrystalline was fabricated by ultrasonic shot peening (USSP) treatment at AZ31 Mg alloy. The effect of nanocrystalline thickness and its placed side (external or internal) on the bendability was studied by a V-bending test. Three durations, 5, 10, and 15 min, were applied to form the surface nanocrystalline with thicknesses of 51, 79, and 145 µm, respectively. Two-side treatment led to a similar bendability as that of as-received. One-side internal treatment for 5 min resulted in an improved bendability while the improvement was limited and degenerated for longer treatment. The improvement was related to the drawing back of the neutral axis. The one-side external treatment also improved the bendability, and the improvement was due to the redistribution of strain and stress during bending. With nanocrystalline at external side, it resulted in a larger stress but a smaller strain at the convex, which prevented the happening of crack during bending. [ABSTRACT FROM AUTHOR]

Ultimate strength is an important design consideration for the safety of intact or damaged ship structures. The simplified progressive collapse method is a commonly used iterative method to obtain the accurate ultimate strength of ships. Since the accuracy of the neutral axis position directly affects the accuracy of the ultimate strength, the force equilibrium criterion and the force vector equilibrium criterion are adopted to search for the height and angle of the neutral axis, especially for damaged ships. However, the search for the neutral axis position based on the two criteria requires iterative computation which decreases the calculation efficiency. In this paper, the relationship between the results of the iterative process and the neutral axis position is studied, and it is found that the relationship is approximately linear. Then a new iterative method based on the linear equation is proposed to obtain the neutral axis position and is adopted to improve the simplified progressive collapse method. Finally, the new method is used to calculate the neutral axis position of a damaged VLCC. The comparison of the ultimate strength results shows that the improved simplified progressive collapse method based on the linear equation has improved efficiency and good accuracy. • It is found that the results of the equilibrium criterion vary approximately linearly for small movements of neutral axis. • An improved method based on the derived linear equation is proposed for the search of the location of neutral axis. • Comparison of the proposed method with existing methods shows that it is accurate and more computationally efficient. [ABSTRACT FROM AUTHOR]

Due to the high cost of laboratory testing, many researchers are considering developing methods to predict the behavior of unreinforced and reinforced wood beams. This work aims to create either numerical or analytical models useful for extrapolating already conducted tests to other schemes/materials used as reinforcement. In the case of timber structures, due to the complexity of timber, this task is difficult. The first part of the article presents an analysis of the suitability of using a simplified mathematical model based on the equivalent cross-section method to describe the behavior of unreinforced and reinforced with carbon-fibre-reinforced polymer (CFRP) composite full-size laminated veneer lumber (LVL) beams. The theoretical results were compared with the results of conducted experimental tests. The scope of the analysis includes the estimation of modulus of rupture, bending stiffness, and determination of the neutral axis position. The equivalent cross-section method showed good agreement in determining the bending stiffness and neutral axis position of the strengthened sections. However, the suitability of using the equivalent cross-section method to estimate the load-carrying capacity of a cross-section reinforced with fiber composites still needs to be confirmed, which, according to the authors, is due to the differences between the assumed (linear) and actual (nonlinear) strain distribution in the compression zone. The second part uses the equivalent cross-section method to estimate the predicted bending stiffness of LVL beams strengthened with aramid-fibre-reinforced polymer (AFRP), glass-fibre-reinforced polymer (GFRP), and ultra-high modulus carbon-fibre-reinforced polymer (CFRP UHM) sheets. The proposed method can be used for preliminary evaluation of strengthening effectiveness of LVL beams.

Conocer el comportamiento real de una estructura de hormigón armado es difícil. debido a los múltiples factores que influyen en el mismo. La heterogeneidad del hormigón y la evolución de sus características mecánicas y físicas a lo largo de la vida útil del material, hace que podamos obtener valores aproximados de su comportamiento. El objetivo de este trabajo de investigación es evaluar de una manera más precisa este comportamiento, mediante la inclusión en las estructuras de sensores de fibra óptica. Estos sensores nos proporcionan valores precisos de deformación en tiempo real, durante toda la vida de la estructura. Para obtener estos resultados, se han embebido los sensores en una viga de hormigón armado y se ha analizado realmente lo que le ocurre cuando la solicitamos a diferentes escalones de carga. Los resultados obtenidos los hemos comparado con los teóricos obtenidos del cálculo de resistencia de materiales, llegando a la conclusión de que, en efecto, las estructuras de hormigón armado son elementos complejos, pero que, con este sistema de monitorización, podremos obtener resultados más precisos de su comportamiento. Abstract Knowing the real behavior of a reinforced concrete structure is a difficult task due to the multiple factors that influence it. The heterogeneity of the work and the evolution of its mechanical and physical characteristics throughout the useful life of the material, makes it possible to obtain approximate values of its behaviour. The objective of this research work is to evaluate this behavior in a more precise way, through the inclusion of fiber optic sensor structures. These sensors provide us with precise values of deformation in real time, throughout the life of the structure. I have embedded the sensors in a reinforced concrete beam and I have really analyzed what happens when we request it at different load stages. The obtained results have been compared with the theoretical ones obtained from the calculation of resistance of materials, arriving at the conclusion that, in fact, reinforced concrete structures are complex elements, but that, with this monitoring system, we can obtain more precise results of his behavior

The intersection of neutral layer and the transverse section is called neutral axis. The position of neutral-axis will be changed when the corresponding beam structure is damaged. In this work, the static loading test of recycled concrete beam is carried out to verify the damage detection method based on neutral axis position. Experimental results show that structural damage can be detected by the change of the neutral-axis position.

Structural Health Monitoring (SHM) has enabled the condition of large structures, like bridges, to be evaluated in real time. In order to monitor behavioral changes, it is essential to identify parameters of the structure that are sensitive enough to capture damage as it develops while being stable enough during ambient behavior of the structure. Research has shown that monitoring the neutral axis (N.A.) position satisfies the first criterion of sensitivity; however, monitoring N.A. location is challenging because its position is affected by the loads applied to the structure. The motivation behind this research comes from the greater than expected impact of various load characteristics on observed N.A. location. This paper develops an indirect way to estimate the characteristics of vehicular loads (magnitude and lateral position of the load) and uses a data mining approach to predict the expected location of the N.A. Instead of monitoring the behavior of the N.A., in the proposed method the residuals between the monitored and predicted N.A. location are monitored. Using actual SHM data collected from a cable-stayed bridge, over a 2-year period, the paper presents the steps to be followed for creating a data mining model to predict N.A. location, the use of monthly sample residuals of N.A. to capture behavioral changes, the ability of the method to distinguish between changes in the load characteristics from behavioral changes of the structure (e.g. change in response due to cracking, bearings becoming frozen, cables losing tension, etc.), and the high sensitivity of the method that allows capturing of minor changes.

In this study, a polynomial higher-order shear deformation theory is introduced and developed for static analysis of functionally graded material (FGM) beams. The presented theory has strong similarities with Timoshenko beam theory in some aspects, such as equations of motion, boundary conditions and stress expressions. The developed theory does not require shear correction factor and satisfies the stress-free boundary conditions, such that the transverse shear stress varies parabolically through the beam thickness. The mechanical properties of the FGM beam are assumed to vary continuously in the thickness direction based on power-law distribution in terms of the volume fractions of the constituents. The influences of material distribution, boundary conditions, aspect ratio and neutral axis on the mid-plane deflection, normal stress and shear stress are figured out. The results obtained are compared with the data available in the literature to verify the correctness and the accuracy of the developed theory. The presented theory can provide a reference which other researchers can use for their studies. [ABSTRACT FROM AUTHOR]

Due to unphysical coupling induced by the material inhomogeneity, FG (functionally graded) nanobeam problems were formulated in a very complex way so that they cannot be analytically solved. In this paper, an uncoupled theory is proposed for FG nanobeams considering their small size effects. First, with the aid of the neutral axis, the axial displacement is expressed in terms of generalized displacements for FG nanobeams. Based on the nonlocal strain gradient theory, the generalized stresses and strains are accordingly defined and uncoupled constitutive relations are derived. Based on the principle of virtual work, an uncoupled theory is eventually established, including governing equations and boundary conditions. Within the present framework, analytical solutions to FG nanobeams are obtained for the first time for general boundary conditions. These solutions not only re-evaluate the previous results but shed light on the small size effects of FG nanobeams. [ABSTRACT FROM AUTHOR]

The results of an extensive experimental program into the location of the neutral axis in cracked fiber‐reinforced concrete (FRC) are reported. In total, 74 prisms are tested in a monotonic (51 specimens) and cyclic (23 specimens) bending test in accordance with EN 14651. In the program, 13 different FRCs are considered with 9 different fiber types and dosages. A normal strength concrete with residual strength values between 1b and 2d, cf. Model Code 2010 (MC10), is considered. The deformation profile in the cracked section is measured by side‐mounted linear variable displacement transducers on the prisms, and the position of the neutral axis is calculated. The experimental results are compared against predictions of the MC10. Based on a simplified stress diagram, the MC10 predicts that the location of the neutral axis depends on the residual strength of the FRC at the serviceability limit state: increasing the strength results in a larger compressive zone and vice versa. However, the results obtained within this study do not confirm this relation. The cyclic results indicate that the neutral axis shifts upward during unloading and subsequent reloading decreases the neutral axis again to preunloading levels. Finally, for all reported FRC types, the neutral axis lies very high in the cracked section, even at very small crack mouth opening displacement values. [ABSTRACT FROM AUTHOR]

An experimental study was conducted to evaluate the ductility of reinforced concrete beams longitudinally reinforced with hybrid Fiber Reinforced Polymer (FRP)–steel bars. The specimens were fourteen reinforced concrete beams with and without hybrid reinforcement. The test variables were bar positions, ratio of longitudinal reinforcement, and type of FRP. The beams were loaded until failure using a four-point bending test. The performance of the tested beams was observed using the load–deflection curve obtained from the test. Numerical analysis using the fiber element model was carried out to examine the growth of neutral axis due to the effects of the test variables. The neutral axis curves were then used to estimate the neutral axis angles and displacement indices. The test results showed that the reinforcement position did not significantly affect the flexural capacity of beams with a higher ratio of hybrid reinforcement, but was quite significant in beams with a lower ratio of hybrid reinforcement. It was observed from the test that the flexural capacity of beams with hybrid reinforcement was 15–45% higher than that of beams with conventional steel bars, depending on bar positions and the ratio of longitudinal reinforcement. The ductility of beams with hybrid reinforcement was significantly increased compared to that of beams with FRP, but decreased as the hybrid reinforcement ratio (Af/As) increased. This study also showed that the developed numerical model could predict the flexural behavior of beams with hybrid reinforcement with reasonable accuracy. Based on the test results, parametric analysis, and data obtained from the literature, the use of the neutral axis angle and displacement index value to evaluate the ductility of cross-sections with hybrid reinforcement is proposed.

The fatigue damage behavior of bone has attracted significant attention in both the mechanical and orthopedic fields. However, due to the complex and hierarchical structure of bone, describing the damage process quantitively or qualitatively is still a significant challenge for researchers in this area. In this study, a nonlinear bi-modulus gradient model was proposed to quantify the neutral axis skewing under fatigue load in a four-point bending test. The digital image correlation technique was used to analyze the tensile and compressive strains during the fatigue process. The results showed that the compressive strain demonstrated an obvious two-stage ascending behavior, whereas the tensile strain revealed a slow upward progression during the fatigue process. Subsequently, a theoretical model was proposed to describe the degradation process of the elastic modulus and the movement of the neutral axis. The changes in the bone properties were determined using the FEM method based on the newly developed model. The results obtained from two different methods exhibited a good degree of consistency. The results obtained in this study are of help in terms of effectively exploring the damage evolution of the bone materials.

Composite action between steel girders and concrete slab is an important mechanical feature that needs to be maintained so that bridges can carry the applied load safely. This mechanical feature is maintained through the shear studs installed at the top flange of the steel girders. These shear studs keep the steel girders and the concrete slab working as one unit, resulting in a stronger section than if each element works separately. The composite action can be investigated using several methods of which one is the study of the position of the neutral axis (NA). The variation of the position of the NA over time gives an indication about the structural performance of the composite section. In this study, the variation of the position of the NA over time is investigated. Two bridges located in Manitoba were investigated in this study. The variation of the NA is observed as a result of variation of ambient temperature (temperature). Regression models are suggested to relate variation of the NA to the temperature that was measured beside the web of one of the bridge girders. Repeatability analysis over 4 years was conducted, confirming that the NA varies cyclically over years. It is suggested that this variation indicates that there is a change in the degree of composite action assuming that cold temperatures will induce more connection between the steel girders and the concrete slab as a result of thermal contraction of the shear studs. In addition, the stiffness of the material could be affected due to change of temperature. The other possibility is that an axial force develops in the beam as a result of the bearing restraint during the passing of vehicles on the bridge. The results found in this study will eventually lead to enhancements of the design procedures that currently assume a fixed position of the NA over time of composite sections of bridges, similar to the bridges presented in this study. [ABSTRACT FROM AUTHOR]

Recently, the problem faced by the construction industry is a significant shortage of raw materials of concrete. Thus, the main idea of this research is to replace the use of concrete at the middle area of neutral axis of beam with voided system by incorporating PVC pipe. This research aims to reduce the concrete usage; structure's self-weight without neglecting its strength performance. The experimental work consists of casting and testing the 1200 x 160 x 160 mm beams with (Ø40 mm, Ø50 mm, and Ø100 mm) and without void at the neutral axis. The test results indicated that the strength performance of all RC beams with voided section is stronger than the ordinary RC beam where the V50 RC beam is able to withstand loads up to 38.25 kN and has a strength increment of 49.2% compared to the ordinary RC beam. By this material optimization, the reduction of concrete usage and self-weight of the V100 RC beam recorded a reduction of up to 35.14% but in terms of its strength is relatively low compared to the V40 RC beam and V50 RC beam. This findings show a positive result in reducing the dead load without affecting the strength of the structure. Besides aiming to the reduction of concrete usage and structure's self-weight, the idea of this research could be used and implemented in producing a lightweight structure with easy handling and installing, and at the same time focusing to meet the IBS system. [ABSTRACT FROM AUTHOR]

Bending is a conventional manufacturing process of sheet forming. This process induces reasonable residual stress through the thickness. Prediction of this residual stress profile is more difficult in bilayer sheet bending due to different material properties and thickness of layers. In this article, the residual stress distribution will be derived analytically for a bilayer sheet. The induced stress profile due to loading and released stress after unloading has been derived by integration along with the thickness. Also, the neutral axis movement due to non-uniform plastic deformation has been involved in the solution. The stress distribution has been derived analytically for elastic–perfect plastic, elastic–linear plastic and elastic–power law hardening material behavior. The results obtained from the proposed equation are compared by a finite element analysis. The finite element analysis contains bending a bilayer sheet to a specified curvature radius by a three-roll bending process. Comparing the results of the analytical solution and finite element analysis shows good agreement. The location of the neutral axis and the maximum of residual stresses in the thickness have been predicted very well with the proposed equation. [ABSTRACT FROM AUTHOR]

In conventional RC beam, the transition from compression to tension zone of the beam when load applied producing ineffective region at the middle area of the neutral axis. This is because, the area experiencing less compression and tension compare to the region above and below the neutral axis. Thus, the purpose of this research is to replace the use of concrete at the middle of the neutral axis by incorporating 4 PVC pipes to reduce cost and the self-weight of the structure. 4 pipes with a diameter of 20mm, 25mm and 50mm will be combined together to form a continuous voided square beam of V40, V50 and V100. The size of RC beam specimens is 1200mm x 160mm x 160mm, these beams were test with 3-point load test to identify the flexural strength. From the test, the ordinary beam recorded lowest maximum load, which is 15,35kN and VRB 100mm is the strongest beam with the maximum load 33.75kN and has the highest strength increment compared to another voided rectangular beam. Besides that, VRB 100mm also can reduced until 42.69% self-weight of RC beam and reduce until 37.5% of the concrete usage. From this study, it shows that the Voided Square Beam can reduce the self-weight of beam and reduce the concrete usage. Besides that, this idea also can implement to produce the lightweight structure that meet the standard of Industrialized Building System (IBS). [ABSTRACT FROM AUTHOR]

This paper uses long-term bridge monitoring data to quantitatively assess the composite action exhibited in slab-on-girder highway bridges and investigates the potential relationship between composite action and deck deterioration over negative bending regions. A three-span highway bridge in Michigan is instrumented with a structural monitoring system to observe the flexural response of the spans to vehicular loads. The monitoring system is designed to offer data for quantitative assessment of the degree of composite action in composite and noncomposite sections of the bridge spans using the position of neutral axis and the magnitude of slip strain as key response parameters correlated to composite action. It is shown that unintended nonlinear partial composite action exists in negative bending regions of the bridge. A calibrated analytical model and a finite-element model are developed based on empirical observation allowing tensile strains in the deck to be estimated under load. Estimated surface strains are compared with those with the design assumption of no composite action at the slab–girder interface. It is concluded that the observed partial composite action results in higher tensile strains in the deck which is a likely culprit to accelerated deck deterioration. [ABSTRACT FROM AUTHOR]

Carbon Fiber Reinforced polymer (CFRP) bars are weak in yielding property which results in sudden failure of structure at failure load. Inclusion of non-pretensioned steel reinforcement in the tension side of CFRP based prestressed concrete beam will balance the yielding requirements of member and it will show the definite crack failure pattern before failure. Experimental investigation has been carried out to study the deflection behavior of partially prestressed beam. Experimental works includes four beam specimens stressed by varying degree of prestressing. The Partial Prestressing Ratio (PPR) of specimen is considered for experimental works in the range of 0.6 to 0.8. A new deflection model is recommended in the present study considering the strain contribution of CFRP bar and steel reinforcement for the fully bonded member. New deflection model converges to experimental results with the error of less than 5% .

The continual increase of truck weights on our transportation system is a growing concern among bridge engineers. The load carrying capacity of the structures within the system must withstand this ever-growing demand. For multi-girder steel bridges, the load carrying capacity is heavily influenced by the presence of composite action between the girders and the concrete deck slab. While detailing to ensure reliable composite action is typically included in new designs, for many existing structures, the owner may not fully know the level of composite action. This may be due to administrative issues like insufficient original construction drawings or mechanical issues like breakdown of the shear transfer components. Even in situations where composite action was not intended there exists some partial interaction due to chemical bond and friction. Clearly understanding the presence and reliability of composite action in multi-girder structures is key to managing these structures effectively. This paper explores how load testing has been utilized to identify the level of composite action for existing bridges. The challenges associated with field identification of composite action are presented. In addition, three case studies of truck load testing are discussed. The first case utilized uncontrolled ambient truck measurements of an instrumented structure to field determine the composite behavior. The second and third cases perform a controlled load test with variations in truck weights and positions. Overall, the paper illustrates the advantages and disadvantages of truck load testing for identification of composite action and provides recommendations for future studies.

Featured Application: This study substantiates a curable area with self-healing in concrete material using a flexural test. The neutral axis was estimated as tension strains from attached successive strain gauge, and this before and after healing specified the curable area. The self-healing nature of concrete has been proved in many studies using various methods. However, the underlying mechanisms and the distinct area of self-healing have not been identified in detail. This study focuses on the limits of the area of self-healing. A bending specimen with a notch is used herein, and its flexural strength and stiffness before and after healing are compared and used for self-healing assessment. In addition, the neutral axis of the specimen was measured using successive strain gauges attached to the crack propagation part. Although the strength and stiffness of the concrete recovered after self-healing, the change in the location of the neutral axis before and after healing was insignificant, which indicates that physical recovery did not occur for once-opened crack areas. [ABSTRACT FROM AUTHOR]

Abstract The reduced-order modeling and performance of single-layered functionally graded piezoelectric energy harvesting systems are investigated. The choice of single-layered functionally graded materials gives the opportunity to minimize the volume of the energy harvesting system and hence increases its power density. Also, the unique composition of a functionally graded material allows for the creation of durable piezoelectric energy harvesters. As for the modeling of functionally graded piezoelectric materials, there has been some debate due to the location of the neutral axis compared to the central axis of the system. To this end, the use of the geometric central axis as the neutral axis to approximate the behavior of single-layered functionally graded cantilever piezoelectric energy harvesters and the possibility of getting erroneous predictions are explored. The effects of the material distribution and the scaling of the energy harvesting system form macro- to nano-scale are also considered. It is proved that the use of the central axis model can lead to significant inaccuracies in the estimation of the natural frequencies of the energy harvester for certain material distributions. Additionally, the central axis approximation exhibits a reduced coupling between the electrical circuit and the beam structure which could result in inefficient design of the energy harvester. It is also shown that the percentage of the metallic material can significantly affect both the natural frequencies and the power density of the system. The obtained results show the importance of considering the neutral axis modeling for efficient and optimal design of functionally graded piezoelectric energy harvesters. [ABSTRACT FROM AUTHOR]

The neutral axis position is considered as a potential parameter of early abnormal and long term performance for flexural members of structures. This paper is to propose the Neutral Axis Indicator (NA) based on strain measurements, to evaluate the behavior of NA, and to investigate challenges associated with the neutral axis for structural health monitoring purpose. A numerical example of a simply supported reinforced concrete (RC) beam was first developed and analyzed followed by an experimental study for further verification. With the aim of application to real bridges, a case study was conducted on Gantao River Bridge, a typical concrete box girder bridge, for detailed analysis using field data. The numerical and experimental examples, as well as field tests, aim to figure out: (1) the sensitivity of NA to structural damages, especially at early age; (2) stability and uncertainty of NA using field data; (3) capability of NA on detecting abrupt and slowly changing structural degradation. The results show that: NA takes on good index accuracy and damage sensitivity on numerical and experimental cases; NA tends to keep constant during linear elastic phase, while responses quickly and sharply to nonlinear behaviors such as concrete cracking and hardening; and NA is a potentially reliable indicator both to capture nonlinear performance and to detect minute damage. Additionally, the uncertainty of multiple disturbing effects can be mostly eliminated through statistical analysis. Thus, it can be employed effectively in condition assessment of concrete box girder bridges for long-term health monitoring. [ABSTRACT FROM AUTHOR]

Abstract: The energy harvesting by utilizing the piezoelectric effect for the conversion of oscillatory mechanical energy to useful electrical energy has been promising for self-powered devices. The output power can be controlled by designing the size and shape of the constituents of the harvester. This study demonstrates the effect of Ti plate (elastic layer) thickness on the resonant frequency, neutral axis position, vibration amplitude and energy harvesting performance of the cantilever structured piezoelectric energy harvester (PEH). Here, the each harvester had the same dimensions of piezoelectric layer and the same proof mass position at the end of the cantilever while it had the different elastic layer thicknesses (70-300 μm). The analysis revealed that the output power showed the opposite trend in vibration amplitude with varying the elastic layer thickness. Among all of the PEHs, the configuration with the largest elastic layer thickness (300 μm) exhibited a maximum output power of 48 μW at 76 Hz under 0.2 g acceleration, despite of the smallest vibration amplitude and the highest resonant frequency. The outcomes suggest that the thickness ratio of the piezoelectric and elastic layers should be optimized to realize the best harvesting performance.Graphical Abstract: [ABSTRACT FROM AUTHOR]

Holes contribute to the non-homogeneous nature of solid wood and shift the neutral axis of wood beams away from the centroid. Based on the plane-section assumption and idealized trapezoidal distribution, new calculating formulas will be presented in terms of the location of neutral axis for clear beams and wood beams with a hole at the center, compression zone and tension zone. To verify the results of theoretical analysis and formulas, four-point bending experiments of wood beams were performed by a digital image correlation (DIC) technique. There is a reasonable agreement between calculated and experimental results with a hole at the center or in the compression zone of the beams. Concerning a hole in the tension zone, on the other hand, the calculated locations of neutral axis are not in agreement with the experimental results, due to the plastic behavior on both the compression and tension zones of the beams in the inelastic stage. [ABSTRACT FROM AUTHOR]

Organic light-emitting diode-based flexible and rollable displays have become a promising candidate for next-generation flexible electronics. For this reason, the design of surface multi-layered barriers should be optimized to enhance the long-term mechanical reliability of a flexible encapsulation that prevents the penetration of oxygen and vapor. In this study, finite element-based stress simulation was proposed to estimate the mechanical reliability of gas/vapor barrier design with low-k/silicon nitride (low-k/SiN x ) stacking architecture. Consequently, stress-induced failure of critical thin films within the flexible display under various bending conditions must be considered. The feasibility of one pair SiO 2 /SiN x barrier design, which overcomes the complex lamination process, and the critical bending radius, which is decreased to 1.22 mm, were also examined. In addition, the influence of distance between neutral axes to the concerned layer surface dominated the induced-stress magnitude rather than the stress compliant mechanism provided from stacked low-k films. [ABSTRACT FROM AUTHOR]

Three-point bending tests are performed on center-notched graphite beams to study the fracture properties of IG11 graphite. Electronic speckle pattern interferometry (ESPI) is used to measure the full-field deformation of the graphite beams. A clip gauge is used to measure the crack mouth opening displacement (CMOD) of the beams, which validates the ESPI measurements. In addition, finite element (FE) analysis is performed by using the ABAQUS code coupled with the extended FE method to simulate the growth of cracks in graphite. A combined stress-energy based fracture criterion, specifically, damage for traction separation laws based on maximum principal stress damage initiation and energy based damage evolution with linear softening is applied. The numerical results are compared with the experimental results which show exceptional agreement, thus confirming the accuracy of the FE model. The fracture toughness K Ic , fracture energy G F , peak load P max and critical displacements at the peak load of each specimen are determined. From the displacement contours measured by ESPI, the positions of the neutral axis and crack opening displacement (COD) profiles at different loading levels are estimated. From the phase maps, the changes in the fracture process zone (FPZ) are analyzed and the size of the FPZ is determined. The strain contours at different loadings indicate that the material near the crack tip experiences biaxial tensile stress. [ABSTRACT FROM AUTHOR]

This paper proposes a method for the nonlinear analysis of laterally loaded single reinforced concrete piles based on the beam-on-nonlinear-Winkler-foundation approach. A nonlinear fiber beam-column element is used to model the nonlinear behavior of a pile. The pile is divided into a series of segments, of which the cross section is assumed to be plane and normal to the longitudinal axis. The internal force of a segment is derived by integrating the nonlinear stress-strain relationships of all steel and concrete fibers within the cross section of the segment. The substructure technique is introduced to calculate the stiffness matrix of the segments. The nonlinear behavior of soils surrounding the pile is characterized by a modified strain wedge model. The results show that (1) the predicted results using the proposed method are consistent with the measurements for all three full-scale tested piles, and (2) updating the neutral axis of segments has a significant effect on the calculated lateral deflection; however, it has a slight effect on the calculated bending moment. Moreover, an empirical equation is derived from the numerical analyses for estimating the cracked flexural rigidity of bored piles subjected to lateral loading. [ABSTRACT FROM AUTHOR]

According to the postulate concerning a local change of the “actual active radius” with a bending angle in the bend zone, a generalized model of strain during metal tube bending was derived. The tubes should be subjected to bending at tube bending machines by the method of wrapping at the rotating template and with the use of a lubricated steel mandrel. The model is represented by three components of strain in the analytic form, including displacement of the neutral axis. Generalization of the model during bending metal tubes at the tube bending machines as compared with the existing papers (Śloderbach, 1999; Śloderbach and Rechul, 2000) consists in including the neutral axis displacement and possibility of determination of strains at each point along the thickness of the wall of the bent tube in the bending and bend zone. The derived scheme of strain satisfies initial and boundary kinematic conditions of the bending process, conditions of continuity and inseparability of strains. The obtained analytic expressions can be classified as acceptable from the kinematic point of view

The self-healing nature of concrete has been proved in many studies using various methods. However, the underlying mechanisms and the distinct area of self-healing have not been identified in detail. This study focuses on the limits of the area of self-healing. A bending specimen with a notch is used herein, and its flexural strength and stiffness before and after healing are compared and used for self-healing assessment. In addition, the neutral axis of the specimen was measured using successive strain gauges attached to the crack propagation part. Although the strength and stiffness of the concrete recovered after self-healing, the change in the location of the neutral axis before and after healing was insignificant, which indicates that physical recovery did not occur for once-opened crack areas.

• Changes in the centroid of the cross-section stiffness of girders due to temperature gradient. • Theoretically thermal-varying model of the neutral axis position for the conventional and composite girders. • The neutral axis position is affected by the vertical temperature gradient and the average temperature. • Influencing factors include girder height and thermal coefficient of elastic modulus. • A theoretical law to eliminate the temperature-induced uncertainty. The neutral axis position is sensitive to changes in the cross-sectional area and stiffness of bridge girders but is inevitably influenced by the temperature effect. In the present study, simplified theoretical models between the neutral axis position and the structural temperature were established for both conventional girders and composite girders by introducing the relationship between the elastic modulus and the temperature. The theoretical results of four girders with specified section parameters were then validated by the model girders with different vertical temperature gradients and thermal coefficients of the elastic modulus. The results indicate that the neutral axis position is influenced by the vertical temperature gradient, weighted-average temperature, thermal coefficients of the elastic modulus, and girder height. The relationship between the neutral axis position and the weighted-average temperature of the composite girder is different from that of the conventional girder when the vertical temperature gradient is zero and negative. In addition, the amounts of the thermal-induced variation in the neutral axis position cannot be disregarded in view of the detection of minor damage to the main girder of bridges. [ABSTRACT FROM AUTHOR]

Adjacent segment degeneration typically follows anterior cervical spine fusion. However, the primary cause of adjacent segment degeneration remains unknown. Therefore, in order to identify the loading effects that cause adjacent segment degeneration, this study examined the loading effects to superior segments adjacent to fused bone following anterior cervical spine fusion. The C3–C6 cervical spine segments of 12 sheep were examined. Specimens were divided into the following groups: intact spine (group 1); and C5–C6 segments that were fused via cage-instrumented plate fixation (group 2). Specimens were cycled between 20° flexion and 15° extension with a displacement control of 1°/second. The tested parameters included the range of motion (ROM) of each segment, torque and strain on both the body and inferior articular process at the superior segments (C3–C4) adjacent to the fused bone, and the position of the neutral axis of stress at under 20° flexion and 15° extension. Under flexion and Group 2, torque, ROM, and strain on both the bodies and facets of superior segments adjacent to the fused bone were higher than those of Group 1. Under extension and Group 2, ROM for the fused segment was less than that of Group 1; torque, ROM, and stress on both the bodies and facets of superior segments adjacent to the fused bone were higher than those of Group 1. These analytical results indicate that the muscles and ligaments require greater force to achieve cervical motion than the intact spine following anterior cervical spine fusion. In addition, ROM and stress on the bodies and facets of the joint segments adjacent to the fused bone were significantly increased. Under flexion, the neutral axis of the stress on the adjacent segment moved backward, and the stress on the bodies of the segments adjacent to the fused bone increased. These comparative results indicate that increased stress on the adjacent segments is caused by stress-shielding effects. Furthermore, increased stress and ROM of the adjacent segments after long-term bone fusion may accelerate degeneration in adjacent segment.

The study analyses the behaviour of reinforced concrete beams strengthened with high-performance fibre-reinforced cementitious composite (HPFRCC). Six beams were divided into two equal groups and strengthened. In total, nine beams were tested, including three control beams that were not strengthened. Control beams were over-reinforced. The beams of the first group were strengthened in the compressed part while those of the second group were strength­ened in the compressed and tensioned parts of the section. The experimental results of all tested beams were compared with numerical results. The positive and negative effects of strengthening the resistance and serviceability of the beams were experimentally determined. The obtained results showed that the load-carrying capacity of all strengthened beams increased and their deflections decreased; however, crack width in the beams of the second group increased while that of the beams of the first group decreased. The width of cracks increased because the number of cracks decreased. The findings of this study show a comparison of strains, deflections, cracking and load-carrying capacity and indicate that strengthening changed the failure of the beams.

Numerical model analysis was carried out to study the deflection behaviour of FRP-based prestressed concrete (PSC) beam, because it does not resemble the existing deflection model of steel tendon-based PSC beam due to its non-ductile property. Deflection model by various researchers for the FRP-based PSC beams are underestimating as compared to experimental results which lead to unsafe design. There were 51 numbers of experimental results which were collected from various research articles for the numerical model analysis. Lagrange dual function convex optimisation used to predict the effective moment of inertia and shift of neutral axis distance. It reveals that the deflection of FRP tendon beam depends on deformability of material, degree of prestressing and bond strength. Design chart suggested for calculation of effective moment of inertia and effective neutral axis distance with respect to deformability index. The maximum deflection error by the proposed method is less than 5% as compared to experimental results. [ABSTRACT FROM PUBLISHER]

The study analyses the behaviour of reinforced concrete beams strengthened with high-performance fibre-reinforced cementitious composite (HPFRCC). Six beams were divided into two equal groups and strengthened. In total, nine beams were tested, including three control beams that were not strengthened. Control beams were over-reinforced. The beams of the first group were strengthened in the compressed part while those of the second group were strengthened in the compressed and tensioned parts of the section. The experimental results of all tested beams were compared with numerical results. The positive and negative effects of strengthening the resistance and serviceability of the beams were experimentally determined. The obtained results showed that the load-carrying capacity of all strengthened beams increased and their deflections decreased; however, crack width in the beams of the second group increased while that of the beams of the first group decreased. The width of cracks increased because the number of cracks decreased. The findings of this study show a comparison of strains, deflections, cracking and load-carrying capacity and indicate that strengthening changed the failure of the beams. [ABSTRACT FROM PUBLISHER]

For the Bi2223/Ag composite tape, on the existence of thermally residual stress, the neutral axis usually shifts away from the center of the cross section due to the Bauschinger effect of Ag and Ag alloy under the bending deformation. The movement of the neutral axis causes the redistribution of the stress and strain in the tape and further affects its critical current. In this paper, based on our modified model with the damage stress of the Bi2223 superconducting filaments, the movement of the neutral axis, the influence of the movement on the relation of the critical current versus the bending strain, and the distribution of the stress and strain on the cross section have been studied. The calculated results show that, the relation of the normalized critical current I/ I versus the bending strain with taking account of the movement of the neutral axis is closer to the experimental data than without that, the neutral axis moves always to the compressive side of the tape, and the movement increases with the bending radius R decreasing (i.e., the bending deformation increasing). Furthermore, in the different cases of the Bauschinger effect factor (BEF), the elastic modulus and volume fraction of the superconducting filaments, the movement of the neutral axis, the normalized critical current I/ I with the bending radius R, and the distributions of the stress on the cross section have been comprehensively investigated. [ABSTRACT FROM AUTHOR]

Within the past few years robust superconductor known as Secondgeneration (2G) High Temperature Superconductor (HTS) were developed for different industrial applications. Their fabrication includes a phase of large bending, which induces both axial and shear stresses, which could lead to the degradation of the super-conductive substrate. The design of HTS requires analysis of the stress and strains induced during their fabrication. The use of the finite element method for the analysis of this complex material requires large meshes and computation time, because of the ultra-small thickness of the supra-conductive substrate. In this paper, we present a simplified model, which is based on the classical beam theory together with the discretization of each layer in small sub-layers working under purely axial stress. The model takes into consideration the plastic behaviour of the HTS constitutive materials. The model is validated by its confrontation to finite element analyses. Then it is used for the optimal design of HTS by the analysis of different industrial configurations. Analyses lead to some recommendations concerning the optimal configurations that reduce the stresses in the supra-conductive substrate. [ABSTRACT FROM AUTHOR]

Structural health monitoring (SHM) is the process of continuously or periodically measuring structural parameters over time and the transformation of the acquired data into information about the actual structural behavior. The main goal of SHM is to provide quantitative and actionable information to infrastructure managers on a system-wide level. However, to achieve this goal, damage sensitive universal parameters need to be researched, identified, and implemented into SHM processes and data analysis. The neutral axis location has been identified as a potential parameter for damage detection, performance evaluation, and condition assessment of beam-like structures. This paper is intended to serve as a reference for researchers who are interested in the state of the art in evaluation of the neutral axis location, facts about the neutral axis behavior, and challenges associated with using the neutral axis for SHM purposes. Studies of the neutral axis in laboratory settings, controlled on-site testing, and on real structures in on-site conditions are presented and discussed. The main difficulties in using the neutral axis location for SHM purposes that are identified in this paper are: (1) its sensitivity to environmental effects such as temperature, humidity, and loading positions, (2) its natural variation in healthy cross-sections, (3) quantification of its sensitivity to damage, i.e. its damage detection capabilities in terms of the damage size and its distance from sensors, and (4) correlation between the neutral axis location and the capacity, performance, and condition of the monitored structure. The proof of concept has been provided with numerical modeling, and in the laboratory, and to some extent through controlled testing; however, a general on-site validation still remains a major challenge. [ABSTRACT FROM AUTHOR]

This paper reports the experimental investigation of the durability of screen printed conductor-based strain gauges on four fabrics of different stiffness by examining the change in the electrical resistances during and after bending. Emphasis is placed on improving the durability of the gauges for both positive and negative bending e-textile applications. The electrical resistance of the printed gauges is generally shown to degrade faster from positive bending than from negative bending. Compressive strain affects the behaviour of the gauges during bending but gauges perform best when they are close to the neutral axis of the printed fabric.