Longitudinal Strain Distribution Research Articles

Experimental and numerical investigation of a cold-formed steel system used to restore old buildings floor

This paper presents a novel configuration of built-up cold-formed steel (CFS) flooring system in the shape of a box section. A new technique is applied to produce the components of the flooring system, which are fastened by self-drilling screws. This box section consists of a cast-in-situ concrete slab, trapezoidal steel decking, two sigma section, steel plate and stiffening equal angles. The main objectives of this system is to enable rapid construction and decrease the time, requirements, and cost. As a result, the proposed system is designed to use the decking in a longitudinal direction. Many old buildings have sturdy structures but their floors were ruined due to being fabricated from timber. This flooring system will be implemented to increase their quality of life and be reused. The loading experiments of four specimens were carried out. The failure modes of the CFS flooring system, load-deflection relation curves, longitudinal strain distribution at different heights were obtained. The experimental results show that the flooring system has high stiffness and flexural performance and can reach ultimate strength without local buckling failure. The failure occurs due to distortion at the end supports. Then, the capacity of the flooring system was calculated theoretically. Then, the practical and theoretical results were compared. The calculated results agree well with the test results. A three-dimensional finite element model is also established to investigate structural performance of the proposed system.

Study on eccentric compressive performance of circular double skin concrete filled steel tube connected by thread through inside lining tube

Connection method of lengthening the steel tube of circular hollow sandwich concrete-filled steel tube by inside lining tube and thread is proposed. Twelve circular hollow sandwich concrete filled steel tubular beam-column connected by thread through inside lining tube are designed and fabricated using the length of the thread along the axial direction, the working height of the thread, and the position of the thread as parameters; In addition, one unconnected specimen and two welded specimens also are designed and fabricated to conduct controlled experimental research. The test phenomena and failure modes, axial compressive load-compression curve, axial compressive load-lateral deflection curve, and axial compressive load-strain in steel tube curve, as well as bearing capacity, strength reservation, deflection curve shape, lateral stiffness, ductility and plane section assumption are analyzed. The research results indicate that, within the parameter range studied, the thread connection through inside lining tube is reliable before tripping, and the experimental phenomenon of specimens connected by thread is basically consistent with that of the unconnected specimens. The axial compressive load-compression curve and axial compressive load-lateral deflection curve of all specimens can be approximately divided into elastic stage, elasto-plastic stage, and descending stage. The peak load of all specimens is relatively close, while although experiencing almost the same loading process, the strength reserve of the specimens connected by thread is insufficient. During the entire loading process, the shape of the deflection curve of all specimens is close to the sine half wave curve, and the distribution of longitudinal strain in the steel tube along the height of the middle cross-section basically conforms to the plane section assumption. Calculation method for bearing capacity of circular hollow sandwich concrete filled steel tubular beam-column connected by thread through inside lining tube is suggested.

Effect of size on eccentric compression performance of steel tube and sandwiched concrete jacketed CFST columns

This study investigated the size effect of steel tube and sandwiched concrete jacketed CFST columns under eccentric compression. A series of eccentric compression tests were conducted on 3 geometrically similar un-strengthened CFST columns and 13 strengthened CFST columns with varying structural sizes (with a ratio of 1:1.5:2), different eccentricities, and different outer steel ratios. The eccentric performance of the specimens, including their failure behaviours, load-axial displacement curves, and longitudinal and circumferential strain distribution were explored. Additionally, the size effect on nominal stress-longitudinal displacement relationships, nominal axial strength, nominal ultimate deflection and ductility index were investigated. The test results confirmed the presence of a size effect in both un-strengthened and strengthened CFST columns, with nominal strengths closely following Bažant's proposed "size effect law (SEL)". Finally, considering the influence of size effect, this study proposed axial force-bending moment (N-M) correlation curves for predicting the bearing capacity of strengthened CFST stub columns based on EC4, AISC-360, AIJ and GB 50936. Among these codes, AIJ provided the most accurate predictions when compared to the test results. Introducing the size effect coefficients mitigated the tendency to overestimate the load-bearing capacity of large-size retrofitted columns.

Normal values and distribution of ventricular global longitudinal strain in 513 healthy fetuses measured by two-dimensional speckle-tracking echocardiography: a multi-institutional cohort study.

This study aimed to determine the normal reference values and distribution of global longitudinal strain (GLS) in the right and left ventricles of healthy Japanese fetuses during pregnancy. This multi-institutional cohort study included healthy Japanese fetuses during normal pregnancies without maternal or fetal complications between 18 and 40weeks of gestation. Two-dimensional fetal echocardiographic images of the four-chamber view with a high frame rate were acquired and stored as DICOM clips. Data were collected and analyzed in a central laboratory to measure the left ventricular (LV) and right ventricular (RV) GLS using two-dimensional speckle tracking. In total, 513 fetuses were enrolled. The mean LV-GLS and RV-GLS were - 24.3% ± 3.5% and - 23.5% ± 3.7%, respectively. The magnitude of the GLS, with normal limits in both ventricles, decreased with advancing gestation. LV values were r = 0.34 (95% confidence interval, 0.27-0.42) and p < 0.0001; RV values were r = 0.33 (95% confidence interval, 0.25-0.41) and p < 0.0001. The normal values of healthy Japanese fetuses in healthy pregnancies is the first to be established by the large-scale, multi-institutional cohort study as LV-GLS of 24.3% ± 3.5% and RV-GLS of - 23.5% ± 3.7%, respectively. This can serve as a basic reference for assessing the cardiac functions in Japanese fetuses with various heart diseases.

Seismic response of mountain tunnel induced by fault slip

With the rapid development of Chinese transportation networks, such as the Sichuan-Tibet railway, numerous tunnels are under construction or planned in mountainous regions. Some of these tunnels must traverse or be situated near active fault zones, which could suffer damage from fault slip. In this study, the seismic response of a mountain tunnel subjected to coseismic faulting was analyzed using a fault-structure system in a two-step process. Firstly, a nonuniform slip model was proposed to calculate the ground deformations and internal displacements induced by a specific active fault on a geological scale, considering nonuniform slips on the fault plane. The 1989 Loma Prieta and 2022 Menyuan earthquakes were chosen as case studies to validate the proposed slip model. Secondly, the calculated displacement of the Menyuan earthquake was used as the input load for the discrete–continuous coupling analysis of the Daliang tunnel on an engineering scale. The simulated deformation of the Daliang tunnel aligned with the on-site damage observations following the Menyuan earthquake. Lastly, the effects of different fault conditions on the tunnel seismic response were investigated. The results indicate that the distribution of the peak longitudinal strain of the lining is governed by fault mechanisms, and the degree of fault slip significantly influences the response of the tunnel. A tunnel passing through an active fault with a wider fault fracture zone and smaller dip angle experience less damage.

Flexural behaviour of damaged concrete T-beams reinforced with ultra-high performance concrete filling

To improve the flexural performance of damaged reinforced concrete T-beams, a method of filling ultra-high performance concrete (UHPC) in the damaged area was adopted. Experimental studies were conducted on two UHPC-reinforced concrete T-beams with different lengths of damaged areas and one undamaged concrete T-beam as a reference. Crack distribution, failure modes, cracking loads, flexural capacities, and strain variation of the specimens were analyzed. Subsequently, a nonlinear finite element (FE) model of the UHPC-reinforced T-beam was developed using ABAQUS, and the FE model results were compared with the experimental results to validate the accuracy of the FE simulation method. The results indicated that the two UHPC-reinforced T-beams exhibited a similar flexural failure process to the undamaged T-beam. The longitudinal tensile strain distribution at the mid-span section showed that the composite section formed by the filling of UHPC in the damaged region still adhered the assumption of the planar section. Owing to the excellent bond performance between UHPC and the existing concrete, the main cracks of the UHPC-reinforced T-beams appeared in the chiseled area, and the crack widths of the UHPC-reinforced T-beams under the same load were smaller than those of the reference T-beam. Overall, the reinforcing method of filling UHPC in the damaged region can restore or even enhance the flexural performance of the damaged reinforced concrete T-beams.

Experimental study on the bond-slip behavior of steel tube-coal gangue concrete

This study investigated the bond-slip behavior at the interface between steel tubes and coal gangue concrete, considering the coal gangue coarse aggregate replacement rate, the strength grade of coal gangue concrete, and the bond length as variable parameters. Eleven groups of push out tests were conducted on steel tube coal gangue concrete specimens. The bond slip curve and the longitudinal strain distribution curve of the steel tubes were obtained, and the effects of these parameters on bond strength were analyzed. The results showed that the load-slip curves at both the loading and free ends of the specimens were similar, with slip occurring earlier at the loading end. The regularity of the test curves in repeated experiments indicated that interfacial bond stress was primarily determined by friction in the later stages. The longitudinal strain of steel tubes was approximately exponentially distributed along their length. The interfacial bond strength increased with the increase of coal gangue aggregate replacement rate and was more pronounced in specimens with higher strength coal gangue concrete. Longer bond lengths resulted in greater bond failure loads, with a lower rate of increase in higher strength coal gangue concrete specimens compared to those with lower strength. Based on the three stage bond stress-slip relationship for steel tube-concrete, a bond-slip constitutive model for steel tube-coal gangue concrete was established. This provided a reference for mechanical analysis and interface performance design of steel tube-coal gangue concrete.

Experimental and analytical investigation on eccentric performance of circular CFST columns jacketed by concrete-filled square tube

This paper presents an experimental and analytical investigation of the eccentric behaviour of circular CFST columns strengthened by a square steel tube and sandwiched concrete jackets. The main parameters include the eccentricity, strength of sandwiched concrete, and thickness of the outer steel tube. The failure modes, load-axial displacement curves, load-lateral deflection curves, and longitudinal strain distributions are presented. The effects of these parameters on the ultimate strength, ductility index, and lateral deflection are discussed in detail. Based on the longitudinal strain results obtained from the experiment and basic hypotheses, the possible positions of the neutral axis in the column section at the ultimate limit state were analysed, and three failure patterns of the specimens were determined. Analytical formulas corresponding to each failure pattern were derived to calculate the eccentric load-bearing capacity of the strengthened columns based on the limit equilibrium theory. Finally, a simplified formula was proposed to serve as the basis for future designs and applications.

Research on the interfacial bonding performance of novel composite L‐shaped concrete‐filled steel tubes

SummaryThis study aims to investigate the bonding performance of novel composite specially shaped concrete‐filled steel tubes (CFSTs). Seven novel composite L‐shaped CFST specimens were designed utilizing variations in steel tube wall thickness, steel tube length, and concrete strength as the primary parameters. Their failure modes, load–slip relationships, and longitudinal strain distribution patterns were examined through push‐out tests. Additionally, finite element models of the members were established using nonlinear spring elements based on the experimental data and subjected to numerical analysis. The research findings indicate that the ultimate bond strength of the composite L‐shaped CFSTs is positively correlated with steel tube wall thickness, steel tube length, and concrete strength. The strain distributions on the concave and convex faces of the L‐shaped steel tubes are identical. The results obtained from the finite element analysis closely match the experimental findings.

Определение разновидностей оптических волокон и ранняя диагностика их физического состояния на основе анализа характеристик рассеяния Мандельштама–Бриллюэна

Research results into the automating the processing of measurement data obtained from the Brillouin optical reflectometer, light guides containing various types of optical fibers are presented in this paper. By analyzing the parameters of the Mandelstam — Brillouin scatter obtained from Brillouin reflectograms, we can classify optical fibers in the studied telecommunication optical cables. This makes it possible to evaluate the change of the Brillouin frequency shift and determine the longitudinal fiber tension. The initial values of the Brillouin frequency shift and the profile of the Mandelstam — Brillouin scatter spectrum are different for each fiber type. The programs for automated processing of Brillouin reflectogram data are discussed. Estimation of the level of the back-reflected signal allows you to identify the factor, that had a predominant effect on the parameters of the Mandelstam — Brillouin scatter signal in the studied sections of optical fibers, and to compensate for the influence of temperature changes in the longitudinal strain distribution graphs. After that, we can plot a graph of the distribution of longitudinal strain along the fiber, caused precisely by mechanical influences on optical fibers. Conclusions about the accuracy of the estimates obtained by various algorithms, based on the accumulated experience in working with the presented programs are drawn.

Diagnostic accuracy of apical sparing pattern in transthyretin-derived cardiac amyloidosis assessed by two-dimensional strain echocardiography

Abstract Background Cardiac amyloidosis (CA) is a rapidly progressive disease that portends poor prognosis. Recently, transthyretin-derived CA (ATTR-CA) has attracted attention due to the emergence of specific drugs, and its simple and accurate diagnosis is required. Apical sparing pattern of regional longitudinal strain (LS) distribution has been known as specific echocardiographic finding for CA. However, its diagnostic significance is unclear when limited to ATTR-CA. Aims This study aimed to investigate the diagnostic accuracy of apical sparing pattern to distinguish ATTR-CA from other left ventricular hypertrophic diseases. Methods This was a retrospective study evaluating 32 patients underwent endomyocardial biopsy for differentiation of left ventricular hypertrophy from November 2018 to August 2022. Based on clinical data, patients were classified into 9 patients in ATTR-CA, 14 patients in hypertrophic cardiomyopathy (HCM), and 9 patients in hypertensive heart disease (HHD). In addition to routine echocardiographic findings, left ventricular LS analysis was performed. Relative regional strain ratio (RRSR) as an index of apical sparing pattern was measured as the average of apical LS divided by the sum of the average of mid and basal LS values. Results RRSR in ATTR-CA group was significantly higher than in HCM and HHD groups (0.96 vs. 0.68 vs. 0.72, P=0.004) (Table). In the receiver-operating characteristic analysis of RRSR for differentiating ATTR-CA from HCM and HHD, the optimal cut-off value of RRSR for the diagnosis of ATTR-CA was 0.93 (sensitivity 67%, specificity 96%, area under the curve 0.84) (Figure). Conclusions Apical sparing pattern may have acceptable accuracy in diagnosing ATTR-CA versus other left ventricular hypertrophic diseases, but the relatively low sensitivity may be a clinical limitation.Table:Echocardiographic dataFigure

An automation of the detection processes of the strain characteristics of optical fibers, classification of their varieties and identification the influence factor according to Brillouin reflectograms

Research results into the automating the processing of measurement data obtained from the Brillouin optical reflectometer, light guides containing various types of optical fibers are presented in this paper. By analyzing the parameters of the Mandelstam–Brillouin scatter obtained from Brillouin reflectograms, we can classify optical fibers in the studied telecommunication optical cables. This makes it possible to evaluate the change of the Brillouin frequency shift and determine the longitudinal fiber tension. The initial values of the Brillouin frequency shift and the profile of the Mandelstam–Brillouin scatter spectrum are different for each fiber type. The programs for automated processing of Brillouin reflectogram data are discussed. Estimation of the level of the back-reflected signal allows you to identify the factor, that had a predominant effect on the parameters of the Mandelstam–Brillouin scatter signal in the studied sections of optical fibers, and to compensate for the influence of temperature changes in the longitudinal strain distribution graphs. After that, we can plot a graph of the distribution of longitudinal strain along the fiber, caused precisely by mechanical influences on optical fibers. Conclusions about the accuracy of the estimates obtained by various algorithms, based on the accumulated experience in working with the presented programs are drawn.

Load introduction and transfer mechanism of K-type CFST circular section connections

This paper investigates the mechanism of load introduction and transfers for K-type concrete-filled steel tubular (CFST) circular section connections experimentally and numerically. Six K-type CFST connections were tested. Three-dimensional finite element (FE) models were then developed and validated against the test results, where the degradation and failure of the direct bond interaction were considered explicitly. The longitudinal strain distribution along the circumferential direction of chord-wall demonstrated that the non-uniform force transfer in the chord was caused by the one side load introduction through braces. The effects of the chord length, cross-sectional slenderness and interfacial interactions on the force transfer of tube-concrete interface were evaluated: 1) the chord length above the connecting region has a positive influence on the force transfer; 2) for the K-type CFST connections in this study, the material strength of concrete in the chord with non-compact and slender sections could not be fully utilized due to the insufficient force transfer; 3) the direct shear interaction dominated the force-transferring process from chord-wall to concrete for the compact section chord with reinforcing plates. Furthermore, the test and FE result confirmed that the load introduction length of the CFST chord with braces included the chord above the connecting region and the full connecting region. In addition, the equation of effective load introduction length for the CFST chord of the K-type connections was proposed.

Eccentric compressive behavior of square concrete-filled stainless steel tube (CFSST) stub columns

To study the eccentric compressive behavior and mechanism of square concrete-filled stainless steel tube (CFSST) stub columns, a total of 12 specimens with different steel ratio and load eccentricity under eccentric load was investigated. The results demonstrated that the failure modes of all square CFSST stub columns were the outward local buckling of the stainless steel tube at the compression side and two adjacent sides. The load-longitudinal deformation curve of specimens exhibited three stages, including elastic stage, elastic-plastic stage, and descending stage. The longitudinal strain distribution in the cross section at the mid-height of the specimens generally satisfied the plane-section assumption during the loading process. Increasing the steel ratio of specimens significantly improved the ultimate bearing capacity. Meanwhile, the ultimate bearing capacity of the specimens decreased with the load eccentricity, and the second-order effect became more pronounced with the increase in eccentricity. Finally, based on the existing specification, this study proposed a prediction formula for the eccentric bearing capacity of square CFSST stub columns by modifying the eccentric reduction coefficient accompanied by adopting the method of equivalent cross section. The formula was verified using an established database of eccentric compression CFST stub columns in the existing literatures.

Profile defects caused by inhomogeneous longitudinal strain distribution in roll forming

Roll forming is a sheet metal forming operation that incrementally forms flat sheets into a desired profile geometry. The process is characterized by a high material utilization and a high output quantity. Concomitant with these advantages, profile defects such as bow and twist of the profile can occur. In the literature, an inhomogeneous longitudinal strain distribution across the profile cross-section is considered to be the cause of these defects. However, a quantitative cause and effect analysis is missing up to now. This paper presents an analytical model that shows a quantitative relationship between profile defects and the underlying longitudinal strain distributions. The model can be used to calculate the longitudinal strain distribution of a roll-formed profile across its cross-section based on given values for bow and twist or vice versa. It is compared with results from simulations and experiments and clearly reveals the cause for twist and bow in roll forming.Graphical abstract

Performance investigation and parameter identification of inverse variable cross-section energy harvester

An important issue in traditional energy harvesters is that the best performance of the device is limited to the uneven longitudinal strain and electric displacement distributions. One solution to this challenge is to incorporate of variable cross-section design and rotational motion. In this study, we propose a new rotational inverse complex piezoelectric energy harvester featuring two beams for ultra-low-frequency rotation applications. A comprehensive electromechanical model is developed based on the extended Hamilton's principle, and the analytical models are extracted for vibration response and electric performance under ultra-low-frequency excitations. Closed-form analytical expressions of the rotational frequency, electrical load resistance, and centrifugal coefficient are derived to give in-depth insights into the influence mechanism of the centrifugal softening effect for the extreme conditions of RL→0 and RL→∞. Moreover, we propose a parameter identification method to recognize optimal electrical load resistance for ultra-low-frequency rotational scenarios in the absence case of experimental equipment. Based on the validated theoretical model, parametric studies are conducted to investigate the effects of the structural parameters on the dynamic behaviors and output electric performance, it can be concluded that the appropriation selection of the structural parameters can change the dynamic behaviors of the harvester and enhance the energy harvesting performance. Besides, the prototype of the proposed harvester was designed and fabricated and experiments were carried out. Both analytical simulation and experimental results show that the proposed inverse energy harvester has an excellent harvesting performance at the ultra-low-frequency rotational excitations, and the output voltage of the proposed inverse energy harvester is 12% larger than that of a traditional inverse energy harvester.

Straight roll formed profiles through partial rolling

Roll forming is a sheet-metal forming operation that incrementally forms a flat sheet into a desired profile by successively arranged rolls. Due to the process-related longitudinal strains, profile defects such as vertical and horizontal bow and twist occur. In this paper, a new straightening method is investigated that homogenizes the longitudinal strain distribution to eliminate profile defects by partial rolling. An experimental implementation of partial rolling for an asymmetrical hat-profile proves the feasibility of the method. This method is compared numerically with conventional methods which show that profiles can be straightened more efficiently with the help of partial rolling.

Longitudinal strain and wrinkling analysis of variable depth flexible roll forming

Flexible roll forming (FRF) enables the forming of high-strength sheet metal materials into complex shapes relevant to the transportation industry until recently, however, has been limited to the forming of variable-width profiles where the web section is flat with a curved flange. Recent developments in 3D flexible roll forming now enable forming of variable depth components that have a curved web with flat flanges; these shapes are better suited for automotive applications. However, wrinkling in the flange due to excessive compressive longitudinal stress remains a major challenge. Deformation strain and stress analysis has been applied in previous studies to estimate the wrinkling tendency, but current analytical equations are limited to variable-width shapes with limited accuracy, particularly regarding the level and distribution of longitudinal strain. In the current study, a new analytical model is developed to analyse the distribution and level of longitudinal edge strain for a variable depth component shape. The analytical predictions are compared with experimental measurements for key conditions. This shows that the new analytical equations developed in this study provide higher accuracy compared to existing models and enable for the first time the prediction of the distribution of longitudinal strain in the flange of a flexible roll forming component. For some of the tested conditions, flange wrinkling was observed and there the model correlation was poor given the theory assumes a wrinkle-free flange. The strain deviation observed here is associated with the shape deviation due to wrinkling. The analytical model predicts the strains that are required to form a perfect part shape. Wrinkling reduces the compressive longitudinal strains that are formed into the flange, and this leads to a poor correlation between the experimental and the predicted strain values if the wrinkling severity is high. The model brings some insights into the wrinkling behaviour in variable depth flexible roll forming by predicting the variation of the peak strain and overall distribution with key geometric parameters. The new analytical model for longitudinal edge strain presented in this study will enable a more rapid process design and optimisation before time-consuming FEA analysis is performed. It, therefore, presents a vital step towards a wider spread in the application of flexible roll forming in the automotive and transport industries.

Mechanical performances of high‐strength concrete‐filled steel tubular medium–long columns with square cross section

AbstractIn order to investigate the influence of concrete strength, slenderness ratio, and eccentricity on the ultimate bearing capacity, initial stiffness, and other mechanical properties of square high‐strength steel tubular medium–long column, a total of 11 square column specimens were designed and made. The compression tests were carried out, and the load–longitudinal deformation curve, load–deflection curve, longitudinal strain distribution curve of mid‐span section, and several failure modes of the composite column were obtained. Numerical simulations were conducted, and the results are in good agreement with the experimental results. It is found that the concrete strength has little effect on the initial stiffness of the square high‐strength concrete‐filled steel tubular medium–long column, and the ultimate bearing capacity and initial stiffness decrease with the increase of slenderness ratio and eccentricity, and the eccentricity has a particularly significant influence on the bearing capacity.

Push-out tests of CFST columns strengthened with self-compacting and self-stressing concrete filled square steel tube

There are two dominant interfaces in concrete-filled steel tube (CFST) columns strengthened with CFST jacketing: (a) interface between the sandwiched concrete and the outer wall of the inner steel tube (interface Ti); (b) interface between the sandwiched concrete and the inner wall of the outer steel tube (interface To). 16 push-out tests were conducted on CFST columns strengthened with self-compacting and self-stressing concrete filled square steel tube to study the bond behaviour of the two interfaces. The experimental parameters included the sandwiched concrete strength (C50, C60 and C70), thickness of outer steel tube (3.5, 4.5 and 5.5 mm), self-stressing (with and without) and interface type (interface Ti and interface To). The influence of different parameters on the bond behaviour was assessed and the longitudinal strain distribution of interfaces To and Ti along the length of the outer and inner steel tubes was analyzed, respectively. The results indicate that the interfacial bond stress presents as an exponential function in the direction of interface length. Interface Ti has higher average ultimate bond strength compared with corresponding interface To. The bond strengths of both interfaces increase with increasing sandwiched concrete strength and thickness of outer steel tube. However, the self-stressing only has evident effect on the bond strength of interface To. In addition, formulas for calculating the bond strengths of both interfaces in retrofitted columns were proposed, and the experimental results from previous studies were also compared with predictions from proposed formulas and design codes.