Section Geometry Research Articles

Development of Spring Hinge Models to Simulate Structural Elements of Spherical Graphite Reinforced Concrete

The goals of the study were the formation of a model of concentrated plasticity based on spherical graphite fibers. The goal was to present indicators of the cyclic behavior of structural elements due to the lack of consideration in modern scientific research of the issue of increasing the technical level and reliability of structures due to the addition of innovative materials during the development of structural elements. Taking into account the fundamental shortcomings in construction in the conditions of installing an excess amount of reinforcement, as one of the main mechanisms for achieving strength and reliability. The aim of the study was to develop a method of improving the quality of structural elements using innovative materials through building spring hinge models. The study involved the mathematical simulation, comparison, and system analysis. The result of the work is a developed spring hinge model for simulating reinforced concrete structural elements. The work emphasizes that the obtained experimental model converges to reference data and does not reflect a significant error with the increased number of cycles. It is emphasized that the model degrades with significant calibration, while the numerical strength and hysteresis behaviour matches the experimental data at higher deformation levels. The model of concentrated plasticity based on spherical graphite fibers was developed for the range of indicators of the cyclic behaviour of structural elements. The main characteristics of the reinforced concrete structural elements under consideration in the framework of the study are provided in a table in order to visually separate the groups of structures according to the main parameters. A non-linear model of a spring hinge is graphically shown, which shows the moment of movement of the spring when a monotonous load is applied. An urgent need to build a system of indicators of the structural elements’ cyclic behaviour was emphasized. A concentrated plasticity model based on spherical graphite fibers was built for this purpose. A beam-column was chosen as a reinforced concrete structure, which is based on a zero-length spring pivot hinge at the end of each individual element. This spring pivot hinge is a uniaxial material model with a moment-rotation dependency. Such a dependency is the fundamental basis of the spring hinge model used to simulate reinforced concrete structural elements. The comparison chart of reference and cyclic strength of a spherical graphite reinforced concrete beam is presented graphically. Prospects for further research involve the development of an empirical system of equations depending on the section geometry and the properties of the structure material based on prognostic variables from the list of potential variable characteristics.

Relationship between Highway Geometric Characteristics and Accident Risk: A Multilayer Perceptron Model (MLP) Approach

The traffic safety of mountain highway has always been one of the taking point. This study aims to collect road design data in large-scale research and analyzes the accident risk of highway geometric alignment. Accordingly, a method based on satellite maps and clustering algorithms is proposed to calculate the geometric alignment of the highway plane and its longitudinal section. The reliability of the method was verified on Nanfu highway in Chongqing, China. The planar and longitudinal sectional geometries of the four highways in Chongqing were obtained by the above method, and the corresponding 36,439 traffic accidents which occurred from 2010 to 2016 were used as the research objects. The accident risk of the highway geometry was analyzed based on the SHAP and MLP theories. The results show that the fitting and prediction abilities of the MLP model are better than those of the negative binomial model, and its correlation coefficient is improved by 33.2%. In addition, compared with the negative binomial model, the MLP model can estimate more accurately and flexibly the complex nonlinear relationship between the independent and the dependent variables.

Axial compressive behaviour of corroded steel reinforced concrete columns retrofitted with a basalt fibre reinforced polymer-ultrahigh performance concrete jacket

• An accelerated retrofit approach is developed. • The axial compressive behaviour of retrofitted columns are analyzed in detail. • A simple model was proposed with relatively conservative predictions. Steel-reinforced concrete (SRC) members suffer from severe corrosion in some scenarios. Therefore, new techniques and materials are required for the timely rehabilitation of the deficient structures. To address this challenge, the authors have developed an accelerated retrofit approach using a basalt fibre-reinforced polymer (BFRP) sheet combined with an ultrahigh-performance concrete (UHPC) jacket. The BFRP sheet was internally embedded within the UHPC matrix to enhance its durability under marine environmental conditions. The treatment of corroded steel stirrups in SRC columns replaced with fiber-reinforced polymer (FRP) composites is also considered in the retrofit approach. The authors then investigated the axial compressive behaviour of a series of corroded RC columns retrofitted with a BFRP–UHPC jacket or with a UHPC jacket. Specifically, 16 RC columns (six control specimens and 10 retrofitted specimens) were prepared and tested under monotonic axial compression. The test variables were the sectional geometry (i.e. circular or square cross -section), transverse steel reinforcement ratio (i.e. two different stirrup spacings), and retrofitting method (i.e. BFRP–UHPC jacket or UHPC jacket). The test results showed that the maximum increase in the peak load after retrofitting was as large as 145.89%. The authors also developed a simple model for retrofitted RC columns that can provide reasonably accurate but relatively conservative predictions.

Relationship between the geometry of the transition section and the loads acting on the conveyor belt

Relationship between the geometry of the transition section and the loads acting on the conveyor belt

Evaluation of a method to calculate debris-flow volume based on observations of flow depth

The volume of a debris flow is a critical parameter in hazard analysis, yet accurate estimates of volume are often unavailable due to mixing with larger rivers at the downstream end of alluvial fans. We describe a method to calculate the volume of debris flows using flow depth data collected at a check dam, using a Manning friction relation to describe the velocity of the debris flow as a function of flow depth, and the geometry of the channel cross section. The method is evaluated using a published data set from the USGS debris-flow flume where event volume and stage information have been accurately measured, and results in volume estimates either somewhat smaller than or up to 50% larger than observed volumes. We further demonstrate the method to single-surge and a multiple-surge debris flows observed at Illgraben.

Surface topography and melt pool behavior in rapid turnaround regions of laser powder bed fusion additive manufacturing of nickel superalloy 625

The complexity and vast number of influencing variables in laser powder bed fusion have hindered the development of correlations between surface topography and part performance or process variables. To address this, we investigated the melt pool behavior in regions of the part where a rapid back-and-forth scan strategy occurs. Analysis of surface topography and melt pool cross section geometry on nickel superalloy 625 samples helped identify their relationship. From this, a conceptual model was developed and the implication this has for the development of strong, process-informed correlations is discussed.

НАДЕЖНОСТЬ И ДОЛГОВЕЧНОСТЬ ТРУБЧАТЫХ ЭЛЕМЕНТОВ СТАЛЬНЫХ КОНСТРУКЦИЙ ПРИ НЕРАВНОМЕРНЫХ КОРРОЗИОННЫХ ПОВРЕЖДЕНИЯХ

Modern approaches and requirements for the design and expert assessment of the buildings and structures state require the quantitative determination of their reliability indicators. This determines the relevance of the development of methods for calculating the reliability of building systems, taking into account their properties and operating conditions. Corrosion damage to elements of metal structures can lead to loss of their functionality over time. The purpose of the research presented in the article is to identify and quantitatively describe changes over time in the reliability characteristics, according to the strength criterion, of an initially centrally tensile steel rod structural element of an annular section, taking into account uneven corrosive wear, which causes the occurrence of complex resistance of the rod, namely tension with bending. A calculation apparatus and an algorithm for determining the reliability and durability of an element were constructed using methods of reliability theory and the proposed spatio-time corrosion model. Calculations of these characteristics were carried out by varying the stochastic properties of the parameters of the rod’s cross section geometry, its stress state and the corrosion model at various degrees of corrosion factor aggressiveness. The loading of the rod was modeled by a stationary random function. The results of calculations of reliability, failure probability, corrosion coefficient and time density of failure probability are presented in graphs of the dependences of these values on time. The influence of the main design characteristics of the rod and the corrosion damage model on the reliability and durability of the structural element was assessed. The effect of a significant increase in the probability of failure and a decrease in durability with corrosion wear, uneven along the contour of the section, was revealed, in comparison with the case of a constant thickness of the corrosion layer, with comparable values of corrosion coefficients. The methodology and calculation results presented in the article can be used to obtain solutions to similar problems in other formulations (by cross-sectional shape, corrosion model, under non-stationary loading conditions, etc.), as well as to perform engineering reliability calculations when designing metal structures.

METHODOLOGICAL PROPOSAL FOR THE SELECTION AND ANALYSIS OF THE PERFORMANCE OF RIGID SAILS CONSIDERING PRE-STALL AND POST-STALL AERODYNAMIC CONDITIONS

The shipping industry is increasingly considering the issues of "green shipping" and "zero-emission shipping", which are closely related to reducing the consumption of fossil fuels to mitigate its environmental impact. In this way, the use of renewable energies is increasingly perceived as part of the energy mix, with the use of rigid sails (wind energy) being one of the tested alternatives as auxiliary propulsion systems. This work studied the fluid-mechanical optimization of the airfoil that defines the cross section geometry of the rigid sail. A methodology was developed to obtain the aerodynamic coefficients of the rigid sail for any position of the sail with respect to the wind depending on the tested airfoil. Once the aerodynamic coefficients were modeled for several angles of attack, the thrust and overturning components generated by the sail force on the boat were computed from before and after airfoil stalling predictive models of the aerodynamic coefficients. From the obtained results, the following two main conclusions can be stated. i) The use of the sail in post-stall conditions for higher angles of incidence (from approximately 90°) substantially improved the thrust generated on the boat. For the case of small incidence angles, it is recommended to set the sail at an angle of attack less than the airfoil stall. ii) Within the symmetrical four-digit NACA series, the symmetrical NACA 0015 airfoil turned out to be the best choice for geometrically defining the rigid sail cross section, as it provided the highest possible thrust while minimizing the overturning force. Key Words: rigid sails, wind powered, airfoil, aerodynamic coefficients, CFD

Экспериментальные исследования колебаний трамвая «Витязь-М»

Objective: Based on experimental studies of vibrations of Vityaz-M tram car occurring at speeds of 50 km/h or more on track straight sections with P65 rails on reinforced-concrete sleepers, to evaluate the effect of transversal vibrations on traffic safety and passenger comfort. To show the inconsistency of existing regulatory documentation on the structure and maintenance of tram tracks and tram chassis with the development prospects. Methods: Experimental measurements of vibration accelerations of tram body and tram chassis, having different mileage, when moving along track experimental section. Measurement and analysis of geometric parameters of rail track experimental section and of trams. Results: Measurements of vibration accelerations occurring during tram motion with 20 to 50 km/h speeds were performed as well as geometric parameter analysis for rail track experimental section and rolling stock wheels’ profiles, participated in the tests, was pursued. During the races, vibration accelerations that occur during movement were measured in three directions — longitudinal, transversal and vertical. The appearance of transversal vibrations of tram body affecting passenger discomfort and traffic safety has been confirmed. The root mean-square values of the amplitudes of vibration accelerations towards three directions in acceleration gravity (g) fractions have been obtained in two variants — at trolley motion between joints and at joints. Vibration acceleration frequency analysis has confirmed a sharp increase in the amplitude of transversal vibrations at frequencies in the region of 1–2 Hz at a speed of 50 km/h for a tram with worn wheels. The compliance of rail track experimental section geometry with the accepted standards as well as the compliance of rolling stock wheels dimensions with constructive documentation are noted. Practical significance: The need for further comprehensive study of the interaction of track and rolling stock while high-speed tram introduction with the purpose to improve existing standards on the structure and maintenance of tram tracks and tram chassis.

NUMERICAL INVESTIGATION OF HVAF-SPRAYED Fe-BASED AMORPHOUS COATINGS

A numerical analysis was performed to predict the effect of the convergent section geometry of a gun nozzle on the high-velocity air-fuel (HVAF) thermal spray Fe-based amorphous coating (AC) process. A computational fluid dynamics model was applied to investigate the gas-flow field and the behavior of in-flight particles at nozzle entrance convergent section length ranging from 28 mm to 56.8 mm and different shapes of the Laval nozzle convergent section (a straight line and Vitosinski convergence curve). On the one hand, the change in the gas-flame flow characteristics for the Vitosinski curve shows a uniform and stable flame compared with the straight-line curve in the convergent section. The straight-line curve shape of the Laval nozzle convergent section has a higher particle temperature compared with the Vitosinski-curve shape of the Laval nozzle convergent section. The particle dwell time for the straight-line curve shape of the Laval nozzle convergent section is longer than that for the Vitosinski curve shape of the Laval nozzle convergent section. On the other hand, the nozzle entrance convergent section length obviously affects the particle temperature, and the particle dwell time increases with the increasing nozzle entrance convergent section length. By analyzing both the melt status of the particles and particle velocity, the optimal gun configuration (0.7 V) producing low-porosity coatings was predicted. These calculations were experimentally verified by producing a low-porosity (1.37 %) Fe-based AC, fabricated with HVAF using the predicted optimal gun configuration.

Effects of support type and geometric shape of steel tube on concrete-encased concrete-filled steel tube beam under low velocity impact

Concrete-encased concrete-filled steel tube (CEFST) beams prepared by placing steel tube in RC beam is a beam type that has widespread use. The current study examines the effects of steel tube geometry and support conditions on the behavior of CEFST beams under low velocity impact loading. First, CEFST beam specimens with different lengths and different tube section geometries (circular and square) were produced in the laboratory. These four test specimens with two different support conditions were exposed to low velocity impact load tests. Finite element models of the test specimens were created using Abaqus\\Explicit software. In the next stage, 4 finite element models were verified by the experimentally obtained damage conditions, maximum displacements, and support reaction forces. In the final stage, as parametric study 12 finite element models were prepared in addition to 4 verified models and analyzed under low velocity impact loading. In addition to experimental values, Von Mises stresses, Equivalent plastic strain, Friction energy, and Damage energy values were also obtained by the numerical study and thus the effects of steel tube geometry and support conditions were comparatively examined. The obtained results showed that CEFST beams with a square tube section exhibited better performance under a sudden load such as impact compared to the beams with a circular tube section. Moreover, both numerical and experimental results pointed out that the beam length beyond support has a positive impact on the performance of beam under impact loading.

Analytical moment-curvature solutions for generalized textile-reinforced concrete sections

A piecewise linear parametric constitutive model of elastic-plastic-hardening in tension and elastic-plastic in compression is used to develop closed-form solutions for flexural moment-curvature of generalized sections. Brittle matrix composite such as Textile Reinforced Concrete (TRC) is homogenized using three zones of elastic, distributed cracking, and tension stiffening up to the maximum tensile strength. Linear segments of the tensile and compressive constitutive responses are integrated for various states of strain and extended to geometrical structural shapes such as steel W-, T-, and C- sections. The closed-form moment-curvature response is obtained using two independent variables of strain distribution and neutral axis location and extended to obtain the stress distribution, curvature, rotation, and deflection profile of statically determinate load cases using an input strain. The solutions for serviceability-based criteria and limit state parameters such as curvature, rotation, and deflection distribution as a function of the applied load can be obtained. The generalized parametric solutions are applied to the elastic-plastic flexural response of quasi-brittle or ductile beams of structural steel with unique cross-sectional geometries. Case studies of the correlation of tensile and flexural tests of TRC with variables such as types and direction of the weave, number of textile layers, and section geometry are validated. The parametric nature of the formulation offers computational efficiency for applications that address material and shape optimization, as well as serviceability-based flexural design using different limit states.

The Improvement of a Traction Model for Agricultural Tire–Soil Interaction

The goodness-of-fit analysis performed over the results provided by a model presented in a previous paper proved that the theoretical data were very well correlated with the experimental data with regard to the traction force (with Pearson coefficient r2 over 0.9); however, the model was less accurate in predicting traction efficiency, with r2 = 0.203. In order improve the model and obtain a better fit between the theoretical and experimental data (especially for the traction efficiency), the model was updated and modified by taking into account the geometry of the tire cross section, which was considered to be a deformable ellipse. Due to the deformable cross section, the minor axis of the tire–ground contact super ellipse decreased compared with the previous model (from 0.367 m to 0.222 m), while the major axis increased (from 0.530 m to 0.534 m). As a result, different data for the traction force and traction efficiency were obtained. The effect of the wheel travel reduction (wheel slip) over the tire–soil shear area was also investigated, and the hypothesis of a constant shear area (independent of wheel slip) provided the most accurate results. The goodness-of-fit analysis performed using the data predicted by the modified model showed that the Pearson coefficient increased significantly with regard to the traction efficiency (from 0.203 to 0.838), while it decreased by only 2.7% with regard to the data for the traction force, still preserving a high value (r2 = 0.896).

Analysis of effective thermal conductivity and tortuosity modeling in membrane distillation simulation

Porous hydrophobic membranes are the main elements in MD (membrane distillation) desalination systems and need to be adequately modeled in terms of transport mechanisms to allow for theoretical assessments toward process design. The objective of this work is twofold. First, illustrate the rational choice of models based on the morphology and structure of a couple of selected membranes for which micrographs and experimental results for distillate mass flux are readily available in the literature. Second, provide a comparative analysis of well-established models for membrane effective thermal conductivity and tortuosity, so as to confirm the adequacy of the proposed model selection path. Theoretical results of the distillate flux were obtained from the numerical simulation of the heat and mass transfer phenomena in the MD process for the DCMD (direct contact membrane distillation) configuration, using a multi-region approach with OpenFOAM @ . The comparative analysis is performed for PVDF membranes with different morphologies in the transversal section, for both flat and hollow fiber geometries. For the membrane with sponge-like morphology, the employment of the parallel-resistance model for the effective thermal conductivity and the fractal tortuosity model, designed for porous media characterized by randomly distributed obstructions in spherical format, led to the best agreement with respect to the experimental data for the distillate flux. On the other hand, for the membrane with macro voids in the cross-section (presence of finger-like channels), asymmetrical morphological structure, and narrow pore size distribution, it was found that the employment of the parallel-resistance model for effective thermal conductivity and the Euclidian-based tortuosity model for the random arrangement of highly interconnected pores provided the best agreement between experimental and theoretical data. The results confirm the appropriate model selection path for effective thermal conductivity and tortuosity in MD simulation by taking into consideration solely the membrane morphology. • A rational choice of membrane distillation (MD) models is considered based on the morphology and structure of the membranes. • A comparison of models for membrane effective thermal conductivity and tortuosity confirms the proposed MD modelling path. • Verifies that membrane surface modification for hydrophobicity enhancement increases distillate mass flux. • Introduces a modified membrane thickness model due to liquid/vapor interface increase in distillate mass flux prediction. • Temperature polarization may overcome the increase in distillate flux due to reduction in diffusion path by pore wetting.

Numerical Modelling of Forced Convection of Nanofluids in Smooth, Round Tubes: A Review

A comprehensive review of published works dealing with numerical modelling of forced convection heat transfer and hydrodynamics of nanofluids is presented. Due to the extensive literature, the review is limited to straight, smooth, circular tubes, as this is the basic geometry in shell-and-tube exchangers. Works on numerical modelling of forced convection in tubes are presented chronologically in the first part of the article. Particular attention was paid to the method of the solution of governing equations, geometry of the heating section, and boundary conditions assumed. Influence of nanoparticles on heat transfer and flow resistance are discussed. Basic information is summarized in tabular form, separately for single-phase approach and two-phase models. The second part of the article contains the correlation equations proposed in the presented papers for the calculation of the Nusselt (Nu) number or heat transfer coefficient, separately for laminar and turbulent flow. Details of the type of nanofluids, the concentration of nanoparticles, and the Reynolds (Re) number range are also presented. Finally, advantages and disadvantages of individual numerical approaches are discussed.

Optimal location of acoustic emission sensors for detecting rail damage

To detect cracks in rail sections, various experiments using the acoustic emission technique have been carried out by earlier researchers. However, the literature suggests that studies investigating the optimum location of acoustic emission sensors for the detection of cracks in railway tracks are rare. It is difficult to detect defects without the optimal placement of the sensor, owing to the complex geometry of the rail section as well as the high cost of sensors. Hence an attempt was made to find the optimum placement of a single sensor on a rail section to detect cracks precisely. A pencil lead break, which simulates a crack, was applied in the rail section to initiate such a crack. The obtained signal was analysed using wavelet transformation to establish a relationship with the group velocity to localise the simulated crack. From the investigation, it was found that the optimum placement of the sensor was between 75 mm to 375 mm for a 1.9 m length of rail section in laboratory conditions.

Use of polar coordinates for improving the measurement of resistant cross-sections of existing timber elements combining laser scanner and drilling resistance tests

Historic timber structures typically have elements with irregular cross-sections often with decayed segments, making of extreme importance to have proper methods to obtain the resistant cross-section. Knowing as accurately as possible the measurements of the resistant section of these beams is fundamental for the structural safety analysis. Small changes on the size and geometry of the resistant cross-section may be fundamental in an intervention decision process. In this work an algorithm was created that allows to obtain the geometry of the resistant section of existing timber beams by use of data obtained by laser scanning of the external apparent sections combined with drilling resistance tests. The algorithm is based on polar coordinates and proved to obtain more reliable resistant cross-sections than those obtained solely by common practice using drilling resistant tests. The developed algorithm was calibrated with a laboratory beam and subsequently applied and validated in a case study.

Structural behaviour of cold-formed steel built-up closed section beam–columns

In order to examine the beam–column behaviour of cold-formed steel (CFS) built-up closed sections, a numerical study was performed and is presented in this paper. The finite element model with careful considerations of material nonlinearity and initial geometric imperfections was established for the thin-walled section components under eccentric compression and verified against the existing experimental results. Then, the calibrated finite element model was adopted to obtain the numerical predictions of additional 280 beam–columns over an extensive scope of sectional geometries and initial loading eccentricities. Underpinned by the newly generated numerical predictions of 280 members and the existing test results of 30 specimens, the design approaches using codified interaction formulae and a bi-linear interaction expression proposed in the recent research for CFS built-up open section beam–columns together with the nominal compressive and flexural resistances determined by direct strength method (DSM) were assessed for thin-walled built-up closed section members under combined loading. Based on the nominal resistances determined by DSM, the interaction formulae in the ANSI/AISC 360 and EN 1993-1-3 as well as the available bi-linear interaction expression were overall unconservative for the design of built-up closed section beam–columns, while the interaction curve specified in the AISI S100 generally offered slightly conservative strength predictions. Furthermore, it was revealed that the interaction relationship in the AS/NZS 4600 and the bi-linear interaction expression modified in this study could provide accurate predictions for the CFS built-up closed section beam–columns, whereas the predictions obtained by the modified bi-linear interaction expression were overall less scattered.

Risk-based inspection planning for internal surface defected oil pipelines exposed to fatigue

The pipelines should be inspected periodically to minimize the probability of failure. The timing of these periodic inspections can be determined by a risk assessment that considers the probability of failure of the pipeline and the potential undesirable effects of the chemical transferred. These are referred to as risk-based inspection methods in the literature. We evaluate pipelines with internal surface defects and under the effect of variable pressure in this study. Internal surface defects were considered production-related, and there is a lack of studies in the literature examining such kinds of defects. These defects generate the concentration of stress on the pipeline section. The reliability variation of the pipeline depends on some factors, namely, surface defect geometry, the pipe section geometry, and the mechanical properties of the pipe. Fatigue is accepted as the crucial damage mechanism. The cause of variable load is considered as the number of operations. As a result of the study, the probability of fatigue failure for pipelines with internal surface defects was evaluated. Then, a new approach was proposed for risk-based inspection planning of the pipelines. As a case study, the probability of fatigue failure on a fuel pipeline established between a refinery and an oil terminal operating in Turkey was calculated. Also, we tried to determine the most appropriate inspection time. The data used in the planning phase was collected from a measurement process performed on the pipeline using PIG (Pipe Inspection Gauge). Finite element analysis was used to calculate stress concentration factors. Finally, we used the Monte Carlo simulation method to obtain the probability of failure.

Applicable Equivalent Bow Imperfections in GMNIA for Eurocode Buckling Curves – in Case of Box Sections

AbstractThe flexural buckling resistance of compressed columns is typically determined using the flexural buckling curves of EN1993‐1‐1. With advances in computing capabilities, it has become possible to obtain the flexural buckling resistance as a result of a geometrically and materially nonlinear analysis (GMNIA) using imperfections. In design practice, equivalent geometric imperfections are usually used, but their values are calibrated against GNIA analysis. In the present research work, welded box‐section columns are investigated and a proposal for relative slenderness and yield strength dependent equivalent geometric imperfection magnitudes is developed. The required equivalent bow imperfection magnitude is determined to achieve the same resistance level as the calculation according to Eurocode‐based buckling curves. GMNIA analysis are conducted on simply supported columns subjected to concentrated force. The steel grade varied between S235 and S960. Several different section geometries are studied, the relative slenderness ratio is varied between 0.3 and 2.2. Design curve is fitted to the results and recommendation is given for applicable equivalent geometric imperfection magnitudes for steel welded box‐section columns.