Oval Section Research Articles

Вплив форми дозвукової частини надзвукового вхідного пристрою на коефіцієнт збереження повного тиску

The subject of this study is the total pressure conservation coefficient. The object of this study is the channel of the subsonic part of a supersonic input device of rectangular and oval shape, equivalent in size. The purpose of this study is to study the shape of the subsonic part of a supersonic external compression input device. To achieve this purpose, the following tasks were solved: modeling the flow in the subsonic part of a supersonic inlet external compression input device of rectangular and oval shape; calculation of the total pressure conservation coefficient in the subsonic part of the rectangular and oval supersonic inlet external compression input device. When studying the shape of the subsonic part of the supersonic inlet external compression device, the method of numerical experiment was used. The studies were conducted at an estimated altitude of 12 km and an estimated Mach number M = 2.5. The influence of the fuselage on the operation of the input device was not considered. To study the influence of the cross-sectional shape of the studied subsonic parts of the inlet device, the coefficient of conservation of total pressure in 7 cross sections along the length of the inlet device was calculated. To obtain the initial data for modeling the flow in a subsonic channel, an analytical calculation of the flow parameters in the supersonic part of the input device was performed. The results of flow modeling showed that the total pressure conservation coefficient of the subsonic part of the studied inlet devices when operating at an altitude of 12 km was 0.982 in the subsonic part of the supersonic inlet device with oval sections and 0.993 in the subsonic part of the supersonic inlet device with rectangular sections. The resulting visualization of streamlines in the studied channels demonstrates the presence of a paired vortex formed in the initial section of the channel with oval cross-sections, which leads to significant losses in total pressure. The scientific novelty and practical significance of this study lie in the fact that new data were obtained regarding the comparison of the total pressure conservation coefficient for equivalent subsonic parts of a supersonic oval and rectangular inlet device. Recommendations on the rational form of the subsonic part of the supersonic inlet external compression device were obtained.

Numerical Investigation of Heat Exchanger Enhancement for a Staggered Arrangement with Corrugated Rods in Front

The heat exchanger is used in many industrial and engineering activities.Where, numerous applications confirms on a large heat transfer rate. However, the twisted tube is one of heat transfer rate enhancement methods. Also, the turbulent flows are often used instead of laminar for enhancement heat transfer rate. Therefore, the tube arrangement can be used in a suitable way for utilized this purpose. The shape features of tubes in the heat exchangers are very important for enhancing their performance. As well, the pressure drop and heat transfer rate have a remarkable effect on the thermal efficiency of the heat exchanger. In this research, a numerical investigation with a new way for heat exchanger tube staggered arrangement is presented. Where new solid spiral rods with oval sections are inserted in front of main tubes to induce high turbulent flow intensity as well as redistribution airflow over exchanger tubes. However, the new air distribution will help the airflow pressure over all the tubes to push the thermal boundary symmetrically behind the tubes. Therefore, two different sectional tubes were presented (circular and elliptical). These cross-sectional areas for both types have the same values. The main tubes have no twisted to prevent decreases in pressure. The numerical analysis used the K- ε model at a low Reynolds number to the simulation of this situation. Where, the eddy will generate in the vicinity region to pipe walls due to twisted pipe as well as the obstruction the cross flow. However, there are a good improvement of heat transfer rate without spend any energy depending on the control the shape and arrangement of pipes. The results show that the corrugated rod will increase the Nusselt number at different values of Reynolds. However, the elliptic tube gives the best results for heat transfer rate and maximum Nusselt number. The results compared with others works and give a good agreement.

Briquetage in early Hellenistic Etruscan Spina (Ferrara, Italy)

Excavations in the urban area of the Etruscan port city of Spina near Ferrara (Italy) have shown that the city had a roughly trapezoidal ground plan and covered an area of about 6 ha. In the east it was situated on the ancient course of the river Po (Padus Vetus) and in the west and south-west probably on a lagoon and another smaller river. The study project of the University of Zurich (2008–2017) had the goal of providing a clear stratigraphical sequence of the settlement phases as well as a geophysical investigation of the entire city area and indications of the natural environment. The excavation revealed several phases with wooden houses from the late sixth to the end of the fourth century BCE bordered by orthogonal water canals of different scales. After the violent destruction of the house, built between 375 and 350 B.C., in the third quarter of the fourth century the site changed its character. Not only was the level artificially raised, but the canals were abandoned and the area acquired a new function around 300 BCE. A series of very small, flat, round or oval impressions were found in the floor, in the vicinity of which lay a large quantity of thick, reddish terracotta fragments, coarsely tempered with organic material, very brittle, with cord impressions and finger marks. Fewer in number are accessory supports, round, or oval in section. Given their special technique, their large number, their distribution and the type of accumulation on the site, these fragments can be interpreted as briquetage deliberately smashed after use in order to remove the salt yielded by boiling. The fragments probably belonged to smaller, rectangular basins which stood on the round supports. The deeper channels from earlier phases had become in the last phase shallow gullies which served to supply fresh water.

Elastic buckling analysis and optimization of thin-walled bamboo-like pipe beam subjected to pure bending

In this paper, a stiffening design imitating the bamboo node is proposed for weight reduction of the long composite pipe beam subjected to bending load. The distribution of bamboo nodes can efficiently suppress the ovalization of the section, thus significantly improving the bending resistance of the bamboo. Based on this principle, ring stiffeners are proposed to be fixed to the pipe beam, making the long beam equivalent to the combination of a series of short pipes that suffered less section ovalization. A database of the optimal laminate orientations for different normalized lengths is obtained through optimizations, where the discreteness of the ply count is considered. Based on this database, weight optimizations are conducted, and the optimal designs of beams with and without stiffeners are obtained and compared. The comparison results show that the proposed bamboo-like stiffened beam not only regains a near-linear load–displacement relationship, but also reduces the weight by up to 16% under the same buckling load. In addition, it is found that for the pipe beams with radius-to-thickness ratios of more than 18, increasing the radius leads to a decrease in elastic buckling resistance when the weight remains a constant, which is opposite to the design for strength and stiffness. The model and database developed in this paper can provide a reference for weight reduction design and weight estimation for composite pipe beams.

Exact solution of a geometrically nonlinear problem for a long three-layer cylindrical panel of oval section

A statement is given and an exact solution of a geometrically nonlinear problem is given for a long open three-layer cylindrical shell of an oval cross-section susceptible to transverse shear under the action of a uniform surface load. The main equations are written according to the geometrically nonlinear theory of smooth shells in the quadratic approximation, in which Tymoshenko's hypotheses hold for the entire package of shell layers. The solution of the problem is obtained in a parametric form with the value of the tangential force as a parameter. For a shell with hinged longitudinal edges, the exact values of the components of the stress-strain state were obtained, the limit values of the generalized geometric parameter were determined, and a system of equations for finding the critical load was constructed. As partial cases, the obtained solution yields the corresponding results for the Kirchhoff–Leav model, the shell of a circular cross-section, and the single-layer shell. The obtained results can be a reference for approximate and numerical methods.

Effect mechanism of torsion on flat oval profile free bending

Six-axis free bending and twisting (6FBT) technology is suitable for the integral bending of complex profiles with torsional characteristics for the cross-section. However, the influence and mechanism of section torsion on bending deformation during the forming process of this technology have not been studied. In this paper, a new theoretical analysis model describing the relationship between a torsion angle of a section and the radius after bending springback is proposed for 304 stainless steel flat oval section hollow profiles. Using the proposed model, the trend of the influence of section torsion on bending deformation when bending along the long and short axes of the flat oval profile is derived, and the theoretical derivation matches well with the simulation and experimental results. The findings show that when the flat oval profile is bent along its long axis, the springback of the bending radius is positively related to the torsion angle, while when bending along the short axis direction, the rebound of the bending radius is negatively correlated with the torsion angle. The paper also explains for this phenomenon in terms of stress and strain, and establishes for the first time a “U-R-γ” model that introduces section torsion and reflects the relationship between the radius and eccentricity.

Numerical Analysis on Natural Vibration of Cylindrical shell with Different Cross-section

Cylindrical shell in engineering has different cross-section, i.e., circular section, oval section, rectangular section, and so on. In this work, numerical analysis is conducted on natural vibration of cylindrical shell with different cross-section, and the difference is studied between modal frequency and modal shape from different section shell. Numerical results show that, with the same length, width /thickness and boundary condition, the first 10 order modal frequency from circular section shell is nearly 60% bigger than that from the rectangular section shell. This indicates that the load carry ability of circular cylindrical shell is much better than rectangular cylindrical shell, which will help to support the design of cylindrical shell in engineering.

On the pressure–torsion response of a flexible pipe with section ovalization

Ovalization, as an important factor affecting the performance of flexible pipes, is unavoidable in the manufacturing process. In this paper, a model of a flexible pipe with initial ovalization is established numerically. The numerical model is verified by a case analysis, and the influence of ovalization on the torsional response of a flexible pipe is discussed. It is found that the ovalization always has a negative effect on the torsional stiffness of the flexible pipe. Then, the effective numerical model is used to calculate the torsional response of a flexible pipe with initial ovalization under dry and wet annulus pressure. It is found that the dry annulus pressure improves the torsional stiffness of the flexible pipe by advancing the interaction between the layers and hindering the radial expansion of the outer tensile armor layer. However, the dry annulus pressure also increases the stress of the tensile armor layers, which reduces the withstanding capacity of the flexible pipe. Especially with the increase of ovalization, the loading capacity decreases more obviously. The wet annulus pressure has little effect on the torsional response of the flexible pipe, but it extends the risk of radial collapse of the carcass layer.

Баклаги салтівської культури в збірці Дніпропетровського національного історичного музею імені Дмитра Яворницького

Проаналізовано колекцію баклаг кінця VIII – першої половини ІХ століття, виготовлених нагончарному крузі, зі збірки Дніпропетровського національного історичного музею імені ДмитраЯворницького. Ці вироби салтівської культури – специфічний і малочисельний тип посуду. Доколекції увійшли три баклаги ІХ століття, знайдені на території колишньої Катеринославськоїгубернії та м. Дніпра, а також одна баклага, передана 2010 року з с. Лобойківка Петриківськогорайону Дніпропетровської області. Проаналізовано відмінності між зразками цього загаломтипового посуду. Подано відомості про аналогії цим посудинам, знайдені на пам’ятках степовогота лісостепового варіантів салтівської культури. Among the antiquities of the Saltiv culture there is a specific and non-numerical type of ceramicutensils – water bottles or flasks, which were used to transport a small amount of liquid.The article deals with three water bottles of the late 8th – early 9th centuries, which are stored in thefunds of the Dmytro Yavornytsky National Historical Museum of Dnipro and one water bottle, which wastransferred to the museum from the village of Loboykivka of the Petrykivka District of the DnipropetrovskRegion in 2010. The location of one of these water bottles is unknown. One of them has been found in thegrated former Ekaterinoslav Government, and the second one has been found in 1958 at the mouth ofthe Shiyanka river, now it’s a territory of the city of Dnipro. All four vessels have a curved front surface,a flat or slightly concave back surface, a cylindrical body, a high throat (lost in one water bottle), formedseparately and then attached to the main part of the vessel, two handles, oval in cross section, fixed onopposite sides from the throat. One water bottle is decorated with a pentagonal star in a round medallion,and two – with medallions. The medallions are formed from the same clay as the water bottle itself. Onthe water bottle, found in 2010, there are remnants of a color ornament. These are elements applied withbrown, light brown paint and white engobes.The article also analyzes the differences between different samples of this mostly the same type ofutensils – the shape of the crown, the shape of the handles, the ornament (or lack thereof). The authorconcludes that these differences are not enough to distinguish certain types and kinds of this crock.The described water bottles are characteristic of the antiquities of the Saltiv culture and havea number of analogies on the monuments of its steppe and forest-steppe variants – settlements, nomadicstations, cemeteries, as well as in the form of accidental finds. They were made in the workshops of theCrimea to order of the steppe and forest-steppe population, most likely for horsemen. Mostly made of thesame clay as amphorae and in the same workshops. But there are single water bottles that are made ofanother clay mass with the addition of chalk and hardness. It is possible that they are not made in Crimeanworkshops, but are imitations of these forms by local craftsmen.Water bottles from the Dmytro Yavornytsky National Historical Museum of Dnipro complementa number of already known and published vessels and expand the range of their existence.

The research on the critical loading path of thick-walled pipes under external pressure and cyclic bending

The effects of combined external pressure and cyclic bending on the pipe buckling mechanism are investigated by experiments and finite element analysis. Ten experiments are conducted and it is found that the loading paths of external pressure and cyclic bending have a great influence on the buckling pressure of thick-walled pipes. The loading path of pressure followed by cyclic bending (p→ck) is more dangerous than that of cyclic bending followed by pressure (ck→p). The material properties of kinematic hardening, loading application and mesh convergence are taken into consideration in rigorous FE models. The reason of the critical loading path is revealed from the aspects of section ovality and stress-strain accumulation. Sensitivity analysis is conducted on the loading patterns and axial tension. With the application of axial force, the pipe laying process is simulated more precisely which shows that pipe buckling capacity is more sensitive to the bending cycles in the presence of axial force. The comparison between numerical results and present specification shows that the API specification is conservative in predicting the collapse pressure of thick-walled pipes (D/t = 15–21) whose underestimation is about 11%~37% under the effect of cyclic bending.

Numerical study of fixed ended Lean duplex stainless steel (LDSS) flat oval hollow stub column with square perforation under pure axial compression

This paper presents the parametric study of single square perforated fixed ended LDSS (Lean Duplex Stainless Steel) flat oval section stub columns, by varying the square perforation size, location of perforation along transversely as well as longitudinally, using the Finite element software Abaqus (2009). Based on the Finite element study, a near-linear reduction in ultimate load capacity with perforation size has been observed. The reduction is found to be higher for the stockier cross-sections as compared to slender sections. The percentage drop in ultimate load capacity remains relatively unaffected for larger perforation when the section is slender and located at the flat element. It is seen that, in comparison to the slender section, perforated stocky sections showed a mild drop in ultimate load as the perforation is located toward the corner junction of flat and curve portion from the mid-flat region. Further, in general, it is observed that the reduction in load capacity to be highest when the perforation is located near the mid-height. A design approach based on modified ASDM (Automotive Steel Design Manual) has been proposed to estimate the design capacity of single square perforated flat oval LDSS hollow columns

A redescription of Lophorhothon atopus (Ornithopoda: Dinosauria) from the Late Cretaceous of Alabama based on new material1

Diagnostic dinosaur fossils of the southeastern United States are rare discoveries, and even more precious are those fossils that preserve a large portion of a skeleton. Sixty years ago, the dinosaur Lophorhothon atopus was described from Upper Cretaceous sediments of Alabama. It then represented the oldest, most complete, dinosaur in the southeastern United States. Based on a reexamination of the holotype material and a new specimen collected from the same beds, we provide a new diagnosis of this taxon. In particular, the solid nasal crest has several autapomorphies including caudally projecting frontal processes that are oval in cross section, meaning that they did not coalesce at the midline. Other autapomorphies are found on the prefrontal and squamosal. Combining the two Lophorhothon specimens provides nearly the entire skeleton for phylogenetic analysis, which we find as a hadrosauromorph just outside of Hadrosauridae. The original diagnosis of this taxon included the frontonasal fontanelle as a distinguishing character, but comparing the many examples of frontonasal openings across hadrosauromorph taxa shows that in at least a few species, such as Lophorhothon, the structures should be considered a frontonasal fenestra instead of a fontanelle. Additionally, the notion that dinosaurs from the East Coast of the United States represent primitive relicts is an idea that originated before many of the European and Asian hadrosauromorphs known today had been discovered. With new dating and phylogenetic information, it appears that Appalachian dinosaurs are on par evolutionarily with most of the global community and the term ”relict fauna” should be abandoned.

Обоснование овальности формы сечений стволов деревьев при их росте с наклоном

It is known that it is possible to determine the age of a tree and the conditions for its growth by some external features. These features include the number of annual layers on the tree trunk cross section, the correct geometric shape of these layers. The stem taper indicates where this tree grew: in an overstocked stand or in open areas. The oval shape of the cross sections of the trunk is common to the trees with irregular crown or grown inclined to the horizon. A powerful external action of a prevailing wind load influences on the cross sections shaping of tree trunks. Trunk, crown and corresponding cross-breaking strength and compression resistance along the wood fibers of a tree are formed in response to all external influences during its growth. The collaborative effect of these factors is the size, shape and location of the core and sapwood zones in the tree trunks, on which the strength, density, and location of wood defects are dependent, and which affect the quality of wood products in-service. The authors chose the initial stress formed during the tree growth as a uniform criterion for assessing the influence of the natural features of wood on the quality and strength of wooden building structures. The value of which can be fairly estimated by the size and shape of the core and sapwood zones of the tree trunks cross sections. The size and shape of these zones can be measured by scanning. The log sawing pattern should be selected using appropriate computer software that allow obtaining the high-quality sawn timber for the construction purposes. The research purpose is to develop a method for determining the size and shape of the core and sapwood zones of the tree trunk sections that have a natural curvature and grow vertically or with an inclination to the horizon; and what is more, to substantiate the connection between the shape and size of the tree trunk oval sections with the initial stresses developing during growth and the wood strength under tension, compression along the fibers and static bending.

The research on pipe structural behavior of 3D UOE manufacturing process

A 3D UOE manufacturing process is established by ABAQUS software in this study with the consideration of detailed boundary conditions. From two aspects of geometric profile and material distribution, the effects of each forming step are determined from three directions: circumferential direction, radial direction and longitudinal direction. As for the geometric profile of the 3D UOE model, the radius distribution of X70 is more concentrate around the nominal value than X80 pipe. As the longitudinal deformation in O forming and expansion step is not uniform, greater compression ratio and expansion ratio are needed for reducing section ovality. Under the effect of twice expansion steps, the ovality in the overlapping area is smaller than that in the region subjected to one-step calibration. As for the structural behavior of UOE pipe, the weakest position of the pipe after UOE manufacturing process is determined according to the principle of Bauschinger effect. Different with 2D model, 3D UOE pipe has a stronger collapse resistance under the effect of low ovality and the supporting of neighboring sections. Comparing with the offshore standard DNV-OS-F101, the accuracy of 3D UOE model is verified whose resistance to the external pressure is more sensitive with the expansion ratio than the internal pressure.

A new naturalized plant in Korea: Carex molestiformis Reznicek and Rothrock (Cyperaceae)

국내 ë¯¸ê¸°ë¡ì¢ ê°€ëŠ”íƒ€ëž˜ì‚¬ì´ˆ(Carex molestiformis Reznik and Rothrock)를 강원도 평창군 ë²½íŒŒë ¹ 일대 에서 처음으로 발견하였다. 본 분류군의 원산지는 북아메리카 미국의 남부지역(Missouri, Oklahoma, Arkansas등 11개 주)으로, 자생지에서는 주로 개활지나 강둑, 범람원 등에서 무리지어 밀생한다. íƒ€ëž˜ì‚¬ì´ˆì ˆ (sect. Ovales)에 속하며, ìžì› ì„± 소수를 갖는 ë‹¤ë „ìƒ 초본으로, 한 화서에 달리는 소수의 수가 2–4개로 ì ê³ , 과낭의 폭이 2.6–3.4 mm로 넓으며, 과낭 배면의 맥이 6–9개로 많아 국내에 자생하는 ê·¼ì—°ì¢ ì¸ 타래사초(C. maackii Maxim.) 및 ê·€í™”ì¢ ì¸ 한석사초(C. scoparia)와 ëª í™•ížˆ 구별된다. êµ­ëª ì€ 본 분류군이 í˜•íƒœì ìœ¼ë¡œ 타 래사초와 ìœ ì‚¬í•˜ë©°, 식물체가 ì „ì²´ì ìœ¼ë¡œ 가늘어 ‘가는타래사초’로 ì‹ ì¹­í•˜ì˜€ê³ , 분류군에 대한 기재문, 화상 자료 및 도해 ê·¸ë¦¬ê³ ìœ ì‚¬ì¢ ì— 대한 검색표를 ì œì‹œí•˜ì˜€ë‹¤. 또한, 가는타래사초와 ê·¼ì—°ì¢ ì˜ ìœ ì „ì  차이를 확 ì¸í•˜ê³ ìž 3개(chloroplast DNA matK, ndhF, nuclear ribosomal DNA internal transcribed spacer) DNA barcode 지역의 부분 염기서열을 비교하여, 총 8개의 가는타래사초의 ì¢ íŠ¹ì´ì  단일염기다형성(single nucleotide polymorphisms)을 확인하였다. 주요어: ë¯¸ê¸°ë¡ì¢ , 가는타래사초, íƒ€ëž˜ì‚¬ì´ˆì ˆ, 사초과

Analysis of buried pipelines laid under the pipelines operation, is subjected to operational loads

Today’s successful operation within the oil and gas industry is based on the triangle “Safety – Reliability – Profitability (Efficiency)”. It is of high importance to properly balance these different and sometimes opposite positions. The article describes the characteristics of the strength of the buried offshore pipeline. Pipe geometric imperfections as the cross section ovality, combined load effects as axial and bending loads superimposed to the external pressure, material properties as compressive yield strength in the circumferential direction and across the wall thickness etc., significantly interfere in the definition of the demanding, in such projects, minimum wall thickness requirements.

Reducing Surgeon's Physical Stress in Minimally Invasive Neurosurgery.

Various minimally invasive approaches are used in neurosurgery. Surgeons must perform nondynamic fine movements in a narrow corridor, so specially designed surgical devices are essential. Unsophisticated instruments may pose potential hazards. The purpose of this study was to assess the factors associated with muscle fatigue during minimally invasive neurosurgery and to investigate whether physical stress can be reduced by refining the devices used. Four physical aspects of a handpiece were investigated: torque of conduits (0.20, 0.28, and 0.37 kgf*cm), shape of hand grip (five types), angle of the nozzle (0, 20, and 40 degrees), and weight balance (neutral, proximal, and distal). To evaluate muscle fatigue, surface electromyography was recorded from the extensor carpi radialis muscle and flexor carpi radialis muscle during a geometric tracing task. The maximum voluntary contraction (MVC) of each muscle and %MVC (muscle contraction during a task/MVC × 100) were used as the indexes of muscle fatigue. The shape of the hand grip significantly reduced %MVC, which is associated with muscle fatigue. The torque of conduits and angle of the nozzle tended to reduce muscle fatigue but not significantly. Weight balance did not affect muscle fatigue. Based on these results, we made two refined models: model α (torque of conduits 0.2 kgf*cm, angle of nozzle 20 degrees, neutral balance, hand grip with a 2.9 × 2.0-cm oval section with angled finger rest), and model β (torque of conduits 0.2 kgf*cm, angle of nozzle 20 degrees, neutral balance, hand grip with a 2.9-cm round section with a curved finger rest). The %MVC was significantly decreased with both types (p < 0.05 and p < 0.01, respectively), indicating reduction of muscle fatigue. The geometrically refined surgical device can improve muscle load during surgery and reduce the surgeon's physical stress, thus minimizing the risk of complications.

Dimensional correlation between morphology and root canal anatomy in mesiobuccal root of permanent maxillary first molar: An ex vivo study

Aim: The aim of the present study was to establish a correlation between morphology and root canal anatomy of mesiobuccal (MB) root of the permanent maxillary first molar using cone-beam computed tomography (CBCT) and stereomicroscope. Methodology: Access cavities were prepared on sixty permanent maxillary first molars. Efforts were made to locate MB second (MB2) canals without magnification and with magnification using methylene blue dye and ultrasonic troughing. The number of teeth possessing MB2 canal with both methods was recorded. Thereafter, the MB root was resected and observed under CBCT. The MB root was then sectioned at different levels and observed under stereomicroscope. Both the methods were used to assess the number of canals and root forms which were classified as long oval, oval, and round. The data thus obtained were then subjected to statistical analysis using ANOVA and Z-test. Results: Clinical techniques such as magnification, dyes, and troughing were found to be more efficient in the detection of MB2 canals as compared to unaided techniques. As observed with CBCT and stereomicroscope, the incidence of MB2 canal was significantly more in coronal as compared to middle and apical, and a statistical correlation between root form and number of canals was observed. Conclusion: Majority of the MB roots were long oval and oval in axial section and the incidence of finding MB2 in long oval and oval root forms was found to be greater as compared to round root form, although it is not necessary that all long oval or oval roots shall have two or more canals.

Mechanical behaviour analysis of buried pipeline subject to ground loading

TO STUDY THE EFFECT of ground loading on the mechanical behaviour of buried pipelines, a three-dimensional pipeline-soil coupling model was established. The influences of ground load, radius-thickness ratio, internal pressure and elastic modulus of backfill soil on stress, displacement and section ovality of the pipeline were analysed in this paper. The results show that the high stress area appears at the top of the pipeline and the shape is an oval under the ground load. As the ground load increases, the stress concentration phenomenon appears on the left and right sides of the pipeline. As the radius-thickness ratio decreases, the ability of the pipeline to resist deformation increases and the stress zone at the top of the pipeline gradually decreases. As the elastic modulus of the backfill soil increases, the displacement of the pipeline section gradually decreases. With the increasing of the internal pressure, the stress and strain of the upper pipeline is reduced and the bottom stress of the pipelne is increased. Protective measures should be used for the buried pipelines in dangerous areas.

Axial Compressive Stress-Strain Model Developed for FRP-Confined Concrete Columns with Elliptical Cross Sections

Most existing studies conducted on fiber-reinforced polymer (FRP)-confined concrete have considered circular and square concrete columns, while limited studies have considered columns with rectangular sections. Studies have confirmed that the circular cross-sections exhibited higher confinement effectiveness, whereas in the case of non-circular cross-sections the efficiency of FRP confinement decreases with an increase of the sectional aspect ratio and there is no significant increase, particularly for columns with the aspect ratio of 2.0. As recently suggested by researchers, to significantly increase the effectiveness of FRP-confinement for these columns involves changing a rectangular section into an elliptical or oval section. According to the literature, most of the existing confinement models for FRP-confined concrete under axial compression have been proposed for columns with circular and rectangular cross-sections. However, modeling of the axial strength and strain of concrete confined with FRP in elliptical cross-sections under compression is limited. Therefore, this paper provides new expressions based on limited experimental data available in the literature. For a sufficient amount of FRP-confinement, the threshold value was proposed to be 0.02. Finally, the accuracy of the proposed model was verified by comparing its predictions with the same test database, together with those from the existing models.