Three-dimensional Nonlinear Finite Element Method Research Articles

Examination of Thinning Inspection Method for Ferromagnetic Steel Tubes Using Velocity Effect of Static Magnetic Field

The high-speed movement of an electromagnetic sensor comprising static excitation and detection coils in a steel tube generates an eddy current in the tube. The presence of a defect in the steel tube may be detected via changes in the eddy current. In general, the ferromagnetic heat transfer tubes in oil and chemical plants are inspected for defects by moving an internally inserted electromagnetic sensor at a high speed of 1 m/s. Although previous studies have focused on the detection of localized thinning in the steel tube, there are no reports on a wide range of thinning in the steel tube. Therefore, this study investigated a thickness measurement method for a wide range of thinning in the steel tube using only static magnetic field. Consequently, the possibility of measuring the thickness in the steel tube based on the flux density inside the detection coil of the proposed static magnetic inspection sensor moving at 1 m/s was demonstrated. The flux density in the steel tube was evaluated by the three-dimensional nonlinear finite element method considering the velocity effect.

Cyclic performance welded steel reduced beam section moment connections using longitudinal slots in flanges

A new type of steel reduced beam section connection using longitudinal slots in the beam flanges is introduced. The effect of different parameters has been studied by the non-linear three-dimensional finite element method. Parameters have been the distance between the slot and column face, the length and width of the slot, the distance between the slot and the edge of the beam flange, the number of slots, the distance between slots, and the dimensions of the beam. The displacement controlled cyclic loading protocol recommended by SAC has been imposed. The von Mises yield criterion has been used. Obtained results show that creating the slots in the beam flange improves considerably the performance of the connection. The bending moment at the column face and plastic strains in the weld decrease by 32% and 94%, respectively, by increasing the slot length by 264%. The bending moment and dissipated energy reduce by 59% and 66%, respectively, when the slot width is increased by 430%. By increasing the length and width of the slot from a specific value and by moving the slot towards the beam web, the behaviour of the connection becomes unsatisfactory. The effect of the beam height is more than that of other dimensions of the beam. Based on the results obtained, recommendations for the design implications related to the geometric dimensions of the slots have been formulated.

Experimental and numerical investigation on masonry arch bridges under uniform and line loads

In this paper, the performance of Persian skewed brick masonry arch bridges under uniform and line loads has been investigated. Three types of semi-circular, pointed and four-centred arches have been studied. Bridges with two spans and six spans have been analysed using the three-dimensional non-linear finite element method. The parameters considered are four skew angles, three pier width to span ratios, three bridge width to span ratios, three pier height to span ratios, and three deck thickness to span ratios. Loading includes uniformly distributed load on the entire surface of the bridge deck, line load at the middle of the middle pier, and line load at the apex of one of the arches. The suitable ranges of the skew angle to create the maximum load-bearing capacity have been obtained for different loadings, different types of the arches and other parameters.

Comparison of the structural behaviour of monolithic and masonry obelisks: Obelisk of Theodosius and Walled Obelisk in Istanbul

In this paper, the structural behaviour of the Obelisk of Theodosius and Walled Obelisk, located near the Sultan Ahmed Mosque in Istanbul, is investigated. The Obelisk of Theodosius is made of an integrated and solid red granite that stands on four pieces of bronze cubes and large pieces of stone cubes. The Walled Obelisk is made of small pieces of limestone that stand on only one large piece of stone cube, without bronze cubes. The purpose of this study is the comparison of the structural behaviour of these two obelisks and the effect of their supporting base on their performance under seismic loading. The nonlinear three-dimensional finite element method is used for modelling and the Willam-Warnke failure criterion is adopted for investigation of brittle fracture mechanism. The results of analysis show that the Walled Obelisk is more flexible than the Obelisk of Theodosius. However, the existence of four bronze cubes and four red granite cubes at the corners of the supporting base increases the flexibility of the Obelisk of Theodosius.

Determination of bend angle and shape imperfection effect on collapse load of pipe bends under in-plane opening moment

This study uses a three-dimensional nonlinear finite-element method to investigate the effects of bend angle ([Formula: see text]) and shape imperfection on the collapse load of pipe bends subjected to in-plane opening bending moment using large displacement analysis. ABAQUS was used to create a pipe bend model, whereas by virtue of symmetry about the longitudinal axis, half of the pipe bend model was built. The bend angle was varied from 30° to 180° with an interval of 30°, and shape imperfections, namely ovality ( Co) and thinning ( Ct), were varied from 0% to 20% each at 5% intervals. Elastic-perfectly plastic is thought to be the material of choice for the pipe bend. The results show that the bend angle has a significant impact on the collapse load of pipe bends between 30° and 120°, after which a significant decline was observed. The ovality impact increases with an increase in bend angle for pipe bends with a large thickness, whereas the opposite effect was found for smaller thicknesses with a small bend radius. The effect of bend radius and thickness was significant for large bend angles. Thinning ( Ct) and thickening ( Cth) have no effect on collapse load. A new mathematical equation has been proposed to predict the integrated effect of bend angle and shape imperfection.

Wear failure analysis of suction valve for high pressure and large flow water hydraulic plunger pump

The failure mechanism of suction valve in high pressure and large flow water hydraulic plunger pump used in coal mine is studied. Previous studies believe that in traditional plunger pump with low pressure and small flow, the impact caused by the dynamic contact between the valve plate and the valve seat is the main reason for the performance deterioration of suction valve. However, in the practical use of high-pressure and large-flow hydraulic plunger pump, it is found that there are signs of rotating wear and material loss on the sealing surface of the suction valve plate. In order to explain the premature failure of the valve, the mathematical model of the force and movement of the valve plate during the suction process of the high-pressure and large-flow hydraulic plunger pump is established. Three-dimensional computational fluid dynamics (CFD) method and nonlinear finite element method are used to numerically analyze the operation process and dangerous conditions of the valve plate. The results show that under the action of the uneven flow field, the combination effects of low speed rotation and heavy load during closing process is the key factor causing material loss. According to the microstructure and elemental composition of the worn surface, the specific wear failure mechanism is determined, and the effectiveness of the numerical method is verified. Finally, the improved valve plate materials are proposed. The field test of high pressure and large flow pump proves that the wear of the valve plate is significantly reduced after the improvement.

Dynamics and Energy Analysis of Nonequatorial Space Elevator Using Three-Dimensional Nonlinear Finite Element Method Extended to Noninertial Coordinate System

A space elevator is a futuristic space transportation technology that enables low-cost and versatile payload transportation using climbers on a tether deployed from the geostationary orbit (GEO). In particular, a nonequatorial space elevator, which contains an anchor in a region with latitudes on the Earth, has recently attracted attention. It has several advantages, such as extending the construction range and avoiding collisions with spacecraft in the GEO. Prior research has focused on rigid-body or spring-mass models with low fidelity. This paper proposes a modeling method for nonequatorial space elevators using a nodal-position finite element method (NPFEM) extended to a rotational coordinate system. The NPFEM is a three-dimensional finite element method that considers geometric nonlinearity. Conventional NPFEMs have only been formulated using inertial coordinate systems. This paper proposes a method to formulate the NPFEM in a noninertial coordinate system and derive the inertial forces and Jacobian matrices. In addition, a three-dimensional analysis of a nonequatorial space elevator was performed based on the proposed method. After determining the equilibrium position of the NPFEM, the dynamic response of the tether during climber ascent was analyzed. Moreover, parametric studies were conducted by varying several properties of the nonequatorial space elevator. Furthermore, the energy exchange between the components was analyzed to validate the proposed method and to discuss the energy perspective of the space elevator. The results revealed that the proposed nonequatorial space elevator model experienced a more tensioned equilibrium and exhibited a more significant dynamic response than conventional models.

Study on Flexural Behaviour of Reinforced Concrete Beam With Effective Openings

Reinforced Concrete (RC) beams are essential structural elements that transfer loads from the slabs to the columns through flexure and shear. Openings in Reinforced Concrete (RC) beams are required for a variety of architectural and mechanical reasons. The purpose of this article is to investigate the flexural behaviour of an RC beam with circular openings running the length of it. The three-dimensional nonlinear finite element method was used to investigate a supported RC beam with circular web openings of varying diameters using ANSYS, a finite element software package. The study’s primary characteristic is the variation in diameter and location of reinforcement around the openings. Five RC beams with simple supports were constructed, and tested were conducted under two-point loads. Beams were constructed with one conventional specimen without any openings in beams and two beams with unstrengthen circular openings located in the flexure zone with varying diameters such as 80mm and 100mm considered as a control beam. In contrast, the remaining two beams provided effective diagonal reinforcement around the openings. The load-bearing capacity and load-deflection behaviour of such openings in beams were studied and analysed in detail. To increase the ultimate strength of the beam, effective diagonal reinforcement and short stirrups at the top and bottom of openings are used to prevent the beam from collapsing prematurely.

Three-Dimensional Modeling of Thermal-Mechanical Behavior of Accident Tolerant Fuels

Considering the safety issues of the traditional UO2-Zr fuel, a variety of accident-tolerant fuel (ATF) candidates have been proposed in recent years. Among the several ATFs, U3Si2, and UN are the two promising candidates for fuel materials owing to their high thermal conductivity and high uranium density. The FeCrAl alloy and the SiC/SiC composite material are the two promising candidates for cladding owing to their high oxidation resistance and high strength. In order to quantitatively evaluate the performance of ATFs, this study summarizes the physical models of typical ATF cladding materials (FeCrAl and SiC) and pellet materials (UN and U3Si2). Then a three-dimensional non-linear finite element method is applied to simulate the thermal-mechanical behavior of several typical fuel-cladding combinations, including UO2-FeCrAl, UN-FeCrAl, U3Si2-FeCrAl, U3Si2-Zr, and U3Si2-SiC. The important physical quantities, such as the fuel centerline temperature, the deformation of the pellet and the cladding as well as the pellet-cladding mechanical interaction (PCMI) were studied. The fission gas release model was also verified and improved.

The effect of GFRP on reinforcing the buried and internally pressurized steel pipes against terrorist attacks

In recent years, the occurrence of numerous intentional and accidental explosions in buried pipelines, especially in oil and gas pipelines, has been turned to a proper subject of research. The present research, for the first time, studies the utilization of GFRP for reducing the deformation of buried and internally pressurized steel pipes against explosions through the non-linear three-dimensional finite element method. The Combined Eulerian-Lagrangian (CEL) algorithm is used for modeling simulation. It means that the pipe and GFRP are modeled using the Lagrangian algorithm and air, soil and explosives are modeled using the Eulerian algorithm. The studied pipe is API-X65 with an outside diameter of 914.4 mm and the burial depth of 2.5 m. The explosive material is TNT with 10 kg of weight and in the 1 m height below the ground. The results of the model were compared to the results of field tests and the experimental equations presented by previous researchers, and good compatibility was observed. Utilization of GFRP decreases maximum equivalent strain, transverse deformation, longitudinal strain and explosion energy imposed on the pressurized pipeline for about 35.3, 29.6, 13 and 63%; respectively. The internally pressurized pipeline of API-X65 with the wall thickness of 15.88 mm and with the GFRP reinforcement with 7 mm of thickness has acceptable resistance against explosion, in a way that transverse deformation of it is in the acceptable limit and its longitudinal strain is lower than the yield strain. Using the results of this research, we can protect the under-construction or operation buried pipelines against the sub-surface explosions.

Pull-out and bond-slip performance of steel fibers with various ends shapes embedded in polymer-modified concrete

The bond-slip behavior between matrix and fibers highly depends on the geometric and mechanical characteristics of fibers. Thus, by considering various geometric of fiber end shapes, the pull-out behavior of steel fibers from polymer-modified concrete is studied in the present study. For that, a three-dimensional non-linear finite element method is employed for simulations. For considering more real guess, interaction among matrix and fibers is simulated via Interfacial Transition Zone (ITZ), and its factors are attained from experimental results of the fiber pull-out test. After validating the results, the effect of geometric parameters of the fibers end shape on the bond-slip properties with polymer composite is investigated. The results from the load-slip curves indicate that there are different mechanisms in the behavior of the fibers depending on the diameter and angle of the fibers. For fibers with 2 mm diameter, increasing the angle of the hook from 0 to 90 degrees increases the pull-out force of hook and half-hook fibers by about 35% and 15%, respectively. Whereas a further increase in hook angle reduces pull-out parameters of the hook-shaped fibers.

Failure mechanisms and cracking performance of T-shaped SCC beam-column connections at top floor: Test results and FE modeling

In recent decades, self-compacting concrete (SCC) has gradually gained popularity based on its unique workability without any internal and external vibration. SCC development must ensure an acceptable level of balance between deformability and stability by following the characteristics of materials and the mix proportions. In the case of the structural performance of reinforced concrete (RC) structures throughout the earthquake, beam-column connections behavior is one of the most common causes of failures. On the other hand, T-shaped beam-column connections on the top floor have a critical condition based on the different types of live loads. As an alternative, SCC with specific properties includes workability and resilience against segregation, which is a great solution to improving the behavior of RC connections in a seismic area. In this paper, experimentally and numerically, investigation of six T-shaped SCC beam-column connections through different reinforcing bars ratio (ρ) are presented to better understand their behavior during the gravitational load like heavy snow, particularly in terms of failure mechanisms and cracking performance. In the experimental stage, firstly, the mechanical specifications of SCC have been examined in terms of slump flow, V funnel, J ring, and L box tests. Secondly, the load-displacement performance of T-shaped beam-column connections at the top floor has been reported in terms of bonding behavior, ductility, and energy dissipation capacity. The displacement ductility of the experimental results are decreased from 12.4 to 3.5 while the ratio of the reinforcing bars was increased from %15 to %66 of the balanced section, and the energy dissipations capacity was increased by increasing the reinforcing ratios until %56 of the balanced section then started to decrease. In the theoretical part of the study, a three-dimensional nonlinear finite element method (FEM) model (ABAQUS) was employed along with the load-deflection curves were reported to compare the experimental results with the numerical output. The test results demonstrate, employing SCC as a type of concrete that has enough workability in RC connections had successful fulfillment in terms of ductility, load-carrying capacity, and energy dissipation.

A computational study on the effect of bending number on superelastic behavior of NiTi for medical application

NiTi self-expanding stents can be exploited in medical applications such as thoracic aortic aneurysm owing to its effects on minimizing problems such as low twistability, unsuitable dynamic performance, and inadequate radial mechanical strength. The present simulation models NiTi superelasticity based on the thermodynamics of the Helmholtz free energy (Auricchio theory) and the thermodynamics of the Gibbs free energy (Lagoudas theory). The three-dimensional nonlinear finite element method is used to evaluate the influences of bend number on the superelastic manners of new geometries designed for Z-shaped thoracic aortic aneurysm NiTi stents by the use of a radial strain (crimping) test. NiTi stents with the lowest number of bends and highest segment length showed the best mechanical performance owing to their lower chronic outward force, higher radial resistive force, and whole superelastic behavior. This numerical study can provide a suitable way of assessing the biomechanical properties of thoracic aortic aneurysm stents given the effects of geometrical parameters.

EVALUATION OF REINFORCING BARS RATIO EFFECTS ON SCC BEAM-COLUMN JOINT PERFORMANCE

Beam-column joints require a high ductility during the unexpected loadings that necessitate the need for ductile concrete in such unprotected locations. Alternatively, self-compacting concrete (SCC) is a sort of concrete which has generated tremendous interest throughout the last decades in order to reach a ductile structural elements during the seismic actions. Specific properties of this type of concrete include high performance, high resistance against segregation and needless to internal or external vibration in order to compact. In the seismic regions, ductility is one of the most important factors in the design of reinforced concrete (RC) members, especially structural joints flexural performance; it is due to the enhance in the capability of plastic deformability. This paper describes load-displacement behavior of experimental and theoretical analysis of four SCC beam-column joints with different percentage of the ratio of the reinforcing bars (ρ). In the theoretical phase of this investigation three-dimensional nonlinear finite element method (FEM) model i.e., Seismostruct was used and the load-deflection diagrams were plotted to compare the test results with the numerical output. The experimental results and nonlinear FEM modeling indicate that using SCC as a workable concrete in beam-column joints of reinforced concrete structures has satisfactory performance in terms of ductility and energy dissipations.

Investigation of the shear resistances of steel–concrete–steel composite structures with bidirectional webs

Steel–concrete–steel composite structures with bidirectional steel webs (SCSBWs) are used in large-scale immersed tunnels, and have been shown to have high capacity, ductility, waterproofness, and impact resistance compared to traditional structural types. Moreover, versatile construction procedures can be utilised to improve construction efficiency, because the steel plates can function as a framework during concrete casting. Recent studies have shown that there are multiple shear mechanisms in SCSBWs, and the shear resistance of these structures deserves further investigation to achieve more rational designs. Based on previous experimental and theoretical studies, numerical investigations are carried out in this study to investigate the shear resistance of an SCSBW, and an elaborate three-dimensional nonlinear finite element method (FEM) model is proposed. Based on this elaborate FEM model, a series of analyses are conducted to investigate the loading process, stress development, concrete cracking, stress state, and interfacial behaviour of SCSBWs under shear. Mutual verifications are obtained between results of the FEM model, experiments, and theory. Based on the analysis of the interfacial properties, the FEM model is simplified, and the simplified model is shown to be accurate and efficient. Further, parametric analyses are conducted, revealing that the concrete, axial web, flanges, and shear–span ratio have a significant influence on the shear resistance. Finally, a modified theoretical method is proposed to consider the influences of dowel action and small shear–span ratios, with which the accuracy of predicting the shear resistance of SCSBWs can be improved.

Lateral performance of CRCS connections with tube plate

This paper presents experimental and analytical studies to evaluate the cyclic behaviour of Circular Reinforced Concrete column Steel beam (CRCS) connections. Two 3/4-scale CRCS specimens are tested under quasi-static reversed cyclic loading. Specimens were strengthened with a tube plate (TP) and a steel doubler plate (SDP). Furthermore; nine interior beam-through type RCS connections are simulated using nonlinear three-dimensional finite element method using ABAQUS software and are verified with experimental results. The results revealed that using the TP improves the performance of the panel zone by providing better confinement to the concrete. Utilizing the TP at the panel zone may absorb and distribute stress in this region. Results demonstrate that TP can be used instead of SDP. Test records indicate that specimens with TP, with and without SDP maintained their maximum strength up to 4% drift angle, satisfying the recommendation given by AISC341-2016 for composite special moment-resisting frames.

Nonlinear finite element parametric analysis of prestressed steel reinforced concrete beams

Prestressed steel reinforced concrete beam(PSRCB) is a new type prestressed composite beam which uses prestressing technology in steel reinforced concrete beam (SRCB). The complete failure procedure of PSRCB was analysised by three-dimensional nonlinear finite element method. Numerical results agree well with experimental results. Then the numerical model was used to conduct some parametric studies including tensile rebar ratio, concrete compressive strength, H-section steel ratio, effective stress of prestressing strands and degree of prestressing.

Numerical evaluation of pile group effect of a composite group

Pile group effects of a composite pile group that consists of a group of subgroups are investigated based on a series of static pushover analysis with the help of the nonlinear three-dimensional finite element method (FEM). The numerical result suggests that there is an interaction between subgroups as well as an interaction within each subgroup; the former interaction effect is very similar to the latter if the distance between subgroups is normalized with respect to an equivalent pile diameter of each subgroup. A simplified method to estimate pile group effects of a composite pile group is then proposed in which the interaction effects within and between the subgroups are both accounted for using the same P-multiplier approach commonly employed for a pile group. The P-multipliers estimated by the proposed method show a fairly good agreement with those estimated from the FEM analyses.

Numerical analysis of tunnel in rock with basalt fiber reinforced concrete lining subjected to internal blast load

The present study focuses on the performance of basalt fiber reinforced concrete (BFRC) lining in tunnel situated in sandstone rock when subjected to internal blast loading. The blast analysis of the lined tunnel is carried out using the threedimensional (3-D) nonlinear finite element (FE) method. The stress-strain response of the sandstone rock is simulated using a crushable plasticity model which can simulate the brittle behavior of rock and that of BFRC lining is analyzed using a damaged plasticity model for concrete capturing damage response. The strain rate dependent material properties of BFRC are collected from the literature and that of rock are taken from the authors\' previous work using split Hopkinson pressure bar (SHPB). The constitutive model performance is validated through the FE simulation of SHPB test and the comparison of simulation results with the experimental data. Further, blast loading in the tunnel is simulated for 10 kg and 50 kg Trinitrotoluene (TNT) charge weights using the equivalent pressure-time curves obtained through hydrocode simulations. The analysis results are studied for the stress and displacement response of rock and tunnel lining. Blast performance of BFRC lining is compared with that of plain concrete (PC) and steel fiber reinforced concrete (SFRC) lining materials. It is observed that the BFRC lining exhibits almost 65% lesser displacement as compared to PC and 30% lesser displacement as compared to SFRC tunnel linings.

Modelling of Bonded Post-Tensioned Concrete Cantilever Beams under Flexural Loading

Prestressing is widely used technic all over the world for constructions of buildings, bridges, towers, offshore structures etc. due to its efficiency and economy for achieving requirements of long span with small depth. It is used for flexural strengthening of reinforced concrete structures for improving cracking loads and decreasing deflections due to service loads. There are two methods for prestressing (pre-tensioning and post-tensioning). In this paper, a three-dimensional nonlinear Finite Element (FE) method is used to determine the behaviour of Post-Tensioned (PT) concrete cantilever beams with different tendon profiles. Numerical analyses ANSYS package program is used for analysis of beams. The results from FE analysis is verified by experimental reference test result and good agreement is achieved. This paper is focused on the effect of different tendon profiles on the flexural behaviour of Bonded Post Tensioned (BPT) reinforced concrete cantilever beams. Six models with different tendon profiles are investigated. These models are without tendons, two tendons at the bottom, middle, top, parabolic tendons with one draped point and two draped points. Failure loads, deflections, and load versus deflection relationships for all models are examined and it is seen that the beam with one draped tendon profile shows a highest performance.