Circumferential Bending Research Articles

Long-term performance of concrete pipes under fatigue traffic loads

In recent years, there has been a concerning increase in road collapses triggered by failures in urban drainage systems. Concrete pipes, commonly uesd in urban drainage pipelines, endure prolonged cyclic loading from traffic above. However, the mechanisms governing the long-term performance and fatigue damage remain unclear. Through conducting fatigue model box tests on concrete pipes, the effects of different fatigue loading cycles on the circumferential strain of concrete pipes were investigated. A fatigue life prediction equation for concrete pipes was proposed, and the crack propagation under various fatigue loading cycles was observed. Additionally, corresponding 3D FE models of concrete pipe-soil interaction with bell-and-spigot joints and gaskets were constructed. These models were used to explore the vertical displacements, circumferential bending moments, and circumferential stresses of the concrete pipes under different fatigue loading cycles, the damage and failure mechanisms of the concrete pipes under fatigue loading were revealed. The results indicate that the potential failure location of concrete pipes is within the inner crown of the bell under the fatigue traffic loads. The circumferential strains and crack propagation exhibiting a three-stage evolution pattern under fatigue loads. The proposed fatigue life prediction equation accurately predicts the remaining life of concrete pipes. Upon reaching 21.89 million loading cycles, the strain at the inner crown of the bell reaches 575.0 με, resulting in complete failure. Cracks on the inner crown of the bell extend inward and to the right from the middle of the joint, forming a channel for crack propagation. The vertical displacements at the crown and the circumferential bending moments of the bell and spigot exhibit rapid increases, stabilization, and subsequent declines with the increasing loading cycles. When concrete pipes undergo fatigue fracture, the maximum vertical displacement and circumferential bending moment at the bell are measured as 2.26 mm and 17.82 kN·m/m, respectively. Stress concentration at the bell and spigot during fatigue loading leads to crack propagation and convergence, causing redistribution of stress fields characterized by an initial increase followed by a decrease in the inner crown and invert of the bell.

Failure analysis and comparative study on tunnels under strike-slip fault and oblique-slip fault movements

To deeply study and compare the failure characteristics of tunnels under strike-slip and oblique-slip active faults, with the engineering background of a railway tunnel in western China crossing both strike-slip and oblique-slip active faults, two sets of large-scale indoor model tests with a geometric similarity ratio of 1:35 were conducted. The fissure development patterns and strain trends of the tunnel under the movement of both types of faults were monitored and analyzed. Meanwhile, a three-dimensional model of tunnel-rock-fault interaction was established using ABAQUS finite element analysis software to determine the variation patterns of bending moments and shear forces of the tunnel under the movement of both types of faults. The results showed that under the movement of strike-slip and oblique-slip active faults, circumferential bending fissures appear at the right waist of the hanging wall and the left waist of the footwall of the tunnel, and shear oblique fissures appear at the vault of the fault fracture zone. Among them, the number of cracks, the range of tunnel cracking and the degree of crack damage under the condition of the oblique-slip fault are obviously more serious than those under the condition of the strike-slip fault. Under the dislocation of the oblique-slip fault, a large area of broken zone appears in the vault of the fault fracture zone, the lining falls off, the steel bar is exposed, and there is an obvious uplift phenomenon. The right waist of the tunnel’s hanging wall mainly experiences tension while the left waist experiences compression, whereas on the hanging wall, the right waist experiences compression while the left waist experiences tension. Under the fault movement, the maximum bending moment value mainly occurs at a distance of 10 m from the fault fracture zone on both the hanging wall and the footwall, with the bending moment values at the fault fracture zone nearly approaching zero. The maximum shear force value occurs at the fault fracture zone. Under the movement of both types of faults, the failure mode of the tunnel is mainly characterized by bending failure of the hanging wall and the footwall and shear failure at the fault fracture zone. Compared to strike-slip active faults, the development of fissures in tunnels under oblique-slip active faults is more severe, with larger bending moment and shear force values, and a wider range of tunnel failure. These results can provide theoretical and technical experience for future similar projects.

Modal signal analysis of parabolic shell structures with flexoelectric sensors

The flexoelectric effect, garnering extensive attention in recent years, is an electro-mechanical coupled gradient effect that widely exists in dielectric materials and holds great potential for applications in structural sensing and actuation. The parabolic shell structure, characterized by line focusing, finds widespread use in key structural components such as solar trough collectors and communication antennas. Distributed sensing of the structural states of these parabolic shells is critical for vibration control, health monitoring, and shape control of precision structural systems. Therefore, flexoelectric sensing research based on parabolic shell structure has become an important topic. This study establishes a mathematical model for flexoelectric sensing in a parabolic shell with four-sided simply supported boundary conditions. The model is based on the direct flexoelectric effect, and thin shell assumption, and incorporates specific Lamé parameters and curvature radius. The electro-mechanical strain gradient/signal generation characteristics and distributed modal flexoelectric signals on the parabolic shell are investigated. The sensing signal under the open-circuit conditions is deduced, and the flexoelectric sensing signal and sensing characteristics of different modes are analyzed. The formulation of the flexoelectric neural sensing signal for the parabolic shell structure is provided and divided into two components: a circumferential bending component and a longitudinal bending component. In the case studies, the effects of design parameters such as flexoelectric sensor thickness, size, and aspect ratios are evaluated and compared. The analysis and results of this study offer a theoretical foundation and reference for refining the design parameters of the flexoelectric sensor and determining its optimal sensing position, and potentially paving the way for new applications of flexoelectric sensing technology.

Influence of erosion voids and traffic loads on buried large-diameter reinforced concrete pipes

Geotechnical centrifuge tests were conducted to examine the influence of invert voids and surface traffic loads on 1400 mm diameter reinforced concrete pipes buried with a shallow soil cover depth of 700 mm. Void formation beneath the pipe was simulated during centrifuge testing. The test results revealed that before void formation, the surface load directly above the middle of the pipe caused a significant increase in not only the circumferential bending moments but also the longitudinal bending moments, the latter of which was considerable and could not be ignored. Void formation beneath the middle of the pipe led to a reduction in both the circumferential bending moments and longitudinal bending moments at all measuring positions, i.e., crown, springline, and invert. The most significant reduction occurred at the invert, and there was even a reversal in the sign of the invert longitudinal bending moment. A comparison was made between centrifuge tests with erosion voids and surface loads at different horizontal positions, which had a marked influence even when the positions differed by half a pipe length. Joint rotation played an important role in relieving large bending moments of pipe barrels in a jointed pipeline when the void and surface load were located at the joint.

Multiobjective Optimization Study On the Aerodynamic Performance and Anti-Erosion Characteristics of a Single-Stage Dusty Flue Gas Turbine

Abstract Solid particle erosion of dusty energy recovery turbine blades has a great impact on the operating economics and safety of the unit. To mitigate the erosion of blade and improve the aerodynamic performance of the turbine, a multiobjective optimization method for turbine cascade based on the experimental design method, genetic algorithm and CFD multiphase flow simulation was developed. The optimization results show that the number of stator and rotor blades and the trailing edge angle at 50% blade span are the main parameters affecting the efficiency and blade erosion of the dusty turbine. By reducing the number of stator blades and the circumferential bending angle of the stator trailing edge, the impingement velocity and impingement probability of particles impinging on the stator trailing edge decrease by 7.5%~16.8% and 8.9%~46.2%, respectively. Additionally, compared with the original design, the flow separation loss and secondary flow intensity of the rotor cascade are suppressed by adjusting the load distribution and inlet attack angle of the rotor; thus, the turbine efficiency effectively improves by 2.28%. Meanwhile, the optimized blade reduces the particle impingement velocity and probability on the rotor leading edge, and the erosion condition of the rotor leading edge decreases by 70%.

TO THE CALCULATION OF RING PLATES ON A VARIABLE ELASTIC BASE

The article examines the bending of ring plates on a variable elastic base. There are different models of elastic base. The simplest is the Winkler model, or the spring model. For beams on a constant elastic base, this model allows obtaining an exact solution, but not for slabs. The case is even more complicated when the elastic basis is variable. There is no single approach to building a universal analytical solution. Therefore, numerical calculation methods are used in engineering practice. The analytical method of direct integration and computer modeling in PC LIRA-CAD with subsequent calculations by the method of finite elements are used. Two examples are considered: a steel plate, which is rigidly clamped along the inner contour, and its outer contour is hinged, and a concrete slab, which is rigidly clamped along the outer contour, and its inner contour is hinged. The results of the numerical implementation show that the values of deflections when calculated by the author's method and the method of finite elements in PC LIRA-CAD practically coincide, and the difference in the values of bending moments reaches 10%. Moreover, the difference in deflections is manifested only in the fourth (and sometimes in the fifth) sign after the comma. It is noted that the method of direct integration demonstrated very high accuracy when solving numerous test problems that have an exact solution. The authors explain the discrepancy in the values of the bending moments obtained here by the semi-automatic breakdown of the finite-element mesh in PC LIRA-CAD. This statement is based on the fact that when the mesh is thickened in the circumferential direction, the results obtained by the two methods for determining the radial and circumferential bending moments are substantially converged.

Experimental Study of the Effect of Temperature on the Circumferential Bending Performance of GFRP Pipes

Glass Fiber Reinforced Plastic (GFRP) pipes are widely used as polymer-based composite pipes in various engineering fields where the temperature influences their performance. This paper investigated the circumferential bending properties of GFRP pipes with different continuous fiber contents at 30 °C, 50 °C and 70 °C. GFRP pipes are classified into three types according to their component content: type I, type II and type III. The results show that the bending performance of GFRP pipes tends to decrease with increasing temperature, with the retention of circumferential stiffness being 80-85% and the retention of bending strength and damage displacement being about 25-40% from 30 °C to 70 °C. The rate of decay of ring stiffness, bending strength and damage displacement is significantly higher from 30 °C to 50 °C than from 50 °C to 70 °C. Both temperature and continuous fiber content greatly influenced the damage pattern. At 30 °C, delamination damage occurred at the top and bottom of the Type I GFRP pipe before fracture damage happened at the left and right ends and fracture damage occurred at both the left and right ends of Type II and Type III GFRP pipes. Delamination damage happened at the upper and lower ends of the GFRP pipes at 50 °C and 70 °C. In addition, the paper analyses the mechanisms of the associated effects.

CALCULATION OF ANNULAR PLATES ON AN ELASTIC BASE WITH A VARIABLE BEDDING FACTOR

The application of the analytical method ‒ the method of direct integration ‒ to calculations of building structures in the form of circular plates and plates on a continuous variable elastic base is considered. It is noted that there are no proposals for a general analytical method for calculation of annular plates on a variable elastic base in the literature. And the need for such a method is obvious, since it makes it possible to estimate the accuracy of finite element analysis. A detailed description of the algorithm of the direct integration method is not given in the paper, and all the calculation formulas for the circular plate are taken from the authors’ already published article. The results of numerical implementation of this algorithm for specific examples are considered. In order to verify the results of calculations by the author’s method, computer modeling of the considered circular plates in PC LIRA-SAPR and their calculations by the finite element method have been performed. The reaction of the foundation is described by the Winkler model with a variable bedding factor. The calculation of a concrete slab that is rigidly pinched on the inner contour and articulated on the outer contour is performed. And calculation of a steel plate with rigid pinching on the outer contour and articulated on the inner contour. In the first case, the bedding factor is assumed constant, and in the second case, it changes according to the linear law. The calculations showed that the discrepancy between deflections calculated by the finite-element method and the author’s method does not exceed 1%, and the results of radial and circumferential moments calculation differ more considerably, amounting to 10%. The authors explain this difference by the inaccuracy of the numerical analysis associated with a semi-automatic method of constructing a finite-element mesh, which should be made finer. The densification of the mesh in the manual mode of its partitioning significantly reduces the discrepancy between the results of calculating the deflections, radial and circumferential bending moments by the finite-element method and the author’s method.

ANALYTICAL METHOD FOR CALCULATING ANNULAR PLATES ON A VARIABLE ELASTIC BASE

The paper considers the application of the method of direct integration to calculations of annular plates and slabs on a continuous variable elastic base. Ring-shaped plates with variable geometric and mechanical parameters are increasingly used. Not only the elastic base, but also the plate thickness and cylindrical stiffness can be variable parameters here. The need for an analytical method for calculating such structures raises no doubts, since it makes it possible to evaluate the accuracy of finite-element analysis. To date, there are no proposals in the literature regarding a general analytical method for the calculation of annular plates on a variable elastic base. A detailed description of the algorithm of the direct integration method is not given in the paper, and all the calculation formulas for the annular plate are taken from the authors' already published article. The results of numerical implementation of this algorithm for specific examples are considered: a concrete plate, which is rigidly pinch on the inner contour, and its outer contour is free, and a steel plate, which is rigidly pinch on the outer contour, and its inner contour is free. To estimate the results of calculation by the author's method, computer modeling of the considered structures in PC LIRA-SAPR and their calculations by the finite-element method have been executed. The foundation reaction is described by Winkler model with a variable bedding factor. In the first case a bed factor is assumed constant, and in the second case it changes under the linear law. Calculations have shown that discrepancy between deflections calculated by the finite-element method and the author's method does not exceed 1 %, and the results of radial and circumferential moments calculation differ more considerably, amounting to 10 %. The authors explain this difference by the inaccuracy of the numerical analysis associated with the semi-automatic method of constructing a finite-element mesh, which should be made finer. The densification of the mesh in the manual mode of its partitioning significantly reduces the discrepancy between the results of calculating the deflections, radial and circumferential bending moments by the finite-element method and the author's method.

Dynamic modeling of rotary blade crack with regard to three-dimensional tip clearance

To investigate the dynamic characteristics of the three-dimensional blade tip clearance (3D-BTC) of rotary blade cracks, a novel dynamic model of the rotary blade crack with regard to the 3D-BTC is derived based on the Timoshenko beam theory. In this model, the modal shape functions of the blade are derived based on the transfer matrix method, and the axial and circumferential aerodynamic loads are introduced to better obtain the dynamic responses of the blade vibration. Then, a breathing crack model of the blade trailing edge crack is established by considering the coupling effects of the centrifugal stress, axial bending stress, and circumferential bending stress. The crack opening width is introduced into the breathing crack model to comprehensively depict the crack together with the crack depth and crack location. Moreover, a numerical calculation method for the 3D-BTC is proposed for the rotary blade with cracks. The dynamic model is validated by comparing it with the finite element model and the experiment. Finally, the effects of the blade trailing edge crack on the 3D-BTC are analyzed. The results show that the cracked blade's first-order natural frequency decreases with the crack depth increase, and it increases first and then decreases slightly when the crack location moves away from the blade root. The effects of crack opening width on the first-order natural frequency are relatively small due to its small size. In the meantime, the nonlinear damage indicators (NDIs) of the 3D-BTC are calculated. The results show that the NDIs can reflect the severity of the blade crack, and the proposed model can comprehensively analyze the effects of rotary blade crack on the 3D-BTC, which is beneficial for the diagnosis method for blade cracks based on the 3D-BTC.

Impact of erosion voids and internal corrosion on concrete pipes under traffic loads

The disaster testing system of buried pipes developed in this work is innovatively used to examine intact pipes, internally corroded pipes without erosion voids, and internally corroded pipes with erosion voids. The measured data are verified by the finite element models. Parametric analyses are conducted to investigate the statistical relationship between the maximum principal stress on the pipe and the defect parameters, and a multiparameter formula used to predict the maximum stress on the pipes is finally derived. The results show that the corroded pipes without erosion voids have the largest circumferential bending moment. The circumferential bending moments of the bell and spigot of the pipes with erosion voids and internal corrosion decline with an increase in the width and length of the void. The parametric sensitivity analysis demonstrates that the stress on the pipes with erosion voids and internal corrosion has a positive linear relationship with the corrosion depth, a quadratic polynomial relationship with the width and length of corrosion, and a negative linear correlation with the width and length of the void. The proposed multiparameter formula can accurately predict the maximum principal stress on the pipes with erosion voids and internal corrosion. The results fully reveal the mechanism of the combined effect of corrosion and voids on the mechanical properties of concrete pipes.

Mechanical behavior of concrete pipes with erosion voids and the effectiveness evaluation of the polyurethane grouting

Research on pipes ringed by erosion voids is mainly concerned with circumferential mechanical behavior but ignores longitudinal bending responses induced by the relative motion of the pipe joints at voids. There has been limited innovative experimental investigation into pipe behavior that assesses the effectiveness of polyurethane (PU) grouting in rehabilitating erosion voids. Mechanical behavior tests of concrete pipes of intact, with an erosion void at the invert, and PU grouted were performed using a self-developed large-scale disaster testing system, and the measured results were numerically verified. Results show that the peaks of the positive and negative longitudinal bending moments of the intact pipes and pipes with a void at the invert appear at SgL2 and SgR2, SgL3 and SgR3, respectively, and the positive longitudinal bending moment is about 1.6–3.0 times higher than the negative ones. Voids at the invert have a significant effect on the longitudinal bending moments of the pipe segments located on the adjacent sides of the void. The longitudinal bending moments of the pipes with different void widths decrease with the increase of void width at SgL1 and SgR1 and increase with the increase of void width at SgL2 and SgR2, SgL3 and SgR3. The longitudinal bending moments of the pipes with different void lengths increase with the increase of void length in the whole longitudinal length. The circumferential bending moments at the bell-and-spigot decrease as the void width and void length increase. The maximum increases in the vertical displacements and maximum shear displacements of the pipes with different void widths and void lengths are 63–150% and 150–221%, 225–325%, and 325–550%, respectively, compared with the intact pipes. The rehabilitation efficiencies of the longitudinal and circumferential bending moments and the vertical displacement ranged from 85–93% and 85–94%.

Investigation of mechanical properties of corroded concrete pipes after cured-in-place-pipe (CIPP) rehabilitation under multi-field coupling

The pipeline is mainly subjected to soil load, fluid load and traffic load, the mechanical properties of corroded concrete pipes after cured-in-place-pipe (CIPP) rehabilitation under multi-field coupling have not been revealed. In this paper, a 3D numerical model of buried concrete pipes after CIPP rehabilitation under the coupled effects of the soil load, traffic load and fluid load were established based on the results of the full-scale test. The influence of cover depth, traffic load and fluid load on the maximum principal stress of the pipeline, vertical displacement of the pipeline, the von Mises stress of the CIPP liner and the circumferential bending moment of pipe-liner composite structure were analyzed. Results showed that the cover depth and traffic load have a greater influence on the crown, invert, and springline of the pipe and has a lesser influence on the shoulder and haunch of the pipe; The stress and the circumferential bending moment of the pipeline is mainly caused by the soil load, the vertical displacement of the pipeline and the von Mises stress of CIPP liner is mainly caused by the traffic load, and the fluid load has little effect on the pipe-liner composite structure.

1 g Model Test on the Use of Isolation Piles for Tunnel Protection Adjacent to Soft Soil Excavation

As the rapid development of urbanisation, the available land resource is getting gradually limited. In correspondence, underground constructions become popular and the influence of soil excavation adjacent to shield tunnel has become a great concern. However, the role of isolation piles for tunnel protection in soft soil conditions has not been well understood, owing to a lack of practical data. In this paper, an 1 g model test, with three experimental patterns, that is, C1 (no isolation piles), C2 (non-buried isolation piles) and C3 (buried isolation piles), was designed based on a prototype work in Zhejiang Province (China). A similarity concept was considered for the rescaling of the model test. The displacements and bending moments of the retaining wall, isolation piles and shield tunnel, were monitored and assessed, respectively. The results showed a barrier role of isolation piles which could restrict the displacements and bending moments of the retaining wall, particularly C2 with non-buried isolation piles which was shown to be more effective than the buried isolation piles in C3. The buried isolation piles played a better barrier role than that of the non-buried isolation piles in terms of restricting the tunnel displacements. The circumferential bending moment of the tunnel could not be restricted by using isolation piles under the investigated scenarios. The working mechanism of isolation piles was evaluated, which suggested the importance of a proper designed locations of foundation pit and isolation piles. Regardless of the limitations, the findings obtained from this study would be useful for future applications of isolation piles in tunnel protection with adjacent soil excavation.

Effect of trailing edge bending and sweeping on brake impeller of low-temperature turbo-expander

With the continuous development of low-temperature turbo-expanders, the rotation speed of the rotor is getting faster. The diameter of the impeller has become one of the factors that limit the rotation speed. In this article, a new idea to improve braking capability and reduce the diameter of the brake impeller is proposed. The brake impeller of a small low-temperature air turbo-expander test bench is used as a prototype, influence of the combination of circumferential bending and sweeping at the trailing edge of the brake impeller on the braking ability is studied. It is found that the braking ability is significantly improved. To simplify the description, the combination of a forward bending of 10° and a sweeping of 20° is called combination 1. For the current brake impeller, combination 1 is the most suitable. Compared with the original impeller, the braking power of combination 1 has increased by 99.6 W, an increase of 10.4 %. Forward bending and forward sweep substantially increase the wrap angle of the brake impeller, thereby increasing the air outlet speed and improving the braking ability, but at the expense of the flow stability of the brake impeller.

Mechanical response of inclined TBM tunnel due to drainage settlement of deep sandstone aquifer

Drainage of deep aquifers can cause stratum settlement, which has significant effects on the architectural structures within them. Especially for inclined TBM tunnels, the settlement may lead to the longitudinal differential deformation and damage of segments. However, most previous studies on the effects of aquifer drainage settlement on deep structures have focused on the vertical shaft in coal mines, and little attention has been paid to inclined TBM tunnels in deep sandstone aquifers. Through the physical model test and numerical simulation, in this study, the mechanical characteristics and deformation behavior of an inclined TBM tunnel in the deep water-bearing sandstone and impermeable mudstone before and after the aquifer drainage were investigated. The distribution and variation of stresses, internal forces, and deformation on tunnel segments before and after drainage were systematically analyzed along the tunnel longitudinal and circumferential directions. Results show that the whole tunnel is always under compression and mainly subjected to the coupling effect of bending moment and axial compression in the longitudinal direction. After drainage, the longitudinal and circumferential stresses as well as circumferential axial force increase remarkably at the tunnel sidewall but decrease at the tunnel crown and invert. While for the circumferential bending moment, by contrast, it increases at the three positions. In addition, the tunnel experiences a noticeable bending at the junction of the two strata after drainage due to the synchronous settlement with the sandstone, resulting in severe stress concentrations and the formation of the longitudinal shear band at the stratigraphic junction.

Blade Serial Number Identification Based on Blade Tip Clearance without OPR Sensor

Blade serial number identification is one of the key issues in blade tip-timing vibration measurement without once-per-revolution (OPR) sensor. In order to overcome the shortcomings of the existing blade serial number identification methods without OPR sensor, a new identification method of blade serial number based on blade tip clearance is proposed in this paper. The relationship between blade tip-timing data and blade serial number can be identified by the matching relationship between blade tip clearance under static state and dynamic state. According to the finite element simulation and experimental data, the accuracy of the blade serial number identification method based on blade tip clearance is verified by using the OPR sensor method. The results show that in the nonresonant rotation speed region, the method can identify the blade serial number, and the identification result is consistent with the result of the OPR sensor method. In the resonance rotation speed region, when the blade tip clearance change caused by the blade circumferential bending vibration is less than the dispersion of initial blade tip clearance, the method in this paper can accurately identify the blade serial number. Otherwise, the inference method can be used. It provides theoretical support and technical basis for the engineering application of blade tip-timing vibration measurement technology without OPR sensor.

A comparative study of the effect of the soil constitutive model on the seismic response of buried concrete pipes

No attention has been given in previous studies to understand the influence of the sophistication of the soil constitutive model on the response of buried concrete pipes subjected to transverse seismic effect. This research, therefore, has been conducted to address this gap in knowledge by analyzing the behavior of a buried concrete pipe subjected to transverse seismic shake employing the linear elastic (LE) model, elasto-plastic Mohr-Coulomb (MC) model, hardening soil (Hs) model, and hardening soil model with small strain stiffness (Hs small) to provide a benchmark study that helps the designers and the researchers to select the most suitable and less computationally demanding soil constitutive model. The cases of good and poor installation conditions have been considered in the analyses. In addition, numerous earthquake records have been used to allow the consideration of wide range of earthquake intensities to aid general conclusions. It was found that all of the considered constitutive models produce the same trend of the circumferential bending moment (BM) that is developed around the pipe. In general, the maximum BM produced using the LE and MC models is significantly lower than that produced using the Hs and Hs small models with one exception for the LE model for a predominant frequency of 0.66 Hz. Furthermore, the maximum BM produced using the LE and MC models is not sensitive to the increase of the peak ground acceleration (PGA). More importantly, the Hs and Hs small models produce almost similar results with a percentage difference ranges between 1% to 9%. In addition, the Hs and Hs small models show a decrease of the maximum BM as the predominant frequency rises and an increase of the maximum BM as the PGA rises.

Evaluation of seismic mechanical response of tunnel linings using shaking table tests and numerical analyses

This paper investigates seismically induced circumferential forces and bending moment of tunnel linings using a series of large shaking table tests and numerical analyses. In this regard, a scaled-down tunnel, embedded in two different depths of sandy soil, was tested under different frequencies of input motion. Then, dynamic finite difference analyses, first verified using the results of the performed large scale shaking table tests, were conducted to study the effects of depth ratio (h/a; h: depth of tunnel centerline and a = radius of the tunnel), flexibility ratio (1.2, 10 and 110) and different frequencies of input motion, corresponding to the dimensionless periods (λ/D), on the mechanical behavior of the tunnel lining. The results indicated that, low frequencies of input motions for the tunnel with low flexibility ratio resulted in greater circumferential bending moment values of the tunnel lining. Furthermore, the tunnel depth and adjacent surface foundation intensified the bending moment, shear, and axial forces of the shallow tunnel by about 43 and 17% and did not affect the maximum bending moment and forces locations in the tunnel lining. It is, therefore, necessary to consider the effect of a surface foundation on tunnel lining when constructing shallow subway tunnels in urban areas.

Multi-patient study for coronary vulnerable plaque model comparisons: 2D/3D and fluid\u2013structure interaction simulations

Several image-based computational models have been used to perform mechanical analysis for atherosclerotic plaque progression and vulnerability investigations. However, differences of computational predictions from those models have not been quantified at multi-patient level. In vivo intravascular ultrasound (IVUS) coronary plaque data were acquired from seven patients. Seven 2D/3D models with/without circumferential shrink, cyclic bending and fluid–structure interactions (FSI) were constructed for the seven patients to perform model comparisons and quantify impact of 2D simplification, circumferential shrink, FSI and cyclic bending plaque wall stress/strain (PWS/PWSn) and flow shear stress (FSS) calculations. PWS/PWSn and FSS averages from seven patients (388 slices for 2D and 3D thin-layer models) were used for comparison. Compared to 2D models with shrink process, 2D models without shrink process overestimated PWS by 17.26%. PWS change at location with greatest curvature change from 3D FSI models with/without cyclic bending varied from 15.07% to 49.52% for the seven patients (average = 30.13%). Mean Max-FSS, Min-FSS and Ave-FSS from the flow-only models under maximum pressure condition were 4.02%, 11.29% and 5.45% higher than those from full FSI models with cycle bending, respectively. Mean PWS and PWSn differences between FSI and structure-only models were only 4.38% and 1.78%. Model differences had noticeable patient variations. FSI and flow-only model differences were greater for minimum FSS predictions, notable since low FSS is known to be related to plaque progression. Structure-only models could provide PWS/PWSn calculations as good approximations to FSI models for simplicity and time savings in calculation.