Typical Arch Research Articles

Effect of typical arch structure on slipstream and wake flow of 600 km/h maglev train

PurposeThe aerodynamic differences between the head car (HC) and tail car (TC) of a high-speed maglev train are significant, resulting in control difficulties and safety challenges in operation. The arch structure has a significant effect on the improvement of the aerodynamic lift of the HC and TC of the maglev train. Therefore, this study aims to investigate the effect of a streamlined arch structure on the aerodynamic performance of a 600 km/h maglev train.Design/methodology/approachThree typical streamlined arch structures for maglev trains are selected, i.e. single-arch, double-arch and triple-arch maglev trains. The vortex structure, pressure of train surface, boundary layer, slipstream and aerodynamic forces of the maglev trains with different arch structures are compared by adopting improved delayed detached eddy simulation numerical calculation method. The effects of the arch structures on the aerodynamic performance of the maglev train are analyzed.FindingsThe dynamic topological structure of the wake flow shows that a change in arch structure can reduce the vortex size in the wake region; the vortex size with double-arch and triple-arch maglev trains is reduced by 15.9% and 23%, respectively, compared with a single-arch maglev train. The peak slipstream decreases with an increase in arch structures; double-arch and triple-arch maglev trains reduce it by 8.89% and 16.67%, respectively, compared with a single-arch maglev train. The aerodynamic force indicates that arch structures improve the lift imbalance between the HC and TC of a maglev train; double-arch and triple-arch maglev trains improve it by 22.4% and 36.8%, respectively, compared to a single-arch maglev train.Originality/valueThis study compares the effects of a streamlined arch structure on a maglev train and its surrounding flow field. The results of the study provide data support for the design and safe operation of high-speed maglev trains.

Seismic Performance Analysis of CFST Stiff Skeleton Concrete Arch Bridge considering Non-planar Sectional Stress Induced by Balanced Ring-casting Construction

ABSTRACT Concrete-filled steel tube (CFST) stiff skeleton concrete arch bridges can be designed with longer spans using balanced ring-casting construction. However, this construction method induces non-planar sectional stress in the arch rings. To investigate the influence of the non-planar sectional stress on the seismic performance of arch bridges, we developed two numerical models of a typical arch bridge. The first model simulates the construction process of balanced ring-casting, while the second model ignores the construction process. The dynamic analysis results reveal that, if the construction process is ignored, the seismic risks of concrete cracking and reinforcement yielding in the arch rings will be underestimated.

Centroid deformation-based nonlinear safety monitoring model for arch dam performance evaluation

The purpose of this study is evaluating the arch dam performance through modelling on the defined centroid deformation with the measured data. The space-time distribution characteristics of the arch dam deformation are firstly identified through the comparative analysis of typical arch dams with height of 200–300 m in China. Subsequently, the geometry centroid of the deflection curve of an arch or a cantilever, composed of multiple monitoring points, is defined to indicate the global structural behavior of the arch dams. In order to evaluate the future performance of the arch dams, the space–time monitoring model for the centroid is established by introducing its initial coordinates based on the traditional statistical models. Afterwards, a novel centroid prediction model is developed based on the least squares support vector machine to balance the empirical risk and generalization ability of the statistical regression models. The input factors of the prediction model are determined in advance by principal component analysis to eliminate the multi-collinearity and reduce the computational complexity. The model construction and validation of the centroid deformation method are implemented on the world’s highest arch dam through evaluating its structural behavior and predicting the development trend. The results can provide strong technical support to better grasp its performance during long-term operation.

Elastic-plastic time-history analysis of steel-tube stiff-frame arch bridge without inner filling concrete

Based on a case study of a typical arch bridge with hollow steel tube and stiffness frame located in the high intensity region of western China, this paper adopts the onlinear time- history method to analyze the structural response of the overall bridge elastic-plastic model under seismic action. Under the force of Wolong wave in Wenchuan Earthquake, the main load-bearing members of the structure have a good seismic performance. Only part of the columns on the main arch ring enter the plastic hinge state for energy dissipation, and the lower columns have a more obvious energy dissipation effect than the higher ones. The result indicates that the design idea of structure which is similar to that of strong column and weak beam in ductility design, has the characteristics of “strong arch and weak beam” and can therefore improve the ability of structure to resist collapse under earthquake action.

Design and Analysis of Concrete-Filled Rectangular Steel Tubular Truss-Arch Composite Bridge Stiffened with PBL

Under the influence of long time load actions, shrinkage and creep of concrete, temperature variation, and concrete pouring quality, debonding may occur between steel tube and concrete. Debonding affects the mechanism behavior of arch rib and joint and even threatens the integrity of an entire bridge. To reduce such possibility, a concrete-filled steel tubular arch bridge stiffened with perfobond ribs (PBL) is proposed. Based on a concrete-filled rectangular steel tubular truss-arch composite bridge stiffened with PBL in Xining City, Qing Hai province, we conduct force analysis of the bridge on the aspects of the arch ribs and the truss-arch composite system. According to the mechanical properties of the bridge, we establish finite-element models, including joint models in which web members bore relatively large axial force and a typical arch rib model. Based on the models, the local mechanical property of joints, and the interfacial properties between steel tube and concrete under solar radiation are studied. Results show that PBL reduces the length of force transmission and improves the stress and deformation concentration of the joints. PBL also alleviates the debonding between steel tube and concrete. This bridge scheme meets the requirements of function, aesthetics, and safety.

Investigation of Stochastic Seismic Response and Index Correlation of an Arch Dam Using Endurance Time Analysis Method

The seismic dynamic response and correlation between various indicators of an arch dam under a series of stochastic earthquake excitation are analysed. Seismic response assessment of a concrete arch dam is conducted through nonlinear endurance time analysis (ETA) of a typical arch dam. The 289 m high Baihetan arch dam in Southwest China (as a case study) is subjected to a set of 10 three‐component endurance time acceleration histories (ETAHs) synthesised on the basis of the design site acceleration response spectrum to increasing peak ground acceleration (PGA). The effects of dam‐reservoir‐foundation interaction, radiation damping of infinite rock foundation, and nonlinearities of dam material and joint contact elements are considered. The indices to failure modes of damage propagation through the dam body and the deformation and joint opening beyond the limit states of the arch dam are identified. Dynamic responses, including deformation, joint opening, and damage distribution, are statistically analysed. The dispersion and correlation of indicators are analysed by employing the coefficient of variation and coefficient of correlation, respectively. The deterministic relationships between contraction joint opening, displacement, and damage volume ratio are obtained by using a multivariate fitting method. The results show that those failure indices have similar exponential trends, and seismic intensity parameters exert a significant influence on seismic response and damage under increasing PGA. The results of correlation and fragility analysis demonstrate that damage volume ratio and the sum of joint opening are consistent, which can provide a strong scientific basis for predicting earthquake damage.

Experimental Investigation of the Behavior of Self-Form Segmental Concrete Masonry Arches

This research aims to introduce a new technique—off-site and self-form segmental concrete masonry arches fabrication, without the need of construction formwork or centering. The innovative construction method in the current study encompasses two construction materials forms the self-form masonry arches, wedge-shape plain concrete voussoirs, and carbon fiber-reinforced polymer (CFRP) composites. The employment of CFRP fabrics was for two main reasons: bonding the voussoirs and forming the masonry arches. In addition, CFRP proved to be efficient for strengthening the extrados of the arch rings under service loadings. An experimental test was conducted on four sophisticated masonry arch specimens. The research parameters were the Keystone thickness and the strengthening of the self-form arch ring at the intrados. The major test finding was that the use of thicker Keystone alters the behavior of the self-form arch and considerably increases the load carrying capacity by 79%. Partial strengthening of the intrados with CFRP fabrics of typical arch ring Keystone resulted considerable increase in the debonding load of fabrication CFRP sheets by 81%, increase in the localized crushing load by 13% and considerably increase voussoir sliding load by 107%.

SA2USING GENETIC INSTRUMENTS TO ASSESS CAUSAL PATHWAYS TO EDUCATIONAL ATTAINMENT IN ADHD AND AUTISM: EVIDENCE FROM A TWO SAMPLE MENDELIAN RANDOMISATION STUDY

Fluid–structure interaction formulated in the Lagrangian–Eulerian approach with pressure-based fluid elements, which inherently results in non-symmetric matrices, is commonly treated by either direct un-symmetric solvers or staggered solution methods. Developing an in-house finite element code called SNACS, we implement the pressure-based Eulerian formulation so that a usual symmetric solver can be employed for dam–reservoir interaction analyses. The equilibrium equations of motion for such a coupled system are directly integrated herein by the HHT time marching algorithm in an incremental–iterative solution procedure to tackle a highly nonlinear dynamic analysis of jointed arch dams. The HHT time integration scheme is able to damp out high-frequency noises resulting from sudden changes in the stiffness due to opening/closing of pre-existing joints during an earthquake. First, a Pseudo-Symmetric technique is proposed to store the total matrices and solve the coupled non-symmetric equations in a symmetric manner. Then, the interface element formulation and stress update procedures of two discrete crack constitutive models suitable for contraction and peripheral joints of arch dams are detailed. Afterwards, results of the analysis on a typical arch dam are compared with the case in which the interaction is approximately represented by added masses as a widely-used method in dam engineering practice to illustrate the effects of water compressibility and reservoir bottom absorption. Besides, the straightforward implementation of pressure-based fluid–structure interaction utilizing a symmetric solution strategy is validated herein to be efficient for a 3-D large scale practical usage in other finite element codes even the commercial ones to avoid using un-symmetric solvers. Employing this symmetric implementation for the dam–water interaction drastically reduces the computational effort, particularly when an iterative scheme is required to solve such a highly nonlinear system.

Numerical Analysis for Selection of New Arch Framework Structures Made of Precast Block Materials for Highway Slope Protection

Arch framework structure is one of the common forms of highway slope protection in actual projects, and the rapid development and wide application of new type arch framework structures made of precast block material are for their convenient construction and environmental protection. The article selects two typical arch shaped framework structures made of traditional mortar rubble, and precast block material over mortar foundation respectively. According to actual structure sizes, finite element analysis models were built to calculate and analyze the displacement and stress of two structures under same vertical loading pressure. The results of the numerical analysis and laboratory test results show that, the difference of the displacement between the two structures is small, and the displacement of new structure is a little bigger. The stress of new structure is significantly less than traditional structure. The new type structure of precast block material over mortar foundation possesses better over-all performances among the chosen two structures and can be used widely.

A symmetric implementation of pressure-based fluid–structure interaction for nonlinear dynamic analysis of arch dams

Fluid–structure interaction formulated in the Lagrangian–Eulerian approach with pressure-based fluid elements, which inherently results in non-symmetric matrices, is commonly treated by either direct un-symmetric solvers or staggered solution methods. Developing an in-house finite element code called SNACS, we implement the pressure-based Eulerian formulation so that a usual symmetric solver can be employed for dam–reservoir interaction analyses. The equilibrium equations of motion for such a coupled system are directly integrated herein by the HHT time marching algorithm in an incremental–iterative solution procedure to tackle a highly nonlinear dynamic analysis of jointed arch dams. The HHT time integration scheme is able to damp out high-frequency noises resulting from sudden changes in the stiffness due to opening/closing of pre-existing joints during an earthquake. First, a Pseudo-Symmetric technique is proposed to store the total matrices and solve the coupled non-symmetric equations in a symmetric manner. Then, the interface element formulation and stress update procedures of two discrete crack constitutive models suitable for contraction and peripheral joints of arch dams are detailed. Afterwards, results of the analysis on a typical arch dam are compared with the case in which the interaction is approximately represented by added masses as a widely-used method in dam engineering practice to illustrate the effects of water compressibility and reservoir bottom absorption. Besides, the straightforward implementation of pressure-based fluid–structure interaction utilizing a symmetric solution strategy is validated herein to be efficient for a 3-D large scale practical usage in other finite element codes even the commercial ones to avoid using un-symmetric solvers. Employing this symmetric implementation for the dam–water interaction drastically reduces the computational effort, particularly when an iterative scheme is required to solve such a highly nonlinear system.

Impact of load combination on the stability analysis of an arch dam subjected to stochastic non-uniform excitations

In the present paper, impact of the non-uniform excitation due to spatially varying earthquake ground motion (SVEGM) is investigated on the linear response of a typical concrete arch dam. An iterative scheme is utilised to generate the stochastic acceleration time histories at several locations along the foundation boundaries which are compatible with the target response spectra and are correlated according to a given complex coherence function. A typical arch dam is selected as the case study in which the reservoir is modelled as a compressible medium and the foundation is assumed to be massless. Various load combinations are considered based on the corresponding reservoir water levels and the thermal loads. It is observed that, in general, considering SVEGM leads to higher tensile stresses and increases the percentage of the overstressed area within the dam body especially in vicinity of the foundation in comparison with uniform excitation. Thus, for more realistic assessment of the dam behaviour, SVEGM effect should be incorporated in seismic analyses especially in high seismicity regions.

Contributions of Flexible-Arch Configurations in Shimenzi Arch Dam: New Evidence from Field Measurements

This paper presents a retrospective investigation into the performance of a new type of flexible-arch configurations in Shimenzi arch dam based on the past ten-year-long field measurements. The flexible-arch configurations are mainly comprised of artificial short joints at the middle downstream surface and a middle contraction joint with hinged well and enlarged arch ends with bending joints. Fundamental design considerations of these components are provided, and their contributions to the performance of Shimenzi arch dam are discussed in detail using the monitoring data from joint meters, strain gauges, and thermometers. Some elementary numerical studies have been conducted on a typical arch structure with different arrangements of artificial joints. Both the field data and numerical results prove well the effectiveness of the purposely built short joints and the middle contraction joint on the relaxation of tensile stress mobilization. Field survey data also clearly demonstrate the significance of the hinged well at the upstream side of the middle joint for a continuous arch force transfer.

Damage assessment of a concrete arch dam through nonlinear incremental dynamic analysis

Damage assessment of concrete arch dams is carried out through nonlinear Incremental Dynamic Analysis (IDA) of a typical arch dam. In this study the Morrow Point arch dam is subjected to a set of 12 three-component earthquakes each scaled to 12 increasing intensity levels. The dam–foundation interaction effects have been investigated by varying foundation's modulus of elasticity to be equal and half of dam concrete's modulus of elasticity. Damage propagation through the dam body is investigated and various IDA curves are created. The performance and various limit-states of the dam structure are examined based on the obtained results. Simple damage indices are proposed through comparison of response demands in earthquake analysis with the determined structural capacities. It was found that the proposed damage indices can properly indicate state of damage in the dam body.

Modelling of contraction joint and shear sliding effects on earthquake response of arch dams

In an arch dam, adjacent monoliths separated by vertical contraction joints may move relative to each other during an earthquake, resulting in the gradual opening and closing and possible shear movement at the joint surfaces. This paper presents the formulation of a joint constitutive model for a zero-thickness joint element that can simulate both the opening and closing and shear sliding behaviour, as well as the non-linear shear key effects of the joint. The proposed joint element has been implemented in the concrete arch dam finite element analysis program ADAP-88. The response of a typical arch dam subjected to earthquake ground motion is presented to demonstrate the capability of the proposed joint model. Results from a parametric study carried out to study the sensitivity of the response to the joint properties are discussed. The joint parameters considered in the parametric study include apparent cohesion, friction coefficient, and whether the joint has beveled or unbeveled shear key, or the joint is unrestrained in shear sliding. The analysis results show that joint opening and shear slippage at the contraction joints can have significant effects on the response of an arch dam. © 1998 John Wiley & Sons, Ltd.

Geomorphology of the Ross Sea and adjacent oceanic provinces

The shelf morphology of the Ross Sea is controlled by tectonism resulting from continental rifting and recurrent faulting accented by glacial erosion. Volcanism related to continental break-up or a hot spot is also a significant factor. The continental slope and rise are incised by numerous submarine canyons which, during times of lower sea level, must have been an important conduit transporting sediment from the shelf to the ocean basin. The ocean basin is dominated by the mid-ocean ridge system. The western part (Vincennes Plateau) is a simple elevated arch with no fracture zone. Its morphology is probably due to the proximity of a hot spot. The ridge from 161° E to 170° W is highly complex with numerous large fracture zones. East of 175° W, the ridge is a typical arch with occasional NW—SE fracture zones.Plate reconstruction models for the area become increasingly difficult with age. There is general agreement that eastern New Zealand separated from West Antarctica approximately 80 m.y.B.P. The Tasman Sea opened at about the same time, separating the Lord Howe Rise and western New Zealand from Australia; however, this movement ceased approximately 60 m.y.B.P., and coincides with the separation of Australia and East Antarctica. The faulted nature and poor fit of the Iselin Bank and perhaps South Tasman Rise suggests this area may have acted as an independent platelet during the separation of Australia and Antarctica. The complex Pacific—Antarctica fracture zones now represent shear motion between Indian—Antarctic spreading and Pacific—Antarctic spreading.

Hinge for a unilateral maxillary arch prosthesis

This article describes a technique for the fabrication of a hinge that may be incorporated into a maxillary removable partial denture with a unilateral distal-extension denture base. The hinge breaks the stress that would be transmitted to the dentulous arch segment through the retentive portion. Figs. 7 and 8 show a typical arch situation where the Palatar hinge may be incorpoated.