Bridge Force Research Articles

Density segregation of dry and wet granular mixtures in gas fluidized beds

The Discrete Element Method combined with Computational Fluid Dynamics was coupled to a capillary liquid bridge force model for computational studies of mixing and segregation behaviors in gas fluidized beds containing dry or wet mixtures of granular materials with different densities. The tendency for density segregation decreased with increasing fluidizing velocity, coefficient of restitution, and amount of liquid present. Due to the presence of strong capillary forces between wet particles, there was a high tendency for particles to form agglomerates during the fluidization process, resulting in lower segregation efficiency in comparison with fluidization of dry particles. Particle‐particle collision forces were on average stronger than both fluid drag forces and capillary forces. The magnitudes of drag forces and particle‐particle collision forces increased with increasing fluidizing velocity and this led to higher mixing or segregation efficiencies observed in dry particles as well as in wet particles at higher fluidizing velocities. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4069–4086, 2015

Assessment of AASHTO LRFD guidelines for analysis of regular bridges subjected to transverse earthquake ground motions

This paper evaluates the two procedures given in AASHTO LRFD specifications for the transverse analysis of regular bridges subjected to transverse earthquake ground motions. The Single Mode Spectral Analysis (SMSA) method and the Uniform Load (UL) method are evaluated for different bridge geometries, rigidities, and ground motion levels and were also compared to the sine shape function approximation and the computer methods. Two-span, three-span and four span continuous units were investigated. The effect of reduced column stiffness was also evaluated. The results from this study showed that for some bridges in certain seismic zones, the differences in column elastic shears and deformations from the UL method can be about 10% lower than those from the SMSA method and the other methods. Abutment elastic forces from the UL method were about 25% to 300% higher than those from the SMSA and other methods. The UL method, permitted by AASHTO LRFD may not be a conservative analysis method for predicting pier forces and deflections for certain bridges. The method also significantly over estimates abutment forces for longer bridges thus making them overdesigned and uneconomical.

A mixed approach for determination of initial cable forces in cable-stayed bridges and the parameters variability

The determination of initial cable forces in cable-stayed bridges is an important first step in design and analysis of the structure under external loads. Adjustments of stay forces are often required during construction in order to assure the requested behaviour of the bridge in terms of final geometrical configuration and internal force distribution. An accurate assessment of the stay tensioning system allows designers to obtain a good result at the end of construction, by considering the parameters involved as deterministic quantities, assuring the observance of the execution tolerances during works. Actual loads and their variations need instead a stochastic approach which can give useful indications about the effects of parameter variations. Particularly, the measurement on site of the actual values of stay elongations contains errors and the actual values of prestressing forces and working site loads are subjected to unknown variations. In this paper a procedure is implemented which takes into account the stochastic variation of stay elongations and the related uncertainties. The presented method does not require large computational efforts or computer memory. By approximating the probability density distribution of the variables involved by the Gaussian curve, a closed form expression of the imposed elongations given to stays and their variations during erection is provided. The main aim is to obtain an accurate prediction of the differences between the deterministic quantities found by the design analyses and the actual values of deck deformations and stresses in the erection of steel cable-stayed bridges.

Agglomeration behavior in fluidized-bed evaporator for thermal seawater desalination

A novel seawater desalination process using a fluidized-bed evaporator was proposed to prevent scale deposition on the heat-transfer surface for the co-production of salt and pure water. In this evaporator, seawater is fed from the top of the bed and evaporation is caused by collision with heated fluidized particles. Because the liquid feed in the proposed evaporator may cause agglomeration of fluidized particles leading to defluidization, the agglomeration behavior was investigated. Seawater evaporation experiments indicated that when seawater is fed into the fluidized bed, agglomerates of fluidized particles are formed by liquid bridge of seawater feed initially. Subsequently, when liquid bridge breaks during evaporation, solid bridge forms between the particles, leading to their growth. With the repetition of this process, the agglomerates gradually increase. When the size of the grown agglomerates exceeds the mass that can be supported in the bed by the fluidizing gas, the accumulation of agglomerates begins. To describe the agglomeration behavior, we used the force balance of liquid bridge, solid bridge and hydrodynamic forces. Finally, a conceptual model, which can explain the agglomeration behavior, was developed.

Mode-I pullout model of nanofibers with surface effects

A mode-I pullout model is proposed to investigate the bridging mechanism of nanofibers in composites. Surface effects are characterized in terms of surface tension and surface elasticity by using the theory of surface elasticity. Our analysis shows that surface effects may either enhance or impede the bridging effect, depending on the residual surface stress and surface moduli. The effects of volume fraction, aspect ratio, and aggregation of nanofibers are also examined. It is found that the aspect ratio and aggregation have significant influences on the bridging force while the effect of volume fraction is relatively small.

A novel liquid bridge model for estimating SWCC and permeability of granular material

As traditional liquid bridge model based on Yang–Laplace theory fails to model behaviors of unsaturated granular materials when liquid bridges fuse with each other in funicular and capillary regimes, a method called “Redistribution of Air Volume and Reduction of Liquid Bridge Force” is proposed, and incorporated into the original discrete element method to resolve this issue. Both soil water characteristic curve and suction stress characteristic curve are worked out by the modified discrete element method, the results of which coincide with theoretical solutions for simple cubic packing and tetrahedral packing of granular materials. Furthermore, parameter study shows that soil water characteristic curve depends on effective particle diameter, particle size distribution and packing density. Typical soil water characteristic curves of sand and silt are obtained using the modified method, with a trend similar to that of experiment qualitatively. With the help of Mualem model and Kozeny–Carman equation, permeability is also predicated for granular materials. In particular, the air entry value coincides with or close to those of typical sand and silt in magnitude. Finally, a case study of SWCC prediction for sandy soil is implemented with acceptable results. We may conclude that the modified discrete element method is capable of predicting hydraulic properties of granular materials qualitatively and semi-quantitatively.

Effect of Temperature Variation and Type of Embankment Soil on Integral Abutment Bridges in Sudan

The Integral-Abutment Bridge (IAB) concept was developed at least as far back as the 1930s to solve longterm structural problems that can occur with conventional bridge designs. Due to limited funding sources for bridge maintenance, it is desirable to establish strategies for eliminating joints as much as possible and converting/retrofitting bridges with troublesome joints to jointless design. IABs or jointless bridges have many advantages over full height abutment or stub abutment bridges. They eliminate expansion joints in bridge superstructures. They also simplify design, detailing, and construction. In spite of many of these recognized benefits, the behavior of such structures is not yet fully understood, and nationally adopted design criteria are still lacking. This paper presents results of finite element analysis of four IABs at Kassala State (Sudan), the four bridges are considered one of the first fully integral bridges designed and constructed in Sudan. The structural system adopted for these bridges is: RC walls on single row of piles at abutments and piers; hollow-core RC slab at deck. The temperature change is varied between 10°C and 50°C and three types of locally available soil are applied behind the abutments. The effects of varying temperature and embankment soil type in the deflection, maximum bending moments, and maximum shear forces are presented and discussed. The effect of temperature change and bridge length in the bridge forces is also presented; Useful comments on the optimum IAB length to be locally adopted are suggested.

Optimization of Pre-Tensioning Cable Forces in Highly Redundant Cable-Stayed Bridges

Cable-stayed bridges have been developing rapidly in the last decade and have become one of the most popular types of long-span bridges. One of the important issues in the design and analysis of cable-stayed bridges is determining the pre-tensioning cable forces that optimize the structural performance of the bridge. Appropriate pre-tensioning cable forces improve the damaging effect of unbalanced loading due to the deck dead load. Because the cable-stayed structure is a highly undetermined system, there is no unique solution for directly calculating the initial cable forces. Numerous studies have been conducted on the specification of cable pre-tensioning forces for cable-stayed bridges. However, most of the proposed methods are limited in their ability to optimize the structural performance. This paper presents an effective multi-constraint optimization strategy for cable-stayed bridges based on the application of an inverse problem through unit load method (ULM). The proposed method results in less stresses in the bridge members, more stability and a shorter simulation time than the existing approaches. The finite element (FE) model of the Tatara Bridge in Japan is considered in this study. The results show that the proposed method successfully restricts the pylon displacement and establishes a uniform deck moment distribution in the simulated cable-stayed bridge; thus, it might be a useful tool for designing other long-span cable-stayed bridges.

Numerical Simulation of the Emergency Brake Process in Granular Material Transportation Using DEM: Effect of the Liquid Bridge

A numerical simulation of the emergency brake process in granular material transportation was carried out using the Discrete Element Method (DEM). The interaction laws between the particles were based on the contact mechanics in which the normal force was calculated by the Hertz contact law and the incremental tangential force was evaluated by the Mindlin-Deresiewicz theory. Moreover, the liquid bridge force was considered in the wet particle simulation and the effect was especially discussed. Two strategies including the spatial segmentation and reconstruction of orthogonal grids were introduced to analyze the interaction force on the truck during the braking and backfilling processes. It is found that the particles concentrated in front of the truck in the brake process with a slope forming on the upper surface of the agglomerating particles. The liquid bridge force can significantly influence on the particle and force distribution trends. When the liquid bridge force was considered, the particles moved more slowly, the slope was gentler and the force on both the bottom and front wall of the truck was higher. The findings in this study reveal that the liquid bridge force plays an important role on the instantaneous distribution of the particles and pressure on the truck walls and thus cannot be ignored in the simulation.

Simulation of Capillary Bridges between Particles

Capillary forces between particles often dominate other adhesion forces. However, the calculation of the shape of capillary bridges and the resulting force is complex, so often assumptions and approximations are used. These assumptions are not useful for nanoscale particles. Therefore, a simulation method was established to calculate numerically the shape of the meniscus and derive the corresponding capillary bridge force. The main focus are nanoscaled particles with liquid bridges formed by condensing air humidity. The dependence of the capillary force on various parameters such as particle sizes, contact angle and humidity was investigated and it is demonstrated that often-used assumptions cannot be used for nanoscaled particles without remarkable mistake.

Static behaviour of multi-row stud shear connectors in high- strength concrete

In regions of high shear forces in composite bridges, headed stud shear connectors need to be arranged with a small spacing in order to satisfy the design requirement of resisting the high interface shear force present at this location. Despite this, studies related to groups of headed studs are somewhat rare. This paper presents an investigation of the static behaviour of grouped stud shear connectors in high-strength concrete. Descriptions are given of five push-out test specimens with different arrangements of the studs that were fabricated and tested, and the failure modes, load-slip response, ultimate load capacities and related slip values that were obtained are reported. It is found that the load-slip equation given by some researchers based on a single stud shear connector in normal strength concrete do not apply to grouped stud shear connectors in high-strength concrete, and an algebraic load-slip expression is proposed based on the test results. Comparisons between the test results and the formulae provided by some national codes show that the equations for the ultimate capacity provided in these codes are conservative when used for connectors in high-strength concrete. A reduction coefficient is proposed to take into account the effect of the studs being in a group.

Hydrophobic, electrostatic, and dynamic polymer forces at silicone surfaces modified with long-chain bolaform surfactants.

Surfactant self-assembly on surfaces is an effective way to tailor the complex forces at and between hydrophobic-water interfaces. Here, the range of structures and forces that are possible at surfactant-adsorbed hydrophobic surfaces are demonstrated: certain long-chain bolaform surfactants-containing a polydimethylsiloxane (PDMS) mid-block domain and two cationic α, ω-quarternary ammonium end-groups-readily adsorb onto thin PDMS films and form dynamically fluctuating nanostructures. Through measurements with the surface forces apparatus (SFA), it is found that these soft protruding nanostructures display polymer-like exploration behavior at the PDMS surface and give rise to a long-ranged, temperature- and rate-dependent attractive bridging force (not due to viscous forces) on approach to a hydrophilic bare mica surface. Coulombic interactions between the cationic surfactant end-groups and negatively-charged mica result in a rate-dependent polymer bridging force during separation as the hydrophobic surfactant mid-blocks are pulled out from the PDMS interface, yielding strong adhesion energies. Thus, (i) the versatile array of surfactant structures that may form at hydrophobic surfaces is highlighted, (ii) the need to consider the interaction dynamics of such self-assembled polymer layers is emphasized, and (iii) it is shown that long-chain surfactants can promote robust adhesion in aqueous solutions.

Fracture toughness of free-standing nanocrystalline copper–chromium composite thin films

In this paper, a hybrid method of experiments and numerical analyses for measuring the fracture toughness of electron-transparent thin films (∼50–100nm thick) with a nanocrystalline grain size is presented. Electron-transparent, free-standing copper–chromium composite thin films were produced by electron beam deposition coupled with electron beam lithography and deformed in situ in a transmission electron microscope (TEM) in tension. Crack growth in these nanocrystalline thin films was observed and recorded in situ in the TEM. The recorded crack opening profiles are used to estimate the local as well as the global fracture toughness of the nanocomposite by employing inverse analyses. The yield strength, the plastic hardening modulus and the toughness of the copper matrix are determined by the inverse finite element method by matching numerical crack opening profiles with the experimental counterpart. Knowing the matrix toughness, crack kinking angles at the copper–chromium interfaces are used to estimate the interface toughness. The global composite toughness is then obtained by estimating the bridging forces of crack-face ligaments with a limit analysis. The inverse analyses give the yield stress as ∼800MPa, the plastic hardening modulus as ∼1GPa and the local toughness as ∼64Jm−2 for the nanocrystalline copper matrix. The toughness of the copper–chromium interface is determined to be ∼27Jm−2; this weak interface provides crack-face bridging that increases the global toughness of the composite film by ∼38% to ∼89Jm−2.

Studies on the Mechanical Performance of Long Span Continuous Rigid Frame Bridge under the Influences of Different Curvature Radius

The effect of curvature radius on the mechanical properties of continuous rigid frame bridge with high pier and long span is studied in this paper. Taking the Wayaobao Bridge as the research object, the models including both of the linear rigid frame bridge and the different radius of curvature rigid frame bridge are established by using the finite element software MIDAS/Civil, and the mechanical properties of the finished stage are analyzed, and the influence of the radius of curvature on the deformation and internal force of continuous rigid frame bridge are researched. The alteration in curvature radius almost had no influence on the bridge vertical displacement, vertical bending moment. The tangential displacement gradually become smaller, but little change with the decrease of bridge’s curvature radius.The radial displacement, transverse bending moment, torque of the bridge increased with the decrease of bridge’s curvature radius.The force and deformation of the bridge structure are more unfavorable with the decrease of bridge's curvature radius. The study can provide some suggestions for design and construction control of curved frame bridge.

Study on Cable Forces in Cable-Stayed Bridges Based on Forward Simulation Method

According to cable tension calculation of cable-stayed bridge on construction, and combining with the example of Xinzao Pearl River Grand Bridge, this work proposes forward-calculation method to analyze cable tension force on construction and establishes geometric calculation simulation model to compare measured cable tension with theoretical cable tension. This paper introduces some kinds of methods calculating cable tension force on construction. It importantly discusses the principle and method of forward-calculation and the practical application in the actual project. Spacial finite element model is established for analysis based on finite element software MIDAS and the application of forward-analysis iterative method is considered to analyze the cable tension on construction , then the method of determining cable force on construction is explored. Finally the result shows that the cable tension based on forward-calculation method is usually accurate, the measured value is approximately equal to the theoretical value and the error is in the extent permitted. The correctness and reliability of the frequency method is effectively confirmed and the cable tension calculation of the similar bridge on construction is compatibly applied.

A novel experimental investigation into sintered neck tensile strength of ash at high temperatures

The adhesive behavior between ash particles plays a significant role in ash deposition behavior. Studies of the solid bridge force, which is an important type of adhesive force, are scarce at present. In this work, a novel instrument, termed a High Temperature Solid Bridge Force Device (HTSBFD), has been designed and developed which allows for the main parameters that play a fundamental role in enhancing adhesion and cohesion to be investigated. The maximum temperature of this device is 1600°C. The results showed that the neck tensile strength increased with the bonding time and pressure. The temperature dependence of the neck tensile strength development showed a bimodal distribution. The tensile strength of ash was also measured and was compared with neck tensile strength. The results disproved the applicability of the customary views on the relationship of neck tensile strength and tensile strength. The ash samples were also characterized by XRD and optical microscope. The results provide an original contribution towards the understanding of the adhesion mechanisms of ash at different operative conditions. The HTSBFD is a useful tool in determining the fundamental mechanisms of the deposition process and in predicting the ash behavior.

The Confirmation of Closure Jacking Force in Continuous Rigid Frame Bridge

The theory deduces the formula of closure jacking force in the closure of mid-span in the continuous rigid bridge, and introduced the computation and accomplishment of jacking force in continuous rigid bridge, taking the example of Anwen Bridge.

“Surplus in Man” and the capability-based sustained/total human development

Purpose – This paper aims to define a capability-based sustained/total human development, after reviewing both the concept of “Surplus in Man” as the source for achieving the Vedântic ideal of transcendence, and the capability approach to human development. Design/methodology/approach – The capability-based sustained/total human development has been defined by integrating the Vedântic concept of “Surplus in Man” and the deontological theories of morality into the basic approach to capability-based human development. Findings – An answer to the question: “How to apply a holistic approach to our daily life?” is outlined. Practical implications – An example is provided on the role of yoga and meditation as the key initial bridging forces between the Western and Eastern concept of mental health. Also, the recent trend in a morally demanding lifestyle of a section of people in the Western societies for moving towards a galloping spiritual pluralism has been exemplified. Originality/value – Role of responsibility of an individual human being along with his or her right has explicitly been emphasized in the approach to capability-based sustained/total human development.

Influence of Error of Unstressed Cable Length on Mechanical Behavior of Thousand-Meter-Scale Hybrid Girder Cable-Stayed Bridge

AbstractTaking Edong Yangtze River Bridge as the research subject, the influence of error of unstressed cable length on the geometric shape and internal force of super-span hybrid girder cable-stayed bridge during completion is studied on the basis of the geometry control method with full consideration of the structural nonlinear geometrical effect. Moreover, the mechanical behaviors of the center and side spans of the bridge and their control strategies are discussed. The analysis shows that structural differences between the center and side spans exerted an influence on the geometric shape and internal force. The influence of unstressed cable length error on the geometric shape in the center span of the completed bridge is greater than that of the side span, whereas the impact on internal force in the side span is greater than that in the center span. The mechanical behavior is relatively independent between span types. In addition, the percentage change of the girder stress reaches the maximum level in...

Experiments on the Removal of Fine Particles in Existing Air Pollution Control Devices by Chemical Agglomeration

The removals of PM2.5from coal combustion by electrostatic precipitator (ESP) and wet flue gas desulfurization (WFGD) system with adding chemical agglomeration solution were investigated experimentally based on coal-fired thermal system. The experimental results show that the average diameter of particles could grow more than four times with the effect of wetting, liquid bridge force and adsorption bridging, and the PM2.5concentration of ESP outlet can decrease 40% under typical flue gas conditions. The removal efficiency of fine PM2.5is improved about 30% when adding chemical agglomeration solution before desulfurization tower.