Effect Of Lateral Confinement Research Articles

Effects of finite water depth and lateral confinement on ships wakes and resistance

Wash waves produced by ships disintegrate river banks and coastal lines. This phenomenon of bank erosion is mainly due to the height of the waves. Various factors govern the formation of these waves and their amplitudes: the geometry of the water channel, the shape and the speed of the boat, etc.. These factors play an important role on the wave generation, in addition on the resistance of the ship and so on its fuel consumption. Whether to study the impact of wash waves on the ship's environment or its resistance, the analysis of the generated wake is essential. Hence a fine characterization of the wave field is necessary. This study proposes a comparison of wakes generated by two generic ships based on a Wigley hull with block coefficients 0.67 and 0.89 respectively representative of maritime and fluvial ships. The wakes generated in deep water and confined water configurations have been measured for different Froude numbers by a non-intrusive optical stereo-correlation method, giving access to a detailed and complete definition of the generated wave fields. The resistance of the ship hulls has been measured in deep and confined water configurations with a hydrodynamic balance. The results permit one to study the influence of both hull and water channel geometries on the ship wake, on the amplitude of the far-field generated waves and on the near-field hydrodynamic response. Moreover, resistance curves are obtained for both configurations and highlight the effect of both hull and water channel geometries on the resistance coefficient of the ship. A comparison of the resistance curves with or without the ship trim is conducted and shows the influence of the trim on the resistance coefficient in the different ship speed regimes.

Analysis of the mechanical properties of polymer materials considering lateral confinement effects

Abstract The mechanical properties of polyurethane foam (PUF) and glass fiber-reinforced PUF (R-PUF), which are widely used in various fields, were investigated considering the influence of lateral confinement. PUF and R-PUF – representative polymeric foams with a porous structure – are suitable for severe environments (e.g. the cryogenic field) because they have an excellent adiabatic function and load-bearing capability. However, when PUF and R-PUF are used in actual structures, the mechanical performance of the foam materials may change depending on the conditions. Assuming that a compressive load acts on these polymeric foams in a confined space, analysis of the material properties resulting from the confining pressure of the adjacent structures is necessary. Therefore, in this study, a comparison and evaluation of the mechanical behavior of PUF and R-PUF were performed with regard to the constraint. The results suggest that it is possible to provide an experimental basis for measuring the strength performance for the application of insulation in a confined space.

Effect of lateral confinement on crystallization behavior of a small-molecule semiconductor during capillary force lithography for use in high-performance OFETs

In the current work, we carry out an analysis on micro-patterned 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) crystals grown by capillary force lithography (CFL) to investigate the effect of lateral confinement on the crystallization. From systematic analysis on the crystal orientation and crystallinity depending on the line widths of the crystal patterns, it is revealed that crystals grown from highly confined conditions, namely from patterns with line widths of 5 μm, are observed to be more uniaxially aligned, have much fewer grain boundaries, and yield better field-effect mobility (μFET) as high as 1.66 cm2/(V s) in organic field-effect transistors (OFETs) compared to the wider line widths. These results demonstrate that the lateral confinement during CFL is able to promote the growth of well-aligned TIPS-pentacene crystals with high crystallinity. Thus, we expect our systematic work with CFL, a type of soft lithography, could provide insight for OFETs to step toward their integration in commercial devices.

On the effective elastic properties of isotactic polypropylene

Calculating the effective elastic properties of semi-crystalline polymers is challenging due to a pronounced phase stiffness contrast, complex micro-structures and extreme anisotropies of the crystalline phases. To estimate the effective Young modulus of isotactic polypropylene depending on the crystallinity, we construct complex and simple homogenization schemes that unify the micro-scale interaction mechanisms that have been identified by Bartenev and Valishin [4], Bédoui et al. [5], Parenteau et al. [38]. This is achieved by a two-step homogenization approach, namely a local laminate stiffness that is then subjected to orientation averaging. The resulting estimates show good agreement to experimental results. They further suggest that the relatively high effective stiffness of isotactic polypropylene when compared to polyethylene may in part be a result of the stronger lateral confinement effect on the laminate level.

THE EFFECT OF LATERAL CONFINEMENT ON THE SETTLEMENT CHARACTERISTICS OF SHALLOW FOUNDATIONS ON SAND

Free to read on publisher website Today, most of the high rise buildings consist of basements as part of the substructure. Basement construction is usually supported by embedded type retaining walls such as secant pile walls or diaphragm walls. This provides lateral confinement and the performance of shallow foundations would be affected by this lateral confinement. In this study, the effect of lateral confinement on the settlement characteristics of shallow foundations on sand was studied experimentally and numerically. First, experimental investigation using small-scale laboratory models were carried out and the results were used to validate the finite element (FE), model. Changing the depth of lateral confinement and the distance to the edge of the shallow foundation from the lateral confinement, the stress immediately below the footings corresponding to a settlement of 25 mm was compared. Furthermore, the effect of lateral confinement due to embedded retaining wall on the settlement characteristics of a raft foundation on sand was also studied using the validated finite element model. In scaled physical models of confined foundations, there was an enhancement in allowable bearing capacity at the tolerable settlement with the increase in depth of embedment and the reduction of distance to the confinement. It was observed, for the study variables considered in this study that the bearing capacity can be improved up to 4 times by laterally confining the footing. However, in the analysis of confined raft foundations on sand, there was no significant change in bearing pressure for a 50 mm tolerable settlement with the change of study variables.

Design of high‐strength steel reinforced concrete columns – a Eurocode 4 approach

AbstractIn Memoriam of Prof. Dr. Bernt JohanssonThe current design codes for steel reinforced concrete (SRC) columns are, in general, only applicable to normal‐strength materials. In Eurocode 4, concrete grades C20/25 to C50/60 and steel grades S235 to S460 are allowed to be used in composite columns, whereas it is possible to use higher‐strength concrete (up to C90/105) in Eurocode 2 and S690 steel in Eurocode 3. In this paper, an analytical method is proposed to predict the ultimate strength of SRC columns, taking into account the effect of strain compatibility and lateral confinement. A finite element model is developed to analyse the behaviour of SRC columns under axial loading using ABAQUS. The parametric studies are conducted by varying the diameter, spacing and volumetric ratio of the lateral reinforcement and the column length. It was found that the full plastic method given in EC4 overestimated the strength of SRC columns with high‐strength steel. Nevertheless, the proposed method can predict the strength of SRC columns with concrete strengths up to 90 N/mm2 and steel strengths up to 690 N/mm2.

The influence of metal cluster lattices on the screening of image potential state electrons on graphene.

The bound unoccupied electronic state structure of an Ir(111)/graphene surface covered by differently sized and spaced Ir clusters was investigated by means of two-photon photoemission spectroscopy. The cluster lattice was found to affect the image potential states of the substrate to a surprisingly large extent. This effect can be related to the influence of the cluster lattice on the screening of the image state electron trapped in front of the surface. The symmetric arrangement of Ir clusters considerably reduces the lateral extension of graphene areas with a homogeneous local work function, and from a certain minimum area size, the excitation of an electron to a stable state in a Coulomb-like potential is not possible anymore. Furthermore, lateral confinement effects could be observed due to the decreasing extension of bare graphene areas.

Experimental study on the scour due to a water jet subjected to lateral confinement

The effect of lateral confinement due to very close side walls, on erosion caused by a water jet issuing from a rectangular sluice aperture, has been studied experimentally in a narrow laboratory flume. Velocimetry (PIV) in presence of a smooth, no erodible bottom, revealed self-similar velocity profiles with the structure of a wall jet, but upward-shifted with respect to the classical two-dimensional profile. The classical definition of the Shields number was modified, to include the influence of the relative roughness and the inlet aspect ratio. This last coefficient was also relevant in the definition of a suitable length scale to account for the effect of the lateral confinement. Scour patterns in the narrow flume have also shown differences with respect to erosion by two-dimensional wall jets: the downstream mound undergoes a morphological transition, from triangular to trapezoidal, at the early stage of the scour development, and grains move downhill driven by gravity inside the granular wedge, in a regime of steady recirculation (SR). Above this regime, a digging–refilling (DR) cycle, with periods of the order of seconds, triggers at a well-defined Shields number.

Push-out test of large perfobond connectors in steel–concrete joints of hybrid bridges

The size of perfobond connectors in steel–concrete joints of hybrid bridges is typically less than 75 mm. Given the limited capacity of connectors, it is essential to tightly arrange the connectors for transmitting large internal forces. Large-sized perfobond connectors with increased capacity act as an excellent alternative to reduce the number of connections, thereby simplifying the structure in steel–concrete joints. Additionally, an increased diameter can contribute to the flow of concrete coarse aggregate. To verify the mechanical properties of large perfobond connectors, 13 groups of 39 push-out specimens are introduced. The effects of hole size, hole shape, perforating rebar, concrete strength, and lateral confinement are investigated on the failure modes and load–slip curves of large perfobond connectors. The test results indicated that, under a high level of confinement of a concrete dowel, increases the geometrical size of the hole significantly improve its bearing capacity without weakening its ductility. Finally, an empirical formula is proposed for the shear capacity considering various influencing factors.

On the Time-Dependent Behavior of EPS Geofoam: Experimental and Numerical Investigations

Expanded polystyrene geofoam (EPS) is used as a lightweight fill material in a wide range of geotechnical engineering applications, including, embankments, retaining walls, and buried structures. Under high compressive loads, EPS may experience long-term compression that needs to be taken into consideration during design. This study presents the results of an experimental investigation that has been conducted to evaluate the creep response of two different EPS geofoam materials (EPS15 and EPS22) under uniaxial compression loading. Four identical setups have been designed and built to allow for multiple geofoam samples to be simultaneously tested under different applied pressures. The effect of stress level on the creep strain is investigated. Results showed that, for the two investigated EPS materials, creep strains started to develop when the applied pressure exceeded 50% of the uniaxial compressive strength of the material and became significant at applied pressure of about 70% of the material strength. A three-dimensional numerical model that is capable of capturing the creep response of soft soils is adapted and calibrated using the available experimental data. The suitability of the model to investigate the effect of lateral confinement on the creep deformation of the geofoam samples is also examined. It is concluded that, although soft soil creep models are able to capture the uniaxial creep response of geofoam, it is not suitable to model the effect of lateral confinement, particularly for low density EPS material.

Strain rate effects on the compressive response of wood and energy absorption capabilities – Part B: Experimental investigation under rigid lateral confinement

The compressive properties of spruce and beech wood species at a large range of strain rates – from 0.001 to 600 s-1 – under rigid lateral confinement have been investigated, using an original experimental device especially developed for the purpose. The work is motivated by the need to explore the dynamic behavior of wood up to large strains close to 70%. Three experimental apparatus have been used to obtain the compressive responses: the quasi-static tests have been performed using a Sintech 20D test system, the compressive responses at intermediate strain rates have been obtained with an Instron VHS65/20 apparatus and the dynamic tests have been conducted using a Split Hopkinson Pressure Bars (SHPB) system. The strain rate sensitivity of wood is clearly visible on the crushing strength with an increase between 80 and 155% but also on the plastic like behavior. In addition, the entire responses exhibit an elastic-plastic like behavior whereas an elastic brittle behavior could be observed, in the previous Part A which was focused on the compression configuration without lateral confinement. Even if no significant effect of the rigid lateral confinement is observed on the apparent Young modulus and the crushing strength values for both species, the wood energy absorption capability is better when longitudinal failure mechanisms are restricted thanks to the rigid lateral confinement.

Dynamic impact behaviors and constitutive model of super-fine stainless wire reinforced reactive powder concrete

The dynamic impact behavior of super-fine stainless wire (SSW) reinforced reactive powder concrete (RPC) was studied through split hopkinson pressure bar test with the strain rate range from 94/s to 926/s in this paper. The modification mechanisms of SSW to the dynamic impact performance of RPC were revealed via computed tomography and scanning electron microscope analysis. Experimental results showed that the dynamic impact compressive strength of SSW reinforced RPC increases with the strain rate. The dynamic increase factor of compressive strength is decreased and the strain-rate strengthening effect of RPC is weakened by SSW. The maximum dynamic peak strain of SSW reinforced RPC reaches up to 34,070 µε at the strain rate of 305/s. The limit strain of RPC is decreased because of the lateral confinement effect of SSW. The stress-strain curves of SSW reinforced RPC include elastic stage, elastic-plastic stage and descending stage. The addition of SSW leads 43.5% and 58.2% of increase in dynamic impact toughness and impact dissipate energy of RPC, respectively. Increasing SSW volume fraction makes more SSW to inhibit the generation and propagation of cracks in RPC, thus leading to the decrease of destruction degree. The formation of inter-anchored interface among bundling SSW increases the resistance of RPC to crack development. The dynamic impact constitutive model established on the basis of revised visco-elastic and damage theory can well describe the stress-strain relationship of SSW reinforced RPC at different strain rates, in which the strain threshold is governed by strain rate and SSW volume fraction simultaneously.

Size Scaling of Photonic Crystal Surface Emitting Lasers on Silicon Substrates

We report here the lateral cavity size scaling and confinement effects on the lasing performance in defect-free photonic crystal surface-emitting lasers (PCSEL) on silicon substrates. Hybrid PCSELs with different lateral cavity sizes and different lateral confinement geometries have been fabricated using transfer printing technology and controlled selective etching. The measured lasing properties show a strong dependence on the lateral cavity size below 100 μ m. In particular, the finite lateral dimension significantly affects the laser threshold and side mode suppression ratio (SMSR) of the PCSEL devices. On the other hand, by controlling the lateral confinement using vertical etching, a reduction of the laser threshold is observed. The experimental results agree well with theoretical predictions. The work presented here can lead to ultra-compact PCSELs for on-chip integration with excellent energy efficiency.

Experimental observations on sorting patterns of heterogeneous sediment mixtures in low constrained flows

Field and laboratory investigations indicate that gravel bed rivers with bimodal grain size distribution and low lateral confinement, such as in the case of braided or multi-channel rivers, can present simultaneously active channel variations, both in the planimetric and altimetric directions, together with planimetric and vertical sorting. Such aspects were reproduced in new flume experiments considering three flow confinements with characteristic aspect ratios from about 80 to 5. Three long runs of about 60 hours were carried out under constant feeding rate conditions, with a bimodal mixture of natural sediments, a fixed flume slope of 3.18 %, and width imposed by lateral walls from 0.50 m to 0.12 m. We present here the results obtained with the first run, with a width of 0.5 m. We observed fluctuations of bed surface granulometric composition, bed slope, and outlet solid discharge; each of which with its own periodicity. In particular, the rearrangement of the bed surface texture was rapid. Cyclic bed states were observed: a stage of coarsening and aggradation corresponding to low values of outlet solid discharge; a stage of fining and degradation concomitant to high values of transport rate. The other two on-going runs (narrower configurations) aim at investigate the effect of lateral confinement on the morphodynamics of the system.

Experimental study on the bond behavior between corroded rebar and concrete under dual action of FRP confinement and sustained loading

The corrosion of reinforcing steel bars (rebar) in reinforced concrete (RC) is the main cause of the degradation of interfacial bond behavior between rebar and concrete, which can further induce the degradation of structural performance. In this paper, the bond behavior between corroded rebar and concrete was experimentally studied focusing on the coupling effects of lateral confinement and sustained load for the first time. Continuous and uniform confining pressures were imposed on the corroded rebars via fiber reinforced polymer (FRP) and sustained loads were applied to the corroded rebar by a self-developed loading device. The effects of corrosion ratio, sustained load and lateral confinement on the bond behavior were tested and analyzed. The test results demonstrated that FRP lateral confinement could effectively restrain the corrosion rate of rebar and thus significantly improved the bond performance; moreover, the dual action of FRP lateral confinement and sustained load could significantly enhance the interfacial bond strength and ductility due to their great contribution to the prevention of corrosion expansion. However, without FRP lateral confinement, the interfacial bond strength and ductility would be weakened by sustained load.

Cyclic stress-strain model incorporating buckling effect for steel reinforcing bars embedded in FRP-confined concrete

Buckling of steel reinforcement usually causes a sudden loss of the load-carrying capacity and the ultimate state of conventional reinforced concrete (RC) cylinders. However, reinforcing bars behave differently in fiber-reinforced polymer (FRP)-confined RC cylinders due to the lateral confinement effect of FRP. This paper presents a theoretical study into the buckling behavior of longitudinal steel reinforcing bars embedded in FRP-confined concrete subjected to cyclic axial compression. An empirical monotonic compressive stress-strain model considering the buckling effects proposed previously for laterally supported reinforcing bars is extended to a cyclic model by combining the monotonic envelope and the Menegotto-Pinto model accounting for the cyclic loops. The cyclic stress-strain models for both laterally supported reinforcing bars and FRP-confined plain concrete are then implemented into the OpenSees software platform and validated through comparisons with compressive test results on cyclically loaded FRP-confined plain and RC cylinders. The proposed cyclic stress-strain model for laterally supported reinforcing bars is expected to serve as a fundamental model for predicting the seismic behavior of FRP-strengthened RC cylinders with widely-spaced transverse ties under cyclic axial compression, in which case the local buckling of reinforcing bars usually occurs between two adjacent transverse ties.

A mechanistic-empirical approach to quantify the influence of geogrid on the performance of flexible pavement structures

The objective of this study was to develop a methodology for quantifying the influence of geogrid on the performance of flexible pavement structures in a manner that would allow incorporation into Pavement Mechanistic-Empirical (ME) Design. The finite element technique was used to develop the geogrid-reinforced flexible pavement structure models, which focused on the characterization of the lateral confinement and vertical membrane effect of geogrid. A full-scale Soil Tank test was conducted to assess the validity of the developed geogrid-reinforced models by comparing the model predicted pavement responses (i.e., surface deflections, tensile strain at the bottom of asphalt concrete, and vertical stress distributions) to those tank test measurements. In general, the developed finite element models were capable of accurately predicting the responses of geogrid-reinforced and unreinforced pavement structures. It was found that the placement of geogrid increases the stiffness of base course and significantly reduces the vertical stresses around the geogrid layer, but cannot effectively reduce the tensile strain at the bottom of asphalt concrete. This indicated that the geogrid reinforcement is beneficial for reducing the rutting damage in base course and subgrade, but not effective in prolonging the fatigue life of flexible pavement. To quantify the influence of geogrid, the geogrid-reinforced flexible pavement structure was equivalent to an unreinforced flexible pavement structure with the modified material properties, which was based on a pavement response equivalency approach. The determined modified material properties was then input into Pavement ME Design software to predict the performance of geogrid-reinforced flexible pavement structures. Two case studies were conducted to predict the performance of two geogrid-reinforced pavement sections that were identified from the Long-Term Pavement Performance (LTPP) database. The predicted performance results (i.e., rutting depth and fatigue cracking area) were coincident with those field measurements, which validated the prediction accuracy of the proposed approach.

Connection bridge effect on a DNA‐like two‐spiral‐up‐tower building

SummaryIn the recent years, more and more great ideas about architectural design were inspired from bionics, that is, the China National Stadium, Taipei 101, and India Lotus Temple were first inspired from bird's nest, bamboo, and blooming lotus, respectively. However, being a feast to the eyes, those innovative architectures with complex structural behavior and unknown seismic performance are always being a challenge to structural engineers. Hereinafter, a DNA‐like high‐rise building with two separate spiral‐up towers was first outlined, in which each of the tower consist of an interior reinforced concrete core with inserted steel columns and an exterior composite frame made of steel beams and steel pipe–concrete columns. To study the influence of the connection bridges on the seismic performance under different level of earthquake excitation and torsional effect under gravity load, the load transfer mechanism of vertical force and lateral force was conducted, and a finite element model was built with parametrical studies. It can be concluded from the results from the parametrical studies that the drift angle was sharply decreased at the locations where the connection bridges combines two single towers, indicating that the lateral confinement effect of the connection bridges not only strengthen the whole structure but also leads to a discontinuity of the structural stiffness.

Effects of lateral confinement in natural and leveed reaches of a gravel‐bed river: Snake River, Wyoming, USA

AbstractThis study examined the effects of natural and anthropogenic changes in confining margin width by applying remote sensing techniques – fusing LiDAR topography with image‐derived bathymetry – over a large spatial extent: 58 km of the Snake River, Wyoming, USA. Fused digital elevation models from 2007 and 2012 were differenced to quantify changes in the volume of stored sediment, develop morphological sediment budgets, and infer spatial gradients in bed material transport. Our study spanned two similar reaches that were subject to different controls on confining margin width: natural terraces versus artificial levees. Channel planform in reaches with similar slope and confining margin width differed depending on whether the margins were natural or anthropogenic. The effects of tributaries also differed between the two reaches. Generally, the natural reach featured greater confining margin widths and was depositional, whereas artificial lateral constriction in the leveed reach produced a sediment budget that was closer to balanced. Although our remote sensing methods provided topographic data over a large area, net volumetric changes were not statistically significant due to the uncertainty associated with bed elevation estimates. We therefore focused on along‐channel spatial differences in bed material transport rather than absolute volumes of sediment. To complement indirect estimates of sediment transport derived by morphological sediment budgeting, we collected field data on bed mobility through a tracer study. Surface and subsurface grain size measurements were combined with bed mobility observations to calculate armoring and dimensionless sediment transport ratios, which indicated that sediment supply exceeded transport capacity in the natural reach and vice versa in the leveed reach. We hypothesize that constriction by levees induced an initial phase of incision and bed armoring. Because levees prevented bank erosion, the channel excavated sediment by migrating rapidly across the restricted braidplain and eroding bars and islands. Copyright © 2017 John Wiley & Sons, Ltd.

Surfactant Assemblies on Selected Nanostructured Surfaces: Evidence, Driving Forces, and Applications.

Surfactant adsorption at solid-liquid interfaces is critical for a number of applications of vast industrial interest and can also be used to seed surface-modification processes. Many of the surfaces of interest are nanostructured, as they might present surface roughness at the molecular scale, chemical heterogeneity, as well as a combination of both surface roughness and chemical heterogeneity. These effects provide lateral confinement on the surfactant aggregates. It is of interest to quantify how much surfactant adsorbs on such nanostructured surfaces and how the surfactant aggregates vary as the degree of lateral confinement changes. This review focuses on experimental evidence on selected substrates, including gold- and carbon-based substrates, suggesting that lateral confinement can have pronounced effects both on the amount adsorbed and on the morphology of the aggregates as well as on a systematic study, via diverse simulation approaches, on the effect of lateral confinement on the structure of the surfactant aggregates. Atomistic and coarse-grained simulations conducted for surfactants on graphene sheets and carbon nanotubes are reviewed, as well as coarse-grained simulations for surfactant adsorption on nanostructured surfaces. Finally, we suggest a few possible extensions of these studies that could positively impact a few practical applications. In particular, the simultaneous effect of lateral confinement and of the coadsorption of molecular compounds within the surface aggregates is expected to yield interesting fundamental results with long-lasting consequences in applications ranging from drug delivery to the design of advanced materials.