Helical Plates Research Articles

Plate‐loaded folded monopole antenna on a ground‐plane edge

AbstractA folded monopole antenna loaded with a rectangular plate placed at the edge of the ground plane is proposed and its characteristics are evaluated by numerical analysis with the FDTD method and by experiments. This antenna is characterized by a structure in which one of the two conductors forming a folded monopole element is a rectangular plate. The structure is suitable for surface mounting on a printed circuit board. In this paper, mainly for an antenna using a dielectric chip with a permittivity of 2.6, the configurations of the feed line and the short‐circuited line and the shape of the loading conductor plate affecting the antenna characteristics are investigated. It is made clear that the element height and the shape of the loading plate along the longer side mainly contribute to the determination of the resonant frequency. The changes in the characteristics due to the finite size of the ground plane are studied both from the input characteristics and from the radiation characteristics. It is shown that the present antenna has radiation characteristics essentially identical to those of the monopole antenna and that the disturbance in the radiation patterns is caused by the fact that the length of one side of the ground plane is close to resonance. Also, the characteristics of the antenna with a helical loading plate and the effect of the permittivity of the core materials used for size reduction of the antenna are evaluated. It is shown that an antenna with the electrical dimensions of the element reduced to one‐half can be realized by a combination of the helical loading plate and a material with a permittivity of 10.2. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(8): 24–37, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10214

Wood anatomy of the dicotyledons indigenous to New Zealand 26. Rutaceae*

Wood anatomy of Melicope ternata, M. simplex, and Phebalium nudum is described. In M. simplex and M. ternata vessels have no helical thickenings, most perforation plates are simple but some are scalariform or reticulate, grooves connect pit apertures, and vessel to ray pits are sometimes unilaterally compound. Disjunctive ray and axial parenchyma cells are present. Melicope simplex is distinguished from M. ternata in having narrower rays, more disjunctive ray cells, and narrower boundary bands of axial parenchyma. The vessel elements of P. nudum have helical thickenings and simple perforation plates, and lack unilaterally compound pits. Disjunctive axial parenchyma cells are absent and disjunctive ray cells are rare. Boundary axial parenchyma and rays are usually only 1-2 cells wide. Vasicentric tracheids are common in P. nudum but rare in M. simplex and M. ternata. Silica bodies occur in the parenchyma cells of all three species.

Lateral Capacity of Helical Piles in Clays

In this paper, the behavior of helical piles under lateral loads in clayey soils is examined through an experimental investigation on model piles. Tests were conducted on rigid helical piles with different numbers of plates. Model anchors were made of 13.8 mm diameter mild steel shafts to which mild steel plates of 33 mm diameter were welded. For comparison, a single straight shaft with a diameter of 13.8 mm was also tested. Test results revealed that the lateral capacity of helical piles is greater than that of straight shaft piles. A simple theoretical model is suggested to estimate the lateral capacity of rigid helical piles. The theoretical model suggested incorporates lateral resistance of the soil on the shaft, bearing resistance on the bottom of the helical plate, uplift resistance on the top of the helical plate, and frictional resistance on the surface of the helical plate. The validity of this model is examined.

Behaviour of embedded model screw anchors in soft clays

In recent years helical anchors have been used extensively in the construction of transmission tower foundations, pipelines and braced excavations. This Paper describes an experimental programme carried out to show the behaviour of multiple helical anchors at different embedment ratios in soft marine clays. The number of helical plates, their diameters and spacings are varied. Pullout tests were conducted by anchors installed in a soft marine clayey bed prepared in test tanks and at embedment ratios of 0-10. The results indicate that the anchor capacity increases with embedment ratio. The uplift capacity at any embedment ratio is explained in terms of the contribution of cohesive resistance between the top and bottom helical plates, the bearing resistance of the top helical plate alone and the shaft adhesion above. Based on embedment ratio and observations during testing, the anchors are classified as shallow, transit and deep anchors. Formulations are suggested for estimating and calculating the capacities of helical anchors which agree well with the results of previous investigators. Depuis quelques années, les ancrages hélicoïdaux ont été largement utilisés dans la construction de fondations de tours de transmission, de conduites et d'excavations armées. L'article décrit le programme expérimental mis en oeuvre pour montrer le comportement d'ancrages hélicoïdaux, dans des argiles molles marines, pour différents encastrements. Le nombre des plaques hélicoïdales, leur diamètre et l'espacement entre plaques sont variables. Des essais d'arrachement ont été réalisés sur des ancrages mis en place dans des lits d'argile molle marine préparés dans des cuves expérimentales, et ce pour des valeurs d'encastrement variant de 0 à 10. Les résultats obtenus montrent que la charge admissible des ancrages augmente avec le rapport d'encastrement. La charge verticale pour différents rapports d'encastrement peut être expliquée par une contribution de la résistance de cohésion entre le sommet et la base des plaques hélicoïdales, par la résistance ultime au sommet de la plaque et par l'adhérence latérale au dessus de celle-ci. A partir des rapports d'encastrement et des observations faites au cours des essais, les ancrages ont été répartis en trois groupes: ancrages superficiels, intermédiaires et profonds. Des équations permettant d'estimer et de calculer la charge des ancrages hélicoïdaux sont proposées. Elles se révèlent être en bon accord les résultats trouvés par les autres chercheurs.

Estimation of Uplift Capacity of Helical Anchors in Clays

Currently, helical anchors are being extensively used in the construction of transmission tower foundations, pipelines, and braced excavations. To arrive at the uplift capacity of these anchors, it is necessary to assume certain type of failure surface and in a few cases, cylindrical failure surface has been suggested. However, in this type of formulations the effect of spacing of helical plates is to be given due consideration and in the present study, this aspect has been taken into account. Pullout tests are conducted on four type of model anchors fabricated with different number of helical plates and spacing ratios in soft marine clay. From the test results, it is found that continuous cylindrical failure surfaces are formed in the case of anchors with helical plates spaced at a spacing ratio of 1.5. But in the case of anchors with helical plates at higher spacing ratios, well‐defined cylindrical failure surfaces could not be observed and in these cases; empirical formulations are suggested to estimate the capacities. The suggested formulations are verified with the reported lab and field test results and are found to be in good agreement.

Behavior of a helical anchor under vertical repetitive loading

Abstract In the field of ocean engineering, anchors are used for several purposes. This article studies the behavior of a helical anchor embedded in soft marine clay under vertical repetitive loading. Helical anchors are simple steel shafts to which one or more helical plates are attached at regular intervals. The tests are conducted on a model helical anchor installed in a soft marine clay bed prepared in a test tank. Repetitive loading is applied using a pneumatic loading arrangement. Different cyclic load ratios and time periods are adopted. In each test, after the application of repetitive loading, poststatic‐pullout tests are conducted to observe the effect of repetitive loading on anchor behavior. From the test results, it is found that, up to a cyclic load ratio of 55%, there is no reduction in capacity. Instead, there seems to be a marginal increase in capacity and reduction in displacement. The reasons for this behavior are explained in terms of induced changes in strength and deformation behavio...

The Behaviour of Model Screw Piles in Cohesive Soils

ABSTRACT Anchors are being extensively used in foundations for the structures subjected to both compressive and tensile forces. An attempt has been made to develop screw piles as anchors in clayey soils. The screw piles are made of hollow galvanized iron pipes (dia. 25 mm, 44 mm, 60 mm and length 640 mm and 1000 mm) to which helical plates (dia. 75 mm, 100 mm, 150 mm) are welded. Number of plates are varied from 2 to 4 and there are different spacings of these plates adopted. These piles are screwed into soft to medium stiff clay bed prepared in a test tank. Standard type of loading frames have been made for effecting both compressive and tensile forces. In all about 40 Nos. of tests have been conducted in three soils. The behaviour of these piles has been studied through the load deformation curves. Decrease in the moisture contents leads to significant increases in the capacity of the piles. By keeping the ratio of the spacing of the helical plates to diameter of the helical plates between 1. 0 and 1. 5, optimum capacities of the piles could be obtained. The test results indicate that theoretical predictions for the load carrying capacities can be made by making use of the measured shear strength of the soils.