Cross Arm Length Research Articles

Global Stability Behavior of Pre-Cast Cable-Stiffened Steel Columns

Cable-stiffened steel columns (CSSC) have a high load-carrying capacity and strong stability compared to ordinary steel columns. In practical engineering, the connection between the crossarm and main column of a CSSC is usually welded. However, the welding-residual stress adversely affects the steel column. In this study, pre-cast CSSCs, with a pinned connection between the crossarm and main column, are presented. The new type of pre-cast CSSCs avoid the welding-residual and are easy to disassemble. A model test and numerical analysis of its global stability behavior under eccentric compression is conducted. Based on the analysis, the buckling modes of these columns are defined and a method for determining the governing imperfection in a nonlinear buckling analysis is proposed. The effects of slenderness ratio, cross-arm length, cable diameter, and other parameters on the load-carrying capacities of the columns are investigated using the proposed method. The results of this study can be used as a reference for the engineering designs and specifications of pre-cast CSSCs.

Design and study of novel square electromagnetic sensing based on stepped eddy current thermography

Nondestructive testing of internal corrosion defects is a key task to evaluate whether the material is repaired and replaced. In this paper, a novel square ferrite magnetic open sensing structure is designed for detecting volumetric corrosion defects on the inner surface of oil and gas storage tanks. A theoretical model of the structure is developed and the characteristics of the guided distribution of the electromagnetic field are resolved. The proposed model provides a region of interest with a uniform magnetic field. This greatly improves the detectability and thermal comparison of corrosion defects on the inner surface. In addition, the inspection is performed under weak excitation conditions and in the full open field of view of the infrared camera. This configuration greatly improves the portability and efficiency of workpiece inspection. Several open architecture sensors are evaluated and compared regarding temperature rise uniformity, model passability, and lightweight level. Meanwhile, the geometrical parameters of the square sensor, the operating parameters, and the material properties of the detected samples are investigated, including the coil height, the cross-arm length, the lifting distance, the operating frequency, the relative magnetic permeability of the sample, and the electrical conductivity of the sample. Finally, the detection capability of the sensors was verified through experiments with different steel plate thicknesses and defect morphologies.

Research on the lightning shielding performance of strained angled tower for the [formula omitted]1100 kV UHVDC transmission project

Rigid jumper is usually used in the strained angled tower for the UHV transmission project, which makes the protection angle of the ground wire to the jumper end larger, thus the lightning shielding failure risk of the strained angled tower may increase. In order to study the lightning shielding performance of strained angled tower for the ±1100 kV ultra-high voltage direct current (UHVDC) transmission project, a numerical model for the simulation of lightning attachment to the strained angled tower was established based on the research results in the aspects of lightning downward leader, inception and propagation characteristic of upward connecting leader and so on. The maximum lightning shielding failure current and the shielding failure flashover rate (SFFOR) of rigid jumper were calculated under different line angles and overhead ground wire cross-arm lengths based on the proposed model. Results show that the lightning flashover of rigid jumper mainly occurs on the outer side while the rigid jumper on the inner side is in a good shielding state. When the cross-arm length of overhead ground wire on the outer side of J27104A1 tower with 90° line angle is greater than 21.7 m, the SFFOR of rigid jumper will be below 0.1 times/(100 km a), which can meet the operation requirement. The analysis provides technical references for the lightning protection design of strained angled tower for the UHVDC transmission project.

Experimental investigation into the buckling behaviour of cable-stiffened steel columns

In this study, cable-stiffened steel columns (CSSCs), which primarily aim to enhance compression behaviour, were experimentally investigated. In contrast to other stiffened column types, the cable-stiffened steel columns investigated in this work were equipped with a three-branch crossarm system. A series of tests were performed on 2.4 m CSSCs with two different crossarm–main column connection types (i.e., rigid and scissor types). In addition to the connection types, the effects of crossarm length and initial pretension on the load carrying capacities of CSSCs were also studied experimentally. The experimental results indicate that the three-branch crossarm system is effective in improving the buckling load of ordinary compression columns. The findings prove that the scissor-type connections between the crossarms and the main column could also be used in practical applications. Moreover, a unique, asymmetric post-buckling mode for a CSSC with a three-branch crossarm system was observed. The effects of crossarm length and pretension in cables are also demonstrated. This results presented in this work could be of assistance in the further design of CSSCs.

A novel strategy for the crossarm length optimization of PSSCs based on multi-dimensional global optimization algorithms

Prestressed stayed steel columns (PSSCs) offer a lightweight alternative for the design of slender compression columns. The stability of compression columns can be significantly enhanced by introducing crossarms. Previous research on this subject has primarily focused on load-carrying capacity estimation or analyses of the influencing factors of PSSCs. Thus, investigations of the design optimization of PSSCs remain scant. This work proposes a novel strategy for crossarm length optimization of PSSCs based on multi-dimensional global optimization algorithms. A multi-population genetic algorithm is introduced in the optimization process. The proposed optimization algorithm was demonstrated to be efficient and accurate in terms of determining the optimal crossarm length of PSSCs.

Prestressed stayed beam-columns: Sensitivity to prestressing levels, pre-cambering and imperfections

The behaviour and structural performance of imperfect beam-columns with crossarms and externally prestressed cable stays are studied numerically, where the combination of bending and compression is assumed to be derived from the system self-weight acting orthogonally to the applied axial load. Both doubly-symmetric and mono-symmetric systems are studied. Sensitivity of the structural response to varying prestressing levels, pre-cambering and initial imperfections is investigated. Different initial imperfection levels and combinations are considered to facilitate the exploration of interactive buckling. The optimum prestressing force in terms of ultimate resistance and two structural efficiency indicators is also studied. It is found that relatively small crossarm lengths, stay diameters and crossarm length ratios should be avoided. Moreover, mono-symmetric cases are more sensitive to the level of pre-cambering than their doubly-symmetric counterparts. Considering both load-carrying capacity and structural efficiency, doubly-symmetric cases perform best with zero pre-cambering, but mono-symmetric cases perform best with upward pre-cambering. As for the true optimum prestressing levels, these are recommended to be significantly above the linearly obtained optimum to maximize the structural efficiency.

Crossarm length optimization and post-buckling analysis of prestressed stayed steel columns

Abstract A prestressed stayed steel column is an efficient and lightweight method of enhancing the stability of a traditional compression steel column. In the past, a large number of repeated numerical analyses had to be conducted to determine the optimal crossarm length of a structural system. This motivates the study of an optimization method that can be adopted to determine the optimal crossarm length directly. A sensitivity analysis of the linear buckling load is carried out based on the finite element theory, and an optimization algorithm is adopted to capture the optimal crossarm length. The optimization method is programmed in MATLAB and validated by numerical analysis. The post-buckling behavior of prestressed stayed steel columns with different crossarm arrangement schemes is also comparatively analyzed. It is demonstrated that the proposed optimization method is sufficiently accurate to predict an optimal crossarm length that corresponds to the maximum buckling load. The results presented in this study should be of great assistance in updating design procedures for prestressed stayed steel columns.

Numerical investigation into prestressed stayed steel box section columns under eccentric loading

The behaviour of prestressed stayed steel columns under axial compression has been intensively investigated; however, research on their behaviour under eccentric loading has not been conducted. This current work investigates the stability behaviour of prestressed stayed steel box section columns under eccentric loading by using finite element analysis. It was demonstrated that the load carrying capacity could be decreased by the load eccentricity. A reduction factor that quantitatively denotes the effect of load eccentricity on the load carrying capacities was defined, and approximate formulae calculating the reduction factor have also been proposed. Further, it has been found that the effect of eccentricity on the load carrying capacity is significantly affected by the critical buckling modes of prestressed stayed steel columns. In addition, the effects of slenderness ratio, crossarm length, and stay diameter have also been presented in this work. The results will be of great assistance when designing this type of column under eccentric loading.

Buckling Behaviour of Three-Dimensional Prestressed Stayed Columns

Slender columns exhibit instability under compression, which causes buckling. Prestressed stayed system can be used to improve the load carrying capacity of these columns. In this study, three-dimensional prestressed stayed column was investigated through the use of commercially available finite element software-ABAQUS. Although many numerical studies into the buckling behavior of stayed columns exist, these have mainly focused on two-dimensional (2D) systems. In order to fully understand the behavior of these structural systems, three-dimensional (3D) numerical studies are essential. In this work, the buckling behavior of three-dimensional prestressed stayed columns was investigated through linear perturbation method. The critical buckling loads and modes of four-branch and three-branch columns were investigated. The effect of varying the cross-arm length on the buckling load of the four-branch column was also investigated and compared with the theoretical values. It was found that the theoretical buckling loads reported in previous research with 2D systems were conservative and largely underestimated the buckling capacities of prestressed stayed columns. Furthermore, it was observed that transition point from the symmetric to antisymmetric buckling mode occurs at a higher value of cross-arm to column length ratio for the 3D prestressed stayed columns compared to the 2D model.

Numerical Studies on the Buckling Behaviour of Cable-stiffened Steel Columns With Pin-connected Crossarm Systems

In this study, the buckling behaviour of a cable-stiffened steel column with a four-branch pin-connected crossarm system is investigated. A new geometric imperfection distribution is constructed with a nonlinear buckling analysis to trigger interactive buckling, and a method to obtain the actual load carrying capacity of the cable-stiffened steel column is proposed. The effects of different parameters, including the stay diameter, crossarm length, pretension in cables, and imperfection size, have also been analysed and discussed in this article. The findings of this study show that the interactive buckling of steel column stiffened by the four-branch pin-connected crossarms must be taken into account for accurate analysis. It is also demonstrated that the cable-stiffened steel columns are imperfection sensitive, particularly when the critical buckling mode is located at the transition between symmetric and antisymmetric buckling, though the corresponding configuration is proved to be optimal with respect to the material utilisation rate.

Optical transmission through metallic split-ring resonator with inner cross dimer array

We investigate numerically the optical properties through gold split-ring resonator (SRR) with inner cross dimer array by using the finite difference time domain (FDTD) method. The dependence of the geometrical parameters on the optical properties of SRR with inner cross dimer array is studied. The study covers the change of transmission spectra with the metallic cross arm length, width of air slits, width of SRRs and environmental dielectric constants. The spatial distributions of the electric and magnetic fields are also discussed to further understand more basic physical mechanisms behind some dip and peak.

Metal mesh filters based on Ti, ITO and Cu thin films for terahertz waves

In this study, we have investigated the spectral performance of resonant terahertz (THz) bandpass filters which were produced from thin films with a metal-mesh shape. The aforementioned filters were fabricated from titanium, copper and indium tin oxide thin films on fused silica substrates by UV lithography with an array of cross-shaped apertures. Since the mesh period, cross-arm length and its width specify the spectral characteristics of the filters, we were able to reveal the performance of these filters experimentally using both a THz time domain spectrometer and a Fourier transform infrared spectrometer. A commercial electromagnetic simulation software, CST microwave studio, was used to verify the experimental data. The transmission of the filters are in the range 20–55 % at their relevant center frequencies. To our knowledge this study is the first to show that fabricated patterns based on ITO thin films can be used to filter THz radiation.

Design and Strength Analysis of FSAE Suspension

China FSAE race introduced formula racing gradually in the university campus in order to make FSAE racing have better ride comfort, handling and stability. Design and strength analysis of FSAE suspension were also proposed. Firstly, according to the whole layout of FSAE racing, the suspension mode was selected, both front and rear suspension were unequal push rod type double wishbone independent suspensions. Secondly, the main parameters and the orientation structure of the front and rear suspension were preliminarily designed. The wheels alignment parameters were selected with all kinds of stiffness, damping coefficient, followed by cross arm length calculation. According to the design parameters, suitable rim and shock absorber were chosen to determine the structure of the suspension’s main components . Thirdly, the front and rear suspension models were set up by the SolidWorks 3D software. Finally, the analysis of static stress on the main components of FSAE racing using the simulation module was performed to form the car suspension system so that it meets the design requirements of the FSAE regulations. This paper could provide references for the real vehicle development.

3-D FEM Calculation of Potential Distribution Along Porcelain String Insulators

Porcelain string insulators are widely used in high voltage transmission lines. Calculation of potential distribution is extensively performed to design and develop high voltage insulators. In this paper a three-dimensional (3-D) potential analysis software (Maxwell) is applied to calculate potential distribution of 230 kV porcelain suspension insulators. The effects of tower cross arm's length, number of units and corona ring parameters for I-string and II-string insulators on the potential distribution along the porcelain suspension insulators are investigated. The result can be served as a basic reference in the optimum design and proper use of line insulators in practice

Numerical Studies on the Buckling Resistance of Prestressed Stayed Columns

The structural behaviour of prestressed stayed columns is investigated through nonlinear finite element modelling. The models were developed using the commercial software ABAQUS and validated against a series of recently conducted experiments. The sensitivity of the load-carrying capacity to the geometry of the stayed column, the initially applied prestress level within the stays and the initial global imperfection is investigated through parametric studies. It is found that there is a substantial increase in load-carrying capacity with increasing cross-arm length, provided the critical buckling mode remains symmetric. Once the critical buckling mode becomes antisymmetric, mode interaction becomes significant and the load-carrying capacity reaches a plateau and the component generally becomes more sensitive to imperfections. It is also found that the relative level of initial prestress required to maximize the load-carrying capacity of a given stayed column tends to reduce with increasing cross-arm length.

Band-pass filters for THz spectral range fabricated by laser ablation

The terahertz resonant metal-mesh filters were fabricated using the laser direct writing technique. UV picosecond laser was employed to cut matrixes of cross-shaped holes in stainless steel foil and molybdenum layer deposited on polyimide substrate. Different laser processing strategies were developed: holes were cut through in the metal foil and the molybdenum film was removed from the polyimide by laser ablation. Band-pass filters with a different center frequency were designed and fabricated. The regular shape, smoothness of edges and sharpness of corners of the cross-shaped holes in the metal were the main attributes for quality assessment for the laser ablation process. Spectral characteristics of the filters, determined by the mesh period, cross-arm length, and its width, were investigated by terahertz time-domain spectroscopy and conventional space-domain Fourier transform spectroscopy. Experimental data were supported by three-dimensional finite-difference time-domain simulations.

Dark and bright localized surface plasmons in nanocrosses

A metallic nanocross geometry sustaining broad dipole and sharp higher order localized surface plasmon resonances is investigated. Spectral tunability is achieved by changing the cross arm length and the angle between the arms. The degree of rotational symmetry of the nanocross is varied by adding extra arms, changing the arm angle and shifting the arm intersection point. The particle's symmetry is shown to have a crucial influence on the plasmon coupling to incident radiation. Pronounced dipole, quadrupole, octupole and Fano resonances are observed in individual cross structures. Furthermore, the nanocross geometry proves to be a useful building block for coherently coupled plasmonic dimers and trimers where the reduced symmetry results in hybridized subradiant and superradiant modes and multiple Fano interferences. Finite difference time domain calculations of absorption and scattering cross-sections as well as charge density profiles are used to reveal the nature of the different plasmon modes. Experimental spectra for the discussed geometries support the calculations.

Calculation of Voltage Distribution along Porcelain Suspension Insulators Based on Finite Element Method

Porcelain string insulators are widely used in high-voltage transmission lines. Calculation of potential distribution is extensively performed in the design and development of high-voltage insulators. This article applies a three-dimensional electromagnetic analysis program to calculate the potential distribution of 230-kV porcelain suspension insulators under clean and dry conditions. The effects of cross-arm length, number of units, corona ring parameters, and also effects of wind force on the potential distribution along the porcelain suspension insulators are investigated and discussed. The results are useful for analyzing the potential distribution for porcelain suspension insulators.

Optimum design of stayed columns with split-up cross arm

The columns considered in this paper consist of a central mast; a split-up cross arm hinged or fixed to the central mast and optimally stressed stays. The buckling load of these columns is calculated and the influence of the geometrical parameters is examined. The indicator of volume, W, is proposed as a measure of the efficiency of different structures that are designed to transmit the same load P. This paper demonstrates that the stayed columns with a split-up cross arm have a number of advantages with respect to the stayed columns examined previously. It further reveals that both the sections of the stays and the cross arm length influence the buckling load and the efficiency decisively. Compared to other columns with one cross arm, an efficiency increase of more than 20% can be achieved. The efficiency is defined as the minimal volume of material needed to sustain a given load P. The theory of morphological indicators is used to propose a design procedure for stayed columns. This procedure takes constraints (such as local buckling, yielding, choice of the morphology…) into consideration and proposes the most efficient column. Furthermore, it takes imperfection into account as prescribed by the construction code (Eurocode 3) [Eurocode Steel/3. Belgian Standard NBN ENV 1993-1-1: 1992/AX (1992)].

Design Rules to Minimize the Effect of Joule Heating in Greek Cross Test Structures

This paper presents work on the analysis of the effect of Joule heating on sheet resistivity measurements using Greek cross test structures. As part of this work, design rules have been derived to minimize the heating effect associated with currents forced during their measurement. To accomplish this, finite-element (FE) simulations were employed to identify the location of heat generation and cooling mechanisms in the structures. This identified that the temperature could be minimized by: firstly, decreasing cross arm length, and therefore both electrical and thermal resistance of the arms; and secondly, by integrating pads and leads to improve the heat sink effect. These results were confirmed by sheet resistance measurements of four different Greek cross designs which demonstrated that the proposed design rules reduced the Joule heating effects on the sheet resistance measurements by up to 25%.