Hollow Beam Research Articles

Experimental Study of RC Hollow Beams with Embedded PVC Pipes

This study investigated the behaviour of reinforced concrete (RC) hollow beams under incremental static loads. Polyvinyl Chloride (PVC) pipes were used to create longitudinal voids in hollow beams. The parameters studied included the size (25 mm, 50 mm and 75 mm diameter) and location (39 mm and 139 mm from beam soffit) of the PVC pipes in the beam. Nine specimens were tested under the four-point load test setup. The loads were progressively increased until the specimens failed. The specimens were analysed based on the failure modes, load-displacement responses and mechanical properties. The hollow beams gave a 2% to 36% lower strength than the solid beams. In terms of the strength per unit concrete, the hollow beams were less efficient than the solid beams. The efficiency ratio of hollow beams ranged from 0.67 to 1.0. For that, none of the proposed hollow beams was recommended.

Multifractal analytical method and experimental study on crack evolution of dismantled RC hollow-slab beam

Reinforced concrete is the earliest and most commonly used bridge construction material and there are a large number of RC bridges in service all over the world. Due to a long-time operation and external load, most concrete bridges suffer from various degrees of damage. The most common method used in the maintenance of these bridges is visual inspection, which is highly subjective, lacks quantitative means and provides little information about the mechanical properties of the structure. Therefore, this paper conducts a set of failure experiment of the reinforced concrete hollow slab beams based on multifractal theory, and then proposes a convenient damage detection method for reinforced concrete beam bridges based on crack distribution images. Firstly, this paper introduces the basis of multifractal theory and an example of its application to the cracking characteristics of concrete beam members. Then a set of failure experiment on demolished members of in-service reinforced concrete hollow slab bridges was conducted, and two high-precision industrial cameras were used to record the full process of crack development on the surface of the beams. Then the multifractal theory was used to quantitatively characterize the crack distribution characteristics of the beams during the load process. The function relationship between the fractal dimension and the bending moment and the main mechanical properties (mid-span deflection, maximum crack width) of the test beam was analyzed and the damage index based on fractal dimension is calculated. The results show that the multifractal theory performs appropriate in describing the crack distribution of the beam, the points on the multifractal spectrum continuously move to larger values as the bending moment increases, and the generalized fractal dimension values have similar conclusions. The functional correlation between main mechanical properties and the fractal dimension is strong. Based on the experiment results, the damage classification criteria for reinforced concrete bridges are proposed referred to the IAEA guidelines. Three damage classes and corresponding the range of values of fractal dimension (FD) and the damage index (DI) are given. These findings provide a useful tool for exploring the cracking performance and rapid detection of reinforced concrete bridges.

Pull Out Resistance of Glued in Rod Parallel to Grain in Laminated Bamboo

Research on hollow cross section beams and columns made of laminated bamboo has been carried out. So that the two elements can be assembled into a building structure, it is necessary to do connection. Glued in rod is a new connecting tool whose mechanical properties still need to be studied. For this reasons this research was conducted. To achieve this objective, an experiment was conducted with the independent variables (1) the distance between the two edges, (2) the diameter of the threaded rod, and (3) the embedded length. The results showed that (1) the greater the distance between the two edges, the greater the pull out strength of the glued in rod, (2) the larger the diameter of the threaded rod, the greater the pull out of the glued in rod, (3) the greater the embedded length of the threaded rod, the stronger the pull out of glued in rod, (4) the value of the slip modulus is affected by variations in diameter and embedded length but is not affected by the distance between the two edges. The greatest pull out strength, which is 34.85kN, is achieved at a glued in rod diameter of 12mm with an edge distance of 4.5d and a embedded length of 6d, while the lowest value is 14.38kN lies in steel rods with a diameter of 8mm with a embedded length of 5d and a distance of two edges is 2.5d. The highest slip modulus or the highest stiffness value of 9.75kN/mm is achieved at a diameter of 12 mm with an embedded length of 6d and a distance of two edges of 3.50d. The smallest slip modulus value of 3.75kN/mm was achieved at a diameter variation of 8 mm with an embedded length of 5d and a distance of two edges 2.5d

Two-photon microscopy with enhanced resolution and signal-to-background ratio using hollow Gaussian beam excitation.

Two-photon microscopy (TPM) offers deeper imaging depth inside the scattering medium, however, it suffers from limited resolution owing to the longer excitation wavelength. We demonstrate the use of a hollow Gaussian beam (HGB) at the therapeutic window to improve the resolution and signal-to-background ratio (SBR). The HGB was produced by omitting the azimuthal phase term from the vortex mode, and the excitation point spread function (PSF) can be readily tuned by the mode order. The performance of the TPM with HGB was evaluated by experimentally imaging 100 nm fluorescent beads to estimate the PSF. The HGB improved the lateral resolution of the TPM by 36% in contrast to the conventional TPM. The HGB also furnishes an improvement of SBR by eliminating the out-of-focus light owing to its ring shape. Furthermore, we have used a translating lens-based module for additional lateral resolution tuning and reduced the resolution further down to 44% with respect to conventional TPM. Finally, we have performed imaging with merely two-dimensional scanning of a 50 µm thick mouse brain slice (Thy-YFP H-line) using the developed TPM with HGB. Our compact, robust, and low-cost design of the HGB generation scheme can easily be integrated into the commercial TPM to accommodate the improvements.

Comparative Additional Factor for Diffraction Loss On (TEM01) Mode from That of (TEM00) Mode

Comparative Additional Factor for Diffraction Loss On (TEM01) Mode from That of (TEM00) Mode

Experimental investigation on torsional behaviors of ultra-high-performance fiber-reinforced concrete hollow beams

Limited studies have been conducted on the torsional performance of ultra-high-performance fiber-reinforced concrete (UHPFRC) hollow beams. This paper presents experimental investigations on eight UHPFRC hollow beams with various cross-sectional dimensions, wall thicknesses, and cross-section types. Their torsional responses, including the failure modes, torque−twist curves, torque−strain curves, torsional stiffness, and ductility indexes, are presented. Theoretical methods were employed to evaluate the cracking and ultimate torques. The results indicated that the UHPFRC hollow beams with and without flange plates exhibited a similar failure model, with the main cracks penetrating spirally. The cross-sectional dimensions, wall thicknesses, and cross-section types significantly affected the ultimate torque, whereas the cracking torque was affected only by the cross-sectional dimensions. A comparison of the experimental and theoretical results indicated that the American Concrete Institute code provisions provided good predictions for the cracking torque, whereas the existing theoretical methods offered unsatisfactory predictions for the ultimate torque. Thus, the equivalent wall thickness of UHPFRC hollow beams must be evaluated with a higher accuracy.

Experimental and Numerical Nonlinear Analysis of Hollow RC Beams Reinforced with Rectangular Spiral Stirrups under Torsion

Experimental and Numerical Nonlinear Analysis of Hollow RC Beams Reinforced with Rectangular Spiral Stirrups under Torsion

Design and Experiment of a Hollow Beam Electron Optics System for Ka-Band Extended Interaction Klystrons

In this article, the design and experiment of a hollow electron beam (HEB) electron optics system (EOS) for Ka-band extended interaction klystrons (EIKs) are presented. To realize the fast switch of the current emission at a low cutoff voltage, an electron gun with two focus electrodes (FEs) is chosen. The emitting surface of cathode is a ringed spherical surface. The first focus electrode (FE1) is around the cathode, and the second focus electrode (FE2) is set in the central hole of the cathode. The current emitted from the cathode surface is about 2A, when the operating voltage is 25 kV. Three simulation codes, Egun, Superfish, and CST, are used for designing the electron gun and the permanent magnet focusing system (PMFS). Some sensitivity analyses with respect to the PMFS’s critical parameters are presented. The simulation shows the dc beam transmission is 100%. The electron beam, confined by 6000 Gauss uniform field, propagates through the drift tube of 37 mm with good laminarity and small ripple. The emission current can be suppressed when the voltage of the FEs is −3.4 kV. According to the results of simulation, the Ka-band EIK had been constructed and the hot-test experiments had been fulfilled in succession. The experimental results exhibit that the dc beam transmission is about 99% and the beam can sustain 98% transmission at high frequency (HF) operation. In addition, the output power is higher than 8 kW in the bandwidth of over 100 MHz.

Integrated all-fiber structures for generating doughnut beam arrays and hollow Bessel-like beams

Two all-fiber structures for generating doughnut beam arrays and hollow Bessel-like beams are demonstrated experimentally based on mode-selective couplers at the visible band. The mode-selective couplers are acted as mode converters to produce doughnut beams, which have the properties of high mode conversion efficiency (94%), low insertion loss (<0.5 dB) and wide bandwidth (∼100 nm). A compact and efficient approach is presented through integrating a tapered multicore fiber with a mode-selective coupler, and a doughnut beam array with nearly equal power distribution is obtained based on the mechanism of coupled-power theory in the tapered multicore fiber. The hollow Bessel-like beams with different cylindrical vector modes and orbital angular momentum are achieved by fabricating a polymer microtip at the facet of the few-mode fiber output port of a mode-selective coupler. The self-healing characteristics of a Bessel-like beam are investigated in detail and the application in an optical tweezer system of a hollow Bessel-like beam exhibits a longer focal depth than that of a Gaussian beam. Both methods used for generating all-fiber-based doughnut beam arrays and hollow Bessel-like beams have the advantages of compactness, flexibility, and easy integration with free-space optical systems. Generated two kinds of beams show huge potentials for the application fields of super-resolution microscopy, laser material process and optical trapping and so on.

Achieving ultracold Bose–Fermi mixture of 87Rb and 40K with dual dark magnetic-optical-trap

We demonstrate that dual dark magnetic-optical-traps (MOTs) have great importance in the two-species 87Rb and 40K mixture compared with dual bright MOTs. The dark MOT has a little improvement in the trapping of single-species 87Rb or 40K gases compared with bright MOT. For the case of loading two-species 87Rb and 40K simultaneously, the improvement of 40K in the dual dark MOTs is mainly from the reduction of light-assisted collision losses. The dual dark MOTs employ a pair of conical lenses to produce the hollow beam for repump laser with high efficiency. The number and density of 87Rb and 40K atoms after evaporative cooling in the hybrid magnetic trap with dark MOT loading are compared with those in bright MOT. The atoms with large number and high density make it easier to realize the quantum degenerate of Bose–Fermi mixture.

Structural rationalities of tapered hollow cylindrical beams and their use in Japanese traditional bamboo fishing rods

Bamboo has historically been used in Japan as a structural material and for building tools such as fishing rods owing to its remarkable structural properties. In recent years, the materials used for manufacturing fishing rods have changed greatly owing to the development of composite materials; however, the basic slender tapered hollow cylindrical fishing rod design has remained unchanged throughout the long history of fishing. However, the mechanical rationale behind this structural design has not yet been sufficiently verified, and this study clarifies this. The analysis was performed by solving the nonlinear bending equation of a slender tapered cantilever beam with a concentrated load at the tip, which causes large deflection, using the Runge–Kutta method. The deflection curves and bending stresses were obtained, and the structural design to minimize the stresses was explored. Our results may prove useful for bamboo-inspired bionic design and bring to light our ancestors’ deep knowledge of natural materials and their advanced technological capabilities.

Beam propagation factor of Hollow higher-order Cosh-Gaussian beams

Based on the second-order moments definition, the beam propagation factor of a new mathematical model of Hollow higher-order Cosh-Gaussian (HhCG) beams is investigated. Analytical formula for the M2-factor of HhCG beams is derived, which depends on the hollowness parameter l, the beam order n, the parameter of the cosh part δ and the beam waist ω0. The influences of these parameters are illustrated with numerical examples. The result provides more general characteristics because the higher-order Cosh-Gaussian, Cosh-Gaussian and Gaussian beams are obtained as specials cases of HhCG beams.

Behavior of hollow concrete-filled rectangular GFRP tube beams under bending

Concrete-filled fiber reinforced polymer (FRP) tube (CFFT) members have become increasing popular, while the study on CFFT beams especially hollow CFFT beams is rather limited. This paper presents an experimental study on the flexural behaviour of hollow concrete-filled rectangular glass fiber reinforced polymer (GFRP) tubes beams. A total of six beams was fabricated and tested by using four-point bending. The parameters investigated in this study included the size of the hollow cores (0%, 5.7%, 12%, 27%) and the shape of the hollow cores (circle and rectangle). The experimental results show that the hollow CFFT beams exhibit an almost linear load–displacement behaviour and a brittle failure mode. The flexural stiffness of the hollow CFFT beams is slightly affected by the size and shape of the hollow cores. In addition, the proposed theoretical model verifies that the hollow core in the tension region also has a small effect on flexural strength of the hollow CFFT beams, and the flexural behavior is highly depended on the material properties of the GFRP tubes. In comparison with the conventional steel reinforced concrete beams, the hollow CFFTs beams have a lighter dead weight and a higher load-carry capacity.

Super-Diffraction Longitudinally Polarized Optical Needle With Ultra-Long Focal Depth Generated by a Radially Polarized High-Dimensional Circular Hollow Sinh-Gaussian Beam

In this paper, the incident beam called high-dimensional circular hollow sinh-Gaussian (HD-CHsG) beam with a novel wavefront is proposed, which is determined by three parameters ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> , <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">σ</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">σ</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> ). Based on the Richards-wolf vector diffraction theory, it can be focused into a longitudinal polarized optical needle through a high numerical aperture lens. The effects of the three parameters ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> , <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">σ</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">σ</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> ) on the resolution and depth of focus of the longitudinally polarized optical needle are simulated and analyzed. In the condition of ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> , <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">σ</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">σ</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> ) = (8, 0.6, 0.125), a super-diffraction longitudinal optical needle with ultra-long focal depth (resolution 0.40 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ</i> , focal depth 18.36 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ</i> , depth-to-width ratio 45.9:1) is generated. In addition, compared with a radially polarized incident beam whose amplitude distribution is Gaussian and circular hollow sinh-Gaussian (CHsG) distribution, the resolution and depth of focus of the longitudinally polarized optical needle obtained by focusing the HD-CHsG beam are higher. Both simulations and experiments are carried out to demonstrate the availability of our method. Our findings are of great significance to the production, manipulation, and application of longitudinally polarized optical needle.

Numerical modelling strategies for reinforced 3D concrete printed elements

Extrusion-based 3D concrete printing (3DCP) prompts a new age of reinforced concrete structures by virtue of the exponential advancements in process, control, material, and fresh-state analysis technologies. Notwithstanding these advancements, latency exists in the numerical analysis of complex geometric forms produced by 3DCP technology. In this research, two finite element (FE) modelling strategies are proposed for the numerical analysis of 3DCP building elements. The objective of these models is to predict the hardened state structural capacity and failure mechanisms of singularly and dually reinforced concrete deep beams under various loading configurations. To validate the proposed FE modelling strategies, the reinforced 3DCP deep beams are experimentally evaluated. An analogy between masonry and 3DCP structures provides premise to the presented FE modelling strategies, and succinct descriptions of the respective modelling strategies, adaptions to the 3DCP design space, and material model prescriptions are provided. Strikingly, the recommended input parameters provide sound agreement with the experimentally evaluated configurations, with all simulations exhibiting a load carry capacity within 14% of the experimental observations. Not only is the load-displacement response deemed appropriate, but also the numerically produced cracking patterns, placing confidence in the proposed numerical simulation strategies. Furthermore, it is shown that the advent of a 2D plane stress simplification of the fibre-reinforced hollow beam geometry yields adequate agreement while significantly reducing the computational expense required to simulate the nonlinear response of anisotropic printed composites. • Design and fabrication rules to ensure structural integrity in 3DCP elements is presented. • The mechanical performance of reinforced 3DCP beams is experimentally investigated. • Two hardened state anisotropic numerical simulation frameworks for 3DCP are proposed. • A 2D plane stress simplification of cellular infill geometry is proposed and validated.

Multiple electron beam generation with different energies and comparable currents from a single cathode potential for high power traveling wave tubes (TWTs)

We present a technique for generating multiple electron beams with different energies and comparable currents from a single cathode stalk at a single potential using nested magnetically insulated coaxial diodes (MICDs). The application is for a multi-stream traveling wave tube. Particle-in-cell simulations are performed for an experimental parameter-based geometry where two thin-walled intense relativistic electron beams immersed in a strong uniform magnetic field propagate through a cylindrical vacuum channel. The analytically derived results are obtained by extending Fedosov’s solution for generating a hollow electron beam from an MICD on a cathode stalk in an infinite magnetic field. Two electron beams are generated and accelerated downstream assuming zero initial kinetic energy of the electrons from the cathodes. Results show both electron beam currents ranging from 66 to 2.8 kA with an energy difference ranging from 6% to 27% depending on voltages applied from 100 to 600 kV and the geometry of the two MICDs. An optimal geometry is a crucial factor in achieving the maximum energy difference between the electron beams for comparable currents. The analytical and numerical simulation results show good agreement. We are currently in the process of planning experiments using the electron beam accelerator (SINUS-6 at UNM) to validate the analytical and simulation results.

Structural Efficiency of Non-Prismatic Hollow Reinforced Concrete Beams Retrofitted with CFRP Sheets

Non-prismatic reinforced concrete (RC) beams are widely used for various practical purposes, including enhancing architectural aesthetics and increasing the overall thickness in the support area above the column, which gives high assurance to services that this will not result in the distortion of construction features and can reduce heights. The hollow sections (recess) can also be used for the maintenance of large structural sections and the safe passage of utility lines of water, gas, telecommunications, electricity, etc. They are generally used in large and complex civil engineering works like bridges. This study conducted a numerical study using the commercial finite element software ANSYS version 15 for analysing RC beams, hollow longitudinally sectioned and retrofitted with carbon fibre reinforced polymers (CFRPs), which were subjected to concentrated vertical loads. The numerical analysis results on the simulated beam models were in excellent agreements with the previous experimental test results. This convergence was confirmed by a statistical analysis, which considered the correlation coefficients, individual arithmetic means and standard deviations for all the calculated deflections of the simulated beam models. A proposed numerical simulation model with the hypotheses can be considered suitable for modelling the behaviours of simple supported non-prismatic RC beams under vertical concentrated loads. The numerical results showed that altering the cross-section from solid to hollow could reduce the load carrying capacities of the beams by up to 53% and increase the corresponding deflections by up to 40%, respectively. Using steel pipes for making recesses could enhance the loading capacity by up to 56%, increase the ductility, and reduce the corresponding deflections by up to 30%, respectively. Finally, it was found that bonding the CFRP sheets in the lower middle tensile areas of the hollow beams could improve the resistance and reduce the deformations by up to 27%. The failure patterns for all the numerical models were shear failure. The cylinder compressive strength could be used as a mechanical parameter for modelling and assessing the structural behaviours of the beam models, as its increase could improve the load carrying capacities and reduce the deflections by 30–50%.

Focusing of radially polarized bessel gaussian and hollow gaussian beam of high NA to achieve super resolution

To achieve super-resolution, a radially polarized Bessel Gaussian and a Hollow Gaussian Beam with high NA are focused. For both Bessel Gaussian and Hollow Gaussian Beams with high numerical aperture NA, the radially polarized component with two equal-intensity peaks covers 25% of the total intensity, while the longitudinally polarized component covers the rest. By focusing radially polarized Bessel and Hollow Gaussian beams, it is possible to generate various focal spots with different dimensions that are applicable for various applications in optical trapping, data storage, biomedical imaging, laser cutting, material processing, and microscopy. The effects of various Bessel beam characteristics are investigated. It was found that the beam radius reaches a minimum at a specified starting beam radius for all propagation distances and that the optimum starting beam radius is also large at long propagation distances. This findings are of great significance in optical trapping, data storage, biomedical imaging, and laser cutting.

Enhancement of image quality in planar Airy light-sheet microscopy via subtraction method

The use of propagation-invariant Airy beams enables a light-sheet microscopy with a large field-of-view. Without relying upon two-photon excitation or deconvolution-based processing to eliminate out-of focus blur caused by the side lobes, here, we present how the subtraction method is applied to enhance the image quality in digital scanned light-sheet microscopy with Airy beam. In the proposed method, planar Airy beam with the symmetric transversal structure is used to excite the sample. A hollow Airy beam with zero intensity at the focal plane is created, which is mainly used to excite the out-of-focus signal. By scanning the sample twice with the normal planar Airy beam and the hollow Airy beam, digital post-processing of the obtained images by subtraction allows for the rejection of out-of-focus blur and improves the optical sectioning, the axial resolution and the intensity distribution uniformity of the light-sheet microscopy.

Investigation of torsional effect of UHPFR concrete hollow beams

A significant handful of hollow ultra-high-performance fiber-reinforced (UHPFR) concrete beams have been tested for torsional strength. Various cross sections, wall thicknesses, and cross-section forms of UHPFRC hollow beams were tested in this study. An investigation of these materials is carried out to determine their failure mechanisms and their torque-twist and torque–strain curves. In addition, they are analyzed as well. The cracking and ultimate torques were calculated utilizing theoretical methodologies. Either with or without flange plates, significant fractures entering spirally in UHPFRC hollow beams led to the same failure. Despite the fact that cross-sectional dimensions had an impact on the ultimate torque, wall thickness and cross-sectional type had little influence on cracking torque. The cracking torque was well predicted by the American Concrete Institute code requirements, but the maximum torque was poorly predicted by the existing theoretical methodologies, according to an examination of actual and theoretical data. For hollow beams made of UHPFRC, the wall thickness should be estimated more precisely.