Hollow Circular Tubes Research Articles

Mechanical properties of lotus petiole bio-inspired structures under quasi-static radial load

The lotus petiole in nature is characterized by its porous structure and high bending resistance. Inspired by this, in this paper, random sampling of lotus petiole was carried out to clarify the porous distribution pattern of lotus petiole in cross section. On this basis, the original structures with 12 and 13 wells (Os-12w, Os-13w) were constructed, and equal mass hollow circular tube (Emhct) was also designed for comparison. Based on the experimentally verified finite element models, Os-12w, Os-13w and Emhct were comparatively analyzed. In addition, comparisons were made with five other bionic circular structures Compared to the rest of the structures, Os-13w performs better in all comprehensive properties. The bending and traction in the core region of the bionic structure caused the surrounding structures to join in the buckling earlier, creating a global crushing trend. More interestingly, further bending and traction in the core region creates a negative Poisson's ratio phenomenon. In addition, the results of the parametric study show that the optimum loading angle of Os-12w is between 60° and 90°, and the proper adjustment of its core cross-section characteristics can improve the mechanical properties of the structure. This study provides some reference for the development of thin-walled porous structures under radial loading conditions.

Rebar-concrete bond behaviour in grouted sleeve connectors

Grouted sleeve connectors (GSCs) are commonly used in precast/prefabricated concrete structures. To ensure force transfer, connectors tend to be overdesigned, and this has a detrimental effect on the plastic deformation capacity of the connection region and the displacement ductility of the precast structure. To enable improvements in the design of precast RC connections involving GSCs, an accurate analysis of the bond behaviour of GSCs is required. This paper presents an analytical model for the local bond behaviour under the particular sleeve confinement. A representative cross-section of a GSC is treated as interconnected hollow circular tubes. Three stages are identified according to the state of the grout, namely elastic, partially cracked, and fully cracked. The confining pressure is formulated within the cross-section, and the bond stress is subsequently evaluated by a modified bond stress-slip law accounting explicitly for the confinement. Compared with traditional bond-slip laws, the model is capable of representing the evolution of confining stress in the loading process. Comparison with relevant experimental results show good agreement. A subsequent parametric study demonstrates the trends of influence of various parameters, and notably, within allowable limits, a reduction of the grout thickness tends to increase the bond strength in the connectors.

Research on a Variable Pressure Driving Method for Soft Robots Based on the Electromagnetic Effect.

This study proposes a novel variable air pressure supply structure based on the electromagnetic effect. This structure can be implemented in various soft robots driven by air pressure, including pneumatic artificial muscles, pneumatic soft grippers, and other soft robots. The structure's main body comprises a hollow circular tube, a magnetic piston arranged in the tube, and an electromagnetic solenoid nested outside the tube. The electromagnetic solenoid is designed with special winding and power supply access modes, generating either an attractive force or a repulsive force on the magnetic piston. This solenoid conforms with the magnetic piston expectation in the tube by changing the polarity direction. The interior of the whole structure is a closed space. The gas is conveyed to the soft robot by the gas guide hoses at the two ends of the structure, and the expansion energy of the compressed gas is fully utilized. Then, the gas supply pressure is controlled to drive the robot. The mathematical model of the structure is established based on the analysis of the electromagnetic force and gas pressure on the piston. The simulation results show that the structure's inherent vibration characteristics under various parameters align with expectations. The real-time automatic optimization of the controller parameters is realized by optimizing the incremental proportional-integral-derivative (PID) controller based on a neural network. The simulation results show that the structure can meet the application requirements. The experimental results show that the proposed gas supply structure can provide a continuous pressure supply curve with any frequency in a specific amplitude range and has an excellent tracking effect on the sinusoidal-like pressure curve.

Energy absorption characteristics of the bionic lotus petiole structure under transverse load

Porous structures are often used as energy absorbing devices due to their light weight and high strength; therefore, the mechanical properties and collapse behavior of porous structures under various loads have attracted much attention. In this paper, two bionic lotus petiole structures: 12-wells original structure (Os-12w) and 13-wells original structure (Os-13w) are proposed to improve the energy absorption properties of porous structures, which are inspired by the light weight and collapse resistance of lotus petiole. Then a comparative study of Os-12w, Os-13w, hollow square tube and hollow circular tube based on quasi-static mechanical experimentally(loading speed is 3 mm/min) validated finite element models was carried out to explore the energy absorption characteristics of different structures under lateral loading. The results showed that the specific energy absorption (SEA) of Os-12w and Os-13w increased by about 88.9% and 77.8%, respectively, and the crushing force efficiency (CFE) increased by about 178.8% and 178%, respectively, compared with the hollow square tube. Compared with the hollow circular tube, the peak crushing force (PCF) of Os-12w and Os-13w were reduced by about 28.2% and 36.8%, respectively. Collectively, Os-12w has a greater energy absorption potential than Os-13w. The simulation results of the experiment explain why the energy absorption performance of the bionic structure is better than that of the hollow tube. Then, through further simulation analysis, the effects of the bearing angle and quarter windmill-like structural parameters on the energy absorption characteristics of Os-12w were explored. Valuable suggestions and guidance are provided for the subsequent development of thin-walled porous structures.

A numerical study on energy absorption capability of lateral corrugated composite tube under axial crushing

In this study, a comprehensive numerical investigation is carried out to evaluate the crashworthy behavior and the energy absorbing capacity of lateral corrugated composite tubes under axial loading. In this regard, a new lateral corrugated circle tube with a sinusoidal cross-section is proposed. To investigate the process of energy absorption, material model 54 in non-linear FE software LS-DYNA is applied for modelling axial crushing behavior. In order to validate the numerical simulations, the crushing results of hollow circular tube with uniform diameter are compared with available experimental data and a good agreement is observed. Afterward, crashworthiness analysis of lateral corrugated composite tubes is conducted by controlling the shape of the cross-section through the amplitude and the number of corrugations. The energy-absorbed performances such as specific energy absorption, initial peak crashing force, and mean crashing force of tubes are analyzed and discussed. Numerical analysis reveals that the lateral corrugated composite tubes have significantly obvious effects on the structural crashworthiness compared with ordinary circular tube under axial loading. Also, the results indicate that the geometrical shape of corrugation plays an important role in increasing the efficiency, controllability and failure patterns of corrugated tubes.

Effect of concrete infill on local buckling capacity of circular tubes

For circular steel sections, axial slenderness limits are typically defined in terms of the diameter-to-thickness ratio and indicate whether the member will first yield or locally buckle under axial compression. The common opinion is that filling a hollow structural section with concrete would enhance its resistance against local buckling by restraining its inward deformations. On the basis of this concept, the axial slenderness limits stipulated by most international design standards are notably higher for filled sections when compared to their hollow counterparts. Although there is extensive evidence in support of this approach for box sections, the available data for circular sections is limited and, in some cases, inconsistent. While some studies and most international design standards suggest that filled circular sections should have a notably higher axial slenderness limit compared to hollow circular sections, a number of studies argue that the concrete infill is in fact not very effective in increasing the local buckling strength of circular sections. Such studies are however very limited in the literature and often incomplete. Consequently, a comprehensive numerical study with over 140 analyses is conducted herein considering different material types, a wide range of slenderness values, and five initial imperfection modelling techniques to clarify the role of concrete infill in the local buckling behaviour of circular sections. Results of the study strongly suggest that the concrete infill has limited effect on enhancing the local buckling strength of circular tubes. The enhancement is found to be much lower than that implied in international design standards. The roots for this discrepancy are identified and recommendations are proposed in light of the findings of the study. The results suggest that the axial slenderness limit for hollow circular tubes can be significantly relaxed to bring it closer to that of filled circular tubes.

A fully-enclosed wrist-wearable hybrid nanogenerator for self-powered sensors

In this paper, a fully-enclosed wrist-wearable hybrid nanogenerator (WHN) based on electromagnetic-triboelectric mechanism is reported with an outstanding energy harvesting performance. The proposed WHN integrates rolling electromagnetic induction and electrostatic induction of a free-standing spherical magnetic inside a hollow circular tube. The human wrist motion initiates the magnetic ball to freely roll inside the tube, generating both electromagnetic and triboelectric energy. The WHN is capable of converting diverse human wrist biomechanical energy such swinging, waving, shaking, etc. into a useful electrical energy which can continuously power the wrist-wearable electronic devices and sensors such as wrist-watch, fitness band and so on. The experimental results show that the WHN can deliver the average power of 3.46 mW under the load resistance of 100 Ω. A commercial electronic wrist-watch is successfully powered continuously for more than 18 mins from just 5 s of wrist motion by wearing WHN on wrist. Also, a commercial temperature sensor is driven for 132 s form 88 s of slow walking by wearing WHN on wrist. Remarkably, the experimental results and outstanding demonstration shows the wide potential of the WHN as a sustainable power supply for developing self-powered wearable healthcare monitoring sensors.

Design of Tapered Flatted End Tube for Tension and Compression Loading

Hollow circular tube has the most efficient section in space structure. Hollow circular tube joint either welding or bolting but welding aluminum structural alloys lead to unavoidable annealing which can reduce efficiency to the order of only 50%. The efficiency of riveted and bolted joints is usually assumed to be around 75% in both aluminum and steel construction. Welded connections give the maximum strength in steel space structures and used for large spans. Hollow circular tube flatted at the end for single bolted connection and at flatted end increase this thickness for reducing stresses and this thicker plate make a hole for single bolted connection. Study this performance for varies the tapered flattened angle tube. Apply vertically upward and downward incremental load on the tapered flatted end tube at fixed bolted joint in ANSYS. Run this model for maximum shear stress and maximum principal stress. Find out the allowable tensile and compression stress in simple hollow circular tube in SAP2000 as per IS800-2007.. Find out the design load as per maximum shear stress theories and maximum principal stress theories

A fully enclosed, 3D printed, hybridized nanogenerator with flexible flux concentrator for harvesting diverse human biomechanical energy

Human body motion is highly regarded as a promising source of energy for powering body-worn electronic devices and health monitoring sensors. Transforming the human biomechanical energy into an electrical energy provides a sustainable energy to drive those devices and sensors, reducing their battery dependency. This work presents a fully-enclosed wrist-wearable hybridized electromagnetic-triboelectric nanogenerator (FEHN) for effectively scavenging energy from the low-frequency natural human wrist-motion (≤ 5 Hz). The FEHN incorporates the rolling electrostatic induction and electromagnetic induction using a freely moving magnetic ball inside a hollow circular tube. The materials used in 3D printing technology are used as energy harvesting material for easy, quick and worthwhile fabrication of the FEHN. A thin flexible flux concentrating material is introduced to increase the emf and enhances the electromagnetic output performance. The FEHN can harvest energy under the diverse circumstances and irregular wrist-motions, such as swinging, waving, shaking, etc. Following the experiments, the FEHN achieves an average power density of 0.118 mW cm−3 and can drive a commercial wrist-watch continuously for more than 23 min from just 5 s of wrist motion. This successful demonstration renders an effective approach for scavenging wasted biomechanical energy and provides a promising solution towards the development of sustainable power supply for wearable electronic devices and self-powered healthcare monitoring sensors.

Hurricane risk assessment of offshore wind turbines

Abstract A barrier to the development of the offshore wind resource along the U.S. Atlantic coast is a lack of quantitative measures of the risk to offshore wind turbines (OWTs) from hurricanes. The research presented in this paper quantifies the risk of failure of OWTs to hurricane-induced wind and waves by developing and implementing a risk assessment framework that is adapted from a well-established framework in performance-based earthquake engineering. Both frameworks involve the convolution of hazard intensity measures (IMs) with engineering demand parameters (EDPs) and damage measures (DMs) to estimate probabilities of damage or failure. The adapted framework in this study is implemented and applied to a hypothetical scenario wherein portions of nine existing Wind Farm Areas (WFAs), spanning the U.S. Atlantic coast, are populated with ∼7000 5 MW OWTs supported by monopiles. The IMs of wind and wave are calculated with a catalog representing 100,000 years of simulated hurricane activity for the Atlantic basin, the EDPs are calculated with 24 1-h time history simulations, and a fragility function for DM is estimated by combining variability observed in over one hundred flexural tests of hollow circular tubes found in the literature. The results of the study are that, for hurricane-induced wind and wave, the mean lifetime (i.e., 20-year) probability of structural failure of the tower or monopile of OWTs installed within the nine WFAs along the U.S. Atlantic coast ranges between 7.3 × 10−10 and 3.4 × 10−4 for a functional yaw control system and between 1.5 × 10−7 and 1.6 × 10−3 for a non-functional yaw control system.

Core-shell coaxially structured triboelectric nanogenerator for energy harvesting and motion sensing.

Converting sustainable human motion energy into electric energy has become an urgent task for the advancement of next-generation wearable and portable electronics. Herein, a core–shell coaxially structured triboelectric nanogenerator (CSTN) was fabricated by inserting an inner hollow circular tube into an outer hollow circular tube, and a gasbag is constructed within the space between the inner and outer tubes. Both Ni-coated polyester conductive textile and the conductive silicone rubber were used as effective electrode materials. The CSTN has excellent properties, including flexibility, light weight, sustainability and biological compatibility due to its unique structural design and materials selection. The CSTN can convert various forms of human motion energy, such as pressing, bending and twisting motion, into electric energy. A high short-circuit current of 11 μA and an open-circuit voltage of 380 V can be obtained from a CSTN with a length of 6 cm, corresponding to a high peak power of 1.638 mW at a load resistance of about 10 MΩ. When six such CSTNs are connected in parallel and placed under shoes, the electric energy output by normal walking can light up 60 LEDs connected serially and power up a competition-timer. The device can also sense different bending angles or twisting angles according to its signal outputs under different deformation angles. This study indicates the promising application prospects of the CSTN for next-generation devices, including self-powered illuminating devices, portable electronics, body motion sensing and health monitoring.

03.07: Robustness in fire of a new type of beam‐to‐column connection

ABSTRACTIn this paper a new type of beam‐to‐column connection is introduced, which is capable of absorbing both very large rotations and axial movements, due firstly to thermal elongation and subsequently to extreme weakening of the connected beam. The main idea is to connect the beam and column using a special connector bolted to the column flange using a face‐plate and to the beam web using a fin‐plate. Between these a highly ductile element, which is in this case a hollow circular tube, is included. This plays the crucial role in absorbing beam‐end movements occurring firstly during the expansion of the beam and secondly during its catenary behaviour at very high temperatures.This study aims to extend the research on this connection to structural case studies in the context of performance‐based structural fire engineering design. The connection has been modelled using different approaches, starting with 3‐D finite element modelling and proceeding to validated simplifications which feed into a component‐based model. In order to make calculations feasible, the mathematical model of the ductile component is developed and calibrated using the information provided by parametrized numerical FEM computations. The component model is developed to be capable of representing the hysteresis occurring due to deformation‐reversals as temperatures rise, as well as failure corresponding to fracture in tension. Thus, the component model is described as a function of displacement and temperature, including sufficiently realistic plastic deformation and fracture criteria. This model is then implemented into global FEM models and utilized to assemble the stiffness matrix of a special connector element used to join the beam and column nodes. This component‐based connection model is then applied in some comparative studies.

Rigid-plastic torsion of a hollow tube in strain-gradient plasticity

Closed-form expressions for the Cauchy stress, microstress, moment-stress, and the torque-twist relationship in a twisted hollow circular tube are derived for a rigid-plastic strain-gradient plasticity. This is accomplished for any of the gradient-enhanced effective plastic strain measures from a considered broad class of these measures. Numerical results are given and discussed for the two most frequently utilized measures and for the three adopted stress-strain relationships modeling the uniaxial tension test. Solid circular rods and thin-walled tubes are both considered. The existence of the line forces is also discussed from the standpoint of the basic equilibrium considerations and the principle of virtual work.

Low-Cycle Fatigue Testing of a Novel Aluminum Alloy Buckling-Restrained Brace

Compared with steel buckling-restrained braces, aluminum alloy BRBs show excellent advantages in structures where severe corrosion effects can be expected. At the same time, in order to avoid the effect of welding discussed in the previous research, a novel Aluminum alloy Bamboo-shaped Buckling-Restrained Brace (AL-BBRB) consisting of a bamboo-shaped inner core and an outer hollow circular tube was proposed and tested herein. Parametric studies with design variables including cross-sectional sizes of slubs and length of segments were conducted. A series of low-cycle fatigue tests, containing 4 specimens, were performed to address the low-cycle fatigue behavior of AL-BBRB specimens. According to test results of all specimens, stable hysteretic curves were obtained without any local and overall buckling. Consequently, the hysteretic behavior of AL-BBRB specimens is highly concerned with the design variables. Besides, failure positions of AL-BBRB specimens often concentrates on the end of the segment, which can be exactly predicted. Based on test results of all specimens, AL-BBRB specimens show a promising future for wide application in new or retrofitted buildings/bridges where lack the excellent seismic behavior and durability.

On the recoverable and dissipative parts of higher order stresses in strain gradient plasticity

The expressions for the free energy in two recent formulations of strain gradient plasticity are extended to include the locked-in strain energy around statistically stored dislocations. This is accomplished by using the strain dependent factor η(ep), which represents the fraction of the rate of plastic work converted into heat in accordance with the latent heat measurements from classical metal plasticity. The expressions for the plastic work in the two formulations differ by different representations of the portion of plastic work associated with the existence of plastic strain gradients and the corresponding network of geometrically necessary dislocations, while the dissipative parts of plastic work are assumed to be the same in both formulations. The expressions for the recoverable and dissipative parts of the higher order stresses, defined as the work-conjugates to plastic strain and its gradient, are then derived. It is shown that the stress and strain fields of isothermal boundary-value problems of strain gradient plasticity are independent of η, but that this factor may be of importance for non-isothermal analysis in which the dissipated plastic work acts as an internal heat source. The effects of plastic strain gradient on the plastic response of twisted hollow circular tubes made of a rigid-plastic material with different hardening properties are then evaluated and discussed.

Sectional Capacity of Circular Steel Tubes under Combined Loading

A complete equation is presented that predicts the sectional capacities of hollow circular tubes, and accounts for interactions among four (axial, bending, radial torsional moments) loading parameters. The interaction equation for the plastic failure of a circular tube including axial force, radial pressure, and torsion is derived for the von Mises criterion of yielding. Graphic representations of the equation are presented to provide insights on the member behavior and the mechanism of interactions among the loading parameters.