High Torsional Rigidity Research Articles

Buckling behavior and failure mechanism of cold-formed steel built-up special shape cross-section columns

This paper introduces a new type of cold-formed steel (CFS) built-up closed cross-section (CBC-C) column to connect multi-directional wall panels easily. Axial compression experiments and numerical analysis on 18 columns as well as theoretical calculations are carried out to evaluate the stability and bearing capacity of the proposed column. The effect of factors such as width-to-thickness, slenderness ratios, and screw spacing on the buckling behavior and failure mechanism was studied. As the slenderness ratio increased, the ultimate bearing capacity of specimens with the same section decreased. For specimens with a web width of 140 mm, the ultimate strength increased by 7.35 % when the slenderness ratio was reduced from 26.7 to 3.2. It was observed that the failure modes of short and intermediate long columns were generally local and distortion-related buckling, while the long columns experienced local, distortional, and finally global buckling when the slenderness ratio reached 36.73. The local buckling load and ultimate strength of specimens of the same length and section were reduced with the growth of the width-to-thickness ratio. On average, as the web width-to-thickness ratio increased by 10 %, the local buckling load decreased and the ultimate bearing capacity decreased by 22.37 % and 14.79 %, respectively. It was found that changing the section thickness had a greater effect on the stability and strength of the specimens compared to changing the web width of the CBC-C column. The mechanical properties of the CBC-C were not affected by the screw spacing and the differences among data were less than 5 %. Finally, the effective width method (EWM) and the direct strength method (DSM) in the AISI S100-16 wereassessed for CBC-C. The novel built-up column proposed in this paper has advantages in modular structures for their flexibility in configurations as well as high torsional rigidity and good stability.

Design and Kinematics of a Robotic Instrument for Natural Orifice Transluminal Endoscopic Surgery

Natural orifice transluminal endoscopic surgery (NOTES) has attracted continuous attention in recent decades, but its confined workspace restricts the dexterity and manipulability of instruments. Instruments with multiple degrees of freedom (DOF) and variable stiffness are desired to achieve flexible operation with sufficient load capacity. This article presents a novel robotic instrument, which can assist NOTES. The instrument is 6.5 mm in diameter with 7 DOFs. The three continuum elastic joints are made of helical springs with high torsional rigidity, whose wires have a rectangular cross section. Patterned concentric tubes are designed to change the stiffness of the force transmission structure of the passive arm so that the stability and rigidity of the instrument can be improved. Analytical solutions of inverse kinematics are obtained based on the arrangement of coupled joints designed for creating triangulation. The disk-elastomer model is established to simplify the derivation of kinematics, and the relationship between the slack of the driving cable and the joint parameters is derived. The trajectory tracking accuracy, bending accuracy, and the ability of variable stiffness of the proposed instrument are verified with experiments.

Design of aluminium Sigma sections for web crippling behaviour under Interior Two Flange (ITF) load case

AbstractAluminium sections have been emerged in the industry due to the advantages such as light weight, resistance to corrosion, recyclability, and flexibility. While the construction industry is moving towards to modular construction trend, aluminium sections are considered as a vital key to achieve the desirable outputs of modular industry. Modular industry needs high performing structural elements as well as light weight elements to reduce the overall weight of the modules which directly affects the transport cost, flexibility of the modular connections, construction duration, capacity of the equipment or machineries and required numbers of construction workers for assemble. Hence, the requirement of light weight elements is evident, and the aluminium sections have been considered to replace the conventional sections. However, the structural performance of aluminium sections has to be analysed to check the appropriateness of utilization though it is reasonable. Hence, aluminium sigma sections were selected in this study to check their performance in the web crippling scenario under Interior‐Two‐Flange (ITF) loading case. Sigma sections were opted based on the merits including high torsional rigidity and resistance towards local and distortional buckling. Appropriate numerical approach was selected, and the procedure was validated with experimental results. Accordingly, comprehensive numerical investigation was carried out by including different parameters such as depth, thickness, yield, and ultimate strength and bearing length. Subsequently, the results were compared with all critical parameters and the results were provided. Suggestions and recommendations were stated to utilise the aluminium sigma sections in the industry.

A Novel Strain Wave Gear Reducer with Double Flexsplines

Strain wave gear reducers, also known as harmonic drives, are widely used in industrial robots and collaborative robots. The zero-backlash feature is very important for these applications. However, this places extremely high demands on the machining accuracy of the strain wave gear reducer. Excessive manufacturing errors will lead to excessive backlash, affecting transmission accuracy or making installation difficult, and the flexible spline (or flexspline) is prone to wear, resulting in reduced accuracy with use. This study proposes a novel strain wave gear reducer with a double flexspline structure. The original “circular spline” which was rigid will be redesigned to be slightly flexible and deformable with an additional deformation adjustment structure, which reduces the requirements for machining accuracy, and realizes the same zero-backlash characteristic of traditional structure. The experimental results show that the new strain wave gear reducer has extremely low lost motion, hysteresis loss, and high torsional rigidity. The new strain wave gear reducer provides a more economical way to realize the zero-backlash reducer and helps to solve the problem of the accuracy decline of the strain wave gear reducer due to the wear of the flexspline.

Кинематика волновых зубчатых передач с генератором волн внешнего деформирования

The development of automatic control systems, tracking systems and industrial robotics requires the creation of new generation drive systems with high efficiency, kinematic accuracy, reliability, durability with small axial and radial dimensions and weight. To implement tracking systems with power differentials, transmission mechanisms with two degrees of freedom are required to provide the transformation and summation of two movements of drive motors into the required movement of the drive output shaft. These requirements in single-channel tracking systems are well met by strain wave gears (SWG) with low-inertia disk and ring wave generators. They allow for wide layout possibilities, the ability to route cables through the hollow central shaft of the drive, high torsional rigidity and low moments of inertia, which are in the range of 250 to 400 times less than those of cam wave generators, thus ensuring high drive speed. There are practically no publications, except domestic ones, devoted to the study of SWG with ring wave generators. This scientific direction of research is carried out at the Bauman Moscow State Technical University. Structural schemes of SWG with ring generators of external deformation waves are considered, the features of the kinematics of these gears are studied, and recommendations for improving their quality indicatorsare proposed

Time-dependent creep and shrinkage analysis of curved steel–concrete composite box beams

Curved steel–concrete composite box beams are widely used in urban overpasses and ramp bridges as they are light in weight, have large spanning ability and high torsional rigidity. One-dimensional models are generally used to analyze bridge performance due to their calculation and numerical efficiencies. An incremental step-by-step method based on the Kelvin rheological model together with a discrete algorithm in finite element space is adopted in this study to analyze the mechanical behavior of curved composite box beams. A model with a beam finite element with 26 degrees of freedom (DOFs) is proposed for curved composite box beams that considers the constrained torsion, distortion, shear lag, biaxial slip at the interface and time-dependent effects. Furthermore, the experimental results of the long-term loading tests of three curved composite box beams are selected to validate the proposed beam element model. Finally, the proposed model is applied to analyze the long-term behavior of a curved composite box beam that is used in real engineering applications.

Double-HSS Seismic Resistant Beam-to-Column Moment Connections

AbstractHollow structural sections (HSSs) are highly efficient in resisting compression, torsion, and bending. Their high torsional rigidity generally eliminates lateral-torsional buckling (LTB), w...

Seismic behavior of double-HSS links for eccentrically braced frames

This study experimentally and analytically investigates an innovative double-HSS link (DHL) used as the active link in eccentrically braced frames (EBFs). Hollow structural sections (HSS) are mechanically efficient and are used in resisting compression, torsion, and bending. Their high torsional rigidity generally eliminates lateral-torsional buckling (LTB). As a result, the plastic rotational capacity and strength degradation rate are mainly governed by flange local buckling (FLB) and web local buckling (WLB). The proposed configuration consists of a double-HSS connected to braces or columns through a center gusset plate secured by flare-bevel groove welds. The advantages of the proposed configurations are: (1) They effectively reduce the width-thickness ratios (b/t) of the flanges by using two HSSs with much shorter flanges, which considerably increases the compactness thereby enabling a large rotational capacity. (2) They provide simple and practical connection details between the link and braces or columns. (3) Typically, double-HSS sections have an e/(Mp/Vp) ratio much larger than that of wide-flange sections due to the fact that double-HSS sections have four webs which significantly increase the shear capacity. Consequently, a DHL can yield in flexure even with a length similar to that of a wide-flange shear yielding link. This in turn eliminates the need for web stiffeners. (4) The welding requirement for DHLs is less than that of the conventional shear links since no stiffeners are required. (5) The overstrength factor due to strain hardening produced by flexural yielding links is generally less than that produced by shear yielding links leading to more economical designs for the elastic portion of the frame, and (6) the iteration design process is minimized by balancing the link length and rotational demand because of a single flexural yielding mode. Furthermore, experimental and analytical results indicated that the novel DHLs can sustain larger plastic rotations and meet AISC 341′s acceptance criterion for shear yielding links. In addition, DHLs can be potentially used in D-braced EBFs with links attached to columns because the link-to-column connection of DHL remains essentially elastic. DHLs can also be used as a replaceable link which is attached to the beam and column through bolted end plates.

A Novel Fiber Bragg Grating Vibration Sensor Based on Orthogonal Flexure Hinge Structure

A novel two-dimensional (2-D) fiber Bragg grating (FBG) vibration sensor based on an orthogonal flexure hinge structure has been proposed in this paper. The elastic element of this sensor which contains an inertial body, flexure hinge pair and base has been designed in small size and integrally fabricated by using wire cutting. Two FBGs are arranged in the vertical direction by two ends pasted setup to measure the vibration-induced structure displacement. The theoretical and simulation model of the FBG vibration sensor is established. The analysis shows that this structure with a 3 mm length hinge could achieve a high working frequency and low cross-interference. The dynamic characteristics of the sensor have been measured by excitation experiments. The results match the model well that the resonant frequency of the sensor in the X and Y-directions is around 1275 Hz and 1482 Hz, respectively. The third-order natural frequency of 4932 Hz, which indicates that the sensor has high torsional rigidity and strong torsional vibration resistance. The sensor has a broad flat frequency range from 20 to 800 Hz and a sensitivity 41.2/34.5 pm/g in the X/Y-direction. The cross-interference in two directions is less than 6%. The sensor has high frequency and low cross-sensitivity, which is suitable for structural health monitoring of mechanical equipment.

Superplastic forming with diffusion bonding of titanium alloys

The ability of materials to display extensive plastic deformation at elevated temperature before permanent deformation without necking is known as super plasticity. The optimization of superplastic forming can be evaluated by application of gas pressure at elevated temperatures using hot superplastic forming set up. The diffusion bonding process involves keeping together the required titanium alloy sheets or titanium alloy with any other metal with the help of load at elevated temperatures and in an inert environment preferably in vacuum for the bonding process to complete. This method is used to eliminate many bonding defects such as distortions and cracking which can occur in conventional joining methods such as welding and brazing or riveting. The resulting micro structure at the interface can be evaluated using scanning electron microscope (SEM) photography and also the bond strength can be determined using micro hardness tester. Titanium based alloys are super- plastic in nature at elevated temperatures, and they also display exceptional mechanical properties such as a great strength to weight ratio, good fatigue life good corrosion resistance, high torsional rigidity and excellent bio compatibility. The components bonded using both super plasticity and diffusion bonding possesses high tensile strength which is makes it reliable for aerospace applications.

Effect of residual stress and geometric imperfection on the strength of steel box girders

In the recent years, steel box girder bridges have been extensively used due to high bending stiffness, torsional rigidity, and rapid construction. Therefore, researches related to this girder bridge have been widely conducted. This paper investigates the effect of residual stresses and geometric imperfections on the load-carrying capacity of steel box girder bridges spanning 30 m and 50 m. A three – dimensional finite element model of the steel box girder with a closed section was developed and analyzed using ABAQUS software. Nonlinear inelastic analysis was used to capture the actual response of the girder bridge accurately. Based on the results of analyses, the superimposed mode of webs and flanges was recommended for considering the influence of initial geometric imperfections of the steel box model. In addition, 4% and 16% strength reduction rates on the load – carrying capacity of the perfect structural system were respectively recommended for the girders with compact and non-compact sections, whose designs satisfy the requirements specified in AASHTO LRFD standard. As a consequence, the research results would help designers eliminate the complexity in modeling residual stresses and geometric imperfections when designing the steel box girder bridge.

A novel hybridized metaheuristic technique in enhancing the diagnosis of cross‐sectional dent damaged offshore platform members

AbstractOffshore jacket platforms are widely used for oil and gas extraction as well as transportation in shallow to moderate water depth. Tubular cross‐sectional elements are used to construct offshore platforms. Tubular cross sections impart higher resistance against hydrodynamic forces and have high torsional rigidity. During operation, the members can be partially or fully damaged due to lateral impacts. The lateral impacts can be due to ship collisions or through the impact of falling objects. The impact forces can weaken some members that influence the overall performance of the platform. This demonstrates an urgent need to develop a framework that can accurately forecast dent depth as well as dent angle of the affected members. This study investigates the use of an adaptive metaheuristics algorithm to provide automatic detection of denting damage in an offshore structure. The damage information includes dent depth and the dent angle. A model is developed in combination with the percentage of the dent depth of the damaged member and is used to assess the performance of the method. It demonstrates that small changes in stiffness of individual damaged bracing members are detectable from measurements of global structural motion.

Optimization of a Composite Monocoque Chassis for Structural Performance: A Comprehensive Approach

Lately, numerous studies have been performed to design composite monocoque’s with high strength and low weight for various student-level racing contests. The objective of this paper is to develop an insightful methodology to design and developed a lightweight composite monocoque. The monocoque is designed to pass the mandatory static load tests laid down by the International Automobile Federation (FIA) Formula 3. These Formula 3 tests are considered the baseline of the desired structural integrity of the composite monocoque. The presented design technique emphasizes on a monocoque developed for Sports Car Club of America races. The three standard load tests performed on the monocoque are survival cell side test, fuel tank test and side intrusion test. A sandwich layup of bidirectional-woven carbon/epoxy prepreg and aluminum honeycomb is optimized for minimum weight while predicting the unknown properties of layup, and ensuring the monocoque does not experience failure. The approach intends to achieve minimum weight with high torsional rigidity and is capable of being used for the design and analysis of any kind of formula-type composite monocoque.

Investigating the sequence-dependent mechanical properties of DNA nicks for applications in twisted DNA nanostructure design.

DNA nick can be used as a design motif in programming the shape and reconfigurable deformation of synthetic DNA nanostructures, but its mechanical properties have rarely been systematically characterized at the level of base sequences. Here, we investigated sequence-dependent mechanical properties of DNA nicks through molecular dynamics simulation for a comprehensive set of distinct DNA oligomers constructed using all possible base-pair steps with and without a nick. We found that torsional rigidity was reduced by 28–82% at the nick depending on its sequence and location although bending and stretching rigidities remained similar to those of regular base-pair steps. No significant effect of a nick on mechanically coupled deformation such as the twist-stretch coupling was observed. These results suggest that the primary structural role of nick is the relaxation of torsional constraint by backbones known to be responsible for relatively high torsional rigidity of DNA. Moreover, we experimentally demonstrated the usefulness of quantified nick properties in self-assembling DNA nanostructure design by constructing twisted DNA origami structures to show that sequence design of nicks successfully controls the twist angle of structures. Our study illustrates the importance as well as the opportunities of considering sequence-dependent properties in structural DNA nanotechnology.

Parametric Study of Stiffeners in Steel Composite Tub Girders

Closed structural sections (rectangular, circular, trapezoidal shape) possess high rotational rigidity compared to open sections like I girder. For highly curved bridges, closed sections with high torsional rigidity is an absolute choice. This paper suggests the use of steel – composite Tub girder instead of concrete I girder in rail bridges. Stiffeners were used to strengthen the girder. Deflection and stress study has been done for the entire girder on various thickness of stiffeners under different loading.

Stress Evaluation for Segmental Concrete Box Girder Diaphragm

The box girder component is a major breakthrough in the construction field for its effective geometry behavior and high torsional rigidity. However, the analysis and design of the box girder are complex due to its three dimensional behavior i.e. torsion, distortion and bending in longitudinal and transverse direction. In this paper, the use of finite element model in evaluating the stresses behavior for segmental box girder diaphragm under static loading is demonstrated. The analysis is carried out for both permanent and variable actions based on Eurocode. Parametric study is carried out to evaluate the effects of different parameters on the stress behavior for box girder. This study contributes to a better insight of the stress behavior for box girder such that, under service, the stresses developed will not contribute to significance structural cracks that will affect the serviceability of the structure.

Vibration Behavior of Gravity-Loaded Whirling Micro-Scale Shafts Influenced by an Axial Magnetic Field

Some high-speed rotating micro-machines and micro-vibration devices rely on the use of whirling micro-shafts subject to the effect of gravity and magnetic fields. At present, the consequences of the interaction between the elastic deformation of such shafts and the magnetic/gravitational field effects remain unresolved. Focusing on micro-scale whirling shafts with very high torsional rigidity, this study presents a theoretical treatment grounded in the theory of micro-continuum elasticity to examine the ramification of this interaction. The differential transformation method (DTM) is used to obtain extensive numerical results for qualitative assessments of the magnetic-gravitational effects interaction on standing, hanging and horizontally positioned spinning micro-scale shafts. The influence of bearing-support flexibility on the response of the whirling micro-shaft is also considered with rotational and translational springs. The gravitational sag reduces the stability of whirling standing micro-shafts and increases that of the hanging micro-shafts. Further, for all the micro-shafts configurations investigated, the magnetic field is observed to stiffen the response of the shaft and favorably shifts the critical points of vibration of the whirling shafts forward.

Comparison of the moment rotation capacities of rectangular and polygonal hollow sections

Thin-walled rectangular hollow sections (RHS) have very high torsional rigidity, and thus make a very economic choice for applications which are susceptible to lateral torsional buckling. However, as the depth of a thin-walled RHS increases to ensure adequate bending stiffness, its depth-to-thickness ratio increases and the section is now susceptible to web-crippling/local buckling failure. This causes a reduction in its moment rotation capacity. Therefore, deep thin-walled RHS are not efficient when used as long un-braced spans that require high bending strength and rotation capacity. As such, a new polygonal hollow section (PHS) is proposed. This paper compares the moment rotation capacities of the proposed PHS to those of typical RHS via an experimental program comprising four-point and three-point bending tests. A total of 12 bending tests were conducted and the results showed that the proposed PHS has almost four times the moment rotation capacity of a comparable RHS and the potential to minimize web-crippling failure.

Rozdział poprzeczny obciążeń ruchomych w belkowo-płytowym moście drogowym z dźwigarami kompozytowymi FRP

The paper presents an analysis of the parameters of live load transverse distribution in the span of a road bridge that is made of four box FRP composite girders and a composite deck slab made of lightweight concrete. The parameters were determined experimentally and computationally using the orthotropic plate model included in the Cusens-Pam solution and also the numerical FEM model. The measured values of load transverse distribution factors and influence lines were determined during bridge load testing. A comparison of the measured and calculated load transverse distribution factors is shown on the basis of the analysis of the girders' deflection in their cross-section in the middle of the bridge span. As a result of this comparison, it was proved that the analytical model of the orthotropic plate and also the numerical shell-solid FEM model have a high compliance of load transverse distribution with the distribution obtained from the measurements. In addition, computational analysis and tests showed a sufficient flexural rigidity and high torsional rigidity of the bridge span (the bridge construction belongs to a group of structures with a low overall rigidity of k = 300 kN/mm), confirming that the FRP composite girders that were used for its construction can be an alternative to the concrete and steel girders that are commonly used in the construction of bridges.

Torsional rigidity of harmonic gear drives

A model is proposed for harmonic gear drives. The model takes into account that harmonic engagement involves multiple pairs and multiple zones and also takes account of the manufacturing and assembly errors, the deformation of the drive components, and the adjustment of the gaps in the engagement under load. By means of the model, harmonic gear drives with high torsional rigidity may be designed.