Torsional Response Research Articles

Torsional Behaviour of Irregular Buildings with Single Eccentricity

Torsional response in building structural systems arise from two sources: a) eccentricity between the centre of mass and centre of stiffness of vertical lateral force resisting elements and (b) accidental torsion due to the rotational component of ground motion about a vertical axis, the eccentricity between assumed and actual stiffness and mass, uncertainty in live load distribution, and uncertainty in dead loads due to variations in labour and materials. This paper addresses the effect of the ratio Ω between structure uncoupled torsional frequency (ωƟ) to uncoupled transition frequency (ωx) or (ωy), on the torsional behaviour of the structure. A parametric study is carried out using the equivalent static force (ELF) method applied to one story building with single eccentricity by examining different values of Ω. The study shows that structures with ratio Ω > 1.0 are torsionally stiff and displacements values are not sensitive to the increment in eccentricity ratio, in other words, the structure shows planer frame behaviour and the deformations are mainly transitional rather than torsional. Conversely structures with ratio Ω < 1.0 are torsionally flexible and displacements values are sensitive to increases in eccentricity ratio, therefore, the deformations are mainly torsionally twisting rather than transitional motion. It is also observed that when Ω = 1.0, no significant increase in torsional response occurs. Torsional irregularities coefficient as defined by ASCE 7-10 building code, i.e., the ratio between maximum story drift at one end of the structure to the average story drifts at the two ends of the structure, have been calculated for different values of the ratio Ω. Results shows that irregularity coefficient increases as the ratio Ω decreases. In addition, structures with Ω < 1.0 are more sensitive to the value of eccentricity between centre of mass and centre of rigidity. Subsequently irregularity coefficient increases dramatically, and excessive torsion occurs as the value of eccentricity increases for structures with ratio Ω < 1.0, while minor increment is observed on the value of irregularity coefficient when eccentricity increases. This paper discusses the significance of utilizing the frequency ratio Ω to control the torsional behaviour of building structures.

Experimental determination of the two-dimensional aerodynamic admittance of typical bridge decks

In this paper, the two-dimensional lift, drag and pitching moment aerodynamic admittances of three typical bridge deck sections, including a streamlined box section, an edge section and a truss section are identified by wind tunnel tests using a statistical identification approach and high-frequency dynamic balance measurement technique. An empirical formula for determining the two-dimensional aerodynamic admittance is proposed and compared with the commonly used Sears function and Davenport function. The results show that the two-dimensional lift and moment aerodynamic admittances for the three types of bridge decks are larger than Sears’ function in the concerned wavenumber range of the buffeting analysis. This indicates that the Sears function may underestimate the vertical and torsional buffeting response of prototype long-span bridges. The two-dimensional drag aerodynamic admittance of the truss section corresponds strongly with Davenport’s function, which verifies the reasonableness of Davenport’s function that was originally developed for the two-dimensional drag aerodynamic admittance of open lattice structures. Furthermore, it was found that the two-dimensional aerodynamic admittance is insensitive to the mean wind velocity. The effect of wind attack angle on the two-dimensional aerodynamic admittance of bridge decks cannot be neglected.

Fiber Ring Laser Directional Torsion Sensor with Ultra-Wide Linear Response.

In this paper, a comprehensive passive torsion measurement is performed firstly in a 40-cm-long polarization maintaining fiber-based Sagnac interferometer (PMF-SI), and the non-linear torsion response is found and investigated. Then, a fiber laser torsion sensor (FLTS) with a dual-ring-cavity structure is proposed and experimentally demonstrated, in which the PMF-SI is utilized as the optical filter as well as the sensing unit. In particular, the highly sensitive linear range is adjusted through fine phase modulation, and owing to the flat-top feature of fringes, an ~83.6% sensitivity difference is effectively compressed by the generated lasing. The experimental results show that, without any pre-twisting, the ultra-wide linear response from –175 to 175 rad/m is gained, and the torsion sensitivities are 2.46 and 1.55 nm/rad with high linearity (>0.99) in the clockwise and anti-clockwise directions, respectively. Additionally, a high extinction ratio (>42 dB) and small line-width (~0.14 nm) are obtained in the proposed FLTS, and the corresponding detection limit reaches 0.015 rad/m.

On the torsional vibration of nanorods surrounded by elastic matrix via nonlocal FEM

Nonlocal dynamic torsional response of nanorods embedded in elastic media is investigated. It is considered that mechanical behavior of elastic media is supposed to be like linear foundation model. The nonlocal dynamic torsion equation is obtained according to Hamilton's Principle. Application of solved motion of equation is performed for nanorod models that have torsional spring attachment at the one end as well as three different general boundary conditions. Moreover, the formulation of nonlocal finite element method (NL–FEM) based on weighted residual that considers stiffness of elastic media and attachment ratio is attained; this finite element formula is new in the literature. The nondimensional torsional frequencies are presented under nanorod length, nondimensional nonlocal parameter, slenderness ratio, nondimensional media stiffness parameter and stiffness ratio of attachment as tables and graphics comparatively with NL–FEM. This study is exhibited that NL–FEM can be used for torsional vibration analysis of nanorods embedded in elastic media.

Effect of Axial Compression and Wet Collapse Loads on Torsional Response of Flexible Pipe

Flexible pipes connect the two critical systems of the floating production platform and underwater production, which play an important role in the transportation of oil and gas as well as water injection. However, flexible pipes are often subjected to multiple loads that threaten their stability in the service process. In this study, a model of a flexible pipe containing practical cross section in all layers is established to study the effects of axial compression and wet collapse loads on clockwise and anticlockwise torsional responses. The results of calculation show that the axial compression and radial expansion of the flexible pipe are caused by the axial compression load, which reduces clockwise torsional stiffness. The wet collapse load induces the bending deformation of the flexible pipes in clockwise and anticlockwise torsion, where the bending deformation of clockwise torsion is significantly affected by the change in the Young’s modulus of the tensile armor layers. This study shows that clockwise torsional stiffness is small and exhibits a trend of axial compression. Clockwise torsion has poor stability in combination with axial compression and wet collapse loads, respectively. Therefore, to prevent instability in flexible pipes, clockwise torsion load, or which coupled with axial compression and wet collapse load, should be avoided.

Generalized Softened Variable Angle Truss Model for RC Hollow Beams under Torsion.

In recent studies, a new softened truss model called Generalized Softened Variable Angle Truss Model (GSVATM) has been proposed to compute the full torsional response of reinforced concrete (RC) rectangular solid beams under pure torsion. In this article, the GSVATM is extended to cover RC hollow beams under torsion. The modification of the calculation procedure, in order to account for the specific behavior of RC hollow beams for low loading levels, as well as the final solution procedure, is presented. The theoretical predictions from the extended GSVATM are compared with experimental results of RC hollow beams under torsion found in the literature. Good agreement is observed between the experimental and theoretical results, for both high and low loading levels.

No handedness effect on spatial orientation or ocular counter-roll during lateral head tilts.

Although vestibular inputs are bilaterally represented within the cerebral hemispheres, the higher level vestibular functions exhibit hemispheric asymmetries. Previous studies have suggested that such asymmetries are associated with handedness. Here, we studied the impact of handedness (i.e., hemispheric lateralization) on spatial orientation using a subjective visual vertical (SVV) task. We tested 22 right‐handed and 22 left‐handed subjects in upright position, during prolonged lateral head tilts of 20° (~15 min), and after the head returned to upright position. The corresponding changes in torsional eye position were measured simultaneously using video‐oculography. During lateral head tilts, both right‐ and left‐handers had initial SVV biases in the opposite direction of the head tilt (right‐handers: left tilt 3.0 ± 1.3°, right tilt −4.7 ± 1.5°; left‐handers: left tilt 3.4 ± 1.1°, right tilt −4.1 ± 1.0°). The SVV subsequently drifted in the direction of the head tilt, and there was an aftereffect in the same direction when the head was brought back upright. The ocular torsion initially changed in the opposite direction of the head tilt (right‐handers: left tilt 3.8 ± 0.4°, right tilt −3.8 ± 0.4°; left‐handers: left tilt 4.2 ± 0.5°, right tilt −4.5 ± 0.5°), and there were also drift and aftereffect in the same direction as the head tilt. The changes in upright perception and ocular torsion did not differ between right‐ and left‐handers. These findings show no functional laterality, neither in the higher level neural mechanisms that maintain spatial orientation, nor in the lower level mechanisms that generate the ocular torsion response during lateral head tilt.

Experimental studies on in-plane performance of plasterboard sheathed ceiling diaphragms

The ultimate goal of this study is to develop a model representing the in-plane behaviour of plasterboard ceiling diaphragms, as part of the efforts towards performance-based seismic engineering of low-rise light timber-framed (LTF) residential buildings in New Zealand (NZ).&#x0D; LTF residential buildings in NZ are constructed according to a prescriptive standard – NZS 3604 Timber-framed buildings [1]. With regards to seismic resisting systems, LTF buildings constructed to NZS3604 often have irregular bracing arrangements within a floor plan. A damage survey of LTF buildings after the Canterbury earthquake revealed that structural irregularity (irregular bracing arrangement within a plan) significantly exacerbated the earthquake damage to LTF buildings. When a building has irregular bracing arrangements, the building will have not only translational deflections but also a torsional response in earthquakes. How effectively the induced torsion can be resolved depends on the stiffness of the floors/roof diaphragms. Ceiling and floor diaphragms in LTF buildings in NZ have different construction details from the rest of the world and there appears to be no information available on timber diaphragms typical of NZ practice.&#x0D; This paper presents experimental studies undertaken on plasterboard ceiling diaphragms as typical of NZ residential practice. Based on the test results, a mathematical model simulating the in-plane stiffness of plasterboard ceiling diaphragms was developed, and the developed model has a similar format to that of plasterboard bracing wall elements presented in an accompany paper by Liu [2]. With these two models, three-dimensional non-linear push-over studies of LTF buildings can be undertaken to calculate seismic performance of irregular LTF buildings.

Nonlinear Dynamic Analysis on Planetary Gears-Rotor System in Geared Turbofan Engines

Rotor fatigue and gear noise triggered by nonlinear vibration are the key concerns in Geared Turbofan (GTF) engine which features a new configuration by introducing planetary gears into low-pressure compressor. A nonlinear analytical model of the GTF planetary gears-rotor system is developed, where the torsional effect of rotor and pivotal parameters from gears are incorporated. The nonlinear behavior of the model can be obtained by focusing on the relative torsional vibration responses between gear and rotor. The torsional nonlinear responses are illustrated with bifurcation diagrams, the largest Lyapunov exponents (LLE), Poincaré maps, phase diagrams and spectrum waterfall. Numerical results reveal that the gears-rotor system exhibits abundant torsional nonlinear behaviors, including multiperiodic, quasi-periodic, and chaotic motions. Furthermore, the roads to chaos via quasi-periodicity, period-doubling scenario, mutation and intermittence are demonstrated. The ring gear stiffness at a low value can propel the system into chaos. The damping may complicate the motion, i.e. the system may enter chaos with increasing damping. These results provide an understanding of undesirable torsional dynamic motion for the GTF engine rotor system and therefore serve as a useful reference for engineers in designing and controlling such system.

Pushover-Based Seismic Capacity Evaluation of Uto City Hall Damaged by the 2016 Kumamoto Earthquake

The seismic capacity of the main Uto City Hall building, which was severely damaged by the 2016 Kumamoto Earthquake, was evaluated by the proposed pushover-based procedure. In this procedure, the seismic capacity index of the building is defined as the maximum scaling factor of the seismic input, for which the local responses do not exceed their limit values. From the pushover analysis result, the displacement limit of the equivalent single-degree-of-freedom model was determined. Then, the seismic capacity index was evaluated using an equivalent linearization technique. The evaluated index was re-evaluated by considering the bidirectional excitation. The pushover analysis result revealed that the torsional response is significant in the nonlinear behavior of this building. The evaluated seismic capacity implied that some structural damages, including the yielding of the beam-column joint, may have occurred during the first earthquake on 14 April 2016.

Torsional response and Liouville anomaly in Weyl semimetals with dislocations

Weyl nodes in three-dimensional Weyl semimetals break the Liouville equation, leading to the Liouville anomaly. Here we present a new approach to derive the semiclassical action and equations of motion for Weyl fermions in the presence of electromagnetic fields and torsions from the quantum field theory: combining the Wigner transformation with band projection operation. It has been shown that the Liouville anomaly, including a new pure torsion anomaly term, a mixing term between the electromagnetic fields and torsions as well as the conventional chiral anomaly, entirely differs from the counterpart of axial gauge fields. We find various torsional responses and reproduce the chiral vortical effect and the torsional chiral magnetic effect. A new torsion modified anomalous Hall effect due to the mixing term in the Liouville anomaly is predicted and its implementation is also discussed. Therefore, our work not only provides new insights into the torsional responses for Weyl fermions but also acts as a starting point to investigate their topological responses.

Investigation of Vibration Characteristics of Titanium Wide-Chord Fan Blade

The vibration characteristics of a wide-chord fan blade affect the safety, reliability, and operability of high-bypass ratio turbofan engines. In this study, the vibration characteristics of a fan blade were investigated using numerical and experimental methods. First, the natural frequencies and mode shapes were obtained and verified. Then, the rotating speed and frequency margins were employed to analyze the stability of the blade. The critical crossings in the Campbell diagram were indicated and evaluated. Next, the strain energy density index and weaklink were used to evaluate the dangerous locations for the high-cycle fatigue characteristics of the blade. Finally, single- and multi-axis random-excitation tests were performed. Results indicated that low-order bending modes were dominant under circumferential- and axial-direction excitations, while the torsional mode response was higher under radial-direction excitation. The weaklinks for different excitation directions exhibited different characteristics. This work presents a comprehensive understanding of the fan-blade vibration and response characteristics.

Mass eccentricity effects on the torsional response of inelastic buildings

This paper investigates the role of accidental mass eccentricities on the inelastic torsional behaviour of multi-storey asymmetric buildings with a mixed type lateral load resisting system subjected to the Erzincan-1992 and Kobe-1995 ground motions. The numerical modelling results show that the effects of spatial variations of mass eccentricities are lower and smoother in the inelastic rather than the elastic state of deformation, but both the elastic and inelastic torsional response is pointing to the same optimum location of the key element for which the torsional response of the structure is minimized.

Increment Dynamic Analysis for One-Story Asymmetric Plan Systems under Hard Soil Site

Considering the multi-dimensional feature of earthquake motions and the torsion response can aggravate destroying of structure, the one-storey asymmetric plan system with three degree of freedom is established. The yield rule of this asymmetric system is determined by two-dimensional yield-surface plasticity function. Bi-directional Earthquake motion records for hard soil site are selected as the excitations of this asymmetric system. The increment dynamic analysis for this system is conducted, and increment dynamic analysis capacity curves are given in which peak ground acceleration is used as earthquake intensity parameter, the ductility factor and the maximum rotation angle are used as performance parameters, respectively. The effect of eccentricity, frequency ratio on responses of the one-storey asymmetric plan system, are analyzed based on the two types of capacity curves.

Incorporation of Torsional &amp; Higher-Mode Responses in Displacement-Based Seismic Design of Asymmetric RC Frame Buildings

Direct displacement-based design (DDBD) is currently a widely used displacement-based seismic design method. DDBD accounts for the torsional response of reinforced concrete (RC) frame buildings by using semi-empirical equations formulated for wall-type buildings. Higher-mode responses are incorporated by using equations obtained from only a few parametric studies of regular planar frames. In this paper, there is an attempt to eliminate torsional responses by proportioning frames’ secant stiffnesses so that the centers of rigidity and supported mass (the mass on and above each story) coincide. Once the torsional rotations are significantly reduced and only translational motions are achieved, higher-mode responses are included using a technique developed by the authors in their recent paper. The efficiency of the proposed design procedure in fulfilling the intended performance objective is checked by two plan-asymmetric 20-story RC frame building cases. Case-I has the same-plan configuration while Case-II has a different-plan configuration along the height. Both cases have different bay widths in orthogonal directions. Verification of the case studies by nonlinear time history analysis (NTHA) has shown that the proposed method results in designs that satisfy the performance objective with reasonable accuracy without redesigning members. It is believed that a step forward is undertaken toward rendering design verification by NTHA less necessary, thereby saving computational resources and effort.

Piles Subjected to Torsional Cyclic Load: Numerical Analysis

Pile foundations supporting large structures (such as high-rise buildings, oil drilling platforms, bridges etc.) are often subjected to eccentric lateral load (in addition to the vertical loads) due to the action of wind, waves, high speed traffic and ship impacts etc. The eccentric lateral load, which is usually cyclic (repetitive) in nature, induces torsion in the pile foundation. This paper presents a numerical model based on boundary element approach to study the performance of a single pile subjected to the torsional cyclic load. The model is initially validated by comparing it with the experimental data available from the literature. Thereafter, the model has been utilised to conduct a parametric study to understand the influence of the torsional cyclic loading parameters on the axial pile capacity. The results indicated that the model is able to capture the degradation in the axial pile capacity due to the torsional cyclic loading with a reasonable accuracy. Moreover, the parametric study showed that the frequency, amplitude and number of cycles play a significant role in the torsional cyclic response of the pile. The present study is essential for the development of design guidelines for pile foundations subjected to torsional cyclic load.

Effects of gear eccentricity on time-varying mesh stiffness and dynamic behavior of a two-stage gear system

Gear eccentricity, one of the most common defects of gear systems, affects not only dynamic behavior but also mesh stiffness. Accurate mesh stiffness under defect conditions is vital for the dynamic simulation and fault diagnosis of gear systems. Hence, the timevarying mesh stiffness affected by gear eccentricity, which is commonly neglected in most studies, is incorporated in the proposed twostage spur gear dynamic model and calculated by a novel gear mesh model with an improved potential energy method. The effects of mesh stiffness with and without gear eccentricity on the gear system are compared on the basis of the constructed dynamic model. The influences of gear eccentricity on dynamic transverse and torsional responses, as well as dynamic transmission errors, are also quantitatively studied. Some helpful analytical results are then presented.

보강된 복합재 원형 스파의 비틀림 거동

보강된 복합재 원형 스파의 비틀림 거동

Analytical and simplified models for dynamic analysis of short skew bridges under moving loads

Skew bridges induce inherently coupled bending and torsion response. The actual relevance of this coupling for the dynamic response under moving loads such as those arising in high-speed railways is not well known, introducing uncertainties unless costly three-dimensional dynamic models are used. In this work, models are developed based on beam theory and analytical extraction of vibration modes, which are both simple and fast. First, a general three-dimensional beam model is derived, involving both bending and torsional modes. In the following, a simplified beam model is proposed involving only bending modes. In both cases, the eigenfrequencies, eigenmodes and orthogonality relationships are determined analytically from the boundary conditions, and the dynamic response is obtained numerically in the time domain. Both models are validated through representative realistic examples by comparing with two types of finite element models: a stick model with three-dimensional beams and a full three-dimensional model with shell elements. Finally, parametric studies are performed with the simplified beam model for identifying parameters that influence the dynamic response under traffic loads. The results show that the degree of skewness has an important influence on the vertical displacement, but hardly on the vertical acceleration of the bridge. The torsional stiffness has a significant effect on the vertical displacement when the skew angle is large. Finally, the span length reduces the skewness effect on the dynamic behaviour of the bridge.

Torsional strengthening of reinforced concrete beams with externally bonded composites: A state of the art review

The use of externally bonded (EB) fiber reinforced composites to strengthen reinforced concrete (RC) structures has been explored extensively in recent decades. While many studies have been conducted on the flexural, shear, and axial strengthening of RC members, far fewer studies have been conducted on torsional strengthening. Thus, the knowledge on the behavior of RC members strengthened in torsion with EB composites is rather limited. The aim of this paper was to present a comprehensive review and evaluation of torsional strengthening of RC beams using EB composites. A detailed survey of the literature was conducted, and a database of experimental tests was developed. The database includes beams reinforced with EB fiber reinforced polymer (FRP) and EB fiber reinforced cementitious matrix (FRCM) composites. The effectiveness of the strengthening system was examined in terms of geometrical and mechanical characteristics of the RC beam, composite type, and composite wrapping configuration. Different modes of failure of the strengthened beams were also discussed. Additionally, analytical and numerical methods developed to predict the torsional response of RC beams strengthened with EB composites were summarized and discussed. Finally, design provisions were examined based on the knowledge gained from this study.