Showing papers on "Bending moment published in 2011"

A novel type of angle steel buckling‐restrained brace: Cyclic behavior and failure mechanism

Abstract: A novel type of angle steel buckling-restrained brace (ABRB) has been developed for easier control on initial geometric imperfection in the core, more design flexibility in the buckling restraining mechanism and easier assembly work. The steel core is composed of four angle steels to form a non-welded cruciform shape restrained by two external angle steels, which are welded longitudinally to form an external tube. Component test was conducted on seven ABRB specimens under uniaxial quasi-static cyclic loading. The test results reveal that the consistency between the actual and design behavior of ABRB can be well achieved without the effect of weld in the core. The ABRBs with proper details exhibited stable cyclic behavior and satisfactory cumulative plastic ductility capacity, so that they can serve as effective hysteretic dampers. However, compression–flexure failure at the steel core projection was found to be the primary failure mode for the ABRBs with hinge connections even though the cross-section of the core projection was reinforced two times that of the yielding segment. The failure mechanism is further discussed by investigating the Nu– Mu correlation curve. It is found that the bending moment response developed in the core projection induced by end rotation was the main cause for such a failure mode, and it is suggested that core projection should be kept within elastic stage under the possible maximum axial load and bending moment response. Copyright © 2010 John Wiley & Sons, Ltd.

Dynamics and stability of transverse vibrations of nonlocal nanobeams with a variable axial load

Abstract: This paper investigates the natural frequency, steady-state resonance and stability for the transverse vibrations of a nanobeam subjected to a variable initial axial force, including axial tension and axial compression, based on nonlocal elasticity theory. It is reported that the nonlocal nanoscale has significant effects on vibration behavior, which results in a new effective nonlocal bending moment different to but dependent on the corresponding nonlocal bending moment. The effects of nonlocal nanoscale and the variation of initial axial force on the natural frequency as well as the instability regions are analyzed by the perturbation method. It concludes that both the nonlocal nanoscale and the initial tension, including static and dynamic tensions, cause an increase in natural frequency, while an initial compression causes the natural frequency to decrease. Instability regions are also greatly influenced by the nonlocal nanoscale and initial tension and they become smaller with stronger nonlocal effects or larger initial tension.

Analytical solutions for vibration of simply supported nonlocal nanobeams with an axial force

Abstract: This paper presents exact, analytical solutions for the transverse vibration of simply supported nanobeams subjected to an initial axial force based on nonlocal elasticity theory. Classical continuum theory is inherently size independent while nonlocal elasticity exhibits size dependence. The latter has significant effects on bending moment, which results in a conceptually different definition of a new effective nonlocal bending moment with respect to the corresponding classical bending moment. A sixth-order partial differential governing equation is subsequently obtained. The effects of nonlocal nanoscale on the vibration frequencies and mode shapes are considered and analytical solutions are solved. Effects of the nonlocal nanoscale and dimensionless axial force including axial tension and axial compression on the first three mode frequencies are presented and discussed. It is found that the nonlocal nanoscale induces higher natural frequencies and stiffness of the nano structures.

Aeroelastic properties of backward swept blades

Abstract: It is investigated how the nonlinear geometric coupling between torsion and flapwise bending of backward swept blades affects their static and dynamic aeroelastic properties. A geometrically nonlinear co-rotational finite beam element formulation coupled with the Blade Element Momentum method is used to compute the steady state blade deflection and aerodynamic power and thrust (assuming uniform wind and neglecting tower shadow and gravity effects) of a blade with different backward sweep shapes. A linearization of this aeroelastic model with the addition of an unsteady aerodynamic model is used to compute frequencies, damping and mode shapes of the aeroelastic blade modes from eigenvalue analysis, and to compute the transfer function from mean wind speed variations to variations in the blade root bending moments. Using the blade of the 5 MW NREL reference turbine as a baseline, it is shown that the backward sweep creates torsion towards feathering for downwind flapwise defl ection in thefirst flapwise bending mode. This torsional component is shown to cause the frequency of the first aeroelastic flapwise bending mode to increase compared to the frequency of the corresponding structural mode, and this increase becomes larger for larger sweep. The frequency response of the flapwise blade root moment from wind excitation is shown to decrease below the increased first flapwise frequency which explains the reduced flapwise loads found in previous studies of backward swept blades. Computations of the classical flutter speed show that it decreases with the backward sweep.

Friction modeling in concentric tube robots

Abstract: Concentric tube robots are a novel class of continuum robots that are constructed by combining precurved elastic tubes such that the overall shape of the robot is a function of the relative rotations and translations of the constituent tubes. Frictionless kinematic and quasistatic force models for this class of robots have been developed that incorporate bending and twisting of the tubes. Experimental evaluation of these models has revealed, however, a directional dependence of tube rotation on robot shape that is not predicted by these models. To explain this behavior, this paper models the contributions of friction arising from two sources: the distributed forces of contact between the tubes along their length and the concentrated bending moments generated at discontinuities in curvature and at the boundaries. It is shown that while friction due to distributed forces is insufficient to explain the experimentally observed tube twisting, a simple model of frictional torque arising from concentrated moments provides a good match with the experimental data.

The Peeling Behavior of Thin Films with Finite Bending Stiffness and the Implications on Gecko Adhesion

Abstract: Analytical thin film peeling models, such as the Kendall model, are formulated under restricting assumptions concerning the strip geometry, the material behavior, the peeling kinematics, and the contact behavior. Recently, such models have been applied to study the peeling of gecko spatulae, although the gecko spatula is significantly different from an idealized thin film. The bending stiffness of the spatula especially has a strong influence on the peeling force which is neglected in the Kendall model. This is demonstrated here by several detailed finite element computations, based on a geometrically exact deformation model and a refined contact description for van der Waals adhesion. Therefore, the peeling of an elastic strip is considered and the influence of the bending stiffness is studied. It is shown that the adhesion induces a bending moment within the strip that can become very large and must, therefore, be accounted for in the strip formulation and evaluation of the work of adhesion. Further, th...

Bearing capacity and technical advantages of composite bucket foundation of offshore wind turbines

Abstract: Based on mechanical characteristics such as large vertical load, large horizontal load, large bending moment and complex geological conditions, a large scale composite bucket foundation (CBF) is put forward. Both the theoretical analysis and numerical simulation are employed to study the bearing capacity of CBF and the relationship between loads and ground deformation. Furthermore, monopile, high-rise pile cap, tripod and CBF designs are compared to analyze the bearing capacity and ground deformation, with a 3-MW wind generator as an example. The results indicate that CBF can effectively bear horizontal load and large bending moment resulting from upper structures and environmental load.

Application of nonlocal beam models to double-walled carbon nanotubes under a moving nanoparticle. Part I: theoretical formulations

Abstract: The current work suggests mathematical models for the vibration of double-walled carbon nanotubes (DWCNTs) subjected to a moving nanoparticle by using nonlocal classical and shear deformable beam theories. The van der Waals interaction forces between atoms of the innermost and outermost tubes are modeled by an elastic layer. The equations of motion are derived for the nonlocal double body Euler–Bernoulli, Timoshenko and higher-order beams connected by a flexible layer under excitation of a moving nanoparticle. Analytical solutions of the problem are provided for the aforementioned nonlocal beam models with simply supported boundary conditions. The dynamical deflections and nonlocal bending moments of the innermost and outermost tubes are then obtained during the courses of excitation and free vibration. Finally, the critical velocities of the moving nanoparticle associated with the nonlocal beam theories are expressed in terms of small-scale effect parameter, geometry, and material properties of DWCNTs.

Hysteretic shear–flexure interaction model of reinforced concrete columns for seismic response assessment of bridges

Abstract: This paper presents the methodology, model description, and calibration as well as the application of a coupled hysteretic model to account for nonlinear shear–flexure interactive behavior of RC columns under earthquakes, a critical consideration for seismic demand evaluation of bridges. The proposed hysteretic model consists of a flexure and a shear spring coupled at element level, whose nonlinear behavior are governed by the primary curves and a set of loading/unloading rules to capture the pinching, stiffness softening, and strength deterioration of columns due to combined effects of axial load, shear force, and bending moment. The shear–flexure interaction (SFI) is considered both at section level when theoretically generating the primary curves and at element level through global and local equilibrium. The model is implemented in a displacement-based finite element framework and calibrated against a large number of column specimens from static cyclic tests to dynamic shake table tests. The numerical predictions by the proposed model show very good agreement with experimental data for both flexure- and shear-dominated columns. The application of the proposed model for seismic assessment of bridges has been successfully demonstrated for a realistic prototype bridge. The factors affecting the SFI and its significance on bridge system response are also discussed. Copyright © 2010 John Wiley & Sons, Ltd.

A Zero-Stiffness Elastic Shell Structure

Abstract: A remarkable shell structure is described that, due to a particular combination of geometry and initial stress, has zero stiffness for any finite deformation along a twisting path; the shell is in a neutrally stable state of equilibrium Initially the shell is straight in a longitudinal direction, but has a constant, nonzero curvature in the transverse direction If residual stresses are induced in the shell by, for example, plastic deformation, to leave a particular resultant bending moment, then an analytical inextensional model of the shell shows it to have no change in energy along a path of twisted configurations Real shells become closer to the inextensional idealization as their thickness is decreased; experimental thin-shell models have confirmed the neutrally stable configurations predicted by the inextensional theory A simple model is described that shows that the resultant bending moment that leads to zero stiffness gives the shell a hidden symmetry, which explains this remarkable property

Investigating new symmetry classes in magnetorheological elastomers: cantilever bending behavior

Abstract: This work defines and examines four classes of magnetorheological elastomers (MREs) based upon permutations of particle alignment‐magnetization pairs. Particle alignments may either be unaligned (e.g. random) or aligned. Particle magnetizations may either be soft-magnetic or hard-magnetic. Together, these designations yield four material types: A‐S, U‐S, A‐H, and U‐H. Traditional MREs comprise only the A‐S and U‐S classes. Samples made from 325-mesh iron and 40 μm barium hexaferrite powders cured with or without the presence of a magnetic field served as proxies for the four classes. Cantilever bending actuating tests measuring the magnetically-induced restoring force at the cantilever tip on 50 mm × 20 mm × 5 mm samples yielded ∼350 mN at μ0 H = 0.09 T for classes A‐H, A‐S, and U‐S while class U‐H showed only ∼40 mN. Furthermore, while classes U‐S and A‐S exerted forces proportional to tip deflection, they exerted no force in the undeformed state whereas class A‐H exerted a relatively constant tip force over its entire range of deformation. Beam theory calculations and models with elastic strain energy density coupled with demagnetizing effects in the magnetic energy density were used to ascertain the magnitude of the internal bending moment in the cantilever and to predict material response with good results. This work highlights the ability of the newly developed A‐H MRE materials, and only that material class, to operate as remotely powered bidirectional actuators. (Some figures in this article are in colour only in the electronic version)

Bolted steel connections with 3-d jacket plates and tension rods

Abstract: This new versatile steel connection has three unique features: (1) utilizes three dimensional connection plates in a simple and consistent manner, and is suitable for all possible connection type that is made of steel W-sections; (2) uses through the depth steel rods, coupled with typical web stiffeners to transfer shear and bending moment across the connection. The shear transfer mechanism is similar to stirrups in reinforced concrete beams; (3) all components and parts can be prefabricated in shop, and conveniently bolted together at field. The merits of the connections include higher strength and ductility, stronger yet simpler connections, higher quality, small components for easy storage and transportation. In one word, it eliminates all of the inherent drawbacks and problems of conventional bolted and/or welded connections.

Application of nonlocal beam models to double-walled carbon nanotubes under a moving nanoparticle. Part II: parametric study

Abstract: The capabilities of the proposed nonlocal beam models in the companion paper in capturing the critical velocity of a moving nanoparticle as well as the dynamic response of double-walled carbon nano- tubes (DWCNTs) under a moving nanoparticle are scrutinized in some detail. The role of the small-scale effect parameter, slenderness of DWCNTs and velocity of the moving nanoparticle on dynamic deflections and nonlocal bending moments of the innermost and outermost tubes as well as their maximum values are then investigated. The results reveal that the critical velocity increases with the slenderness of DWCNTs and the magnitude of the van der Waals interaction force. Nevertheless, the critical velocity generally decreases with the small-scale effect as well as the ratio of the mean diameter to the thickness of the innermost tube. Additionally, the predicted maximum dynamic deflections and nonlocal bending moments of the innermost and outermost tubes by using the nonlocal Euler-Bernoulli and Timoshenko beam theories are generally the lower and upper bounds of those obtained by the nonlocal higher-order beam theory (NHOBT). In the case of λ1 < 20, the use of the NHOBT is highly recommended for more realistic prediction of dynamic response of DWCNTs under a moving nanoparticle.

Solution of Shear Wall Location in Multi­Storey Building

Abstract: Shear wall systems are one of the most commonly used lateral-load resisting systems in high-rise buildings. Shear walls have very high in-plane stiffness and strength, which can be used to simultaneously resist large horizontal loads and support gravity loads, making them quite advantageous in many structural engineering applications. There are lots of literatures available to design and analyse the shear wall. However, the decision about the location of shear wall in multi-storey building is not much discussed in any literatures. In this paper, therefore, main focus is to determine the solution for shear wall location in multi-storey building based on its both elastic and elasto-plastic behaviours. An earthquake load is calculated and applied to a building of fifteen stories located in zone IV. Elastic and elasto-plastic analyses were performed using both STAAD Pro 2004 and SAP V 10.0.5 (2000) software packages. Shear forces, bending moment and story drift were computed in both the cases and location of shear wall was established based upon the above computations.