Simplified procedures for vibration serviceability analysis of footbridges subjected to realistic walking loads

This paper deals with the vibration serviceability analysis of footbridges subjected to realistic pedestrian traffic conditions, based on a probabilistic characterization of pedestrian-induced forces. The dynamic response to three different loading conditions is analysed through a non-dimensional approach, which permits the identification of the essential non-dimensional parameters governing the dynamic behaviour. Two simplified procedures are then proposed, founded on the sound definition of two coefficients, the Equivalent Amplification Factor and the Equivalent Synchronization Factor, which allow the evaluation of the vibration serviceability without requiring numerical analyses. Final applications confirm the efficiency of the proposed methods.     

母杜柴登矿立井井塔结构振动分析

母杜柴登矿立井井塔在68.37m楼层上安装有一套提升系统,当提升机组以13m/s全速运转时,井塔第7层西区楼板的中部及第6层南区、北区楼板的中部楼板体系产生了较大的振动。针对上述问题,采用振动动态测试方法对提升机组、井塔不同位置的时域和频域信号进行了测量和分析,结果表明,井塔第6层、第7层楼板的自振频率非常接近提升机组电动机的固有振动频率(22.1Hz),需调整提升设备的动力系统或井塔的第6层、第7层楼板体系的刚度,避免提升机-井塔结构耦合体系发生共振;随着提升速度的增加,第6层、第7层楼板的振动烈度逐渐变大,需提高提升设备机座与基梁间的装配精度,降低楼板振动位移。     

Dynamic response of orthotropic curved bridge decks due to moving loads

The dynamic response of horizontally curved bridge decks simply supported along the radial edges under the action of the moving vehicle is investigated. The bridge deck is idealised as a number of finite strips with orthotropic elastic properties. The stiffness and mass matrix of an individual element were derived using a homogeneous differential equation of an orthotropic plate in polar co-ordinates. The vehicle is idealized as a sprung mass moving at a constant speed in a circular path parallel to the central line of the bridge. The unsprung mass of the vehicle is assumed to be always in contact with the bridge surface during its motion. Viscous damping is taken into account for both bridge and vehicle. Dynamic deflections and moments are presented for the mid-point of the bridge deck and the values have been compared with the available analytical solution.     

Finite difference analysis of plate response to random loads

The application of the finite difference method to analyse the response of plates subjected to stationary random loading is presented. The discrete forced dynamical system generated by the finite difference approximations is analysed by a generalised harmonic analysis. The power spectral density (PSD) for displacement at each node is calculated directly for particular frequencies and subsequently these PSDs are integrated numerically over the frequency range to yield the mean square response. Both viscous and structural damping have been considered. For illustrative purposes the random excitation is taken to be clipped white noise with uniform spatial correlation. To validate the numerical procedure, further verification was obtained by comparing the numerical results with an analytic and with another numerical solution.     

Nonlocal thermoelastic model for temperature-dependent thermal conductivity nanobeams due to dynamic varying loads

Microsystem Technologies - The present paper produces a new nonlocal model for thermoelastic nanobeams of temperature-dependent thermal conductivity. A nanobeam excited by harmonically varying heat...     

Simulation of inelastic deformation in road structures due to cyclic mechanical and thermal loads

The paper presents modeling and simulation of inelastic deformation in road structures leading to rutting. Two material models, one for asphalt-concrete and another for unbound materials, have been calibrated to laboratory test data. The models account for the time and temperature dependent deformation of the asphalt-concrete as well as the friction and cyclic compaction of the unbound layers. The models have been used in simulations of a complete road structure exposed to cyclic mechanical and thermal loads. The simulation results are qualitatively similar to the rutting observed in reality. The simulations can either trace the complete history of the individual load cycles, or can be performed to directly obtain the accumulated effect after a certain number of load cycles. This makes it possible to get quickly the result due to a large number of loadings as desired in engineering design practice.     

Numerical analysis of anisotropic rotational shells subjected to nonsymmetric loads

Through the use of an integral transform, the present paper extends the applicability of the multisegment numerical integration technique to include the solution of general macroscopically anisotropic multilayered shells of revolution. It is found that compared with orthotropic shells, material anisotropy induces a doubling in the number of transformed fundamental equations characterizing the static response. Employing the transform together with the multisegment integration technique and several concepts from the direct stiffness method of structural analysis, procedures are developed which can handle branched anisotropic multilayered shells of revolution in a more effective manner than was previously possible. Based on the procedures outlined in the paper, numerical studies are presented which show the effect of segment size on the solution accuracy and the effects of material anisotropy on selected shell configurations.     

The estimation and control of terrestrial inertial navigation system errors due to vertical deflections

Deflections of the vertical introduce errors into terrestrial inertial navigation systems. In many situations, these errors prove to be intolerable. However, if vertical deflection data are available prior to a mission, this information can in principle be used to reduce the navigation system errors. It is assumed that measurements of vertical deflections plus noise are available at equally spaced points on a square grid. The accuracy to which the Schuler loop errors can be controlled, given this set of measurements, is bounded by the accuracy to which the uncontrolled Schuler loop errors can be estimated given the same set of measurements. Thus lower bounds on the accuracy of the compensated system may be established by obtaining the optimal error covariances of the equivalent estimation problem. It is shown that the estimation problem can be modeled as a linear smoothing problem if the vehicle travels at a constant heading and at a constant velocity. The appropriate error covariances are found using the known techniques of optimal linear estimation theory, Kalman filtering and smoothing, both at and between the grid points.     

Recent advances in maneuver loads analysis

The conceptual design of an aircraft system requires a number of analysis cycles involving the study of various configurations for which aerodynamic and structural properties are not well defined. The aeroelastic stability and structural strength considerations are very important factors in the determination of the aerodynamic and the structural configurations. Therefore, this paper briefly reviews the specifications leading to the design loads criteria and the current analysis methods. Suggestions for research activities required in the development of a computational fluid dynamics (CFD) code and its application to predict the design loads are also included.     

Postbuckling analysis of functionally graded plates subject to compressive and thermal loads

Postbuckling analysis of functionally graded ceramic–metal plates under edge compression and temperature field conditions is presented using the element-free kp-Ritz method. The first-order shear deformation plate theory is employed to account for the transverse shear strains, and the von Kármán-type nonlinear strain–displacement relationship is adopted. The effective material properties of the functionally graded plates are assumed to vary through their thickness direction according to the power-law distribution of the volume fractions of the constituents. The displacement fields are approximated in terms of a set of mesh-free kernel particle functions. Bending stiffness is estimated using a stabilised conforming nodal integration approach, and, to eliminate the membrane and shear locking effects for thin plates, the shear and membrane terms are evaluated using a direct nodal integration technique. The solutions are obtained using the arc–length iterative algorithm in combination with the modified Newton–Raphson method. The effects of the volume fraction exponent, boundary conditions and temperature distribution on postbuckling behaviour are examined.     

Flow due to a sink near a vertical wall, in infinitely deep fluid

Flow caused by a point sink in an otherwise stagnant fluid is studied using numerical methods based on integral-equation techniques and an asymptotic solution for small Froude number. There is a vertical wall present on a plane close to the sink, so that the flow is fully three dimensional. The fluid is of infinite depth, but a free-surface bounds it above. Steady solutions are presented for various Froude numbers and distances of the source from the wall. It is shown that the numerical results and asymptotic formula are in good agreement for small Froude numbers, but the results suggest that the non-linear solution ultimately forms some limiting structure at sufficiently large Froude number.     

Vibration analysis of waffle floors

Two-way grillage or waffle floors are used extensively in semiconductor factories as they provide high impedance mounts for manufacturing equipment that is extremely vibration sensitive. This paper presents a mathematical model for the analysis of vibration at the center of a bay and the transmission of vibration along a waffle floor. The mathematical model is compared with finite element models and experimental results from several manufacturing buildings, and shows good agreement. Trends are shown for the displacement and resonance frequency of the floor as the thickness of the floor, size of the bays and the stiffness of the columns are varied.     

Elasto-plastic analysis of axisymmetric structures subject to arbitrary loads by hybrid-stress finite elements

A semi-analytic finite element method in conjuction with a hybrid-stress functional based on the initial stress approach is presented for elasto-plastic analysis. A three-dimensional solid element based on hybrid-stress model is also implemented for the elasto-plastic analysis. A procedure to compute the non-linear effects in terms of Fourier series in the hybrid-stress model is described. The accuracy and efficiency of the semi-analytic method is evaluated via numerical examples by comparing the solution with a full 3-D solution. The semi-analytic method is observed to be a viable alternative to 3-D analysis in elasto-plastic analysis of axisymmetric structures subject to arbitrary loads.     

Vibration response due to lateral tape motion and impulse force in a linear tape drive

Next-generation, high track-density linear tape drives will require improved tape guiding and dimensional stability in order to achieve better performance and higher storage capacities. Drive vibrations, tape degradation, debris formation, and tape guiding all contribute to unwanted lateral tape motion, which can lead to write errors on the tape. Collisions between the guide and tape edge can be simulated as single-impact events by dropping a mass onto a lever situated below the bottom tape edge. The objective of this study is to evaluate the frequency content of measured lateral tape motion under various operating conditions. The effect of impact location and impulse energy is investigated in a static test where the tape drive is not in operation (tape is stationary). Next, a dynamic test is performed to study the effects of tape speed, tape tension, impact energy, and tape thickness. Finally a durability wear test is conducted to determine the effects of cycling up to 5000 cycles. Lateral tape motion is recorded and the power spectrum density of the signal is determined for each test. Additionally, optical microscopy is employed to quantify the quality of the tape edge after wear testing to investigate any correlation between tape wear and frequency analysis.Financial support for this study was provided in part by the membership of the Nanotribology Laboratory for Information Storage and MEMS/NEMS (NLIM) and Imation Corp.-Advanced Technology Program (Program Manager, Ted Schwarz, Peregrine Technology, St. Paul MN), National Institute of Science and Technology, as part of Cooperative Agreement 70NANB2H3040. The authors thank Richard E. Jewett and Todd L. Ethen of Imation Corp. for beneficial discussions throughout the study. The authors also thank Dr. Anton Goldade of Maxtor Corp. for invaluable advice, insight, and assistance throughout the study. The authors finally thank Walter Hansen, Steve McDonough, Shashank Aggarwal, and Tony Alfano of NLIM for various beneficial discussions and data processing skill.     

Vibration analysis of composite plate wing

Vibration characteristics, including natural frequencies and mode shapes for various shaped composite wings, are evaluated using finite elements based on the shear deformable theory. The present analysis gives the influence of the sweep angle, the fiber orientation, the aspect ratio, and the taper ratio of a composite wing on the vibration properties. Natural frequencies have been obtained for a composite wing which has symmetric stacking sequences of laminates. Frequency closeness phenomena of different modes can be observed for the negative fiber angles. The present analysis uses eight-node quadrilateral elements which provide very accurate results.     

Vibration analysis of cable-driven parallel manipulators

A cable-driven parallel manipulator is a manipulator whose end-effector is driven by a number of parallel cables instead of rigid links. Since cables always have more flexibility than rigid links, a cable manipulator bears a concern of possible vibration. Thus, investigation of vibration of cable manipulators caused by cable flexibility is important for applications requiring high system stiffness or bandwidth. This paper provides a vibration analysis of general 6-DOF cable-driven parallel manipulators. Based on the analysis of the natural frequencies of the multibody system, the study demonstrates that a cable manipulator can be designed stiff enough for special applications like the cable-manipulator based hardware-in-the-loop simulation of contact dynamics. Moreover, under an excitation, a cable may vibrate not only in its axial direction, but also in its transversal direction. The paper also analyzes the vibration of cable manipulators caused by cable flexibilities in both axial and transversal directions. It is shown that the vibration of a cable manipulator due to the transversal vibration of cables can be ignored comparing to that due to the axial flexibility of cables.     

Low cost analysis of building frames for lateral loads

A new rational method for the analysis of plane frame by microcomputer is presented. The distribution of the vertical and rotational displacements at the nodes of a story is characterised by the concept of distribution factors which are relative nodal displacements. The distribution factors are allowed to vary from floor to floor and are determined by using three floors at a time. These are calculated once only for floors having identical members. By means of the distribution factors, the number of degrees of freedom is reduced to three at any one floor. Therefore, it is possible for a micro—computer to handle a large number of stories without difficulty. The resulting displacements and internal forces compared very well with full finite element analyses for a number of cases even with sudden changes of stiffness. The method should find applications in other regular structures with arbitrary stiffness distributions.     

Finite element analysis of multi-level interconnection under cyclic thermomechanical loads

Microsystem Technologies - In manufacturing processing, using copper wire for connecting each micro-device and constructing logical circuit to reduce RC time delay is a major technique. However,...