Performance of a Tied-Arch Reinforced Concrete Railway Bridge: Rating, Safety Assessment, and Bond Length Evaluation

This study presents investigations regarding visual inspection, dynamic testing, and finite-element modeling of an approximately 80-year old reinforced concrete tied-arch railway bridge that is still in service in Turkey. Investigations were conducted as part of a systematic periodic inspection along Ankara-Zonguldak railway line. The bridge is subject to heavy freight trains with increasing axle loads. Field tests such as material tests and dynamic tests were used to calibrate the finite-element model of the bridge. Detailed information regarding testing and model updating procedure is given. Based on test results, computer model was refined. The calibrated model of the bridge structure was then used for structural assessment and evaluation. Despite sufficient overall safety, local details were found to be problematic. Due to insufficient bond length in hanger-to-arch connection, a strengthening scheme using steel channel sections was proposed.     

Magnetic Properties of Zn1?x Ni x O (0.25≤x≤ 0.50) Prepared by Solid-State Reactions

In this study the origin of ferromagnetism in ZnO-based bulk systems has been investigated using Ni-doped ZnO samples, Zn_1−x Ni _x O with 0.25≤x≤0.50, prepared by solid-state reactions. The structural characterizations indicated that the Ni²⁺ ions almost uniformly distributed in all the samples, and the samples have hexagonal wurtzite structure; however, when x is increased toward 0.50, a new NiO phase is formed. A ferromagnetism (FM) has been observed for all the samples at and below the room temperature. In other words, the room temperature results of (M–H) curves show that the FM observed is intrinsic for all the Ni-doped ZnO samples. However, the saturated magnetizations decrease gradually with increasing Ni concentration. This indicates that, in addition to FM, the excessive doping of Ni in ZnO also causes an antiferromagnetic (AFM) contribution which increases with increasing Ni amount. This result is also supported by the magnetization against temperature measurements. Furthermore, the trend of the ac-susceptibility (χ) versus temperature curves, measured under an ac-magnetic field of 100 Oe, also support our conclusion about the antiferromagnetic contribution to ferromagnetism in our samples.     

A note on conservation principles in classical mechanics

Summary In the following we examine the notion of conserved quantities in problems of elastostatics and elastodynamics. We show that the well known formulation which leads toT+V=Constant can be generalised yielding conservation properties to some new and at times unexpected quantities. These new conservation properties may at times be the only means for verifying results obtained by numerical techniques.     

In-plane vibration of plates by continuous mass matrix method

The continuous mass matrix method derived for frameworks is extended to the analysis of in-plane vibration of plates. A continuous mass distribution which is the same as the actual mass distribution of the plate is considered over each rectangular finite element. Taking into account that the rigid body movement produces inertial forces in dynamic analysis for a rectangular plate element eight independent conditions are provided to satisfy eight independent freedoms. Each condition is obtained from an independent displacement distribution satisfying the equations of motion at any point of the element and not only at the nodes of the rectangle. The dynamic element stiffness matrix thus obtained is a function of the natural circular frequency. The limit of the dynamic element stiffness matrix when the value of the natural circular frequency tends to zero is the static, stress compatible element stiffness matrix. The analysis of plates under forcing forces is performed by modal analysis after the natural circular frequencies and the corresponding modal shapes have been obtained from the free vibrations, for all the forcing forces are assumed to be function of the same time variation. Otherwise one must recur to a numerical analysis. The effect of the sizes, number of the meshes, the additional static load on the plate and the rigidity of the boundaries on the vibration of the plate is discussed. Few example problems are solved in order to illustrate the above mentioned effects. The numerical results obtained by continuous mass matrix method are compared with those of consistent mass matrix method. The convergence in terms of the sizes of meshes and the limit of convergence are examined.     

Dynamics of frameworks by continuous mass method

The continuous mass matrix method has been extended to include the forced vibration in the dynamic analysis of plane and space frameworks. The forcing forces may be continuous of discontinuous functions of time but all the forcing forces acting simultaneously on a framework must have the same time variation in order that the modal analysis can be applied. The damping has been neglected. The concept of code numbers in the case of static loading has been extended to the dynamics of structures. The validity of the two orthogonality conditions of the modal shapes has been proved for the continuous mass matrix method so that the modal analysis could be applied easily. The set of simultaneous equations of motion has been converted to equivalent one-degree-of-freedom systems. In the case where the forcing forces have different time variation functions a numerical analysis can be performed. Illustrative sample problems have been solved and the results are given in tabular form.     

Nonlinear free bending vibrations of plates

A general solution for the Helmholtz differential equations is obtained in the complex domain and applied to the nonlinear, free, bending vibrations of plates. The analysis is based on the decoupled nonlinear von Karman field equations by Berger assumption for the large deformations of plates. The decoupled differential equation in terms of the deflection function is a fourth order Helmholtz differential equation. Its solution, called the dynamic deflection function, is obtained in the complex domain by means of newly defined first and second kind and modified Bessel functions. The dynamic deflection function can be applied to any plates having any shape and any boundary condition under any arbitrary dynamic loads. For plates with smooth boundary, the parameters of the dynamic deflection function are determined from the boundary conditions of the plates and the initial conditions of the vibrations. The analyses of plates with piece-wise smooth boundaries are obtained on the mapped planes. The nonlinear, free vibration of circular plates are investigated by the dynamic deflection function. The effect of stretching on the natural circular frequencies are illustrated.     

Estimation and evaluation of sub-bands on LF and HF base-bands in HRV for Ventricular Tachyarrhythmia patients

Heart Rate Variability (HRV) is an efficient tool for assessment of Sympathovagal Balance (SB) and classification of cardiac disturbances. However, its index may be not enough for classification and evaluation of some disease. This study presents 32 new sub-bands over LF and HF base-bands that are accepted in the literature. Moreover, it determines dominant sub-bands over both base-bands in VTA database. These sub-bands are obtained using Wavelet Packet Transform (WPT) and evaluated using Multilayer Perceptron Neural Networks (MLPNN). Results are compared with obtained results from normal datasets. The domination effects of these sub-bands are assessed according to comparison of each other related to MLPNN training and test accuracy percentages by selecting different width of windows. As a result, obtained results showed that the LF zone including LF₁, LF₂ and LF₃ sub-bands on 0.0390625–0.0859375 Hz frequency range is the most dominant over the LF base-band and, the HF zone including HF1, HF2 and HF3 on 0.1953125–0.28125 Hz frequency range is the most dominant over the HF base-band. In normal datasets, distinctive domination effect has not been determined.     

Dominancy of antiferromagnetism in Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Co<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O diluted magnetic semiconductors

The outline of magnetic interactions in DMSs was determined using Zn_1−x Co _x O particles, where “x” was changed as 0.01, 0.05, 0.10, 0.15, and 0.20. The syntheses were accomplished though mechanical milling and thermal treatment, known as solid state reaction. The formation of each synthesis was monitored by differential thermal and thermo gravimetric methods (DT-TGA). Substitution of Co²⁺ ions with Zn²⁺ host atoms in a ZnO lattice was analyzed using X-ray diffraction (XRD) patterns, Fourier transform infrared (FT-IR) spectroscopy, energy dispersive X-ray spectrometry (EDS) data, transmission electron microscopy (TEM) figures, scanning area electron diffraction (SAED) patterns, and X-ray photo spectroscopy (XPS) spectrum. The measured Co contents in ZnO lattice were found to be ~0.7% less than the expected result. In addition to Zn_1−x Co _x O particles, tungsten (W) contaminations were noticed in the variations of 1.5 ± 0.2%, as originating from the abrasion between the miller and balls. The progressive replacement of Co²⁺ with Zn²⁺ host ions in ZnO lattice from 1% to 20% decreased the band edge from 3.03 ± 0.01 eV to 2.95 ± 0.01 eV, respectively. Co doping has also changed the magnetic nature of the ZnO. Although having both interactions (ferromagnetic and antiferromagnetic), dominance of ferromagnetic behavior was only observed for Zn_0.99Co_0.01O with the coercivity of ~154 ± 50 Oe and positive Curie–Weiss temperature as 79 ± 1 K. However, the calculated \frac2J_\textex k_\textB {\frac{{2J_{\text{ex}} }}{{k_{\text{B}} }}} values have proved that the higher Co²⁺ concentrations in ZnO lattice have increased the efficiency of antiferromagnetic interactions. Surprisingly, there was no rapid change at \frac2J_\textex k_\textB {\frac{{2J_{\text{ex}} }}{{k_{\text{B}} }}} values as mentioned in previous works.     

Nonlinearities in the analysis of frames

The material nonlinearity is introduced in the analysis through the representation of the stress-strain variations by continuous functions. The stress function can be adjusted to describe the stress-strain diagrams for various materials such as: steel, aluminum, concrete, etc., by varying the parameters related to the material properties. The continuous variation of the stresses from linear to nonlinear elastic, to plastic states is included in the formulation. For members exhibiting material nonlinearity within some parts of its span, the calculation for the locations of the transition of the stresses from the linear to nonlinear stages is not necessary. The geometrical nonlinearity analysis is also included in the derivations. The analysis can be performed either by an incremental or by an iterative approach, or by using an iterative process within each increment. The third approach is faster and better for structures subjected to high magnitude of nonlinearity. The stability of the structures due to nonlinearities is investigated. A software is modified to include the new formulations. Illustrative examples are provided for the comparisons of the results obtained with those solved previously.     

Equilibrium modelling of individual and simultaneous biosorption of chromium(VI) and nickel(II) onto dried activated sludge

The biosorption of chromium(VI) and nickel(II) ions, both singly and in combination, by dried activated sludge was investigated in a batch system as a function of initial pH and single- and dual-metal ion concentrations. The working initial pH values for single chromium(VI) and nickel(II) biosorptions were determined as 1.0 and 4.5, respectively. It was observed that the co-ion effect on the equilibrium uptake became more pronounced as the co-ion concentration in solution increased and pH level increased for chromium(VI) and decreased for nickel(II). Adsorption isotherms were developed for both the single- and dual-metal ion systems at these two pH values and expressed by the mono- and multi-component Langmuir and Freundlich adsorption models and model parameters were estimated by the non-linear regression. It was seen that the mono-component adsorption equilibrium data fitted very well to both the mono-component adsorption models for both the components and the pH values studied while the multi-component Freundlich adsorption model adequately predicted the multi-component adsorption equilibrium data at moderate ranges of initial mixture concentrations for both the studied pH values.