Ming L. Wang

Optimal transducer placement for health monitoring of long span bridge

In experimental modal testing, the measurement locations and the number of measurements have a major influence on the quality of the results. In general, there are several alternative schemes for sensor placement, and the accuracy of the data increases as the number of sensors utilized increases. However, the number of transducers that can be attached to a real structure is limited by economic constraints. Therefore, algorithms that address the issue of limited instrumentation and its effects on resolution and accuracy are important from the standpoint of experimental modal analysis. The authors are particularly interested in structural dynamics based damage evaluation of large structures, and the development and implementation of suitable sensor location algorithms are critical for such a problem. A kinetic energy optimization technique (EOT) has been derived, and numerical issues are addressed and applied to real experimental data obtained from a model of an asymmetric long span bridge. Using experimental data from the bridge model, the algorithm proposed in this paper is compared to Kammers EIM algorithm, which optimizes the transducer placement for identification and control purposes.

Temperature effects on cable stayed bridge using health monitoring system: a case study

The Zhanjiang Bay Bridge, located in an inner gulf of South China, is a cable stayed bridge with a main span of 480 m. An analysis on the thermal effects experienced by the bridge is presented according to a health monitoring system (HMS) that began operation in 2006. The parameters studied in the analysis include thermal time lags and gradients of the steel box girder, concrete tower, and stayed cables, as well as displacements at center span and tops of the towers. Among the findings, temperature gradient in the steel girder was larger than the design specification, concrete temperature lagged significantly behind ambient air, and stayed cable temperatures were between those of ambient air and concrete. Additional findings were obtained by comparing the measured data to values calculated using a finite element model. The comparison made it possible to approximate the unmeasured thermal gradient on the surface of the towers, and to determine that an expansion joint was likely jammed and contributing to the bridge’s asymmetrical displacement. This article presents these findings in a thorough manner, and in doing so conveys the ability of a HMS to provide realistic examples of thermal behavior, to estimate conditions at locations free of measurement devices, and to suggest areas of concern for future manual inspections. Furthermore, it provides evidence that a HMS is not only helpful for bridge design and management, but also for the development of itself.

Taper Design of Vivaldi and Co-Planar Tapered Slot Antenna (TSA) by Chebyshev Transformer

A new method for the flares opening rate for a single radiator tapered slot antenna (TSA) is presented. A stepped quarter-wave Chebyshev transformer is calculated to minimize the frequency domain reflection and maximize the power transfer gain. Then slot widths are computed to match the Chebychev design, and smooth curves are fit to the computed steps. Different smoothing functions are compared, including the conventional exponential function, as well as cubic spline and Gaussian. The validity of the method is verified through simulations and measurements of experimental designs for the 1 to 3 GHz frequency range. In this work the TSA is fabricated on one side of a single layer Duroid substrate with dielectric constant 6.15. Although the Chebyshev transformer is an old concept, the novelty of this method is applying the transformer to design the TSA slotline taper profile, leading to a closed design procedure rather than an optimization. Advantages of this novel method are the straightforward mathematics of the design and that a simple simulation program can be written in a short time.

Application of EM Stress Sensors in Large Steel Cables

The employment of elastomagnetic (EM) stress sensors on large steel cables of Qiangjiang No. 4 Bridge in China is discussed. As an engineering application in the field of ferromagnetic magnetoelasticity, the EM sensors make possible non-contact stress monitoring for steel cables and pre-stressed tendons on suspension bridges, cable-stayed bridges, and other ferromagnetic structures. The correlation of the relative permeability and tensile stress is derived from the calibration. Automatic maneuvering is fulfilled by formalizing the calibration function with the temperature-influencing factor. Calibration reveals that the magnetoelastical characteristics of multi-wire hangers are analogous while that of post-tensioned tendons are similar to single wires. Insitu measurements on Qiangjiang No.4 Bridge demonstrate the reliability of the EM stress sensors.

A health monitoring system for large structural systems

A structural dynamic based health monitoring system for large structural systems has been proposed in this article. The proposed method has been verified numerically and experimentally by implementing the scheme on a model of a long span bridge. In the implementation process, the following steps have been identified as being important: (1) finite element modeling for the purpose of establishing the base line, (2) optimal sensor placement to make a scheme economical and (3) damage identification. In the process the authors have identified and discussed the various difficulties that have been encountered and have made suitable recommendations for circumventing the problems.

Dynamic characterization of a long span bridge: A finite element based approach

Abstract Aging bridges coupled with increasing traffic loads are producing a severe toll on the nations infrastructure. This has made it necessary to take a closer look at the health of existing bridges and develop automated damage identification methods if possible. Recent works in the field of structural dynamics have shown that damage detection techniques utilizing parameters like mode shapes, modal frequencies and damping ratios can be used to identify damage in structural systems. It is, however, important to be able to establish a baseline model for the structure first, and then a model updating technique can be utilized to evaluate the condition of the structure from time to time. It is with this goal in mind that the authors have decided to establish the process for obtaining a baseline model for a long span bridge. Based on the actual design drawings of a bridge, finite element (FE) models of the bridge in question are developed using SDRC-IDEAS. Three models of the bridge are simulated using Normal Mode Dynamics solver in SDRC-IDEAS to obtain the modal parameters of interest, in this case the modal frequencies and the mode shapes. A modal assurance criteria (MAC) is utilized to compare the different simulated mode shapes and, finally, the modal frequencies that have been obtained from the FE analysis are compared to frequencies that have been obtained from some preliminary field tests.

The effects of confinement on the failure orientation in cementitious materials experimental observations

Abstract The literature is replete with studies of cementitious and geologic materials under multiaxial states of stress. However, there still exists division over the character of the failure mode under multiaxial states of stress. Some experts state that the failure is diffuse. The classical barrel-shaped specimen removed from a test cell intact is cited as evidence. Other researchers state that the failure is characterized by failure planes orientated parallel to the maximum compressive stress for all values of hydrostatic pressure. Tests on geologic materials have shown that the failure is nearly parallel to the maximum compressive stress under uniaxial stress. The orientation increases angle with respect to the maximum compressive stress as the confining pressure increases. Other sources simply state that there is a change in mode from splitting failure to crushing failure as confinement increases. The objective of this research is to better define the character of the failure mechanism as confining pressure increases. In this study triaxial tests on 95 mortar cylinders show that there is a change in the orientation of the failure plane as confining pressure is increased. The failure is characterized by a distinct failure surface or surfaces that change orientation from nearly vertical to angled as confinement increases. Furthermore, test data indicate that localized deformations occur within 5% of the peak stress. These results imply that the failure is truly characterized through localized deformations and is not diffuse. Knowledge of such behavior is important because it places restrictions on the form of the constitutive model in order to predict these features. The implications of these findings on the constitutive model are discussed in detail in a companion paper.

Influence of SiO2 modification on phosphorus enrichment in P bearing steelmaking slag

Abstract In order to effect enrichment of phosphorus in the converter slag, phosphorus enrichment was researched by slag modification with SiO2. The SiO2 modification process was evaluated thermodynamically, and phosphorus rich phase was separated from experimental slag by magnetic separation. The results show that n2CaO.SiO2–3CaO.P2O5 (nC2S–C3P) solid solution is generated by the reaction of Ca3(PO4)2 phase in the slag with precipitated Ca2SiO4 phase at 1623 K, and Ca2SiO4 in the solid solution is reduced with increasing SiO2; hence, the phosphorus content in the solid solution is increased. If the addition of SiO2 is excessive, the amount of Ca2SiO4 precipitation in the slag is decreased remarkably (and even disappeared), CaSiO3 phase is generated and the generation of nC2S–C3P solid solution is reduced, which is not favourable to phosphorus enrichment. Through magnetic separation, the non-magnetic fraction was increased by 10–74·68% compared with the original slag. The distribution ratio of P2O5 was increased from 2·71 to 5·48. As 84·57% of the phosphorus in the slag is in the collected non-magnetic substances, the work demonstrates that most of the phosphorus is able to be effectively recycled.

Novel NiZnAl-ferrites and strong magnetoelectric coupling in NiZnAl-ferrite/PZT multiferroic heterostructures

Magnetic/piezoelectric multiferroic heterostructures with strong magnetoelectric (ME) coupling have recently attracted considerable interest. Since the ratio of magnetostriction ?s over saturation magnetization Ms is a key factor to achieve strong magnetoelectric coupling in ferrite/piezoelectric multiferroic heterostructures, here we find a solution to tune ?s/Ms by aluminum doping. We report aluminum-substituted NiZn-ferrites with different compositions (Ni0.65Zn0.35Fe2?xAlxO4, x?=?0, 0.1, 0.3, 0.4, 0.6, 0.8 and 1) fabricated by a solid-state sintering process. The saturation magnetization of these NiZnAl-ferrites was reduced from 6000 to 900?G with increased Al doping, which was accompanied by a significantly narrowed ferromagnetic resonance linewidth from 1870 to 340?Oe. Meanwhile, saturation magnetostriction of these NiZnAl-ferrites was reduced from 6.67 to 1.40?ppm with increased amount of Al doping. Strong ME coupling was demonstrated in the NiZnAl-ferrites/PZT multiferroic heterostructures. A large piezoelectric deformation induced ferromagnetic resonance field change up to 42?Oe was observed in Ni0.65Zn0.35Fe1.2Al0.8O4/PZT heterostructures, corresponding to a large microwave ME coefficient of 4.2?Oe?cm?kV?1. These AlNiZn-ferrites and NiZnAl-ferrites/PZT heterostructures with large ME coupling provide a great opportunity for electrical tuning microwave devices.

Comparative Field Study of Cable Tension Measurement for a Cable-Stayed Bridge

Cable tension is one of the important indexes of cable integrity as well as bridge stability and can be measured by various tension measurement methods. In this study, three widely used methods (i.e., the lift-off test, electromagnetic sensor method, and vibration method) have been implemented for two multistrand cables of a cable-stayed bridge under construction. The test bridge is Hwamyung Bridge in Korea, which has a prestressed concrete box girder. The field tests are executed during the second tensioning stage just after the installation of the key segment. The tensions are estimated before and after tensioning the cable and 5 days later (i.e., after finishing the tensioning of all the cables). The tensions measured by the three methods are compared with the design tension of the tensioning stage, and all three methods show very good performance in accuracy with minimal difference. Their cost and difficulty are compared based on test experiences. Additionally, an improved vibration method is proposed by ignoring apparent negative bending stiffness identified from measurement errors and validated in this test by improving the accuracy.