A validated methodology to estimate the reliability and safety of suspension bridge cables

The safety of suspension bridges depends on its main cables which are constructed of thousands of high strength steel wires radially clamped together at certain locations along the cable. After many years of service, these cables are showing signs of serious distress with many wires corroded and even broken inside. A new methodology to determine the reliability and safety of this structure is suggested in this research work. A three dimensional random field simulation is used to determine the remaining tensile strength in the cable. The key idea is to determine how an individual wire break affects the load transfer to the surrounding wires. This local damage eventually causes a global reduction in the load carrying capacity of the cable, up to a complete failure. A Monte Carlo technique is used to generate realizations of the wires' strength within a finite element model. Among the major contributions of the thesis is a novel technique for modeling the contact-friction mechanism between thousands of wires that account for load recovery in broken wires due to friction induced by radial clamps. The idea is to place elasto-plastic springs at the contact points between wires. These springs have varying parameters depending on their proximity to the clamping loads and are assigned according to the Boussinesq's solution to a point load in half space. While traditional contact algorithms have difficulties converging on this problem, this technique converges in few iterations. Moreover, parallelization of the problem enables a full stochastic analysis to determine the effect of corrosion uncertainty on the cable's failure load. This method represents a dramatic improvement compared to the current inspection methods that are unreliable and expensive

Practical considerations regarding results from static and dynamic load testing of bridges

Bridge tests are a helpful tool for bridge assessment and evaluation. Both in the case of a static and dynamic load testing, each element of the test: the load selection and application, the creation of a numerical model to follow the progress of the test or to check the validity of the test results, the measurement process itself and the comparative analysis of experimental results and calculations could be a source of errors in the bridge final evaluation if these errors and uncertainties are not properly considered. The article presents some of the most important factors that may bring errors in the interpretation of the test results and their comparison to targeted values or values derived from a numerical model. This, at the end, may result in the adoption of decisions that are not accurate and appropriate. The selected sources of feasible errors are presented with the division into static and dynamic loading tests. The presented examples of bridge load testing show how the use of improper test methods could lead to significant errors in bridge assessment and evaluation and, consequently, to wrong decisions.Peer ReviewedPostprint (published version

Estimating magnetic fields of homes near transmission lines in the California Power Line Study.

The California Power Line Study is a case-control study investigating the relation between residences near transmission lines and risk of childhood leukemia. It includes 5788 childhood leukemia cases and 5788 matched primary controls born between 1986 and 2007. We describe the methodology for estimating magnetic fields at study residences as well as for characterizing sources of uncertainty in these estimates. Birth residences of study subjects were geocoded and their distances to transmission lines were ascertained. 302 residences were deemed sufficiently close to transmission lines to have non-zero magnetic fields attributable to the lines. These residences were visited and detailed data, describing the physical configuration and dimensions of the lines contributing to the magnetic field at the residence, were collected. Phasing, loading, and directional load flow data for years of birth and diagnosis for each subject as well as for the day of site visit were obtained from utilities when available; when yearly average load for a particular year was not available, extrapolated values based on expert knowledge and prediction models were obtained. These data were used to estimate the magnetic fields at the center, closest and farthest point of each residence. We found good correlation between calculated fields and spot measurements of fields taken on site during visits. Our modeling strategies yielded similar calculated field estimates, and they were in high agreement with utility extrapolations. Phasing was known for over 90% of the lines. Important sources of uncertainty included a lack of information on the precise location of residences located within apartment buildings or other complexes. Our findings suggest that we were able to achieve high specificity in exposure assessment, which is essential for examining the association between distance to or magnetic fields from power lines and childhood leukemia risk

A Structural Safety Analysis of Buildings During Construction

The safety of steel buildings, constructed by the tier method, is evaluated. The probability of failure of steel frames supported on temporary connections is examined during the different stages of completion. The principal loading of concern is the maximum wind load over the critical stages of construction.National Science Foundation Grants ENG 77-02007, ENV 77-09090, and PFR 80-0258

A Measurement of Newton's Gravitational Constant

A precision measurement of the gravitational constant $G$ has been made using a beam balance. Special attention has been given to determining the calibration, the effect of a possible nonlinearity of the balance and the zero-point variation of the balance. The equipment, the measurements and the analysis are described in detail. The value obtained for G is 6.674252(109)(54) 10^{-11} m3 kg-1 s-2. The relative statistical and systematic uncertainties of this result are 16.3 10^{-6} and 8.1 10^{-6}, respectively.Comment: 26 pages, 20 figures, Accepted for publication by Phys. Rev.

Stochastic prediction of wire coupling interference

Many EMC analyses of complex systems frequently result in a statement that insufficient knowledge is available to describe accurately the internal relationships of the system's components. This lack of information precludes any rigorous deterministic prediction and, in principle, requires that we express the uncertainties within the model. This paper shows the practical feasibility of stochastic prediction, as an alternative to deterministic simulation, applied to a class of EMC problems intrinsically affected by randomness. The evaluation of the crosstalk in standard cable bundles, in which several wires are tightly and randomly wrapped together, is the concrete problem that we investigate in this context. We developed a technique based on solving the nonuniform multiconductor transmission lines (MTL) for many randomly generated wires' geometries to obtain many crosstalk samples for a single frequency. Finally we validated the method, setting up a case study with published experimental result