Cast iron piers of a disused 90 year old multispan railway bridge located close to the Pacific Ocean were extensively sampled for remaining wall thickness to determine corrosion loss and pit depth. From this, a corrosion loss model for the full 90 years was developed. In addition, the statistics for uncertainty in corrosion loss were obtained. Corrosion varied with elevation relative to mean water level and was negligible in the atmospheric zone, about 2-3 mm in the immersion zone and 5-6 mm in the splash and lower tidal zones. This variation is consistent with accelerated low water corrosion. It indicates that water pollution occurred sometime during the life of the bridge. Maximum pit depths were determined and analysed using extreme value statistics. The corrosion model for such long term exposure and the related statistical results are unique and important for assessment of remaining life of the many other cast iron structures still in existence in many parts of the world.
It is possible to detect the presence of leaks in underground water pipes by measuring, at remote locations such as hydrants, the noise or vibration caused by the leak. The time delay of the leak noise reaching the different sensors can be computed using the cross correlation, and with knowledge of the wavespeed in the pipe, the location of the leak may be pinpointed. This paper presents a new technique for leak detection which employs the cepstrum, rather than the cross correlation, for estimation of the delay time. The delay time manifests as a series of peaks in the cepstrum, rather than a single peak in the correlation, allowing a more robust estimate. A number of cepstrum formulations are presented which are derived from correlation estimators, and it is found that the time delay information is actually contained in the phase component of the cross spectrum. Based on this, a phase cepstrum estimator is developed.
Cast iron bridge piers, often more than 100 years old, are still in service in rail and road bridges in many parts of Australia. Increasingly, the effect of corrosion on their present and future structural safety is of interest. Field investigations and observations to assess corrosion losses and pitting of the cast iron piers of four different operational railway bridges located in tidal marine exposure conditions are described, noting that direct visual examination usually is rendered difficult by immersion, marine growth and the presence of the graphitised layer. Measured corrosion losses and pit depths showed considerable variability between piers and between bridges. Evidence was found for the influence of microbiological corrosion, fostered by nitrogenous pollution. Implications for structural safety assessment are discussed and an example given of the estimation of likely future rate of (long-term) corrosion, necessary for assessment of remaining structural safe life. demolition (Melchers, Herron, and Emslie 2013). The present paper describes the investigations that were conducted, summarises the observations and conclusions and provides guidance for future investigations.The next section gives a short overview of what is known about the corrosion of grey cast iron in marine environments and the corrosion mechanisms involved.The following section provides a series of field observations typical of the corrosion of grey cast iron, including general corrosion loss, localised or pitting corrosion and the so-called 'graphitised' layer usually present on the exterior surface of cast iron once corrosion has commenced. Since one of the bridges showed relatively more severe corrosion, consideration was given to the possibility of microbiologically influenced corrosion (MIC). It required water quality analysis and interpretation of the results relative to previous observations for corrosion of steel in marine waters. The Discussion section considers some of these matters in more detail and also outlines an approach for predicting the likely future rate of corrosion of grey cast iron piers in the immersion zone.Much of the material disclosed below is based on a series of consulting reports. For obvious reasons, the locations and precise details of the bridges cannot be disclosed. However, the results were considered sufficient engineering importance for the bridge owners and managers (Queensland Rail) to agree to wider circulation of the outcomes in the context of results in the available literature.
Minimising the impact of music practice and "Garage Band" performances upon neighbours in a residential area is challenging in terms of noise emissions from musical instruments, but particularly so when drums and percussion instruments are involved. Normal residential building façades and roofing designs offer limited low frequency noise attenuation and domestic building construction methods can severely compromise the performance of seemingly adequate partition construction details. This paper presents the results of design, construction and testing activities for a private drum studio that was required to meet stringent boundary noise emission targets in order to comply with local council Development Application requirements. High transmission loss lightweight partition test data is provided for the as-built final installation, along with details of cavity absorption, panel damping and vibration isolation treatments that contributed to maximising façade sound reduction performance. A range of room internal absorption treatments, including low frequency "tube traps", corner traps and diffusers were successfully employed to achieve compliance with BBC recommended reverberation times for small recording studios
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