Infrastructure Engineering - Research Publications
Now showing items 1-12 of 1093
Developing a new framework based on solid models for 3D cadastres
3D cadastres aim to record, manage, and visualise spatial dimensions of volumetric legal objects in a 3D digital information environment. Definition of the geometry and topology of volumetric representations of legal objects is predicated on solid modelling approaches which are widely used in 3D modelling applications. Some solid modelling approaches are more user friendly for constructing legal objects while others enable the creation of 3D legal objects with a higher level of spatial complexity. This study aims to assess the capabilities of solid models in managing the geometry and topology of 3D legal objects with various spatial complexities. The assessment was conducted based on identification of the fundamental principles for defining geometry and topology in 3D cadastres. Various 3D legal objects with different geometric shapes were examined according to the topological principles for ensuring both internal and external validity of 3D legal objects. The identified geometric and topological principles were used to propose a new framework based on solid modelling for 3D cadastres. Our suggested framework would provide the basis for modifying land subdivision policies to adopt solid models in upgrading current cadastral systems into 3D digital environments.
Decay of Torsional Stiffness in RC U-Shaped Walls
(American Society of Civil Engineers (ASCE), 2020-09)
Reinforced concrete (RC) U-shaped walls are a popular construction choice, commonly used to resist the lateral loads from wind and earthquakes. In many buildings, the center of stiffness of a floor is eccentric from the center of mass and the building will therefore undergo some twist. Often, U-shaped walls contribute significantly to the torsional stiffness of the building and the analysis of the structure therefore requires an estimate of the torsional stiffness. This research investigates the dependency of the torsional stiffness of U-shaped walls on the translational displacement demands using experimental evidence and advanced numerical models. The experimental results show that the torsional stiffness decreases with increasing translational displacement. Furthermore, the numerical and experimental results indicate that the torsional stiffness degrades at a similar rate as the translational stiffness of the walls. The rotational stiffness of the wall is smaller when it is centered than when it is subjected to a translation. This effect is attributed to the longitudinal stresses throughout the cross section that are already present due to the imposed flexural displacement. In particular, the compression zone resulting from the translational displacement imposed on the wall stiffens the wall with regard to the twisting. As a result, the effective torsional stiffness increases with increasing axial load ratio. Current codes do not provide reduction factors for the torsional stiffness, but the results show that the reduction factors for the shear stiffness can serve as estimate, albeit they do not capture the dependence on the axial load ratio.
Soil Amplification in Low-to-Moderate Seismic Regions
(Springer Verlag (Germany), 2017-05)
The results of a study that investigates potential revisions of the spectral shape factors used in standards in regions of low-to-moderate seismicity are presented here. Using an equivalent linear analysis, the investigation particularly focuses on the effects of seismic intensity associated with rare and very rare intraplate earthquake events on site response. The Pacific Earthquake Engineering Research Center ground motion database (PEER) is used in selecting appropriate acceleration-time histories for the intraplate region. The results are normalised for comparison with the current spectral shape factors given in the Australian Standards for Earthquake Actions AS 1170.4:2007, with some differences being observed. The dependency of site amplification on seismic intensity was only observed for soil classes Ce, De and Ee. The rock site of class Be had considerably higher response in the short period range relative to class Ee. The records from the PEER ground motion database were also used for comparison with the results from this study, using a modified normalisation approach. The results from this study correlate well with the records from PEER.
Plastic Hinge Length for Lightly Reinforced Rectangular Concrete Walls
(Taylor & Francis, 2018-01-01)
This research investigates the plastic hinge length in lightly reinforced rectangular walls typically found in regions of low-to-moderate seismicity. Poor performance has been exhibited by lightly reinforced concrete walls in past earthquake events. A series of finite element analyses have been carried out which demonstrate that if the longitudinal reinforcement ratio in the wall is below a certain threshold value, there will not be sufficient reinforcement to cause secondary cracking, and instead fracture of the longitudinal reinforcement at a single crack could occur. A plastic hinge length equation has been derived based on the results from the numerical simulations.
Plastic hinge analysis for lightly reinforced and unconfined concrete structural walls
(Springer (part of Springer Nature), 2018-10-01)
Poor performance of lightly reinforced and unconfined concrete structural walls have been observed in recent earthquake events. This research investigates the displacement capacity of such walls by comparing the results of a series of state-of-the-art finite element analyses for a range of different structural walls to that estimated using plastic hinge analyses. The common expressions used in estimating the yield curvature, yield displacement and plastic displacement are scrutinised for these types of walls. Some recommendations are given to improve the prediction of the displacement capacity of lightly reinforced and unconfined rectangular and C-shaped walls for flexural actions using a plastic hinge analysis. Importantly, a parameter has been recommended to be used in a “modified” approach for estimating the nominal yield displacement of lightly reinforced concrete walls. Different expressions are also recommended depending on the amount of longitudinal reinforcement used in the wall in comparison to that required to initiate secondary cracking. This is important for providing better estimations of the displacement capacity of RC structural wall buildings in low-to-moderate seismic regions such that vulnerability studies can be conducted.
D-Log: A WiFi Log-based differential scheme for enhanced indoor localization with single RSSI source and infrequent sampling rate
Currently, large amounts of Wi-Fi access logs are collected in diverse indoor environments, but cannot be widely used for fine-grained spatio-temporal analysis due to coarse positioning. We present a Log-based Differential (D-Log) scheme for post-hoc localization based on differentiated location estimates obtained from large-scale Access Point (AP) logs of WiFi connectivity traces, which can be used for data analysis and knowledge discovery of visitor behaviours. Specifically, the location estimates are calculated by utilizing a combination of Received Signal Strength Indicator (RSSI) records from two neighbouring APs. D-Log exploits real-world industry WiFi logs where RSSI data sampled at low rates from single AP sources are recorded in each connectivity trace. The approach is independent of device and network infrastructure type. D-Log is evaluated using WiFi logs collected from controlled environment as well as real-world uncontrolled public indoor spaces, which includes discrete single-AP RSSI traces of around 100,000 mobile devices over a one-year period. The experiment results indicate that, despite of the challenges with the infrequent sampling rate and the limitations of the data that only records RSSI from single AP sources in each instance, D-Log performs comparatively well to the state-of-the-art RSSI-based localization methods and presents a viable alternative for many application areas where high-accuracy positioning infrastructure may not be cost effective or where positioning applications are considered on legacy information infrastructure.
Performance of multi-storey prefabricated modular buildings with infill concrete walls subjected to earthquake loads
(Concrete Institute of Australia (CIA), 2017-09-14)
Prefabricated modules are increasingly becoming popular in the construction industry as they result in achieving cost efficient buildings in a very short time. This increasing demand for modular construction has expanded to multi-storey applications where the effect of lateral loads, such as earthquake loads, becomes critical. However, there is a shortage of detailed engineering research into the performance of modular structural systems subjected to earthquake loads. This paper evaluates a modified corner supported modular structural system that uses infill concrete walls to enhance its lateral stiffness. The performance of the overall structural system against earthquake loads and the contribution of modules containing infill concrete walls to the overall lateral load resisting system is discussed in this paper.
Testing the event witnessing status of micro-bloggers from evidence in their micro-blogs
(PUBLIC LIBRARY SCIENCE, 2017-12-12)
This paper demonstrates a framework of processes for identifying potential witnesses of events from evidence they post to social media. The research defines original evidence models for micro-blog content sources, the relative uncertainty of different evidence types, and models for testing evidence by combination. Methods to filter and extract evidence using automated and semi-automated means are demonstrated using a Twitter case study event. Further, an implementation to test extracted evidence using Dempster Shafer Theory of Evidence are presented. The results indicate that the inclusion of evidence from micro-blog text and linked image content can increase the number of micro-bloggers identified at events, in comparison to the number of micro-bloggers identified from geotags alone. Additionally, the number of micro-bloggers that can be tested for evidence corroboration or conflict, is increased by incorporating evidence identified in their posting history.
Predicting Knee Osteoarthritis
(Springer US, 2016)
Treatment options for osteoarthritis (OA) beyond pain relief or total knee replacement are very limited. Because of this, attention has shifted to identifying which factors increase the risk of OA in vulnerable populations in order to be able to give recommendations to delay disease onset or to slow disease progression. The gold standard is then to use principles of risk management, first to provide subject-specific estimates of risk and then to find ways of reducing that risk. Population studies of OA risk based on statistical associations do not provide such individually tailored information. Here we argue that mechanistic models of cartilage tissue maintenance and damage coupled to statistical models incorporating model uncertainty, united within the framework of structural reliability analysis, provide an avenue for bridging the disciplines of epidemiology, cell biology, genetics and biomechanics. Such models promise subject-specific OA risk assessment and personalized strategies for mitigating or even avoiding OA. We illustrate the proposed approach with a simple model of cartilage extracellular matrix synthesis and loss regulated by daily physical activity.
A mathematical model for targeting chemicals to tissues by exploiting complex degradation
(BIOMED CENTRAL LTD, 2011-09-22)
BACKGROUND: In many biological and therapeutic contexts, it is highly desirable to target a chemical specifically to a particular tissue where it exerts its biological effect. In this paper, we present a simple, generic, mathematical model that elucidates a general method for targeting a chemical to particular tissues. The model consists of coupled reaction-diffusion equations to describe the evolution within the tissue of the concentrations of three chemical species: a (concentration of free chemical), b (binding protein) and their complex, c (chemical bound to binding protein). We assume that all species are free to diffuse, and that a and b undergo a reversible reaction to form c. In addition, the complex, c, can be broken down by a process (e.g. an enzyme in the tissue) that results in the release of the chemical, a, which is then free to exert its biological action. RESULTS: For simplicity, we consider a one-dimensional geometry. In the special case where the rate of complex formation is small (compared to the diffusion timescale of the species within the tissue) the system can be solved analytically. This analytic solution allows us to show how the concentration of free chemical, a, in the tissue can be increased over the concentration of free chemical at the tissue boundary. We show that, under certain conditions, the maximum concentration of a can occur at the centre of the tissue, and give an upper bound on this maximum level. Numerical simulations are then used to determine how the behaviour of the system changes when the assumption of negligible complex formation rate is relaxed. CONCLUSIONS: We have shown, using our mathematical model, how complex degradation can potentially be exploited to target a chemical to a particular tissue, and how the level of the active chemical depends on factors such as the diffusion coefficients and degradation/production rates of each species. The biological significance of these results in terms of potential applications in cartilage tissue engineering and chemotherapy is discussed. In particular, we believe these results may be of use in determining the most promising prodrug candidates.
Meridional and vertical variations of the water vapour isotopic composition in the marine boundary layer over the Atlantic and Southern Ocean
(Copernicus Publications, 2020-05-15)
Stable water isotopologues (SWIs) are useful tracers of moist diabatic processes in the atmospheric water cycle. They provide a framework to analyse moist processes on a range of timescales from large-scale moisture transport to cloud formation, precipitation and small-scale turbulent mixing. Laser spectrometric measurements on research vessels produce high-resolution time series of the variability of the water vapour isotopic composition in the marine boundary layer. In this study, we present a 5-month continuous time series of such ship-based measurements of δ2H and δ18O from the Antarctic Circumnavigation Expedition (ACE) in the Atlantic and the Southern Ocean in the time period from November 2016 to April 2017. We analyse the drivers of meridional SWI variations in the marine boundary layer across diverse climate zones in the Atlantic and Southern Ocean using Lagrangian moisture source diagnostics and relate vertical SWI differences to near-surface wind speed and ocean surface state. The median values of δ18O, δ2H and deuterium excess during ACE decrease continuously from low to high latitudes. These meridional SWI distributions reflect climatic conditions at the measurement and moisture source locations, such as air temperature, specific humidity and relative humidity with respect to sea surface temperature. The SWI variability at a given latitude is highest in the extratropics and polar regions with decreasing values equatorwards. This meridional distribution of SWI variability is explained by the variability in moisture source locations and its associated environmental conditions as well as transport processes. The westward-located moisture sources of water vapour in the extratropics are highly variable in extent and latitude due to the frequent passage of cyclones and thus widen the range of encountered SWI values in the marine boundary layer. Moisture loss during transport further contributes to the high SWI variability in the extratropics. In the subtropics and tropics, persistent anticyclones lead to well-confined narrow easterly moisture source regions, which is reflected in the weak SWI variability in these regions. Thus, the expected range of SWI signals at a given latitude strongly depends on the large-scale circulation. Furthermore, the ACE SWI time series recorded at 8.0 and 13.5 m above the ocean surface provide estimates of vertical SWI gradients in the lowermost marine boundary layer. On average, the vertical gradients with height found during ACE are −0.1‰m−1 for δ18O, −0.5‰m−1 for δ2H and 0.3 ‰ m−1 for deuterium excess. Careful calibration and post-processing of the SWI data and a detailed uncertainty analysis provide a solid basis for the presented gradients. Using sea spray concentrations and sea state conditions, we show that the vertical SWI gradients are particularly large during high wind speed conditions with increased contribution of sea spray evaporation or during low wind speed conditions due to weak vertical turbulent mixing. Although further SWI measurements at a higher vertical resolution are required to validate these findings, the simultaneous SWI measurements at several heights during ACE show the potential of SWIs as tracers for vertical mixing and sea spray evaporation in the lowermost marine boundary layer.
Unmanned Aerial Vehicle (UAV)-Based Thermal Infra-Red (TIR) and Optical Imagery Reveals Multi-Spatial Scale Controls of Cold-Water Areas Over a Groundwater-Dominated Riverscape
(Frontiers Media, 2020-05-27)
The forecast of warmer weather, and reduced precipitation and streamflow under climate change makes freshwater biota particularly vulnerable to being exposed to temperature extremes. Given the importance of temperature to regulate vital physiological processes, the availability of discrete cold-water patches (CWPs) in rivers to act as potential thermal refugia is critical to support freshwater ecosystem function. Being able to predict their spatial distribution at riverscape scales is the first step to understanding the capacity to maintain thermal refuges and to inform future river management strategies. Novel Unmanned Aerial Vehicle (UAV)-based Thermal Infra-Red (TIR) imagery technologies provide an opportunity to assess riverscape stream temperature. On the example of a 50 km linear length of the groundwater-dominated Upper Ovens River (Australia), this study presents a methodology addressing critical challenges in UAV-based TIR and optical data acquisition, processing, and interpretation. Our methodological approach generated 49 georeferenced high-resolution TIR and optical orthomosaicked imagery sets. The imagery sets allowed us to identify river-length longitudinal patterns of temperature and to detect, characterize, and classify 260 CWPs. Both stream and CWPs temperatures increased but presented considerable variability with downstream distance. CWPs were non-uniformly distributed along the riverscape, with emergent hyporheic water types dominating, followed by deep pools, shading, side channels, and tributaries. We found associations between CWPs and key physical controls including land use, riparian vegetation, longitudinal and lateral CWP location, and CWP area size, illustrating processes acting at multiple spatial scales. This study provides a basis for future works on the thermal associations with physical controls over a riverscape, and it highlights the major challenges and limitations of the use of UAV-based TIR and optical imagery to be used in future applications. In conjunction with studies of thermally linked ecological processes, the predictions of CWPs can help prioritize river restoration measures as effective climate adaptation tools.