title: Axial capacity of face-to-face built-up aluminium alloy columns: Numerical simulation and design proposal

authors: Samarasinghe, Nishantha

subjects: aluminium alloy

abstract: In recent years, aluminum alloy has seen increased use in construction due to its exceptional corrosion resistance and mechanical strength, especially in structural elements like channel sections, hollow pipes, and angles. Cold-formed aluminum alloy face-to-face (CAAFTF) built up channel sections with web holes or without web holes have emerged as a significant development in the construction industry, focusing on streamlining the installation of plumbing and electrical services as well as Glass walls in front of buildings. Previous research indicated that these aluminum alloy sections were studied on bending capacity with web holes and found the bending modified formula for plain webs as well as the web with perforated sections. However, no comprehensive study has been reported in the literature for such aluminum alloy built up face to face columns subjected to compression. 
This study investigates the axial compression behaviour of aluminium alloy columns with perforated webs, focusing on the influence of screws and perforations on axial capacity. A numerical analysis was conducted on screw-fastened, perforated, face-to-face built-up aluminium alloy channel sections under axial compression. The finite element (FE) model developed using abaqus was validated against 29 experimental results from the literature. The validated nonlinear elasto-plastic FE model was then extended to analyse 495 parametric FE models to examine the effects of key parameters, including modified slenderness, screw number, number of web holes, hole diameter, and section thickness, on the axial strength.
The parametric analysis revealed a reduction in axial strength by approximately 8% for every 0.2 increment in the diameter-to-web width ratio (a/h). Axial strength results from experimental tests and FE analysis were compared with current design guidelines in the Australian/New Zealand Standards (AS/NZS 4600). The analysis showed that AS/NZS design strengths were overestimated by 15% for single perforated webs and underestimated strengths by 12% for multiple perforated web sections but AS/NZS estimation for plain section is more closely match with experimental results.
A new strength reduction factor equation was developed for aluminium alloy face-to-face built-up channel sections with single and multiple perforated webs. Reliability analysis confirmed the accuracy of the proposed equation, which is applicable within specific limits of slenderness ratio, web width-to-length ratio, and web width-to-thickness ratio. The findings indicate that introducing perforations reduces the axial capacity of plain sections by 8% to 16% for single and multiple perforated webs, respectively. This study provides valuable insights for the design and optimization of aluminium alloy built-up sections with perforated webs.

text: Axial capacity of face-to-face built-up aluminium alloy columns: Numerical simulation and design proposal In recent years, aluminum alloy has seen increased use in construction due to its exceptional corrosion resistance and mechanical strength, especially in structural elements like channel sections, hollow pipes, and angles. Cold-formed aluminum alloy face-to-face (CAAFTF) built up channel sections with web holes or without web holes have emerged as a significant development in the construction industry, focusing on streamlining the installation of plumbing and electrical services as well as Glass walls in front of buildings. Previous research indicated that these aluminum alloy sections were studied on bending capacity with web holes and found the bending modified formula for plain webs as well as the web with perforated sections. However, no comprehensive study has been reported in the literature for such aluminum alloy built up face to face columns subjected to compression. 
This study investigates the axial compression behaviour of aluminium alloy columns with perforated webs, focusing on the influence of screws and perforations on axial capacity. A numerical analysis was conducted on screw-fastened, perforated, face-to-face built-up aluminium alloy channel sections under axial compression. The finite element (FE) model developed using abaqus was validated against 29 experimental results from the literature. The validated nonlinear elasto-plastic FE model was then extended to analyse 495 parametric FE models to examine the effects of key parameters, including modified slenderness, screw number, number of web holes, hole diameter, and section thickness, on the axial strength.
The parametric analysis revealed a reduction in axial strength by approximately 8% for every 0.2 increment in the diameter-to-web width ratio (a/h). Axial strength results from experimental tests and FE analysis were compared with current design guidelines in the Australian/New Zealand Standards (AS/NZS 4600). The analysis showed that AS/NZS design strengths were overestimated by 15% for single perforated webs and underestimated strengths by 12% for multiple perforated web sections but AS/NZS estimation for plain section is more closely match with experimental results.
A new strength reduction factor equation was developed for aluminium alloy face-to-face built-up channel sections with single and multiple perforated webs. Reliability analysis confirmed the accuracy of the proposed equation, which is applicable within specific limits of slenderness ratio, web width-to-length ratio, and web width-to-thickness ratio. The findings indicate that introducing perforations reduces the axial capacity of plain sections by 8% to 16% for single and multiple perforated webs, respectively. This study provides valuable insights for the design and optimization of aluminium alloy built-up sections with perforated webs.

year: 2025-03-25

title: Incremental Capacity and Voltammetry of Batteries, and Implications for Electrochemical Impedance Spectroscopy

authors: Dunn, Christopher

abstract: Incremental capacity analysis (ICA), where incremental charge (Q) movements associated with changes in potential are tracked, and cyclic voltammetry (CV), where current response to a linear voltage sweep is recorded, are used to investigate the properties of electrochemical systems. Electrochemical impedance spectroscopy (EIS), on the other hand, is a powerful, non-destructive technique that can be used to determine small-signal AC impedance over a wide frequency range. It is frequently used to design battery equivalent-circuit models. This manuscript explores the relationships between ICA, CV and EIS and demonstrates how sweep rate in CV is related to charging (C) rate in ICA. In addition, it shows the connection between observations linked to rate of charge movement in CV and ICA and intermittent, irregular behavior seen in EIS when performed on a battery. It also explains the use of an additional DC stimulus during EIS to ensure reliability of battery impedance data and to facilitate equivalent-circuit modeling, and suggests a method for obtaining data analogous to CV from a whole battery without risking its destruction.

text: Incremental Capacity and Voltammetry of Batteries, and Implications for Electrochemical Impedance Spectroscopy Incremental capacity analysis (ICA), where incremental charge (Q) movements associated with changes in potential are tracked, and cyclic voltammetry (CV), where current response to a linear voltage sweep is recorded, are used to investigate the properties of electrochemical systems. Electrochemical impedance spectroscopy (EIS), on the other hand, is a powerful, non-destructive technique that can be used to determine small-signal AC impedance over a wide frequency range. It is frequently used to design battery equivalent-circuit models. This manuscript explores the relationships between ICA, CV and EIS and demonstrates how sweep rate in CV is related to charging (C) rate in ICA. In addition, it shows the connection between observations linked to rate of charge movement in CV and ICA and intermittent, irregular behavior seen in EIS when performed on a battery. It also explains the use of an additional DC stimulus during EIS to ensure reliability of battery impedance data and to facilitate equivalent-circuit modeling, and suggests a method for obtaining data analogous to CV from a whole battery without risking its destruction.

year: 2025

title: Quantifying relationships between kōura  (Paranephrops planifrons) abundance and micro-habitat features in Waikato hill-country streams

authors: Parata, Riki Neihana

subjects: kōura

abstract: Kōura (Paranephrops planifrons) is considered a taonga species by Māori and was once an abundant traditional fishery harvested throughout New Zealand. Kōura populations are under pressure in Waikato hill-country streams due to a range of factors including habitat loss and water quality degradation. Now that stakeholders have been engaging in collaborative decision-making and practices to restore/enhance biodiversity and ecosystem health within the Waikato catchment, there is opportunity to implement measures specifically targeted at kōura. Information on kōura habitat requirements to assist with the development of habitat enhancement work is therefore timely.
This research comprised two discrete studies which, in combination, provide important insights into daytime habitat use by kōura in Waikato hill-country streams. The first study was a field survey that examined in-stream habitat characteristics affecting kōura density and size, with a focus on juveniles ≤ 8 mm orbital carapace length (OCL), across a range of scales ranging from habitat patches to streams with contrasting catchment and riparian vegetation treatments – pasture, early or late riparian planting, and native forest. Micro-habitat variables related to kōura density included water depth and velocity, substrate size, and the area of bank undercuts and organic cover types, with root mat area significantly and positively related to juvenile densities across all scales. Although there was no significant effect of treatment type, there were strong associations between kōura and ponga logs, root systems, and coarse particulate organic matter (CPOM) across scales within and between streams.
The second study was a habitat manipulation experiment conducted to investigate whether kōura abundances, in particular juveniles, could be enhanced by additions of organic habitat consisting of 0.5 m² coconut fibre matting to simulate ponga (Cyathea dealbata) root systems that occur on the stream bank, and 1 m² ponga frond bundles to simulate the natural habitat structures formed in native forested areas. These two artificial habitats were compared with natural in-stream cobble habitats. Kōura and toi toi (Gobiomorphus spp.), both showed a preference for ponga frond habitats which were predicted to provide submerged habitat for more than 200 days. Although the coconut fibre matting was predicted to outlast ponga frond bundles by up to 107 days, it was more susceptible to sedimentation and did not provide adequate habitat for kōura due to its dense structure.
This study highlighted the influence of riparian treatments, hydrological processes, and inorganic and organic habitats on kōura populations. Information from this study can provide restoration managers with guidance on how to enhance in-stream and stream edge habitat suitability for kōura and can be used with existing mātauranga Māori, and western and community science, to determine suitable vegetation for riparian planting, assess what factors and drivers contribute to in-stream habitat availability and sustainability, and identify important habitat features that relate to kōura when conducting habitat restoration.

text: Quantifying relationships between kōura  (Paranephrops planifrons) abundance and micro-habitat features in Waikato hill-country streams Kōura (Paranephrops planifrons) is considered a taonga species by Māori and was once an abundant traditional fishery harvested throughout New Zealand. Kōura populations are under pressure in Waikato hill-country streams due to a range of factors including habitat loss and water quality degradation. Now that stakeholders have been engaging in collaborative decision-making and practices to restore/enhance biodiversity and ecosystem health within the Waikato catchment, there is opportunity to implement measures specifically targeted at kōura. Information on kōura habitat requirements to assist with the development of habitat enhancement work is therefore timely.
This research comprised two discrete studies which, in combination, provide important insights into daytime habitat use by kōura in Waikato hill-country streams. The first study was a field survey that examined in-stream habitat characteristics affecting kōura density and size, with a focus on juveniles ≤ 8 mm orbital carapace length (OCL), across a range of scales ranging from habitat patches to streams with contrasting catchment and riparian vegetation treatments – pasture, early or late riparian planting, and native forest. Micro-habitat variables related to kōura density included water depth and velocity, substrate size, and the area of bank undercuts and organic cover types, with root mat area significantly and positively related to juvenile densities across all scales. Although there was no significant effect of treatment type, there were strong associations between kōura and ponga logs, root systems, and coarse particulate organic matter (CPOM) across scales within and between streams.
The second study was a habitat manipulation experiment conducted to investigate whether kōura abundances, in particular juveniles, could be enhanced by additions of organic habitat consisting of 0.5 m² coconut fibre matting to simulate ponga (Cyathea dealbata) root systems that occur on the stream bank, and 1 m² ponga frond bundles to simulate the natural habitat structures formed in native forested areas. These two artificial habitats were compared with natural in-stream cobble habitats. Kōura and toi toi (Gobiomorphus spp.), both showed a preference for ponga frond habitats which were predicted to provide submerged habitat for more than 200 days. Although the coconut fibre matting was predicted to outlast ponga frond bundles by up to 107 days, it was more susceptible to sedimentation and did not provide adequate habitat for kōura due to its dense structure.
This study highlighted the influence of riparian treatments, hydrological processes, and inorganic and organic habitats on kōura populations. Information from this study can provide restoration managers with guidance on how to enhance in-stream and stream edge habitat suitability for kōura and can be used with existing mātauranga Māori, and western and community science, to determine suitable vegetation for riparian planting, assess what factors and drivers contribute to in-stream habitat availability and sustainability, and identify important habitat features that relate to kōura when conducting habitat restoration.

year: 2019