190 research outputs found
Sustainable Composite Construction Materials
No full textOften, a project's sustainability is centred on building services and energy, but we need to have a comprehensive view of how we integrate deeper sustainability. Traditionally, we have neglected embodied carbon generated during building construction, which has led to significant carbon emissions over the last few decades, causing global warming and other related problems. The aim of this Special Issue was to collect the results of research and practice experiences in sustainable building structures, made from steel, concrete, timber, and other composite materials. Dr Roy and Dr Ananthi warmly invited authors to submit their papers for potential inclusion in this Special Issue of “Sustainable construction using steel, concrete, timber, and other composite materials”, in the journal of Journal of Composites Science
Assessing the viability of foldable-expandable container homes for post-disaster housing in New Zealand
No full textNatural disasters frequently demolish New Zealand, with its diverse landscapes. It is particularly susceptible to various natural disasters due to its unique geological position on the edge of the Pacific Ring of Fire (McKinnon, Scott, and Margaret Cook, 2020). This makes it prone to earthquakes, volcanic activity, tsunamis, and extreme weather events. A notable example of such a disaster is Cyclone Gabrielle, which struck the Hawke's Bay region in New Zealand. It creates wide damage in housing properties, leaving damaged bridges and culverts, buried roads, significant dropouts, and isolated communities in its wake. One of the major difficulties for government authorities and policymakers is to build houses for the victims of such natural disasters within as short a period as possible. The rapid provision of safe, durable, and affordable shelters is essential to restore a sense of normalcy for affected populations. Traditional reconstruction methods are often slow, expensive, and complex, particularly in regions with limited resources or logistical challenges. This has led to the exploration of alternative housing solutions, such as the use of modified shipping containers.
In New Zealand, as it is a reality, expeditious and resilient housing options are crucial for recovery after a natural disaster. Therefore, strategic solutions should be introduced to assist the responsible entities and agencies in providing shelters to the disaster victims within a short duration.
Container homes offer a unique combination of structural integrity, portability, and affordability, making them an attractive option for post-disaster housing. Their inherent durability allows them to withstand harsh environmental conditions, and their modular nature facilitates quick assembly and scalability. Additionally, container homes can be prefabricated and easily transported to disaster sites, reducing the time required for construction and enabling immediate relief efforts. This thesis explores the feasibility of using double-wing expandable foldable container homes as an innovative post-disaster housing solution in New Zealand, focusing on the aftermath of Cyclone Gabrielle in Hawke's Bay.
Findings indicate that container homes offer significant advantages, including reduced construction timelines, cost savings, and the adaptability needed for fast recovery in disaster-affected regions. However, challenges remain in achieving compliance with New Zealand’s stringent building codes and in adapting the homes to withstand several factors such as seismic/ wind resistance, waterproofing, etc. which are prevalent in many disaster-prone areas. Regulatory requirements, such as PS1 and PS4 design approvals and local council consents, emerge as pivotal considerations that can delay deployment if not streamlined
Machine learning applications for studying the structural behaviour of cold-formed steel columns with web openings
No full textThis study presents a data-driven machine learning (ML) approach to study the structural
behaviour of cold-formed steel (CFS) columns with web openings. A total of 23 experimental
results from literature were employed for validation purposes. It was shown that the
validation ratio is reasonable as the average ratio of experimental to FEA strengths (FEXP/FFEA)
is 1.07. Afterwards, a total of 15,000 data points for training selected ML algorithms are
generated from elasto plastic finite element analysis (FEA), which incorporates both initial
geometric imperfections and residual stresses. The input features of this study are the overall
lip width of the section, web height, section thickness, length of channel section, hole and
edge configuration (number, spacing, radius). A total of six machine learning (ML)
algorithms, namely, XGBoost, Decision tree, Artificial Neural Network, Random Forest,
Lasso Regression, and Linear Regression, are evaluated to examine the structural behaviour
of CFS columns with web openings. 10-fold cross-validations are performed on selected ML
algorithms. It was found that the proposed XGBoost model outperformed other previously
described machine learning (ML) algorithms in comparison. The XGBoost algorithm
produced the best accurate predictions (99%) with the shortest training time. In addition, the
XGBoost model has the lowest mean root squared error and mean absolute error. An
investigation of the importance of input factors found that lip width of the section and length
of channel section were the most relevant features
Evaluation of machine-learning models for load-carrying capacity assessment of components of light metal structures
No full textIn the thesis, a machine learning based framework is presented to predict the load carrying capacity of components in light metal structures. The study includes investigations on cold formed steel channel sections with and without openings, subjected to axial compression and web crippling, as well as a separate study on aluminium roof sheeting under wind uplift. To begin, nonlinear finite element models are developed and validated using experimental tests reported in existing literature. The validated finite element (FE) models are then utilized to train machine learning models such as Deep belief network (DBN) and eXtreme Gradient Boosting (XGBoost). The evaluation involves comparing the performance of existing design guidelines with predictions derived from experimental testing, finite element analysis (FEA), and machine learning techniques. The findings demonstrate that the machine learning methods outperform other approaches, yielding highly accurate load carrying capacity predictions. Furthermore, design equations for each study are proposed based on bivariate linear regression analysis using the predictive models. The feasibility of these design equations is confirmed through reliability analysis, confirming their accuracy in predicting the capacity
Life Cycle Assessment of Light Steel and Timber Framed Residental Buildings In New Zealand
No full textFull Text is available to authenticated members of The University of Auckland only.New Zealand has committed to a vision of net-zero carbon by 2050 to reduce all greenhouse gases. A whole building embodied carbon reduction framework has been introduced to the Building and construction industry to meet the carbon reduction target. The carbon emissions are attributable across the building life cycle. This includes emissions from the whole supply chain of construction materials manufacturing, construction process, repairing and demolishing process at the end of life. Therefore, the net-zero carbon 2050 vision also prioritizes building whole life cycle embodied carbon assessment as part of the building consent process. Subsequently, buildings will be required to meet a mandatory standard of whole life embodied carbon to obtain the building consent. Following this agenda, the aim of this research to present the environmental impacts produced by light steel (LS) and timber-framed residential buildings under the quantitative approach of life cycle assessment (LCA). A limited number of LCA studies have been undertaken in New Zealand, and none of their scopes compare the embodied carbon impacts between LS vs timber-framed buildings. Timber is the most dominating building material, especially in New Zealand's residential projects over the last 100 years. Timber softwood like ―Pinus radiate‖ and ―Douglas fir‖ are commercially used for structural framing. Moreover, the alternative LS framing option has been gradually increasing in the local construction projects. The main advantages of the LS framings are the flexible on-site assembly and high content of recyclability. Therefore, the scope of this research had assessed embodied carbon and energy impacts to illustrate a comparative environmental performance of modern LS framings against conventional timber framings of the buildings. The research methodology has introduced a framework for developing life cycle inventory (LCI) through integrated building information modelling (BIM), analysing and comparing the quantitative impacts between LS and timber-framed buildings in New Zealand. The ―Cradle to Cradle‖ LCA system boundary results have confirmed that timber-framed buildings produced 43% less Global warming potential (GWP) impacts, whereas 55% less embodied energy consumed by the LS framed building. The timber-framed building has the most significant advantage showing the lowest carbon impacts but no benefits after the end of life. Indeed, LS framed buildings are potentially developing carbon impacts at the production stage but still ensure high recycling scraps after demolition, reducing the demand for virgin raw products in the further manufacturing stage
Cross-sectional Shape Optimization of Cold-Formed Steel Columns for Better Structural and Thermal Performances
No full textFull Text is available to authenticated members of The University of Auckland only.Cold-formed steel (CFS) sections can be rolled into different cross-sectional shapes, and optimizing these shapes can further improve their load-bearing capacities, resulting in a more economical and efficient building solution. However, the high thermal conductivity of steel can lead to thermal bridges, which can significantly reduce the building's thermal performance and energy efficiency. Although many studies can be found regarding the optimization of CFS sections for better structural behaviours, or thermal performance improvement, there is no existing research found in the literature on the optimization of CFS sections from both perspectives at the same time. Therefore, this research aims to find an optimal cross-sectional shape for a CFS column that maximizes its thermal resistance and axial strength with fixed coil width and given thickness.
An extensive parametric study was undertaken to numerically investigate the effect of CFS columns' cross-sectional shape and size on the thermal and structural performances. Three cross-sectional shapes were considered, unlipped channel sections, simple lipped channel sections, and simple lipped channel sections with flange indentations. The parametric study also varied the steel thickness, web depth, flange length, lip size, flange indent size, indent width, and indent angle. In total, 324 FE models were computed and analyzed regarding thermal and structural performances, respectively. According to the obtained results, the thermal resistance of the CFS framed wall decreases with increased steel thickness, while the strength of the CFS section increases with the thickness. The thermal resistance of the CFS framed wall decreases when the flange length increases due to the increased steel flange contact surface. Furthermore, the results enhance the need for a small indentation in the flange to increase the thermal resistance. The average increase in the thermal resistance was found to be 1.41%, 2.61%, and 3.74% for an indent size of 2, 5, and 8 mm, respectively, considering a steel thickness of 2.5 mm. However, this flange indentation adversely affected the axial capacity of the CFS section. The average percentage of decrease in the strength is 0.87%, 2.05%, and 4.72% for a flange indent size of 2, 5, and 8 mm, respectively, considering a steel thickness of 2.5 mm. The optimal design of the CFS columns found among the 324 FE models with the greatest thermal resistance and axial capacity for each cross-sectional shape was present in this research. The maximization of thermal resistance always leads to decreased axial strength, and, oppositely, the maximization of axial strength always leads to a drop in thermal resistance. A set of Pareto-optimal solutions was also presented
Structural behaviour of cold-formed steel built-up stiffened box sections under bending, axial compression and web crippling
No full textThe use of cold-formed steel (CFS) built-up sections in engineering practice is widely gaining popularity due to their ability to provide sustainable solutions and optimised section design opportunities. The aim of this research is to investigate the structural performance of novel CFS built-up stiffened box sections under bending, axial compression and web crippling. In total, 38 experimental tests were conducted, covering bending tests, axial compression tests, and web crippling tests. The material properties of test specimens were obtained from tensile coupon tests. Nonlinear finite element (FE) models were also developed and validated against the experimental test results, which showed good agreement. The validated FE models were then used to conduct a parametric study involving a total of 1700 FE models to investigate the effects of key parameters on the resistance of such CFS built-up stiffened box sections.
Because these new sections are very different from those for which current design guidelines in the standards comprising AISI S100 (2016), AS/NZS 4600 (2018) and EN 1993-1-3 (2006) have been developed, the comparison shows that the design strengths predicted by these standards are not a good predictor of the actual performance for all three loading cases.
Based on the experimental and numerical results, modified design equations in the form of the Direct Strength Method were proposed for calculating the resistance of CFS built-up stiffened box sections. A reliability analysis was conducted to evaluate the feasibility of the proposed design equations. The results indicated that the proposed design equations can closely predict the resistance of CFS built-up stiffened box sections under bending, axial compression and web crippling
Innovative cold-formed steel nested tapered box section portal frames with bolted-side plate joints
No full textNested tapered box (NTB) portal frames made entirely of cold-formed steel (CFS) are widely used in New Zealand. Shahmohammadi (2019) recently described a full-scale test of such a system. The tested frame had a span of 18.16 meters and a height to the eaves of 4.27 meters. The joints of this NTB portal frame were rigid, constructed with bolted end plates. However, bolted end plate joints can be expensive due to the full penetration butt weld. This thesis proposes an alternative jointing system that uses bolted-side plates. The numerical work conducted in this study yields the following findings:
• A shell finite element (FE) model was developed and validated using previously conducted full-scale portal frame tests. This validated model was then employed to compare the performance of bolted-side plate joints with bolted end-plate joints. The analysis revealed that a portal frame with 10 mm thick bolted side plates could sustain the same load as an NTB portal frame with bolted end-plate joints. Increasing the thickness of the bolted-side plates from 10 mm to 16 mm resulted in a 20% increase in load-carrying capacity. This improvement was due to the confinement effect provided by the side plates, which reduced the slenderness ratio near the eaves joint. However, the NTB portal frame with bolted-side plates exhibited greater apex displacement compared to the frame with bolted end-plate joints.
• FE models were developed for both the eaves and apex joints of the NTB portal frame. A parametric study was then carried out involving 1,000 FE models. Using FE models, design equations are proposed for the moment capacities of the eaves and apex bolted side plates, accounting for both opening and closing moments under partial restraint.
• A parametric study was conducted using the developed design method on eight models, considering a range of spans from 25m to 40m and eaves heights from 5.5m to 6.25m, with a consistent frame spacing of 7.5m. The results showed that portal frames with bolted-side plates can carry on average 7% more load compared to those with bolted end plate joints.
• A methodology was presented to predict the load-carrying capacity of portal frames with back-to-back channel sections. It was shown that the predicted vertical loads from the proposed approach were, on average, within 1% (on an average) of the FEA results for portal frames. The same approach was applied to NTB portal frames through worked examples in Appendix B and C, demonstrating good accuracy
Capacity of cold-formed steel channels with edge-stiffened web holes in bending, shear and web crippling
No full textThin-walled structural channel members as floor joists and bearers are commonly manufactured
with cut-outs to allow access for building services such as plumbing, electrical, and heating
systems in the walls and ceilings. The presence of web holes in the members will cause changes
in the stress distribution and consequently, there will be changes in the buckling characteristics
and ultimate strength. Traditional web holes are normally punched or bored and are un-stiffened,
which can restrict the size and spacing of web holes. To overcome these restrictions, a new
generation of cold-formed steel (CFS) channel beams with edge-stiffened web holes developed
by the CFS industry has been widely used. Such CFS channel beams, when used as floor joists
and bearers, are often subjected to concentrated loads; hence experiencing shear failure, bending
failure, and web crippling failure. However, in the literature, limited work is available on the
behaviour of such CFS channel beams in bending, shear, and web crippling. Furthermore, the
current design guidelines, such as the American Iron and Steel Institute (AISI, 2016) and the
Australian and New Zealand Standards (AS/NZS, 2018), do not provide any design guidelines for
determining the capacity of such CFS channel beams with edge-stiffened web holes.
The aim of this research is to investigate the effects of edge-stiffened web holes on the capacity
of such CFS channel beams in bending, shear, and web crippling. In total, 82 laboratory tests were
performed, covering web crippling tests, bending tests, and shear tests. For comparison,
specimens with un-stiffened web holes and plain webs were also tested. The material properties
of test specimens were determined from tensile coupon tests. The results obtained from laboratory
tests show that the CFS channel beams with edge-stiffened web holes performed better than those
with un-stiffened web holes in terms of ultimate capacity for all three loading cases.
Nonlinear finite-element (FE) models were also established and validated against the
experimental results, which showed good agreement both in terms of ultimate capacity and
deformed shapes. The validated FE models were then used to perform a parametric study
involving 1335 FE models to investigate the effects of different parameters on the capacity of
such channel beams.
To evaluate the performance and accuracy of current design guidelines of CFS channel beams
with un-stiffened web holes, the test and FE results were compared against the design capacities
predicted by the current design guidelines such as AISI (2016) and AS/NZS (2018). The
comparison results show that design capacities predicted by AISI (2016) and AS/NZS (2018) are
conservative and unsafe for calculating the capacity of CFS channel beams with edge-stiffened
web holes for all three loading cases.
Based on the experimental and numerical results, suitable design equations in the form of capacity
reduction factors were developed using bivariate linear regression analysis for calculating the
shear capacity of CFS channel beams with edge-stiffened web holes. A reliability analysis was
carried out to evaluate the accuracy and reliability of the proposed design equations, indicating
that the proposed design equations can closely predict the shear capacity reduction factors of CFS
channel beams with edge-stiffened web holes
Web crippling behaviour of cold-formed stainless steel lipped channel sections with edge-stiffened web holes under two-flange loading conditions
No full textIn New Zealand, edge-stiffened holes have been recently introduced to cold-formed steel channels (CFS) to facilitate the installation of plumbing and electrical systems. Previous studies on cold-formed carbon steel (CFCS) channels have demonstrated that using edge-stiffened web holes provides nearly the same strength as an equivalent channel section with a plain web when facing web crippling. However, there is a lack of experimental or numerical investigations into the application of edge-stiffened web holes in cold-formed stainless steel (CFSS) channels in the existing literature.
This thesis builds upon previous studies conducted on CFCS channel sections. It presents a comprehensive numerical examination of the web crippling behavior of CFSS channel sections with edge-stiffened circular web holes under interior-two-flange (ITF) and end-two-flange (ETF) loading conditions. Three stainless steel grades were considered: EN 1.4509 (Ferritic), EN 1.4462 (Duplex), and EN 1.4301 (Austenitic). A parametric study involving 3,744 non-linear finite element (FE) models was developed for both fastened and un-fastened flange cases. The study covered the impact of different hole sizes, edge-stiffener lengths, channel inner radius, and the length of the bearing plates.
The results of the parametric study were used to establish new equations for web crippling strength and strength reduction factors through non-linear regression analysis. These proposed design equations outperformed predictions from American Society of Civil Engineers Specification (ASCE 8-02), American Iron and Steel Institute Specification, Australian/New Zealand Standard (AISI&AS/NZS), and Eurocode 3. Finally, a reliability analysis was conducted, revealing that the proposed design equations accurately predict the web crippling strength of CFSS channel sections with plain webs, unstiffened web holes, and edge-stiffened web holes under two-flange loading conditions
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