Dr An Huynh

An extension of the isogeometric analysis method is used for the description of the material property and investigate the free vibration characteristics of bidirectional functionally graded (BDFG) Timoshenko beam. One-dimensional Non-uniform Rational B-Spline (NURBS) basis functions are used to construct the beam geometry as well as approximate the solution, whereas the gradations of material property are represented by two-dimensional basis functions. Different control nets are used for interpolation of material property variations throughout the domain as well as the geometry and the analysis. Four specific types of symmetrical and asymmetrical material property distributions are studied and the volume fractions of constituents are defined by power and exponential laws. In particular, the combination of both degree elevation and knot insertion, namely k-refinement, is implemented due to its ability to control the continuity. The symmetric material distribution is defined to be C

0

Geopolymer concrete offers a favourable alternative to conventional Portland concrete due to its reduced embodied carbon dioxide (CO2) content. Engineering properties of geopolymer concrete, such as compressive strength, are commonly characterised based on experimental practices requiring large volumes of raw materials, time for sample preparation, and costly equipment. To help address this inefficiency, this study proposes machine learning-assisted numerical methods to predict compressive strength of fly ash-based geopolymer (FAGP) concrete. Methods assessed included artificial neural network (ANN), deep neural network (DNN), and deep residual network (ResNet), based on experimentally collected data. Performance of the proposed approaches were evaluated using various statistical measures including R-squared (R2), root mean square error (RMSE), and mean absolute percentage error (MAPE). Sensitivity analysis was carried out to identify effects of the following six input variables on the compressive strength of FAGP concrete: sodium hydroxide/sodium silicate ratio, fly ash/aggregate ratio, alkali activator/fly ash ratio, concentration of sodium hydroxide, curing time, and temperature. Fly ash/aggregate ratio was found to significantly affect compressive strength of FAGP concrete. Results obtained indicate that the proposed approaches offer reliable methods for FAGP design and optimisation. Of note was ResNet, which demonstrated the highest R2 and lowest RMSE and MAPE values.

This paper presents two case studies of the repurposing projects of decommissioned wind turbine blades in architectural and structural engineering applications conducted under a multinational research project is entitled “Re-Wind” (www.re-wind.info) that was funded by the US-Ireland Tripartite program. The group has worked closely together in the Re-Wind Network over the past five years to conduct research on the topic of repurposing of decommissioned FRP wind turbine blades. Repurposing is defined by the ReWind team as the reverse engineering, redesigning and remanufacturing of a wind blade that has reached the end of its life on a turbine and taken out of service and then reused as a load-bearing structural element in a new structure (e.g., bridge, transmission pole, sound barrier, sea-wall, shelter). Further repurposing examples are provided in a publicly available Re-Wind Design Catalog. The Re-Wind Network was the first group to develop practical methods and design procedures to make these new “second-life” structures. The Network has developed design and construction details for two full-size prototype demonstration structures – a pedesrian bridge constructed in Cork, Ireland in January 2022 and a transmission pole to be constructed at the Smoky Hills Wind Farm in Lincoln and Ellsworth Counties, in Kansas, USA in the late 2022. The paper pro-vides details on the planning, design, analysis, testing and construction of these two demonstration projects.

A study on the bending, buckling and free vibration of functionally graded curved beams with variable curvatures using isogeometric analysis is presented here. Non-uniform rational B-splines, known from computer aided geometric design, are employed to describe the exact geometry and approximate the unknown fields of a curved beam element based on Timoshenko model. Material properties of the beam are assumed to vary continuously through the thickness direction according to the power law form. The numerical examples investigated in this paper deal with circular, elliptic, parabolic and cycloid curved beams. Results have been verified with the previously published works in both cases of straight functionally graded beam and isotropic curved beam. The effects of material distribution, aspect ratio and slenderness ratio on the response of the beam with different boundary conditions are numerically studied. Furthermore, an interesting phenomenon of changing mode shapes for both buckling and free vibration characteristics corresponding to the variation in the parameters mentioned above is also examined.

In the field of sustainable concrete practices, this review paper focuses on the concerns of the high percentage of embodied carbon dioxide present in the earth’s atmosphere by addressing the pivotal impact concrete has on this. Cement being a main ingredient in concrete has a great share in the amount of carbon dioxide embodied into the world. The substantial environmental impact of cement production on a regular basis underscores the urgency to explore alternatives and substitutions. Previous studies by scientists and engineers have successfully demonstrated the viability of partial cement replacement by percentages in concrete by enhancing its properties and reducing the environmental impact. This review paper will focus on the idea of potentially complete cement replacement in concrete. This potential idea is build based on the foundation laid by previous engineering researchers and scientists that have explored and delved into the study of potential and possible cement replacements. By recognizing that cement is a major and a main component in concrete and is a major sustainable challenge to overcome, the analysis of previous results and research will be explored based on the feasibility and implication of eliminating cement entirely from the concrete mix. Numerous tests performed previously has been conducted and recorded on partial cement replacements have shown promising results indicating the suitability of cement-free concrete for low to medium structural applications. This review goes beyond traditional studied that gradually replace cement, instead it highlights a paradigm shift towards complete replacement. A critical evaluation of existing research and findings with the aim of contributing to a more sustainable future for concrete applications. By conducting a critical evaluation and an inclusion and exclusion method to identify the gaps in the analysis, this review paper will not only highlight the successful partial replacements of cement but will also identify the gaps in literature, providing a guiding future investigation and prompting a more environmentally friendly and a conscious approach towards the concrete production in the engineering world. Being an informative resource for both industry experts and newcomers.

This paper presents two case studies of the repurposing projects of decommissioned wind tur- bine blades in architectural and structural engineering applications conducted under a multinational research project is entitled “Re-Wind” (www.re-wind.info) that was funded by the US-Ireland Tripartite program. The group has worked closely together in the Re-Wind Network over the past five years to conduct research on the topic of repurposing of decommissioned FRP wind turbine blades. Repurposing is defined by the Re- Wind team as the reverse engineering, redesigning and remanufacturing of a wind blade that has reached the end of its life on a turbine and taken out of service and then reused as a load-bearing structural element in a new structure (e.g., bridge, transmission pole, sound barrier, sea-wall, shelter). Further repurposing examples are provided in a publicly available Re-Wind Design Catalog. The Re-Wind Network was the first group to develop practical methods and design procedures to make these new “second-life” structures. The Network has developed design and construction details for two full-size prototype demonstration structures – a pedes- trian bridge constructed in Cork, Ireland in January 2022 and a transmission pole to be constructed at the Smoky Hills Wind Farm in Lincoln and Ellsworth Counties, in Kansas, USA in the late 2022. The paper pro- vides details on the planning, design, analysis, testing and construction of these two demonstration projects. This chapter presents two case studies of the repurposing projects of decommissioned wind turbine blades in architectural and structural engineering applications conducted under a multinational research project is entitled "Re-Wind" that was funded by the US-Ireland Tripartite program. Using wind turbine blades in second-life structural applications raises several structural issues. The loads that the blades will experience in these applications differ greatly from those experienced while the blades were in service, and there is the added possibility of adhesive failure with the different air-foil components. The design of the BladeBridge occurred in two phases, where initial renderings were created for use in communicating with various stakeholders and to determine aesthetic details, and a final structural design was then completed by the MTU team for use in construction. The BladePole team is focused on the repurposing of blades as vertical tangent poles for 230 kiloVolt transmission lines, which is the basis for structural analysis and comparisons.

Geopolymer concrete is known as an alternative to Portland cement, with low carbon dioxide emissions compared with the conventional building materials. In this research, the influence of curing conditions and alkali hydroxide were investigated, using curing temperatures between 40 to 100℃, curing times from 4 to 12 hours, and various types of hydroxide and concentrations of sodium hydroxide solution. Geopolymerization needs energy and time to occur, and higher curing temperatures resulted in larger compressive strength, while longer curing times resulted in higher compressive strength. At the same curing temperature, longer curing time resulted in a higher compressive strength because the longer curing time extends the chemical reaction. For geopolymer concrete, sodium hydroxide is a better property than potassium hydroxide, because the atomic size of sodium anion is smaller than potassium. Further, the strength of concrete increased when the concentration of sodium hydroxide increased. In conclusion, geopolymer concrete is suitable for traditional building materials. Finding renewable materials to satisfy the increasing demand for building structures will be the primary challenge in future.

Fiber reinforced polymer (FRP) composite materials have been used in a variety of civil and infrastructure applications since the early1980s, including in wind turbine blades. The world is now confronting the problem of how to dispose of decommissioned blades in an environmentally sustainable manner. One proposed solution is to repurpose the blades for use in new structures. One promising repurposing application is in pedestrian and cycle bridges. This paper reports on the characterization of a 13.4-m long FRP wind blade manufactured by LM Windpower (Kolding, Demark) in 1994. Two blades of this type were used as girders for a pedestrian bridge on a greenway (walking and biking trail) in Cork, Ireland. The as-received geometric, material, and structural properties of the 27 year-old blade were obtained for use in the structural design of the bridge. The material tests included physical (volume fraction and laminate architecture) and mechanical (tension and compression) tests at multiple locations. Full-scale flexural testing of a 4-m long section of the blade between 7 and 11 m from the root of the blade was performed to determine the load-deflection behavior, ultimate capacity, strain history, and failure modes when loaded to failure. Key details of the testing and the results are provided. The results of the testing revealed that the FRP material is still in excellent condition and that the blade has the strength and stiffness in flexure to serve as a girder for the bridge constructed.

High-performance fibre-reinforced concrete (HPFRC), a type of cementitious composite material known for its exceptional mechanical performance, has widespread applications in structures exposed to severe dynamic loading conditions. However, understanding nonlinear HPFRC fracture behaviour, particularly under high strain rates, remains challenging given the complexities of assessment procedures and cost-intensive nature of experiments. This study presents an interpretable framework for modelling and analysing HPFRC fracture strength at high strain rates. A wide range of machine learning methods, including ensemble techniques, were employed to capture multivariate effects of eight essential input features (e.g., mortar compressive strength, fibre physical and mechanical properties, cross-sectional area, and strain rate) on fracture strength response. To assess the derived models, a novel evaluation procedure was proposed involving a data-based analysis, employing established metrics (i.e., coefficient of determination, root mean squared error, and mean absolute error via K-fold cross-validation) and a domain experts-involved evaluation utilising global sensitivity analysis to discern first-order and higher-order interactions among input factors. The proposed approach efficiently yielded both quantitative and qualitative insights into crucial input factors governing HPFRC fracture strength with limited experimental data. The obtained findings highlight the significance of multivariate effects, such as the interaction between strain rate and fibre tensile strength, and between fibre volume and fibre diameter, on fracture behaviour. The proposed interpretable framework aims to provide a powerful tool for proactive material failure analysis by understanding fracture behaviour and identifying potential weak and strong interactions among input factors of HPFRC-based samples. Moreover, the utilisation of the proposed approach enables researchers and civil engineers to efficiently focus on the most critical input parameters during the early design stage and ensuring the structural integrity and safety of HPFRC-based constructions.

This paper describes repurposing projects using decommissioned wind turbine blades in bridges conducted under a multinational research project entitled “Re-Wind”. Repurposing is defined by the Re-Wind Network as the re-engineering, redesigning, and remanufacturing of a wind blade that has reached the end of its life on a turbine and taken out of service and then reused as a load-bearing structural element in a new structure (e.g., bridge, transmission pole, sound barrier, seawall, shelter). The issue of end-of-life of wind turbine blades is becoming a significant sustainability concern for wind turbine manufacturers, many of whom have committed to the 2030 or 2040 sustainability goals that include zero-waste for their products. Repurposing is the most sustainable end-of-life solution for wind turbine blades from an environmental, economic, and social perspective. The Network has designed and constructed two full-size pedestrian/cycle bridges—one on a greenway in Cork, Ireland and the other in a quarry in Draperstown, Northern Ireland, UK. The paper describes the design, testing, and construction of the two bridges and provides cost data for the bridges. Two additional bridges that are currently being designed for construction in Atlanta, GA, USA are also described. The paper also presents a step-by-step procedure for designing and building civil structures using decommissioned wind turbine blades. The steps are: project planning and funding, blade sourcing, blade geometric characterization, material testing, structural testing, designing, cost estimating, and construction.

Concrete production’s reliance on traditional Portland cement is a significant contributor to global construction and development. Concrete production’s reliance on traditional Portland cement is a significant contributor up to 10% global CO2 emissions, prompting a need for sustainable alternatives. This study explores the use of geopolymer binders, composed of industrial and agricultural by-products ground granulated blast furnace slag (GGBS) and metakaolin (MK), as a low-carbon alternative to conventional cement. An experimental investigation has been conducted to assess the workability and compressive strength of various cement free concrete mixes, tested at intervals of 5, 7, 28, and 91 days. The study also examined the impact of different curing methods (air and water curing) and activator-to-binder (a/b) ratios on the concrete’s mechanical properties. The findings revealed that both the binder composition and curing method significantly influence the compressive strength, with certain mixes demonstrating superior long-term performance, particularly those with optimized a/b ratios and higher GGBS content. These insights underscore the potential of geopolymer binders as a sustainable alternative to Portland cement, offering a viable path to reducing the carbon footprint of concrete production while maintaining structural integrity.

This article considers semi-flexible composite (SFC) pavement materials made with reclaimed asphalt planings (RAP) and geopolymer cement-based grouts. Geopolymer grouts were developed and used to fill the internal void structure of coarse RAP skeletons with varying levels of porosity. The geopolymer grouts were formulated at ambient temperature using industrial by-products to offer economic and environmental savings relative to conventional Portland cement-based grouting systems. They were characterised on flowability, setting time, and compressive strength. The effect of grout and RAP on SFC material performance was evaluated using permeable porosity, compressive strength, and ultrasonic pulse velocity. SFC performance was significantly influenced by both grout type and RAP content. Improved performance was associated with mixtures of high-flowability/high-strength grout and low RAP content. A practical limitation was identified for combination of grout with low-flowability/fast-setting time and well-compacted RAP skeletons. Solids content exceeding 49% by volume was not feasible, owing to inadequate grout penetration. A suite of SFC materials was produced offering performance levels for a range of practical pavement applications. Preliminary relationships enabling prediction of SFC elastic modulus based on strength and/or ultrasonic pulse velocity test data are given. A pavement design is given using SFC as a sub-base layer for an industrial hardstanding.

In this study, the nurbs-based isogeometric analysis is developed to optimize natural frequencies of bidirectional functionally graded (BFG) beams by tailoring their material distribution. One-dimensional Non-Uniform Rational B-Spline (NURBS) basis functions are utilized to construct the geometry of beam as well as approximate solutions, whereas the gradation of material property is represented by two-dimensional basis functions. To optimize the material composition, the spatial distribution of volume fractions of material constituents is defined using the higher order interpolation of volume fraction values that are specified at a finite number of control points. As an optimization algorithm, the differential evolution (DE) algorithm is employed to optimize the volume fraction distribution that maximizes each of the first three natural frequencies of BFG beams. A numerical analysis is performed on the examples of BFG beams with various boundary conditions and slenderness ratios. The obtained results are compared with the previously published results in order to show the accuracy and effectiveness of the present approach. The effects of number of elements, boundary conditions and slenderness ratios on the optimized natural frequencies of BFG beams are investigated.