Zidi Yan

Preservative penetration checks for copper chrome arsenate treated timber in Australia are commonly performed using the manual spot tests; PAN (1-(2-pyridylazo)-2-naphthol (CAS 85-85-8)) for copper, and Variamine Blue RT salt (VBRT) ((N-phenyl-p-phenylenediamine, diaozonium salt) (CAS 4477-28-5) for sapwood in conifers) testing, followed by visual interpretation against AS/NZS 1604.1 requirements. In practice, these checks are subjective, especially when colour evidence is discontinuous, low contrast, or affected by lighting, surface texture, and timber anatomy. This can lead to inconsistent " Pass " or " Fail " outcomes between assessors, slower release decisions, and harder to defend quality assurance records. This paper presents a machine learning assisted workflow that converts paired PAN and VBRT images into repeatable measurements and traceable decision outputs aligned with H3 penetration logic for 35 mm × 70 mm timber boards. The workflow standardises image size through cropping, uses manual annotations to generate reference masks, and then derives quantitative metrics including treated sapwood coverage, detection of major surface connected untreated gaps, penetration depth from each exposed face with a 5 mm target, and the fraction of unpenetrated heartwood under an allowance check consistent with AS 1604.1 logic. These metrics serve two purposes. First, they support a rule-based compliance check using predefined thresholds. Second, they are used as input features for supervised classification. A dataset of approximately 2,000 paired images was planned to be established, with 497 specimens used for model evaluation and training at the current preliminary stage. The trained model achieved an overall accuracy of 73.2% across these 497 specimens. A separate verification test on 125 additional unseen specimens achieved 80% accuracy, demonstrating the feasibility of an AI assisted decision tool for improving consistency and transparency in treated timber penetration assessment. A full 2,000 data set will be analysed, and the algorithms will be improved. The current workflow provides a practical baseline that addresses the core consistency issue, and the next stage is focused on systematic improvement through continual learning and deployment feedback.

A long-term field trial was established in June 1996 to evaluate the performance of preservative-treated Pinus radiata in above-ground, weather-exposed decking applications, with particular emphasis on the role of preservative penetration into heartwood. The study, first documented by Gardner et al. (1997), compared treated and untreated heartwood and sapwood at two sites representing different decay hazards: Beerburrum, Queensland (Scheffer’s Index ≈ 42; moderate hazard), and Coopernook, New South Wales (Scheffer’s Index ≈ 65; high hazard).

Boards (1000 × 90 × 45 mm) were treated with one of four preservative systems: Protim 235WR (tri-n-butyl tin naphthenate and permethrin), Protim 70WR (copper naphthenate and permethrin), Tanalith O (CCA), and ACQ 2100 Type B (copper oxide and didecyldimethyl ammonium chloride). Decks were constructed in accordance with draft specifications of the Protocols for Assessment of Wood Preservatives (AWPC, 1997), with 12 boards per deck. To examine potential treatment vulnerabilities, half the boards were drilled before treatment and half after treatment. In addition, half of the decks were covered with shade cloth to moderate drying.

The Beerburrum site was destroyed by a bushfire in 2000. The Coopernook decks remained in service for 28 years and were harvested in early 2024. Individual boards were assessed and the decks reconstructed on 100 × 100 mm CCA (H4) treated pine bearers, incorporating both treated (H3) and untreated pine palings to encourage biological pressure. Decks were reinstalled at the Queensland Department of Primary Industries Maroochy Research Facility, Nambour, in August 2025.

Over time, dense vegetation grew through and around the decks at the Coopernook site due to minimal site maintenance, creating persistently wet conditions more severe than those prescribed for Hazard Class H3 exposures. These conditions likely increased decay hazard beyond above-ground expectations.

After 28 years, CCA-treated boards performed best, with 163 boards remaining, followed by ACQ (133 boards). Protim 70WR had only 15 surviving boards, while Protim 235WR (TBTN and permethrin) effectively failed, with only three boards remaining. For both ACQ and CCA, a higher proportion of surviving boards comprised 100% heartwood, suggesting that heartwood presence contributed to improved long-term performance, although heartwood penetration levels were unknown.

All surviving boards exhibited severe surface weathering. Although many remained biologically serviceable, aesthetic degradation and checking would likely necessitate replacement in practice. The long intervals between assessments highlight the challenges of modelling deterioration in multi-decade trials and emphasise the importance of sustained frameworks to support long-term durability research.

Self-tapping screws are increasingly used in Australian timber construction, yet their performance under climate induced degradation in chemically treated timber remains insufficiently quantified. This paper reports a pilot study from a broader programme, examining two preservative systems (H2F and CCA) and two screw coatings (hot dip galvanised, GAL, and Tufcote, TU) under two exposure regimes: full outdoor exposure (FE) and controlled water exposure (WE). Test samples were tested at 0-month (control), 3-month, and 6-month durations. Structural performance was evaluated using screw withdrawal (SW) and screw shear (SS) tests, with density corrected results reported and compared with the latest Eurocode 5 prediction equations. Overall, withdrawal behaviour was more sensitive to exposure. FE led to clear capacity reductions by 6 months in multiple groups, while WE produced mixed responses, including short term gains in some cases that were not always retained at 6 months. Coating and treatment interactions were evident, with TU generally showing larger early reductions under FE. These findings provide preliminary evidence to support environment specific fastener selection and motivate durability informed connection design for Australian treated timber systems.

Withdrawal testing is being used for various reasons such as testing hypotheses on durability or developing new connectors using various screw-types or nails. New research questions extend these testing methods to other topics such as rammed-in electrodes for moisture content determination by the electrical resistance method. Three Australian wood species, Corymbia maculata, Eucalyptus nitens, and Pinus radiata D. Don., are therefore investigated using a fixed load rate. This paper outlines the methodologies employed in withdrawal testing and highlights key findings. Preliminary results indicate that moisture variations affect the fit of any pin-shaped object in wood, impacting their withdrawal load peak values. These findings contribute to understanding the impact of moisture on contact pressure and withdrawal capacity, crucial not only for designing reliable timber connections in construction, but also other applications such as wood moisture determination.

Australia faces a housing crisis marked by high mortgages for oversized, underperforming homes, making home ownership increasingly inaccessible for younger generations. Adaptable housing allows homes to evolve with household needs and incorporates future-proof design principles. This paper present findings of applied research aimed to explore the technical feasibility of adaptable housing in Southeast Queensland using a novel modular, reconfigurable, and relocatable light timber-framed building system that can respond to changing occupant needs. Design considerations, technical challenges and corresponding solutions are presented with a focus on structural and hygrothermal design and performance.

Connections play an important role in timber structures as they govern the overall stiffness, load-carrying capacity, and most of the ductility in a timber structure. Due to the high axial load-carrying capacity and ease of installation, self-tapping screws are nowadays one of the most widely used fasteners in timber construction. However, variations in national standards, regulations, or even timber species might lead to incorrect predictions for the screw's load-carrying capacity. The current Australian Timber Standard AS 1720.1-2010 has some fundamental limitations since it was primarily derived from old North American research and supplemented in the 1970s with empirical data on Australian hardwoods and a few softwoods. Modern European fasteners are increasingly employed in the Australian building industry, making it critical to examine their performance consistency in the context of Australian timber products. This research work, therefore, aimed to a) evaluate the interactions of numbers of penetration layers, screw tip, and screw characteristic withdrawal strength, b) evaluate the influence of inclination angles on characteristic withdrawal strength, and c) compare experimental results with existing models and provide recommendations.

The increased use of wood products for construction has intensified the need to understand how moisture affects the mechanical properties of timber connections. The withdrawal capacity of dowel-type fasteners, such as screws, needs to be measured, or estimated, for the design of timber systems having connections with axially loaded dowel-type fasteners. The influence of the moisture content changes on the timber is often examined, but its effect on the mechanical performance of connections is poorly considered, including the design codes. This work examined changes in the screw withdrawal capacity in light organic solvent preservative-treated and untreated Radiata pine with type 17 screws inserted perpendicular and parallel to the grain and subjected to repeated wetting and drying cycles. A comparison of the screw withdrawal capacities with those predicted from Australian and European codes was performed. The results presented here are part of a larger project that includes the study of embedment strength and lateral resistance in combination with different wood treatments and pine species.

The impact of moisture in timber structures is associated with the deterioration of timber, and loss of mechanical performance. Methods have been developed to treat timber using chemicals to inhibit deterioration, however, water intrusion has much more immediate effects on the mechanical properties of timber associated with swelling and shrinkage of the wood. The effects of moisture on the mechanical performance of timber have been widely studied. Nevertheless, timber must be connected to create a structure and these connections are usually the most critical part of a structure. They are designed to fail in ductile mode as it allows enough time to identify further failures and prevent dangerous consequences for the occupants. Despite the critical importance of timber connections, the effects of moisture on their mechanical performance remain poorly understood. This work aims to assess the effect of repeated moisture cycles on the performance of laterally loaded single-shear nailed joints using LOSP-treated and untreated Radiata pine. The mechanical performance of the connections was evaluated through monotonic shear tests from which the maximum strength and initial stiffness were determined. A comparison of the experimental results with those predicted from the Australian and European standards is also presented. Results showed the mechanical performance of the connections was not affected by up to 8 moisture cycles. Specimens built with untreated wood showed a significant loss in capacity after 12 moisture cycles, whereas the specimens built with LOSP-treated wood showed a significant loss after 16 moisture cycles. This could be to the presence of residual solvent in the treated wood that prevents moisture ingression around the fasteners. The maximum strength after 16 moisture cycles was statistically the same for specimens built with both treated and untreated wood, which probably means the residual solvent was evaporated or leached. A comparison of the maximum strength with that from the Australian standard showed the current standard was unable to safely predict the loss of performance of the connection caused by moisture. The European standard utilises more system characteristics for the predictions but was not designed to be applied to Australian timber species, failing to produce safe estimations.