Chi-Hsiang Wang

Probabilistic procedure for design of untreated timber poles in-ground under attack of decay fungi

Based on first-order probability theory, this paper presents a probabilistic procedure for design of timber poles in ground contact under attack of decay fungi. Fungal attack prediction model developed in a multi-disciplinary national project in Australia, sponsored by the Forestry and Wood Products Research and Development Corporation, is used in this study for decay progress modelling. A durability design factor, kD, is derived and proposed for consideration in practical design of timber construction. Examples for computation of kD for untreated timber poles installed at two sites in Australia are given.

Design of Exposed Timber Structures

Abstract This paper describes a procedure that has been proposed for the engineering design of timber structures located above ground and subjected to attack by decay fungi. The parameters required for engineering design are the timber properties, climate parameters and structural configuration. For practical purposes, timber species are grouped into four durability classes and climate effects are grouped in terms of four climate hazard zones. The computed loss of timber section may be used to derive a residual section, which is then used as a basis for the design of either serviceability or ultimate limit states.

Assessment of Urban Heat Island and Mitigation by Urban Green Coverage

Urban heat island (UHI) is a growing threat to human well-being and poses increasing pressure on urban utility infrastructure, especially during summer months. This study examined the UHI in Melbourne using remote sensing imagery from MODIS to derive land surface temperature (LST) for the summer of 2009. Then, the potential of urban green coverage in reducing extreme summer temperatures in Melbourne was investigated using an urban climate model for 2009 and for projected 2050 and 2090 future climates. Modeling results showed that the average summer daily maximum (ASDM) temperature differences between Melbourne CBD, suburbs and rural areas were in the range of 0.5–2.0 °C. It was also found that despite the projected climate warming in 2050 and 2090, the cooling benefit in terms of the reduction in the average summer daily maximum temperature due to various urban forms and vegetation schemes remains similar to that estimated for 2009. Thus, the cooling benefit due to various urban forms and green schemes in future climates can be reasonably projected based on the benefits identified with the present-day climate.

Probabilistic procedure for design of untreated timber piles under marine borer attack

This paper presents a probabilistic design procedure for untreated timber piles under attack of marine borers, in which a new probabilistic-based durability factor is derived and introduced into the current Australian engineering design procedure. In evaluating this durability factor, a prediction model of marine borer attack on timber piles, which was developed in a national project in Australia is used for modeling the attack progress. Examples of the durability factor computed for untreated timber piles with different diameters or located at different coastal zones are provided.

A reliability model for assessing the risk of termite attack on housing in Australia

This paper describes a reliability model that was developed to estimate the risk of a successful termite attack on a house in Australia. The model of termite attack was based on the use of information obtained from a national database and on a formal survey of expert opinion. This information was embedded in a reliability model that is used to predict risk. Such models are an essential component of risk management strategies.

Rising tides: adaptation policy alternatives for coastal residential buildings in Australia

In this work, a risk-based assessment method and benefit-cost analysis to support policy decisions for adapting Australian coastal residential buildings to future coastal inundation hazard is presented. Future coastal inundation is mainly influenced by storm surge and rising sea level. The sea level rises projected by the A1FI, A1B and B1 emissions scenarios developed by the Intergovernmental Panel on Climate Change are considered. The effects of economic and population growth are accounted for by three urban development scenarios: (a) business as usual, (b) urban consolidation and (c) regional development. The adaptation policy actions investigated include a ‘protect’ stance (involving the construction of seawalls), an ‘accommodate’ stance that mandates raising house floors to a certain height (e.g. at heights of 100-year events) and an ‘avoid’ stance that limits new developments in hazardous areas. Policy stances classified as reactive (i.e. action taken after damage being incurred) and anticipatory (i.e. action taken anticipating what will happen) are developed for asset investment choices. In general, adaptation costs are an order of magnitude lower than benefits gained from avoided damages. The results highlight that adaptation action for coastal inundation has a no-regrets character and provides a strong case for reform to ensure that Australia-wide adaptation opportunities are realised.

Corrosion effects in the structural design of metal fasteners for timber construction

There has been growing recognition of the need for a more explicit consideration of material degradation effects in structural design. This article presents a procedure for the design of metal fasteners used in exposed timber structures that is suitable for use in modern reliability-based engineering design codes. The procedure is focused on the computation of the effective loss of structural section that is related to a specified service life. The fasteners are considered to be subjected to two types of corrosion: (1) the corrosion of exposed parts of the fasteners, where the corrosive agents are airborne salinity and pollution agents and (2) the corrosion of parts of the fasteners embedded in wood, where the corrosive agents are the wood acidity and preservatives. The corrosion of zinc and steel, and the effects of copper chrome arsenate preservative treatment are considered. The main design method, illustrated through a worked example in an Australian context, is applicable to most common types of mechanical joint in timber structures, but a special design procedure is required – and presented – for the shanks of bolts. The concept and format are applicable worldwide, when suitably modified according to local data and experience. Limitations and future research are suggested.

Constructing weather data for building simulation considering urban heat island

This study proposed a method to construct urban hourly weather data by adopting the ‘morphing’ approach considering urban heat islands. The method starts with the surrounding rural weather as the ‘baseline climate’ and an Urban Canopy Model is used to provide the differences in the monthly average values of major climate parameters due to urban heat islands. The ‘baseline climate’ is then morphed to generate the urban hourly weather file for building simulations. It was demonstrated that the constructed hourly weather data agree well with the observations. When used for building thermal simulations, the differences between the proposed approach and the observation in the total energy requirement of space heating and cooling and heat stress risk index were within 5% and 1.0℃, respectively. Practical applications: The proposed approach will allow academics and building engineers to construct realistic urban hourly weather data to analyse the impacts of urban heat islands on energy requirements and thermal stress for different urban planning and design options.

A reliability assessment of railway track buckling during an extreme heatwave

This paper presents a reliability assessment of railway track buckling during extreme heatwave events. Monte Carlo simulation is used to estimate the probability of track buckling. The effects of important predictor parameters such as the effective buckling length and buckling modes of the rails, as well as the rail temperatures at the time of their installation and during the heatwave are taken into account in the simulation. The results show that the probability of the buckling of tracks during an extreme heatwave similar to the event that took place in Melbourne in January 2009 is about 2/100,000 on average, which is a good estimate of the number of the track segments that were actually observed to have buckled in the Melbourne railway network. This assessment demonstrates a science-based approach to reliability assessment for track buckling during heatwaves.

Design wind speeds for temporary structures

Abstract This note discusses various approaches to determine design wind speeds for temporary structures for Australian conditions and provides recommendations that are consistent with the regulatory approach of the Building Code of Australia (BCA). Temporary structures are defined as structures with a total period of use to perform its intended purpose less than one year. The design wind speeds for these temporary structures could be reduced up to 50% of those recommended in the BCA depending on the Importance Level.