Robert H. Leicester

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.

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.

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.

Identification of Strength-Reducing Characteristics in Lumber Using Microwave Scanners

An application of the microwave technology to identify the strength-reducing characteristics in structural lumber is presented. The microwave scanners that have been developed at the Commonwealth Scientific & Industrial Research Organisation of Australia (CSIRO) in recent years can effectively detect two types of strength-reducing characteristics along the lumber: knot and slope of grain. The technique is shown to be simple, fast, safe, effective and reliable. Based on the data from the microwave scanners, an algorithm is then developed to identify juvenile lumber, which has very unfavourable physical and anatomical properties for appearances and structural uses. The use of the microwave scanners is found to be very useful in developing a strength prediction algorithm for stress grading of lumber. Some considerations for commercial uses and their expected benefits are presented.

Service Life Design for Timber Piles Attacked by Marine Borers

Abstract This paper presents a proposed procedure for the design of timber piles or posts used in marine structures subjected to marine borer attack. It is assumed that the most severe borer attack, regardless of borer species, can be represented by a narrow front along the perimeter of the timber pile cross-section within the tidal zone. The parameters chosen for engineering design relate to timber properties, environment parameters and structural configurations. For practical purposes, untreated timber species are grouped into four marine durability classes, and treated timber sapwood is classified according to the preservative retention. The environment effects are considered in terms of seven coastal zones and three salinity classes of seawater. Using the proposed procedure, the design attack depth and hence the loss of cross-section can be computed, from which the load capacity can be evaluated for a design service life.

Uncertainty and risk

The structure of houses tends to be a complex mix of ill-defined and uncontrolled elements. In 1970, a research team in CSIRO initiated the idea of using conventional structural engineering methods to assess the structural adequacy of Australian housing. The research results were promoted by running a series of workshops around Australia. This proved to be a difficult task. Essentially, we were recommending to builders that they spend more time and money without any obvious monetary returns. In 1974, while chasing further venues for our workshops, I contacted an engineer, Imants Rumpe, to suggest that we bring our housing workshop to Darwin. Imants had been a close friend of mine in University days and he was the chief construction engineer with the Darwin Department of Housing and Construction at that time. The response he obtained was not totally unexpected. ‘Sorry mate. The local builders here have been building houses for more than 30 years and have not experienced any problems. They are not interested’. Well, 1974 was the year that cyclone Tracy destroyed Darwin. It also destroyed Imants’ house! The count was 71 people killed, 80% of houses destroyed and 80% of people evacuated. Every type of housing was affected. This included houses with structures constructed with timber, concrete, masonry, steel and aluminium. That this enormous amount of destruction occurred was remarkable in view of the fact that the peak wind speeds during the height of Tracy were similar to those specified in the post-Tracy building codes. The cause of the extensive destruction was the fact that the building industry was calibrated to conditions that existed for the non-cyclonic winds of the preceding years. Many years earlier, in 1956, Imants and I had shared another lesson in applied statistics. During our student years in WA, we obtained a six-month job in gauging the flow of the Ord river which was shortly to be dammed. The gauging station was set to be placed at the 6.0-m water height mark. In response to our naïve concerns about this height, we were told that the river level had never been higher ‘in the history of white man’. Well, that year the river rose to the 28.0-m mark and wiped out our camp. This was deemed to be well above the estimated 1000-year return water level. Three years later the Ord river did it again, and the design engineers had to search for a new statistical model. Professional engineers need to be clever in selecting the correct statistical models for estimating extreme loads. Housing