Ultimate limit states design of concrete railway sleepers

The railway industry has been slow to adopt limit states principles in the structural design of concrete sleepers for its tracks, despite the global take up of this form of design for almost every other type of structural element. Concrete sleeper design is still based on limiting stresses but is widely perceived by track engineers to lead to untapped reserves of strength in the sleepers. Limit design is a more rational philosophy, especially where it is based on the ultimate dynamic capacity of the concrete sleepers. The paper describes the development of equations and factors for a limit design methodology for concrete sleepers in flexure using a probabilistic evaluation of sleeper loading. The new method will also permit a cogent, defensible means of establishing the true capacity of the billions of concrete sleepers that are currently in-track around the world, leading to better utilisation of track infrastructure. The paper demonstrates how significant cost savings may be achieved by track owners.

Briefing: Limit states design of railway concrete sleepers

Recently updated information has raised a concern over not only the existing cost-ineffective design method but also the unrealistic analysis mode of railroad prestressed concrete sleepers. Because of the deficient knowledge in the past, railway civil engineers have been mostly aware of the over-conservative design methods for structural components in any railway track, which rely on allowable stresses and material strength reductions. Based on a number of proven experiments and field data, it is believed that the concrete sleepers which complied with the allowable stress concept possess unduly untapped fracture toughness. A collaborative research project run by the Australian Cooperative Research Centre for Railway Engineering and Technologies (RailCRC) was initiated to ascertain the reserved capacity of Australian railway prestressed concrete sleepers designed using the existing design code. The findings have led to the development of a new limit states design concept. This briefing highlights the conventional and the new limit states design philosophies and their implication to both the railway and the public community.

Numerical study of impact forces on railway sleepers under wheel flat

Wheel-rail interaction is one of the most important research topics in railway engineering. It includes track vibration, track impact response and safety of the track. Track structure failures caused by impact forces can lead to significant economic loss for track owners through damage to rails and to the sleepers beneath. The wheel-rail impact forces occur because of imperfections on the wheels or rails such as wheel flats, irregular wheel profile, rail corrugation and differences in the height of rails connected at a welded joint. The vehicle speed and static wheel load are important factors of the track design, because they are related to the impact forces under wheel-rail defects. In this paper, a 3-Dimensional finite element model for the study of wheel flat impact is developed by use of the FEA software package ANSYS. The effects of the wheel flat to impact force on sleepers with various speeds and static wheel loads under a critical wheel flat size are investigated. It has found that both wheel-rail impact force and impact force on sleeper induced by wheel flat are varying nonlinearly by increasing the vehicle speed; both impact forces are nonlinearly and monotonically increasing by increasing the static wheel load. The relationships between both of impact forces induced by wheel flat and vehicles speed or static load are important to the track engineers to improve the design and maintenance methods in railway industry.

A non-linear dynamic analysis of heavy haul track line sleepers under wheel flat

Significant wheel-rail dynamic forces occur because of imperfections in the wheels and/or rail. One of the key responses to the transmission of these forces down through the track is impact force on the sleepers. Dynamic analysis of nonlinear systems is very complicated and does not lend itself easily to a classical solution of multiple equations. Trying to deduce the behaviour of track components from experimental data is very difficult because such data is hard to obtain and applies to only the particular conditions of the track being tested. The finite element method can be the best solution to this dilemma. This paper describes a finite element model using the software package ANSYS for various sized flat defects in the tread of a wheel rolling at a typical speed on heavy haul track. The paper explores the dynamic response of a prestressed concrete sleeper to these defects.

Ultimate flexural limit states analysis of prestressed concrete sleeper

Railway is one of the most important, reliable and widely used means of transportation, carrying freight, passengers, minerals, grains, etc. Thus, research on railway tracks is extremely important for the development of railway engineering and technologies. The safe operation of a railway track is based on the railway track structure that includes rails, fasteners, pads, sleepers, ballast, subballast and formation. Sleepers are very important components of the entire structure and may be made of timber, concrete, steel or synthetic materials. Concrete sleepers were first installed around the middle of last century and currently are installed in great numbers around the world. Consequently, the design of concrete sleepers has a direct impact on the safe operation of railways. The "permissible stress" method is currently most commonly used to design sleepers. However, the permissible stress principle does not consider the ultimate strength of materials, probabilities of actual loads, and the risks associated with failure, all of which could lead to the conclusion of cost-ineffectiveness and over design of current prestressed concrete sleepers. Recently the limit states design method, which appeared in the last century and has been already applied in the design of buildings, bridges, etc, is proposed as a better method for the design of prestressed concrete sleepers. The limit states design has significant advantages compared to the permissible stress design, such as the utilisation of the full strength of the member, and a rational analysis of the probabilities related to sleeper strength and applied loads. This research aims to apply the ultimate limit states design to the prestressed concrete sleeper, namely to obtain the load factors of both static and dynamic loads for the ultimate limit states design equations. However, the sleepers in rail tracks require different safety levels for different types of tracks, which mean the different types of tracks have different load factors of limit states design equations. Therefore, the core tasks of this research are to find the load factors of the static component and dynamic component of loads on track and the strength reduction factor of the sleeper bending strength for the ultimate limit states design equations for four main types of tracks, i.e., heavy haul, freight, medium speed passenger and high speed passenger tracks. To find those factors, the multiple samples of static loads, dynamic loads and their distributions are needed. In the four types of tracks, the heavy haul track has the measured data from Braeside Line (A heavy haul line in Central Queensland), and the distributions of both static and dynamic loads can be found from these data. The other three types of tracks have no measured data from sites and the experimental data are hardly available. In order to generate the data samples and obtain their distributions, the computer based simulations were employed and assumed the wheel-track impacts as induced by different sizes of wheel flats. A valid simulation package named DTrack was firstly employed to generate the dynamic loads for the freight and medium speed passenger tracks. However, DTrack is only valid for the tracks which carry low or medium speed vehicles. Therefore, a 3-D finite element (FE) model was then established for the wheel-track impact analysis of the high speed track. This FE model has been validated by comparing its simulation results with the DTrack simulation results, and with the results from traditional theoretical calculations based on the case of heavy haul track. Furthermore, the dynamic load data of the high speed track were obtained from the FE model and the distributions of both static and dynamic loads were extracted accordingly. All derived distributions of loads were fitted by appropriate functions. Through extrapolating those distributions, the important parameters of distributions for the static load induced sleeper bending moment and the extreme wheel-rail impact force induced sleeper dynamic bending moments and finally, the load factors, were obtained. Eventually, the load factors were obtained by the limit states design calibration based on reliability analyses with the derived distributions. After that, a sensitivity analysis was performed and the reliability of the achieved limit states design equations was confirmed. It has been found that the limit states design can be effectively applied to railway concrete sleepers. This research significantly contributes to railway engineering and the track safety area. It helps to decrease the failure and risks of track structure and accidents; better determines the load range for existing sleepers in track; better rates the strength of concrete sleepers to support bigger impact and loads on railway track; increases the reliability of the concrete sleepers and hugely saves investments on railway industries. Based on this research, many other bodies of research can be promoted in the future. Firstly, it has been found that the 3-D FE model is suitable for the study of track loadings and track structure vibrations. Secondly, the equations for serviceability and damageability limit states can be developed based on the concepts of limit states design equations of concrete sleepers obtained in this research, which are for the ultimate limit states.

Perceived obstacles to multi-storey timber-frame construction : an Australian study

The contemporary default materials for multi-storey buildings – namely concrete and steel – are all significant generators of carbon and the use of timber products provides a technically, economically and environmentally viable alternative. In particular, timber’s sustainability can drive increased use and subsequent evolution of the Blue economy as a new economic model. National research to date, however, indicates a resistance to the uptake of timber technologies in Australia. To investigate this further, a preliminary study involving a convenience sample of 15 experts was conducted to identify the main barriers involved in the use of timber frames in multi-storey buildings. A closed-ended questionnaire survey involving 74 experienced construction industry participants was then undertaken to rate the relative importance of the barriers. The survey confirmed the most significant barriers to be a perceived increase in maintenance costs and fire risk, together with a limited awareness of the emerging timber technologies available. It is expected that the results will benefit government and the timber industry, contributing to environmental improvement by developing strategies to increase the use of timber technologies in multi-storey buildings by countering perceived barriers in the Australian context.

Effect of vertical misalignment of adjacent sleepers on the increase in dynamic loads around rail joints

In spite of the extensive usage of continuous welded rails, a number of rail joints still exist in the track. Although a number of them exist as part of turnouts in the yards where the speed is not of concern, the Insultated Rail Joints (IRJs) that exist in ballasted tracks remain a source of significant impact loading. A portion of the dynamic load generated at the rail joints due to wheel passage is transmitted to the support system which leads to permanent settlements of the ballast layer with subsequent vertical misalignment of the sleepers around the rail joints. The vertical misalignment of the adjacent sleepers forms a source of high frequency dynamic load raisers causing significant maintenance work including localised grinding of railhead around the joint, re-alignment of the sleepers and/or ballast tamping or track component renewals/repairs. These localised maintenance activities often require manual inspections and disruptions to the train traffic loading to significant costs to the rail industry. Whilst a number of studies have modelled the effect of joints as dips, none have specifically attended to the effect of vertical misalignment of the sleepers on the dynamic response of rail joints. This paper presents a coupled finite element track model and rigid body track-vehicle interaction model through which the effects of vertical of sleepers on the increase in dynamic loads around the IRJ are studied. The finite element track model is employed to determine the generated dip from elastic deformations as well as the vertical displacement of sleepers around the joint. These data (dip and vertical misalignments) are then imported into the rigid body vehicle-track interaction model to calculate the dynamic loads.

Effect of surface-applied treatments on the above-ground performance of simulated timber joinery

We examined the effect of surface-applied treatments on the above-ground decay resistance of the tenon of mortice-and-tenon timber joints designed to simulate joinery that is exposed to the weather. Joints made from untreated radiata pine, Douglas-fir, brush box, spotted gum and copper-chrome-arsenic (CCA) treated radiata pine were exposed to the weather for 9 y on above-ground racks at five sites throughout eastern Australia. Results indicate (1) a poorly maintained external paint film generally accelerated decay, (2) a brush coat of water-repellent preservative inside the joints often extended serviceability (in some cases by a factor of up to seven times that of untreated joints) and (3) the level of protection provided by a coat of primer applied inside the joint varied and in most cases was not as effective as the water-repellent preservative treatment.

Field assessment of the resistance of timber products to termite (Isoptera) damage: Results can change with the amount of bait wood

Whether or not termites initiate damage to timber via the end grain may determine the need for spot-treating the exposed untreated cut ends of envelope-treated softwood framing material. Australian Coptotermes acinaciformis (Froggatt) were field-tested for their ability to initiate feeding via the end grain of timber (35 × 90 mm) treated with a repellent Tanalith® T envelope. Specimens of commercial radiata pine Pinus radiata D.Don framing timber (untreated) and slash pine Pinus elliottii Englem. (untreated and envelope-treated) were partially clad in fine stainless steel mesh. Clad and unclad specimens were exposed to C. acinaciformis near Townsville, North Queensland, Australia, for four months. Results showed that this species of termite can indeed damage timber via the end grain, including exposed untreated cut ends of envelope-treated material as demonstrated earlier for different populations of C. acinaciformis. Differences between the test conditions in field trials carried out at different times (where C. acinaciformis either did or did not damage timber via the end grain) are discussed. Clearly, outcomes from field studies with preservative-treated materials are dependent upon experimental conditions. Notably, the amount of bait wood (highly termite-susceptible timber substrate) offered in a given method can strongly influence the termite response. Further investigation is required to standardise this aspect of conditions in protocols for the assessment of wood preservatives.

Accelerated drying of plantation grown Eucalyptus cloeziana and Eucalyptus pellita sawn timber

The objective of this study was to gain an understanding for drying sawn timber produced from fast-grown, well-managed Queensland hardwood plantations using accelerated drying methods. Due to limited resources, this was a preliminary study and further work will be required to optimize schedules for industrial implementation. Three conventional kiln trials, including two for 38-mm-thick, 19-year-old plantation Gympie messmate (Eucalyptus cloeziana F. Muell.) and one for 25mm thick, 15-year-old plantation red mahogany (Eucalyptus pellita F. Muell.), and two vacuum kiln drying trials, one each for 38- and 25mm thick Gympie messmate, were conducted. Measurements of final cross-sectional moisture content, moisture content gradient, residual drying stress, and internal and surface checking were used to quantify dried quality. Drying schedules were chosen based on either existing published schedules or, in the case of the vacuum drying trials, existing schedules for species with similar wood density and dying degrade properties, or manipulated schedules based on the results of trials conducted during this study. The findings indicate that both species can be dried using conventional drying techniques with acceptable grade quality in approximately 75 percent of the drying time that industry is currently achieving when drying native forest timber of the same species. The vacuum drying time was 60 percent less than conventional drying for 38-mm-thick, 19-year-old Gympie messmate, although drying quality needs improving. The findings have shown that through careful schedule manipulation and adjustment, the grade quality can be optimized to suit the desired expectation. Additional research is required to further optimize the schedules to ensure acceptable grade qualities can be reliably achieved across all drying criteria and exploit opportunities to reduce drying times further.

Hydrofluoroalkanes as carrier solvents for timber preservation

Hydrofluoroalkanes are a specific category of hydrofluorocarbon (HFC) commonly used in refrigeration applications. Some HFCs hold potential for use as carrier fluids for preservatives used to protect timber above ground. They do not share the most significant disadvantages of currently used carriers for these applications. At ‘conventional’ operating pressures, they are capable of rapid, full penetration of some timbers generally considered refractory, such as spruce and the heartwood of radiata pine. But they are comparatively expensive and, while they are not detrimental to the ozone layer, they would contribute significantly to the greenhouse effect if released. Impregnation process conditions can be optimised to maximise biocide solubility and impregnation speed and depth.

Improving added value and small medium enterprises capacity in the utilisation of plantation timber for furniture production in Jepara region

Improving added value and Small Medium Enterprises capacity in the utilisation of plantation timber for furniture production in Jepara region of Indonesia: improving recovery, design, manufacturing, R&D and training capacities.

Australian Timber Pole Resources for Energy Networks. A review

More than 5 million timber utility poles are currently in-service throughout Australia’s energy networks. Most were produced from select native forest-grown hardwood species having the required structural characteristics and naturally-durable heartwood. Anecdotal evidence suggests that up to 70% of the timber poles that are currently in-service were installed over the 20 years following the end of World War Two, and these poles are likely to require replacement or remedial maintenance over the next decade. The purposes of this review were to clarify the supply and demand situation for traditional timber poles, and to investigate alternatives in terms of their potential availability and suitability.

Evaluation of wood characteristics of tropical post-mid rotation plantation Eucalyptus cloeziana and E. pellita: Part (a) Natural durability of timber.

This project evaluated the timber quality, processing and performance characteristics of 19-year-old Eucalyptus cloeziana (Gympie messmate) and 15-year-old Eucalyptus pellita (red mahogany). Studies were undertaken to evaluate wood and mechanical properties, accelerated seasoning and veneer and plywood production. Above-ground and in-ground durability field tests were established at three locations in Queensland. Ground proixmity tests and L-joint tests were installed to gather data applicable to above-ground, weather-exposed end-use applications, and stake tests were installed to gather data applicable to in-ground, weather-exposed end-use applications.