Yew-Chaye Loo

Application of the finite element method in dental implant research.

This article provides a review of the achievements and advancements in dental technology brought about by computer-aided design and the all powerful finite element method (FEM) of analysis. The scope of the review covers dental implants, jawbone surrounding the implant and the biomechanical implant and jawbone interaction. Prevailing assumptions made in the published finite element analysis (FEA) and their limitations are discussed in some detail which helps identify the gaps in research as well as future research direction.

Flexural and Shear Failure Analysis of Reinforced Concrete Slabs and Flat Plates

A nonlinear layered finite element procedure is presented for flexural and shear failure analysis of reinforced concrete slabs and flat plates. A degenerated shell element employing a layered discretization scheme is adopted. This provides a simple and effective means of accounting for the nonlinear behaviour of concrete and steel reinforcement over the thickness of the slab or flat plate. The procedure is capable of determining the load-deflection response, the ultimate load capacity and crack patterns of concrete slab structures, as well as computing the punching shear strength at slab-column connections of concrete flat plates. To verify the accuracy and reliability of the proposed method of analysis, comparative studies are carried out on a collection of reinforced concrete slabs, single slab-column connections and multi-column flat plates which were tested by other researchers. In general, good correlations are obtained with the published test results.

A study of the effects of pavement ageing on binder deterioration

This paper discusses the ageing of asphalt binder of long-term pavement performance (LTPP) sites in Southeast Queensland. The effects of pavement age on binder deterioration were examined by performing ‘Shell’ sliding plate micro-viscometer laboratory tests in accordance with Australian and New Zealand Standard AS/NZS 2341.5: 1997. The tests were carried out on bituminous core samples obtained from the LTPP sites to determine the apparent viscosity of the asphalt binder. A binder deterioration model (BDM) was developed by establishing a relationship between the apparent viscosities of the binder with pavement age. The apparent viscosity data generated using the BDM were compared with that computed using the bitumen hardening model developed by Oliver (2003). The two models show a consistent trend in the binder deterioration, and the results were analysed statistically using regression analysis, Root Mean Square Error and t-test methods. The t-test shows that the data generated by the BDM have no significant deviation from the prediction by Olivers model.

On the prevailing construction waste recycling practices : a South East Queensland study

Waste generated from construction and building demolition work constitutes about 68% of all solid waste generated each year in South East Queensland. Consequently, it has created a serious waste management problem. The State Governments of Victoria and New South Wales have been encouraging the use of recycled materials from construction and related waste; they have also promulgated specifications for their use. In Queensland, however, similar regulations are not anticipated in the near future, which explains the lack of funded research conducted in this important arena. This paper presents an evaluation of the prevailing waste recycling practices in Queensland. Nine sites were visited, including two construction sites, three demolition sites, three recycling plants and one landfill in South East Queensland. The difficulties encountered by the recycling programme operators and their associates at these sites are described and the benefits of recycling construction materials are presented. One of the major barriers is that the local councils disallow the use of recycled materials in new construction work. To help rectify these impediments to recycling, recommendations are given to increase the use of recycled construction waste in South East Queensland.

Development of an Integrated Method for Probabilistic Bridge-Deterioration Modeling

Probabilistic deterioration models such as state-based and time-based models are only capable of predicting future bridge-condition ratings when a sufficient amount of condition data and reasonable data distribution are available. However, such are usually difficult to acquire from limited bridge-inspection records. As a result, these probabilistic models cannot guarantee reliable long-term prediction for each of the bridge elements concerned. To minimize this shortcoming, this paper proposes an advanced integrated method to construct workable transition probabilities for predicting long-term bridge performance. A selection process within this method automatically chooses a suitable prediction procedure for a given situation in terms of available inspection data. The backward prediction model (BPM) is also incorporated to effectively predict the bridge performance when sufficient inspection data are unavailable. Four different situations in regard to the available inspection data are predefined in this study to demonstrate the capabilities of the proposed integrated method. The outcomes show that the method can help develop an effective prediction model for various situations in terms of the quantity and distribution of available condition-rating data.

The Damping Analysis of Experimental Concrete Beams under Free-Vibration:

This paper presents an overview of the free-vibration damping analysis technique commonly employed by laboratories to determine the amount of material damping contained by a concrete specimen. From laboratory investigations the difficulties associated with a technique often employed for the extraction of damping from the free-vibration decay curve are identified. Extensive free-vibration tests undertaken on a wide variety of concrete beams indicate that for the traditional logdec technique, damping is to be extracted from the optimal peak ratio (An/A1) region of the free-vibration decay curve. An analysis of the effect of experimental test variables; hammer weight and hammer excitation position, on the calculation of damping is undertaken. The results show that neither test variable produces measurable impact on the calculation of damping.

Factors Influencing Spacing and Width of Cracks in Reinforced Concrete; New Prediction Formulae

An analytical method is used to calculate the spacing and width of cracks for a series of reinforced concrete beams having different material and sectional properties. The calculated values are used to investigate the effects of different variables on the spacing and width of cracks. Bar diameter, effective width of the beam per bar, concrete cover and the effective depth are shown to be the most significant parameters affecting the spacing and width of cracks at a given load level. A parametric study is subsequently carried out utilising the above significant parameters, and the spacing and width of cracks are re-calculated. Results of this parametric study are used to develop simplified prediction formulae. Finally a comparative study is undertaken, which indicates that the spacing and width of cracks calculated by the new formulae agree well with the test results of other investigators.

Damping Formulae for Reinforced and Partially Prestressed Concrete Beams

A full-size test program was carried out on 26 simply-supported and continuous reinforced and partially prestressed concrete beams to study the cracking behaviour and damping characteristics of concrete beams. The beams were subjected to free vibration tests and logarithmic decrement values corresponding to each load level were measured. Separate regression analyses on the reinforced and the partially prestressed beams were undertaken. These analyses resulted in two separate empirical formulae for predicting the logarithmic decrement of damping in reinforced and in partially prestressed beams. Comparison with test results from all 26 beams indicates that the predictions are accurate. It is also found that the damping formula for reinforced beams is applicable to both single and continuous spans. The proposed damping formulae predict damping from the residual crack widths of the beams. As such, formulae developed for predicting residual crack widths from given variables defining the beams and their deflection-span ratios are also reported.

Automatic Bridge Crack Detection A Texture Analysis-Based Approach

To date, identifying cracks in bridges and determining bridge conditions primarily involve manual labour. Bridge inspection by human experts has some drawbacks such as the inability to physically examine all parts of the bridge, sole dependency on the expert knowledge of the bridge inspector. Moreover it requires proper training of the human resource and overall it is not cost effective. This article proposes an automatic bridge inspection approach exploiting wavelet-based image features along with Support Vector Machines for automatic detection of cracks in bridge images. A two-stage approach is followed, where in the first stage a decision is made as whether an image should undergo a pre-processing step (depending on image characteristics), and later in the second stage, wavelet features are extracted from the image using a sliding window-based technique. We obtained an overall accuracy of 92.11% while conducting experiments even on noisy and complex bridge images.

Prediction of Long-Term Bridge Performance: Integrated Deterioration Approach with Case Studies

AbstractA bridge-deterioration approach is to predict the condition ratings and the deterioration pattern of bridge elements for determining optimal maintenance strategies and estimating future funding requirements. To effectively predict long-term bridge performance, an advanced integrated deterioration approach has been developed that incorporates a time-based model, a state-based model with the Elman neural network (ENN) and a backward prediction model (BPM). The proposed approach involves the categorization of the selected inspection records by bridge components, material types, traffic volume, and the construction era. The primary advantage of such categorization is to group similar components together, thereby identifying the common deterioration patterns. A selection process embedded in the proposed approach offers the ability to automatically select the most appropriate model for predicting future bridge condition ratings. To demonstrate the advantage of the proposed approach in predicting long-te...