Rudi Cobus Van Staden

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.

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.

In Situ Assessment of Pavement Subgrade Using Falling Weight Deflectometer

The stiffness modulus and density of pavement subgrade contribute significantly to the long-term performance of a pavement structure. Subgrade functions primarily as a support for road pavement structures. Poor performance of the pavement structure is often a result of a lack of quality control during the construction of the subgrade layer. This paper presents a case study in which a falling weight deflectometer (FWD) test was used to evaluate whether the subgrade layer had achieved the required design stiffness modulus and density during construction. The characteristics of the FWD deflection basins were analyzed and the stiffness modulus was back-calculated using the CIRCLY5 pavement analysis program. The problems associated with FWD testing directly on subgrade are discussed, and an appropriate test load is proposed. Deflection-based models are developed by relating the FWD center deflection with the in situ stiffness modulus and density of the subgrade layer. A dynamic cone penetrometer test was carried out to determine the in situ stiffness modulus, and the results are compared with the back-calculated stiffness from CIRCLY5.

Effect of Dowel Looseness on Response of Jointed Concrete Pavements Using Three-Dimensional Finite Element Analysis

This paper evaluated an effect of dowel looseness on response of jointed concrete pavement using 3D finite-element analyses of rigid pavement systems that relies on an embedded formulation of a beam element. This embedded element allows the efficient modelling of dowel looseness using nodal contact approach and permits the dowels to be exactly located irrespective of the slab mesh lines. These studies indicate that significant reduction in load transfer efficiency and increase in both slab and base course stresses can be expected due to small gaps varies from 0.25 to 1.25mm between the dowels and the slabs. For the worst case the LTE were reduced to 11.3% and 11.6% respectively for single wheel loading and odd dual wheel loading case while there were voids present at the base course layer for 1.25 cases 4.

Development of prediction model for Doweled joint concrete pavement using three-dimensional finite element analysis

The load transfer mechanism between the dowel and the concrete is a complex phenomenon. This mechanism depends mainly on a parameter known as the modulus of dowel support (K), the value of which can be determined by load testing. A high modulus of dowel support value indicates a good contact between the concrete and the steel dowel. There is a lack of sound approach to identify with any degree of accuracy the modulus of dowel support (k), which makes it difficult to rely on the analytically developed formulas that are sensitive to its value. The obtained numerical results were validated with classical analytical solutions of shear and moment along the dowel. The group action of the dowel bar system was examined and useful relationships have been developed for estimation of the relative load shared by individual dowel bars. These useful relationships have been used to developed prediction Model to predict the shear force in dowel group action of dowel bar system and deflection at the loading nodal point. The prediction Model results for shear force in dowel group action of dowel bar system and deflection at the loading nodal point were relatively close to the F.E. Model results, with the different range between 2.2% to 7%.

Performance Evaluation of Bone–Implant System During Implantation Process: Dynamic Modelling and Analysis

Inappropriate choice of dental implant type in relation to the detailed structure of bone at the site, and inadequate surgical technique has led to 5 % failure of dental implants worldwide. By using the finite element method, three typical implant insertion scenarios are modelled and evaluated in this chapter. The scenarios are implant thread forming, cutting and the combination of forming and cutting. The bone–implant system is modelled using three-dimensional finite element technique which incorporates realistic material properties in simulating the cancellous and cortical bone. The bone–implant contact is defined using ‘surface-to-surface’ discretisation and the arbitrary Lagrangian–Eulerian adaptive meshing scheme. In current practice many implant companies recommend thread cutting for normal bone and forming for compact bone so that implant stability can be ensured. Based on the findings of the present study, the combination of forming and cutting may also be recommended for clinical practice because it best matches the specified ideal stress level resulting in positive bone stimulation with minimum resorption. Stress information obtained in these three implant insertion scenarios will advance the understanding of bone response at an early stage of the osseointegration process and primary stability.

Evaluation of Doweled Joints in Concrete Pavements Using Three-Dimensional Finite Element Analysis

Transverse joints in rigid pavements are the locations where most pavement distress appears, leading to deteriorating riding quality and featuring high-maintenance costs. The state of stresses in the concrete surrounding dowel bars in dowel-jointed concrete pavements is a major factor that contributes to transverse joint distress. As such, a three-dimensional finite element model was developed for analyzing dowel-jointed concrete pavement. The effect of different pavement and joint related parameters on the load transfer characteristics of a joint has been evaluated using the finite element (FE) model. Group action of the dowel bar system has also been examined. Five loading cases were applied to replicate realistic vehicular loadings approaching and leaving the joint. The structural behavior of the pavement at the doweled joint was investigated for (1) pavement with and without voids, (2) dowel spacing variation, (3) pavement with and without lean concrete base, (4) slab thickness (5) tire pressure, and (6) single and dual wheel loads. The amount of load transfer was obtained from the shear force in the beam elements that simulate dowels. Results show that the voids underneath the joint causes an increase in the vertical displacement of the concrete slab and vertical stress at concrete/dowel bar interface, which could result in crushing of the concrete and dowel loosening. Wider dowel spacings result in increased shear forces and the size of the region containing engaged dowels does not change significantly with dowel spacing, only effecting the distribution of shear forces. Maximum principle stress (MPS) is about 6.7 times greater and steeper in the distribution pattern in the concrete pavement without lean concrete base (LCB). A thick concrete slab provides a significant benefit of higher load transfer and less curvature along the loaded side of the joint. The deformed shape explains why more dowels are engaged in the load transfer for the thicker concrete slab models. There were no significant effects on load transfer ratio with the increase applied wheel load. This phenomenon is also evident in the dowel shear force distribution. However, it will increases the demand on a few inner dowels beneath the wheel load, which may cause more damage to the joints and eventually lead to pavement failure. The study shows that the dowel bars perform effectively as a load transfer device in the concrete pavement system even under severe conditions.

Three-Dimensional Finite Element Analysis of Doweled Joints in Concrete Pavements

Concrete pavements are usually selected by pavement engineers for roads subjected to heavy traffic loading and feature high maintenance and construction costs. As such, the structural behaviour of concrete pavements with doweled joints is evaluated herein using Finite Element Method. The pavement system is modelled using three-dimensional brick elements and five loading cases are applied to replicate realistic vehicular loadings approaching and leaving the joint. The structural behaviour of the pavement at the doweled joint is investigated for: (1) pavement with and without voids, and (2) different dowel bar spacing. The amount of load transfer was obtained from the shear force in the beam elements that simulate dowels. Results show that the voids underneath the joint causes an increase in the vertical displacement of the concrete slab and vertical stress at concrete/dowel bar interface which may result in crushing of the concrete and dowel loosening. Wider dowel spacings result in increased shear forces and the size of the region containing engaged dowels does not change significantly with dowel spacing, only effecting the distribution of shear forces. The study shows that the dowel bars perform effectively as a load transfer device in the concrete pavement system even under severe conditions.