Pavement designers have a choice of two types of wearing course: either an asphalt
wearing course or a surfacing seal. While asphalt surfacing design has received much
attention, road seal design has remained dependent on empirical modelling and
experience. With the modern trend of increased traffic loading and contact stresses,
varying oil resources and related refining processes and by-products, it is postulated
that current seal design assumptions and practice may not be directly applicable to the
changing situation in practice, and require re-examination (Milne 2004).
In 1998 performance testing of road surfacing seals was initiated under the Chair
in Pavement Engineering, University of Stellenbosch. The model mobile load simulator
(MMLS3) was identified and a test method developed. From 1998 to 2002 a test regime
using five different seal binders and three temperature regimes was implemented. A
method of evaluating seal performance was developed to enable evaluation of the
seals' behaviour. This paper presents a summary of the test results and provides an
insight to the performance of the different seal binders under similar imposed loads
and environment. Insight is provided for the identification of critical seal performance
influences and criteria. A comparative performance test protocol was developed, with an
initial seal performance visual assessment method.
<br>The need for a mechanistic based numerical model enabling comparative numerical
prediction of seal performance was identified as an additional design tool (Milne 2004).
A finite element methods (FEM) prototype model of a single seal was developed and
is demonstrated. The potential value to practice of both methods of comparative
performance assessment were postulated after synthesis of the results.
With the common and widespread use of PC-based design packages in the design of
steel structures, it is of fundamental importance to revisit the basic principles contained in
and sometimes omitted from common analysis packages. The basic methods of stability
analysis are briefly discussed and the influence of inelastic buckling incorporated and
then illustrated by using representative case studies. Common errors in the use of such
design packages, and the importance of simple calibration checks are used to illustrate
the problems which can lead to failures.