M.F.A.M. van Maarseveen

Simulation of HMA Compaction by using FEM

This paper introduces a simulation tool for the compaction process of hot mix asphalt (HMA) using a roller under varying external conditions. The focus is on the use of the finite element model (FEM) with code DiekA, on its necessary requirements and on the presentation of simulation results. The approach requires the availability of a suitable material model, equipment to measure material parameters and a laboratory-testing program for fitting the correct material parameters. Subsequently, in discussing the simulation results attention is paid to; the principal stresses, strains and shear stresses inside the material during rolling, and the incremental displacements of the material. Furthermore, the simulated density path as a function of depth inside the layer is presented for a series of applied roller passes. In conclusion it can be stated that FEM approaches in general are well suited to simulate compaction processes of HMA on condition that the selected FEM comprises the right features.

Interactive Cumulative Burden Assessment: Engaging Stakeholders in an Adaptive, Participatory and Transdisciplinary Approach

Cumulative burden assessment (CuBA) has the potential to inform planning and decision-making on health disparities related to multiple environmental burdens. However, scholars have raised concerns about the social complexity to be dealt with while conducting CuBA, suggesting that it should be addressed in an adaptive, participatory and transdisciplinary (APT) approach. APT calls for deliberation among stakeholders by engaging them in a process of social learning and knowledge co-production. We propose an interactive stakeholder-based approach that facilitates a science-based stakeholder dialogue as an interface for combining different knowledge domains and engendering social learning in CuBA processes. Our approach allows participants to interact with each other using a flexible and auditable CuBA model implemented within a shared workspace. In two workshops we explored the usefulness and practicality of the approach. Results show that stakeholders were enabled to deliberate on cumulative burdens collaboratively, to learn about the technical uncertainties and social challenges associated with CuBA, and to co-produce knowledge in a realm of both technical and societal challenges. The paper identifies potential benefits relevant for responding to social complexity in the CuBA and further recommends exploration of how our approach can enable or constraint social learning and knowledge co-production in CuBA processes under various institutional, social and political contexts.

The characteristics of bike-sharing usage : case study in Zhongshan, China

Public bike systems have grown in popularity and are expanding rapidly across cities worldwide. Such systems provide access to pickup and drop-off public bikes at numerous bike stations for free or for an affordable fee and aim at increasing bike use and extending the accessibility of traditional public transport systems. A variety of studies have examined the characteristics of bike-sharing systems, mostly in American and European cities and with a focus on user demographics. The objective of this study is to investigate the general characteristics of system usage, in terms of system efficiency, trip characteristics and bike activity patterns, for Zhongshan’s public bike system during a five-month period. The findings show that the system is not very efficient based on usage metrics which are low compared to successful systems in other countries. Demand is relatively high in city centre zones due to high population and activity density. However, there is no clear direction of inbound or outbound trips in rush hours. This may be attributed not only to mixed land use patterns throughout the city, but also to the fact that most trips are local trips over short distance. This could indicate that public bike trips are mainly substitute for walking trips rather than for car or PT trips. On the outskirts, demand and system efficiency are low, indicating that location allocation of stations needs adjustment. In the conclusions, we discuss how these findings can be used for improving the system.