ICE - Institution of Civil Engineers - Virtual Library

• Putting marketing into practice

• Concept of segmentation

• Dimensions and scope of segmentation

• Segmentation as an analytic tool

• Introduction

• General arrangement

• Casting of segments

• Storage and transportation of segments

• Segment erection, general

• Segment erection by the balanced cantilever method

• Segment erection by the span-by-span method

• Segment erection by the progressive placement method

• Design aspects associated with precast segmental decks

• References

A traffic accident results from the combination of various factors each of which plays a role in its occurrence. It is logical that accidents with different causes should not be considered together as accident cause is one of the most important factors for prioritising high crash road segments. In the present study, the main cause of an accident in a high crash road segment were identified and then the accidents in each segment was classified based on their cause. A new model was developed for prioritising high crash road segments based on the causes of accidents. This model is different from the current models and renders different and more accurate prioritisation results. According to the developed model, a segment may be compared with another and identified to be highly accident-prone with the same cause, whereas, the total number of accidents that occurred in the former may be less than that in the latter. The model was evaluated based on real data collected from highway segments in Tehran.

The precast segmental approach structure of the Sutong Bridge with 75m span length was constructed using balanced cantilever method. This precast segmental viaduct was characterized by deep foundation in the riverbed, 60m high columns connecting the main bridge and relatively long end spans in the balanced cantilever deck. This paper covers the construction methods and logistics adopted to suit the particular site conditions. It discusses the casting yard selection and set up in the vicinity of the river bank, the design of the special equipment such as the short-line match casting moulds and two 160m long launching girders which were tailor-made for this project. The value engineering exercise in the post Contract award stage for facilitating construction is detailed. The geometry control method used in both the casting yard and erection front, the temporary works and stabilizing system are delineated. This paper also highlights the construction difficulties encountered and solutions to the problems.

• Abstract

• Introduction

• Bridge Characteristics

• Value Engineering

• Foundation

• Column

• Segment Casting

• Segment Erection

• Conclusions

• Acknowledgment

The road user costs accruing on road networks due to the poor quality of road markings are significant. There is therefore a need for an automated process to provide an objective assessment of the performance characteristics of road marking, such as wear and both day- and night-time visibility. Digital analysis of road surface images seems to be a versatile approach that may enable road agencies to evaluate the state of markings in an objective manner with increased accuracy. The analysis is effected by a series of processes that include image acquisition and digitisation, storage, segmentation, enhancement and feature description. This paper focuses on image segmentation, the process by which the road markings are identified from their background. The paper presents a number of techniques used for image segmentation that have been considered for inclusion in a prototype road marking analysis system. The techniques presented are the variance method, moment preserving thresholding, minimum error thresholding, relaxation thresholding, and a technique known as sub-image thresholding, which combines minimum error thresholding with a method suggested for the analysis of images of the heart. Each of the techniques is presented, discussed and evaluated for its ability to segment images containing road markings. By considering a set of appropriate test data, an investigation was carried out that indicated that the sub-image thresholding method performed satisfactorily on all images analysed in terms of accuracy and speed of computation.