| Summary: | 碩士 === 國立高雄第一科技大學 === 營建工程所 === 94 === Sewage system is a large scale infrastructural public work actively
promoted in recent years. Due to shortages and limited financial resources, the
government has sought to involve private capital with efficiency of the private
sector. To that end, the government has introduced models of private sector
involvement in public works. With necessary incentives, major public
infrastructures can be completed with joint cooperation of public and private
sectors. The current practice of estimating return on investment, in the private
sector, is to consider only the construction and concessionary operation period.
However, sewage system constructed via the BOT method is a permanent public
facility. Financial assessment based on the concessionary period does not lead
to a practical reflection of the financial performance. A more logical approach
is to consider the sewage system works from perpetual life perspective.
This study focused on four of the most popular pipe materials used in the
sewer works: reinforced concrete pipes, vitrified clay pipes, ductile iron pipes
and polyvinyl chloride pipes. The sewage system BOT project conditions of Nantzu
District of Kaohsiung City were utilized in the study. Annual worth method was
used as the analytical tool. Various discounting periods were studied, which
included the actual service life of the pipe material, extended service life
after repair, and, continued service after replacement. The cost differences
between various types of pipe materials were evaluated under varying rates of
return on investment for the BOT project. The results are as follows.
1. The service life of sewage system can be continually extended after
maintenance, using various types of repair methodologies. In selecting BOT
project, it is more appropriate to consider the perpetual service life.
Evaluations of average annual worth based on the concessionary period,
without considering the actual service life of the pipe material used, the
results indicate that as long as the initial investment cost remained low,
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the average annual worth will be proportionally low. In relative terms, the
cost efficiency is always the best. Hence, evaluation techniques that ignore
the residual value at the expiry of the concessionary period, will not lead
to choice of the most suitable pipe material for BOT sewage system works.
2. Various pipe materials for sewage system BOT projects were evaluated under
the perpetual service life scenario. Using various rates of return on
investment, evaluation was done in conjunction with the service life data
solicited from Public Works Commission and foreign literature. The higher
the rate of return, the lower the benefits of using pipe material with better
erosion resistance. However, when the rate of return is reduced to below
10%, pipe material with better erosion resistance were relatively lower in
maintenance cost. Under consideration of overall cost efficiency, the higher
the opportunity of being selected for use.
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