Precasting of effective PC structures
1. Overview
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The Ministry of Land, Infrastructure, Transport and Tourism designated 2016 as the first year of a “productivity revolution” and has since been promoting i-construction as a means of increasing productivity. Precasting is an effective, specific measure that can be used to improve productivity in PC structures, and, until now, has been focused on as a labor-saving and manpower-saving means of shortening the construction period; although, it is also a promising approach for realizing highly durable structures and for reducing costs by diverting equipment and materials for use elsewhere. Furthermore, precasting not only reduces initial costs, it is beneficial economically due to the fact that, by shortening the construction period, it helps eliminate construction-related traffic congestion more quickly, as well as provides various other value-added benefits associated with a reduction in construction site-related impact on the surrounding environment.
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Precasting of PC structures is commonly used for JIS girders and segment girders in civil engineering (bridges) and PCaPC beams, columns and PC slabs in building construction; however, below are some examples of precast PC member usage in various other structures.
2. Construction Examples
[Rainwater reservoir] Shortened construction period, reduced construction costs and improved seismic performance due to utilization of precast members
In 1999 and 2003, the area around Hakata Station in Fukuoka Prefecture’s Mikasa river basin was severely damaged by flooding. In response, Fukuoka City undertook comprehensive flood control development around Hakata Station, including extension of the rainwater reservoir. Precast members were incorporated into the underground reservoir structure in order to improve the economic efficiency of the project, as well as shorten the construction period.
Reservoir structural overview
Precast floor slab installation
After completion
2. 2 [Stadium] High quality, durability and increased span length of stepped floor slabs due to utilization of precasting
This project involved the construction of a stadium in Kitakyushu City, next to Kokura Port, to serve as a new symbol for the city.
Given the harsh impact of the site environment on durability, as well as the time and effort required to assemble concrete forms for so many steps on-site, precast members were utilized in order to achieve a high level of durability via factory production as well as to increase the efficiency of on-site work.
Also, precast PC members allowing for longer spans were utilized for the stepped floor slabs.
*Step beams, stepped floor slabs, diagonal columns, binding joists and cantilever slabs were all precast
Structural overview (back stand)
Layout of corrugated plate steel
Step beam installation
Stepped floor slab installation
Full view of stands
2.3 [Parapet] Shortened renewal work construction period due to use of precasting
Parapet replacement was performed in order to ensure better seismic performance during earthquakes, as well as to improve maintenance management of girder end structures which incorporate expansion devices. And, given the significant impact on the community caused by lengthy highway traffic restrictions, precasting of parapet members was performed in order to shorten the construction period, as well as to improve durability.
Parapet replacement overview
Installed precast parapet
Joining with existing abutment