How it began
In the 1980s the contractor PT Hutama Karya was building an elevated toll road above Jalan Ahmad Yani in Jakarta, between Cawang and Tanjung Priok, a route that could not be closed. Its engineer Tjokorda Raka Sukawati proposed casting each concrete pier head in the median, parallel to the traffic, and then turning it into place. On July 27, 1988, a pier head of about 440 tonnes was rotated for the first time using oil pumped to a pressure of 78 kgf per square centimeter.
Before it existed
According to the account published by Universitas Medan Area, no method existed at the time for building a flyover without closing the road beneath it. Conventional pier construction needed formwork across the carriageway, which meant shutting a road that carried very heavy traffic.
How it works
The pier shaft is built first between the lanes. The pier head is poured on top of it, lengthwise along the road. Under the head sits a bearing made of two discs about 80 centimeters in diameter inside a container, with lubricating oil pumped between them through a small pipe and held in by a rubber seal. Under pressure the oil carries the load with almost no friction, so the head can be pushed around 90 degrees to sit across the road.
How it spread
The technique was used beyond Indonesia. Wikipedia reports that the longest stretch of overpass built with it is the Metro Manila Skyway in the Philippines, and lists projects in Malaysia, Thailand and Singapore, though parts of that list carry citation-needed tags. A Japanese patent was granted in 1992 and an Indonesian patent in 1995.
Where it stands today
President Soeharto named the method Sosrobahu in November 1989; the name comes from Old Javanese and means "thousand shoulders". Indonesian sources describe the technique as returning to use on later elevated toll roads, including the Jakarta-Cikampek elevated road.
