Crews in Guangxi, China are packing list items and dismantling the project site for what is now the world’s longest steel-reinforced concrete arch bridge. The Tian’e Longtan Bridge, with a main span of 600 meters, exceeds the third PingNan Bridge by 25 m.
The contractor Guangxi Road and Bridge Engineering Group Co., Ltd. (GRBG) began construction of the approximately 2,500 m long bridge in 2020 as part of the Nandan-to-Tian’e Expressway through the mountainous region of Tian’e County.
The bridge crosses a reservoir over the Hongshuihe River that is up to 900m wide and approximately 130m deep, according to a contractor report provided to ENR. The deck of the bridge rises 140 m above the reservoir.
The box-shaped steel tube arch structure, supported by 13 horizontal struts, carries four lanes of traffic. Crews used a cantilever construction method using tin cables without any falsework support, a method developed by bridge designer Jielian Zheng in 1968. According to a technical paper he wrote at Guangxi University, China has more than 300 arch bridges built this way, Zheng said. T-shaped prestressed concrete beams have spans of 40 m.
The five longest arch bridges in the world are in China, notes Man-Chung Tang, president of the China branch of TY Lin International and an adviser to the project.
“An arch can only support itself after the entire rib of the arch has been completed,” says Tang. “In the past, the ribs of an arch bridge had to be fully supported by formwork or formwork during construction before the entire arch rib was completely finished and the abutments poured. This limited the arch lights we could build because otherwise the formwork would be too expensive and less stable. Long-span arch bridges became possible only after Professor Zheng developed this cable-stayed method of arch construction. In addition, he developed methods to ensure that the concrete inside the steel tubes was fully bonded to the steel casing.”
Evolving technologies such as vacuum-assisted graded pumping, non-shrinkage concrete and instant tension load regulation of arch rings also enabled the 600m span, according to the contractor.
The steel “skeleton” of the bridge is 8,200 tons and is divided into 44 segments. The largest segment is 23.35 m long, 9.91 m high and 5.2 m wide. “After a careful search, we found an abandoned soil disposal site, approximately 60,000 cubic meters in size,” which was converted into a steel manufacturing plant, according to the contractor. “Also, it is close to the river, which makes it convenient to take these segments on large ships.”
Access to the site was a challenge. “In terms of land transport, there is a connection with a secondary road 16 km away via country roads on a margin,” according to the contractor. “On the other side, the country roads that connect to the nearest secondary road are about 35km away, with a drop of about 100m, making it virtually unusable.”
Crews improved the paths on the first bank and built docks on both banks to accommodate the transport of material and equipment.
In his paper, Zheng says that technologies must continue to advance to increase the length of the arc. They include the need to “improve the fatigue resistance of welded joints; to study a more convenient connection between the hanging sections… a new method of calculating the bearing capacity section i [a] the rapid construction method is studied.”
He added: “At present, we have demonstrated the feasibility of the concrete-filled steel tube arch bridge with a net span of 700 m, and we expect the concrete arch bridge with a span of more than 700 m as soon as possible.”
