| Bridge Name: | Rama IX Bridge |
| Native Name: | สะพานพระราม ๙ |
| Carries: | Chaloem Maha Nakhon Expressway |
| Crosses: | Chao Phraya River |
| Locale: | Bangkok, Thailand |
| Design: | cable-stayed |
| Mainspan: | 450 m |
| Length: | 781.20 m |
| Width: | 33 m |
| Height: | 87 m |
| Below: | 41 m |
| Lanes: | 6 |
| Begin: | 1 October 1984 |
| Open: | 5 December 1987 |
| Coordinates: | 13.6821°N 100.519°W |
Rama IX Bridge (Thai: สะพานพระราม ๙,, in Thai pronounced as /sā.pʰāːn pʰráʔ rāːm kâːw/) is a bridge in Bangkok, Thailand over the Chao Phraya River. It connects the Yan Nawa District to Rat Burana District as a part of the Tha Ruea – Dao Khanong Section of Chaloem Maha Nakhon Expressway.[1] [2] [3]
The bridge was named in the honor of King Bhumibol Adulyadej's 60th birthday. The opening date coincided with the king's birthday, with a million people walking over it.[4] It was the first cable-stayed bridge in Thailand and had the second-longest cable-stayed span in the world when it opened in 1987.[5] [6]
The original colour scheme, with white pylons and black cables, was replaced with an all yellow scheme representing the king in 2006.[7] [8]
A new eight-lane double-pylon cable-stayed bridge paralleling the Rama IX Bridge has been under construction for some time. Part of the Rama III-Dao Khanong-Western Bangkok Outer Ring Road expressway project, it is intended to relieve traffic congestion on the existing single-pylon bridge. The new bridge's official opening will be in early 2024, after which the Rama IX bridge will be closed for an extensive renovation, which includes a sensor system for added safety.[9]
The steel superstructure includes the bridge, rigged mast, and cable. The main span of the bridge, which is stretched between two poles, has a length of 450 meters. The main span is a trapezoid 33 meters wide. The bridge has a walkway along its side. The bridge has two main pylons 3 meters × 4.50 meters. This serves to hold the tension of the cable and weight into the pylon pier. The 121 – 167 mm diameter cables consist of many small wires wound together. The cables vary in length from 50 to 223 meters can absorb the tension for 1,500–3,000 tons.[10]
The gradually sloping viaducts on each side of the river are dual-double-T, post-tensioned, concrete structures with thirteen 50-metre double spans on each bank cast in-situ with a steel travelling shutter, up to 40 metres above the ground for sufficient shipping clearance.[4]
The senior engineer Peter Hines[11] overcame a major construction problem: On releasing the 950-ton travelling shuttering, the suction of the shutters could pull the new concrete off. I suggested that as we were only carrying the dead load at the time, we should stress the work to about 2/3rds the finally required stress so that the material would not “hog” (rise in the middle) so much – this worked well. After removing the shuttering, we applied the full stress.[4]