Things You didn’t Know about Chaotianmen Bridge – World Record Steel Arch Bridge

The Chaotianmen Bridge is built across the Yangtze River, Chongqing, China. The total length of the main bridge and both west and east approaches is 1741 m, the span layout of Yangtze River Bridge is 190 + 552 + 190 m to adopt half-through continuous steel truss arch with tie girders in double-level traffic arrangement type.

The lengths of west and east approaches are 314 m and 495 m respectively, both of them are con­tinuous pre-stressed concrete (PSC) box girder bridges. Double-level traffic ar­rangement is adopted with upper deck to be designed in two-way 6 lanes and both side pedestrian lanes, with lower deck in middle two-way municipal light rails and 2 two-way lanes on each side. It is the longest arch bridge in the world.

The span of this Bridge (552 m) is larger than the 550 m span of the Lupu Bridge completed in Shanghai in 2003, and was completed in 2009. This article introduces the design of the main bridge and its components.

Technical Design Criteria

Lane arrangement on decks:

• Two-way 3 lanes on upper deck with lane width of 3.75 m,
• 2 side pedestrian lanes with to­tal widths 2 x 2.5 m;
• 2 two-way lanes on the lower deck with the clear road height ≥5 m.
• Boundary of rail traffic with clear width ≥ 9.2 m, and clear height over rail top ≥6,5 m.

Design velocity: Upper deck road is 60 km/h. and of lower deck rail line is 80 km/h, allowable max. of 100 km/h,

Seismic Load: Fundamental Seismic intensity of de­gree VI, design of this bridge according to degree VII.

Wind load: Average max. wind velocity of 26.7 m/s,

Thermal action:

• Highest design tempera­ture +45 degree centigrade, lowest –5 °C,
• System temperature following 20 °C,
• Temperature difference following ±25 °C.

Crowd load:

• 5 kN/m2 on whole bridge in gen­eral calculation,
• 0 kN/m2 on pedestrian in calculation of local members.

Permanent load :

• Self-weight of the structure.
• Pavement of upper deck: 22 kN/m;
• Pave­ment of lower deck: 12 kN/m;
• Guarding rail­ing of upper deck: 1.35 kN/m;
• Railing of low­er deck: 2.7 kN/m;
• Pavement and railing of pedestrian: 0.6 and 1.0 kN/m respectively,
• Open bridge of rail communication on lower deck : 8.0 kN/ m,

Variable loads

• Traffic load: calculated traffic load accord­ing to urban highway grade I and checked following load of urban-A. Total bridge de­signed according to 6 lanes.
• Rail communication load: B-typed metro trains as those of light rail traffic with 5 trains in a team with every train length of 19.52 m, having 4 axes, and max. axle load = 140 kN.

Main materials

For the main truss, steel Q420qD, Q370D and Q345qD are adopted; for deck system, Q345qD is mainly adopted, which corresponds to 420 and 355 grade steels. High-strength bolts are

1. 35VB is used for the quality of high-strength bolts of grade 10.9S, M30
2. 20MnTiB is used for the quality of high-strength bolts of M24, M22;
3. 45# high-quality carbon steel is used for nuts, wash­ers, high-strength bolts, nuts and washers, etc

Structural Arrangement

Allowable stresses of materials

The yield strength σs of steel is adopted ac­cording to National Standard. The design safety coefficient K = 1,7 and the allowable stresses [σ]=σs/K according to dif­ferent thickness.

Member section of main truss

The chords of main truss are welded box sections that are 1200 to 1600 mm wide, 1240 to1840 mm deep, the plate thickness of 24-50 mm. For web members, box, H and I-shape sections are adopted with box section depths of 1240-1440 m and plate thickness of 24-50mm. Upper tie is welded H-shape section with depth of 1500×1200 mm, t=50 mm.

Lower tie is welded H-shape section with depth of 1700x 1600 mm, t=50 mm.

Deck system

For upper deck system and both side lanes in lower deck, it is adopted the or­thotropic steel plate of 16 mm thick with closed U-type ribs. Light rail is supported over stringer and cross beam system.

General layout

3-span 190 + 552 + 190 m continuous steel truss arch bridge with tie girders has whole length of 934,1 m (including end cross beams). The full width of main bridge is 36,5 m and that of truss 29,0 m, with truss of variable depth in end span, the middle span is steel truss arch with tie girders. The height from arch top to middle supports is 142 m, the lower chord is in quadratic parabola with rise of 128 m and ratio of rise to span is 1/ 4,31.

The major part of upper chord is also in quadratic parabola and to adopt circular curve with R = 700 m for transition between the upper chords of middle and end span. The N-type truss is adopted for the main one with central depth of 14 m, the depths at middle support and at end support are 73,13 m (including the depth of stiffening chord being 40,45 m) and 11,83 m respectively.

Cost of Construction & Contractor

The Contractor of the Chaotianmen Bridge is China Harbour Engineering Company, the Consultant being Dorman Long & Co. Ltd., and the cost is some 3 milliard yuans (CNY) or 360 million dollars (USD). Of its shape the Chaotianmen Bridge resembles the famous Sydney Harbour Bridge in Australia, span 503 m, dated 1932. The steel weight of Chaotianmen Bridge is 45,000 Tons.

Acknowledgements
UAN Xuewei, Juhani VIROLA, DING Dajun