Construction site of the Baijusi Yangtze River Bridge, with closure imminent

"During closure segment construction, pay attention to temperature selection; for the precision control of member installation, fully consider the effects of cable release, counterweighting and release of temporary fixings on the width of the closure gap, so as to ensure construction safety during the closure process..."

On July 4, at the construction site of the Baijusi Yangtze River Bridge in Chongqing, bridge experts from national transport authorities, research institutes and engineering construction enterprises gathered in Chongqing to offer expert advice on the key closure procedure currently under intensive preparation.

The reporter learned that the Baijusi Bridge is striving to complete closure in August this year and to finish ancillary construction of the bridge superstructure within the year.

Closure error must be kept within 2 millimeters

The Baijusi Yangtze River Bridge project, built by CCCC Second Harbor Engineering Co., Ltd., starts in the west at Chenjiage Interchange in Dadukou District, Chongqing, crosses the Yangtze River and ends in the east at Taiyanggang Interchange on the Inner Ring Expressway in Banan District. The project is 3.687 kilometers long in total, of which the controlling works—the Baijusi Yangtze River Bridge—are 1,384 meters long with a main span of 660 meters, making it the world's largest-span cable-stayed bridge with a steel truss girder for both road and rail traffic.

"Closure is an important procedure in bridge construction and also a key stage with high precision control requirements and high construction safety risks." To ensure that the Baijusi Bridge can achieve closure safely and efficiently, the project team invited bridge experts from across the country to form a brain trust and, through on-site inspections and technical review meetings, strengthen technical support for the bridge closure.

National experts review Baijusi Yangtze River Bridge: how is the closure error kept within 2 millimeters?

The Baijusi Bridge will complete its final closure at the mid-span position (approximately in the middle of the Yangtze River), namely the central-span closure segment, which is the last segment of the bridge's steel truss girder structure. At present, the central-span closure gap of the bridge has 7.5 meters remaining.

The main external factor constraining closure of the main bridge's central span is the construction of the steel truss girder over the Qiezixi Railway Station on the Dadukou side. Considering train operation safety, construction over the railway can only be carried out within the 2-hour "skylight period" each day (1:30 a.m. to 3:30 a.m.). Throughout June, due to the middle and high school entrance examinations and other reasons, there were actually only 2 "skylight periods."

"In addition to the influence of side-span construction factors, the construction conditions of the bridge's central-span closure segment are extremely complex." According to Yang Chenghong, deputy chief engineer of the Chongqing Baijusi Yangtze River Bridge Project Management Department of CCCC Second Harbor Engineering Co., Ltd., the central-span closure segment is panel No. 47 of the steel truss girder, and the closure members include 2 upper chord members, 2 lower chord members, 2 web members and 2 edge longitudinal girders, 8 members in total. The cantilever segments on both sides of the central-span closure segment differ in length and weight, making it an asymmetric closure; there are many members in the closure segment, which must be installed within a single "window period."

"Simply put, we need to push apart the two steel girder sections at the two ends of the side spans, each weighing more than 20,000 tonnes, by 20 centimeters." Yang Chenghong said that because temperatures in August are very high, above the 20°C baseline for closure construction, and constrained by the effects of thermal expansion and contraction, the steel girders expand and contract significantly, while the closure error must be controlled within 2 millimeters.

Precision control is difficult. To ensure smooth closure of the bridge, the plan is to carry out the work at night when temperatures are lowest.

Ancillary construction of the bridge superstructure planned for completion within the year

At the expert review meeting on the main bridge closure process in the afternoon, the bridge experts listened to the project department's report on the bridge closure process and conducted technical discussions and analysis on matters including technical, quality and safety precautions for side-span closure, correction of the central-span closure segment length, adjustment of the closure gap, alignment measurement, steel truss girder jacking, member installation and the influence of temperature factors. They clarified approaches to solving the various difficulties in central-span closure construction and gave guidance on details of construction safety risk control.

"This expert review and technical guidance have clarified the direction for closure construction and will help the bridge achieve its construction goal as soon as possible." Ao Chengbiao, head of the Baijusi Bridge project, said that the project team is currently waiting for a suitable opportunity for construction of the side span over the railway section and, in combination with the expert review opinions, is making preparations for central-span closure construction, striving to complete closure of the entire bridge in August this year. After closure is completed, ancillary construction of the bridge superstructure will be carried out, with completion expected within the year.

According to the Chongqing Municipal Housing and Urban-Rural Development Commission, as a controlling node project of Chongqing's Five Horizontal Lines crossing the Yangtze River, the Baijusi Yangtze River Bridge will become an important channel directly connecting the Longzhouwan area of Banan and the Yangtze River Culture and Art Bay Area after completion, facilitating public travel while adding another beautiful new landmark to Chongqing, the City of Bridges.