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- CHANGSHA UNIVERSITY OF SCIENCE Bridge deck width: Clear width: B=2.5+12.25+1.0+12.25+2.5=30.5m Clear width of underlayer passage of rail transit: B=8.6m Design load: urban class A, staddle type monorail train of 352t, pedstrain of 2.4kN/m2 Reference design service life: 100 years - Liu: DESIGN AND CONSTRUCTION OF CAIYUANBA YANGTZE RIVER BRIDGE IN CHONGQING Figure 1: Chongqing Caiyuanba Yangtze River Bridge 2. MAIN INFLUENCING FACTORS OF THE SCHEME DESIGN The arrangement of the bridge span depends on the riverway conditions and navigation clearance required. The riverway where the bridge located had curved navigation channels and branches, with more than 20m distinction between flood and low water level. The bridge location was just 1200m far away from the Shibanpo Yangtze River Bridge, with nonideal navigation condition. Deep water area in riverbed at bridge location was close to south bank. Most of sections at the north bank were low water beaches. Water surfact width at low flow seasons was within 300m at the south bank. Though the river surface in medium and flood seasons was much wider, vessels could only sail at the deep water area with the surface width of 280-350m away from the south bank. Light rail line NO.3 was planned to cross the Yangtze River by this bridge. The two projects were built jointly, including the upper deck for highway and lower deck for railway. - Liu: DESIGN AND CONSTRUCTION OF CAIYUANBA YANGTZE RIVER BRIDGE IN CHONGQING Figure 2: Riverbed section at the bridge location 3. SCHEME DESIGN There was no large span arch bridge among the numerous bridges on the Yangtze River and Jialing River in urban area of Chongqing city, so Chongqing citizens prefer an arch bridge for this bridge by its good appearance. Under the condition of certain economic and technical comparability, an arch bridge was accepted as the solution. However, normal arch bridge with large horizontal thrust forces needed huge bridge pier built in river that may affect water flow and navigation, and it was not suitable to use this type of arch bridge in Chongqing section of Yangtze River because the large water level height difference and to cross the river need more than two spans in Chongiqng. Therefore, a half through tied arch bridge was selected as the basic scheme. This bridge is a double deck bridge with a main girder of sufficient height and rigidity. Open steel truss girder structure was used in order to - Liu: DESIGN AND CONSTRUCTION OF CAIYUANBA YANGTZE RIVER BRIDGE IN CHONGQING meet the open vision demand and to satisfy the passengers enjoying landscape on river. In order to meet clearance requirement and deformation of monorails, the height of the main girder was fixed to 11.2m, so as to form a continnous girder structure with large rigidity. Because the girder has a large rigidity, rigid requirement of arch structure which carrying load together may be decreased. Therefore, arch rib of the bridge was designed to be weak. Moreover, if truss was adoped for both the arch and girder, the bridge may show scattered members so as to interfere with visual landscape on river. Therefore, arch rib was designed as constant sectional basket type steel box arch rib with fine sections. The column on pier was always designed in normal deck through arch bridge to support the main girder. The clairvoyant interpace became broad and the whole bridge structure became concise without the column. The rigidity of the main girder was fully used and the side spans and mid span was resonablly arranged to satisfy the deflection of the main girder, then the column on pier was removed. Figure 3: Side span without the column on pier Liu: DESIGN AND CONSTRUCTION OF CAIYUANBA YANGTZE RIVER BRIDGE IN CHONGQING - After getting rid of the column on pier, the arch sections of the mid span and side spans under the bridge deck were changed into linear girder to form the V shape. Pre stress was used to connect the girders to bridge pier in order to form a integrated structure, and horizontal tie bars were tensioned to form a stable Y shaped rigid frame. Horizontal tie bars were also arranged in the deck of mid span in order to form a deck thourgh bridge system without horizontal push forces. 枯水位162.960m P15 P16 P17 P18 P19 P20 Figure 4: General layout of the bridge scheme(unit：cm) Liu: DESIGN AND CONSTRUCTION OF CAIYUANBA YANGTZE RIVER BRIDGE IN CHONGQING - 4. STRUCTURE DESIGN 4.1 Piers and foundations Spread foundations were used in Pier P15 and P16. Four piles with the diameter of 2.5m and a piles cap with the size of 12 12 4m were used in Pier P19. Solid pile foundation corresponding to the pier size was used in pier P20. Thin-walled structure with constant hollow section was used in Pier P15, P16, P19 and P20. The size of 4.1 4m was used in P15 and P20 and size of 4 4.3m was used in P16 and P19. The main function of the side piers P16 and P19 was to support the main truss girder, and to form the hyperstatic system with the rigid frame with 9 PESH7-91 tied bars arranged at the top of each pier, so it could adjust the internal forces of the main piers with tied bars and vertical bars. 4.2 Y-shaped rigid frame Nine digging piles with the diameter of 3m and a pile cap with the size of 17 17 5m formed the main pier P17. Spread foundation with the size of 17 17 6m was used in main pier P18, and hollow variable thin-walled section was used in pier. Liu: DESIGN AND CONSTRUCTION OF CAIYUANBA YANGTZE RIVER BRIDGE IN CHONGQING - The front and back cantilevers, main beam, the front and back secondary beams, the front and back main beams and anchorages of tie bars composed the Y shape rigid frame. The thin-walled variable hollow section with the size of 10 6 5.2 3.6m was used in front cantilevers. Solid section was used in the parts of 15m calculated along the centerline at the top of each cantilever. The anchorages of the tie bars arranged on the front secondary beam were 50m far away from the center of the pier, and the vertical bars at the supports was arranged at the root of the beam. The front main beam was arranged at 32.91m far away from the pier center. The main beam was arranged at the top of the piers, it connected the main piers and the Y shaped rigid fram on each side. The thin-walled variable hollow section with the size of 10 64 3.6m was used in back Liu: DESIGN AND CONSTRUCTION OF CAIYUANBA YANGTZE RIVER BRIDGE IN CHONGQING - cantilevers. Solid section was used in the parts of 10m calculated along the centerline at the top of each cantilever. The anchorages of the tie bars arranged on the back secondary beam were 102m far away from the center of the pier. The back main beam was arranged at 32.91m far away from the pier center. The anchorages of tie bars and vertical tension bars were arranged on the solid part at the top of the side piers. 4.3 Steel truss girder The combination system of truss and orthotropic deck was used in the steel truss girder of the main bridge. The vertical bars were used as the elastic supportings in the range of 800m long continuous steel truss girder of the arch span. Multiple supports suspension bars supported on the beam were arranged at the connection of the arch and the girder. The bearings were arranged at the down string nodes at the side piers and transiting piers. Except the four longitudinal displacements restricting damps arranged on the beam of the side pier, the steel truss girder had no connection with the main arch structure. The concept of nodes integration and section integration was applied in design of the steel truss girder. The steel bars, nodes and the orthotropic deck sections were fabricated together in plant as the basic elements and delivered on site to lifting and joining together. The 800m Liu: DESIGN AND CONSTRUCTION OF CAIYUANBA YANGTZE RIVER BRIDGE IN CHONGQING - long steel truss girder was divided into 51 sections, among which, the standard sections were 16m long, 39.8m wide, 11.2m high and 240t weight. Figure 5: Integration fabrication of the sections of the steel truss girder 4.4 Main arch The basket type steel box arch with the span of 320m, vector height of 56m was the style of main arch structure. The inclining angle of the main arch rib was 10.67 . The size of the rib box section was 2.4 4.0m. The thick of steel box was varied among 2440 mm. Six transverse steel box bracings connected the two rib together. Each rib along the arch span were divided into 23 sections, including root arch sections, standard sections which separated by whether connected to the transverse bracing and joint sections. The method of lifting the single piece of rib was applied and the heaviest rib section was 92t. Liu: DESIGN AND CONSTRUCTION OF CAIYUANBA YANGTZE RIVER BRIDGE IN CHONGQING - 4.5 Vertical bars and suspension hangers The vertical bars in the truss directly carried the load of vehicles, rail and passengers. It is the most important part in load transfer chain in deck through arch bridge. The standard horizontal distance of the suspension central point along the bridge longitudinal axle was 16m. HDPE shield paralleled steel cables were used in the vertical bars. The cold formed anchorages at the top of the vertical bars were anchored at the inner diaphragms inside the Liu: DESIGN AND CONSTRUCTION OF CAIYUANBA YANGTZE RIVER BRIDGE IN CHONGQING - arch box. The anchorages on the bottom of the bars which connected the deck were steel pins. Besides the vertical bars on arch, the suspension bars connecting arch and girder had the largest load carrying capacity. The suspension bars of 2 6 187 transfer several thousand tons of dead load and living load to the root of front secondary beam of the rigid frame. To reduce the local stress caused by the longitudinal displacement of the steel girder, the running ball hinge was used in the cold formed anchorage at the top of the bar. 4.6 Tie bar The tie bars of this bridge were divided into two groups including the middle span tie bars and the side span tie bars. The tie bars were made of zinc plated steel strand with high strength and low laxity and with HDPE coat outside. There were 8 tie bars in middle span and four tie bars on each side were through the beams under the deck and anchored in the shear keys in the front part of the rigid frame. There are total 14 tie bars in side span and seven on each side. 5. CONSTRUCTION METHOD Liu: DESIGN AND CONSTRUCTION OF CAIYUANBA YANGTZE RIVER BRIDGE IN CHONGQING - The main structure above the bridge foundation can be divided into three parts including concrete pier and Y shaped rigid frame, steel truss girder and steel box arch rib. Normal slip-form method was used in the pier construction. Supporting frames and casting in place concrete method was used in rigid frame construction. The cable crane was used to assemble the steel truss girder sections and steel box arch rib sections. Construction procedure of the bridge is as follows: 1) Construction of foundation, pier, rigid frame and beams on it. 2) Setting up cable crane tower. Constructing Y shaped rigid frame and the temporary supporting frames of main truss girders in side spans at the same time. 3) Casting pre stressed concrete Y shaped rigid frame section by section. Stretching the pre stress steel bars in cantilevers of rigid frame. Remove the supporting frame after concrete of Y shaped frame got to its strength. 4) Hoisting and assembling truss girder of 88m length in side span and 152m length in lateral span on Y shaped rigid frame using the temporary supportings. 5) Stretching a part of side span tie bars, transforming side span and lateral span girder supporting system to support the truss girder on rigid frame and bridge pier. 6) Hoisting the main arch rib with cable, setting up the temporary buckle cable, and adjusting the forces of tie bars in side span and buckle cable to finish the main arch rib construction. Liu: DESIGN AND CONSTRUCTION OF CAIYUANBA YANGTZE RIVER BRIDGE IN CHONGQING - 7) Hosting mid span girder sections and buckling arch rib with suspension cable, and adjusting relevant buckle cable force until closure of the mid span girder. Installing and tensioning mid span tie bars and removing a part of buckle cable. 8) Adjusting tensile force of side span and mid span tie bar, removing all buckle cables and construction tower, then, finishing construction of bridge deck. Liu: DESIGN AND CONSTRUCTION OF CAIYUANBA YANGTZE RIVER BRIDGE IN CHONGQING - The cable hoist system has a span of 420m as shown in Figures 6 and 7. The maximum hoisting weight of this system is 280t and lifted height of 150m. There were two groups of the main cables which has the central distance of 34m. Each cable was made of 1260 mm steel strands. Figure 6: Erection of central arch ribs Figure 7: Typical construction process of the bridge 6. LAST REMARKS Liu: DESIGN AND CONSTRUCTION OF CAIYUANBA YANGTZE RIVER BRIDGE IN CHONGQING - For the advanced structure design and difficulty of technology of Caiyuanba Bridge, also for its operation safety, corresponding research programs were completed, mainly including experimental research of big scale full bridge model wind tunnel, load carrying ability research of the steel-concrete joint of main arch rib and Y shaped rigid frame and joint of front secondary beam and Y shaped rigid frame, experimental research of the main bridge modes and vibration of vehicles coupling, fatigue experimental research of down stringer nodes of steel truss girder and experimental research of suspension bars and tie bars anchorages and fatigues. The above research results proved the credibility and safety of the bridge design concept. After four years construction, the bridge was opened to traffic on Oct. 29th, 2007. Liu: DESIGN AND CONSTRUCTION OF CAIYUANBA YANGTZE RIVER BRIDGE IN CHONGQING - 重庆菜园坝长江大桥设计与施工 刘小慧 重庆通信研究设计院 关键词：公路和铁路桥，刚构，钢桁梁，系杆拱桥，复合材料结构 摘要：重庆菜园坝长江大桥是公铁两用桥梁，具有超长的尺寸。本文重点介 绍的各种外部影响因素，它使用全新的设计理念，提出了连续刚构，钢桁梁，绑 成一个复合结构的拱组成的创新体系下的桥梁设计理念。 该桥自然地与地理条件 相结合，满足功能需求，充分利用材料特性，满足结构能力和景观需求。 1。引言 重庆菜园坝长江大桥是一座总长度为 800 米的城市桥梁。 它位于重庆市重庆 主城区的中心地带,一侧连接渝中区,一侧连接长江南岸区。该桥由主桥，引桥在 北部和南部，经过菜园坝路口，随家呗路口和南城隧道等，总长度 4,000 米。主 桥，作为该项目的主要组成部分，是一个复合结构，包括刚构，钢桁梁,钢箱梁 组成的主跨 420 米，边跨各 88 米的拱桥（图 1）。这是一个公铁两用型桥梁，6 车道的高速公路和两个人行道在上层和其下层的单轨轨道运载。 主桥设计的主要技术规范如下：设计速度为 60km /公路和 75km/铁路; 桥面宽度：清除宽度 B =2.512.25+1.012.25+2.5=30.5 米 轨道交通的底层通道净宽 B =8.6 米 设计荷载：城市类，staddle352 吨式单轨列车，行人荷载 2.4kN/m2 参考设计使用寿命 100 年 图 1：重庆菜园坝长江大桥 2。该计划设计的主要影响因素 Liu: DESIGN AND CONSTRUCTION OF CAIYUANBA YANGTZE RIVER BRIDGE IN CHONGQING - 桥梁跨度的安排,取决于河道条件和通航净空,此桥位于河道弯曲处,并且在此 处有许多支流,分别超过洪水水位和低水位 20 米.桥的位置仅离石板坡长沙大桥 1200 米,通航条件不理想.桥位河床深水区靠近南岸,北岸的大部分路段都是低水 滩.在枯花季节江面宽度在 300 米以内, 虽然在中期和汛期的江面更广， 但是船舶 只能从南岸深水区 280-350 米宽度范围内航行。 轻轨 3 号线计划通过此桥,跨越长 江。上层公路和下层铁桥.这两个项目共同建造. 图 2：桥位河床断面 3。方案设计 在长江和嘉陵江在重庆市市区众多的桥梁中,没有大跨度拱桥,此桥且有良好 的外观,所以重庆市民希望有这样一座拱桥, 在一定的经济和技术的可比性的条 件下，拱桥被接受的解决方案。然而，正常的水平与大推力拱桥，需要巨大的桥 墩建在河里，可能会影响水流量和导航，此处是不适合建造这种类型的拱桥. 在 重庆长江段，因为大的水位高差过河需要两个以上的跨度。因此，系杆拱桥被选 定为基本计划。 这座桥是一座双层桥, 主梁具有足够的高度和刚度。采用开放式钢桁梁结构， 是为了满足乘客有开阔的视野需求能享受河流景观，.为了满足通航要求和单轨 变形，主梁的高度被加大到了到 11.2 米，从而使梁具有了强大的连续结构刚性. 因为梁有一个大的刚性拱结构的刚性需求,承载负荷可能会降低。因此，桥肋拱 设计的要弱。如果是通过桁架拱和梁,桥可能会显示各部分成员分散，会干扰河 流视觉景观。因此，拱肋被设计成细截面篮式钢箱,墩柱通过拱桥设计，支持主 梁在正常的桥面。这样,视野就会变得更宽广,全桥结构也变得简洁.该桥充分利用 和边跨和中跨合理的安排,以使主梁的刚性满足主梁挠度，然后墩柱被移除. Liu: DESIGN AND CONSTRUCTION OF CAIYUANBA YANGTZE RIVER BRIDGE IN CHONGQING - 图 3：边跨不上墩柱 摆脱墩柱后， 拱跨中的部分和边跨桥面的下部分被改变成直线梁， 形成 V 形。 通过预压力来连接主梁，桥墩，拉紧水平拉杆,，以形成一个整体的稳定的 Y 形 刚架。水平拉杆被设置在桥面跨中,使整个桥面形成没有推力的桥面系统. 图 4：桥计划的总体布局（单位：厘米） 4。结构设计 4.1 墩和基础 在 P15 和 P16 桥墩处使用扩大基础, 在 P19 桥墩处使用四个直径 2.5 米的桩 和大小的 12124 米桩帽，p20 桥墩用合适大小的桩来固定基础. 在 P15,P16,P19 和 P20 号桥墩用空心薄壁结构,在 P15 和 P20 号桥墩使用 4.1 4 米的墩帽,在 P16 和 P19 号桥墩使用 44.3 米的墩帽. P16 和 p19 号桥墩的主要功能是支持主桁梁. 9-91 PESH7 绑在每个桥墩的顶部再通过安装钢筋来形成超静定系统,它可以 绑扎钢筋和吊杆来调节主墩的内力. 4.2 Y 形刚架 P17主墩由九个直径 3米的挖孔桩组成,其桩帽尺寸为 17175米. P18号桥 墩采用 17176 米的扩大基础,桥墩为薄壁空心墩. Y 形刚架由正面和背面的悬臂，主梁，正面和背面次梁,正面和背面主梁及拉 杆锚碇组成。 前悬臂使用大小为 1065.23.6 米的薄壁中空变截面. 悬臂顶端 15 米采 用实体截面.次梁拉杆前部的锚锭安装在离中心桥墩 50 米处，支持吊杆被安装在 Liu: DESIGN AND CONSTRUCTION OF CAIYUANBA YANGTZE RIVER BRIDGE IN CHONGQING - 梁的底部。前主梁被安装在远离柱心 32.91 米处。主梁安放在桥墩的顶部，连接 主墩和 Y 形刚架. 在后悬臂使用尺寸为 10643.6m 的薄壁空心变截面. 悬臂顶端 10 米部 分使用实体结构。次梁拉杆前后部锚锭安装在离桥墩中心 102 米处。后主梁被安 装在离桥墩中心 32.91 米处。拉杆和垂直张力锚地被安装在边墩顶部. 4.3 钢桁梁 主桥钢桁梁使用桁架和正交异