What Is a Bascule Bridge?

Bridge opening refers to bridges that can be opened and closed by vertical rotation, horizontal rotation, and lifting for navigation purposes. When land transportation is not very busy, there are ships sailing on the river, and fixed bridges cannot be built above the navigable headroom, it is necessary to build movable bridges to solve water and land transportation. The first way to open the bridge is to move the bridge span structure and the deck in the vertical plane where the bridge axis is located (including horizontal displacement and rotational displacement). For example, the second type of Tower Bridge is the bridge span structure and the bridge deck. Longitudinal axis displacement (including folding displacement and telescopic displacement), such as the Kiel-Horn three-section folding pedestrian opening bridge across the Horn river in Kiel, Germany; the three types are the bridge span structure and the bridge surface at the horizontal plane where the bridge axis is located Internal rotation, such as the Tianjin Jintang Bridge; the fourth type is the span of the bridge structure and the overall rotation of the bridge deck is perpendicular to the longitudinal bridge axis, such as the Gateshead Millennium Bridge in East Gateshead, UK.

1 Overview of Open Bridge 1

Wenzhou Junan Bridge is located between Pingyang County and Cangnan County, Wenzhou City, Zhejiang Province, across the Aojiang River. The bridge connects Aojiang Town of Pingyang County to the north and Longgang Town of Cangnan County to the south. Due to the continuous economic development of the two towns, the flow of people and logistics has increased significantly, and the land traffic of the two towns mainly depends on the upstream Longgang Highway Bridge. The bridge deck is narrow, the standard is low, and it is far from the center of the two towns. Restricting the economic development of the two towns, it is urgent to build a second channel between the two towns.

A total of 3 bridge locations were selected during the study of the plan, from upstream to downstream: three major plantsRenmin Road Bridge, Shengli RoadWenwei Road Bridge, and Xinmeizhou Bridge. The three bridges are located approximately 2.5 km, 4.5 km, and 7 km downstream of the Longgang Highway Bridge. Each of the three bridge locations has advantages and disadvantages. The biggest advantage of the Renmin Road bridge location is that the bridge location upstream of the main ports of the two towns has no adverse impact on shipping and low cost. The biggest advantage of the New American State Bridge is that it is convenient for the downstream development of the two towns. The disadvantage is that it is not conducive to cross-strait personnel exchanges, and it is not obvious to the Longgang Bridge. Shengli Road-Wenwei Road bridge is located between the above two bridge locations, which can effectively divert the vehicles passing the Longgang Bridge, facilitate the flow of people and goods between the two towns, and gradually turn the two town centers to the east, creating further development for the east condition. It is possible to build three bridges in the long run, but in the short term, Shengli RoadWenwei Road is more suitable.

2 Construction Conditions for Opening Bridge 2

2.1 Topography

The towns of Aojiang and Longgang are located on the southeastern coast of Zhejiang and belong to the marine plain. The terrain is flat and the channel is basically stable, but the deposition speed is faster and the navigation capacity is decreasing year by year. The bridge is located in the lower reaches of the Aojiang River near the estuary and is greatly affected by the tide (Aojiang is one of the three major tidal rivers in the country).

2. 2 Hydrology

(1) River conditions at the bridge site: The bridge site is located at the lower reaches of the Aojiang River, approximately 12. 7 km away from the Aojiang River mouth. The bridge is located on the transition between the upper and lower bends of the Aojiang Channel, 1 100 m from the upstream bend, 700 m from the Aojiang main port area, 1 800 m from the downstream bend, and 950 m from the Long Port main port area. The bridge location is about 380 m wide, the shoreline is stable, the water depth is shallow, and the low tide level is about 0.8 m. Ships above 200 t need to wait for the tide to enter the Aojiang port.

(2) Flood tide characteristics: The Aojiang River estuary belongs to the half-day tide estuary, the high tide level at the bridge site is 4.82 m (Yellow Sea, the same below, August 30, 1992), the lowest low tide level-2.32 m (6.1972) (March 12), with an average high tide level of 2.46 m, an average low tide level-1.72 m, a maximum tidal range of 6.41 m, a minimum tidal range of 1.10 m, an average tidal range of 4. 18 m, and an average ebb tide of 0.65 m / s, the average tide velocity is 0.8 m / s.

2.3 Engineering Geology

The Quaternary overburden in the bridge site area is the Neogene marine sedimentary layer, the Pleistocene alluvial sedimentary layer and the marine sedimentary layer, which are mainly silt, silty clay, clay, subclay, and cobble soil.The bedrock burial depth is greater than 120. m.

3 Open Bridge 3 Technical Standard

(1) Line grade on the bridge: Grade II city trunk road.

(2) Calculate driving speed: 40 km / h.

(3) Design load: city A class.

(4) Number of lanes: 4 lanes.

(5) Bridge width: The main bridge is provided with motor vehicles, non-motor vehicles and sidewalks, with a total width of 24.5 m; the approach bridge is provided with only motor vehicle lanes, and the bridge width is 17.0 m.

(6) Maximum longitudinal slope: 3.5% (actual maximum longitudinal slope of 3.3%).

(7) Navigation standard: Designed navigable water level + 4. 63 m. The minimum clear height opening bridge of the main navigation hole is 10 m closed and 23 m opened; the minimum clear width of the main navigation hole is 64 m. The minimum clear height of the auxiliary navigation holes is 6.8 m and the minimum clear width is 35 m. There is one main navigation hole and two auxiliary navigation holes, which are all one-way navigation.

(8) Earthquake intensity: Basic intensity is 6 degrees, fortify at 7 degrees.

4 Opening the bridge 4

4. 1 proposal to open the bridge

The Aojiang Wharf upstream of the bridge site is the main port area of Aojiang Town. It can be used to transport thousands of tons of sea-going vessels by high tide. When the bridge type plan is drafted, the high bridge plan is preferred. The traffic on the bridge and the surface traffic do not interfere with each other. The total length of the bridge is about 2 km. The Longgang side needs to be across Jiangwan Road and Longxiang Road, and the Aojiang side needs to be across Jiangbin Road, Xinhe Road and the planned Binhe Road. Vehicles traveling on the above roads on the bridge need to travel a long distance to cross the river. The bridge's traffic functions have not been fully utilized. At the same time, as Longgang Town only built the town until the 1980s, the demolished houses not only have a shorter service life. At the same time, most of them are multi-storey buildings and facades, and the cost of demolition is high, which is difficult for the government to accept. The low-bridge scheme cannot be navigable to thousands of tons of ships, which affects the port area and regional economic development. Considering various factors, the bridge scheme must meet When passing a thousand-ton sea-going ship, the approach bridge length must be minimized to facilitate cross-strait personnel and vehicles, and promote the coordinated development of the urban economy. The only bridge type that can take into account the high bridge and short approach bridge is the opening bridge, so the opening bridge is the focus of the bridge scheme .

4.2 Feasibility of opening the bridge

The opening of the bridge has set obstacles for the free passage of watercraft and vehicles on the bridge, but considering that when the bridge is not opened, generally ships under 300t can also pass freely, and the number of inward and outward vessels exceeding 300t is limited daily. It can meet the needs of large ships entering and leaving the port.At the same time, due to the decrease in the amount of incoming water from the upper reaches of the Aojiang River year by year, the overall trend of sedimentation and the decrease in navigation capacity year by year. There is a possibility that the bridge will not be opened after a few years of operation, so in the long term, the upstream terminal can only dock small vessels below 300 t, and large vessels can dock at the large-round wharf built downstream. Therefore, in the case of the urgent need to build a bridge and the construction of high bridges is a big controversy, opening the bridge may be a feasible option.

5 Research on Opening the Bridge 5

5.1 Overview

The opening bridge is an ancient bridge type. The country with the largest number of opening bridges in the world is the United States. So far, there are nearly 3,000. China has fewer opening bridges and fewer opening bridges for heavy traffic. There are three common types of open bridges: flat, vertical and helicopter. During the opening process, the two-swing beam span is in a cantilever load state. The beam uses a large amount of steel and the pier foundation is large. To prevent the ship from colliding with the beam when the ship is passing, an anti-collision enclosure must be constructed outside the perimeter of the beam span Weirs or piers have increased engineering investment and blocked the channel. Due to the high cost of flat-spinning and complicated technology, it has been rarely used at home and abroad. The vertical rotation type is convenient to open, and naturally forms a column when opening, which is conducive to the safety protection of passing vehicles. However, due to the limitation of the balance weight, the span of the opening hole beam is larger than the other two types of opening bridges, and the beam structure is large and complicated. From the perspective of the use of this type of bridge, it is not an ideal type of open bridge, and it is rarely used abroad recently. The helicopter has the advantages of fast opening speed, simple structure, and reliable force.The rigidity of the bridge span is good for high-speed driving. The structural details and mechanical and electrical systems are simpler than the other two forms.The initial investment and operation and maintenance costs are also less. Therefore, this bridge recommends the use of a vertical lifting open bridge.

5. 2 Scheme of opening the main components of the bridge

(1) Steel girder: The steel box girder and the through steel truss girder are designed and compared.The steel box girder has the advantages of simple structure and beautiful shape. Under the same conditions of clear navigation height, the bridge deck is higher than the steel truss and the approach bridge is also longer. By comparison, a down-through steel truss is used.

(2) Main tower: There are two types of structures, such as steel trusses and reinforced concrete, in the main tower.This bridge is designed to reduce the structural center of gravity after the bridge is opened, improve structural stability, and reduce the effect of uneven settlement of the tower pier foundation on normal opening. At the same time, considering the bridge landscape effect, the main tower uses a reinforced concrete tower.

(3) Lifting equipment: There are generally two types of lifting systems: hydraulic lifting and mechanical lifting.In the study of the scheme, the hydraulic lifting was considered to be relatively simple, and in-depth research was done, but considering that the lifting height of the bridge reached 13m and the hydraulic rod was longer. However, it is not assured of its reliability after long-term operation, and it is difficult to replace once quality problems occur. Therefore, the hydraulic lifting scheme was finally abandoned, and the conventional mechanical lifting scheme with good reliability was still adopted.

6 Open Bridge 6 Open Bridge Solution Design Introduction

6. 1 Structural design

6. 1. 1 Opening steel beam

(1) Main truss structure: The opening hole adopts a through steel truss beam, the center distance of the main truss is 21. 2 m, and the bridge surface between the main trusses is used for motor vehicles and non-motor vehicles. The outer side of the main truss is 2. 0 m 5 m Wide sidewalk, the total width of the steel truss beam is 26.5 m. The main truss length is 6.0 m, and the truss height is 8.0 m

(2) Deck system: In order to reduce the height of the bridge deck, the bridge deck is made of steel orthotropic plate, the bridge deck top plate is 14 mm thick, and the longitudinal weld thickness is 6 mm U-shaped closed ribs with a spacing of 600 mm and a height of 460 mm. T-shaped stringers with a spacing of 2,000 mm. An inverted T-shaped crossbeam is welded transversely, and its spacing is the same as that between the main truss joints. The crossbeam is 20.6m in length, and both ends are bolted to the main truss joint.

(3) Deck Pavement: A 55-mm-thick modified asphalt concrete pavement is installed between the main truss and a non-motorized vehicle deck, and the sidewalk panel is paved with a lighter 15 mm thick non-slip rubber sheet.

6. 1. 2 main tower

The main tower of the bridge is a gate-shaped reinforced concrete structure. The tower above the platform is 58. 389 m high and the tower above the bridge is 40. 44 m high. It is mainly composed of tower columns, upper beams and lower beams. In order to improve the mechanical performance of the beam and increase the visibility of the bridge, the bottom edges of the upper and lower beams of the main tower are designed as circular curves with a radius of 64.9 m. The upper tower is a box-shaped section with a wall thickness of 0.5 m. The lower tower is designed to be a solid section due to ship collision resistance. The lower beam is a variable-height single-box double-chamber prestressed concrete box girder, and the upper beam is an equal-height curved prestressed concrete box girder. Inside the box are placed opening equipment, a working platform, and an overhead crane. Twelve 1.2 m m bored piles are arranged for each tower column, with a pile length of 83.5 m and a cap thickness of 2.5 m.

6. 2 Main components of lifting equipment

6. 2. 1 Overview

Wenzhou Taonan Bridge is a vertical lifting opening bridge with a span of 72 m and a width of 26.5 m, an opening weight of 1,003 t, a lifting height of 13 m, a lifting speed of about 10 m / min, and an open navigational clearance of 23 m. The movable bridge span is controlled by two lifting mechanisms. The lifting mechanism is installed in the tower at both ends of the movable bridge span. Each hoist has 2 reels, and each reel passes 11 50 mm steel wire ropes, and one end is suspended by steel. Beam, suspended at the other end with a counterweight. Two sets of balance weights of the whole bridge are placed in the two towers respectively, and the two sets of balance weights balance 97% of the weight of the active bridge span. The remaining weight enables the bridge to be implemented on the support. Mechanical shafts are used for rigid synchronization between the two reels in the same tower, and AC motors are used for frequency conversion and speed regulation for the reels between the two towers.

The control console of the opening bridge is set in each of the two towers, and either side can be designated as the main control according to the needs, and the other side is only used for emergency parking. Each tower has an elevator for the staff to get on and off. In order to ensure the smooth movement of the movable bridge span and the safety of road fairway traffic, both ends of the bridge span are also provided with vertical and horizontal guidance devices, up and down locking devices, centering devices, air buffers, road grids and maintenance devices.

After receiving the notification that the bridge span needs to be opened, the operator first sends out an acousto-optic signal that prohibits pedestrians from passing through the vehicle. After no pedestrians on the active bridge span, operate in the following sequence: Close the road barriers at both ends; Lower locking device Unlocking; The brake of the lifting mechanism is opened, and the lifting mechanism of the lifting mechanism stops after it reaches the prescribed height; At this point, the lifting process is completed, and then an acousto-optic signal is issued to allow the vessels under the bridge to navigate. The closing sequence is opposite to the above sequence, and the lifting and lowering process of the active bridge span takes about 120 s.

6. 2. 2 Lifting mechanism

(1) Reel set: The reel is welded as a whole structure, with an outer diameter of 3 460m m, which is 69.2 times the diameter of the wire rope. Its surface is evenly distributed with 11 rope grooves, which are transmitted by the friction between the wire rope and the drum rope grooves. Driving torque.

(2) Brake: Two types of brakes are used in the lifting mechanism. The block brake is used as the auxiliary braking device, and the disc brake is used as the main braking device.

(3) Standby mechanism: This device is an emergency device that opens and closes the movable bridge span when the external power supply is interrupted.There is a toothed clutch on the other output shaft end of the high-speed shaft of the reducer. When the main motor is working, the clutch is in the disengaged state. In the open state, when the backup device is required to work, close the clutch, start the backup generator, release the disc brake and block brake, and drive the drum to open or close the movable bridge span.

6. 2. 3 balance mechanism

(1) Balance weight: It consists of balance weight box, barite concrete, cast iron adjustment block, etc., with a total weight of 486 t, and the weight of the balance box is about 69 t. After pumping 392 t of barite concrete, the remaining 25 t is 50 kg cast iron adjustment blocks each.

(2) Balance weight maintenance device: The steel wire rope is always under tension when the bridge span is opened and closed. The maintenance device can pull up the balance weight when it rises to the position to loosen the wire rope so that the rope can be installed or removed.

6.3 Opening bridge construction and installation

(1) Steel truss girder installation: The bridge site is located on a tidal river, and the tidal water drop is large. To avoid risks and ensure safety, and at the same time to avoid long voyages, when the steel girder is installed, the steel girder parts are hoisted through the waterway. On the formed concrete T-beam bridge surface, first assemble the steel beam on the concrete bridge surface, and at the same time, set up a bracket on the main span to form a steel beam dragging channel. After the steel beam is pulled into place, lift the steel beam, and the main navigation hole bracket is removed. Resume traffic on the main channel.

(2) Installation of lifting equipment: After the main tower is fully capped, install the lifting equipment. No. 4 main tower (longgang side) lifting equipment is installed because the approach bridge is connected to the land, so all the lifting equipment is transferred from the land to the concrete bridge deck for storage. Leave 1 hole T beam for navigation, the main tower is not connected to the land in the isolated river, all lifting equipment is transported from the water to the main tower. The two main tower lifting equipments are made by the contractor's self-made simple hangers and installed with electric hoists. The hanger is supported on the bottom plate of the upper beam and can be moved by its lower roller. After the equipment is lifted to the bottom plate, it is positioned by the 35 t crane in the upper beam.

6.4 Ship safety assurance measures

Compared with general fixed bridges, open bridges need special measures to enhance the safety of watercrafts.

(1) Establish the Open Bridge Management Center, composed of bridge management, maritime, ship management and other personnel. Its responsibilities are mainly to coordinate the relationships between various departments, formulate emergency plans, issue unified instructions, and uniformly dispatch bridge openings, ship crossing bridges, and deck traffic.

(2) Set up a traffic monitoring system, implement effective monitoring of bridge decks and water traffic, and timely discover hidden safety hazards and accident signs, and effectively control the occurrence of accidents.

(3) A lookout was established in the Xiabu area of Longgang Town to observe the bridge entry and exit.

(4) In order to strengthen on-site patrol inspections, patrol boats and motor boats (one each) are equipped to patrol the upper and lower reaches of the bridge.

(5) To cope with emergencies, consider equipping tugboats with corresponding horsepower (or joint configuration with relevant units) for emergency rescue.

(6) Set navigation aids in the waters near the upper and lower reaches of the bridge so as to guide ships to pass safely through the navigation holes.

(7) In order to prevent the ship from colliding with the pier, the pier needs to be equipped with anti-collision facilities.

7 Open Bridge 7

Due to the fast-paced requirements of modern society, the function of open bridges has gradually failed to meet the needs of modern transportation. In recent years, the number of open bridges at home and abroad has gradually decreased, but under certain conditions, open bridges are still an optional bridge type. Still has strong vitality. Taonan Bridge uses a concrete tower with a maximum span of 72 m and a maximum lifting weight of 003 t. It is the largest span and maximum lifting weight in China and Asia after the Tianjin Haimen Opening Bridge (steel truss tower, maximum span of 64 m, and maximum lifting weight of 630 t). The modernization of the bridge is under construction, and the bridge is under construction (see Figure 2). It is expected that the bridge will be opened to traffic in May 2007, and the completion of the bridge will further promote the development of the bridge in China. ^[2]