Three. Construction of pier top section 0
Section 0 is the corner joint between box girder and pier shaft, with the largest internal force, complex stress, dense steel bars and dense prestressed pipes. Therefore, ensuring the construction quality of section 0 is the key to the quality control of box girder construction.
1, supports and templates
The pier top bracket consists of embedded parts embedded in the pier body, longitudinal beams and transverse beams (using N-type universal bars). The bracket has the advantages of simple structure, clear stress, light weight, high rigidity and convenient disassembly. Hanging basket formwork is used at both ends of the outer formwork, large formwork is used for the inner flange plate, and partial pier formwork is used for the lower part. The internal mold is composed of a large-scale shaped template and some small-scale combined steel templates, supplemented by some special-shaped steel templates. The outer variable cross-section is adjusted by the elevation of the bottom die, the inner bottom die is assembled by the hanging basket bottom die, and the outer bottom die is assembled by the platform template.
2, bracket and template installation:
(1) During the construction of the last two piers, embedded parts should be embedded as required, and the embedded parts are used for the connection between the universal bar and the piers.
(2) Dismantle the pier formwork and install the external working platform. The working platform consists of laying wooden boards in a hanging basket welded with steel bars, and hanging on the steel bars at the top of the pier with steel ropes as lifting ropes. The working platform is suspended on two outer sides of each thin wall.
(3) Assemble the universal bar. The main trusses of the support are assembled on the ground, then hoisted to the embedded parts at the pier top, and finally the transverse connection system of each main truss is assembled at the pier top.
(4) Install vertical and horizontal distribution beams. Each transverse distribution beam consists of two [20 channel steel, and each pier top has 10 transverse distribution beams, of which 4 beams are arranged between two thin walls and 2 beams are arranged at the outer end of each thin wall. Each transverse distribution beam is arranged at the joint of the universal bar. 2 1 longitudinal distribution beams are arranged along the longitudinal direction of each pier top, in which two longitudinal beams composed of [20 channel steel are arranged on the outer sides of both sides, and two longitudinal beams composed of [14b channel steel are arranged in the middle.
5] laying transverse square timber and bottom formwork. The transverse square timber size is 14cm× 12cm, and the spacing is 30cm. The bottom die adopts hanging basket bottom die. There is a wedge between the square wood and the longitudinal distribution beam, through which the elevation and demoulding of the bottom die can be adjusted.
[6] Pre-loading of support. Precast reinforced concrete blocks are used for the preloading of the support in the cage, and the preloading load is 1.3 times the calculated load. The preloading load is divided into three stages, the first stage is 0.5 times, the second stage is 1.0 times, and the third stage is 1.3 times. The purpose of preloading is to measure the elastic deformation of the support and eliminate the inelastic deformation of the support, so as to facilitate the setting of the pre-camber of the support.
Once the floor reinforcement is bound and the external formwork is hoisted. After the external formwork is hoisted in blocks, it is assembled on the support. Each hoisted formwork must be firmly supported on the support, and tie rods shall be installed in time to prevent the formwork from overturning.
Being internal model in the bottom plate and web reinforcement, longitudinal prestressed pipe and vertical prestressed reinforcement after the installation is completed.
Pet-name ruby embedded embedded parts and reserved hanging basket after anchor hole, concrete pump hole, manhole and water pipe cable holes.
3, concrete pouring
(1) The concrete quantity of section 0 is 1280m3. In order to ensure the integrity and good appearance quality of the concrete in the No.0 beam section, the pier top bracket is cast three times during the construction of the No.0 beam section. For the first time, it will be poured to the lower edge of the clapboard passing through the manhole (height 3.0m, concrete 380m3), for the second time, it will be poured to the lower side of the reserved channel of longitudinal prestressed steel strand (height 0.43m, concrete 550m3), and for the third time, it will be poured to the roof (height 3. 1m, concrete 350m3).
⑵ Two concrete delivery pumps are used for concrete pouring at each time, pouring from the middle to both ends, and pump pipes are reserved on the pump frame to prevent pipe blockage.
(3) The height of the second concrete pouring is 6.4m In order to ensure the even and dense tamping of concrete, windows with the size of 50cm×60cm are opened at intervals on the internal mold, which is beneficial for the concrete to be rammed into the template and rammer, and attached vibrators are placed on the internal and external molds.
⑷ Vibrating is the key to 0 # concrete construction. Due to the dense 0# steel bars, many prestressed tendons and many reserved channels, there are many corners and chamfers in concrete masonry, which makes concrete vibrating difficult. Care should be taken when vibrating concrete. It is forbidden to collide with prestressed pipes and embedded parts, and vibration should be strengthened at chamfers to ensure the compactness of concrete.
Four, hanging basket selection and structure, performance and characteristics
1, basket selection
Hanging basket is the load-bearing structure of construction beam section, and it is also the job site of construction beam section (cantilever casting, tensioning, etc.). ). The design of the hanging basket should be based on the maximum cross-sectional weight of the beam, the construction load and the most unfavorable load. On the basis of several continuous beam bridges built by our unit in recent years, referring to the structural forms such as flat chord unbalanced hanging basket, diamond hanging basket, bowstring hanging basket and cable-stayed hanging basket, Hanjiadian 1 Bridge decided to adopt triangular hanging basket.
2. The overall structure of triangular hanging basket:
The hanging basket consists of six parts: triangular main frame, bottom formwork platform, internal and external formwork, suspension system, anchoring system and walking system.
⑴ Main frame: The main frame is the main load-bearing structure of the hanging basket. It is a triangular truss structure, which consists of two triangular trusses and a connecting system. Truss members are welded by channel steel, and joints are connected by high-strength bolts under pressure.
⑵ Bottom die platform: It consists of bottom die, longitudinal beam and front and rear beams. Directly bear the concrete weight of the beam section. It also provides operating space for formwork support, steel binding, concrete pouring and other processes.
(3) Internal and external formwork: the external formwork is made of large steel formwork, and the internal formwork is assembled with combined steel formwork and special-shaped steel formwork. The internal mold is a drawer-type structure, which can be pushed and pulled into place by hand from the previous beam section.
(4) Suspension system: its function is to transfer the self-weight of the bottom formwork platform, the weight of the beam section and other construction loads on it to the main frame and the bottom plate of the beam section. The suspension system includes a front sling and a rear sling, both of which are made of 16Mn steel bars. The lower end of the front sling is pinned with the front cross beam of the bottom die platform, and the upper end is supported on the front upper cross beam, equipped with a pole beam and LQ60 manual screw jack, and the elevation of the bottom die can be adjusted at will. The lower end of the rear sling is pinned with the rear cross beam of the bottom die platform, and the upper end is supported on the bottom plate of the beam section.
5] Anchorage system: Its function is to balance the overturning moment generated when pouring concrete and ensure the safety of hanging basket construction. The hanging basket adopts Φ 32 fine-rolled threaded steel bars and post-anchored polar beams, and directly anchors the rear nodes of the main frame together with the walking track of the hanging basket to the vertical prestressed bars of the box girder.
[6] Running system: The running system includes track, front support, anti-buckle wheel and traction equipment. When the hanging basket walks, the front support slides on the top surface of the track, and the anti-buckle wheel connected with the rear node is locked on the I-beam flange and walks along the flange. Through two sets of 20t chain block, the hanging basket is pushed forward, and the bottom die platform and the outer die are driven to advance in place together. The overturning resistance of the hanging basket in the process of moving is transferred from the anti-buckling wheel to the track, and then to the vertical prestress of the box girder. After the steel bar binding is completed, the internal formwork can be manually moved in place along the internal formwork walking beam.
3. Main technical performance and parameters:
Adaptive maximum beam weight: 360 tons.
Applicable construction section length: 4.0m
Liang Kuan (bottom/top):11/22.5m.
Applicable beam height:12.5-3.5m.
Hanging basket weight: 120t.
Walking mode: unbalanced walking
Overturning stability coefficient under working condition: > 2.5.
Overturning stability coefficient in operating state: > 2.0
4. Main features
(1) Compared with the rhombic basket, the triangular basket reduces the height of the front beam, that is, the center of gravity of the basket is greatly reduced, thus improving the stability of the basket when walking.
⑵ Simple structure, convenient assembly and disassembly, light weight, large rigidity and small deformation.
(3) The initial length is short, and the initial length of the hanging basket is12.0m..
(4) The vertical prestressed reinforcement of box girder is used as the back anchor, which has strong overturning resistance and is safe and reliable.
5] The hanging basket adopts a hydraulic walking system, which consists of a guide beam, a walking beam, an anti-buckle wheel and a walking cylinder. The system has the characteristics of accurate positioning of hanging basket, fast running speed, safety and reliability.
[6] The hanging basket has strong universality, and can be used on other bridges with wide beams and highlights with a little modification.
Five, hanging basket production, test and assembly
1, hanging basket making
Because the hanging basket used in this bridge has a huge structure and heavy load, its processing quality is the key to ensure the safety and quality of construction. Therefore, professional manufacturers with qualified quality must be selected for the processing of hanging baskets. The welding quality of suspenders, triangular trusses and other important parts on the front and rear beams of the bottom die must be inspected by flaw detection and loaded one by one. Only after passing the inspection can they leave the factory.
2, hanging basket assembly
After the construction of 0# block is completed, the hanging basket can be installed.
(1) Installation of main frame system
(1) Install the cushion beam, and anchor the cushion beam on the vertical prestressed finish rolled steel bar of the beam body with an anchor;
② Install the lower guide beam, connect the limit guide rail with the limit angle steel with bolts, and fix the guide beam on the cushion beam;
③ Install the main frame. On the ground under the bridge, front and rear diagonal bars, front and rear lower chord bars and columns are assembled to form a main triangular frame; Then it is hoisted to the bridge deck of 0# block, and the main triangle is fixed on the guide beam with cantilever beam and φ32 finish rolled steel bar to prevent overturning;
④ Install the front upper cross beam;
⑤ Install the main frame cross connecting rod.
⑵ Install the bottom die platform.
(1) Build the bottom formwork with sleepers and install the platform;
(2) horizontally assembling the processed block bottom die with bolts to form a bottom die platform;
(3) respectively installing the front and rear lower beams at the front and rear of the bottom die platform;
④ Install the front and rear working platforms.
(3) The bottom die platform is in place.
(1) Lift the bottom die working platform to the design position with tower crane;
② Install the lower arm of the rear lower cross beam;
③ Install the front boom of the front lower cross beam;
④ Check whether the main frame system and the bottom formwork system form a stable load-bearing structure through the suspension system;
⑤ Arrange measuring points and preload the hanging basket.
(4) Install the side formwork system.
(1) Assemble the external formwork truss and external formwork on the ground under the bridge, including the longitudinal connection system between the pieces of the truss, so that the left and right side formwork and the truss form a whole respectively. Requirements template surface roughness of 5 mm or less;
(2) Lift the external formwork with tower crane and fix it with the bottom formwork platform, and install the external formwork safety net of the working platform before installation;
③ Install the front and rear tie rods of the external sliding beam respectively;
(4) After the installation of the main parts of the hanging basket, according to the design position of 1# section, adjust the center line, horizontal position and elevation of each point of the hanging basket, determine the embedded parts and reserved holes, and apply special release agent on the template;
⑤ Install internal formwork, end formwork and cantilever casting of beam.
A) After the outer die and the bottom die are in place, hoisting the bottom plate steel mesh, installing the bottom plate longitudinal prestressed corrugated pipe, and installing the template for the reserved hole of the lower beam hanger;
B, binding the web reinforcement, and installing the longitudinal and vertical prestressed corrugated pipe of the web and the ventilation reserved hole model;
C, fixing the internal injection truss on the internal sliding beam, lifting the sliding beam with a tower crane, fixing the sliding beam with front and rear suspenders, and adjusting the position of the internal injection truss;
D, installing an internal mold and reserving a concrete mold entry window;
E, installing a stay and a web end die between the outer die and the inner die;
F, binding roof steel bars, installing longitudinal and transverse prestressed corrugated pipes on the roof, and pre-reserved hole models of hanging basket external sliding beam and internal sliding beam rear suspenders;
G after inspection, concrete pouring can be carried out.
5] hanging basket assembly process block diagram see page 50:
3, hanging basket preloading
After the hanging basket is installed, the inelastic deformation of the structure must be eliminated by pressure test. Hanging basket preloading adopts the method of tensioning steel strand on the longitudinal distribution beam of the bottom basket. During the concrete construction of the bearing platform, the steel strand connector shall be embedded in the position vertically corresponding to the concrete gravity center of section 1#. 20 φ 15.24 steel strands are embedded under each hanging basket, and the maximum tension of each steel strand is 150KN, and the maximum tension of each hanging basket is 3 100KN, which is 60% of the weight (weight 2376KN) of the largest girder section (1# section, 93m3 concrete). Layout of hanging basket pressure test points, data acquisition mode and frequency, pressure test time, etc. Should be strictly implemented according to the requirements of the monitoring unit.
Six, hanging irrigation construction
1, the working principle of triangular hanging basket
Dismantle the rear anchor system of hanging basket and guide beam, and the rear anchor system of bottom die and bottom plate. The triangular truss moves forward to the position to be poured under the traction system (inverted chain), and the bottom formwork and outer formwork slide synchronously with the triangular truss to the position of the beam section to be poured. The lower guide beam is anchored by the vertical prestressed tendons at the top of the beam, and then the triangular truss is anchored on the lower guide beam. At the same time, anchor the back end of the bottom die at the bottom of the poured beam section, adjust the front elevation of the bottom die to the design position, and adjust the two side dies in place. Tie bottom and web steel bars and install prestressed pipes, support and adjust internal formwork in place, tie top steel bars and install prestressed pipes, and then carry out cast-in-place construction of beam section concrete. After the concrete reaches the design strength, the prestressed tendons are tensioned and grouted, the formwork is removed, and the above process is repeated until the construction of all beam sections is completed.
2, suspension irrigation construction process
(See the attachment for the picture)
3, hanging basket forward
After the concrete strength and elastic modulus of the poured beam meet the design requirements, the hanging basket can move forward only after the longitudinal and transverse prestressing tendons are tensioned. The moving steps of the hanging basket are as follows:
(1) extended orbit.
⑵ Hang the back beam of the bottom die platform on the walking beam of the outer die with chain block.
(3) Dismantle the rear boom of the bottom die platform.
(4) At the same time, lower the front boom, the front boom and the suspension roller of the external mold walking beam, so that the bottom mold platform and the external mold can be demoulded under the self-weight.
5] Remove the rear anchor of the hanging basket.
[6] chain block is installed at the front end of the track, the main frame is dragged forward, and the bottom die platform and the outer die are driven forward.
Once the matters needing attention:
① The hanging baskets at both ends of the T-shaped structure should move at the same time.
(2) Before removing the anchor, carefully check whether the connection of each part of the buckle wheel is reliable, and handle any abnormal situation in time.
(3) Before moving the hanging basket, it is necessary to adjust the level of the bottom formwork platform and side formwork, and carefully check the connection of various parts of the hanging basket, check whether the safety net, steel bar head or other ropes on the hanging basket are linked with the box girder, and handle the problems in time when found.
(4) The movement of the hanging basket should be under unified command, and the two cylinders should be synchronized as far as possible to prevent pulse walking.
(5) In the process of moving, two chain block should be used to hold the rear node of the hanging basket to prevent the car from slipping.
4, hanging basket bottom die, side die elevation and position control
After the hanging basket is installed, the template elevation and centerline can be adjusted. Template control elevation = design elevation+construction camber. The design elevation is provided by the design institute, and the construction camber is provided by the monitoring unit.
5. Tie steel bars and install corrugated pipes
(1) The steel bars shall be cut and bent as required, and shall be stacked according to the list number after molding. When reinforcement is needed, use tower crane to lift it to the hanging basket position and bind it manually;
⑵ First tie the floor reinforcement on the ground, hoist it to the bottom formwork of the hanging basket, then tie the web reinforcement, and install the vertical prestressed reinforcement and corrugated pipe of the floor. After the internal mold moves forward to the proper position, tie the steel bar at the bottom of the roof, install the prestressed pipe on the roof, tie the steel bar at the top of the roof, and install the embedded parts on the roof;
⑶ The prestressed pipe of the whole bridge is perforated with corrugated pipe, and rolled with corrugated pipe machine and steel belt on site. When the flat tube is processed, it is first rolled into a circular tube and then pressed into a flat shape by a machine;
(4) When there is a contradiction between the position of prestressed pipeline and the position of structural reinforcement, it is absolutely necessary to move the position of structural reinforcement appropriately to ensure that the prestressed pipeline is positioned according to the design position, and measures such as thickening the diameter of positioning reinforcement, encrypting the positioning of reinforcement mesh, and firmly spot welding the mesh with the structural reinforcement of box girder are taken to ensure that the position of prestressed pipeline is not displaced and damaged (slurry leakage) when pouring concrete;
5] Before pouring concrete, check whether the joints of prestressed pipes are closely connected and whether the pipes are in good condition. In the process of concrete pouring, it is forbidden to collide with prestressed pipes to prevent displacement, fracture and slurry leakage.
[6] In order to ensure that the corrugated pipe of continuous rigid frame beam is intact, a hard plastic pipe is worn inside the corrugated pipe.
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