Foundation treatment → box girder formwork support installation → support preloading → adjustment of bottom formwork elevation → binding box girder bottom slab reinforcement and beam web reinforcement → installing box girder core formwork → installing top and bottom formwork → binding box girder top slab reinforcement and embedded guardrail reinforcement → pouring box girder bottom slab, web slab and top slab concrete → maintenance → prestress tensioning.
Second, the foundation treatment
(1) If the width of foundation treatment exceeds 0.5m on each side of the support leg, the compaction test shall be conducted after the subgrade is rolled. When the degree of compaction reaches 93%, stop rolling and proceed to the next process; If not, the rolling shall be continued until it reaches 93%.
(2) Spread a 30CM gravel layer on the ground after rolling, compact it with a roller until the degree of compaction reaches over 95%, and then spread 15cm 15 flaky concrete on it to ensure the bearing capacity of the ground reaches 250kPa.
(3) Find a slope of 1% from the center line to both sides on the gravel layer. (4) It is required that the top surface of the treated foundation should be above the ground 15cm.
Third, support erection.
(1) After the basement is accepted as required, scaffolding shall be erected manually according to the scaffolding design drawings. During construction, the chalk line should be played on the ground according to the spacing required by the support design, and the support should be erected in strict accordance with the line, and the connecting joints should be staggered on the first vertical pole to ensure that the joints are horizontal and vertical and locked.
(2) Support preloading
After the bracket is assembled and the bottom die is installed, the bracket is preloaded to eliminate the inelastic deformation of the bracket. The load can be stacked in layers in bagged soil (completely weathered granite) or sandy soil, and the load intensity of the load is consistent with that of the beam. All loading shall be carried out step by step according to 60%, 80%, 100% and 120%. All loading shall be completed in the shortest time, and each loading shall last at least 30 minutes. After the test data is stable, it can be continued, but it shall not be less than 10 minute. After all loading is completed, it should last for about 3 days, and the residual deformation should be measured after unloading.
The elevation control of the bottom die is: h' = h+r+δ.
Where: h': bottom die elevation; H: design beam bottom elevation; R: the design camber of each section in the beam span (the box girder is not the design camber); δ: elastic bending of each corresponding section after preloading;
Fourth, the template project
Box girder formwork consists of bottom formwork, side formwork, end formwork and internal formwork.
(1), installation and positioning of bottom die and side die.
The bottom formwork is made of wood, the side formwork is made of large area steel, the formwork panel is 6mm thick, and [10 stiffening channel steel is set. The bottom die is installed on the square wood, and the height of the bottom die can be adjusted through the adjustable pillar device. The bottom edge of the side formwork frame sits on the square timber and is connected with the bottom formwork through a flange. The support is connected into a whole through the bowl mouth and the cross bar, which increases the bending stiffness of the system and reduces the deformation of the formwork. The size of the upper opening of the template can be adjusted by adjustable struts. Install bearings according to design requirements (bearings can be installed in advance). The bottom die is provided with a reserved window at the mounting position of the support. Pay attention to the gap treatment between the reserved window and the bearing to prevent slurry leakage. In order to ensure the smooth exposed surface of beam concrete and reduce the number of template cleaning and polishing, the release agent must be painted.
(2) Install the internal mold and the end mold
The internal formwork can only be installed after the prestressed reinforcement of bottom plate and inclined web plate is installed and qualified. In order to facilitate the removal and installation of the formwork and reduce the weight of the formwork, a small-sized molding wood mold and an adjustable screw support frame are used in the internal simulation. A certain number of concrete conveying windows (the size is determined according to the diameter of the conveying pipeline) are set at the top of the internal mold to ensure the direct pouring of concrete on the bottom plate and the quality of the beam. The internal formwork is designed as an open wooden formwork with holes at the bottom, which is assembled in sections on the flat ground under the bridge, and then directly hoisted by a 25T truck crane and locked into a whole. When installing the internal mold, only the lower chamfer part and the surrounding frame are connected with the bottom mold frame, and the distance between the bottom and the bottom plate reinforcement is small. In order to ensure the displacement and deformation of the internal model due to self-weight and other loads during construction, some connecting ribs are added to the steel skeleton of the bottom plate as support frames to fix the internal model and prevent the internal model from moving and deforming during construction. According to the design requirements, a special fine stone concrete pad with the same strength is placed between the internal model and the steel bar to ensure that the protective layer of the steel bar meets the design requirements.
Five, steel binding, prestressed channel layout and wear beam
(1) steel binding
All steel bars are processed in the steel bar processing plant and transported to the site for binding after passing the inspection by the supervision engineer. The steel bars are bound or welded on the support, and the formwork installation is carried out in two steps: first, the bottom plate and web plate steel bars are bound, and then the top plate steel bars are bound after the internal formwork installation is completed. During steel bar construction, the interior of formwork should be kept clean and the surface of formwork should be protected to ensure the appearance of beam concrete. When the beam rebar collides with the prestressed rebar, the beam rebar can move or bend properly. The minimum net protective layer of beam reinforcement is 30mm and the maximum net protective layer is 35mm, and the tail of binding wire should not extend into the protective layer. Add corresponding ring steel bars at the reserved holes of all beams; The reinforcement at the bridge deck drainage hole can be moved appropriately, and spiral reinforcement and oblique cross reinforcement are added for reinforcement.
(2) corrugated pipe installation
1× 7-15.2-1860-GB/t5224-2003 prestressed steel strand is used as the prestressed reinforcement, and the longitudinal pipeline is formed by metal corrugated pipe with an inner diameter of 90 mm When installing the corrugated pipe, the joint should be sealed to prevent the pipeline from being blocked when pouring concrete, which will affect the threading of the steel strand. When binding the steel skeleton, weld the corrugated pipe positioning mesh according to the design position. After the steel skeleton is in place, put on the corrugated pipe after passing the inspection, and bind it firmly to ensure that the corrugated pipe will not collapse or float when pouring concrete. After the corrugated pipe is positioned, the allowable deviation of the prestressed pipe position is not more than 4mm, and the quality of the corrugated pipe should be guaranteed when purchasing. When pouring concrete, it is forbidden to contact the corrugated pipe with the vibrating rod to avoid slurry leakage from the pipeline.
The joints of corrugated pipes should be strictly sealed. The extension of corrugated pipe adopts the same type corrugated pipe with larger joint pipe size, and the joint length is 300 mm Both ends of the pipe are sealed with sealant tape or plastic heat shrinkable pipe to prevent slurry leakage at the joint. When corrugated pipe is installed, the height of the corresponding point is directly measured according to the curve coordinates of the beam bottom template and prestressed reinforcement, and marked on the stirrup to determine the curve position of corrugated pipe. Corrugated pipes are fixed with steel bar positioning nets, as shown in the figure below, with a spacing of 500mm. The steel bar positioning net should be welded on the stirrups, and the stirrups should be padded with pads. After the corrugated pipe is installed in place, tie a steel bar at the top of the corrugated pipe to prevent the corrugated pipe from floating and causing serious quality accidents when pouring concrete. When installing corrugated pipe, try to avoid repeated bending to prevent the pipe wall from cracking, and at the same time, prevent welding sparks from burning the pipe wall. After the installation of corrugated pipe, check whether the position and curve shape of corrugated pipe meet the design requirements, whether the corrugated pipe is firmly fixed, whether the joint is in good condition and whether the pipe wall is damaged. If it is damaged, repair it in time.
(3) Steel strand threading
The prestressed reinforcement of this bridge adopts the construction technology of pouring concrete first, then crossing the beam and then tensioning. Before concrete pouring, put the coarse hemp rope into the prestressed channel. When pouring, assign special personnel to drag back and forth at both ends to prevent the occasionally leaked cement slurry from blocking the channel and affecting the tensioning. The blanking length of the steel beam is reserved for the tensioning end of 80cm, and the prestressed steel strand is installed manually and mechanically. During curing, when crossing the beam, align the front end of the beam, tie it tightly and wrap it with adhesive tape, and pass it into the special shuttle. The front end of the shuttle passes through φ5 high-strength steel wire, which is pulled by a slow winch and manually pushed by the back end. Pay attention to the bellows joint when crossing the beam to prevent the joint from being damaged by pulling too fast.
Six, concrete engineering
1, pump truck construction sequence
The concrete pump is arranged on one side of the bridge where the concrete tanker is easy to enter and exit. The construction process of concrete pump is as follows: Start? Hydraulic oil heating? Test pump? Pump mortar? Wet hoppers and pipes? Pump concrete? Remove the conveying pipe cleaning line.
2, pumping concrete construction technology
Box girder concrete shall be poured at one time, and the concrete shall be poured on site by layered method. In the same pouring process, the pier top is poured from the middle of the span, and finally the beam segments and diaphragm beams within the range of about 3 meters on both sides of the pier top or about 3 meters on the longitudinal construction joints are poured to prevent vertical cracks from appearing on the pier top and construction joints during pouring. The special person shall be responsible for the distribution pipe of the delivery pump, control the distribution position and stabilize the distribution pipe. When pouring in sections, the grouting method is adopted, and the sections are inclined and layered horizontally, and a layer of concrete is poured before the initial setting of the next layer of concrete. The moving distance of the vibrating rod shall not be greater than the vibrating radius 1.5 times, and the vibrating rod shall be inserted quickly and pulled slowly. The vibrating time shall be subject to the concrete stopping sinking, no bubbles appearing, and the surface leveling and bleeding. Pay special attention to the vibration of the bottom plate, don't miss the vibration, and don't vibrate. Be careful not to damage the bellows during vibration.
Concrete should be poured continuously every time, and it is forbidden to stop pouring halfway to prevent construction joints. When pouring, pay attention to the position of various embedded parts, and the vibrating rod shall not directly contact the embedded parts. Pay special attention to the vibration outside the anchor pad, and use the No.30 rod for vibration by designated personnel, and someone will stand by to prevent vibration. When pouring roof concrete, the top surface of the box girder should be found, and the elevation control of the top surface should be accurate. Before pouring concrete, sufficient elevation control network should be set up, and generally a control point should be set every 3 ~ 5 meters to facilitate the leveling of the top surface. Every elevation point should be rechecked repeatedly and accurately to prevent the reinforced protective layer from being too large or too small, and the elevation error of the top surface should be controlled within the allowable range.
Seven, concrete curing and ripping
After the completion of concrete firing, after 1 hour (secondary flattening, screeding and rubbing), cover it with geotextile, cover it with impermeable membrane, and start maintenance. Moreover, a canopy (sunshade) is installed on the formwork to prevent concrete from cracking due to sun exposure and achieve the effect of thermal insulation. Concrete curing adopts natural curing or heating curing according to the external environment temperature and the time required for stretching.
In summer, the moon is collected for natural health. Natural conservation means water spraying and covering, and the covering should be double-layered. One layer is water-retaining geotextile, and the other layer is impervious membrane to prevent water evaporation. Natural curing should keep the beam wet all the time. The natural curing time should depend on whether the development of concrete strength can meet the requirements of formwork removal.
When the temperature is lower than 5℃ in winter, the concrete shall be covered and cured by heating. After the initial setting of the beam concrete, the curing agent is sprayed on the upper surface of the beam body, and the electric blankets are evenly distributed, and the distance between the electric blankets is less than 50cm. Blanket covers the whole beam frame with felt, including the beam end. Steam is used for curing in the beam cavity, eight oil drums are evenly distributed in the cavity, and electric water is used to generate steam. During the heating and curing of the beam, assign special personnel to measure and control the temperature to ensure that the temperature rise does not exceed 15℃/h and the temperature drop does not exceed 100℃/h ... In order to prevent the temperature from rising too fast, the electric blanket is electrified at regular intervals.
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