Zhao Xiaoqing
Shanxi Road and Bridge Sixth Engineering Co., Ltd
Abstract: Based on the main characteristics of cast-in-situ box girder disc buckle bracket construction technology, taking a highway bridge project as an example, the construction points of cast-in-situ box girder disc buckle bracket are analyzed from the aspects of pre-construction preparation, foundation treatment, measurement and lofting, bracket construction, bracket preloading, template adjustment, bracket calculation, etc., and the quality control countermeasures of disc buckle bracket construction are proposed. The results show that the construction technology of disc buckle bracket has obvious advantages in terms of safety and economy, and is worthy of popularization and application.
Keywords: cast-in-situ box girder; Disc buckle type; Bracket; construction technology;
About author:ZHAO Xiaoqing (1988—), female, from Jinzhong, Shanxi, engineer, engaged in road and bridge construction.
0 Introduction
Most highway bridge construction units in mainland China often use traditional support construction technologies such as bowl buckle type in the construction process of cast-in-place box girder. In recent years, with the continuous improvement of the level of building construction technology, a new cast-in-place box girder bracket construction technology has emerged, namely disc buckle bracket construction technology. Compared with the traditional bracket construction technology, the disc buckle bracket construction technology has the advantages of high bearing capacity, high safety and strong stability, and can improve the construction efficiency and reduce the construction cost. This article will discuss the construction technology of cast-in-situ box girder disc buckle bracket for your reference.
1. Advantages of cast-in-situ box girder disc buckle bracket construction technology
1.1 Safety
Through in-depth analysis of the disc buckle bracket structure, it is not difficult to find that it is mainly in the form of lattice columns, which has relatively high stability, and the establishment process is not complicated, and a reliable construction scheme of the disc buckle bracket structure can be designed through modeling. The I-beam in the disc buckle bracket is made of aluminum alloy material, which can improve the strength of the disc buckle bracket structure and ensure that the elastic modulus, moment of inertia and cross-sectional size of the disc buckle bracket structure meet the construction requirements.
1.2 Economy
The disc buckle bracket structure is mainly made of aluminum alloy material, which can greatly reduce the construction cost. The scaffold system mainly requires input costs in construction management, materials and transportation, demolition, construction, etc., so it is more economical than traditional bracket structures such as bowl buckles.
2 Case Study
The bridge deck width of a highway bridge project is 25m, and the total length of the bridge is 100m, and the substructure of the highway bridge adopts gravity type abutment to expand the foundation and the pier stud to expand the foundation, wherein the base bearing capacity of the abutment enlarged foundation is greater than or equal to 300kPa, and the base bearing capacity of the pier stud enlarged foundation is greater than or equal to 350kPa. The superstructure adopts a cast-in-place continuous box girder structure. The bridge spans the Ring Expressway. According to the geological exploration report, the annual average temperature of the construction area where the project is located is about 18 °C, and the annual precipitation is between 1400~1600mm, which belongs to the subtropical monsoon humid climate. The topography and landform of the highway bridge engineering construction site are mainly river terraces, denudation mounds, hills, etc., the ground elevation of the construction site area is between 50~100m, and the geological stratigraphy is: metamorphic quartz sandstone, argillaceous slate, silty clay, pebbles, fine sand, planting maps, artificial fill soil, etc. After comprehensive consideration, the project finally decided to choose the cast-in-place box girder disc buckle bracket construction technology.
3 Construction points
The highway bridge project needs to cross the ring highway, adopts the disc buckle type support construction technology, needs to occupy a certain area of road surface, so in the cast-in-place box girder disc buckle support construction process, the construction unit needs to open the roadway door opening and build a protective shed, set up a water barrier at the position of 25m away from the door hole, carry out safety protection to the support pier, so as to ensure the driving safety of highway traffic. The construction process of cast-in-situ box girder disc buckle bracket is shown in Figure 1.
Fig.1 Cast-in-situ box girder disc buckle bracket construction process flow chart Download the original drawing
3.1 Pre-construction preparation
Before the formal construction, the construction personnel need to make preliminary preparations, and strictly inspect whether all the components entering the construction site have qualified certificates and whether the indicators meet the construction technical standards. After ensuring that it is qualified, all the components should be stacked according to the specifications and types of the components, and there shall be no stagnant water in the stacking site. The appearance of the bracket structure accessories should meet the following requirements.
(1) There shall be no grooves, cracks, rust and other defects on the surface of the fittings, and it should be kept smooth. Before proceeding with the construction, it is necessary to completely remove all the sticky sand.
(2) The fittings should be kept straight, and there should be no bevels and burrs at both ends of the fittings, and the planes at both ends should be kept straight.
(3) In order to keep the surface of the frame rods and other accessories smooth, the surface of the accessories needs to be hot-dip galvanized. In the connection part of the accessories, it is strictly forbidden to have welding nodules, burrs, caking and other phenomena. The surface of the tow seat and the adjustment base is cold-galvanized, and the surface layer needs to be kept firm and uniform after the cold-galvanizing treatment is completed.
(4) All welds should be full, and the effective height of the welds should meet the construction requirements. After the welding is finished, the construction personnel need to clean up the remaining solder in time.
3.2 Ground treatment
After the construction of highway bridge abutment and pier stud is completed, in order to ensure the uniformity of the support force, the construction personnel need to level the construction site in time. After the cushion is poured, the elevation of the construction site should be consistent with the height of the disc buckle support. The top surface is filled with filler, rolled and then poured 15 cm thick C25 concrete on top of it.
According to the elevation of the bottom of the bridge beam and the original ground, the surveying technicians stake out the top elevation of the concrete foundation and the top elevation of the disc buckle bracket respectively, calculate the thickness of the gravel cushion, and then replace the poorly treated foundation. After the replacement treatment operation, the construction personnel need to test the bearing capacity of the foundation after the replacement treatment to check whether it meets the construction requirements.
3.3 Measurement lofting
The total station is used to measure the projection line of the pouring box girder on the foundation, and the white ash is used to mark it. According to the projection line, the center line of the cast-in-place box girder is accurately determined, and the white ash is used to mark it. Taking the center line of the cast-in-place box girder as the reference, the disc buckle brackets are symmetrically built on both sides of it.
3.4 Bracket construction
In the process of erecting the disc buckle support, the method of segmented pouring and segmented tensioning is mainly used to pour the superstructure of the cast-in-place box girder. In the cast-in-situ box girder disc buckle support system, the crossbar step distance is 1.2m, the longitudinal spacing and transverse spacing of the upright rod are 0.9m, and 10# channel steel should be installed in the top support groove of the scaffold.
In order to improve the stability of the disc buckle support, the longitudinal spacing of the upright rod at the position of the middle transverse diaphragm is set to 0.6m, and the transverse spacing of the upright rod at the rib of the box girder is set to 0.8m, and at the same time, the scissor brace of the transverse spacing of 5m is respectively arranged on the outside of the center line of the discing buckle bracket and the longitudinal bridge. At the bottom and top of the pole, an adjustable jacking bracket is installed respectively, so that the height of the disc buckle bracket can be adjusted, and the adjustment height does not exceed 0.3m.
3.5 Bracket preload
After the construction of the disc buckle bracket is completed, the bracket should be preloaded. In order to avoid the linear deformation of the cast-in-place box girder caused by foundation settlement and support deformation, the stability of the support should be improved.
The construction steps of bracket preloading are as follows: (1) laying measuring points, using red paint to mark the positions of all measuring points; (2) ballasting, measuring the elevation of each measuring point before preloading the processing support, loading each measuring point, and then measuring the elevation of these measuring points again, if the difference between the two elevations before and after is less than 2mm, indicating that the disc buckle support is stable; (3) Unload all sandbags and re-measure the elevation of each measurement point.
3.6 Template Adjustments
(1) In the process of preloading the disc buckle support, the construction personnel need to carefully detect the settlement of the formwork.
(2) After the unloading of all sandbags, the construction personnel need to reasonably adjust the elevation and flatness of the formwork until it meets the design requirements.
(3) If the elastic deformation of the pre-compressed disc buckle bracket does not meet the design requirements, the construction unit needs to find out the reason in time, and then re-pre-press the disc buckle bracket.
3.7 Bracket design
After the end of each construction step, the support is checked, and the specific content comprises the anti-falling shed check, the door opening bracket check, the load calculation, etc. Taking the stability of the composite bracket as an example, the bearing load of the bracket is 35.1kN, the weight of the channel steel is 0.13kN, and the slenderness ratio of the upright rod is 78. Through calculation, it can be seen that the ultimate load of the composite bracket is 135.48MPa, the actual load is 96.3MPa, and the actual load of the composite bracket is less than its ultimate load, so it is judged that the stability of the composite bracket meets the design requirements.
4. Control measures for the construction quality of disc buckle brackets
4.1 Do a good job of pre-construction preparations
(1) Before building the disc buckle support system, it is necessary to conduct in-depth research and analysis of the geological exploration report, be familiar with and master the soil conditions of the construction site, and then formulate a reasonable and feasible construction organization plan.
(2) In order to ensure the construction quality of the disc buckle bracket, the construction personnel need to receive professional skills training and safety education and training, and can only work after passing the assessment.
(3) In order to ensure the smooth development of the construction of the disc buckle bracket, it is necessary to do a good job in the construction technology disclosure.
4.2 Strictly control the quality of scaffolding
(1) According to the actual size of the step distance, the horizontal rod is reasonably arranged between the vertical rods to ensure that the design stiffness of the vertical and transverse directions meets the design requirements, so as to improve the stability of the template and the support.
(2) For fasteners with matching specifications and outer diameter of the steel pipe, the bolt tightening torque should be controlled between 40~65N·m; The end of the rod should extend at least 0.1 m from the edge, the butt fastener should be opened inward or upward, and the distance between the center point of the rotating fastener and the right-angle fastener should not exceed 20 cm at the key node.
(3) Butt fasteners are adopted, and the step butt pole is staggered, and the distance between the main node and the center point of the joint shall not exceed 1/3 of the step distance; Cross fasteners are used to connect horizontal fasteners, and the lap length shall not be less than 100cm.
4.3 Improve the anti-overturning ability of the disc buckle bracket
The environment of the highway bridge construction site is relatively poor, the whole construction site is relatively empty, the ground wind is larger, and the cast-in-place box girder is higher. In order to improve the stability of the disc buckle bracket, effective protective measures should be taken to improve the anti-overturning ability of the disc buckle bracket system.
In this case project, in order to improve the anti-overturning ability of the disc buckle support, the longitudinal reinforcement rod and the transverse reinforcement rod are used at the position of the pier column of the highway bridge to strengthen the support; In order to increase the stress capacity of the members, three fasteners were selected to connect the members. When the cast-in-place box girder template is installed and the steel bar has not been tied, the anti-overturning ability of the disc buckle bracket is poor, and it is necessary to observe the weather changes in real time and make a good weather prediction. In windy weather, the wire wind-holding equipment should be laid in time in each joint support, and a temporary ground anchor should be set up on the ground by inserting the section steel, and then the temporary ground anchor should be used to connect the wire wind-holding equipment. During the pouring of concrete, it is also necessary to pay close attention to the weather conditions and choose a time when the wind is less to pour the concrete.
4.4 Remove the formwork correctly
In the process of formwork dismantling, the following three points need to be noted: (1) the construction personnel should pass the removed rods to the ground through a special person, and it is strictly forbidden to throw the removed rods to the ground at will, and at the same time, the rods should be classified and recycled and stacked; (2) It is strictly forbidden to use a pry bar and a sledgehammer to dismantle the formwork savagely, if some formwork is difficult to dismantle, the construction personnel can slightly pry the formwork from the bottom, but the edges and corners and surfaces of the concrete shall not be damaged; (3) Dismantle the formwork racks in the order from top to bottom, and it is strictly forbidden to dismantle the upper and lower layers of shelves simultaneously.
4.5 Strictly inspect the construction quality of the bracket
In order to ensure the reliability and stability of the cast-in-situ box girder disc buckle bracket system, it is necessary to conscientiously do a good job in the construction quality acceptance of the disc buckle bracket. In the process of accepting the disc buckle bracket system, the contents to be inspected include the verticality and horizontality of the vertical rod, the verticality and horizontality of the cross bar, the firmness of the fastener, the connection between the base of the vertical rod and the base surface, and the reliability of the inclined rod, longitudinal rod and crossbar bolt of the bracket.
5 Conclusion
Compared with the traditional bracket construction technology, the disc buckle bracket construction technology has more advantages, such as higher stability and safety of the bracket structure, simple construction technology, low construction cost, etc., so the disc buckle bracket construction technology is widely used in highway bridge engineering construction. In this paper, the construction technology of cast-in-situ box girder disc buckle bracket is studied, which can provide some reference for the popularization and application of disc buckle bracket construction technology.
bibliography
[1] Chen Zhen, Pang Jiefu. Construction technology analysis of urban cast-in-situ box girder disc buckle bracket[J].Western Transportation Science and Technology,2022(2):151-154.)
[2] Yoon Ki-yong. Analysis on the key points of construction technology of cast-in-situ box girder socket disc buckle bracket with variable cross-section[J].Transportation Manager World,2021(14):58-60.)
[3] Xie Jihong. Construction technology of cast-in-situ box girder disc buckle full hall support in bridge engineering construction[J].Sichuan Cement,2020(8):140-141.)
[4] Li Shuhong. Research on construction technology of cast-in-situ box girder disc buckle full hall bracket for bridge engineering[J].Transportation World,2020(21):92-93.)
[5] Li Caifang, Zhang Xiwu, Wang Longwang, et al. Construction technology of cast-in-situ box girder disc buckle full hall bracket for bridge engineering[J].Building Technology Development,2020,47(9):36-37.)
[6] Liang Yantao. Construction technology of cast-in-situ box girder disc buckle full hall support for bridge engineering[J].Engineering Construction and Design,2020(8):169-170.)
[7] Ma Chunlei. Construction technology of cast-in-situ box girder disc buckle full hall bracket for bridge engineering[J].Sichuan Building Materials,2020,46(4):112-113.)
[8] Wang Yijun. Construction Technology,2019,48(S1):1208-1210.
[9] Zhang Suwen. Research on key construction technology of cast-in-situ box girder support in the five irrigation section of Chongqing Metro[D].Huainan:Anhui University of Science and Technology,2019.
[10] He Jun. Shanxi Architecture,2016,42(11):174-175.)
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