1 project overview
A bridge project is a rigid reinforced concrete bridge, which has been opened for a long time. Horizontally, the main components of this bridge are six rigid frames, which are connected by the bridge deck and diaphragm and hinged at the arch foot and mid-span position to form a three-hinged inclined-leg rigid frame bridge. When one end of the side span beam is placed on the abutment, the other end is placed on the bracket at the end of the middle span main beam. 2 1.66m is the main bridge span, 26m is the whole bridge length, and 7m is the clear width of the bridge deck. The topographic and hydrogeological features of the bridge are as follows:
Topographic features of 1. 1
The project is relatively flat, with a ground elevation of 6.3-7.5m Hard plastic clay and silty clay deposited in Quaternary inland lakes are exposed within the investigation depth of the bridge site, with a certain amount of muddy soft soil and silty soil at the top, and the bedrock is buried deeply, and no adverse geology appears within the investigation scope.
1.2 Hydrogeological characteristics
5.0-6.0m is the measured buried depth of groundwater level in the survey area, and the pore water is groundwater type, which has great influence on the seasonal water level. Through analysis, it is concluded that groundwater is not corrosive to concrete structures, but weakly corrosive to steel bars, steel structures and groundwater. Due to the influence of many factors, there are some diseases in bridge structure, such as stirrup corrosion and concrete protective layer peeling due to rust expansion. In addition, due to the increasing traffic volume, in order to meet the needs of vehicle operation, bridge reinforcement construction must be carried out.
2 disease investigation and analysis
Before the reinforcement construction, the actual situation of each part of the original bridge should be fully understood in detail, as shown in table 1. Generally speaking, the bridge structure is basically complete, and the stress is clear, so reinforcement measures can be implemented. However, due to the long running time, all components are damaged to varying degrees, the most serious of which are cracks and rust expansion. Therefore, reinforcement construction must be done well to ensure the safety of vehicle traffic.
3 reinforcement scheme analysis
According to the requirements of construction design, combined with the actual situation of this project site, the following construction reinforcement scheme is put forward.
3. 1 substructure reinforcement scheme
The original abutment structure is a combination of "short pile, bearing platform and gravity abutment". The investigation results show that the abutment has no problems such as displacement and surface corrosion, and the geological conditions in the construction area are good and the abutment is thick. This reinforcement construction does not need to change the original abutment, but only needs to spray concrete on the surface crack position to ensure that the position has good flatness and compactness to meet the design requirements, and to avoid crack expansion and internal steel corrosion.
3.2 the superstructure reinforcement scheme
When strengthening, it is necessary to fix the mid-span hinge to ensure that a single rigid frame is statically indeterminate, so as to increase the capacity of the main bridge to bear bending moment, and at the same time, it is necessary to set U-shaped steel plates outside the cross section of the main girder. It is required that the lower edge and mid-span of the beam are the key points of reinforcement. Because the structural system transformation will greatly increase the ability to resist the bending moment of the section. Inclined legs are basically equivalent to arch ribs, which mainly bear axial pressure and corresponding bending moment. The reinforcement method can be wrapped in steel, that is, sticking angle steel on the four corners of the beam section, then welding flat steel hoops to ensure the connection of the four angle steel, and plastering cement mortar on the outside, with a thickness of about 2.5cm, thus constraining the concrete and improving the compressive capacity of concrete materials. For the side-span beam, because it is not connected with the middle-span beam, it can form a simply supported beam with clear force, and there is a large principal tensile stress near the fulcrum. Therefore, carbon fiber reinforcement method can be selected for reinforcement. It is required to stick carbon fiber on the tension side in the middle span, such as the lower side and bottom surface of the beam, with the longitudinal bridge direction as the fiber direction. Because there is a large principal tensile stress near the fulcrum, carbon fiber should be pasted vertically on both sides of the beam rib.
4 bridge engineering reinforcement construction technology
4. 1 carbon fiber structure
4. 1. 1 Before the surface treatment construction, the concrete with poor surface quality of steel members should be cleaned to ensure that the concrete structure layer is exposed, and repair materials can be selected for the surface construction. If there are stress cracks in the construction, joint filling should be done well, and it can be closed if necessary. It is required to smooth the pasted concrete surface and remove impurities such as laitance attached to it until a new concrete structure surface is exposed. Select the leading angle treatment method to treat the corner paste position, and polish it into an arc with a radius greater than 20 mm 4. 1.2 The concrete surface to be cleaned shall be coated with primer, and then coated with primer. Requirements in strict accordance with the specific temperature of the construction site to determine the amount of resin added each time, strictly control the use time. Subsequently, the primer resin is evenly coated on the concrete surface by a roller. After the surface dryness meets the design requirements, the next stage of construction can be carried out. For the uneven position, it can be repaired by leveling material. 4. 1.3 When pasting the carbon fiber cloth, the carbon fiber cloth should be cut according to the design requirements, and the impregnating resin should be evenly coated at the pasting position. Manually press the carbon fiber cloth to the pasting position to ensure that they stick together. Then select a special roller to roll along the fiber direction for many times to extrude bubbles, so as to ensure that the carbon fiber cloth can be soaked by impregnating resin. It is forbidden to cause any damage to carbon fiber cloth during construction. After carbon fiber cloth is pasted and impregnated resin is evenly coated on the surface, the surface of the structure should be strengthened and protected. Sand, plain cement slurry, etc. are required. To the steel surface, and daub the cement mortar with a thickness of about10 mm. ..
4.2 wet bonded steel construction
4.2. 1 Treatment of concrete surface Before construction, the stains and oil stains on the surface of concrete members should be cleaned up, and the paint layer at the joint should be chiseled away. At the same time, grind the bonding surface until the concrete base is exposed. After the polishing operation, the scum on the surface should be cleaned in time, and the surface can be cleaned with acetone. If there are holes and honeycombs on the surface, they need to be repaired. 4.2.2 Surface treatment of steel plate After rust removal, the joint surface of steel plate should be polished to a metallic luster and the surface should be as rough as possible. The polished grain must be perpendicular to the stress direction of the steel plate, and then acetone is selected for cleaning. 4.2.3 Installation of steel plate According to the provisions of the construction specification, the steel plate shall be installed accurately, and the connection position and anchor bolts of the steel plate shall be installed at the same time. The clearance between the steel plate and the base surface shall be controlled between 1 ~ 2mm. 4.2.4 Joints near steel plates shall be sealed with glue pouring steel, and grouting holes shall be reserved, and glue pouring construction shall be carried out according to the established grouting sequence. In the maintenance stage, it is forbidden to disturb the steel plate, and finally do a good job in protecting the steel plate.
4.3 Steel bar detection
When strengthening concrete structures with carbon fiber cloth or resin bonding materials, it is necessary to do a good job in the inspection of each process. If the quality does not meet the construction requirements, practical measures should be taken to remedy it in time. Generally speaking, compared with the design area, the concrete bonding area of carbon fiber sheet should be controlled above the design area, and the error value should be controlled within 10 mm. In order to check whether the carbon fiber sheet is closely bonded with concrete, the surface of carbon fiber sheet can be checked by hand pressing method or knocked with a small hammer to ensure that the overall effective bonding area is controlled above 95%. If the hollow area of carbon fiber cloth is less than 10m2, acupuncture can be selected to repair it. If the empty drum area is above 10m2, the carbon fiber sheet at the empty drum position shall be removed in time, and a new carbon fiber sheet shall be overlapped, and the overlapping length shall be controlled above 10cm. Under special circumstances, samples such as carbon fiber sheets can be taken on site for inspection. In the construction of steel bar bonding, when dismantling temporary fixing equipment, a small hammer can be used to knock the bonded steel plate, and the bonding effect can be judged by sound. When less than 90% is the bonding area of anchorage zone and less than 70% is the bonding area of non-anchorage zone, it can be considered that the quality of bonded parts is unqualified and needs to be removed and re-bonded.
5 concluding remarks
To sum up, with the continuous expansion of bridge construction scale in China, the construction environment is becoming more and more complicated, so it is necessary to choose the corresponding construction technology in combination with the actual situation of the project to ensure the quality and stability of the project. The application of reinforcement technology can effectively improve the bearing capacity of the bridge and meet the needs of traffic operation. In order to overcome the shortcomings of design and construction and further popularize the carbon fiber reinforcement method, it is necessary to strengthen the research on design theory, construction theory and detection technology, which is of great significance to improve the quality of bridge engineering.
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