Analysis on the design points of road and bridge reinforcement and reconstruction?

First, the principle of highway bridge reinforcement

The reinforcement design is generally based on the original bridge. First, the structural type of the original bridge is not changed, and then the main load-bearing members of the original bridge are strengthened. The following points should be considered in the reinforcement design: (1) If the substructure has great potential, it should meet the requirements for large-load vehicles to pass through after reinforcement; If the lower part is a waterway, the reinforcement of its inclined legs or mid-span webs should keep the original clearance as much as possible, and the lower space should not be cut too much; It is necessary to repair the cracked component surface to ensure that the component surface is continuous and smooth. At the same time of maintenance and reinforcement, attention should be paid to the influence of the weight of the reinforcement material itself on the original bridge; After reinforcement, the overall beauty of the bridge should be maintained.

Second, the problems existing in the design of road and bridge reinforcement and reconstruction

Poor building conditions

Interference in the construction process: For example, for bridges that have been opened to traffic, because traffic cannot be interrupted, reinforcement measures can only be implemented under normal traffic conditions, so traffic often interferes with the reinforcement project and affects the construction progress. Limited structural form: the basic principle of general reinforcement is that the original structure must be used, so it can only be strengthened on the basis of the original structure of the bridge, so it has limitations. Combination of old and new structures: including the transition and change of old and new structural systems and the combination of old and new bridges.

(2) The project is difficult and risky.

Because as long as roads and bridges need to be reinforced, most of them are dangerous bridges, and some are already in jeopardy. For example, the deck pavement of some bridges has been damaged, which will cause the vehicle to bump or jump when driving. When it rains, water will form on the bridge deck and even seep downward, which will not only affect the road traffic safety, but also increase the damage of the upper load-bearing members of the bridge, and even cause the arch ring or main beam to crack. Therefore, it is necessary to strengthen the maintenance of the bridge deck, dredge the drainage holes in time and repair the damaged layer of the bridge deck in time. Moreover, old bridges often lack original construction records and design data, which leads to unclear internal structure. In addition, the existing stress situation is different, which increases the difficulty of determining the structural limit of the bridge and the risk of strengthening the old bridge.

Third, the road and bridge reinforcement construction technology

(A) external prestressing reinforcement

In the external reinforcement of prestress, steel strand, thick steel bar, high-strength steel wire and other materials are generally used as force tools to prestress the external superstructure of the bridge, and the internal force of the external load is offset by the part of the pre-stress reaction moment, thus improving the service performance of the bridge and improving its bearing capacity. There are generally two ways to strengthen prestress: prestressed external steel cable reinforcement and prestressed through tie rod reinforcement.

(1) Prestressed external steel cable reinforcement: Prestressed external steel cable is usually reinforced by prestressed steel strand or steel strand bundle, which is arranged in a certain line along the rib side of the bridge, and external prestress is realized by stretching. A certain number of positioning facilities are set at the bottom of the bridge to ensure the line shape of the cable and fix its position. Usually, the anchors of steel cables are fixed at both ends of the bridge. Prestressed steel cables are generally wrapped with protective tubes, or wrapped with concrete after tensioning anchorage is completely fixed to prevent corrosion.

(2) Prestressed brace reinforcement: The forms of prestressed brace are mixed, broken and straight, and the application scope of each brace is different. Hybrid tie bars are suitable for beams with insufficient shear bearing capacity of inclined section and extremely insufficient bending bearing capacity of normal section, and some trusses with lower chord bearing capacity less than end web members. Broken-line tie rods are suitable for beams and trusses with insufficient flexural capacity and shear capacity of inclined section, while straight tie rods are suitable for bridges with insufficient flexural capacity of normal section and trusses with insufficient tensile capacity of lower chord. Used for rigid frames, frames, continuous beams, etc. , should adopt the broken line tie rod corresponding to the structural bending moment diagram.

The specific construction technology is as follows:

(1) Before concrete pouring of the anchor box, the beam at the anchor block and the positioning block shall be roughened; When pouring, ensure no vibration leakage or full vibration; After pouring, spray water for curing in time, and ensure that there are no problems such as honeycomb pits and cavities behind the mold.

(2) The anchor node and steering node are all welded by steel plate (antirust treatment and mechanical derusting) and steel pipe; During installation, it shall be bonded with structural adhesive and fixed with anchor bolts.

(3) Before passing through the tensioning end, the prestressed tendons shall be fixed at the end; When tensioning, it is appropriate to adopt the tensioning technology of symmetrical left and right, graded loading and synchronous whole beam at both ends; In general, the tension control force should be 1209MPa. In each tensioning process, the elongation value should be measured and checked, and the deviation between the measured elongation value and the calculated value should be within 6%.

(2) local repair

Usually, when the bridge deck is damaged locally, it is treated by local repair, and the loose position of the concrete layer on the bridge deck is chiseled with a shovel until the reinforcement is exposed, so as to improve it. After cleaning the cross section with clear water, repair the bridge deck with the same grade cement material, and the traffic can be resumed after the maintenance period. When using this method, we should pay attention to the actual situation of local damage. If the crack depth is deep, the method of removing loose structure should be adopted until the reinforcement is exposed. If the depth is shallow, direct repair can be adopted.

Specific construction technology:

For all concrete cracks with a width not less than 0. 15mm, the grouting method is adopted to repair them. The materials used are epoxy resin with good quality and materials with reasonable viscosity. It is forbidden to add other solvents. Clean the residue on the concrete surface with a brush, and keep the cracks dry when grouting. In the pre-construction treatment stage, the quality and performance of the equipment and materials used should be comprehensively tested to ensure that their performance parameters meet the national building standards. If a large amount of grouting material is needed, the tensile shear degree of the sample should be tested, and the selected sample should be sampled immediately by the relevant technicians. Grouting materials used should be prepared in advance, not now. After the cracks are filled up, maintenance work shall be carried out according to relevant standards. After the cement slurry is solidified, the grouting port should be removed and the concrete surface should be trimmed to make it smooth and bright. It is also necessary to check the results of reinforcement treatment. Once it does not meet the relevant requirements, it is necessary to immediately remedy the grouting technology to ensure the quality of the project.

(3) concrete pouring again

This method is usually used when the bridge deck is damaged or the damaged area is large and the damage degree is serious. This phenomenon is caused by poor concrete quality or improper construction. When the disease cannot be completely improved by other methods, concrete must be used for re-pouring. In the process of construction and repair, firstly, the damaged or existing hazards of the bridge deck should be removed, secondly, an appropriate amount of steel mesh should be laid, and finally the concrete can be poured again. In the process of using this method, we must first master the design strength of the bridge deck, and use materials with the same label as steel bars and cement for construction, so that the strength and bearing capacity of the re-poured bridge deck are unified with the original design standard of the bridge deck.

(4) Reinforcement of bridge deck reinforcement layer

Usually, for old bridges that have been used for a relatively long time, there will be many cracks, peeling and other damage phenomena on their decks. In this case, not only the local treatment method can not be carried out, but also the original bridge deck can not be re-poured. Therefore, the bridge deck reinforcement method is the most effective. Adding concrete or reinforced concrete reinforcement layer on the original bridge deck can not only improve the phenomenon of large-scale cracks and peeling, but also effectively improve the strength and bearing capacity of the bridge deck. In the process of using this method, the traffic flow and the actual bearing capacity of the pavement should be considered to determine the reinforcement thickness and material.

Specific construction technology:

Through certain technical measures, laying a layer of reinforced concrete on the bridge deck can not only increase the thickness of the main bridge, but also improve the bearing capacity of the bridge deck after leveling and air drying. Before pouring reinforced concrete, attention must be paid to the removal of the original cement pavement on the bridge deck, and at the same time, traffic control should be increased to make it dry naturally without being affected by vehicles.

(5) Section reinforcement method

In the case of insufficient bearing capacity or limited strength of the main girder of the bridge, we should strengthen the concrete section of the main bridge and increase the reinforcement. In the process of increasing the cross section, it is realized by thickening the bridge deck or increasing the height and width of the main girder. The construction of segmental reinforcement method is relatively simple, and it is usually suitable for the case of small reinforcement span of municipal roads and bridges. In the process of bridge reconstruction, this method can effectively improve its strength and bearing capacity.

In the process of using this method, the bearing design standard of single pier should be considered, and the relevant data such as span and thickness of main girder should be understood. According to the actual design bearing capacity, the section thickness and width are effectively increased. When it is increased blindly, it will affect the self-weight of grouting and lead to insufficient bearing capacity strength of pier and abutment support.

(6) The method of pasting and strengthening tensile reinforcement materials.

Compared with the design, when the traffic volume exceeds, the bearing capacity of the bridge will be insufficient. By using adhesive or anchor bolts, steel plates or high-strength composite carbon fibers are urged to stick and anchor at the hands and weak parts of the bridge structure, so as to realize effective combination with the bridge body. That is to say, steel plates or high-strength composite carbon fiber materials are used instead of steel bars to improve the bearing capacity of the main girder. The implementation of this method will not destroy the original structure of the bridge, and has the advantages of relatively simple construction technology, short construction period and easy quality control. When using this reinforcement method, materials must be selected according to the specific bridge construction conditions. Only according to the construction conditions of the bridge, the construction materials suitable for the building can be selected to ensure the quality of the bridge.

The specific construction technology is as follows:

(1) Brush evenly the evenly stirred adhesive (primer main agent: curing agent = 4 ∶ 1) on the concrete surface with a roller brush, without brush leakage or foaming;

(2) Compounding putty with adhesive and appropriate mineral filler, and filling the concave part on the concrete surface;

(3) Sticking the carbon fiber cloth: evenly spread the adhesive on the sticking position with a roller brush, gently press the carbon fiber cloth cut according to the required size (the most suitable size is within 2m) on the position to be stuck, and then roll and flatten it several times along the fiber direction with a roller brush and a rubber scraper, so that the carbon fiber cloth is fully infiltrated to form a composite material; After pasting, let it stand for 30 minutes. If any fiber floats out or comes off, flatten it with a roller or rubber scraper to correct it.

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In a word, the reinforcement technology and durability of bridges are a systematic project. When designing the bridge structure, designers should combine the actual situation of our country and make rational use of advanced management experience and design methods. As far as bridge reinforcement technology is concerned, we should pay attention to the effective use and reasonable collocation of various technologies. It is very important to reduce labor intensity and ensure personal safety by standardizing components and structures. Therefore, in the structural design and construction of the bridge, every link must be carried out in strict accordance with the specifications and operation techniques to ensure the engineering quality and maximize the service life of the bridge. If additional maintenance is needed, the technical methods and requirements for road and bridge reinforcement should be strictly followed to extend the service life.

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