Bridge maintenance and reinforcement scheme?

Bridge is the throat of highway traffic, and its use function directly affects the smooth flow of the whole line. Bridges built in towns and highways in the early days bear very large traffic loads and traffic flows. In addition, various historical reasons, such as lack of funds when building bridges, low design load and flood discharge standards, and insufficient technical force. In order to ensure the safe operation, it is necessary to maintain and reinforce the bridge.

First, the content of bridge maintenance and reinforcement

With the increasing development of China's national economy and the rapid growth of traffic volume, the total length of dangerous bridges has gradually increased. If it is demolished and rebuilt, it will not only cost a lot of money but also take a long time. If the existing old bridge is reinforced in a planned and step-by-step manner, after the bridge is reinforced. It can prolong the service life of the bridge, make the bridge meet the traffic demand with a small amount of capital investment, and also ease the concentration of bridge investment, bringing great economic and social benefits to the country.

For bridges and culverts with serious diseases that can not meet the transportation requirements, it is necessary to thoroughly rectify, reinforce, improve and update the equipment, restore the overall use efficiency and prolong the service life of the original bridge building, and improve the load grade and passing capacity of the original bridge building. The main contents of bridge maintenance and reinforcement include: maintenance and reinforcement of upper components of service bridge, maintenance and reinforcement of lower components of service bridge, and widening of bridge carriageway or sidewalk. Improve the height of bridge superstructure and replace the structure of bridge pavement or approach pavement. Partial or total replacement of damaged or damaged bridge structures. The maintenance and reinforcement of bridges must make full use of the original parts. Don't rebuild what can be reinforced, and don't rebuild all what can be partially rebuilt. The maintenance and reinforcement of existing bridges usually take the following steps: check the present situation and damage of bridges; Investigate the historical and technical data of the bridge and the existing traffic conditions; Put forward maintenance, reinforcement or renovation plans, and make analysis and comparison at any time; Determine the scheme and put it into practice, that is, carry out maintenance, reinforcement or transformation.

Second, the method of bridge maintenance and reinforcement

Simply put, reinforcement is to improve the bearing capacity and performance of components and even the whole structure through certain measures to meet the new requirements. Four principles should be paid attention to in bridge maintenance and reinforcement: Bridge reinforcement is a measure to improve the bearing capacity or passing capacity of partial or whole bridge by expanding or repairing bridge components. Therefore, the maintenance and reinforcement of bridges should be based on the principle of not changing the original architectural form, and its structure can only be changed under complicated circumstances. There are many different methods for bridge maintenance and reinforcement. According to the actual situation of existing bridges, the weakening degree of bearing capacity and future tasks, appropriate maintenance and reinforcement methods are adopted. There are four methods for bridge reinforcement: increasing or increasing the section of the original structural members to improve the strength and stiffness of the original structure; Replacing the structure with new structure with insufficient stress: changing the stress system of the original structure to reduce the stress of the original structure; External stress is applied to the original structure to change the stress mode of the original structure and improve the stiffness and strength of the bridge. Old bridge reinforcement methods can be divided into the following categories:

1, structural reinforcement

The reinforcement principle of external prestress method is to set prestressed materials in the tensile area of the lower edge of the beam. By stretching, eccentric prestress is applied to the beam. Under this eccentric pressure, the beam arches upward, which offsets part of the dead weight stress, reduces the structural deformation and crack width, improves the structural stress and greatly improves the bearing capacity of the structure. At present, there are two reinforcement methods: downward-driven prestressed tie rod reinforcement method and external prestressed steel wire bundle reinforcement method. In the case of reasonable arrangement of construction procedures, this method can minimize the impact on traffic on the bridge. It can even organize construction under the condition of limited open traffic, so there are many domestic engineering examples in recent years. For example, the National Highway 30 1 Panjin Interchange Main Line Bridge and Panjin Interchange WH Ramp Bridge are reinforced. However, after reinforcement, the anti-corrosion problem of external prestressed tendons increased the later maintenance cost to some extent.

Generally, it is not the preferred reinforcement method for highway departments. Bonding steel plate or carbon fiber bonding steel plate reinforcement method is to use adhesives and anchors to bond and anchor steel plates in Lamian Noodles or other weak parts of concrete structures, so that steel plates and reinforced concrete structures form a whole, thus improving the bearing capacity of the structure. This method has the advantages of basically not changing the original structural size, simple construction, reliable technology, good short-term reinforcement effect and mature technology. In recent years, it has been widely used by highway departments in the reinforcement and maintenance of reinforced concrete bridges, and it is the most widely used reinforcement method in recent years. Carbon fiber reinforcement technology is a new technology introduced from abroad in recent years. Because of its advantages of high strength, corrosion resistance and simple construction, it has been widely used in practical engineering.

However, due to some defects of carbon fiber itself. Such as brittleness and poor fire resistance, the application of this material is limited. Generally, the reinforcement method of increasing section adopts increasing the size at the bottom or side of the beam and increasing the main reinforcement to improve the effective height of the main beam section, thus improving the bearing capacity of the bridge. However, because all the operations of the enlarged section method need to be carried out at the bottom of the beam, the construction is difficult and the construction quality is difficult to control. Therefore, although the cost is not too large in some cases, the above factors restrict the wide application of this technology, which is generally used for the reinforcement and maintenance of T-section beams. The reinforcement method of changing the stress system of the structure is to improve the overall bearing capacity of the structure by changing the stress system of the bridge structure, which is a reinforcement method of changing passive into active. This technology has the advantages of improving the bearing capacity of the structure, increasing the stiffness of the structure and reducing the deflection. However, this reinforcement method usually involves the reprocessing of bridge deck pavement, which increases the reconstruction cost, and the reinforcement effect is greatly affected by the construction quality in the negative bending moment area, so it is rarely used alone at present. In addition, the structural reinforcement methods include adding main beams and shotcreting.

2. Non-structural reinforcement

Steel fiber reinforced concrete can be used to repair severely damaged bridge deck pavement. Strong crack resistance, impact resistance and wear resistance can prolong the service life of the bridge deck and improve the structural mechanical properties of the beam without increasing the dead load of the bridge. Renewal and transformation of expansion joints In bridge maintenance, there are the following types of expansion joints that have been successfully used. The application effect of "three defenses" expansion joints in large bridges is good; Wool rib expansion joints are widely used in large and medium-sized bridges, and the effect is obvious; The seamless expansion joints of TST and FG series bridges are also widely used in small and medium-sized bridges.

3. Reinforcement of U-shaped Gao Qiao Platform

This reinforcement method is to cover 40 cm reinforced concrete on the front wall and two side walls of the U-shaped bridge, add horizontal prestressed anchor cables on the two side walls, and add ground anchors on the front wall. This scheme is suitable for the disease restoration of Gaoqiao Station, where traffic cannot be interrupted and temporary bridges cannot be erected. Anchors and reinforced concrete hoops are used to grout and solidify the abutment cavity and bearing layer of abutment foundation, and then anchors and channel steel hoops are used. Finally, 25 cm reinforced concrete is sleeved on the front wall and two side walls of the U-shaped abutment, and the old and new walls are connected into a whole with anchor rods. This scheme is suitable for the situation that the bearing capacity of foundation is insufficient and the construction treatment is not in place, which leads to the settlement of abutment wall.

4, pier reinforcement

The main purpose of strengthening the bridge substructure is to improve the overall bearing capacity of the pier. If the pier has structural damage, it can be strengthened by wrapping concrete, sticking steel plates or carbon fibers. However, for structures with large lateral stiffness such as solid piers, the state change is mainly caused by the foundation. At this time, we can focus on backfilling hard soil or grouting the foundation to improve their restraining ability to the pier and improve the overall bearing capacity of the pier. Pile lifting is a common and effective reinforcement method, that is, adding a pile on both sides of the old pile, and expanding the joint force of the cap by planting steel bars. Another method of pile foundation reinforcement is reinforced concrete hoop. Due to the lower pile foundation construction and other reasons, the pile foundation shrinks. The reinforcement method is to remove floating objects from the pile body, and after planting reinforcement, the outer hoop slightly expands the concrete. At present, in many bridge reinforcement and reconstruction, several different methods are adopted for the same bridge according to different parts, different components and different reconstruction reasons. For example, the reinforcement of the Jinsha River Bridge in Mamingxi, Yibin, adopts methods such as adding members, sticking steel plates, carbon fiber reinforcement and deck reinforcement; The Nimu Bridge in Tibet is strengthened by sticking steel plates, carbon fiber reinforcement and deck reinforcement.

Third, the conclusion

In the process of repairing and strengthening the old bridge, there is no need to completely interrupt the traffic except for a small number of heavy vehicles running for a short time. Its social and economic benefits are particularly obvious. In a sense, whether it is the formulation and design calculation of technical transformation scheme or the concrete implementation of technical transformation, relevant workers must keep practicing and learning.

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