Beam bridge superstructure strengthening

There are several kinds of reinforcement and reconstruction techniques for the upper structure of girder Bridges: the expansion and increase of the original structural member section to improve the strength and stiffness of the original structure;To replace the structure of the original resistance with the new structure;The force system of the original structure is changed to reduce the force of the original structure.The prestressing force is applied to the original structure to improve the force performan

Advantages and disadvantages of strengthening method

Technical name		Technical content	Application scope	Advantages and disadvantages
Enlarging the main beam cross section method	Increase the main beam method	The concrete protection layer of the lower edge of the beam ribs is chiseled to expose the primary reinforcement, and the main reinforcement is added to the lower edge of the main bar after cutting and straightening the original hoop reinforcement, and then the protective concrete is reformed to increase the cross section of the reinforced bar.	It is applicable to the condition that the main reinforcement section is insufficient and the clearance under the bridge is limited, and the beam height is not allowed.	It does not reduce the clearance under the bridge, but it needs to be truncated and connected with the long stirrup. The damage to the structure is large, resulting in the increase of the unsafe factors in construction and the complicated construction technology.
	Thickening bridge panel method	After removing the original bridge deck pavement, the bridge deck is cleaned by chisel and shear slot or shear key is set at intervals, and a new layer of reinforced concrete pavement is reproduced.	Suitable for small span T beams or slab girder bridges that allow traffic interruption.	During construction, the traffic on the bridge is blocked, and the bridge which does not allow traffic interruption is not suitable. The bending moment generated by the weight of the structure will increase, and the bearing capacity of the structure will not increase significantly.
	Enlarging ribbed concrete section method	After cleaning the concrete chisel of the joint, the original main tendons are exposed at a certain distance, and the new and old main tendons are firmly connected with the stirrup. The new and old main tendons are exposed at every interval after the concrete chisel of the new and old steel hoof shaped concrete is washed, and the new and old main tendons are firmly connected by the stirrup, and the new Liang Leima is added to the mold to be put into the construction. Hoof shaped concrete	It is suitable for high clearance under the bridge, allowing for increasing the height of the main girder.	The clearance of the bridge will be reduced, and the bridge that requires clearance under the bridge can not be organized and implemented, and the appearance of the bridge will be greatly affected, so it is not suitable for urban bridges.
External bonding reinforcement	Pasting steel plate	After the surface treatment of the concrete and stickup steel plate, the steel plate is pasted on the concrete surface with epoxy resin slurry, and the steel plate is pressed into the concrete surface so as to improve the bending and shearing ability of the beam.		It is difficult to process and shape the steel plate. It needs a certain supporting equipment, and the maintenance work is great during the long term use, and the durability of the bonded material is also worth paying attention to.
	Pasting FRP	After the surface treatment of the pasted concrete and pasted steel plate, the multilayer fiberglass cloth is paving into the glass fiber reinforced glass (at the same time the high strength steel wire can be placed) with the epoxy resin slurry, and then the formed glass steel is pasted on the lower surface of the component.	It is especially suitable for temporary reinforcement of heavy vehicles or large equipment when crossing the bridge.	The elastic modulus of FRP is lower than that of concrete, and the deformation caused by load is larger, and the aging problem of FRP in harsh environment is more prominent.
	Pasting steel bar	After the surface treatment of the concrete and stickup steel plate, the steel bars are bonded to the surface of the concrete with epoxy resin paste and the bars are bonded on the concrete surface, and the steel bar is protected to improve the bending ability of the beam.
Adding auxiliary component method	Increase the main beam	In the new main beam position, the original bridge is cut open, the original cross beam is cut off, the original structure is set up with the template, the main beam of the reinforced concrete is cast, and the original cross beam is connected to ensure the new and old structure as a whole and the common force.	It is applicable to the condition that the main structure is basically intact, but the bearing capacity can not meet the requirements.	The traffic must be interrupted, and the process is complex and the amount of construction is large.
Adding auxiliary component method	Increase the cross beam	To drill the main beam on the new cross beam, set up the steel bar through the whole bridge width, and try to fix the steel bar, and the concrete chisel at the combination of the main beam and the hanging mould after cleaning should be poured.	It is suitable for bridge superstructure because of poor lateral connection.
Change the structure system method	Reinforcement of eight character bracing frame	A steel or reinforced concrete eight way bracing frame is set up in the simply supported bridge to provide two supports for the superstructure of the original bridge, so that the original span simply supported beam can be changed into a three span continuous beam.	It is applicable to the superstructure of bridges built on waterways.	The influence on the clearance of the bridge is very large, and is very unsuitable for strengthening the urban bridge. When the height of the building is large, the volume of the project is large.
Change the structure system method	Continuous system reinforcement	The beam end flange of the original multi span simply supported beam is connected to make the stressed system change from the original simple support to continuous, thereby improving the mechanical performance of the structure.	It is applicable to the situation that the bending capacity of the cross section of the original simply supported beam is obviously insufficient.	Although it is not restricted by clearance, it has an impact on traffic
Adding large side beam method		The new part is relatively independent of the original structure, has little influence on the traffic and is not restricted by the clearance under the bridge. But the new part and the original structure must be connected with the original structure so that it can work together.	It is suitable for bridges with good main structure, potential bearing capacity and wide bridge.	The new part is relatively independent of the original structure, has little influence on the traffic and is not restricted by the clearance under the bridge. But the new part and the original structure must be connected with the original structure so that it can work together.
Cross section conversion method		The lower flange of the multi beam reinforced concrete T beam bridge is closed, so that the bridge is transformed from the opening type to the closed box type structure, and the flexural and torsional rigidity of the section is improved.	Suitable for T beam or beam bridge	The reinforcement effect is good, but the operation space is limited when working under the bridge, especially the pouring of box girder bottom slab concrete is more difficult.