The analysis of the reinforcement of bridges' prestressed carbon fiber plate

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Introduction

According to the test reports, main problems of the south trunk road bridge are as follows:

Surface sealing method

1. Floor System
there are more lateral and diagonal cracks partially on the deck of bridges. The situation of the damages ,cracking and deformation of the railings of bridges is serious.
the cracking of the deck of bridges
the damages of the railings
the deformation of the railings

2.The concrete of the upper structure has deterioration and damages. among them, the leakage of the bottom of the second,third,forth,fifth and eleventh cross beams is obvious. The second and fifth cross beams have used the method of sticking steel plate to reinforce. Now the connection of the steel plate and hollow plate has no abnormality. The corrosion of the surface of the steel plate is obvious.
the water leakage of the bottom of the beam has caused the corrosion of the pasted steel plates.
the weathering and exposed tendons of the concrete
illegal buildings under the bridge

3.there are deterioration, damage and honeycomb of the concrete in the substructure.

Water leakage of the capping beam the honeycomb and damage of the concrete.

4, the result of the measurement of the deck linear
Deck linear is relatively smooth and has no abnormal point. The found Longitudinal is 0.80%.

the found line chart of the road and bridge

Classification

the checking of the structure before the reinforcement

According to the test report, the checking process of the bridges before the reinforcement and the main conclusions are as follows:

1, check the contents
(1) checking of the ultimate limit state of the carrying capacity
(2) checking of the ultimate limit state of the normal use
(3) conclusions of the checking
1) Shear strength of oblique sections of the bridge roadway and sidewalk panels are able to meet regulatory requirements, but its flexural strength of the normal sections can not meet the regulatory requirements;
2) In addition that the normal tensile stress of the concrete of sidewalk board does not meet the cracking requirements of the flexural members of Class A prestressed concrete tensile stress, other stress indicators of the sidewalk board and the roadway plate are to meet specifications for Class A prestressed concrete members in allowable stress requirements.

Repair methods

The design ideas of the reinforcement
1. Design Principles of the reinforcement
(1)scientific and rational design, economic－environmental, meeting the requirements of technology and the use safety.
(2)try not to increase the weight of the structure, and do not cause damage to the main load-bearing members;
(3) after the reinforcement, the bridge can meet the use requirements of the design load’s standard, and has certain safe stock;
(4) the construction is simple and fast. The process of reinforcement and construction minimize the impact on traffic;
(5) after the reinforcement, the durability of bridge is strong and easy to maintain.

The goal of the reinforcement’s design
Through scientific and real evaluation of the actual bearing capacity of the bridge, proposing the recommended scheme of the reinforcement and maintenance, maintaining and reinforcing in order to manage the bridge’s disease, embodying the principle of both safety and economical efficiency, and fixing, completing and designing at any time according to the development of the disease, repairing disease thoroughly,and making the reinforcement’s design satisfy the following points:
(1)restore the bridge structure and achieve -b load grade within the reinforcement,guarantee the strength, stiffness and durability of the bridge, ensure the effect of repairing and normal and safe operation.
(2)the technology of the plan of maintenance and reinforcement is reasonable, the cost is economical and the construction is convenient.

Conclusion

The treatment

The management of the exposed steel bar and the steel bar corrosion

Using the manual work to chisel off the loose and uncompacted concrete around the steel bar until exposing the fresh concrete aggregate

Cleaning the concrete surface with the high-pressure water, removing the rust of the steel bar with the steel wire brush.

After the drying of the concrete surface and steel bar, smearing the epoxy slurry on the steel bar.

Filling the chiseled area with the epoxy mortar, and then tamping and floating.

If the filling area is too large, mixing certain proportion of the clean gravel in the epoxy mortar.

2, Reinforcement scheme of the hollow slab
According to the test report, now the anti-bending bearing capacity of normal section of the hollow slab of the southern trunk road bridge can’t meet the requirements. at the same time normal tensile stress of the pavement slab concrete can’t meet the usage requirements of the prestressing force concrete A-class components, requiring the reinforcement. combined with the current situation of the bridge’s diseases, adopting the method of adding the high strength tensile material at the bottom of the plate to improve the ultimate bearing capacity of structure; At the same time, by imposing the prestressing force to the new added high strength material of the beam bottom, to improve the compressive stress reserves of concrete of the beam bottom.

Adding high strength material at the bottom of the beam, adopting the reinforcement technology of the prestressing force carbon fiber board, placing two carbon fiber board of 50mm×1.4mm at the bottom of the beam, tension the carbon fiber board firstly, and then pasting it at the bottom of beam, the design strength of carbon fiber board is 2400 MPa，tension controlling stress is 1400 MPa, tensioning end and anchoring end should be anchored by the finished waveform anchorage device. the key points of the construction are as follows:

1) drilling, planting steel bar, installing anchorage block

a. when installing the tensioning end of the carbon fiber board and fixed end of the anchorage block, drilling and implanting high strength screw according to the design drawings. before drilling, paying attention to use steel bar detector to mark the position of the steel bars. adjusting the drilling position, avoiding damaging the main steel bar and prestressed steel bar because of drilling;
b. according to the position where plants the high strength screw, drilling on the steel plate of the anchorage block. adopting plastic foam board to monotype the position of the high strength screw,ensuring that the drilling position of the anchorage block steel plate is accurate.
c. installing the anchorage block. after the curing of the screw reaches the design strength, firstly polishing and cleaning the contact surface between the anchorage steel plate and concrete beam, then smearing sticky steel glue, pasting the anchorage block at the bottom of the beam, fixing the anchorage block on the pre-planted high strength screw with nuts.

2) The treatment of the concrete surface

a.after installing the anchorage block, drawing a ligature between the center of the two anchorage block on the concrete surface. within the scope of the 30cm of the ligature there is the position where pastes the prestressed carbon fiber plate. then clearing away the degradation parts( spalling, shrinkage,honeycomb and corrosion of the concrete surface, and cleaning and polishing it, after the surface drying, repairing the concave-convex parts of the concrete surface with the repair material. especially after clearing away the pasted steel plate of the second and fifth straddles’ plate bottom, constructing the prestressed carbon fiber plate.
b.according to the position where pastes the carbon fiber plate, determining the position of cardboard and the position where plants the steel bar. paying attention to avoid damaging the main steel bar and prestressed bar in the position where plants the steel bar.

(3) Blanking and clamping of the carbon fiber plate at the scene

Don’t construct on the rainy day or under the condition that the air humidity is more than 80%, and pasting the carbon fiber plate under the temperature condition of 5~35℃, the selection of the adhesive should meet the requirements of the environment and temperature.
a.according to the position of the anchorage block, further review the blanking length of the carbon fiber plate;
b.according to the blanking length, cutting out the carbon fiber plate
c.within the clamping length of the both ends of the carbon fiber plate, scrubbing the two sides of the carbon fiber plate with the acetone d.making up the special quick bonding glue, smearing it on the top and bottom surface within the clamping length of the carbon fiber plate. then putting it into the tooth fixture anchor, and quickly using electric wrench to screw up the toothed plate up and down of the tooth fixture anchor;
e.cleaning the pasting surface of the carbon fiber plate with the acetone and smearing the bonding glue of the carbon fiber plate; at the same time, smearing the same bonding glue of the carbon fiber plate on the pasting surface of concrete of the beam bottom.

The installation of the carbon fiber plate, tensioning and pasting of the prestressing force

a.by connecting screw,installing the carbon fiber plates of the two ends that have been clamped by the anchorage device on the anchorage block;
b. connecting the tensioning screw with the connected screw by using sleeve, and installing counter-force steel plate;
c. putting the fact between the counter-force steel plate and anchorage block.
d. driving the jack oil pump, doing the prestressed tensioning to the carbon fiber plate. prestressed tensioning should adopt double control of the tensioning and elongation. euro should be controlled in the 6%.
e. scrubbing the pasting surface of the carbon fiber plate with the acetone, and smearing the bonding glue of the carbon fiber plate; at the same time, smearing the same bonding glue of the carbon fiber plate at the pasting surface of the concrete of the beam bottom;
f. after finishing the tensioning of the carbon fiber plate, tightening up the post-anchorage nut, then removing the jack and counter-force steel plate;
g. pasting the carbon fiber plate on the concrete surface with the cardboard, if there is still a large gap between carbon fiber plate and concrete surface, adding bonding glue of the carbon fiber plate and filling the gap completely. finally the hollowing rate of the pasted carbon fiber plate should be less than 5%.

(5) The protection of the carbon fiber plate, anchorage device and anchorage zone

smearing the carbon fiber plate adhesive on the surface of the carbon fiber plate, anchorage block, anchorage device and connected screw. the thickness is more than 5mm. the purpose is to protect the steel components and carbon fiber material;

The construction safety and matters needing attention

safety and operation regulation (JTG H30-2004)", " safety technical regulations for the highway projects construction” and constructing, seeing to it that special equipments for the professional usage.
b. in order to ensure the construction safety, structural safety and smooth working, before the construction, checking and verifying carefully the construction machinery, temporary facilities and other security measures, after ensuring that everything is perfectly safe, then constructing;
c. carbon fiber plate is the conductive material. when using the carbon fiber plate, trying to be away from the electrical equipment and power supply. when using, avoiding the bending of the carbon fiber plate. the resin raw material that is matched with the carbon fiber plate should be sealed storage and away from the fire, avoiding the direct sunlight. the preparation and usage places of the resin should be kept well-ventilated. construction personnel at the scene should adopt the corresponding laboring protective measures according to the used resin material;
d. during the process of the tensioning of the carbon fiber plate, observing the change of the deflection of the beam. if the change of the deflection has something wrong, stopping tensioning and checking the reasons.