Discussion on bridge structure detection technology?

First, the main basis of bridge quality inspection

The inspection of highway and bridge engineering should be based on the laws and regulations, technical standards, design and construction specifications and material test specifications promulgated by the state and the Ministry of Communications. For some new structures and bridges built with new materials and new technologies, when there are no relevant provisions in relevant highway and bridge engineering codes and regulations, we can learn from the relevant provisions of other domestic industries.

Second, the content of bridge quality inspection

In the static load and dynamic load tests of bridges, the detection contents generally include the following aspects:

(1) Test the size of the load.

(2) The stress distribution on the cross section of structural members and its magnitude, reaction force and thrust, etc.

(3) Various static deformations of the structure, including horizontal displacement, deflection, relative slip, rotation angle, etc. Local damage phenomena of structures, such as the distribution, width and depth of cracks.

(4) Dynamic characteristics of the structure, such as natural frequency, period and attenuation, dynamic stress, displacement, velocity and acceleration of the structure under dynamic load.

(5) Appearance inspection is a very important work in bridge inspection. Usually, if there is a disease, there will be some symptoms. Through visual inspection, the causes of these diseases can be analyzed and judged, and remediation measures can be put forward, which is conducive to clarifying the focus of the next work. Appearance inspection requires grasping the key points and striving for comprehensiveness. The inspection points of arch bridge include cracks in the lower edge of arch ring vault and the upper edge of arch foot; Arch axis coordinates; Displacement of pier and so on.

Bridges can generally be divided into superstructure, substructure and accessory structure. The superstructure mainly refers to the main girder in the beam bridge, including the main arch rib, arch wave, stay cable, wind brace and so on. In the arch, it varies according to different structural forms; The substructure includes piers, abutments, foundations, caps and piles. Subsidiary structures include bridge deck pavement, sidewalks, kerbs, railings, expansion joints, etc. While finding out the causes of conventional diseases, we should evaluate them according to their damage degree, and then determine whether it is necessary to reinforce or replace parts to maintain normal operation.

Third, the prestressed concrete structure detection

The biggest difference between prestressed concrete structure and reinforced concrete structure is that concrete structure must be prestressed in advance to improve the bearing capacity of concrete structure. In addition to the inspection items of concrete structures, the inspection of concrete structures should also include the inspection of materials related to prestress, tensioning equipment and tensioning control methods.

1. Test and detection of prestressed steel

Steel used in prestressed concrete structures includes heat-treated steel bars, straightening and tempering steel wires, cold-drawn steel wires, nickel-plated steel wires and steel strands.

The test of prestressed steel such as heat-treated steel bars, prestressed steel wires and prestressed steel strands is mainly carried out from two aspects: appearance inspection and mechanical performance test.

2. Quality inspection of prestressed materials

Strictly control the quality of materials and adopt the products of manufacturers with good reputation and quality. Products must have factory certificates and quality inspection reports, and the materials present can be inspected. The strength, stiffness, tightness, bite fastness and other indicators of spiral seam can be used only after reaching quality standards. Reduce welding operations. Use the bellows of the first size as the sleeve, and the length of the sleeve is 20-30cm. The pipe joint should be aligned and centered in the sleeve. The circumferential gap between the two ends is sealed with adhesive tape.

3. Detection of prestressed anchorage, fixture and connector

3. 1 Prestressed anchorage shall meet the following requirements:

(1) When the prestressed anchorage assembly reaches the measured ultimate tensile force, all components should be cracked or damaged by naked eyes except for the phenomena allowed by the anchorage design.

(2) It shall meet the requirements of tensioning processes such as graded tensioning and supplementary tensioning, and shall have the performance of relaxing prestressed tendons.

(3) Grouting channels should be set on the anchorage or its accessories, and the grouting channels should have sufficient cross-sectional area to ensure the smooth flow of grout.

(4) The internal shrinkage of prestressed tendons in the anchoring process should meet the requirements.

3.2 fixture

Prestressed bar fixture shall have the following properties:

(1) When the prestressed tendon clamp assembly reaches the actual ultimate tensile force, all components should not be cracked and damaged by naked eyes.

(2) It has good self-anchoring performance.

(3) Good anchor loosening performance.

Fixtures that need to be knocked hard to loosen can only be used under the condition that there is no influence on prestressed anchorage and no danger to the safety of operators.

3.3 connector

The prestressed tendon connector used in post-tensioning method must meet the performance requirements of class I anchorage, and the prestressed beam connector used in pre-tensioning method must meet the anchorage performance requirements of fixture.

3.4 Prestressed tendons

Prestressed tendons generally use steel strand and steel wire, and small and medium-sized members or longitudinal and transverse prestressed tendons can also be selected.

The quality inspection of prestressed reinforced concrete engineering is also the key link of quality control. Here is a brief introduction:

Inspection contents: bearing, position, concrete strength, prestressing tendon tension.

(1) pier bearing:

The base must have sufficient strength and rigidity, and shall not fall over or slide.

The deflection of the beam should be greater than 2mm, and warping is not allowed.

The positioning plate of prestressed reinforcement must be installed accurately, and its deflection should not be greater than 65438 0 mm.

(2) Long-line pedestal:

When laying steel wire on the pedestal, measures should be taken to prevent the isolation agent from polluting the prestressed tendons. If it is contaminated, it should be cleaned with an appropriate solvent before use.

(3) Position deviation:

After the prestressed tendons are tensioned, the deviation from the design position should not be greater than 5mm, nor should it be greater than 4% of the shortest side length of the member section.

4. Tension technology and tension control

4. 1 Installation of tensioning equipment

Machines, equipment and instruments used for prestressing shall be used and managed by special personnel, and shall be maintained and calibrated regularly. Jack and pressure gauge should be calibrated to determine the relationship curve between tension and pressure gauge, and calibration should be carried out regularly in legal metrological technical institutions authorized by the competent department.

4.2 Tension control stress

The magnitude of prestress tension control stress directly affects the prestress effect, thus affecting the crack resistance and stiffness of members, so the control stress should not be too low. Of course, the control stress should not be too high, otherwise the load of component cracks will be very close to the failure load, and there will be no obvious signs of failure. Similarly, excessive stretching will make the stress of steel bar exceed the yield point, resulting in plastic deformation, which will affect the accuracy of stress value and the safety of stretching process.

4.3 tension control

(1) The tension control stress of prestressed tendons shall meet the design requirements. When the prestressed tendons need to be overstretched or included in the prestress loss of the anchor ring mouth during construction, it can be increased by 5% compared with the design requirements, but in any case, it shall not exceed the maximum tension control stress specified in the design.

(2) When prestressed tendons are tensioned by stress control method, they should be checked by elongation value, and the difference between actual elongation value and theoretical elongation value meets the design requirements. If there is no provision in the design, the actual elongation value and theoretical elongation value should be controlled within 6%, otherwise the tensioning should be suspended, and the tensioning can be continued only after the reasons are found out and measures are taken to adjust.

4.4 Tension quality control

In the process of tensioning, due to various reasons, the prestressed tendons are broken and slippery, which makes the prestressed tendons uneven and even makes it impossible to establish enough prestress in construction. Therefore, it is necessary to limit the number of broken and slippery wires of prestressed tendons, so control measures should be taken to strengthen the management of tensioning process.

(1) jack and oil pressure gauge should be checked on time, and kept in good working condition to ensure that the error part exceeds the specified value; The chuck and wedge of the jack are correct in size; There is no wear hook groove and dirt, so as not to affect wedging and wedging exit.

(2) The anchorage size should be correct to ensure the machining accuracy. The dimensions of anchor ring and anchor plug should be checked one by one, and those with the same sign error should be used together. That is to say, the size of the anchor ring and the thickness of the anchor plug are only allowed to have errors or negative errors at the same time to ensure the accuracy of taper.

(3) The anchor plug shall ensure the specified hardness value. When the hardness of the anchor plug is insufficient or uneven, it may shrink or even slide after tensioning. In order to prevent the end of the anchor plug from damaging the steel wire, the guide angle on the anchor plug head should be arc-shaped.

(4) The anchor ring should have no internal defects, and this time it should be unfolded on the electromagnetic frame one by one. If the anchor ring is too soft, it will be hard enough, resulting in excessive shrinkage of the anchor plug.

(5) Pre-stressed tendons shall be inspected as required before use: the newly-entered joints shall be circular with uniform thickness, strength and hardness; The steel wire should be carefully combed to avoid cross-confusion; Remove the oil stain and rust on the steel wire surface, and the steel wire will be wedged and tensioned normally.

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