1, bearing capacity detection
Static and dynamic load test of bridge structure is to test the stress, strain and deflection of the structure, as well as the natural frequency, damping ratio and impact coefficient of the structure by applying static and dynamic loads to the designated positions of the bridge structure respectively.
According to relevant regulations, the test holes are determined as: 65m between pier 0#~ 1#, pier 2#~3# 155m, pier 5#~6#15m.
Stress is measured by external strain gauge, and strain is measured by static strain gauge. Measure the deflection of main girder and settlement of pier and abutment with precision level; Measuring pier deflection with total station; Dynamic displacement is tested by INV306 vibration testing system. The vibration frequency, damping and impact coefficient of the structure are obtained by measuring the dynamic strain with dynamic strain gauges. The cracks were observed with JC- 10 reading microscope (magnified 20 times).
1. 1 static load test
In the static load test, we should: a) implement traffic control; Specify the parking position of each test vehicle; Install and debug strain gauge, displacement gauge, precision level, etc. B. Preloading: (A test vehicle passes back and forth twice on the bridge span to be tested, and the bridge span is preloaded; Read the initial values of strain gauge, displacement gauge, precision level, etc. C loading: the test vehicle is gradually put in place according to the specified position and gradually loaded. Read the strain gauge, displacement gauge and precision level after each level of loading is stable 10 minute; Read it again after 5 minutes. Unloading: unload step by step, and after each unloading step stabilizes 10min, read the strain gauge, displacement gauge and precision level; 5-minute interval
Then read it again; After all vehicles leave for half an hour, read the strain gauge, displacement gauge and precision level again.
1.2 dynamic load test
In the dynamic load test, traffic control should be implemented; Debugging INV306 vibration test system and dynamic strain gauge. Two test vehicles pass side by side at the speed of 10, 20, 40 and 60 km/h, which are recorded by the test system and dynamic strain gauge. Two test vehicles passed at a uniform speed of 40 km/h, and the emergency braking, vibration test system and dynamic strain gauge were recorded in the middle of the span. 1 The test vehicle jumps at a speed of 5 km/h, and the vibration test system and dynamic strain gauge are tested.
1.3 crack detection
Testers carefully observe whether cracks appear and develop in each control part under each level of load. If so, the loading should be stopped, and the secondary loading can only be carried out after analyzing the reasons.
1.4 detection precautions
① Test the vehicle. Three five-axle vehicles with a total load of 55t (the front axle is required to weigh 3t, the two intermediate axles are required to weigh 12 and the two rear axles are required to weigh 14t). ; 36 trucks, complete vehicle and load of 20t (front axle weight of 7t, rear axle weight of13t); Static load test is based on the principle of equivalent load of design load (steam exceeding 20t, trailer-120), and equivalent conversion of tonnage and quantity of vehicle load required for each test span according to the most unfavorable effect value of design control load, so as to finally achieve the purpose of load efficiency of 0.8~ 1.05.
(2) The static load test conditions and load distribution positions of each test span should be classified according to the most unfavorable position of the influence line of bridge internal force.
③ Dynamic load test. Simulate the driving speed, braking and jumping of the actual driving load.
④ Arrangement of strain and deflection measuring points. Static and dynamic load and strain measuring points are arranged in the midspan and fulcrum section; Each pier top strain measuring point is arranged on the left and right sides; The deflection (displacement) measuring point is located at the fulcrum 115m, mid-span1/5m+3 times of the integral cast-in-place prestressed concrete box girder between piers 0#~7# on the right line of Shiganshan1Bridge.
5) Layout of temperature measuring points. Set on the bridge and under the bridge near the measuring point! Temperature observation point, in addition, a component surface temperature observation point is set at the main measuring point of the bridge.
2, water seepage detection
Although road workers have gradually realized the harm of water damage to asphalt pavement, the detection and evaluation of asphalt pavement seepage performance and the formulation of corresponding seepage control indicators are still not perfect. So it is necessary to know the detection of water seepage.
2. 1 test formula
Focus on the accuracy and repeatability of instrument test results and the operability of test methods, and finally recommend the calculation formula of pavement permeability coefficient as follows.
k =(lnh 1- ln h2) aL/A t
Where: k is the permeability coefficient; A is the cross-sectional area of the water pipe; L is the height of the specimen, which is assumed to be the thickness of the test layer during the field test; A is the cross-sectional area of the specimen, which is assumed to be the contact area between the water in the seepage meter and the road surface during the field test; T is the seepage time; H 1 is the head height at the beginning of the test; H2 is the head height at the end of the test.
2.2 test methods
Considering that the water seepage of asphalt pavement is often related to segregation, coarse aggregate concentration and insufficient compaction, these indexes are also measured while testing the water seepage coefficient of asphalt pavement. In order to make the measured water permeability coefficient better represent the actual performance of asphalt pavement, there are several measuring point selection methods as follows:
① Considering the influence of asphalt mixture type on the water permeability of asphalt pavement, select the road sections with the same structural layer, the same nominal aggregate particle size and different gradation.
② Considering the influence of thickness on the permeability of asphalt pavement, select the road sections with the same structural layer, the same gradation and different thickness to study the matching relationship between the maximum nominal particle size of aggregate and the thickness.
③ Considering the influence of compaction degree on the permeability of asphalt pavement, select the road sections with the same structural layer and different pavement porosity. The surface drying method is used to measure the pavement porosity, and the data of core samples can be borrowed, or the core can be measured at the detection point after the water permeability coefficient is determined.
④ Considering the influence of structural depth on the permeability of asphalt pavement, the road sections with the same structural layer but different pavement structural depths are selected. The depth of pavement structure is determined by sand laying method.
3. Pile foundation detection
3. 1 hole formation detection
Ultrasonic hole-forming detector adopts ultrasonic reflection technology, which can be used for comprehensive detection of hole-forming and groove-forming quality of various cast-in-place piles (or underground continuous walls). In practice, when the ultrasonic sensor is lowered at a certain speed along the center of the drilling hole filled with mud, the ultrasonic pulse reflection signals in four directions (or two directions) perpendicular to the hole wall are received and recorded during the probe lowering process, which is convenient for monitoring the hole wall conditions in four directions at the same time, and intuitively observing the parameters such as continuous wall slot width, drilling diameter, verticality and hole wall conditions.
3.2 Static load test method
When determining the ultimate bearing capacity of a single pile, it is the most accurate and reliable detection method at present, and judging whether a dynamic load detection method is mature is based on the relative error of static load test results. Therefore, all kinds of foundation design and treatment codes put the static load test of single pile in the first place. In general, the data of static load test of pile foundation, such as bearing capacity and settlement of single pile, are considered to be accurate and reliable.
3.3 Stress wave reflection method integrity detection
Although there has been no substantial progress in the research of this method at home and abroad in recent years, its practicability and popularization have been greatly improved in China, which is not only manifested in the fact that the domestic pile foundation dynamic tester and supporting sensors have reached or approached the advanced instruments abroad, but also in the fact that many units have carefully studied various testing and analysis links, and more importantly, many management departments have begun to seriously summarize the gains and losses of stress wave reflection integrity testing. The application of this method has begun to return to the normal position. For example, Guangdong Province is positioning this method to provide technical preparation for subsequent detection, which completely corresponds to the real ability of this method to solve problems.
3.4 High-strain dynamic pile testing method
In the dynamic testing of pile foundation, domestic instruments and software have reached the international advanced level, and many aspects are more characteristic of China.
3.5 Dynamic and static methods
The dynamic and static method refers to the application of D'Alembert principle to study the dynamics of non-free particle systems. The characteristic of dynamic and static method is to deal with the imbalance problem in dynamics by studying the balance in statics after introducing virtual inertia force.
4. Concluding remarks
Bridge inspection is a long inspection process, complex content, unpredictable and high-tech work. According to the test purpose, the test content and detailed plan should be carefully formulated to ensure the test effect, ensure the test safety and prevent many potential safety hazards.
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