Taohuajiang Bridge is located on the Second Ring Road in Guilin. It is a double-hinged truss arch bridge with a clear span of 60m, a clear rise of 7.5m, a clear rise-span ratio of 1/8, and a quadratic parabola for the arch axis. The total width of the bridge deck is 14m, and the original design load is "car -20 class and trailer-100", which was completed and opened to traffic in June 1988. Due to the long service life of the bridge, the current traffic load is greater than the original design load, and the traffic flow is large, which has a certain impact on the service life of the bridge. According to the conclusion of the report, the author designed the construction drawing of reinforcement and reconstruction.
2. Detection and evaluation of truss arch bridge
On June 5438+ 10, 2006, the Civil Engineering Test and Testing Center of the School of Architecture and Engineering of Guangxi University conducted static and dynamic load tests on taohuajiang Bridge, and submitted the Static and Dynamic Load Test and Safety Assessment Report of Guilin taohuajiang Bridge (Civil Engineering Test and Testing Center of the School of Architecture and Engineering of Guangxi University, 2006. 1.25). For the function evaluation and bearing capacity appraisal of truss arch bridge, the main work includes on-site inspection, indoor analysis, calculation and evaluation. General truss arch bridge inspection includes appearance defect inspection, static load test, strain stress analysis and dynamic load test, which provides accurate data and information for future reinforcement work.
2. 1 Inspection of Appearance Defects of Truss Arch Bridge
(1) pier displacement
Truss arch bridge is statically indeterminate structure, and the displacement of abutment and pier directly affects the stress of bridge structure. Changes in the cross-section of soft soil foundation or riverbed (especially the cross-section near the bridge site) caused by scouring or siltation will cause displacement of abutment and pier. In the structural stress calculation and analysis of truss arch bridge, pier displacement is an important factor and one of the important contents of disease detection.
(2) the change of bridge geometry.
Whether the longitudinal slope, transverse slope and expansion joint of truss arch bridge deck are deformed, and whether the abutment displacement of arch bridge. The existing overall deformation of the bridge is an important basis for inferring the causes of bridge diseases.
Routine inspection of reinforced concrete of truss arch bridge
In the detection of reinforced concrete, it is generally necessary to detect the strength of concrete, the corrosion rate of steel bars and the detection of cracks. Due to the small cross section of truss arch bridge, nondestructive testing method should be adopted. Crack detection is mainly at the vault and arch foot.
2.2 Static Load Test and Strain Stress Analysis
Select test points on the truss arch, attach resistance strain gauges, install sensors such as dial indicators, and test the transverse intermediate load and eccentric load of the truss arch bridge, the strain of concrete and steel bars in the midspan section, quarter section and eighth section along the longitudinal direction of the bridge, and the deflection of the truss arch. , and compared with the theoretical calculation value.
2.3 Dynamic load test
Under the excitation of random load, the first-order natural frequency of the truss arch bridge can be obtained by recording and processing the vibration data of the bridge through vibrometer and other equipment, so as to judge the working state of the bridge structure. Compared with the natural frequency of vehicle spring, it is helpful to judge the possibility of vibration.
2.4 Calculation and analysis
The strength of concrete, the displacement of abutment and pier and the current load standard are used for the analysis and evaluation of bridges. The evaluation results should give the actual bearing capacity of the bridge and the weak members of the bridge under the current load standard, and put forward opinions and suggestions.
2.5 Summary of test report
Corrosion detection of steel plate welds at the transverse joints of arch ribs and diagonal braces: randomly select 15 transverse joints of arch ribs and 6 diagonal braces for corrosion detection of steel plate welds. The original epoxy protective layer was cut open for inspection, and the welds of 2 1 randomly selected steel plates were corroded, most of which were general corrosion, and some were seriously corroded. See fig. 8- 1 ~ fig. 8-2 for joint corrosion. According to the analysis of corrosion, the strength of the joint is not affected at present.
Because the corrosion rate of steel plate weld at the transverse connection joint is 100%, it shows that the original epoxy resin protective layer can no longer play the role of rust prevention, and all joints should be rusted and rusted.
3. Maintenance and reinforcement technology of truss arch bridge.
3. 1 Rust removal and rust prevention treatment at the joint
Before reinforcement, the embedded steel plate at the joint of transverse connecting beam and diagonal brace between arch ribs should be derusted and corroded. Remove the epoxy protective layer on the steel plate, remove the old paint on the surface, and polish until the metal substrate is exposed. Derusting grade must reach Sa2.5 specified in GB8923-88. After rust removal, carry out rust prevention treatment according to the following procedures.
3.2 Maintenance and reinforcement methods for cracks at the top chord end node and the bottom chord arch foot.
3.2. 1 Reinforcement method
The cracks at the joint of the upper and lower chords of the truss caused by the uneven settlement of the abutment and pier have been basically stable and will not develop again. Epoxy mortar can be used for maintenance and reinforcement by sticking steel plates on both sides or on three sides.
3.2.2 Key points of construction
First of all, do a good job of chiseling the concrete surface of the component and derusting the steel plate. If the concrete at the joint falls off seriously, the protective layer concrete should be chiseled away before sticking the steel plate. Secondly, the cracks are treated first, that is, the cracks are grouted (epoxy mortar) first, and then the steel plates are pasted. Thirdly, because the arch foot should always be below the water flow, in order to prevent the steel plate from rusting, the reinforcement of the arch foot should also adopt the method of erecting formwork and pouring concrete after sticking the steel plate.
3.3 Maintenance and reinforcement methods for cracking of beams, tie rods and clapboards.
Incremental method
Because the design standard of truss arch bridge is low and the transverse connection is weak, it can not adapt to heavy traffic or heavy traffic, so the transverse connection system of the whole bridge should be strengthened.
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