How to measure and control cables during the construction of self-anchored suspension bridges?
1 Project Overview
The Wuxi Expressway Taohuayu Yellow River Bridge is located in the northwest suburb of Zhengzhou City. The main bridge is a twin-tower self-anchored suspension bridge with a span of 160m+406m+160m. . The bridge tower adopts a portal tower with a main cable saddle on the top of the tower. The main cable strands are composed of 37 strands of 127 high-strength galvanized steel wires (1670MPa) with a diameter of 5.3mm. They are 800.9m long and the main span-to-span ratio is 1/5.8. , the diameter of the main cable at 20% void ratio is 406mm, and the whole bridge has a total of 110 sets of cable clamps, 12 of which have no suspenders. There are 196 suspension cables in the main bridge, with a basic spacing of 13.5m. The suspender near the tower is 14m away from the center of the tower.
2 Overall construction plan
After the construction of the main tower is completed, the hoisting brackets are assembled on the top of the tower, and the main cable saddle is hoisted from the steel box girder bridge deck; the steel box girder is pushed and after the closing is completed, install the anchorage and loose rope saddle; install the middle span and side span catwalks; erection of the main cable reference strands; erection of the general cable strands; after the main cable erection is completed, tighten the main cable ; After the cable tightening is completed, install the cable clamp; according to the system conversion plan provided by the monitoring unit, perform sling tensioning, cable saddle pushing and weighted concrete pouring step by step to complete the main bridge system conversion.
3 Construction measurement control method
Overall measurement method: Establishing a dense control network for the main bridge construction→Control measurement before and after the steel box girder is closed→Main cable anchorage installation measurement→Steel box girder After the installation is completed, measure the center mileage and elevation of the boom hole → Installation measurement of the main cable saddle and scattered cable saddle → Installation measurement of the mid-span and side span catwalk load-bearing cables → Control measurement of the erection of the base cable strand and the main cable ordinary cable strand → After the main cable tightening is completed, linear measurement, cable clamp setting out and installation measurement → Main tower deflection measurement during the suspension rod tensioning and main cable saddle pushing process
3.1 Establishing the main bridge construction encryption control network< /p>
The plane construction control network adopts the GPS satellite positioning static measurement method, and re-measures according to the B- and C-level GPS network measurement accuracy in the "Global Positioning System (GPS) Measurement Specifications"; the elevation is leveled using a precision electronic level Measurement methods, and laid out a leveling network, and conduct leveling retesting in accordance with the second-class level requirements in the "National First- and Second-class Leveling Measurement Specifications" (GB12897-2006). According to the construction measurement needs of the main bridge cables, construction encryption control points are arranged. There are a maximum of 2 pairs of encryption points, which are arranged upstream and downstream of the bridge tower and on both sides of the bridge. The construction encryption network is regularly tested. The detection period of the construction encryption network generally does not exceed 6 months. .
3.2 Control measurements before and after the steel girder is closed
Overall construction method: The closing construction of the steel box girder is carried out after the ejection is completed. There are two conditions for the steel box girder of this bridge according to the overall construction plan. The first time is the closing of the south anchor beam and the SA10 segment that pushes the front end, and the second time is the closing of the NA10 segment, the north anchor beam, and the NA9 segment. The specific steps are:
1) After the steel guide beam is mounted on the south anchor beam bracket, the steel guide beam is removed one after another;
2) The last sections M0 and M1 of the guide beam are removed and the push is continued. The SA10 section at the front end of the steel main beam is connected to the anchor beam steel box beam (the closing joint should be 20cm at the lowest daily temperature before closing), and the steel box beam of the whole bridge is pushed into place;
3) Lift the NA10 section First store it on the north anchor beam, then lift NA9 and tailor-weld NA9. Hoist NA10 in place and tailor-weld it with the steel main beam and steel anchor beam. At this time, the steel box girder of the whole bridge is closed.
3.2.1 Closed measurement control of steel box girder and south anchor beam
According to the measurement period specified by the monitoring, the distance between measuring points arranged in the Helongkou beam section shall be measured in pairs for 48 hours , record, organize, proofread each other, and use it for matching and cutting of the Helong beam section after confirmation by the supervision engineer.
Figure 2 Schematic diagram of the closing of steel beam segments
Six linear monitoring points are arranged on the end sections of the closing beam sections SA10-SA11 to monitor the splicing of the south anchor beam. Linear shape, as well as monitoring the height difference between the top and bottom openings of the closed opening, center line deviation, etc.
Figure 3 Linear monitoring point layout of steel box girder
The above monitoring data must be continuously measured under different working conditions. If there is a large height difference in the beam section, it should be Make adjustments in time. After the adjustments are completed, the height difference of the measured beam sections must meet the specification requirements before the next step of pushing and closing can be carried out.
Before the steel box girder and the south anchor beam are closed together, the beam end mileage of the SA10 beam section of the steel box girder should be strictly controlled. It should be controlled at 20cm from the design mileage position, and the steel box girder and the south anchor beam should be adjusted properly. The axis deviation of the beam should be within 10mm, and the height difference should be controlled within 2mm. Since there is a 20cm closing gap left between the anchor beam and the steel beam, after all the above work is completed, the steel beam should continue to be pushed until the two beam sections SA10 and SA11 are closed. During this pushing process, since there is only a distance of 20cm, if the axis deviates again, it will be difficult to correct it. Therefore, during the pushing process, the pushing should be carried out multiple times and the axis should be measured continuously until the steel box The precise closing of the beam and the south anchor beam. Quickly use code plates to flatten the joints and perform welding in a timely manner. The welding work must be completed in the shortest time to prevent the increase in temperature difference from affecting the weld width and welding quality of the steel box girder.
3.2.2 Measurement and control of the closing of the north anchor beam and the steel box girder
Before the steel box girder and the north anchor beam are closed, the ends of the NA9 and NA11 beam sections should be Select 3 bottom plates and 3 top plates (set at the two webs and the centerline respectively) for observation points in each section, and continuously observe their elevation changes and axis offsets. Because during the installation and measurement of the NA11 beam section, the one-time positioning of the steel beam on the anchor beam bracket is more accurate, while the end section of the NA9 beam section is in a suspended state, and there will be a certain deviation in the elevation after installation, resulting in the installation of the Helong section. It is prone to twisting when in place. Therefore, the end elevation of the NA9 beam segment must be adjusted. During the adjustment process, not only the end elevation of the NA9 beam segment should be adjusted, but the beam bottom elevations of NA8 and NA7 on the top of the platform should be adjusted accordingly, so that each beam segment is consistent with The design lines are consistent to facilitate the smooth connection of each beam section of the steel beam.
When hoisting and lowering the NA10 beam section in the Helong section, the height difference between the two ends in the longitudinal bridge direction should be adjusted when the crane is lifting. A counterweight needs to be added to one end, and the height difference needs to be controlled within the design height difference. 123mm (the segmental steel beam is located within the vertical curve), so that the NA10 beam section can be smoothly placed into the closing section after being lifted, and the bottom and top openings will not twist.
According to the measurement period designated by the monitoring, continuously measure the distance between the paired measuring points of the adjacent beam sections at the closing opening, record and organize the measurement data, and draw the temperature and closing length changes in each period. value, after the closing temperature and time period are determined (it is advisable to choose a time period with a smaller temperature difference in a day), calculate the length and size value of the Helong section based on the measurement results. Based on the transverse baseline of the Helong section, according to the determined length of the Helong section The dimensional values are used to cut the edges and grooves. In order to ensure smooth closing, the beam segments are effectively restrained from shrinking before welding is completed. Add temporary matching connectors such as the pull screw base at the closing interface. When the temperature reaches the closing temperature, according to the monitoring requirements for the closing period, the closing section is quickly hoisted into place, and rough adjustment, matching, and temporary connection are quickly made. Temporary connection After completion, quickly use a code plate to flatten the joints and perform welding in a timely manner. The welding work must be completed in the shortest time. 3.2.3 Measurement control after the closing is completed
After the whole bridge is closed, linear monitoring of the closing section and other beam sections of the whole bridge will continue, and the linear measurement data will be fed back to the monitoring unit in time to facilitate the monitoring of anchorages and loose cables. It provides a basis for the installation and positioning of the sleeve and provides prerequisites for the smooth erection of the cable.
3.3 Main cable anchorage installation measurement
The anchorage installation is carried out after the installation and positioning of the steel anchor beam is completed and the steel box beam is closed.
Since the anchorage is installed inside the box, the measurement reference point needs to be transferred to the top of the steel box beam. The length of the steel box beam is greatly affected by temperature. The transfer point measurement should be done from late at night to before sunrise. During the period. This turning point is also used for the subsequent positioning and measurement of the saddle.
When measuring, the central three-dimensional coordinates of the front and rear anchor holes (at least 3 observed on each side), the inclination angles of the front and rear anchor surfaces, etc. should be accurately located.
After installation is completed, the allowable error in the center coordinates of the front anchor hole shall not be greater than 10 mm, the angle of the front anchor hole shall not be greater than 0.2 degrees, and the axis deviation of the front and rear anchor lines shall not be greater than 5 mm. And provide the measurement data after the installation is completed to the monitoring unit.
3.4 Measurement of the center mileage and elevation of the boom hole after the steel box girder is installed
After the anchorage is installed, the total length of the steel box girder should be measured at the lowest temperature at night , the center mileage and elevation of the upstream and downstream boom holes are provided to the monitoring unit.
3.5 Installation measurement of the main cable saddle and scattered cable saddle
After the construction of the main tower and upper beam is completed, the main cable saddle is hoisted into place and installed. During the hoisting process of the main cable saddle, the deflection of the hanger should be observed. The longitudinal, transverse and vertical pre-offset and pre-lift values of the main cable saddle base plate and saddle body should be based on the monitoring instruction value of the monitoring unit (the bridge's longitudinal deviation from the side span is 640mm, and the transverse bridge deviation is 5mm from the bridge center).
The construction process of the main cable saddle: Leveling of base plate pads → Measurement and setting out → Bracket installation → Longitudinal movement of the main cable saddle bottom plate to the lifting position → Trial lifting → Lifting → Longitudinal movement → Placement → Adjust the position → Hoist other components of the main cable saddle → Connect the components.
Measurement and setting-out: The leveling of the bottom plate pad is measured with an electronic level. The flatness is required to be controlled at 0.5mm/plane. After installing the grille, accurate measurement of the tower top axis is a prerequisite to ensure the accurate installation position of the main cable saddle. Choose to measure and set out at night when the weather is good and the temperature is stable, and the vertical and horizontal axes upstream and downstream of the tower top are staked out. The installation axis of the main cable saddle is based on the axis set out at the top of the tower as the control line to eliminate the influence of temperature and weather changes on the tower column.
Installation measurement of the loose rope sleeve: During the production process of the anchor beam, place the lower part of the loose rope sleeve on the bottom plate of the box beam close to the installation position of the loose rope sleeve. Before the main cable is erected, follow the monitoring command, use a total station to stake out the designed longitudinal and transverse axes and mileage lines, and mark them with ink lines; use steel brackets to temporarily support the lower part, and set limit end plates at both ends of the loose sling until After all the cable strands are erected, use a hand chain hoist to install the upper part to the designed position, adjust the axis and angle, put on the bolts, and tighten to the designed force value.
3.6 Installation and measurement of mid-span and side-span catwalk load-bearing cables
Since the steel wires used in catwalk load-bearing cables will produce a certain amount of permanent elongation during use, it is necessary to It should be pre-tensioned according to its stress condition to eliminate its inelastic deformation. In this way, the deflection of the catwalk after erection is easier to control. The catwalk is equivalent to a temporary lightweight cable bridge, and its function is to provide an aerial working platform during the erection of the main cable. It is composed of catwalk load-bearing cables, catwalk panel systems, transverse overpasses, and wind-resistant cables. The height of the catwalk surface from the center line of the main cable is generally about 0.8 to 1.2 meters, and is generally arranged symmetrically along the center line of the main cable. .
Every time a load-bearing cable is measured, it should be done before sunrise or after sunset. The elevation of the main cable center is based on the monitoring instructions provided by the monitoring unit. Due to the objective existence of unbalanced horizontal forces during the catwalk laying process, the observation and control of the deviation of the tower top should be strengthened, and the deviation of the main tower must not exceed the requirements of the monitoring party.
3.7 Control measurement of the erection of benchmark cable strands and common cable strands of the main cable
3.7.1 Overall measurement method
The sag adjustment of the main cable strands is divided into benchmarks Cable strand sag adjustment and general cable strand sag adjustment. The method for adjusting the sag of the base cable strand is the absolute elevation method. The general method of adjusting the sag of the cable strand is to adjust the sag relative to the base cable strand.
Figure 4 Main cable section
In order to ensure that the reference strand used for general cable strand adjustment is always in a free-floating state, a general cable strand outside each layer of the main cable is used as the relative The sag of the benchmark cable strand is transmitted by the 1# benchmark cable strand, and then the sag of the general cable strand of the same layer and the previous layer relative to the benchmark cable strand is adjusted by using each layer relative to the benchmark cable strand to achieve the purpose of adjusting the main cable alignment.
In order to eliminate the accumulation of adjustment errors, the adjustment error of each relative to the benchmark cable strand is transferred, that is, when adjusting the next relative to the benchmark cable strand, the theoretical relative sag between them should be subtracted. Remove the adjustment error value of the current relative cable strand to ensure that the adjustment error of each cable strand relative to the benchmark cable is within the allowable range.
3.7.2 Benchmark cable strand measurement
Measurement items: including anchor span mileage and elevation, tower top elevation and offset, main cable saddle pre-offset, main cable sag elevation , the amount of movement of the loose sling, etc.
① Fix the prism in the middle of the cable strand span, and use the total station triangular height measurement.
② Calculate the mid-span sag of the mid-span and side span cable strands, and compare it with the design sag. Based on the sag adjustment chart calculated by monitoring, calculate the length of the cable strands that needs to be moved and adjusted, and make Span, temperature correction.
③ By relaxing or tightening the cable strands at the cable saddle, the purpose of sag adjustment is achieved. First adjust the main span and then adjust the side span sag until it meets the design requirements.
④After the absolute sag of the cable strands meets the requirements, the relative sag of the upstream and downstream two reference cable strands shall be adjusted at the same time, and the relative sag difference shall not be greater than 10mm.
⑤After the sag of the benchmark cable strand is adjusted, stable observation must be carried out for at least 3 days to confirm that the cable strand linear shape fully meets the stability requirements, and all results do not exceed the allowable deviation range. The first cable strand The sag adjustment is completed. The allowable error of absolute elevation is ±L/20000 for mid-span and ±L/10000 for side span.
The arithmetic average of the observation data for three consecutive days will be used as the final line shape of the benchmark index.
3.7.3 General strand measurement
The strands other than the benchmark strand are general strands, and the general strands are based on relative sag adjustment relative to the benchmark strand. The relative base strand method is used for general strand sag adjustment. Use a vernier caliper to measure the sag adjustment amount of the cable strand.
① When installing the upstream and downstream main cables, the first cable strand is usually used as the base cable strand and must be operated carefully. Adjustments should be made on the basis of measuring and calculating the effects of span, sag, temperature changes, etc. The adjustment of the sag must be carried out at night when the wind speed is low and the temperature is relatively stable. After placing it correctly, stay for a period of time and observe and measure continuously for no less than 3 days and nights. If all results do not exceed the allowable deviation range, the sag of the first cable strand will be adjusted.
② In order to ensure the erection quality of the cable strands, 1 to 2 additional base cable strands can be added. The position of the reference cable strand should be set at the edge of the main cable that is not pressed by the general cable strands.
③The allowable deviation of the design sag of the mid-span of the datum cable strand should comply with the provisions of the drawings. Generally, the relative difference of the sag of a cable strand to the benchmark cable strand should be within 0, +5mm; the relative difference of the sag of the benchmark cable strand of the upstream and downstream main cables should be within 10mm. ④ If the accuracy of the benchmark cable strand is affected by the erection of subsequent cable strands, and it is determined after testing that it can no longer function as a benchmark cable strand, a new cable strand should be selected to calculate the span and sag. , measure the influence of temperature, and make adjustments to meet the requirements of (continued from page 115) (continued from page 108) as the benchmark cable strand, and then use this new cable strand as the benchmark cable strand for relative sag adjustment.
Because the main cable is nearly a kilometer long and is very sensitive to temperature, with large changes in length and sag, the temperature of the cable strands must be measured, and the sag measurement must be corrected based on design and monitoring. In the hanging state, the beam section is hexagonal, the wires are parallel, and the wires are not twisted or drummed. After adjusting the sag of the middle span and side span in sequence, the jack finally pushes the anchor head and adds or removes gaskets to adjust the anchor span. When adjusting, the center and side spans shall be based on sag, and the anchor span shall be based on tension. When erecting, attention should be paid to observing the torsion and displacement of the tower top.
3.8 After the main cable tightening is completed, linear measurement and cable clamp setting out and installation measurement
After the general cable strands and reference cable strands of the main cable are installed, tighten the main cable. After the cable tightening is completed, the line shape of the main cable is measured under constant atmospheric temperature conditions at night.
When the main cable line shape is finalized, the monitoring unit will provide the coordinate position of the cable clamp in this state, and make a temporary mark on the main cable along the curve of the main cable with the rough position of the cable clamp during the day. When the temperature is relatively stable at night, use the temporary mark as a reference to quickly stake out the position of the cable clamp. Before installing the cable clamp, the center coordinates of the cable clamp should be calculated based on the main tower top deviation, main cable temperature, atmospheric temperature, tower height, loose rope sleeve apex deviation and other data submitted to the monitoring unit. When installing the cable clamp, check whether the position number of the cable clamp matches the position sequence number on the main cable. After the cable clamp is hoisted in place, the center of the cable clamp should be rechecked. After the recheck is correct, the cable clamp can be installed in place. Since there are a large number of cable clamps, it needs to be completed multiple times. Therefore, the atmospheric temperature and the surface temperature of the main cable should be measured when setting out, and the cable clamps should be set out under basically the same temperature as possible.
3.9 Deflection measurement of the main tower during the process of suspender tensioning and main cable saddle pushing
During the installation process of the main cable saddle, the pre-deflection of the saddle body is the deflection The side span is 64cm. During the tensioning process of the suspender, it should be pushed up in three times according to the monitoring instructions. Pushing the main cable saddle is an important link in the construction of the suspension bridge. The essence of controlling the pushing amount of the cable saddle is It is to control the stress of the tower body not to exceed the allowable value to ensure the safety of the tower body, and to observe the deflection of the main tower in real time during the pushing process to ensure that the deflection of the two main towers is not greater than the monitoring calculation data.
4 Summary
Through the above description of the cable measurement control method during the construction process of the self-anchored suspension bridge, we understand the key points and difficulties that need to be paid attention to during the construction process. When encountering similar tasks in future work, you can plan in advance, quickly enter the working state, and improve work efficiency.
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