Taohuayu Yellow River Bridge in expressway, Wuxi is located in the northwest suburb of Zhengzhou. The main bridge is a self-anchored suspension bridge with two towers, and the span arrangement is 160m+406m+ 160m. The bridge tower is a portal tower with a main cable saddle at the top. The main cable strand consists of 37 strands of high-strength galvanized steel wire (1670MPa) and 127 wires, with a diameter of 5.3mm, a length of 800.9m, a main span rise-span ratio of 1/5.8, a main cable diameter of 406mm and a void ratio of 20%. The main bridge has * * * slings 196, and the basic spacing is13.5m. The suspenders near the tower body are 14m away from the tower center.
2 overall construction scheme
After the construction of the main tower is completed, the hoisting bracket is assembled at the top of the tower, and the main cable saddle is hoisted from the steel box girder bridge deck; After the steel box girder is pushed and closed, install anchorage and cable saddle; Catwalk installation for mid-span and side-span; Erection of main cable reference strand; Installation of common cable inventory; After the erection of the main cable is completed, tighten the main cable; After the cable is tightened, install the cable clamp; According to the system conversion scheme provided by the monitoring unit, cable tension, cable saddle jacking and mass concrete pouring are carried out step by step to complete the system conversion of the main bridge.
3 construction survey control method
Overall survey method: establish the main bridge construction encryption control network → control survey before and after steel box girder closure → installation survey of main cable anchorage → measurement of the center mileage and elevation of suspender hole after installation of steel box girder → installation survey of main cable saddle and loose cable saddle → installation survey of catwalk load-bearing cable in the middle span and side span → erection control survey of main cable reference strand and common cable strand → linear survey after main cable tension and cable clamp lofting and installation survey → suspender tension and main cable saddle.
3. 1 Establishment of encryption control network for main bridge construction
The plane construction control network adopts the static measurement method of GPS satellite positioning, and carries out retest according to the measurement accuracy of Class B and Class C GPS networks in the global positioning system (GPS) measurement specification. The elevation shall be leveled with precision electronic level, and the leveling network shall be laid. The leveling shall be re-measured according to the second-class leveling requirements in the national first-class and second-class leveling standards (GB 12897-2006). According to the needs of cable construction survey of the main bridge, two pairs of construction encryption control points * * * are set up on the upstream and downstream of the bridge tower and on both sides of the river, and the construction encryption network is tested regularly, and the testing period of the construction encryption network is generally less than 6 months.
3.2 Control survey of steel beams before and after closure
Overall construction method: steel box girder is pushed and closed. According to the overall construction plan, the steel box girder of this bridge will be closed in two times, the first time for the south anchor beam and the jacking front SA 10 section, and the second time for the north anchor beam and the NA 10 section. The specific steps are as follows:
1) After the south anchor beam bracket is installed on the steel guide beam, dismantle the steel guide beam one by one;
2) Dismantle the last section M0 and M 1 of the guide beam, continue to push forward the connection between the front section SA 10 of the steel main beam and the steel box girder of the anchor beam (the joint should be 20cm at the lowest temperature of the day before closing), and push the steel box girder of the whole bridge into place;
3) Hoisting NA 10 section is stored on the north anchor beam first, then hoisting NA9, welding NA9, hoisting NA 10 in place, and welding it with the steel main girder and steel anchor beam. At this time, the steel box girder of the whole bridge is closed.
3.2. 1 measurement control of closure of steel box girder and south anchor girder
According to the measurement period specified in monitoring measurement, the distance between measuring points arranged in the closed beam section shall be measured, recorded, collated and checked for 48 hours, which shall be used for splicing and cutting of the closed beam section after being confirmed by the supervision engineer.
Fig. 2 Schematic diagram of steel beam segment closure
Six linear monitoring points are arranged at the end of SA 10-SA 1 1 beam section of the closure, which are used to monitor the splicing alignment of the south anchor beam, as well as the height difference between the top and bottom of the closure and the deviation of the center line.
Fig. 3 Layout of linear monitoring points of steel box girder
The above monitoring data must be continuously measured under different working conditions. If the beam height difference is too large, it should be adjusted in time. After the adjustment is completed, the next pushing work can be carried out only after the measured beam height difference meets the specification requirements.
Before the steel box beam and the south anchor beam are closed, the beam end mileage of the steel box beam SA 10 should be strictly controlled at a distance of 20cm from the design mileage position, and the axis deviation of the steel box beam and the south anchor beam should be adjusted within10 mm.. And the height difference should be controlled within 2 mm Since there is a seam of 20cm between the anchor beam and the steel beam, after all the above work is completed, the steel beam should continue to advance until the two beam segments SA 10 and SA 1 1 are closed. In the process of pushing, because the distance is only 20cm, it is difficult to correct the deviation if the axis deviates again. Therefore, in the process of advancing, the axis should be advanced several times and measured continuously until the steel box beam and the south anchor beam are accurately closed. Quickly align the joint with the code board and weld it in time. The welding work must be completed in the shortest time to prevent the increase of temperature difference from affecting the weld width and welding quality of steel box girder.
3.2.2 Closure Measurement Control of North Anchor Beam and Steel Box Girder
Before the closure of the steel box girder and the north anchor girder, three observation points (three bottom plates and three top plates (located on the two webs and the center line respectively) should be selected at the two ends of NA9 and NA 1 1 girder section to continuously observe the elevation change and axis deviation. Because the steel beam on the anchor beam bracket is accurately positioned at one time during the installation and measurement of NA 1 1 beam section, and the end section of NA9 beam section is suspended, there will be some deviation in elevation after installation, which will easily cause the closure section to be distorted when it is installed in place. Therefore, it is necessary to adjust the end elevation of NA9 beam segment. In the process of adjustment, not only the end elevation of NA9 beam segment, but also the bottom elevation of NA8 and NA7 beam at the top of the platform should be adjusted accordingly, so that each beam segment is consistent with the design alignment and the steel beam segments can be connected smoothly.
When hoisting the NA 10 beam section of the closed section, the height difference between the two ends of the longitudinal bridge should be adjusted when the crane is hoisted, and a counterweight should be added at one end. The height difference should be controlled within the design height difference 123mm (this section of steel beam is located in the vertical curve), so that the NA 10 beam section can be put into the closure section smoothly after hoisting, and the bottom and top openings are not distorted.
According to the measurement period specified in the monitoring, continuously measure the distance between pairs of measuring points divided by adjacent beam segments at the closure mouth, record and sort out the measurement data, and draw the change values of temperature and closure length in each time period. After the closure temperature and time period are determined (it is advisable to select the time period with small temperature difference change in a day), the closure length dimension value is calculated according to the measurement results, and the edge and groove are cut according to the determined closure length dimension value based on the transverse baseline of the closure section, so as to ensure smooth closure. Add a temporary mating connector at the closed interface, such as the base of the reverse tension screw. When the temperature reaches the closing temperature, the closing section will be hoisted in place quickly according to the monitoring requirements, and rough adjustment, coordination and temporary connection will be carried out quickly. After the temporary connection is completed, quickly level the joint with the code board and weld it in time. The welding work must be completed in the shortest time. 3.2.3 Measurement control after closing
After the whole bridge is closed, the alignment of the closed section and other beam sections of the whole bridge will continue to be monitored, and the linear measurement data will be fed back to the monitoring unit in time, which will provide a basis for the installation and positioning of anchorage and loose cable sleeve and make a good premise for the smooth erection of cables.
3.3 Installation survey of main cable anchorage
Anchorage installation shall be carried out after the installation and positioning of the steel anchor beam are completed and the steel box beam is closed.
Because the anchorage is installed in the box, the measuring datum point needs to be transferred to the top of the steel box beam, and the length of the steel box beam is greatly affected by temperature, so the turning point measurement should be carried out from midnight to sunrise. This turning point is also used for the positioning measurement of the slack saddle in the later period.
The three-dimensional coordinates (at least three on each side) of the centers of the front and rear anchor holes and the inclination angles of the front and rear anchor surfaces should be accurately positioned during the measurement.
After installation, the allowable error of the center coordinates of the front anchor hole is not more than 10mm, the angle of the front anchor hole is not more than 0.2 degrees, and the axis deviation of the front and rear anchor connecting lines is not more than 5 mm ... and provide the measured data after installation to the monitoring unit.
3.4 Measurement of center mileage and elevation of suspender hole after installation of steel box girder.
After the installation of the anchorage is completed, the total length of the steel box girder, the center mileage and elevation of the upstream and downstream suspender holes should be measured at the lowest temperature at night, and provided to the monitoring unit.
3.5 Installation survey of main cable saddle and loose cable saddle
After the construction of the main tower and upper beam is completed, hoist the main cable saddle. During the hoisting of the main cable saddle, the deflection of the hanger should be observed. The pre-lifting value of vertical and lateral pre-deflection of the main cable saddle bottom plate and saddle body shall be subject to the monitoring instruction value of the monitoring unit (the longitudinal deviation of the bridge from the side span is 640mm, and the transverse deviation of the bridge from the bridge center is 5mm).
Construction process of the main cable saddle: leveling the bottom cushion → measuring and setting out → bracket installation → longitudinal movement of the bottom plate of the main cable saddle to the hoisting position → trial hoisting → hoisting → longitudinal movement → positioning → position adjustment → hoisting other components of the main cable saddle → component connection.
Measuring and setting out: measure the elevation of the bottom cushion with an electronic level. The flatness should be controlled at 0.5mm/plane. After the grid is installed, accurately measuring the axis of the tower top is the premise to ensure the accurate installation position of the main cable saddle. Choose a night with good weather and stable temperature to measure, and let out the vertical and horizontal axes of the upstream and downstream of the tower top. The installation axis of the main cable saddle takes the lofting axis 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 loose cable sleeve: During the process of making anchor beam, the lower half of loose cable sleeve is placed on the box girder floor near the installation position of loose cable sleeve. Before the main cable is erected, according to the monitoring instructions, set out the designed vertical and horizontal axes and mileage lines with total station and mark them with ink lines; The lower part is temporarily supported by a steel bracket, and limit end plates are installed at both ends of the loose cable sleeve until all cable strands are erected. Then, the upper part is installed to the design position with chain block, the axis and angle are adjusted, bolts are put on, and the force required by the design is tightened.
3.6 Catwalk Load-bearing Cable Span and Side Span Installation Survey
Because the steel wire used in the catwalk load-bearing cable will produce a certain amount of permanent elongation during use, it should be pre-stretched according to its stress state before erection to eliminate its inelastic deformation, so that the catwalk vector after erection is easier to control. The catwalk is equivalent to a temporary light cable bridge, and its function is to provide an aerial work platform during the erection of the main cable. It consists of catwalk bearing cable, catwalk panel system, transverse overpass and wind-resistant cable. The height of catwalk surface layer from the center line of main cable is generally about 0.8 ~ 1.2m, and it is generally symmetrically arranged along the center line of main cable.
Every time the load-bearing cable is measured, it should be done before sunrise or after sunset. The elevation of the main cable center shall be subject to the monitoring instruction provided by the monitoring unit. Due to the objective existence of horizontal force imbalance in the catwalk laying process, it is necessary to strengthen the observation and control of tower top deviation, and ensure that the main tower deviation does not exceed the requirements of the monitoring party.
3.7 Erection control survey of main cable reference stocks and common stocks
3.7. 1 integral measurement method
The sag adjustment of main cable strands can be divided into standard sag adjustment and general sag adjustment. The sag adjustment method of reference cable is absolute elevation method, and the general sag adjustment method is to adjust sag relative to reference cable.
Fig. 4 section of main cable
In order to ensure that the reference strand used in general strand adjustment is always in a free floating state, a general strand on the outer side of each layer of the main cable is used as a relative reference strand, and its sag is transmitted by 1# reference strand, and then the sag of the general strand in the same layer and the relative reference strand in the previous layer is adjusted by using the relative reference strand in each layer to achieve the purpose of linear adjustment of the main cable.
In order to eliminate the accumulation of adjustment error, the adjustment error of each relative reference stock is transmitted, that is, when adjusting the next relative reference stock, the adjustment error of the current relative stock should be subtracted from the theoretical relative sag value between them to ensure that the adjustment error of each relative reference stock is within the allowable range.
3.7.2 benchmark steel strand measurement
Measurement items: including anchor span mileage and elevation, tower top elevation and deviation, main cable saddle pre-deviation, main cable sag elevation, loose cable sleeve movement, etc.
(1) Fix the prism in the cable span, and use the total station to carry out trigonometric leveling.
(2) Calculate the midspan sag of steel strand in midspan and side span, and compare it with the design sag. According to the sag adjustment diagram calculated by monitoring, the length of steel strand that needs to be moved and adjusted is calculated, and the span and temperature are corrected.
(3) Adjust the sag by loosening or tightening the steel strand at the cable saddle, first adjust the sag of the main span, and then adjust the sag of the side span until it meets the design requirements.
(4) After the absolute sag of steel strand meets the requirements, adjust the relative sag of upstream and downstream benchmark steel strand at the same time, and the relative sag difference is not more than 65438+/-00 mm. ..
⑤ After the sag of the benchmark cable strand is adjusted, it must be observed stably for at least 3 days to confirm that the cable strand line shape completely meets the stability requirements, and all the results are within the allowable deviation range. Adjust the sag of the first cable strand. Among them, the allowable error of absolute elevation is mid-span L/20000 and side span L/ 10000.
The observed data for three consecutive days are arithmetically averaged as the final line shape of the reference strand.
3.7.3 General steel strand measurement
Strands other than the reference strand are common strands, and the common strands are adjusted according to the relative sag with respect to the reference strand. The relative reference stock method is used to adjust the sag of general stocks. Measure the sag adjustment of cable strand with vernier caliper.
① When installing the upstream and downstream main cables, the first strand is usually taken as the benchmark, and the operation must be careful. Adjustment should be made on the basis of measuring and calculating the influence of span, sag and temperature change. Sag adjustment must be carried out at night with low wind speed and relatively stable temperature. After the correct placement, stay for a period of time and continuously observe and measure for at least 3 days and nights. If all the results are within the allowable deviation range, the sag of the first strand will be adjusted.
(2) In order to ensure the erection quality of steel strands, 1 ~ 2 benchmark steel strands can be added. The position of the reference strand should be set at the edge of the main cable that is not pressed by the general strand.
(3) The allowable deviation of the design sag in the benchmark cable strand span shall comply with the provisions of the drawings. The relative difference of sag between ordinary steel strand and reference steel strand should be in the range of 0 to +5 mm; The relative sag difference of reference strands of upstream and downstream main cables should be within10 mm. (4) If the accuracy of the benchmark cable strand is affected by the erection of the cable strand installed later, and it can no longer play the role of the benchmark cable strand after detection and judgment, a new cable strand should be selected to measure the calculated span, sag and temperature influence, and adjusted to meet the requirements (continued on page 1 15) (continued on page 108).
Because the main cable is nearly a kilometer long, it is very sensitive to temperature, and its length and sag change greatly, so it is necessary to measure the cable strand temperature, and sag measurement should be revised according to design and monitoring. In the suspended state, the cross section of the beam is hexagonal, the filaments are parallel, and the filaments are not twisted or protruded. After adjusting the sag of the middle span and the side span in turn, the jack finally pushes the anchor head to increase or decrease the gasket to adjust the anchor span. During adjustment, the sag of mid-span and side span shall prevail, and the Zhang Liwei of anchor span shall prevail. During erection, attention should be paid to the torsion and displacement of the tower top.
3.8 Pay-off survey, cable clamp lofting and installation survey after main cable tensioning is completed.
When the general strand and reference strand of the main cable are erected, the main cable shall be tightened and the line shape of the main cable shall be measured under the condition that the atmospheric temperature is constant at night.
After the alignment of the main cable is finalized, the monitoring unit will provide the coordinate position of the cable clamp in this state, and temporarily mark the approximate position of the cable clamp on the main cable along the curve of the main cable during the day. When the temperature is stable at night, take the temporary mark as a reference to quickly determine the position of the wire clamp. Before installing the cable clamp, it should be submitted to the monitoring unit, and the center coordinates of the cable clamp should be calculated according to the data such as the deviation of the main tower top, the temperature of the main cable, the atmospheric temperature, the height of the tower and the deviation of the top of the loose cable sleeve. When installing the cable clamp, check whether the position number of the cable clamp is consistent with the position number on the main cable. After the cable clamp is hoisted in place, the center of the cable clamp shall be rechecked, and the cable clamp shall be installed in place after the rechecking is correct. Due to the large number of cable clips, it needs to be completed many times, so the atmospheric temperature and the surface temperature of the main cable should be measured during lofting, and the cable clips should be lofting at the same temperature as much as possible.
3.9 Deviation measurement of main tower in the process of suspender tension and main cable saddle jacking.
During the installation of the main cable saddle, the pre-deflection of the saddle is 64cm. During the tensioning of the boom, push it three times according to the monitoring instruction. Main cable saddle jacking is an important link in suspension bridge construction. The essence of controlling the jacking amount of cable saddle is to control the stress of tower body not to exceed the allowable value to ensure the safety of tower body, and to observe the deflection of main tower in real time during the jacking process to ensure the two main towers.
4 abstract
Through the above description of the cable measurement control method in the construction process of self-anchored suspension bridge, we can understand the key points and difficulties that need to be paid attention to in the construction process, so as to plan ahead when encountering similar operations in the future, quickly enter the working state and improve work efficiency.
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