Bridge prestress tensioning construction method

Abstract

The invention provides a bridge prestress tension construction method, which belongs to the technical field of bridge prestress tension, and comprises the following steps: prestress tension preparation, tension condition setting and tension process design, prestressing tendon selection and inspection, prestress loss and pipeline friction resistance coefficient design, and old tension by adopting a prestress intelligent tension system. The method comprises the following steps of: setting a tension sequence, setting tension control parameters, blowing an atomized defoaming agent before tension construction and grouting so that the atomized defoaming agent is left on the side edge, and then grouting and sealing anchor soil. A web plate bundle, a top plate bundle and a bottom plate bundle are arranged in a bilateral symmetry mode from outside to inside, so that the tension effect is better, meanwhile, the reserved retraction length is calculated, the requirements of relevant standards can be met in the later-stage stress process, a defoaming agent is used for atomization before grouting, a proper amount of defoaming agent is introduced into a vacuum pipeline, and the grouting efficiency is improved. The inner side contains a defoaming agent, but excessive air is not introduced, so that the later grouting effect is better.

Description

Technical Field

[0001] The present invention relates to the technical field of bridge prestress tensioning, and particularly to a construction method for bridge prestress tensioning. Background Art

[0002] To ensure the reliability, safety and service life of a bridge, it is necessary to construct effective prestress. A large number of investigations and tests on prestressed bridges show that the quality hidden dangers of prestressed bridges mainly come from the non-standard construction technology of prestress tensioning and the lack of effective grouting quality control means. The establishment of effective prestress is directly related to the safety, reliability and service life of the bridge. In post-tensioned prestress construction, it is divided into two steps: prestress tensioning construction and corrugated pipe grouting construction. First, the tensioning accuracy is controlled by a prestress tensioning system, and then grout is injected into the corrugated pipe to wrap the prestressed tendons to ensure the effective transfer of prestress. In the corrugated pipe grouting construction step, when the pressure difference between the grout inlet and the grout outlet remains constant within a certain period of time, it is considered that the corrugated pipe is full. At this time, there are often many independent air bags of different sizes between the grout and the corrugated pipe wall. The existence of these air bags will directly affect the safety, reliability and service life of the bridge. Since the corrugated pipe is pre-buried, it is impossible to directly observe the number and size of the air bags during and after the grouting process. Although defoamers are used in the preparation process of the grout to inhibit the formation of bubbles and destroy the formed bubbles, this mainly reduces the bubbles entrained or generated by the grout itself during the mixing process, and is powerless against the bubbles generated during the flowing grouting process into the corrugated pipe with a large diameter and length. In the prior art, to solve this problem, a method of vacuum-assisted grouting is adopted. Specifically, the air in the corrugated pipe is first sucked out by a vacuum pump to make the vacuum degree of the duct reach a certain level, and then the grout is pressed into the corrugated pipe at the other end of the corrugated pipe. However, vacuum-assisted grouting first requires very good airtightness of the corrugated pipe. Secondly, it increases the vacuum pumping equipment and the vacuum pumping step, greatly increasing the construction cost, and all the complete sets of equipment for the vacuum-assisted grouting system rely on imports. Summary of the Invention

[0003] The purpose of the present invention is to provide a construction method for bridge prestress tensioning to solve the technical problems mentioned in the background art.

[0004] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0005] A construction method for bridge prestress tensioning, the method comprising the following steps:

[0006] Step 1: Technical preparation for prestress tensioning, setting of tensioning conditions and design of tensioning technology;

[0007] Step 2: Selection and inspection of prestressed tendons;

[0008] Step 3: Design of prestress loss and pipeline friction coefficient;

[0009] Step 4: Use the intelligent prestress tensioning system for Lao Zhang;

[0010] Step 5: Set the tensioning sequence;

[0011] Step 6: Set the tensioning control parameters and carry out tensioning construction;

[0012] Step 7: Preparation before grouting and mixing of grouting material;

[0013] Step 8: Before grouting, spray atomized defoamer so that atomized defoamer remains on the side, and then carry out grouting;

[0014] Step 9: After the tensioning and grouting work is completed, timely seal the anchor head to prevent the mortar of the anchor head from cracking and the steel strands from being exposed and corroded. The anchor head concrete uses C55 dry shrinkage-compensated concrete.

[0015] Further, the specific process of Step 1 is as follows:

[0016] Carefully review the layout position and elongation of the designed prestressed tendons, classify and number all prestressed bundles at the prestress end. The identification of the numbers is: T is the prestressed bundle of the top slab, B is the prestressed bundle of the bottom slab, F / W is the prestressed bundle of the web, H is the transverse prestressed bundle of the crossbeam, SA / SC is the vertical prestressed bundle. Calibrate the tensioning jack and the oil gauge. Before tensioning, tensioning and anchoring tests must be carried out, and pipeline friction tests must be carried out to ensure the accuracy of prestress;

[0017] The longitudinal prestress of the main girder is designed for two-stage tensioning. The first prestress tensioning is carried out when the concrete strength and elastic modulus of each construction segment of the crossbeam reach 100% of the design value, the age is not less than 10 days, and under the condition of ensuring the process and quality: 6T1-1, 2B15-1, 4B1-1; 6T1-2, 2B15-2, 4B1-2; 6T1-3, 2B15-3, 4B1-3; 6T1-4, 4B1-4, 2B15-4. Then the first batch of longitudinal prestress tendons are tensioned: 2F1~2F4, 2W1~2W2, 6B10, 2B11~2B14, 4T9. Then the transverse prestress tendons H1~H9 of each beam segment are tensioned, among which H5 is tensioned in a single-end staggered manner. Finally, the vertical prestress tendons of each beam segment are tensioned, and the remaining prestress tendons are tensioned in the second stage, which is completed before the second-stage dead load is applied after the initial tensioning of the suspension cables: 2T7, 2T8, 6B16, 4T6, 4B9, 6T5, 4B8, 6T4, 6T3, 8B6, 6T2, 6B5, 2B4, 2B3, 4B2. The tensioning principle: first tension the long tendons, then the short tendons, and the top and bottom plates are tensioned in a staggered and uniform manner. When the prestress steel tendons are tensioned symmetrically at the beam ends, the maximum unbalanced tendon should not exceed 1 bundle. The prestress tensioning adopts double control of elongation and tensile force, and the prestress value is mainly based on the oil gauge reading, and the prestress elongation is used as a check.

[0018] Furthermore, the specific process of step 2 is as follows:

[0019] The prestress steel cables adopt steel strands with corresponding standard strength, elastic modulus and nominal diameter. Inspection of the prestress steel cables: Each batch of steel strands entering the site must have a factory certificate. At the same time, the laboratory takes samples for tests to check their breaking load, yield load, elastic modulus and ultimate elongation tests. The appearance quality of the steel strands is inspected by the construction team plate by plate. There should be no defects such as cracks, small thorns, mechanical damage, scale, and oil stains on the surface. When the prestress anchors enter the site, it is necessary to comprehensively check the quality indicators and conduct appearance, shape and size, hardness, and static load anchoring coefficient performance tests in batches. The quality must meet the design requirements and the provisions of relevant standards. The inspection quantity is: For prestress anchors for prestressed tendons of the same type, same material and same production process and continuously entering the site, every 5000 sets are regarded as a batch. If the number is less than 5000 sets, it is also regarded as a batch and inspected once; for the inspection of the shape and appearance size, 10% of each batch is sampled and not less than 10 sets; for the hardness test, 5% of each batch is sampled and not less than 5 sets; for the static load anchoring coefficient performance test, each batch is sampled once, which is 3 sets.

[0020] Furthermore, the specific process of Step 3 is as follows: longitudinal and transverse prestress losses: the pipe friction coefficient is 0.23, the pipe deviation coefficient is 0.0025, the anchor retraction is calculated as 6 mm at each end, the relaxation loss and shrinkage creep are calculated according to the "Code for Design of Concrete Structures of Railway Bridges and Culverts", and each parameter is tested before prestress tensioning and compared and analyzed with the parameters given in the design. If the analysis error is greater than the set value, the test data will be provided to the design unit for further verification.

[0021] Furthermore, in Step 3, the prestress intelligent tensioning system includes a prestress intelligent tensioning instrument, intelligent jacks, a laptop with a built-in wireless network card, and high-pressure oil pipes. With stress as the control index and elongation error as the calibration index, data on the working pressure of each jack and the elongation value of the steel strand are collected through sensing technology and transmitted to the laptop with a built-in wireless network card in real time for analysis and judgment. At the same time, the pumping station receives system instructions to achieve real-time and precise control of the tension force and loading speed. According to the preset program, instructions are sent by the laptop with a built-in wireless network card to synchronously control each mechanical action of each device, automatically completing the entire tensioning process.

[0022] Furthermore, the specific process in Step 5 is as follows: the overall tensioning sequence is: first the web tendons, then the top slab tendons, and finally the bottom slab tendons; symmetrically from the outside to the inside on both sides;

[0023] Among them, the first batch of staged tensioning tendons: 6T1-1, 2B15-1, 4B1-1; 6T1-2, 2B15-2, 4B1-2; 6T1-3, 2B15-3, 4B1-3; 6T1-4, 4B1-4, 2B15-4. Then the first batch of longitudinal prestress tendons are tensioned: 2F1~2F4, 2W1~2W2, 6B10, 2B11~2B14, 4T9. Then the transverse prestress tendons H1~H9 of each beam segment are tensioned, among which H5 is tensioned in a single-end staggered manner. Finally, the vertical prestress tendons of each beam segment are tensioned;

[0024] For the second batch of tensioning tendons, the tensioning time is after the tensioning of the suspenders is completed. The remaining prestress tendons are T7, 2T8, 6B16, 4T6, 4B9, 6T5, 4B8, 6T4, 6T3, 8B6, 6T2, 6B5, 2B4, 2B3, 4B2;

[0025] For transverse tensioning, the transverse prestress cables H1~H4 and H5~H9 use circular anchors and are tensioned at both ends. H5 uses a flat anchor and is tensioned in a single-end staggered manner. The transverse prestress uses M15-9 tensioning end anchors and M15-4 tensioning end / fixed end P anchors. The metal corrugated pipe with an inner diameter of 80 mm is used for forming the hole. The control stress for tensioning under the anchor of H1~H9 is 1280 Mpa. After the prestress tensioning is completed, grouting and sealing the anchor are carried out in a timely manner. When the transverse prestress tendons H6 and H7 at the middle support cross the embedded pipe of the arch rib, holes are drilled through the arch rib, and the airtightness and position accuracy of the cableway are ensured;

[0026] Vertical tensioning. For the third construction segment, i.e., the segment where the middle support is located, there are a total of 356 vertical prestressed tendons of SA, SB, and SC, which are composed of 3 - φ15.20 prestressed steel strands. The internal diameter of 55mm iron pipes are used for forming holes, and M15 - 3 type anchorages are adopted. The tension control stress under the anchor is 1280MPa. The vertical prestressed cables are tensioned after the concrete strength of the beam body reaches 100% of the design strength and the age is not less than 7 days. The vertical prestress within the arch feet range shall be carried out after the concrete strength of the arch feet reaches the design strength.

[0027] Furthermore, the specific process of step 6 is as follows: Before the formal start of the tensioning construction, conduct tests on the stress loss at the anchor mouth and the friction resistance of the duct in advance to determine the stress loss during the tensioning process, the retraction of the wedge and the steel strand, the actual elongation of the steel strand under the design stress value, and the influence of the actual elastic modulus of the steel strand on the actual tensioning effect. Comprehensively determine the actual stress control value during tensioning and check it with the elongation of the steel strand; Immediately after the tensioning is completed, mark the steel strand prominently with red paint and observe the retraction amount after relaxation.

[0028] Number each steel strand that has been cut to length, and ensure that it is not damaged or contaminated during subsequent handling. Before tensioning, clean the main beam duct and the trumpet of the anchor backing plate, remove the accumulated water and mortar inside. Put a plastic guide head on one end of the cut steel strand and thread the strands manually one by one. When threading the strands, ensure that the lengths exposed at both ends of the box girder are basically equal. After all the strands are threaded, install the anchor and the wedge. Check the oil pump, pressure gauge, and the oil pipeline and its valve joints of the jack. Before preparing for tensioning, ensure that the jack, pressure gauge, and oil pump have been calibrated, and their errors meet the requirements of the inspection standard and are within the specified service life. If replaced, they must be re - calibrated.

[0029] Start tensioning. The tensioning is loaded in three steps to the required position. The tensioning procedure for each steel tendon is: 0 → 20%δcon → 100%δcon, hold the load for 5 minutes → return the oil and anchor. After returning the oil, record the elongation again. Before and after tensioning, measure the exposed length of the wedge to determine the retraction length of the steel strand. Tensioning is controlled by both stress and strain. The reading of the pressure gauge calculated by the stress value controls the tensioning value, and the elongation of the steel strand is used for verification. When making the final supplementary tensioning, it is controlled by the reading of the oil gauge, but the elongation must be recorded accurately. After tensioning is completed, make obvious marks around the steel strand near the anchor with red paint. Re - check after 12 hours to confirm that there is no wire breakage or slippage.

[0030] Furthermore, in step 7, the gaps between the prestressed steel strands outside the anchor should be blocked with epoxy resin mortar to prevent loss of grouting pressure. Flush the duct: Before grouting, the duct should be flushed with pressured water to remove debris inside the hole. After flushing, use an air compressor to blow out the accumulated water inside the hole, but keep the duct wet to ensure good bonding between the cement mortar and the hole wall. During the flushing process, if water seepage or leakage is found, the leak should be blocked in a timely manner.

[0031] The cement mortar is mixed with a small mixer. When mixing the mortar, early-strength water-reducing agent and expansion agent are added. The strength of the cement mortar is not less than M50, the water-cement ratio is 0.4 - 0.45, the bleeding rate is less than 3%, and the consistency is controlled between 14 - 18 s. The interval time from the modulation of the cement mortar to its injection into the pipe should not exceed 40 minutes. The mixed cement mortar is sieved through a 2.5×2.5 mm fine sieve without stopping the agitation.

[0032] Furthermore, in step 8, first atomize the defoamer with an atomizer, then introduce the atomized defoamer into the duct. After vacuum pumping, perform grouting. First, put in a set and quantified atomized defoamer. The amount of the atomized gas of the defoamer is one-tenth to one-twelfth of the original vacuum-pumped air, so that the sides are adhered with the defoamer and no air space is formed, and then perform grouting.

[0033] The grouting sequence is from bottom to top. Press the holes concentrated in one place at one time. For curved ducts and vertical ducts, grout should be injected from the lowest grouting hole, and air should be exhausted and water should be bled from the highest exhaust hole. Use a piston grouting machine to perform grouting slowly and evenly at a pressure of 0.5 - 0.7 Mpa. Grout from one end to the other end. Since the slurry conveying pipeline is long, increase the pressure. When grouting reaches the maximum pressure, there should be a fixed pressure stabilization time until the cement mortar overflows fully at the other end and cement mortar with the specified consistency is discharged. Control the temperature of the cement mortar at 5 - 25 °C. When the temperature is higher than 35 °C, perform grouting at night.

[0034] Furthermore, in step 10, assemble a small wooden formwork into an anchor recess. The cut-off steel bars at the tensioning notch should be welded and restored before sealing the anchor. Add a layer of steel mesh at the anchorage end and the tensioning end, pour with concrete of the same grade, and vibrate thoroughly with a vibrator. Sprinkle water for curing, and remove the formwork after the strength reaches the required level. After removing the formwork, take waterproof measures such as applying waterproof materials on the concrete surface.

[0035] Due to the adoption of the above technical solutions, the present invention has the following beneficial effects:

[0036] The present invention is carried out symmetrically from the outside to the inside, first for the web bundles, then for the top plate bundles, and finally for the bottom plate bundles, which makes the tensioning effect better. At the same time, the length of the reserved retraction is calculated so that the requirements of relevant standards can be met during the later acceptance process. Before grouting, an antifoaming agent is atomized and introduced into the vacuum pipeline in an appropriate amount, so that the side inside contains the antifoaming agent, but too much air is not introduced, and the later grouting effect is better. Conventionally, the antifoaming agent is directly added to the cement slurry, which has a poor effect. The air bubbles in the cement will be reacted in the early stage, but the air bubbles between the side and the cement cannot be eliminated. However, in this application, the atomized antifoaming agent floats in the internal pipeline and reacts after the cement slurry is introduced, which well avoids the problem of air reservation in the pipeline. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a schematic structural diagram of the prestressed intelligent tensioning system of the present invention;

[0038] Figure 2 is a layout diagram of the longitudinal prestressed tendons of the 1 / 2 mid-span section of the present invention;

[0039] Figure 3 is a layout diagram of the longitudinal prestressed tendons of the 1 / 2 beam end section of the present invention;

[0040] Figure 4 is a layout diagram of the transverse prestressed tendons of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0041] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the following preferred embodiments are cited with reference to the accompanying drawings, and the present invention is further described in detail. However, it should be noted that many details listed in the specification are only for enabling the reader to have a thorough understanding of one or more aspects of the present invention, and these aspects of the present invention can be implemented even without these specific details.

[0042] A construction method for prestressed tensioning of a bridge, the method comprising the following steps:

[0043] Step 1: Technical preparation for prestressed tensioning, setting of tensioning conditions and design of tensioning process. Carefully review the layout position and elongation of the designed prestressed tendons, classify and number all prestressed bundles at the prestressed end. The identification of the numbers is: T is the top plate prestressed bundle, B is the bottom plate prestressed bundle, F / W is the web prestressed bundle, H is the transverse prestressed bundle of the crossbeam, SA / SC is the vertical prestressed bundle. Calibrate the tensioning jack and the oil gauge. Before tensioning, tensioning and anchoring tests must be carried out, and a pipeline friction test must be carried out to ensure the accuracy of the prestress;

[0044] The longitudinal prestress of the main girder is designed for two-stage tensioning. The first prestress tensioning is carried out when the concrete strength and elastic modulus of each construction segment of the crossbeam reach 100% of the design value, the age is not less than 10 days, and under the condition of ensuring the process and quality: 6T1-1, 2B15-1, 4B1-1; 6T1-2, 2B15-2, 4B1-2; 6T1-3, 2B15-3, 4B1-3; 6T1-4, 4B1-4, 2B15-4. Then, the first batch of longitudinal prestress tendons are tensioned: 2F1~2F4, 2W1~2W2, 6B10, 2B11~2B14, 4T9. Then, the transverse prestress tendons H1~H9 of each beam segment are tensioned, among which H5 is tensioned in a single-end staggered manner. Finally, the vertical prestress tendons of each beam segment are tensioned, and the remaining prestress tendons are tensioned in the second stage, which is completed before the second-stage permanent load is applied after the initial tensioning of the suspension cables: 2T7, 2T8, 6B16, 4T6, 4B9, 6T5, 4B8, 6T4, 6T3, 8B6, 6T2, 6B5, 2B4, 2B3, 4B2. The tensioning principle is: first tension the long cables, then the short cables, and the top and bottom plates are tensioned in a staggered and uniform manner. When the prestressed steel tendons are tensioned symmetrically at the beam ends, the maximum unbalanced tendon should not exceed 1 bundle. The prestress tensioning adopts double control of elongation and tensile force, and the prestress value is mainly based on the oil gauge reading, and the prestress elongation is used as a check.

[0045] Step 2: Selection and inspection of prestress tendons. The prestressed steel cables adopt steel strands with corresponding standard strength, elastic modulus and nominal diameter. Inspection of the prestressed steel cables: Each batch of steel strands entering the site must have a factory certificate. At the same time, samples are taken by the laboratory for tests on their breaking load, yield load, elastic modulus, and ultimate elongation rate. The appearance quality of the steel strands is inspected by the construction team one by one. There should be no cracks, small thorns, mechanical damage, scale, or oil stains on the surface. When the prestress anchors enter the site, the quality indicators must be comprehensively inspected, and the appearance, shape and size, hardness, and static load anchoring coefficient performance tests are carried out batch by batch. The quality must meet the design requirements and the provisions of relevant standards. The inspection quantity is: For prestress anchors for prestressed tendons of the same type, made of the same material and with the same production process and continuously entering the site, every 5000 sets are regarded as a batch. If the quantity is less than 5000 sets, it is also regarded as a batch, and a spot check is carried out once; for the inspection of the shape and appearance size, 10% of each batch is spot-checked, and not less than 10 sets; for the hardness test, 5% of each batch is spot-checked, and not less than 5 sets; for the static load anchoring coefficient performance test, each batch is spot-checked once, and 3 sets are tested.

[0046] The prestressed steel cables adopt steel strands with a standard strength fpk = 1860 Mpa, an elastic modulus Ep = 1.95×10 5 MPa and a nominal diameter of Φ15.2mm, and the material complies with the GB / T5224-2014 standard.

[0047] Step 3: Design of prestress loss and pipe friction coefficient. Longitudinal and transverse prestress losses: The pipe friction coefficient is 0.23, the pipe deviation coefficient is 0.0025, the retraction of the anchor is calculated as 6 mm at each end, and the relaxation loss, shrinkage and creep are all calculated according to the "Code for Design of Concrete Structures of Railway Bridges and Culverts". Each parameter is tested before prestress tensioning and compared with the parameters given in the design. If the analysis error is greater than the set value, the test data will be provided to the design unit for further verification.

[0048] Step 4: As Figure 1 shown, use the prestress intelligent tensioning system for the old Zhang. The prestress intelligent tensioning system includes a prestress intelligent tensioning instrument, intelligent jacks, a laptop with a built-in wireless network card, and high-pressure oil pipes. With stress as the control index and elongation error as the calibration index, the working pressure of each jack and the elongation value of the steel strand are collected through sensing technology, and the data is transmitted to the laptop with a built-in wireless network card in real time for analysis and judgment. At the same time, the pump station receives the system command to achieve real-time and precise control of the tension force and loading speed. According to the preset program, the laptop with a built-in wireless network card issues commands to synchronously control each mechanical action of each device and automatically complete the entire tensioning process.

[0049] Step 5: As Figures 2 - 3 shown, set the tensioning sequence. The overall tensioning sequence is: first the web tendons, then the top slab tendons, and finally the bottom slab tendons; symmetrically from outside to inside left and right.

[0050] Among them, the first batch of staged tensioning tendons: 6T1-1, 2B15-1, 4B1-1; 6T1-2, 2B15-2, 4B1-2; 6T1-3, 2B15-3, 4B1-3; 6T1-4, 4B1-4, 2B15-4. Then tension the first batch of longitudinal prestress tendons: 2F1~2F4, 2W1~2W2, 6B10, 2B11~2B14, 4T9. Then tension the transverse prestress tendons H1~H9 of each beam segment, where H5 is tensioned alternately at one end. Finally, tension the vertical prestress tendons of each beam segment.

[0051] For the second batch of tensioning tendons, the tensioning time is after the tensioning of the suspenders is completed. The remaining prestress tendons are T7, 2T8, 6B16, 4T6, 4B9, 6T5, 4B8, 6T4, 6T3, 8B6, 6T2, 6B5, 2B4, 2B3, 4B2.

[0052] Horizontal tensioning. For the horizontal prestressed cables H1 - H4 and H5 - H9, circular anchors are used and tensioning is carried out at both ends. For H5, a flat anchor is used and tensioning is carried out in a staggered manner at one end. M15 - 9 tensioning end anchors and M15 - 4 tensioning / fixed end P anchors are used for the horizontal prestress. Metal bellows with an inner diameter of 80 mm are used for forming the holes. The tension control stress under the anchors of H1 - H9 is 1280 Mpa. After the prestress tensioning is completed, grouting and sealing the anchors are carried out in a timely manner. When the prestressed tendons H6 and H7 in the middle support horizontally cross the embedded pipes of the arch rib, holes are drilled through the arch rib, and the tightness and accurate position of the cableway are ensured.

[0053] As Figure 4 shown, for vertical tensioning, in the third construction segment, that is, the segment where the middle support is located, there are a total of 356 vertical prestressed tendons SA, SB, and SC, which are composed of 3 - φ15.20 prestressed steel strands. Metal pipes with an inner diameter of 55 mm are used for forming the holes. M15 - 3 type anchors are used. The tension control stress under the anchors is 1280 MPa. The vertical prestressed cables are tensioned after the concrete strength of the beam body reaches 100% of the design strength and the age is not less than 7 days. The vertical prestress within the arch foot range should be carried out after the concrete strength of the arch foot reaches the design strength.

[0054] Step 6: Set the tension control parameters and carry out the tensioning construction. Before the formal start of the tensioning construction, tests on the stress loss at the anchor mouth and the friction resistance of the duct are carried out in advance to determine the stress loss during the tensioning process, the retraction of the wedge grips and the steel strands, the actual elongation of the steel strands under the design stress value, and the influence of the actual elastic modulus of the steel strands on the actual tensioning effect. Comprehensively determine the actual stress control value during tensioning and verify it with the elongation of the steel strands; immediately after the tensioning is completed, mark the steel strands prominently with red paint and observe the retraction amount after relaxation.

[0055] Number each steel strand that has been cut to length one by one and ensure that it is not damaged or contaminated during subsequent handling. Before tensioning, clean the main beam duct and the trumpet mouth of the anchor plate, remove the accumulated water and mortar inside. Put a plastic guide head on one end of the cut steel strands and thread the strands manually one by one. When threading the strands, ensure that the lengths exposed at both ends of the box girder are basically equal. After all the strands are threaded, install the anchor and wedge grips, install the tensioning jack, and check the oil pump, pressure gauge, oil pipeline of the jack and its valve joints. Before preparing for tensioning, ensure that the jack, pressure gauge, and oil pump have been calibrated, and their errors meet the requirements of the inspection standards and are within the specified service life. If there is a replacement, it must be recalibrated.

[0056] Initial tensioning is carried out in three steps of loading to the required position. The tensioning procedure for each steel strand bundle is: 0 → 20%δcon → 100%δcon, hold the load for 5 minutes → release the oil and anchor. After releasing the oil, record the elongation again. Before and after tensioning, measure the exposed length of the wedge grips respectively to determine the retraction length of the steel strand. Tensioning is controlled by both stress and strain. The reading of the oil pressure gauge calculated by the stress value is used to control the tensioning value, and the elongation of the steel strand is used for verification. When making the final supplementary tensioning, it is controlled by the oil gauge reading, but the elongation must be recorded accurately. After tensioning, make obvious marks around the steel strand near the anchor with red paint. Recheck after 12 hours to confirm that there is no broken wire or slipping wire.

[0057] Step 7: Preparation before grouting and mixing of the grouting material. The gaps between the prestressed steel strands outside the anchor should be blocked with epoxy resin mortar to avoid loss of grouting pressure. Flush the duct: The duct should be flushed with pressurized water before grouting to remove debris inside the hole. After flushing, use an air compressor to blow out the accumulated water inside the hole, but keep the duct wet to ensure good bonding between the cement paste and the duct wall. During the flushing process, if water leakage or seepage is found, the leak should be blocked in time.

[0058] The cement paste is mixed with a small mixer. When mixing, early-strength water-reducing agent and expansion agent are added. The strength of the cement paste is not less than M50, the water-cement ratio is 0.4 - 0.45, the bleeding rate is less than 3%, and the consistency is controlled between 14 - 18 s. The interval time from the modulation of the cement paste to its injection into the pipe should not exceed 40 minutes. The mixed cement paste is sieved through a 2.5×2.5 mm fine sieve without stopping agitation.

[0059] Step 8: Before grouting, first blow in atomized defoamer so that there is atomized defoamer left on the side, and then carry out grouting. First, atomize the defoamer with an atomizer, then introduce the atomized defoamer into the duct. After vacuuming, carry out grouting. First, put in a set amount of atomized defoamer. The amount of atomized gas of the defoamer is one-tenth to one-twelfth of the original vacuumed air, so that the side is adhered with defoamer and no air space is formed, and then carry out grouting.

[0060] The grouting sequence is from bottom to top. Press the holes concentrated in one place at one time. For curved ducts and vertical ducts, grouting should be carried out from the grouting hole at the lowest point, and air and bleeding should be discharged from the exhaust hole at the highest point. Grouting is carried out slowly and evenly with a piston grouting machine at a pressure of 0.5 - 0.7 Mpa from one end to the other end. Due to the long conveying pipeline, the pressure is increased. When grouting reaches the maximum pressure, there should be a fixed pressure stabilization time until the cement paste overflows fully at the other end and the cement paste of the specified consistency is discharged. The temperature of the cement paste is controlled at 5 - 25 °C. When the temperature is higher than 35 °C, grouting is carried out at night.

[0061] Step 9: After the tensioning and grouting work is completed, the anchor head shall be sealed in time to prevent the mortar at the anchor head from cracking and the steel strands from being exposed and corroded. The concrete for sealing the anchor head shall be C55 dry shrinkage-compensated concrete. Assemble small wooden molds into the anchor hole. The cut-off steel bars at the tensioning notch shall be welded and restored before sealing the anchor. A layer of steel mesh shall be added at the anchorage end and the tensioning end, and concrete of the same grade shall be used for pouring. Use a vibrating rod to vibrate it densely, sprinkle water for curing, and remove the formwork after the strength reaches the required level. After removing the formwork, waterproof measures such as applying waterproof materials to the concrete surface shall be taken.

[0062] After the final tensioning is completed, the duct grouting operation must be carried out within 48 hours. Before duct grouting, the sundries and accumulated water in the duct must be removed, and the cement slurry pumped into the duct shall be full and dense. The time interval from the end of cement slurry mixing to the time of pumping into the duct must be controlled within 40 minutes.

[0063] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A bridge prestressing tensioning construction method, characterized in that: The method comprises the following steps: Step 1: Prestressing tensioning technology preparation, tensioning condition setting and tensioning process design; Step 2: Selection and inspection of prestressed tendons; Step 3: Design of prestress loss and pipeline friction coefficient; Step 4: Use prestressed intelligent tensioning system for tensioning; Step 5: Set the tensioning order; Step 6: Set tension control parameters and carry out tension construction; Step 7: Preparation before grouting and mixing of grouting materials; Step 8: Before grouting, blow in atomized defoamer so that atomized defoamer remains on the side, and then grouting is performed; Step 9: After the tensioning and grouting work is completed, the anchor should be sealed in time to prevent the anchor head mortar from cracking and the steel strands from being exposed and rusted. The anchor sealing concrete should be C55 dry-hard shrinkage compensation concrete.

2. A bridge prestressing tensioning construction method according to claim 1, characterized in that: The specific process of step 1 is: Carefully check the designed prestressed tendon layout and elongation, classify and number all prestressed tendons at the prestressed ends, and the numbers are as follows: T for top plate prestressed tendons, B for bottom plate prestressed tendons, F / W for web plate prestressed tendons, H for tie beam transverse prestressed tendons, SA / SC for vertical prestressed tendons, calibrate the tensioning jacks and oil gauges, and perform tensioning and anchoring tests and pipeline friction tests before tensioning to ensure accurate prestressing; The longitudinal prestressing of the main beam is designed to be tensioned twice. The first prestressing is carried out when the concrete strength and elastic modulus of each construction segment of the tie beam reach 100% of the design value, the age is not less than 10d, and the process and quality are guaranteed: 6T1-1, 2B15-1, 4B1-1; 6T1-2, 2B15-2, 4B1-2; 6T1-3, 2B15-3, 4B1-3; 6T1-4, 4B1-4, 2B15-4, and then the first batch of longitudinal prestressed tendons are tensioned: 2F1~2F4, 2W1~2W2, 6B10, 2B11~2B14, 4T9, and then the transverse prestressed tendons H of each beam segment are tensioned. 1~H9, among which H5 is tensioned at one end in a staggered manner, and finally the vertical prestressed tendons of each beam section are tensioned. The remaining prestressed tendons are tensioned for the second time. After the initial tensioning of the suspender cables, the tensioning is completed before the second phase of the constant load is put on the bridge: 2T7, 2T8, 6B16, 4T6, 4B9, 6T5, 4B8, 6T4, 6T3, 8B6, 6T2, 6B5, 2B4, 2B3, 4B2. The tensioning principle is: long cables first, then short cables, and the top and bottom plates are tensioned evenly and staggered. When the prestressed steel tendons are tensioned symmetrically at the beam ends, the maximum unbalanced tendon should not exceed 1 tendon. The prestressing is controlled by both elongation and tensioning force. The prestress value is mainly based on the oil gauge reading, and the prestressing elongation is used as a check.

3. A bridge prestressing tensioning construction method according to claim 1, characterized in that: The specific process of step 2 is: Prestressed steel cables use steel strands with corresponding standard strength, elastic modulus and nominal diameter. Inspection of prestressed steel cables: Each batch of steel strands entering the site must have a factory certificate. At the same time, the laboratory takes samples for testing to see its breaking load, yield load, elastic modulus, and ultimate elongation. The appearance quality of the steel strands is checked by the construction team for each coil. There must be no cracks, small thorns, mechanical damage, iron oxide, or oil stains on the surface. When prestressed anchors enter the site, the quality indicators must be fully inspected and the appearance and appearance of each batch must be inspected. For shape, size, hardness, static load anchorage coefficient performance tests, the quality must meet the design requirements and relevant standards. The inspection quantity is: 5,000 sets of prestressed tendon anchors of the same type, material and production process and continuously delivered to the site are counted as a batch. If there are less than 5,000 sets, they are also counted as a batch and inspected once; for shape and appearance size inspection, 10% of each batch is inspected, and no less than 10 sets; for hardness test, 5% of each batch is inspected, and no less than 5 sets; for static load anchorage coefficient performance test, 3 sets are inspected once for each batch.

4. A bridge prestressing tensioning construction method according to claim 1, characterized in that: The specific process of step 3 is as follows: longitudinal and transverse prestress loss: the pipeline friction coefficient is 0.23, the pipeline deviation coefficient is 0.0025, the anchor retraction is 6mm at each end, and the relaxation loss and shrinkage creep are calculated according to the "Railway Bridge and Culvert Concrete Structure Design Code". All parameters are tested before prestressing and compared with the design parameters. If the analysis error is greater than the set value, the test data will be provided to the design unit for further verification.

5. A bridge prestressing tensioning construction method according to claim 1, characterized in that: In step 3, the prestressed intelligent tensioning system includes a prestressed intelligent tensioning instrument, an intelligent jack, a laptop computer with a built-in wireless network card, and a high-pressure oil pipe. Stress is used as a control indicator, and the elongation error is used as a calibration indicator. The working pressure of each jack and the elongation value of the steel strand are collected through sensing technology, and the data are transmitted to the laptop computer with a built-in wireless network card in real time for analysis and judgment. At the same time, the pump station receives system instructions to achieve real-time and precise control of the tensioning force and loading speed. According to the preset program, the laptop computer with a built-in wireless network card issues instructions to synchronously control each mechanical action of each device to automatically complete the entire tensioning process.

6. A bridge prestressing tensioning construction method according to claim 1, characterized in that: The specific process in step 5 is that the overall tensioning sequence is: first the web beam, then the top beam, and finally the bottom beam; proceed symmetrically from outside to inside; The first batch of prestressed beams are tensioned in batches: 6T1-1, 2B15-1, 4B1-1; 6T1-2, 2B15-2, 4B1-2; 6T1-3, 2B15-3, 4B1-3; 6T1-4, 4B1-4, 2B15-4, and then the first batch of longitudinal prestressed beams are tensioned: 2F1~2F4, 2W1~2W2, 6B10, 2B11~2B14, 4T9, and then the transverse prestressed beams H1~H9 of each beam section are tensioned, among which H5 is tensioned at a single end and staggered, and finally the vertical prestressed beams of each beam section are tensioned; The second batch of tensioning tendons, tensioning time is after the hanger tensioning is completed, the remaining prestressed tendons T7, 2T8, 6B16, 4T6, 4B9, 6T5, 4B8, 6T4, 6T3, 8B6, 6T2, 6B5, 2B4, 2B3, 4B2; Transverse tensioning: circular anchors are used for transverse prestressed cables H1~H4, H5~H9, and tensioning is performed at both ends. Flat anchors are used for H5, and staggered tensioning is performed at one end. M15-9 tensioning end anchors and M15-4 tensioning end / fixed end P anchors are used for transverse prestressing. Metal corrugated pipes with an inner diameter of 80mm are used for hole formation. The tensioning control stress under the H1~H9 anchor is 1280Mpa. Grouting and anchor sealing are performed in time after prestressing is completed. When the transverse H6 and H7 prestressed bundles at the middle support cross the arch rib embedded pipes, holes are punched through the arch ribs to ensure the tightness and accurate position of the cableway. Vertical tensioning, the third construction section, that is, the section where the middle support is located, has a total of 356 SA, SB, and SC vertical prestressed tendons, which are composed of 3-φ15.20 prestressed steel strands. The holes are made of iron pipes with an inner diameter of 55mm. M15-3 anchors are used. The tensioning control stress under the anchor is 1280MPa. The vertical prestressed cables are tensioned after the concrete strength of the beam body reaches 100% of the design strength and the age is not less than 7d. The vertical prestressing within the arch foot range should be carried out after the concrete strength of the arch foot reaches the design strength.

7. A bridge prestressing tensioning construction method according to claim 1, characterized in that: The specific process of step 6 is to conduct tests on anchor stress loss and channel friction in advance before the formal start of tensioning construction to determine the stress loss during tensioning, the shrinkage of the clips and steel strands, the actual elongation of the steel strands under the design stress value, and the actual elastic modulus of the steel strands on the actual tensioning effect, comprehensively determine the actual stress control value during tensioning, and verify it with the elongation of the steel strands; immediately after the tensioning is completed, use red paint to mark the steel strands and observe the shrinkage after tensioning; The steel strands that have been cut are numbered one by one, and they are ensured not to be damaged or contaminated during the subsequent handling process. Before tensioning, the main beam channel and the bell mouth of the anchor pad are cleaned to remove the accumulated water and mortar inside. The plastic guide head is put on one end of the steel strands that have been cut, and the strands are manually threaded one by one. When threading the strands, ensure that the exposed lengths at both ends of the box beam are basically equal. After all the strands are threaded, start to install anchors and clips, install the tensioning jack, check the oil pump, pressure gauge, jack oil pipeline and its valve joints. Before preparing for tensioning, ensure that the jack, oil pressure gauge and oil pump have been calibrated, and their errors meet the inspection requirements. They are within the specified service life. If they are replaced, they must be re-calibrated. Start tensioning, which is divided into three steps to load into place. The tensioning procedure for each steel strand is: 0→20%δcon→100%δcon, hold the load for 5 minutes→return oil and anchor. After returning oil, record the elongation again. Measure the exposed length of the clip before and after tensioning to determine the retracted length of the steel strand. Stress-strain dual control is adopted for tensioning. The tensioning value is controlled by the oil pressure gauge reading calculated by the stress value, and the elongation of the steel strand is used for verification. The oil gauge reading is used for control during the final tensioning, but the elongation must be recorded realistically. After the tensioning is completed, make obvious marks around the steel strand near the anchor with red paint. Recheck after 12 hours to confirm that there is no broken wire or slipped wire.

8. A bridge prestressing construction method according to claim 1, characterized in that: In step 7, the gaps between the prestressed steel strands outside the anchor should be plugged with epoxy resin mortar to avoid loss of grouting pressure. The holes should be flushed with pressurized water before grouting to remove debris in the holes. After flushing, the water in the holes should be blown away with an air compressor, but the holes should be kept moist to ensure good bonding between the cement slurry and the hole wall. During the flushing process, if water or leakage is found, the leak should be plugged in time. The cement slurry is mixed with a small slurry mixer. Early strength water-reducing agent and expansive agent are added during mixing. The strength of the cement slurry is not less than M50, the water-cement ratio is 0.4-0.45, the water bleeding rate is less than 3%, and the consistency is controlled between 14 and 18 seconds. The interval time from the preparation of the cement slurry to the injection into the pipe should not exceed 40 minutes. The mixed cement slurry is passed through a 2.5×2.5mm fine sieve without stopping stirring.

9. A bridge prestressing tensioning construction method according to claim 1, characterized in that: In step 8, the defoamer is first atomized using an atomizer, and then the atomized defoamer is passed into the channel. After vacuuming, grouting is performed. A set amount of atomized defoamer is first added. The amount of atomized defoamer gas is one tenth to one twelfth of the original vacuumed air, so that the side is adhered to the defoamer and no air space is formed, and then grouting is performed; The grouting sequence is from bottom to top, and all the holes concentrated in one place should be grouted at one time. For curved channels and vertical channels, grouting should be done from the lowest grouting hole, and exhaust and water should be exuded from the highest exhaust hole. Grouting is done slowly and evenly with a piston grouting machine at a pressure of 0.5-0.7Mpa, from one end to the other. Due to the long grouting pipeline, the pressure is increased. When grouting reaches the maximum pressure, there should be a fixed pressure stabilization time until the cement slurry at the other end is full and overflows, and cement slurry of specified consistency is discharged. The cement slurry temperature is controlled at 5-25℃. When the temperature is higher than 35℃, grouting is carried out at night.

10. A bridge prestressing tensioning construction method according to claim 1, characterized in that: In step 10, small wooden molds are used to assemble the anchor holes. The cut steel bars at the tensioning notch should be welded and restored before sealing the anchors. A layer of steel mesh is added at the anchoring end and the tensioning end. The concrete of the same grade is poured and vibrated with a vibrating rod to make it dense. Water is sprinkled for curing. The mold is removed after the strength is reached. After the mold is removed, the concrete surface is waterproofed by brushing waterproof materials.

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