A method for constructing concrete cap beams for multi-span portal piers and the cap beams themselves

Abstract

This invention relates to the field of cap beam construction technology, and discloses a method for constructing multi-span portal pier concrete cap beams and the cap beam itself. The construction method includes first casting the cap beam sections of the central pier and side piers, then constructing the cap beam segments span by span using a single set of truss hoisting equipment, implementing alternating half-width traffic control; and employing a cross-anchored single-end tensioning prestressed system, with the first and second steel strands extending from the top of the central pier to the first and second side piers respectively, and single-end tensioning completed on the side piers away from the central pier. This invention allows for the completion of the entire construction of double-span or even multi-span cap beams using a single set of truss hoisting equipment, eliminating the need for separate equipment for each left and right span, significantly improving equipment utilization across the entire project and substantially reducing total construction costs. Furthermore, the cross-anchored single-end tensioning prestressed arrangement divides the steel strands into two groups, extending from the top of the central pier to the side piers respectively, halving the resistance to strand threading and construction time.

Description

Technical Field

[0001] This invention relates to the field of cap beam construction technology, specifically to a method for constructing a multi-span portal pier concrete cap beam and the cap beam itself. Background Technology

[0002] Portal piers are a common form of bridge substructure, consisting of two or more columns and a cap beam forming a portal-shaped frame structure. Portal piers can be single-span or multi-span structures; the column forms are diverse, including Y-shaped columns, straight columns, and inclined columns. Portal piers are widely used when bridges need to cross existing highways or railways, with the cap beam spanning the existing track, and the superstructure extending from the cap beam to both sides. The cap beam structure mainly includes concrete structures, steel structures, and steel-concrete composite structures.

[0003] Currently, the construction methods and prestressing arrangements for portal pier cap beams mainly include the following: (a) Scaffolding method: The scaffolding method involves erecting a full-span scaffold or steel pipe columns under the cap beam, laying the bottom formwork, tying the reinforcing bars, pouring concrete, and curing it. This method is technologically mature and widely applicable, but it has significant limitations in traffic-sensitive areas: the scaffolding erection requires a large amount of space underneath, causing long-term and widespread disruption to existing traffic; the foundation treatment and stability control of the scaffolding are difficult, especially in narrow spaces such as the median strip of highways; for large-span cap beams, the material consumption and erection period of the scaffolding system increase significantly, resulting in poor economic efficiency.

[0004] (II) Segmental Assembly Method Using Suspended Equipment: To minimize the impact on traffic below, the segmental assembly method using suspended equipment has been developed in recent years. This method divides the cap beam into several precast segments, using specialized suspended equipment suspended between the piers as a load-bearing and operating platform. The segments are then hoisted and assembled one by one, connected together through wet joints to form a whole. Compared to the scaffolding method, this method has less impact on the road space below and is gradually being applied in scenarios with limited construction conditions. However, the traditional segmental assembly method using suspended equipment still faces the following problems in practical applications: (1) Large equipment investment. For a typical double-span portal pier with one span on each side, the traditional approach is to set up a separate suspension system for each span, requiring a total of two sets, such as... Figure 1 As shown, a single large hoisting device can weigh over 100 tons and is equipped with a hydraulic system, traveling mechanism, safety facilities, etc., making it very expensive. For new or expanded bridge projects, a single section typically includes dozens or even hundreds of portal pier cap beams, and the total investment in equipment procurement or leasing may account for 30% of the total cost of cap beam construction.

[0005] (2) Traffic control covers a large area and lasts for a long time. When using two sets of equipment, traffic control is required for a large area regardless of whether the left and right spans are constructed simultaneously or in different time periods. If the left and right spans are constructed simultaneously, most or even all lanes in both directions need to be closed. If the construction is carried out in different time periods, the area of ​​each closure is slightly reduced, but the cumulative control time increases exponentially, and it still involves the repeated closure and reopening of roads on both sides, which puts continuous pressure on the traffic capacity of the regional road network.

[0006] (3) The prestressed steel strands are arranged in a continuous bundle along the entire length, making the tensioning operations at both ends complex. In traditional prestressed systems, the steel strands are arranged continuously along the entire length of the cap beam, such as... Figure 2 As shown, each steel strand has two ends located at both ends of the cap beam, requiring simultaneous tensioning at both ends during construction. For large-span cap beams, the continuous steel strands are long, the resistance to threading is high, and simultaneous tensioning at both ends requires twice the tensioning equipment and personnel, demanding high coordination.

[0007] In prestressed concrete bridges, the arrangement and tensioning methods of steel strands mainly include the following: (1) Continuous bundle with tensioning at both ends. This is the most common arrangement for portal pier cap beams. All steel bundles run through the entire length of the cap beam, and working anchor plates are installed at both ends of each steel bundle. During construction, both ends are tensioned simultaneously. The advantage is that the stress system is clear. The disadvantage is that the steel bundles are long, and the length of a double-span cap beam can reach 40~65m, which makes it difficult to thread the bundles. Tensioning equipment and operators need to be configured at both ends at the same time, and the end anchors are dense.

[0008] (2) Short strand segment arrangement. In continuous beam bridges, there is a practice of arranging prestressed steel strands in segments by span, with independent short strands set in each span, and steel strands in adjacent spans anchored in the pier top area by anchorages. However, this method is mainly used for local reinforcement in the negative bending moment zone of continuous beams, and each segment of steel strand still needs to be tensioned at both ends, without changing the tensioning method of a single steel strand.

[0009] (3) Tensioning in batches. There is a practice of tensioning prestressed steel strands in batches in T-beams and box girders. However, the purpose of batching is to adapt to the change of the stress stage of the structure (such as tensioning some steel strands first to bear the self-weight, and then tensioning the remaining steel strands to bear the second-stage dead load). It does not change the end anchorage method of a single steel strand. For wide cap beams, each steel strand is still tensioned at both ends.

[0010] In summary, existing technologies for the construction of multi-span portal pier cap beams generally suffer from problems such as low equipment utilization, large and prolonged traffic impact, and the inherent requirement of simultaneous construction of multiple spans due to the prestressed system. Existing prestressed steel strand arrangement methods do not involve cross-anchoring arrangements of steel strands in groups or symmetrical single-end tensioning of individual strands. Summary of the Invention

[0011] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for constructing multi-span portal pier concrete cap beams and the cap beam itself. This method utilizes a single set of truss hoisting equipment to complete the entire construction of double-span or even multi-span cap beams, eliminating the need for separate equipment sets for each left and right span. This significantly improves equipment utilization across the entire project and substantially reduces total construction costs. Furthermore, the invention employs a cross-anchoring, single-end tensioning prestressed arrangement, dividing the steel strands into two groups that extend from the top of the central pier to the side piers, halving the resistance to strand threading and construction time.

[0012] To address the aforementioned technical problems, this invention provides a method for constructing a multi-span portal pier concrete cap beam, comprising: Cast-in-place cap beam sections are poured on the middle and side piers of the current portal pier. Prestressed holes are opened on the top and both sides of the cast-in-place cap beam section of the middle pier, and prestressed holes are opened on both sides of the cast-in-place cap beam section of the side pier. Traffic is closed between the central pier and the first side pier, wherein the side piers include the first side pier and the second side pier on both sides of the central pier; The cap beam segment between the central pier and the first side pier, and the cap beam segment on the side of the first side pier away from the central pier; Restore traffic between the central pier and the first side pier; The first steel strand is inserted into the first side pier through the prestressed hole at the top of the middle pier and the anchor is installed. The first steel strand is tensioned at one end on the side pier away from the middle pier. Grouting and anchor sealing are carried out on the corresponding duct of the first steel strand. Traffic between the central pier and the second side pier is closed off; construction is carried out on the cap beam segment between the central pier and the second side pier, as well as the cap beam segment on the side of the second side pier away from the central pier. Restore traffic between the central pier and the second side pier; The second steel strand is inserted from the prestressed hole at the top of the middle pier to the second side pier and the anchor is installed. The second steel strand is tensioned at one end on the side of the second side pier away from the middle pier. Grouting and anchor sealing operations are carried out on the corresponding duct of the second steel strand. Repeat the above steps to construct the next portal pier.

[0013] In some embodiments, all the first steel strands are symmetrically distributed about the vertical centerline of the cap beam on the end face of the tensioning end, and jack operating space is reserved between adjacent first steel strands.

[0014] In some embodiments, at the top of the pier, the first and second steel strands are arranged in a cross pattern on the elevation and staggered by a certain distance on the plane to avoid conflict between the prestressed pipes at the intersection.

[0015] In some embodiments, the cap beam segment between the central pier and the first side pier, and the portion of the cap beam segment on the side of the first side pier away from the central pier, includes: A truss and guide beam are installed on the first side pier, and the guide beam is supported on the middle pier. The movable truss is supported at both ends by the first side pier and the middle pier; The cap beam segments are hoisted using the hoisting mechanism on the truss and connected to the truss by suspension; adjacent cap beam segments are glued together, and cap beam segments and cast-in-place cap beam sections are connected by wet joints.

[0016] In some embodiments, the cap beam segment between the central pier and the first side pier, and the portion of the cap beam segment on the side of the first side pier away from the central pier, includes: Rigid supports are installed on the cast-in-place section of the cap beam of the middle pier, and auxiliary supports and the first flexible support are installed on the cast-in-place section of the cap beam of the first side pier. After the truss and guide beam are connected together on the ground, they are hoisted together to the top of the outriggers. The rigid outriggers are supported on the guide beams, while the auxiliary outriggers and the first flexible outriggers are supported on the truss. The movable truss is supported at both ends by rigid legs on the central pier, auxiliary legs on the first side pier, and a first flexible leg.

[0017] In some embodiments, the cap beam segment between the central pier and the first side pier, and the portion of the cap beam segment on the side of the first side pier away from the central pier, includes: Before hoisting the cap beam segment using the hoisting mechanism on the truss, adjust the auxiliary legs to separate them from the top surface of the cast-in-place cap beam segment of the first side pier, and adjust the first flexible legs to ensure that the truss is in a horizontal working state.

[0018] In some embodiments, the cap beam segment between the central pier and the second side pier, and the portion of the cap beam segment on the side of the second side pier away from the central pier, include: Move the truss and guide beam forward so that both ends of the truss are supported by the middle pier and the second side pier, and remove the guide beam; The cap beam segments are hoisted using the hoisting mechanism on the truss, and then connected to the truss by suspension. Adjacent cap beam segments are glued together, and cap beam segments and cast-in-place cap beam sections are connected by wet joints.

[0019] In some embodiments, moving the truss and guide beam forward includes: The truss moves forward until the auxiliary legs support the rear end of the truss; Using auxiliary legs to lift the truss, the first flexible leg is moved to the middle of the already erected cap beam and anchored to the cap beam segment; The first flexible support leg is used to lift the truss, the auxiliary support leg is removed, and the hoisting mechanism moves between the rigid support leg and the first flexible support leg. The second flexible support leg is installed on the second side pier in advance, and the truss continues to move forward until the front end of the guide beam is supported by the second flexible support leg on the second side pier. The hoisting mechanism moves between the middle pier and the second side pier, releases the anchorage between the first flexible leg and the cap beam segment, and the hydraulic cylinder of the first flexible leg retracts, suspending it below the truss. The truss continues to move forward until the front end of the truss is supported by the second flexible leg on the second side pier; Remove the guide beam.

[0020] In some embodiments, moving the truss and guide beam forward includes: After the guide beam is removed, the truss continues to move forward, so that the position of the truss near the front end is supported by the second flexible leg on the second side pier. The first flexible leg at the rear is lifted by the hoisting mechanism, moved laterally from the internal space of the truss to the front end, and transferred to the ground.

[0021] On the other hand, the present invention provides a cap beam obtained by the aforementioned multi-span portal pier concrete cap beam construction method, wherein a plurality of first prestressed tubes and a plurality of second prestressed tubes are pre-embedded in the cap beam. One end of the plurality of first prestressed tubes extends to the top surface of the middle part of the cap beam, and the other end of the plurality of first prestressed tubes extends to one end face of the cap beam. One end of the plurality of second prestressed tubes extends to the top surface of the middle part of the cap beam, and the other end of the plurality of second prestressed tubes extends to the other end face of the cap beam. Prestressed steel strands are provided in both the first prestressed tubes and the second prestressed tubes. The steel strands include first steel strands passing through the first prestressed tubes and second steel strands passing through the second prestressed tubes. Both the first steel strands and the second steel strands are single-end tensioned and anchored.

[0022] The beneficial effects of this invention are as follows: 1. This invention can complete the construction of double-span or even multi-span cap beams using a single set of truss hoisting equipment, eliminating the need to set up a separate set of equipment for each left and right span, thus greatly improving the equipment utilization rate of the entire project section and significantly reducing the total construction cost.

[0023] 2. The present invention adopts a half-width alternating construction and traffic control scheme, which closes only the half of the road where the construction span is located at any given time, while the other half of the road remains open to traffic; the space above and below the non-construction span of the same portal pier is completely open, and equipment crossing operations can be arranged during the nighttime off-peak traffic period.

[0024] 3. This invention adopts a prestressed arrangement method of cross-anchoring and single-end tensioning, dividing the steel strands into two groups that extend from the top of the central pier to the two side piers respectively. The length of a single steel strand is shortened by about 50%, and the resistance to threading the strands and the construction time are halved. Single-end tensioning reduces the investment in tensioning equipment and operators by about 50%, eliminates the need for synchronous coordination at both ends, and makes tensioning accuracy easier to control. At the same time, the top of the central pier can serve as an operating platform for steel strand unloading, storage, and threading, eliminating the need for an additional end operating platform, further simplifying the construction process.

[0025] 4. The two sets of steel strands (the first steel strand and the second steel strand) of the present invention overlap in the anchorage sector area at the top of the pier, providing sufficient compressive stress reserve for the negative bending moment area at the top of the pier, which fully meets the structural stress requirements. 5. The single-end tensioning combined with the shortened steel strand length of the present invention results in a lower total duct friction loss compared to the traditional long-strand tensioning scheme. The effective prestress at the mid-span and 1 / 4-span sections of the cap beam is essentially equivalent to that of the traditional scheme, ensuring the long-term safety of the structure.

[0026] 6. This invention achieves smooth truss crossing by coordinating rigid legs, auxiliary legs, and flexible legs; during the crossing process, the overturning stability of the guide beam in the maximum cantilever state is calculated in advance to ensure construction safety; after the crossing is completed, the hoisting operation of the secondary span cap beam segment can be carried out immediately, resulting in good construction continuity and effectively shortening the overall construction period. Attached Figure Description

[0027] Figure 1 This is a construction diagram from the existing technology; Figure 2 Elevation and plan views of the steel strand arrangement inside the cap beam in the existing technology; Figure 3 This is a plan view of the steel strand arrangement inside the cap beam of the present invention; Figure 4 for Figure 3 The left view; Figure 5 for Figure 3 Enlarged schematic diagram of the middle structure; Figure 6 This is a schematic diagram of step S1 of the present invention; Figure 7 This is a schematic diagram of the installation of the support legs, truss, and guide beam in step S2 of the present invention; Figure 8 This is a schematic diagram of the hoisting of the cap beam segment in step S2 of the present invention; Figure 9 This is a schematic diagram of the bonding and pouring of wet joints between the cap beam segments in step S2 of the present invention; Figure 10 This is a schematic diagram of the insertion of the first steel strand in step S3 of the present invention; Figure 11 This is a schematic diagram illustrating the disconnection between the suspension and the cap beam segment in step S3 of the present invention. Figure 12 This is a schematic diagram of the truss moving forward to be supported by the auxiliary leg at the tail end of the truss in step S4 of the present invention. Figure 13 This is a schematic diagram of moving the first flexible support leg and disassembling the auxiliary support leg in step S4 of the present invention. Figure 14This is a schematic diagram of the truss moving forward to be supported by the second flexible leg at the front end of the guide beam in step S4 of the present invention; Figure 15 This is a schematic diagram of removing the support of the first flexible leg and dismantling the guide beam in step S4 of the present invention. Figure 16 This is a schematic diagram of removing the first flexible support leg in step S4 of the present invention; Figure 17 This is a schematic diagram of the hoisting of the cap beam segment in step S4 of the present invention; Figure 18 This is a schematic diagram of the bonding and pouring of wet joints between the cap beam segments in step S4 of the present invention. Figure 19 This is a schematic diagram of step S5 of the present invention; Figure 20 This is a schematic diagram illustrating the construction of the cap beam for a portal pier according to the present invention.

[0028] Reference numerals: Central pier 1; First side pier 2; Second side pier 3; Cast-in-place section of cap beam 4; Cap beam segment 5; First steel strand 6; Second steel strand 7; Truss 8; Guide beam 9; Lifting mechanism 10; Rigid support leg 11; Auxiliary support leg 12; First flexible support leg 13; Second flexible support leg 14; Suspension 15. Detailed Implementation

[0029] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0030] This invention provides a method for constructing a multi-span portal pier concrete cap beam, comprising: S1. Cast the cap beam section 4 on the middle pier 1 and the side piers of the current portal pier, such as... Figure 6 As shown, prestressed pipes are pre-embedded in the cast-in-place sections 4 of the cap beams of both the central pier 1 and the side piers. The prestressed pipes are corrugated pipes. The prestressed pipes form prestressed holes at the top and both sides of the cast-in-place section 4 of the cap beam of the central pier 1, and prestressed pipes form prestressed holes on both sides of the cast-in-place section 4 of the cap beam of the side piers.

[0031] The positioning and pre-embedding of prestressed pipes for each cap beam segment 5 shall be completed in advance according to the principles of cross anchoring and symmetrical bundle division.

[0032] S2. Close the traffic between the central pier 1 and the first side pier 2, wherein the side piers include the first side pier 2 and the second side pier 3 on both sides of the central pier 1. In this embodiment, the side pier on the left side of the central pier 1 is the first side pier 2, and the side pier on the right side of the central pier 1 is the second side pier 3. The cap beam segment 5 between pier 1 and the first side pier 2 during construction, and the cap beam segment 5 on the side of the first side pier 2 away from the middle pier 1.

[0033] Step S2 includes: S21, closing the traffic between the central pier 1 and the first side pier 2.

[0034] S22. Install rigid support legs 11 on the cast-in-place section 4 of the cap beam of the middle pier 1. Install auxiliary support legs 12 and first flexible support legs 13 on the cast-in-place section 4 of the cap beam of the first side pier 2. The first flexible support leg 13 is located between the auxiliary support leg 12 and the rigid support leg 11. Both the rigid support leg 11 and the first flexible support leg 13 are anchored to the cast-in-place section 4 of the cap beam through embedded parts. Install the second flexible support leg 14 on the second side pier 3 in advance to prepare for the lateral movement of the hoisting equipment 15 across the span. Set up a walking system on the rigid support leg 11. The walking system is located between the rigid support leg 11 and the truss 8 and is used to push the truss 8 to move. Figure 7 As shown.

[0035] S23. After connecting the truss 8 and the guide beam 9 into a whole on the ground, they are hoisted together to the top of the support leg. At this time, the front end of the guide beam 9 does not encroach on the road boundary above the span. The rigid support leg 11 is supported on the guide beam 9, and the auxiliary support leg 12 and the first flexible support leg 13 are supported on the truss 8. The guide beam 9 is installed at the front end of the truss 8.

[0036] S24. Move the truss 8 so that both ends of the truss 8 are supported by the rigid legs 11 on the central pier 1, the auxiliary legs 12 on the first side pier 2, and the first flexible legs 13. The left end of the truss 8 is located to the left of the first side pier 2. Figure 8 As shown.

[0037] S25. Before hoisting the cap beam segment 5 using the hoisting mechanism 10 (such as a crane) on the truss 8, adjust the auxiliary support leg 12 so that the auxiliary support leg 12 is separated from the top surface of the cap beam cast-in-place segment 4 of the first side pier 2, and adjust the first flexible support leg 13 so that the truss 8 is in a horizontal working state.

[0038] S26. Using the hoisting mechanism 10 on truss 8, hoist the cap beam segment 5 and connect the cap beam segment 5 to truss 8 via the hanger 15; glue adjacent cap beam segments 5 together (using epoxy resin adhesive on mating surfaces), and adjust the alignment to the design elevation, such as... Figure 9 As shown.

[0039] The cap beam segment 5 and the cast-in-place cap beam segment 4 are connected by a wet joint: a wet joint formwork is installed, and wet joint concrete is poured between the cap beam segment 5 and the cast-in-place cap beam segment 4.

[0040] S27. Restore traffic between the central pier 1 and the first side pier 2.

[0041] S3, such as Figure 10As shown, after the wet joint concrete reaches the design strength, the steel strands are cut and prepared at the top of the cap beam segment 5. The first steel strand 6 is inserted from the prestressed hole at the top of the middle pier 1 to the first side pier 2 and anchorages are installed, so that one end of the first steel strand 6 is anchored to the top of the middle pier 1. On the side of the first side pier 2 away from the middle pier 1, jacks are used to tension the first steel strand 6 at one end, and grouting and anchor sealing are carried out in the corresponding ducts of the first steel strand 6. The connection between the hanging device 15 and the cap beam segment 5 is then disconnected. Figure 11 As shown.

[0042] S4. Close traffic between the central pier 1 and the second side pier 3, construct the cap beam segment 5 between the central pier 1 and the second side pier 3, and the partial cap beam segment 5 on the side of the second side pier 3 away from the central pier 1.

[0043] Step S4 includes: S41, truss 8 moves forward until the auxiliary leg 12 supports the tail end of truss 8, as shown. Figure 12 As shown.

[0044] S42. Using the auxiliary support leg 12 to lift the truss 8, move the first flexible support leg 13 to the middle of the already erected cap beam and anchor it to the cap beam segment 5, as follows. Figure 13 As shown.

[0045] S43. The first flexible support leg 13 is used to lift the truss 8 and anchor it to the truss 8. The auxiliary support leg 12 is removed. The hoisting mechanism 10 moves between the rigid support leg 11 and the first flexible support leg 13, so that the center of gravity of the structure above the first flexible support leg 13 and the rigid support leg 11 is located between the rigid support leg 11 and the first flexible support leg 13.

[0046] S44, truss 8 continues to move forward until the front end of guide beam 9 is supported by the second flexible support leg 14 on the second side pier 3, such as Figure 14 As shown. During the forward movement, the position of the hoisting mechanism 10 is adjusted, and the overturning stability of the overall structure consisting of the hoisting mechanism 10 and the cap beam in the maximum front cantilever state of the guide beam 9 is calculated in advance to ensure that overturning will not occur during the crossing.

[0047] S45. The hoisting mechanism 10 moves between the middle pier 1 and the second side pier 3, releases the anchorage between the first flexible support leg 13 and the cap beam segment 5, and the hydraulic cylinder of the first flexible support leg 13 retracts, suspending it below the truss 8. Figure 15 As shown.

[0048] S46, Truss 8 continues to move forward until the front end of Truss 8 is supported by the second flexible leg 14 on the second side pier 3; remove guide beam 9.

[0049] S47. After removing the guide beam 9, the main beam continues to move forward, so that the position of the truss 8 near the front end is supported by the second flexible leg 14 on the second side pier 3. The first flexible leg 13 at the rear is lifted by the hoisting mechanism 10, moved laterally from the internal space of the truss 8 to the front end, and transferred to the ground. Figure 16 As shown.

[0050] S48. Using the hoisting mechanism 10 on the truss 8, hoist the cap beam segment 5 between the middle pier 1 and the second side pier 3, as well as a portion of the cap beam segment 5 on the side of the second side pier 3 away from the middle pier 1. Connect the cap beam segment 5 to the truss 8 via the suspension 15. Figure 17 As shown, adjust the alignment of cap beam segment 5, glue adjacent cap beam segments 5 together, and connect cap beam segment 5 and cast-in-place cap beam segment 4 through a wet joint, as shown. Figure 18 As shown.

[0051] S49. Restore traffic between the central pier 1 and the second side pier 3.

[0052] S5. Insert the second steel strand 7 through the prestressed hole at the top of the middle pier 1 into the second side pier 3 and install the anchorage. Perform single-end tensioning of the second steel strand 7 on the side of the second side pier 3 away from the middle pier 1, and perform grouting and anchor sealing operations on the corresponding ducts of the second steel strand 7. Remove the hanging frame 15, truss 8, and legs, as follows. Figure 20 As shown.

[0053] S6. If there are multiple portal piers in the section, disassemble the hoisting mechanism 10 and move it as a whole to the first span of the next portal pier. Repeat steps S1 to S5 until all cap beams are completed.

[0054] In traditional dual-equipment construction methods, it is difficult to effectively reduce the traffic control area: if the left and right spans are constructed simultaneously (traditional scheme A), the road space on both sides must be closed at the same time, making it impossible to maintain traffic flow; if the left and right spans are constructed in different time periods (traditional scheme B), the area of ​​each closure is slightly reduced, but the cumulative closure time is twice that of a single span construction, and it still involves the alternating closure and reopening of roads on both sides. In addition, the traffic control area of ​​the traditional method also includes the work space for equipment installation and dismantling, material hoisting, etc., further expanding the impact area.

[0055] The half-width alternating traffic scheme of the present invention, based on the characteristic that a single set of equipment only needs to construct one span at a time, has the following advantages: 1) Only one half of the road where the construction span is located will be closed, while the other half will remain open to traffic; 2) The non-construction span of the same portal pier is not subject to any traffic control, and the space above and below it is open for passage; 3) Once the first span is completed and the equipment has crossed the span, the traffic control area will be shifted to the half of the second span, and the original half will be reopened to traffic; 4) At any given time, only one side of the road is affected by traffic.

[0056] 5) The alternating half-width traffic scheme and the sequential operation of single-set equipment across each span are synchronized in terms of timing: when equipment is being constructed on one half of the road, the other half is fully open; the equipment transfer across spans is scheduled during off-peak hours at night, further reducing the impact on traffic. Throughout the entire construction period, the road always maintains at least half-width traffic capacity, and there are no instances of complete road closures.

[0057] Table 1 compares traffic control schemes using 22 portal-type pier cap beams with 44 spans as an example.

[0058] Table 1 Furthermore, while traditional systems require two sets of suspension equipment (truss 8, guide beam 9, suspension 15, overhead crane, etc.), this invention only requires a single set, resulting in a net saving of 2.1 million to 2.75 million yuan per unit after deducting the additional auxiliary facilities.

[0059] On the other hand, the present invention provides a cap beam obtained by the multi-span portal pier concrete cap beam construction method described above. The cap beam has multiple first prestressed pipes and multiple second prestressed pipes pre-embedded inside. One end of the multiple first prestressed pipes extends to the top surface of the middle part of the cap beam, and the other end of the multiple first prestressed pipes extends to one end face of the cap beam. One end of the multiple second prestressed pipes extends to the top surface of the middle part of the cap beam, and the other end of the multiple second prestressed pipes extends to the other end face of the cap beam. Prestressed steel strands are provided in both the first prestressed pipes and the second prestressed pipes.

[0060] The first prestressed tube contains a first steel strand 6, and the second prestressed tube contains a second steel strand 7.

[0061] It should be noted that the tensioning of the first steel strand 6 and the second steel strand 7 in this invention is fundamentally different from the batch tensioning of T-beams and box girders in the prior art: the batch tensioning in the prior art divides the steel strands into early tensioning strands and late tensioning strands according to the stress stage, and each steel strand is still tensioned at both ends; while this invention divides the steel strands into two groups and unifies them to one end for tensioning, changing the anchoring method and tensioning process of a single steel strand.

[0062] like Figure 4 As shown, all the first steel strands 6 in the same group Figure 4 The diagram illustrates eight steel strands symmetrically distributed about the vertical centerline of the cap beam on the end face of the tensioning end, with space reserved between adjacent steel strands for jack operation. At the non-tensioning end of the pier top of pier 1, no space is needed for jack operation; only space is required for steel strand insertion and anchor installation, resulting in a more compact arrangement. This compact arrangement is more conducive to the reinforcement arrangement of the cast-in-place section at the pier top and the reinforcement around the groove.

[0063] At the top of pier 1, such as Figure 5As shown, the two sets of prestressed steel strands are arranged in a crisscross pattern on the facade; as... Figure 20 As shown, the prestressed corrugated pipes are staggered at a certain distance on the plane to avoid conflict and ensure smoothness at the intersection. To coordinate with the cross-anchoring arrangement, the reinforcing steel bars at the top of pier 1 need to be adjusted according to the concentrated distribution of anchorages to ensure local bearing pressure in the anchorage zone and crack resistance safety of the groove. The arrangement of prestressed pipes remains symmetrical within the cap beam cross-section, and is only staggered laterally along the cap beam in the intersection area to avoid conflict.

[0064] Since each steel strand is only about half the length of the original steel strand and is tensioned at one end, the actual benefits are as follows: 1) It is more convenient to thread the steel strands from the top of the middle pier 1 to both sides. The top of the pier provides a platform for cutting and storing steel strands, as well as an operating platform for manual threading. Traditionally, a long strand requires an operating platform to be set up at the end, and the steel strand is inserted by bending backward from the ground or the surface of the cap beam. 2) The resistance and time required for group threading are only about half that of full-length threading; 3) Equipment investment and manpower for single-end tensioning are reduced by approximately 50%; 4) Shorter steel strands mean smoother threading, less friction loss, less material loss, and easier control of tensioning accuracy.

[0065] The mechanical rationale for cross-anchoring: Traditionally, continuous prestressed steel strands are arranged on the upper edge of the cap beam at the top of pier 1 to provide compressive stress to resist negative bending moment and prevent cracking of the top concrete. In cross-anchoring, the anchorage sector areas of the two sets of steel strands overlap, forming a compressive stress reserve in the negative bending moment area at the top of the pier, achieving the same technical effect.

[0066] Analysis of prestress loss in single-end tensioning: The main difference between single-end and double-end tensioning lies in the distribution of prestress loss. 1) Duct friction loss: The friction loss of single-end tensioning increases from the tensioning end to the fixed end along the entire length of the steel strand. However, due to the cross anchoring, there is no shrinkage loss due to the compression anchor at the fixed end. In addition, the length of the steel strand is shortened by nearly 50% by the combination of span-by-span construction. The total friction loss is lower than that of the tensioning scheme at both ends of the continuous strand.

[0067] 2) Anchorage shrinkage loss, prestress relaxation loss and concrete shrinkage and creep loss: These are independent of the tensioning method and are the same as in the traditional scheme.

[0068] Taking all losses into account, the effective prestress of the cross-anchored single-end tensioning scheme is basically equivalent to that of the traditional two-end tensioning scheme at the mid-span and 1 / 4-span sections of the cap beam.

[0069] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A method for constructing a multi-span portal-type pier concrete cap beam, characterized in that: include: Cast-in-place cap beam sections (4) are poured on the middle pier (1) and side pier of the current portal pier. Prestressed holes are opened on the top and sides of the cast-in-place cap beam section (4) of the middle pier (1) and on both sides of the cast-in-place cap beam section (4) of the side pier. Traffic is closed between the central pier (1) and the first side pier (2), wherein the side piers include the first side pier (2) and the second side pier (3) on both sides of the central pier (1); The cap beam segment (5) between the pier (1) and the first side pier (2) during construction, and the cap beam segment (5) on the side of the first side pier (2) away from the middle pier (1); Restore traffic between the central pier (1) and the first side pier (2); The first steel strand (6) is inserted from the prestressed hole at the top of the middle pier (1) into the first side pier (2) and the anchor is installed. The first steel strand (6) is tensioned at one end on the side of the first side pier (2) away from the middle pier (1). Grouting and anchor sealing operations are carried out on the corresponding duct of the first steel strand (6). Traffic between the middle pier (1) and the second side pier (3) is closed off; the cap beam segment (5) between the middle pier (1) and the second side pier (3) is constructed, as well as part of the cap beam segment (5) on the side of the second side pier (3) away from the middle pier (1); Restore traffic between the central pier (1) and the second side pier (3); The second steel strand (7) is inserted from the prestressed hole at the top of the middle pier (1) into the second side pier (3) and the anchor is installed. The second steel strand (7) is tensioned at one end on the side of the second side pier (3) away from the middle pier (1), and the grouting and anchor sealing operations of the corresponding duct of the second steel strand (7) are carried out.

2. The method for constructing a multi-span portal pier concrete cap beam according to claim 1, characterized in that: All the first steel strands (6) are symmetrically distributed about the vertical center line of the cap beam on the end face of the tensioning end, and jack operation space is reserved between adjacent first steel strands (6).

3. The method for constructing a multi-span portal pier concrete cap beam according to claim 2, characterized in that: At the top of the central pier (1), the first steel strand (6) and the second steel strand (7) are arranged in a cross pattern on the elevation and staggered by a certain distance on the plane to avoid conflict between the prestressed pipes at the intersection.

4. The method for constructing a multi-span portal pier concrete cap beam according to any one of claims 1 to 3, characterized in that: The cap beam segment (5) between the pier (1) and the first side pier (2) during construction, and the cap beam segment (5) on the side of the first side pier (2) away from the central pier (1) include: A truss (8) and a guide beam (9) are installed on the first side pier (2), and the guide beam (9) is supported on the middle pier (1); The truss (8) is moved so that both ends of the truss (8) are supported by the first side pier (2) and the middle pier (1); The cap beam segment (5) is hoisted using the hoisting mechanism (10) on the truss (8), and the cap beam segment (5) is connected to the truss (8) by the hanging (15); the two adjacent cap beam segments (5) are glued together, and the cap beam segment (5) and the cast-in-place cap beam segment (4) are connected by a wet joint.

5. The method for constructing a multi-span portal pier concrete cap beam according to claim 4, characterized in that: The cap beam segment (5) between the pier (1) and the first side pier (2) during construction, and the cap beam segment (5) on the side of the first side pier (2) away from the central pier (1) include: A rigid support leg (11) is installed on the cast-in-place section (4) of the cap beam of the middle pier (1), and an auxiliary support leg (12) and a first flexible support leg (13) are installed on the cast-in-place section (4) of the cap beam of the first side pier (2). After the truss (8) and guide beam (9) are connected together on the ground, they are hoisted together to the top of the support leg. The rigid support leg (11) is supported on the guide beam (9), and the auxiliary support leg (12) and the first flexible support leg (13) are supported on the truss (8). The truss (8) is moved so that both ends of the truss (8) are supported by rigid legs (11) on the middle pier (1), auxiliary legs (12) on the first side pier (2) and first flexible legs (13).

6. The method for constructing a multi-span portal pier concrete cap beam according to claim 5, characterized in that: Before hoisting the cap beam segment (5) using the hoisting mechanism (10) on the truss (8), adjust the auxiliary support leg (12) so that the auxiliary support leg (12) is separated from the top surface of the cap beam cast-in-place segment (4) of the first side pier (2), and adjust the first flexible support leg (13) so that the truss (8) is in a horizontal working state.

7. The method for constructing a multi-span portal pier concrete cap beam according to claim 5, characterized in that: The cap beam segment (5) between the central pier (1) and the second side pier (3) and the portion of the cap beam segment (5) on the side of the second side pier (3) away from the central pier (1) include: Move the truss (8) and guide beam (9) forward so that the two ends of the truss (8) are supported by the middle pier (1) and the second side pier (3), and remove the guide beam (9); The cap beam segment (5) is hoisted using the hoisting mechanism (10) on the truss (8), and the cap beam segment (5) is connected to the truss (8) by the hanging (15). Adjacent cap beam segments (5) are glued together, and the cap beam segment (5) and the cast-in-place cap beam segment (4) are connected by a wet joint.

8. The method for constructing a multi-span portal pier concrete cap beam according to claim 7, characterized in that: Moving the truss (8) and guide beam (9) forward includes: The truss (8) moves forward until the auxiliary leg (12) is supported at the tail end of the truss (8); Using the auxiliary support leg (12) to lift the truss (8), the first flexible support leg (13) is moved to the middle of the erected cap beam and anchored to the cap beam segment (5); The first flexible support leg (13) is used to lift the truss (8), the auxiliary support leg (12) is removed, and the hoisting mechanism (10) moves between the rigid support leg (11) and the first flexible support leg (13). The second flexible support leg (14) is installed on the second side pier (3) in advance, and the truss (8) continues to move forward until the front end of the guide beam (9) is supported by the second flexible support leg (14) on the second side pier (3); The hoisting mechanism (10) moves between the middle pier (1) and the second side pier (3), releases the anchorage between the first flexible leg (13) and the cap beam segment (5), and the hydraulic cylinder of the first flexible leg (13) retracts, so that it is suspended below the truss (8). The truss (8) continues to move forward until the front end of the truss (8) is supported by the second flexible leg (14) on the second side pier (3); Remove the guide beam (9).

9. The method for constructing a multi-span portal pier concrete cap beam according to claim 8, characterized in that: Moving the truss (8) and guide beam (9) forward includes: After the guide beam (9) is removed, the truss (8) continues to move forward, so that the position of the truss (8) near the front end is supported by the second flexible leg (14) on the second side pier (3). The first flexible leg (13) at the tail end is lifted by the hoisting mechanism (10), moved laterally from the internal space of the truss (8) to the front end, and transferred to the ground.

10. A cap beam obtained by the construction method of a multi-span portal pier concrete cap beam according to any one of claims 1 to 9, characterized in that: Multiple first prestressed tubes and multiple second prestressed tubes are pre-embedded in the cap beam. One end of the multiple first prestressed tubes extends to the top surface of the middle part of the cap beam, and the other end of the multiple first prestressed tubes extends to one end face of the cap beam. One end of the multiple second prestressed tubes extends to the top surface of the middle part of the cap beam, and the other end of the multiple second prestressed tubes extends to the other end face of the cap beam. Prestressed steel strands are provided in both the first prestressed tubes and the second prestressed tubes. The steel strands include a first steel strand (6) passing through the first prestressed tube and a second steel strand (7) passing through the second prestressed tube. Both the first steel strand (6) and the second steel strand (7) are single-end tensioned anchored.

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