Pre-tensioned ultra-high performance concrete composite beam and its construction method

Abstract

The present invention discloses a pre-tensioned ultra-high performance concrete composite beam and a construction method thereof, comprising a compression zone located at the upper part of the composite beam and a tension zone located at the lower part of the composite beam. The tension zone is made of ultra-high performance concrete, and a plurality of mutually parallel prestressed strands are arranged inside by the pre-tensioning method; the force direction of each prestressed strand is parallel to the tensile force direction borne by the tension zone; the compression zone is made of ordinary concrete, and is fixed to the tension zone by reserved steel bars arranged in the tension zone. During construction, the prestressed strands in the tension zone are tensioned first, and the tension zone is cast with ultra-high performance concrete. After the strength of the tension zone reaches the design strength, the compression zone is cast with ordinary concrete on the tension zone. The present invention makes full use of the high compressive strength of ultra-high performance concrete, avoids the defect of loose grouting of post-tensioning pipes, reduces the size of the component, and realizes the lightweight of ultra-high performance concrete components.

Description

Technical Field

[0001] The invention relates to the technical field of composite beam structure design, and in particular to a pre-tensioned ultra-high performance concrete composite beam and a construction method thereof. Background Art

[0002] Ultra-high performance concrete (UHPC material) is different from traditional high-strength concrete and steel fiber concrete, nor is it the high-strength of the traditional "high-performance concrete". Instead, it is a new type of cement-based structural engineering material with clear performance indicators, and has the characteristics of ultra-high strength, ultra-high toughness and ultra-high durability. Applying ultra-high performance concrete to structural engineering can achieve lightweight structures and increase the service life of structures.

[0003] Since the production cost of ultra-high performance concrete is relatively high, the structural form of combining ultra-high performance concrete with ordinary concrete is an ideal application method - that is, ultra-high performance concrete is used in the tension zone and ordinary concrete is used in the compression zone, in order to fully utilize the strong tensile properties of ultra-high performance concrete.

[0004] For example, the publication number CN108118610A discloses a composite beam of ultra-high performance concrete and ordinary reinforced concrete, including a UHPC prefabricated main beam and a post-cast ordinary reinforced concrete bridge deck. The UHPC main beam is prefabricated in advance, and a shear connector is preset on the top of the UHPC prefabricated beam. After the UHPC prefabricated beam is erected in place, it is used as a construction platform. After a steel mesh is set on the top edge of the UHPC prefabricated beam, ordinary concrete is cast, and the composite beam is formed by combining the shear connector on the top of the UHPC prefabricated beam. This composite beam is a combination of ultra-high performance concrete and ordinary reinforced concrete, emphasizing only the use of UHPC materials to prefabricate the main beam, erect the top plate as a construction platform, and then cast the concrete bridge deck; but this simple combination form does not actually fully utilize and give full play to the performance of UHPC materials.

[0005] For ultra-high performance concrete, although it has super high strength, its compressive strength is much greater than its tensile strength. Generally speaking, the compressive strength of ultra-high performance concrete can reach more than 120MPa, but its axial tensile strength is only about 7-10MPa, which is much higher than ordinary concrete, but much lower than steel.

[0006] In structural applications, even if a composite structure is used, in the ultimate state, the tensile strength is often close to the tensile design strength value, but the compressive strength is far less than its compressive design strength value, that is, the compressive strength is far from being fully utilized and the material properties are not fully utilized.

[0007] In practical applications, existing technologies usually use post-tensioning to utilize the characteristics of UHPC materials, but UHPC prefabricated post-tensioned composite beams have the following defects:

[0008] 1. UHPC prefabricated post-tensioned composite beams need to be pre-buried with corrugated pipes and use anchors to tension stress beams. However, there are minimum size requirements for the layout of anchors and corrugated pipes, which limits the reduction of the main beam size, resulting in material waste and increasing the deadweight.

[0009] 2. UHPC prefabricated post-tensioned composite beams require that the prestressed tendons be tensioned after the beam material reaches the designed strength. After tensioning, the pipeline needs to be grouted, and tension can only be released after the pipeline slurry reaches the strength. Therefore, the construction process is relatively complicated and the construction time is significantly increased.

[0010] 3. Due to the narrowness of the corrugated pipe, the grouting process is prone to the problem of loose grouting;

[0011] 4. After the UHPC prefabricated post-tensioned composite beam forms a composite structure, the prestressed steel strands are tensioned, which cannot fully exert the compressive and tensile properties of ultra-high performance concrete; during the process of tensioning the prestressed steel strands, the ordinary concrete of the top plate may crack when the tension stress is too large.

[0012] Therefore, in structural design, how to combine ultra-high performance concrete with prestressed technology in order to fully utilize the compressive properties of ultra-high performance concrete is a technical problem that has been waiting to be solved in this field. Summary of the invention

[0013] In view of the above-mentioned defects of the prior art, the present invention provides a pre-tensioned ultra-high performance concrete composite beam, the purpose of which is to utilize the ultra-high strength, ultra-high toughness and ultra-high durability of UHPC materials, and to combine the ultra-high performance concrete with prestressed technology more effectively by pre-tensioning, so that the composite beam made of ultra-high performance concrete has a higher compressive stress reserve.

[0014] To achieve the above purpose, the present invention discloses a pre-tensioned ultra-high performance concrete composite beam, including a compression zone located at the upper part of the composite beam and made of ultra-high performance concrete, and a tension zone located at the lower part of the composite beam and made of ordinary concrete.

[0015] Wherein, a plurality of mutually parallel prestressed tendons are arranged inside the tension zone by pre-tensioning method;

[0016] Furthermore, the force direction of each prestressed bundle is parallel to the direction of the tension borne by the tension zone.

[0017] When the tension zone is prefabricated, reserved steel bars are reserved at the connection position with the compression zone; the compression zone and the tension zone are fixed by the reserved steel bars.

[0018] Preferably, the prestressed bundle is a steel strand, a stress-relieving steel wire, a prestressed threaded steel bar or an FRP bundle.

[0019] Preferably, the composite beam is a box beam, and the compression zone is a cover plate portion located on the top surface of the box beam;

[0020] The cross section of the tension zone is a groove-shaped strip structure with an opening at the top;

[0021] And the width below the tension zone is smaller than the width of the cover plate portion.

[0022] Preferably, the composite beam is a trough beam, and the compression zone is a portion of the two side walls of the trough beam close to the upper end;

[0023] The cross section of the tension zone is a groove-shaped strip structure with an opening at the top.

[0024] More preferably, steel bars are arranged in the compression zone.

[0025] More preferably, the compression zone is provided with a compression zone stress bundle by post-tensioning method.

[0026] The present invention also provides a construction method for the above-mentioned pre-tensioned ultra-high performance concrete composite beam, the steps of which are as follows:

[0027] A. Install the formwork on the pre-tensioning pedestal and tension a number of prestressed tendons;

[0028] B. Use ultra-high performance concrete to cast the tension zone, and reserve steel bars for connection with the compression zone during casting;

[0029] C. Curing: when the strength of the tension zone reaches the design strength, shearing off all the prestressed tendons;

[0030] D. Remove the pedestal from the tension zone to which the prestress has been applied, and install the formwork to cast the compression zone;

[0031] E. Maintain the material until the compression zone reaches the design strength.

[0032] Beneficial effects of the present invention:

[0033] The present invention combines the construction of prestressed tendons by the pre-tensioning method of prefabricated parts with ultra-high performance concrete. Ultra-high performance concrete is used in the tension zone and the pre-tensioning method is used to set the prestressed tendons. The high compressive strength of ultra-high performance concrete is utilized to set a larger prestress in the tension zone, thereby improving the load capacity of the tension zone.

[0034] Compared with the existing post-tensioning construction technology, the present invention eliminates the need for arranging anchors and prestressed pipes, avoids the defect of loose grouting of post-tensioning pipes, reduces construction steps, and improves construction efficiency.

[0035] The present invention reduces the overall size of the composite beam, truly realizes the lightweight of the ultra-high performance concrete component, and is more economical.

[0036] The concept, specific structure and technical effects of the present invention will be further described below in conjunction with the accompanying drawings to fully understand the purpose, characteristics and effects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A schematic structural diagram of a box beam according to an embodiment of the present invention is shown.

[0038] Figure 2 A schematic structural diagram of a trough beam according to an embodiment of the present invention is shown.

[0039] Figure 3 A schematic diagram showing the state of a completed tension portion of a box beam in one embodiment of the present invention is shown. DETAILED DESCRIPTION

[0040] Example

[0041] like Figure 1 and Figure 2 As shown, the pre-tensioned ultra-high performance concrete composite beam includes a compression zone 3 located at the upper part of the composite beam and made of ultra-high performance concrete, and a tension zone 2 located at the lower part of the composite beam and made of ordinary concrete.

[0042] A plurality of mutually parallel prestressed tendons 1 are arranged inside the tension zone 2 by the pre-tensioning method; and the force direction of each prestressed tendon 1 is parallel to the direction of the tension borne by the tension zone.

[0043] The principle of the present invention is to divide the composite beam itself into two parts: an upper compression zone 3 and a lower tension zone 2. The tension zone is made of ultra-high performance concrete and a plurality of prestressed beams 1 are set by the pre-tensioning method to apply a larger prestress so that it has a higher compressive stress reserve. The compression zone is made of ordinary concrete.

[0044] When the tension zone 2 is prefabricated, a reserved steel bar 4 is reserved at the connection position with the compression zone 3; the compression zone 3 and the tension zone 2 are fixed by the reserved steel bar.

[0045] The prestressed tendon 1 is usually made of steel strands, stress-relieved steel wires, prestressed threaded steel bars or FRP tendons.

[0046] like Figure 1As shown, in some embodiments, the composite beam is a box beam, and the compression zone 3 is a cover plate portion located on the top surface of the box beam.

[0047] The cross section of the tension zone 2 is a groove-shaped strip structure with an opening at the top.

[0048] And the width below the tension zone 2 is smaller than the width of the cover plate part.

[0049] like Figure 2 As shown, in some embodiments, the composite beam is a trough beam, and the compression zone 3 is the portion of the two side walls of the trough beam close to the upper end.

[0050] The cross section of the tension zone 2 is a groove-shaped strip structure with an opening at the top.

[0051] In some embodiments, steel bars are arranged in the tension zone 2 .

[0052] In some embodiments, the tension zone 2 is provided with stress beams in the compression zone by post-tensioning method.

[0053] like Figure 1 and Figure 3 As shown, the present invention also provides a construction method for a pre-tensioned ultra-high performance concrete composite beam, the steps are as follows:

[0054] A. Install the formwork on the pre-tensioning pedestal and tension a number of prestressed tendons 1;

[0055] B. Use ultra-high performance concrete to cast the tension zone 2, and reserve steel bars 4 for connection with the compression zone 3 during casting;

[0056] C. Maintenance: When the strength of the tension zone 2 reaches the design strength, cut off all prestressed tendons 1;

[0057] D. Remove the pedestal from the prestressed tension zone 2 and install the formwork to cast the compression zone 3;

[0058] E. Cure until the compression zone 3 reaches the design strength.

[0059] Compared with the prior art, the application of the above technology of the present invention has the following significant improvements:

[0060] 1. In the present invention, a plurality of prestressed tendons are directly arranged in the tension zone by the pre-tensioning method, so there is no need to add additional anchors, and there is no need to reserve corrugated pipes, which saves costs and can also significantly reduce the cross-sectional size of the structure;

[0061] 2. The composite beam using the technology of the present invention can be tensioned as long as the beam material reaches the designed strength, without grouting, thus eliminating the grouting process and saving production time; compared with the post-tensioning method of the prior art, the construction is fast and convenient, and the efficiency is higher;

[0062] 3. The composite beam using the technology of the present invention does not require grouting, eliminating the problem of loose grouting of post-tensioned components;

[0063] 4. The composite beam using the technology of the present invention is used to cast the tensile zone of UHPC under the state of prestressing, and the prestressed steel strands are released after the UHPC part reaches the strength, and finally the ordinary concrete part is cast; such operation can fully apply the prestressing effect to the UHPC part, and can give full play to the compressive and tensile properties of UHPC, avoiding the problem of ordinary concrete cracking when the post-tensioning prestressed steel strands are tensioned in the prior art.

[0064] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A construction method for a pre-tensioned ultra-high performance concrete composite beam, comprising a compression zone (3) located at the upper part of the composite beam, and a tension zone (2) located at the lower part of the composite beam; characterized in that: The tension zone (2) is made of ultra-high performance concrete, and a plurality of mutually parallel prestressed tendons (1) are arranged inside by pre-tensioning method; The force direction of each prestressed bundle (1) is parallel to the direction of the tension borne by the tension zone (2); The compression zone (3) is made of ordinary concrete and is fixed to the tension zone (2) by a reserved steel bar (4) arranged in the tension zone (2); The construction steps are as follows: A. Install the formwork on the pre-tensioning pedestal and tension a number of prestressed tendons (1); B. Using ultra-high performance concrete to cast the tension zone (2), and during the casting, reserving a reserved steel bar (4) for connection with the compression zone (3); C. Curing, when the strength of the tension zone (2) reaches the design strength, shearing off all the prestressed tendons (1); D. Remove the pedestal from the tension zone (2) to which the prestress is applied, and install the formwork to cast the compression zone (3); E. Curing until the pressure zone (3) reaches the designed strength.

2. The construction method of pre-tensioned ultra-high performance concrete composite beam according to claim 1, characterized in that: The composite beam is a box beam, the compression zone (3) is a cover plate portion located on the top surface of the box beam; the cross section of the tension zone (2) is a groove-shaped strip structure with an upper opening; and the width below the tension zone (2) is smaller than the width of the cover plate portion.

3. The construction method of pre-tensioned ultra-high performance concrete composite beam according to claim 1, characterized in that: The composite beam is a trough beam, the compression zone (3) is the portion of the two side walls of the trough beam close to the upper end; the cross section of the tension zone (2) is a trough strip structure with an upper opening.

4. The construction method of the pre-tensioned ultra-high performance concrete composite beam according to any one of claims 1 to 3, characterized in that: The prestressed bundle (1) is a steel strand, a stress-relieving steel wire, a prestressed threaded steel bar or an FRP bundle.

5. The construction method of pre-tensioned ultra-high performance concrete composite beam according to claim 1, characterized in that: Steel bars are arranged in the compression zone (3).

6. The construction method of pre-tensioned ultra-high performance concrete composite beam according to claim 5, characterized in that: The compression zone (3) is provided with a compression zone stress bundle by post-tensioning method.

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