A beam end anchor for prestressed prefabricated beams using pre-tensioning method and a method of using the same

Abstract

The present invention relates to a beam end anchor for a prestressed precast beam by pretensioning method and a method for using the same. The anchor comprises an anchor cup, one end of which is provided with a clip for clamping a steel strand, and the other end of the anchor cup is provided with an internal thread for connecting a threaded steel rod. By using the anchor, the loss of prestress caused by the retraction of the clip can be eliminated, ensuring that the steel strand can apply prestress to the concrete beam body within a shorter distance, thereby increasing the prestress effect within the transfer length of the traditional prestressed beam. The use of the anchor of the present invention can solve the problem of insufficient prestress effect within the end transfer length range of the traditional prestressed beam.

Description

Technical Field

[0001] The invention relates to the field of civil engineering, in particular to a beam end anchor for a prestressed prefabricated beam using a pre-tensioning method and a use method thereof. Background Art

[0002] At present, the anchorage of the steel strands of the prestressed beams mainly relies on the grip of the concrete on the steel strands. Therefore, there is a transfer length at the end of the precast component. Within this transfer length, the stress of the steel strands gradually increases from zero to the permanent stress. The transfer length is mainly related to the diameter of the steel strand, the effective prestress value of the prestressed steel bars during tensioning, the shape of the prestressed bars, and the strength grade of the concrete (Design Specifications for Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts JTG 3362-2018). For large-diameter and high-strength prestressed steel strands, the transfer length is very long, about 1.3m or even longer. For precast beams with large spans and open sections, the shear stress near the support is large (including shear stress caused by shear force and shear stress caused by torsion). According to the calculation formula of the principal tensile stress, it can be seen that the principal tensile stress of the concrete near the beam end can be reduced by increasing the precompressive stress provided by the prestressed steel bars. However, the prestress effect within the prestress transfer length of traditional pre-tensioned components is small. Therefore, reducing the transfer length or changing the transfer method of the steel strands allows the steel strands to exert their precompressive stress on the concrete more quickly at the beam ends, which plays a very important role in reducing the principal tensile stress near the support.

[0003] Take a T-beam with a span of 22m and a beam height of 0.95m as an example. The beam support is 0.3m away from the beam end. Within 0.5m of the mid-span side of the support, the shear stress at the junction of the web and the top plate of the T-beam is relatively large. In this range, there is also a positive stress generated by the steel strand. From the previous analysis, it can be seen that the greater the positive stress generated by the steel strand in this range, the smaller the principal tensile stress in this range will be.

[0004] This problem can be solved by setting anchors at the beam ends. However, if traditional clip anchors are used, the prestress cannot be applied to the concrete beams due to the shrinkage of the clips. According to the literature (Highway Reinforced Concrete and Prestressed Concrete Bridge and Culvert Design Specifications JTG 3362-2018), the clip shrinkage of the clip anchor is between 4 and 6 mm. If the shrinkage deformation of the anchor occurs after the concrete hardens, the prestress loss of the steel strand within 1.3m of the beam end will reach 6 / 1300*1.95e5=900MPa. Therefore, special anchors and construction methods must be used to minimize the deformation of the anchor after the concrete hardens. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a beam end anchor for prestressed precast beams by pre-tensioning method, which can greatly reduce the prestress loss of prestressed steel strands caused by the retraction of the anchor clips.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A beam end anchor for prestressed precast beams by pretensioning method, characterized in that the anchor comprises an anchor cup, one end of which is provided with a clip for clamping a steel strand, and the other end of the anchor cup is provided with an internal thread for connecting a threaded steel rod.

[0008] Furthermore, the anchor cup of the anchor is a variable cross-section with one end thinner and the other end thicker, or a uniform cross-section with the same size at both ends. If the anchor cup is thinner at one end and thicker at the other end, the thicker end is provided with an internal thread and the thinner end is provided with a clip.

[0009] Furthermore, the cross section of the anchor cup is circular or rectangular.

[0010] Furthermore, the anchor is embedded in the concrete at the beam end and is in full contact with the concrete.

[0011] The method of using the anchor is as follows:

[0012] Step 1: Insert the steel strand into the clip at one end of the anchor plate and clamp the clip;

[0013] Step 2: Screw the threaded steel rod into the internal thread at one end of the anchor plate;

[0014] Step 3: Use a jack to pull the steel rod for tensioning;

[0015] Step 4: After the steel strands are tensioned to the controlled stress, pour concrete and maintain. The concrete should fully wrap the anchors.

[0016] Step 5: After the release requirements are met, operate the jack to release the sheet;

[0017] Step 6: After the release is completed, rotate the steel rod out of the anchor;

[0018] Step 7: Seal the anchor.

[0019] Compared with the prior art, the anchor for the end of a prestressed precast beam according to the prestressing method of the present invention can greatly reduce the prestress loss of the prestressed steel strand caused by the retraction of the clip of the anchor, ensure that the steel strand can apply prestress to the concrete beam body within a shorter distance, and improve the prestress effect of the beam end of the prestressed prestressed beam. The anchor of the present invention can solve the problem of insufficient prestress effect of the traditional prestressed prestressed beam within the end transfer length range. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is an elevation view of a prestressed beam with an anchor head at the end in Example 1 of the present invention;

[0021] Figure 2 It is a cross-sectional view at the beam end of the prestressed beam with an anchor head at the end in Example 1 of the present invention;

[0022] Figure 3 It is a construction schematic diagram before the steel strands are tensioned during the prefabrication process of the prestressed beam with anchor heads at the ends in Example 1 of the present invention.

[0023] Figure 4 This is a partial enlarged view of the vicinity of the anchor of the present invention in Example 1 of the present invention.

[0024] Figure 5 This is a three-dimensional perspective view of the circular variable cross-section anchor of the present invention in Example 1 of the present invention.

[0025] Figure 6 This is a three-dimensional perspective view of the circular uniform cross-section anchor of the present invention in Example 1 of the present invention.

[0026] Figure 7 This is a three-dimensional perspective view of the rectangular equal-section anchor of the present invention in Example 1 of the present invention.

[0027] Figure 8 The diagram is a stress distribution diagram in the prestressed steel strands near the ends of the beams of the conventional prestressing method and the prestressing method components using the anchor of the present invention.

[0028] In the figure, 1-anchor, 2-steel strand, 3-concrete, 4-threaded steel rod, 5-reaction column, 6-tension beam, 7-jack, 8-end mold, 9-bottom mold, 11-anchor cup, 12-clip, 13-internal thread. DETAILED DESCRIPTION

[0029] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] Example 1

[0031] A prestressed concrete rectangular beam with anchor heads at the ends, 16m long, 0.3m wide, 1.0m high, equipped with 4 steel strands, C50 concrete, its structure is as follows Figure 1 shown.

[0032] The anchor of the present invention is arranged at the end of the beam. The anchor comprises an anchor cup 11, a clamp 12 is arranged at one end of the anchor cup for clamping the steel strand 2, and the other end of the anchor cup has an internal thread 13 for connecting the threaded steel rod 4. The anchor cup of the anchor can be in a shape with one end thick and the other end thin, or in a shape with the same size at both ends, and can be in a circular cross section or a rectangular cross section.

[0033] The main construction steps of the prestressed precast beam are as follows:

[0034] Step 1: Calculate the stress-free length of the steel strand according to the component length, and cut the steel strand according to the calculated stress-free length.

[0035] Step 2: Insert the strand into the thinner end of the anchor and tighten the clip.

[0036] Step 2: Place and position the reinforcement cage and strands in the formwork.

[0037] Step 3: Screw the threaded steel rod into the thicker end of the anchor.

[0038] Step 4: Use a jack to pull the steel rod for tensioning.

[0039] Step 5: Pour concrete and maintain. The concrete should fully wrap the anchor.

[0040] Step 6: After the tensioning requirements are met, both ends of the component are tensioned at the same time.

[0041] Step 7: After the tension is completed, unscrew the steel rod out of the anchor.

[0042] Step 8: Lifting, storage and anchoring of prefabricated beams.

[0043] Taking a T-beam with a span of 22m and a beam height of 0.95m as an example, the distance between the beam support and the beam end is 0.3m. The anchor of the present invention is set at a position about 5cm away from the beam end. Figure 7 The stress distribution 1 and stress distribution 2 in the figure correspond to the stress distribution in the prestressed steel strands near the beam ends in the conventional prestressing method and the prestressing method member using the anchor of the present invention. Obviously, the prestressing effect near the beam ends is greatly improved by the present invention, so the principal tensile stress of the concrete beam at the beam ends will also be greatly reduced.

[0044] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for using a beam end anchor for a prestressed precast beam, characterized in that The anchor comprises an anchor cup, one end of which is provided with a clamping piece for clamping a steel strand, and the other end of the anchor cup is provided with an internal thread for connecting a steel rod with a thread. The anchor is buried in the concrete at the end of the beam and is in full contact with the concrete. The method for using the anchor comprises the following steps: the first step: inserting the steel strand into the clamping piece at one end of the anchor cup and clamping the clamping piece; Step 2: Screw the threaded steel rod into the internal thread at one end of the anchor cup; Step 3: Use a jack to pull the steel rod for tensioning; Step 4: After the steel strands are tensioned to the controlled stress, pour concrete and maintain. The concrete should fully wrap the anchors. Step 5: After the release requirements are met, operate the jack to release the sheet; Step 6: After the release is completed, rotate the steel rod out of the anchor; Step 7: Seal the anchor.

2. The method for using the beam end anchorage for prestressed precast beams according to claim 1, characterized in that: The anchor cup of the anchor is a variable cross-section with one end being thinner and the other end being thicker, or a uniform cross-section with the same size at both ends.

3. The method for using the beam end anchorage for prestressed precast beams according to claim 1, characterized in that: The cross section of the anchor cup is circular or rectangular.

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