Anchor assembly having pre-stressed mandrel

Abstract

Provided is an anchor assembly having a pre-stressed mandrel, which consists of an inner pre-stressed concrete mandrel and an outer cast-in-place anchoring slurry, wherein pre-stressed tendons are arranged inside the concrete mandrel and are prefabricated by a pretensioning method; the anchoring slurry wraps the pre-stressed concrete mandrel, and the cast-in-place anchoring slurry is formed by placing the pre-stressed concrete mandrel in a pile hole, and solidifying after primary grouting or secondary grouting. According to the anchor assembly, the pre-stress is not required to be tensioned and locked on site, so that the quality of the pre-stressed mandrel can be ensured, the on-site construction period can be greatly shortened, and the existing pre-stressed and common non-pre-stressed anchors can be replaced.

Claims

1. An anchor assembly having a pre-stressed mandrel, comprising: a pre-stressed concrete mandrel positioned at an inner side, wherein pre-stressed tendons are arranged inside the pre-stressed concrete mandrel and are prefabricated by a pretensioning method; and a cast-in-place anchoring slurry positioned at an outer side, which wraps the pre-stressed concrete mandrel, and is formed by placing the pre-stressed concrete mandrel in a pile hole and solidifying the anchoring slurry after primary grouting or secondary grouting; wherein the outer peripheral surface of the pre-stressed concrete mandrel is provided with a mandrel positioning device; wherein the mandrel positioning device is a three-way positioning device with protrusions along a circumferential direction of the pre-stressed concrete mandrel; and wherein an outer circumferential surface of the pre-stressed concrete mandrel is further provided with a grouting pipe preformed groove.

2. The anchor assembly having a pre-stressed mandrel according to claim 1, wherein there are three pre-stressed tendons in the pre-stressed concrete mandrel.

3. The anchor assembly having a pre-stressed mandrel according to claim 1, wherein a radius R1 of the pre-stressed concrete mandrel is 50-75 mm, and a thickness of the anchoring slurry is 30-60 mm.

4. The anchor assembly having a pre-stressed mandrel according to claim 1, wherein the anchoring slurry is a cement slurry.

5. The anchor assembly having a pre-stressed mandrel according to claim 1, wherein the pre-stressed concrete mandrel is in a shape of a frustum with a small top and a large bottom.

6. The anchor assembly having a pre-stressed mandrel according to claim 1, wherein the three-way positioning device comprises three protrusions in one turn along a circumferential direction and two turns along a longitudinal direction of a mandrel body of the pre-stressed concrete mandrel, and wherein the protrusions are bamboo-like or point-like protrusions.

7. A construction method of the anchor assembly having a pre-stressed mandrel according to claim 1, comprising the following steps: S1, prefabricating a pre-stressed concrete mandrel by a pretensioning method in a factory, wherein a diameter of the prefabricated mandrel is controlled between 100 mm and 150 mm; tensioning a rebar on a pedestal first, then pouring a concrete mandrel, and preforming a grouting pipeline in the mandrel; after a strength reaches a design value, releasing a tension end to make the mandrel form prestress; at the same time, reserving a section of the rebar at one side of the mandrel for anchoring, and cutting off the rebar at the other side along an end of the mandrel; S2, drilling holes by a drilling machine on a construction site; S3, hole cleaning, binding the grouting pipe, and then lowering the prefabricated mandrel to ensure that the pre-stressed concrete mandrel and the drilling hole are coaxial; S4, performing primary grouting around the pre-stressed concrete mandrel, and performing secondary grouting as a cast-in-place anchoring slurry after solidification and shrinkage followed by the primary grouting; S5, anchoring the rebar preformed in the mandrel into a bottom slab, and pouring the bottom slab so as to complete basement construction.

8. The construction method of the anchor assembly having a pre-stressed mandrel according to claim 7, wherein an expansion agent is added to the concrete when pouring the concrete mandrel in S1.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a construction drawing of a pre-stressed anchor in the prior art;

(2) FIG. 2 is a schematic diagram of the anchor assembly of the present application;

(3) FIG. 3 is a sectional view taken along A-A in FIG. 2;

(4) FIG. 4 is a sectional schematic view of the anchor assembly with a mandrel positioning device;

(5) FIG. 5 is a schematic diagram of the anchor assembly when the mandrel is frustum-shaped;

(6) Reference Signs: pre-stressed concrete mandrel 1, cast-in-place anchoring slurry 2, bottom slab 3, grouting pipe 4, mandrel positioning device 5, pre-stressed tendon 101, mandrel concrete 102, grouting pipe preformed groove 103, and point-like protrusions 104.

DESCRIPTION OF EMBODIMENTS

(7) The purpose and effect of the present application will become more clear by describing the present application in detail according to the drawings and preferred embodiments. It shall be understood that the specific embodiments described here are only intended to explain the present application, and are not used to limit the present application.

(8) The anchor assembly having a pre-stressed mandrel has three innovations: (1) The traditional pre-stressed anti-floating anchors are all poured on site, and the anchor assembly of the present application is a combination of factory prefabrication and on-site pouring; (2) There are only two methods for non-pre-stressed anchor and full pre-stressed anchor. The prefabricated mandrel of the anchor assembly of the present application is a pre-stressed member, while the anchoring slurry poured on site is a non-pre-stressed member; (3) The traditional pre-stressed anti-floating anchor must be tensioned on the basement bottom slab, and it cannot form a complete stress system itself. A prestress is only established in the mandrel body below the bottom slab for this novel anchor, forming a self-balancing system without the bottom slab, and thus achieving better safety under the subsequent basement construction conditions.

(9) As shown in FIG. 2, the anchor assembly having a pre-stressed mandrel of the present application incudes: a pre-stressed concrete mandrel 1 positioned at the inner side, wherein the pre-stressed concrete mandrel 1 is prefabricated by a pretensioning method and internally provided with a pre-stressed tendon 101; a cast-in-place anchoring slurry 2 located at an outer side, which wraps a pre-stressed concrete mandrel 1, and is formed by placing the pre-stressed concrete mandrel 1 in a pile hole and then performing primary grouting and solidification; when the anchoring slurry is a cement slurry, the anchoring slurry will be formed after primary grouting and solidification, but when the anchoring slurry is mixed mortar, the slurry will shrink greatly after primary grouting and solidification, thus causing cracks in the anchoring slurry. At this time, secondary grouting is needed, and the whole anchoring slurry will be obtained after secondary grouting and solidification.

(10) As shown in FIG. 3, due to the small diameter of the anchor, the radius R1 of the pre-stressed concrete mandrel 1 is 50-75 mm, the thickness of the cast-in-place anchoring slurry 2 is 30-60 mm, and a pre-stressed tendon can be used in the pre-stressed concrete mandrel 1; considering factors such as transportation and construction deviation, three pre-stressed tendons can also be set in the mandrel to enhance the bending resistance of the mandrel body. The pre-stressed concrete mandrel 1 can be pre-stressed rebars or steel strands. The cast-in-place anchoring slurry 2 is a cement slurry.

(11) As shown in FIG. 4, in order to enhance the bonding performance between the pre-stressed concrete mandrel 1 and the cast-in-place anchoring paste 2, bamboo-like or point-like protrusions 104 may be provided on the outer peripheral surface of the pre-stressed concrete mandrel 1. The mandrel body is generally round, but it can also adopt square, oval or other cross sections. At the same time, in order to avoid the offset during placing the pre-stressed concrete mandrel in the pile hole, the pre-stressed concrete mandrel 1 is preferably provided with a mandrel positioning device 5, which can be 30×30×h protrusions (h is the distance from the mandrel to the hole wall −0.5 cm), with three protrusions along the circumferential direction and two turns along the longitudinal direction. At the same time, the pre-stressed concrete mandrel 1 is provided with a grouting pipe preformed groove 103 for binding the grouting pipe before the mandrel is lowered into the pile hole. There are 2 grouting pipes, which are used for primary grouting and secondary grouting respectively.

(12) As shown in FIG. 5, the pre-stressed concrete mandrel is preferably frustum-shaped; at this time, under the action of tensile force, the pre-stressed concrete mandrel 1 can squeeze the cast-in-place anchoring slurry 2 and the hole wall, and the anchor assembly has better bearing capacity. In addition, because of the prefabrication in the factory, the mandrel is easy to realize, while the previous on-site grouting anchor cannot be realized.

(13) In order to avoid the offset during the placing process of the mandrel, the mandrel body is preferably provided with a three-way positioning device, which can be 30×30×h protrusions (h is the distance from the mandrel to the hole wall −0.5 cm), with three protrusions arranged along the circumferential direction and two turns arranged along the longitudinal direction. At the same time, the mandrel is provided with a grouting pipe preformed groove for binding the grouting pipe before lowering the hole. There are 2 grouting pipes, which are used for primary grouting and secondary grouting respectively.

(14) The construction method of the anchor assembly having a pre-stressed mandrel of the present application includes the following steps: S1, prefabricating a pre-stressed concrete mandrel 1 by a pretensioning method in a factory, wherein the diameter of the prefabricated mandrel is controlled between 100 mm and 150 mm; tensioning the rebar on the pedestal first, then pouring the concrete mandrel, and preforming a grouting pipeline in the mandrel; after the strength reaches a design value, releasing the tension end to make the mandrel form a prestress; at the same time, reserving a section of the rebar at one side of the mandrel for anchoring, and cutting off the rebar at the other side along an end of the mandrel; S2, drilling holes by a drilling machine on a construction site; S3, hole cleaning, binding the grouting pipe, and then lowering the prefabricated mandrel to ensure that the pre-stressed concrete mandrel and the drilling hole are coaxial; S4, performing primary grouting around the pre-stressed concrete mandrel, and performing secondary grouting as a cast-in-place anchoring slurry after solidification and shrinkage followed by the primary grouting; S5, anchoring the rebar reserved in the mandrel into a bottom slab, and pouring the bottom slab so as to complete basement construction.

(15) Different from the conventional pre-stressed members, because the diameter of the anchor is generally 150-240 mm and the length is 4-15 m, considering the peripheral anchoring slurry, the pre-stressed concrete mandrel 1 of the present application has a smaller diameter, and the application of the prestress must ensure the positioning accuracy of the pre-stressed tendons, avoid the additional bending moment caused by deviation, and better reflect the advantages of prefabricated production in factories.

(16) Because of the small cross section of the mandrel, the prestress degree will be significantly higher than that of ordinary pre-stressed members, and the elastic compression deformation and later shrinkage and creep will further increase the prestress loss. At present, according to the current Specifications for Design of Concrete Structures, the prestress loss of pretensioned axial compression members is shown in the first four items in Table 1. The loss of prestress in the table does not include the loss caused by the compression of the mandrel body caused by the release of the tensioned rebar. In view of the small cross-section of the mandrel, the prestress loss σ.sub.s is supplemented on the basis of existing specifications through analysis.

(17) TABLE-US-00001 TABLE 1 Analysis of prestress loss Causes of prestress loss computing formula remarks Deformation of an anchorage at the tension end ${\sigma }_{l1}=\frac{a}{l}{E}_s$ a-anchorage deformation value l-the distance between the tensioning end and the anchoring end E.sub.s-elastic modulus of the rebar Influence of temperature σ.sub.l3 = 2Δt Δt-temperature difference difference in concrete curing between pre-stressed tendons and equipment under tension Prestress relaxation of σ.sub.l4 = 0.03σ.sub.con σ.sub.con-tension control stress pre-stressed rebar of the pre-stressed rebar Shrinkage and creep of the concrete ${\sigma }_{l5}=\frac{60+340\frac{{\sigma }_{\mathrm{pc}}}{f_{\mathrm{cu}}}}{1+15\rho }$ σ.sub.pc-compressive stress of the pile concrete f.sub.cu-Cubic compressive strength of the pile concrete ρ-rebar ratio of the uplift pile Compression deformation of the concrete ${\sigma }_s=\frac{N_s}{A_s+A_c\frac{E_c}{E_s}}$ N.sub.s-Tension control force of the pre-stressed rebar As, Ac-the areas of the pre-stressed rebar and the concrete, respectively σ.sub.s-loss stress of the pre-stressed rebar E.sub.c-elastic modulus of the concrete

(18) Next, an example is given to prove the superiority of the anchor assembly of the present application and calculate its prestress loss.

(19) The prestress loss of a 8 m composite uplift pile is analyzed, and the calculation results are shown in Table 2, wherein the strength grade of the concrete is C40, and the diameter of pile mandrel is 150 mm; the diameter of the pre-stressed tendons is 12.6 mm, the number is 3, and the tension control stress is 994 Mpa.

(20) TABLE-US-00002 TABLE 2 Analysis of prestress loss of a 15 m composite uplift pile Types of Calculation prestress loss result/(N/mm.sup.2) remarks σ.sub.l1 75 Take α = 3 mm σ.sub.l3 40 Take Δt = 20° C. σ.sub.l4 29.8 — σ.sub.s 164.0 — σ.sub.l5 99.7 —

(21) The example shows that the elastic shrinkage deformation loss accounts for 24.4% of the total loss. In order to reduce this part of the prestress loss, it is preferable to add an appropriate amount of an expansion agent to the mandrel body. The compressive stress in the mandrel body can be ensured by the later expansion of the concrete, and the pressure between the composite pile and the rock and soil can also be increased, thus enhancing the uplift bearing capacity of the anchor assembly. Compared with the non-pre-stressed anchor, the steel consumption is 20-30% of the original consumption.

(22) Those skilled in the art can understand that the above is only a preferred example of the present application, and is not used to limit the present application. Although the present application has been described in detail with reference to the aforementioned examples, for those skilled in the art, they can still modify the technical solutions described in the aforementioned examples, or replace some of the technical features equally. All modifications and equivalent substitutions within the spirit and principles of the present application shall be included in the scope of protection of the present application.