RU150388U1 - COMPOSITE FITTINGS WITH INCREASED SURFACE SPACE AREA - Google Patents

Abstract

Composite reinforcement, which is a supporting rod of high-strength non-metallic fibers impregnated with a polymeric binder, characterized in that the cross-sectional profile of this reinforcement is a combination of an even number of sectors of equal angular measure, alternating and belonging to two concentric circles with diameters Dmin and Dmax, which together add up to full angle.

Description

The utility model relates to construction, namely to non-metallic composite reinforcement, which is used for reinforcing heat-insulating wall structures, monolithic concrete and prefabricated structures, for use in structural elements of buildings as separate rods, for reinforcing the soil of the foundation of buildings and structures, including foundations motorways and roads, for anchoring in the ground retaining walls and structures

Known reinforcing element described in the book of Frolov V.P. “Fiberglass reinforcement and glass concrete structures” (M, Stroyizdat, 1980, pp. 20-27), containing a core of glass fibers impregnated with a polymer binder and fastened with a spiral winding.

The disadvantages of this reinforcement are that the pulling out of the rods, with screw winding glued onto the cylindrical rod, occurs prematurely as a result of its shear separation (shear) from the "body" of the rod and the adhesion to concrete is insufficient for their joint work in the entire range of tensile stresses permissible for this rod.

Known fiberglass reinforcement according to patent No. 2194135 (publ. 2002.12.10) containing a supporting rod of high-strength polymer material and a winding with ledges, which are made in the form of a bundle of threads impregnated with a binder and spirally applied with interference. This type of reinforcement contains a supporting rod of high-strength polymer material (for example, fiberglass GOST 17139-79, SVM TU 6-06-1153-78).

The disadvantages of this reinforcement are the lateral deformations in the fibers of the power rod, arising due to its winding with tension rods and the adhesion to concrete is insufficient for their joint work in the entire range of tensile stresses permissible for this rod.

Known reinforcement for concrete elements according to patent No. 2413059 (publ. February 27, 2011), containing at least one stretched bundle formed from a small number of monofilament yarns, which, when immersed in a binder, form a fiber bundle, the outer surface of which is coated granular material, such as, for example, sand.

The disadvantages of this reinforcement are that when pulling out of concrete, failure occurs prematurely, including along the sand layer on the surface of the reinforcement due to the cutting of its large grains and the adhesion ability of this reinforcement to concrete is insufficient for their joint operation in the entire range of tensile stresses permissible for this reinforcement .

The author revealed that according to the results of tests presented by various manufacturers of composite reinforcement in open sources, the maximum force when pulling such reinforcement from concrete is in the range of 25-40% of the loads corresponding to the tensile strength of these reinforcement.

Thus, we can conclude that these rebars have insufficient adhesion to concrete for their joint work in the entire range of loads permissible for these rebars and, therefore, their high strength properties remain unrealized.

The proposed utility model solves the issue of increasing the ability of adhesion of composite reinforcement to concrete.

Experimental studies of adhesion of composite reinforcement to concrete, conducted in 2013 at the Kazan State University of Architecture and Civil Engineering, showed that adhesion of composite reinforcement to concrete is ensured by adhesion of cement stone with an epoxy coating, and not by mechanical engagement of coils or grains of sand in a concrete matrix (http : //izvestija.kgasu.ru/files/1_2013/214_220_Khozin_Piskunov.pdf).

Adhesion strength is determined by the formula:

τ = F / Cl

where τ is the average adhesion stress, F is the tensile load, C is the equivalent circumference of the composite reinforcement bar, and l is the termination length. (ACI 440.3R-04 Guide Test Methods for Fiber-Reinforced Polymers (FRPs) for Reinforcing or Strengthening Concrete Structures, 2004 - 40p.).

Consequently, an increase in the equivalent circumference of the rod of composite reinforcement, in other words, the perimeter of the cross section while maintaining its area, will make it possible to increase the value of the tensile load when pulling out, i.e. will increase the adhesion ability of this composite reinforcement to concrete and will more fully realize its high strength properties when working in a supporting structure.

, где Dэкв - диаметр такого же по составу, с поперечным сечением равной площади, но имеющим форму круга, арматурного стержня (эквивалентный стержень).To achieve the indicated technical result, the author developed a useful model of composite reinforcement having a cross-section profile made in the form of a combination of an even number of sectors of equal angular measure located alternately and belonging to two concentric circles with diameters Dmin and Dmax, totaling a total angle, and the values of Dmin and Dmax are located within 0 <Dmin <Deq and

, where Deq is the diameter of the same composition, with a cross section of equal area, but having the shape of a circle, of a reinforcing bar (equivalent bar).

The values of Dmin and Dmax are determined by solving a system of equations made up of the condition that the cross-sectional area of the resulting bar remains equal to the cross-sectional area of the same composition but of a round reinforcing bar with a diameter of Deq (equivalent bar), and the perimeter will be changed B times to the value necessary to ensure adhesion of such a rod to the concrete structure up to a tensile load corresponding to the tensile strength of the rod in tension:

where Sn is the cross-sectional area of the resulting rod.

Seq is the cross-sectional area of a round reinforcing bar with a diameter of Deq (equivalent bar).

Pn is the perimeter of the cross section of the resulting rod.

Req is the cross-sectional perimeter of a round reinforcing bar with a diameter of Req (equivalent bar).

B is a coefficient that determines how many times it is necessary to increase the perimeter of such an equivalent rod to provide the required adhesion to the concrete structure.

From the condition of conservation of the cross-sectional area 5n = 5eq, we obtain:

Dekv π · ^2/4 = π · Rmax ^2/8 + π · Rmax ^2/8 where π = 3,14 hence:

where 0 <Dmin <Deq and

From the condition of the ratio of perimeters Pn = B · Req

we get:

π · Dmax / 2 + π · Dmin / 2 + (Dmax-Dmin) · n / 2 = B · π · DEC

where n is the accepted number of sectors

from here:

, из (2) получаем, что значения коэффициента В могут находиться в пределах от 1 до

, т.е. периметр поперечного сечения арматурного стержня может быть увеличен в диапазоне от 1 до

раз по отношению к круглому сечению равной площади.Given that 0 <Dmin <Deq and

, from (2) we obtain that the values of coefficient B can be in the range from 1 to

, i.e. the perimeter of the cross section of the reinforcing bar can be increased in the range from 1 to

times with respect to a circular cross-section of equal area.

It should be noted that the practical sense is the appointment of the number of sectors n in the range of 6-12.

видно что при n=6 1<В<2; при n=8 1<В<2,5; при n=10 1<В<2,95; при n=12 1<В<3,4, что вполне достаточно для увеличения максимальной силы выдергивания таких арматур из бетона в 2-3 раза.So from

it can be seen that for n = 6 1 <B <2; when n = 8 1 <B <2.5; when n = 10 1 <B <2.95; when n = 12 1 <B <3.4, which is quite enough to increase the maximum pulling force of such reinforcement from concrete by 2-3 times.

Having determined how many times it is necessary to increase the perimeter of the rod and accepting the number of sectors of which its profile will consist, we find the values of Dmax and Dmin.

To do this, it is necessary to solve the system of equations:

from (2)

, следовательно подставив это значение Dmax в (1) получим:

, therefore, substituting this value of Dmax in (1) we obtain:

or

This equation is a quadratic equation of the form

ax ² + bx + c = 0, where

;

;

.x = Dmin;

;

;

.

The solutions of the quadratic equation are found by the formulas

и

, где D=b²-4·a·c

and

where D = b ² -4 · a · c

Obviously, under the adopted restrictions, the coefficients a and b will always be positive, and the coefficient c will be negative. Therefore, D> 0 and the equation has two real solutions, of which x ₁ > 0, and x ₂ <0.

In this way

This utility model allows to obtain reinforcing bars with a specific contact area ensuring the compatibility of their work with concrete structures up to a tensile load corresponding to the tensile strength of a given bar.

Due to this feature, a new design of high-strength composite reinforcement with increased adhesion to concrete has been created, which allows to realize its high strength properties when working in a supporting structure.

Consider the foregoing on the example of a composite reinforcing bar with a diameter of 10 mm. according to GOST 31938-2012 “Composite polymer reinforcement for reinforcing concrete structures. General technical conditions ”, which we shall take as equivalent, Deq = 10 mm.

In accordance with the technical requirements of this GOST, the tensile strength σ _in composite polymer reinforcement should be at least 800 MPa.

For a rod with a diameter of 10 mm. this corresponds to a tensile load F = 62.8 kN (F = σ · S, where F is the tensile load, σ is the stress in the rod corresponding to this load, S is the cross-sectional area of the stretched rod).

The same technical requirements indicate that for a given reinforcement, the adhesion strength to concrete τ _γ must be at least 12 MPa.

For a rod with a diameter of 10 mm., When the adhesion length of the reinforcement with concrete is 5d (according to GOST 31938-2012 Appendix D), this corresponds to a tensile load F = 18.84 kN (F = τ · C · l, where F is the tensile load, τ is the average adhesion stress corresponding to a given load, C is the circumference of the rod of the composite reinforcement, l is the termination length).

Obviously, this rod is pulled out of concrete, significantly underutilizing its strength.

To obtain a rod with a bonding strength with concrete increased, for example, 2 times, while maintaining the same tensile strength, we take the value of the coefficient B = 2. Assigning, based on the permissible limits, the number of sectors n equal to, for example, 10 and we find a, b, c and D to determine the values of Dmax and Dmin.

So:

D = b ² -4 · a · s = 9.9805 ² + 4 · 1.2726 · 108.6332 = 652.5967

Substituting the values of n, B, Deq, a, b, c and D in the formulas for Dmin and Dmax

find their values:

.

.

.

.

Thus, we obtain a composite reinforcement bar having a cross-section profile made in the form of a set of 10 alternately arranged and belonging to two concentric circles with diameters of 6.12 and 12.75 mm, sectors of equal angular measure, amounting to a total angle, the limit tensile strength σ _in this reinforcement, like that of an equivalent bar, corresponds to a tensile load of 62.8 kN, and the tensile strength of concrete τ _γ corresponds to a tensile load of 37.68 kN, which allows much make full use of the strength properties of this reinforcement.

Assuming a different value of the number of sectors n or coefficient B, it is possible to obtain sections with other geometric characteristics or adhesion to concrete, respectively.

The proposed design is illustrated by the drawings.

FIG. 1 A cross section of a composite reinforcement consisting of 6 sectors is shown.

FIG. 2 A cross section of a composite reinforcement consisting of 10 sectors is shown.

A method of manufacturing this reinforcement is that after impregnation with a compound, roving threads are sent to a forming die, the cross-sectional characteristics of which are determined by the calculation presented here, where the profile of the reinforcing bar is formed and the binder is polymerized (pultrusion method).

In addition, it is worth noting that this cross section of the reinforcement, in contrast to the circular section, prevents peeling of the protective layer of concrete due to the resulting castle-type connection between concrete and reinforcement in the plane of the cross section of the reinforced element.

The proposed composite reinforcement has the necessary quality characteristics that allow it to be widely used for reinforcing monolithic and prefabricated concrete structures.

Claims (1)

Composite reinforcement, which is a supporting rod of high-strength non-metallic fibers impregnated with a polymeric binder, characterized in that the cross-sectional profile of this reinforcement is a combination of an even number of sectors of equal angular measure, alternating and belonging to two concentric circles with diameters Dmin and Dmax, which together add up to full angle.

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