CN112211346A

CN112211346A - Rubber aggregate concrete beam for FRP rib structure

Info

Publication number: CN112211346A
Application number: CN202011153484.5A
Authority: CN
Inventors: 赵秋红; 王菲; 刘凯
Original assignee: Tianjin University
Current assignee: Tianjin University
Priority date: 2020-10-26
Filing date: 2020-10-26
Publication date: 2021-01-12

Abstract

The invention discloses a rubber aggregate concrete beam for an FRP rib structure, which aims at solving the problems that the ordinary concrete beam of an FRP rib has larger crack width and deflection under the action of static load and has more obvious brittleness characteristic during damage, and replaces ordinary concrete with structural rubber aggregate concrete with larger deformability and excellent crack resistance so as to improve the flexural performance of the FRP rib concrete beam under the action of the static load. The FRP rib structure is formed by a rubber aggregate concrete beam comprising a steel bar frame and poured concrete, wherein the steel bar frame comprises steel bar frame vertical ribs, FRP tensioned ribs and steel bar stirrups, two ends of the FRP tensioned ribs are respectively provided with a hook, the hooks and the FRP tensioned ribs are bound in a cross-shaped mode by glass fiber bundles or nylon ropes and are sealed by epoxy resin glue; the concrete is structural rubber aggregate concrete; and combining the FRP rib and the rubber aggregate concrete for the structure to form the rubber aggregate concrete beam for the FRP rib structure.

Description

Rubber aggregate concrete beam for FRP rib structure

Technical Field

The invention relates to the technical field of civil engineering FRP (fiber reinforced plastic) reinforced concrete structures, in particular to a novel composite structure system, namely a rubber aggregate concrete beam for an FRP rib structure.

Background

The structural damage caused by the corrosion of the steel bars in the concrete structure seriously threatens the long-term safety of the reinforced concrete structure and restricts the healthy development of the concrete structure. Fiber Reinforced Polymer (FRP) ribs are produced by mixing a plurality of strands of continuous long fibers (such as glass fibers, carbon fibers, aramid fibers and the like) with a resin matrix (such as unsaturated polyester, polyethylene resin, polypropylene and the like) according to a certain proportion, adding some auxiliary materials (such as initiators, accelerators and the like) at the same time, and performing a series of processing technologies such as pultrusion and the like. Because the FRP bars have the advantages of good corrosion resistance, light weight, high strength, good electromagnetic insulation, good fatigue resistance, good designability and the like, numerous scholars at home and abroad recommend that the FRP bars replace reinforcing steel bars to be used for reinforcing concrete structures, the problem of reinforcing steel bar corrosion is fundamentally solved, and the maintenance cost and the comprehensive cost of building structures are effectively reduced. Accordingly, FRP reinforced concrete structures have become a focus of attention.

Research shows that the FRP reinforced concrete beam has wider crack width under the action of static load than the reinforced concrete beam, and the anti-cracking performance is lower than that of the reinforced concrete beam, so that the state of the FRP reinforced concrete beam under normal use load cannot meet the standard requirement and the comfort requirement easily. When the FRP reinforced concrete beam is damaged, two damage forms are presented: when the reinforcement ratio is lower, the failure is expressed as the breaking of the FRP reinforcement, namely the tensile failure; when the reinforcement ratio is proper, the concrete in the compression area is crushed, and the damage of the beam shows certain ductility characteristics, namely, the compression damage, which is a more ideal damage form. However, whether the FRP rib is broken or the concrete in the compression area is crushed, the FRP rib and the concrete in the compression area are in a typical brittle failure mode, and compared with the FRP rib and the concrete in the super-reinforced concrete beam, the FRP rib and the concrete in the super-reinforced concrete beam are recommended in domestic and foreign documents.

In view of the above-described problems of the FRP reinforced concrete beam, improvement of concrete type is considered. The rubber aggregate concrete has become a hot spot of the current domestic and foreign research as a novel civil engineering material, and the application of the rubber aggregate reduces the black pollution caused by the accumulation of a large amount of tires to a great extent. The rubber aggregate concrete is special concrete prepared by using rubber particles as a constituent material of cement concrete, is also called elastic concrete, and has the mechanical property of common concrete, and also has the high elasticity and deformation crack resistance of rubber. The fine rubber particles areIs prepared from worn automobile tires by crushing, and has particle diameter of 1-2mm or less and density of 1.0g/cm³. In addition, the rubber aggregate concrete has the advantages of good ductility and toughness, excellent crack resistance, good durability, small density, good impact resistance and damping resistance, heat insulation and sound insulation and the like. The test on the reinforced rubber aggregate concrete beam shows that the ultimate bending bearing capacity of the reinforced rubber aggregate concrete beam is similar to that of the common reinforced concrete beam when the strength grade of the reinforced rubber aggregate concrete beam is the same as that of the common reinforced concrete beam, so that the anti-cracking performance is improved, and the ductility is improved.

Disclosure of Invention

Aiming at the prior art, the invention provides a rubber aggregate concrete beam system for an FRP rib structure. Aiming at the problems that the ordinary FRP rib concrete beam has large crack width and deflection under the action of static load and has obvious brittleness characteristic during damage, the ordinary concrete is replaced by structural rubber aggregate concrete with large deformability and excellent anti-cracking performance so as to improve the bending performance of the FRP rib concrete beam under the action of the static load.

In the ordinary concrete beam with the FRP ribs, the elastic modulus of the FRP material is only 1/4-1/3 of steel, so that the FRP ribs are greatly deformed in the loading process, and the ordinary concrete has small deformability and cannot be well coordinated with the FRP ribs, so that the beam has large cracks and is characterized by brittle failure. The anti-cracking performance and the deformability of the rubber aggregate concrete for the structure are both obviously higher than those of common concrete, the strength of the rubber aggregate concrete for the structure is equal to that of the reference common concrete, the rubber aggregate concrete beam for the FRP rib structure is formed by combining the rubber aggregate concrete beam with the FRP ribs, on one hand, the anti-cracking performance of the beam is improved, on the other hand, the higher deformability of the rubber aggregate concrete beam can be better coordinated with the FRP ribs to deform, the limit deformability of the beam is improved, the advantage of high tensile strength of the FRP ribs can be brought into full play, and the ductility of the beam is improved.

In order to solve the technical problems, the rubber aggregate concrete beam for the FRP rib structure comprises a steel bar frame and poured concrete, wherein the steel bar frame comprises steel bar frame vertical ribs, FRP tension ribs and steel bar stirrups, two ends of the FRP tension ribs are respectively provided with a hook, and the hooks and the FRP tension ribs are bound in a crisscross mode by glass fiber bundles or nylon ropes and are sealed by epoxy resin glue; the concrete is structural rubber aggregate concrete.

Furthermore, the rubber aggregate concrete beam for the FRP rib structure is characterized in that the diameter of the hook is equal to that of the FRP tension rib, and the length of the hook is 5 times of the diameter.

The FRP tensile rib is a GFRP rib or a BFRP rib, and the surface of the FRP tensile rib is non-smooth, is provided with one or more of threads, ribs, indentations and bonded sand, so that the FRP tensile rib and the rubber aggregate concrete for the structure are effectively bonded.

Compared with the prior art, the invention has the beneficial effects that:

(1) the strength of the rubber aggregate concrete is controlled, and the rubber aggregate concrete for the structure is adopted, so that the adverse effect on the bending performance of the FRP concrete beam caused by the reduction of the concrete strength can be avoided.

(2) Rubber particles are introduced into the FRP rib concrete beam, the deformation of the rubber aggregate concrete is coordinated with the deformation of the FRP ribs, the development of cracks is delayed, the tensile strength of the FRP ribs is fully exerted, the ultimate bearing capacity is improved, and the ductility during damage is improved.

(3) The problem of high maintenance cost caused by steel bar corrosion is solved, the service life of a concrete structure is prolonged, waste tires are recycled, and the problem of black pollution caused by the waste tires is reduced.

(4) The FRP rib rubber aggregate concrete member has larger deformability, and the material is expected to keep the elastic characteristic under the action of earthquake, thereby avoiding or greatly reducing the residual deformation and being expected to become a recoverable functional structure.

Drawings

FIG. 1 is a schematic structural view of a rubber aggregate concrete beam for an FRP rib structure according to the present invention;

fig. 2 is a schematic cross-sectional structure of the beam shown in fig. 1.

In the figure: 1-steel bar frame vertical bar, 2-steel bar stirrup, 3-FRP tension bar and 4-structural rubber aggregate concrete.

Detailed Description

The conception of the invention is as follows: the existing research shows that the strength and the elastic modulus of the rubber aggregate concrete are reduced compared with the common concrete, but the reduction of the concrete strength can be reduced by pretreating rubber particles, changing the interface performance of rubber and cement paste or optimally designing the mixing ratio of the rubber aggregate concrete, and the rubber aggregate concrete for the structure is prepared. Meanwhile, rubber aggregate is introduced into the FRP rib concrete beam, the deformation of the rubber aggregate concrete is coordinated with the deformation of the FRP ribs, the development of cracks is delayed, the tensile strength of the FRP ribs is fully exerted, the ultimate bending bearing capacity is improved, and the ductility during damage is improved.

The invention will be further described with reference to the following figures and specific examples, which are not intended to limit the invention in any way.

The rubber aggregate concrete beam for the FRP rib structure is a novel composite structure system, and common concrete is replaced by rubber aggregate concrete with higher ductility and crack resistance on the basis of the common concrete beam for the FRP rib. The introduction of rubber aggregate can improve the crack resistance, ultimate deformability and ductility at failure of the beam. As the bonding property of the FRP ribs and the rubber aggregate concrete is reduced compared with that of common concrete, the beam end needs to be reinforced with anchoring measures. And the FRP tension bar is anchored at the end of the rubber aggregate concrete beam. As shown in fig. 1 and 2, the FRP rib structural rubber aggregate concrete beam of the present invention includes a steel frame composed of a steel frame vertical rib 1, an FRP tension rib 3 and a steel stirrup 2, and structural rubber aggregate concrete. The anchoring of the FRP tensile rib at the end of the rubber aggregate concrete beam adopts the way that hooks are respectively arranged at two ends of the FRP tensile rib 3, and the hooks and the FRP tensile rib 3 are bound by glass fiber bundles or nylon ropes in a crisscross way and are sealed by epoxy resin glue;

the strength of the common rubber aggregate concrete is reduced along with the increase of the mixing amount of the rubber. When the concrete strength is reduced too much, the ultimate bending bearing capacity of the FRP rib concrete beam can be influenced, and the minimum requirement on the concrete strength grade in a concrete structure cannot be met. The prior literature indicates that the rubber aggregate concrete can reach the strength grade of C20-C50 by adjusting the mixing proportion, and the literature indicates that the rubber particles can be pretreated by water, carbon tetrachloride solution, sodium hydroxide saturated solution and the like to reduce the reduction of the strength of the rubber aggregate concrete. Therefore, the rubber aggregate concrete with the same strength as common concrete for the structure can be prepared by comprehensively adopting the method of mixing ratio optimization design and rubber particle modification treatment, and the technicians in the field can adjust the mixing ratio and/or carry out the modification treatment on the rubber particles according to the design requirements under the inspiration of the invention, and the concrete content is as follows:

the optimal design of the mix proportion of the rubber aggregate concrete for the structure is realized by trial assembly, the cement is PO 42.5 grade cement, the fine aggregate is medium sand, the coarse aggregate is crushed stone with the particle size of 5-20mm, and the rubber particle is 1-2 mm. For the mixing amount of the rubber particles, 50kg/m can be selected³、100kg/m³And 150kg/m³Three mixing amounts. Pretreating selected rubber particles: firstly, cleaning dust on the surface of rubber particles with clean water, then soaking the rubber particles in 10% NaOH solution for 30 minutes, washing the rubber particles with clean water until the pH value of the solution is 7, and airing the rubber particles for later use.

The surface treatment mode of the FRP tensioned rib 3 can comprise rib winding, indentation or sand sticking, and a GFRP rib or a novel material BFRP rib which is commonly used in engineering with better economy is selected, but a smooth round FRP rib can not be used. The anchoring of the end part of the FRP tension rib 3 can be performed by crisscross binding with the FRP tension rib by using a short steel bar with the diameter equal to that of the FRP tension rib 3 and the length of about 5d, binding by using a glass fiber bundle or a nylon rope and sealing by using epoxy resin glue.

Example (b):

(1) and controlling the strength grade of the rubber aggregate concrete. The material strength is the key of the structural design, and the fine control of the material strength is beneficial to the reliability and the safety of the structural design. GB 50010 and 2010 concrete structure design Specification stipulates that in a reinforced concrete beam, when the strength grade of a steel bar is HRB400, the strength grade of concrete is not lower than C25. Therefore, it is necessary to find a suitable method for ensuring the preparation of rubber aggregate concrete with the same strength grade as that of ordinary concrete.

(2) And determining the adding mode of the rubber aggregate. The design method of the mix proportion of the rubber aggregate concrete is divided into two types in general: the first is that the rubber particles are substituted for fine aggregate with the same volume, the rubber particles are substituted for coarse aggregate with the same volume, and the rubber particles are substituted for partial fine aggregate and partial coarse aggregate with the same volume, the content of other components is unchanged, and the water-cement ratio and the sand rate are unchanged; the second is that the rubber particles replace a certain proportion of the total volume, the content of the other components is changed, and the water-cement ratio, the sand rate and the content of the water reducing agent are adjusted. The first method of substituting aggregate with rubber particles in equal volume is to reduce the strength of rubber aggregate concrete in different degrees with the increase of the mixing amount, and the latter method can reach the same level with the strength grade of common concrete by adjusting the water-cement ratio, the sand ratio, the content of a water reducing agent and the like, so the second mixing ratio method is selected.

(3) And (3) modifying the rubber particles. In order to reduce the reduction of the strength of the rubber aggregate concrete, the rubber particles are pretreated to improve the interface state between the rubber particles and the cement paste and strengthen the bonding between the rubber particles and the cement paste. Therefore, before stirring, the rubber particles are modified by physical or chemical means such as water, latex cleaning agent, sodium hydroxide solution, carbon tetrachloride solution and the like, so as to make up for the reduction of concrete strength caused by the incorporation of rubber.

(4) And selecting the FRP tension rib type. The FRP ribs can be divided into CFRP ribs, GFRP ribs, AFRP ribs and BFRP ribs according to the types of fibers formed by the FRP ribs, and the FRP ribs are more applied in engineering in consideration of the economy of the GFRP ribs and the BFRP ribs. The prior literature indicates that the bonding property of the smooth round FRP rib and concrete is poor, so the surface of the FRP rib is treated, and the FRP rib with threads, wound ribs, indentations or bonded sand on the surface is selected to enhance the bonding between the FRP rib and the concrete and ensure that the FRP rib and the concrete can bear deformation together.

(5) And the FRP ribs are anchored in the rubber aggregate concrete beam. The prior literature shows that the bonding property of the FRP rib and concrete is reduced along with the increase of the mixing amount of rubber, and certain measures are taken for anchoring the end part of the FRP rib in order to avoid the slippage and damage of the FRP rib rubber aggregate concrete beam in the loading process. The FRP rib with the bent hook at the end can be applied, and reliable mechanical measures can be taken for the FRP rib which can not be directly bent due to the processing technology problem. Namely, a short steel bar with the diameter equal to that of the FRP bar and the length of about 5d is crosswise bound with the tensioned FRP bar, bound by a glass fiber bundle or a nylon rope and then sealed by epoxy resin; and pouring concrete after the epoxy resin is completely cured.

While the present invention has been described with reference to the accompanying drawings, the present invention is not limited to the above-described embodiments, which are illustrative only and not restrictive, and various modifications which do not depart from the spirit of the present invention and which are intended to be covered by the claims of the present invention may be made by those skilled in the art.

Claims

1. A rubber aggregate concrete beam for an FRP (fiber reinforced Plastic) rib structure comprises a steel bar frame and poured concrete, wherein the steel bar frame comprises steel bar frame vertical ribs (1), FRP tension ribs (3) and steel bar stirrups (3), and is characterized in that two ends of the FRP tension ribs (3) are respectively provided with a hook, the hooks and the FRP tension ribs (3) are bound in a cross-shaped manner by glass fiber bundles or nylon ropes and are sealed by epoxy resin glue; the concrete is structural rubber aggregate concrete (4).

2. The FRP rib structural rubber aggregate concrete beam as claimed in claim 1, wherein the hook has a diameter equal to the diameter of the FRP tendon and a length 5 times the diameter.

3. The FRP rib structural rubber aggregate concrete beam as claimed in claim 1, wherein the FRP tendon (3) is selected from GFRP rib or BFRP rib, the surface of the FRP tendon (3) is selected from one or more of non-smooth surface, screw thread, winding rib, indentation and sand sticking, so as to ensure the effective bonding of the FRP tendon (3) and the structural rubber aggregate concrete (4).