Method for replacing steel bars in anti-bending component with modified bamboo bars

Abstract

The invention provides a method for replacing reinforcing steel bars in an anti-bending component with modified bamboo reinforcements, which comprises the following steps: S1, modifying natural bamboo reinforcements by chemical and physical methods to manufacture the modified bamboo reinforcements; s2, steel bar hoops are manufactured, and beam modified bamboo bars and beam steel bars are fixed to the steel bar hoops; s3, reserving anchoring lengths of the beam modified bamboo reinforcements and the beam reinforcements so as to bend and anchor the beam modified bamboo reinforcements and the beam reinforcements on the reinforcements of the reinforced concrete main beam; s4, a formwork is manufactured, and the modified bamboo-steel concrete plates, the modified bamboo-steel concrete beams, the reinforced concrete beams and the reinforced concrete columns are poured; and S5, the concrete is hardened, the formwork is dismantled, and the steel-modified bamboo reinforced concrete structure is formed. According to the method for replacing the steel bars in the bending-resistant component with the modified bamboo bars, the using amount of the steel bars can be greatly reduced so as to reduce the carbon emission generated in the whole life process of civil engineering, and the main performance such as ductile failure of the reinforced concrete bending-resistant component is achieved; and the problem of insufficient brittle failure of plain concrete and natural bamboo reinforced concrete members is overcome.

Description

Technical Field

[0001] The invention relates to the technical field of green, low-carbon and new materials, and in particular to a method for replacing steel bars in bending-resistant members with modified bamboo bars. Background Art

[0002] Reinforced concrete is widely used in various fields of civil engineering due to its excellent mechanical properties exhibited by the nearly perfect combination of two different materials, steel bars and concrete. It has greatly promoted the development and transformation of the construction industry and has become the main material of modern construction. However, the use of reinforced concrete consumes a large amount of non-renewable resources, which has a significant impact on the ecological environment. In addition, the relatively high cost of steel has affected its use in developing countries and economically backward rural areas. For this reason, bamboo bars are used in the construction field to replace the steel bars in reinforced concrete. However, the tensile properties of natural bamboo bars are obviously insufficient, resulting in poor strength of natural bamboo reinforced concrete components. Summary of the invention

[0003] The purpose of the present invention is to provide a method for replacing steel bars in bending-resistant members with modified bamboo bars, so as to solve the technical problem of poor strength of traditional natural bamboo-reinforced concrete members.

[0004] To achieve the above object, the technical solution adopted by the present invention is: to provide a method for replacing steel bars in a bending-resistant member with modified bamboo bars, the method comprising the following steps: S1. Modifying natural bamboo tendons by chemical and physical methods to produce modified bamboo tendons; S2, making steel hoops to fix the beam modified bamboo bars and beam steel bars to the steel hoops; S3, the modified bamboo bars and beam steel bars are reserved with anchorage lengths to be bent and anchored on the steel bars of the reinforced concrete main beam; S4, making formwork, pouring modified bamboo-steel concrete slabs, modified bamboo-steel concrete beams, reinforced concrete beams, and reinforced concrete columns; S5. After the concrete hardens, the formwork is removed to form a steel-modified bamboo reinforced concrete structure.

[0005] In one embodiment, step S1 specifically includes: S11. Material selection: select multi-year-old bamboo as raw material, clean the branches and tips of the bamboo, and cut the bamboo into bamboo pieces of specific sizes; and remove the green and yellow parts of the bamboo pieces by machine or manual method; S12, boiling and soaking, putting bamboo slices into water and boiling to remove water-soluble organic matter and potential residual air; S13, delignification, using peroxyformic acid solution to delignify the bamboo chips under the catalytic action of sulfuric acid until the bamboo chips turn white, so that the molecular structures of lignin and hemicellulose are effectively removed, while the molecular structure of cellulose is well preserved; S14, neutralization extraction, using an alkaline solution to neutralize the bamboo chips after delignification treatment, and then washing the bamboo fibers with deionized water to remove the residual lignin and hemicellulose components on the bamboo chips; S15, post-processing, subjecting the bamboo fiber obtained in S14 to microwave heating, screening and inspection sub-processes; S16, screening, screening the post-processed bamboo fibers to obtain modified bamboo tendons.

[0006] In one embodiment, the modified bamboo-steel concrete slab comprises a concrete slab body and slab-modified bamboo bars and slab steel bars disposed inside the concrete body; The plate steel bars are arranged on the upper and lower sides of the concrete plate body, the plate modified bamboo bars are arranged between the plate steel bars, and the plate modified bamboo bars and the plate steel bars are perpendicular to each other; Before pouring the modified bamboo-steel concrete slab, the slab modified bamboo reinforcement is tied and fixed on the slab reinforcement.

[0007] In one embodiment, the modified bamboo-steel concrete beam comprises a concrete beam body and the steel bar hoop disposed in the concrete beam body; The steel stirrups include beam modified bamboo bars, beam steel bars, and steel stirrups; The modified bamboo bars, beam steel bars and steel stirrups are all located inside the main body of the concrete beam. The steel stirrups are rectangular in structure. The beam steel bars are arranged on the inner side of the bottom angle of the steel stirrups. The modified bamboo bars are arranged on the inner side of the top angle of the steel stirrups. The modified bamboo bars are also arranged at the bottom of the steel stirrups. The modified bamboo bars and beam steel bars are both perpendicular to the plane where the steel stirrups are located.

[0008] In one embodiment, the beam-modified bamboo reinforcement at the bottom of the steel stirrup is arranged on one side of the bottom of the steel stirrup.

[0009] In one embodiment, the steel-modified bamboo reinforced concrete structure includes reinforced concrete columns, reinforced concrete main beams, modified bamboo-steel concrete slabs, and modified bamboo-steel concrete beams; wherein the reinforced concrete columns are arranged at four corners, the two ends of the reinforced concrete main beams are connected to the reinforced concrete columns to form a rectangular frame, the two ends of the modified bamboo-steel concrete beams are fixed on the reinforced concrete main beams, and the modified bamboo-steel concrete slabs are laid on the modified bamboo-steel concrete beams and the reinforced concrete main beams.

[0010] In one embodiment, the modified bamboo reinforcement obtained in S1 is further processed by brushing epoxy resin on the surface of the bamboo reinforcement and air-drying it naturally; after air-drying, epoxy resin and polyamide resin curing agent are brushed on the surface of the bamboo reinforcement again, and corundum particles are evenly sprayed on the surface of the bamboo reinforcement to enhance the roughness, corrosion resistance and water resistance of the bamboo reinforcement; the treated modified bamboo reinforcement is left to stand at room temperature and away from light for at least 3 days to ensure that the epoxy resin is fully cured and bonds the bamboo reinforcement and corundum.

[0011] In one embodiment, in S4, before pouring concrete, the mold needs to be fully cleaned to ensure that it is flat, free of cracks and wear, and the mold is wetted with a release agent and padded with paper in advance to facilitate demoulding.

[0012] One or more of the above technical solutions in the embodiments of the present invention have at least the following technical effects or advantages: Since the tensile properties of natural bamboo reinforcement are obviously insufficient, this application chemically and physically modifies natural bamboo reinforcement to make it have high strength and high elastic modulus. The modified bamboo reinforcement material replaces the steel bars in civil engineering components, which can reduce the carbon emissions generated by the entire civil engineering construction process. In addition, the modified bamboo-reinforced concrete flexural members made by using modified bamboo reinforcement materials to replace steel bars can not only greatly reduce the amount of steel bars, but also have the main properties of reinforced concrete flexural members such as ductile failure, overcoming the shortcomings of brittle failure of plain concrete and natural bamboo reinforcement concrete members. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0014] Figure 1 A plan view of a steel-modified bamboo reinforced concrete structure provided by an embodiment of the present invention; Figure 2 A schematic structural diagram of a modified bamboo-steel concrete beam provided in an embodiment of the present invention; Figure 3 A schematic structural diagram of a modified bamboo-steel concrete slab provided in an embodiment of the present invention; Figure 4 The cracking loads of the flexural members at different alternative positions of the upper part provided by the embodiments of the present invention; Figure 5 The relationship between the ultimate load and the upper replacement position of the bending-resistant member provided in the embodiment of the present invention; Figure 6The cracking loads of the flexural members with different alternative numbers of upper portions provided by the embodiments of the present invention; Figure 7 The relationship between the ultimate load and the number of upper replacements of the bending-resistant member provided in the embodiment of the present invention; Figure 8 Provides a relationship between the ultimate load of a bending member and the lower alternative position for an embodiment of the present invention; Fig. 9 The relationship between the cracking load and the number of lower replacements of the bending-resistant member provided in the embodiment of the present invention; Fig.10 The relationship between the ultimate load and the number of lower replacements of the bending-resistant member provided in the embodiment of the present invention; Fig.11 The relationship between the load and the number of overall replacements of the bending-resistant member provided in the embodiment of the present invention; Fig.12 The present invention provides an embodiment of the present invention provides a change trend of the ultimate load reduction rate of the bending member.

[0015] The respective reference numerals are as follows: 1. Reinforced concrete column; 2. Reinforced concrete main beam; 3. Modified bamboo-steel concrete beam; 4. Modified bamboo-steel concrete slab; 5. Modified bamboo reinforcement in beam; 6. Beam reinforcement; 7. Steel stirrups; 8. Concrete beam body; 9. Modified bamboo reinforcement in slab; 10. Slab reinforcement; 11. Concrete body. DETAILED DESCRIPTION

[0016] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0017] In the description of the present invention, it should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0018] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0019] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0020] See also Figures 1 to 3 The embodiment of the present application provides a method for replacing steel bars in bending-resistant members with modified bamboo bars, comprising the following steps: S1, modifying natural bamboo bars by chemical and physical methods to produce modified bamboo bars; S2, producing steel bar hoops to fix the modified bamboo bars 5 and the beam steel bars 6 to the steel hoops 7; S3, reserving anchoring lengths for the modified bamboo bars 5 and the beam steel bars 6 to be bent and anchored on the steel bars of the reinforced concrete main beam 2; S4, producing formwork to cast modified bamboo-steel concrete slabs 4, modified bamboo-steel concrete beams 3, reinforced concrete beams, and reinforced concrete columns 1; S5, the concrete hardens, and the formwork is removed to form a steel-modified bamboo bar concrete structure.

[0021] The method for replacing steel bars in flexural members with modified bamboo bars provided in this embodiment is to chemically and physically modify natural bamboo bars so that they have high strength and high elastic modulus. The modified bamboo bar material replaces the steel bars in civil engineering members, which can reduce the carbon emissions generated by the entire life cycle of civil engineering. In addition, the modified bamboo-reinforced concrete flexural members made by using modified bamboo bar materials to replace steel bars can not only greatly reduce the amount of steel bars, but also have the main properties of reinforced concrete flexural members such as ductile failure, overcoming the shortcomings of brittle failure of plain concrete and natural bamboo reinforced concrete members.

[0022] In one embodiment, step S1 specifically includes: S11. Material selection: select multi-year-old bamboo as raw material (preferably 4-year-old bamboo), clean the branches and tips of the bamboo, and cut the bamboo into bamboo pieces of specific sizes; and remove the green and yellow parts of the bamboo pieces by machine or manual method; S12, boiling and soaking, putting bamboo slices into water and boiling to remove water-soluble organic matter and potential residual air; S13, delignification, using peroxy formic acid solution under the catalytic action of sulfuric acid (at 40°C~45°C) to delignify the bamboo chips (sodium hydroxide and sodium sulfite solution or ammonia solution can also be used instead of peroxy formic acid solution to delignify the bamboo chips) until the bamboo chips turn white, so that the molecular structure of lignin and hemicellulose is effectively removed, while the molecular structure of cellulose is well preserved; S14, neutralization extraction, using an alkaline solution (such as sodium hydroxide solution, etc.) to neutralize the bamboo chips after delignification treatment, and then washing the bamboo fibers with deionized water to remove the residual lignin and hemicellulose components on the bamboo chips; S15, post-processing, subjecting the bamboo fiber obtained in S14 to microwave heating, screening and inspection sub-processes; S16, screening, screening the post-processed bamboo fibers to obtain modified bamboo tendons.

[0023] See also Figure 3 In one embodiment, the modified bamboo-steel concrete slab 4 includes a concrete slab body, a board-modified bamboo reinforcement 9 and a board-reinforced steel bar 10 arranged inside the concrete body 11; the board-reinforced steel bar 10 is arranged on the upper and lower sides of the concrete slab body, the board-modified bamboo reinforcement 9 is arranged between the board-reinforced steel bar 10, and the board-modified bamboo reinforcement 9 and the board-reinforced steel bar 10 are perpendicular to each other; before casting the modified bamboo-steel concrete slab 4, the board-modified bamboo reinforcement 9 is tied and fixed to the board-reinforced steel bar 10. Since the short-span reinforcement on the outside is more important, the long-span reinforcement on the inside is relatively less important, so the board-modified bamboo reinforcement 9 is used to replace the long-span reinforcement on the inside. In addition, the board-modified bamboo reinforcement 9 can also be conveniently fixed on the board-reinforced steel bar 10.

[0024] See also Figure 1 In one embodiment, the steel-modified bamboo reinforced concrete structure includes a reinforced concrete column 1, a reinforced concrete main beam 2, a modified bamboo-steel concrete slab 4, and a modified bamboo-steel concrete beam 3; wherein the reinforced concrete column 1 is arranged at the four corners, the two ends of the reinforced concrete main beam 2 are connected to the reinforced concrete column 1 to form a rectangular frame, the two ends of the modified bamboo-steel concrete beam 3 are fixed on the reinforced concrete main beam 2, and the modified bamboo-steel concrete slab 4 is laid on the modified bamboo-steel concrete beam 3 and the reinforced concrete main beam 2.

[0025] In the steel-modified bamboo reinforced concrete structure, the columns and the reinforced concrete main beam 2 are the main load-bearing parts, so the traditional reinforced concrete structure is adopted. The sub-beams and concrete slabs located between the reinforced concrete main beams 2 are less important than the columns and the reinforced concrete main beams 2. Therefore, modified bamboo-steel concrete slabs 4 and modified bamboo-steel concrete beams 3 can be set to save the consumption of steel bars in the concrete structure while meeting the required strength of the structure to the greatest extent.

[0026] In one embodiment, the modified bamboo reinforcement obtained in S1 is further processed by brushing epoxy resin on the surface of the bamboo reinforcement and air-drying it naturally; after air-drying, epoxy resin and polyamide resin curing agent are brushed on the surface of the bamboo reinforcement again, and corundum particles are evenly sprayed on the surface of the bamboo reinforcement to enhance the roughness, corrosion resistance and water resistance of the bamboo reinforcement; the treated modified bamboo reinforcement is left to stand at room temperature and away from light for at least 3 days to ensure that the epoxy resin is fully cured and bonds the bamboo reinforcement and corundum.

[0027] In one embodiment, in S4, before pouring concrete, the mold needs to be fully cleaned to ensure that it is flat, free of cracks and wear, and the mold is wetted with a release agent and padded with paper in advance to facilitate demoulding.

[0028] See also Figure 2 In one embodiment, the modified bamboo-steel concrete beam 3 includes a concrete beam body 8 and a steel bar hoops arranged in the concrete beam body 8; the steel bar hoops include beam modified bamboo bars 5, beam steel bars 6, and steel hoop bars 7; the beam modified bamboo bars 5, beam steel bars 6, and steel hoop bars 7 are all located inside the concrete beam body 8, and the steel hoop bars 7 are of a rectangular structure. The beam steel bars 6 are arranged on the inner side of the bottom angle of the steel hoop bars 7, and the beam modified bamboo bars 5 are arranged on the inner side of the top angle of the steel hoop bars 7. The bottom of the steel hoop bars 7 is also provided with beam modified bamboo bars 5, and the beam modified bamboo bars 5 and beam steel bars 6 are both perpendicular to the plane where the steel hoop bars 7 are located.

[0029] In order to explore the number of replaceable beam reinforcements in reinforced concrete beams and the positions of the beam reinforcements that should be replaced. In this embodiment, 33 different control groups are designed, and 3 specimens are made corresponding to each group of variables, totaling 99 specimens. The specimen numbers and corresponding variables are shown in Table 1, and C20, C30, and C40 represent different concrete strength grades. For example, KW01-C20 represents a modified bamboo-reinforced concrete flexural member with a concrete strength grade of C20.

[0030] Specifically, the specimen size is 150×150×600mm (width×height×length), and the cross-sectional size of the modified bamboo reinforcement is 10×5mm (width×height). Three reinforcements are configured at the bottom and two reinforcements are configured at the top. The reinforcement positions are fixed by stirrups and binding wires to ensure the stability of the specimen structure. The protective layer thickness is 25mm, and the concrete strength grades are C20, C30 and C40 (the average compressive strength of each grade of concrete is 23.2MPa, 33.9MPa and 42.7MPa, respectively).

[0031] Table 1 Numbers and variables of modified bamboo-reinforced concrete flexural members

[0032] 1.1 Impact of replacing upper reinforcement 1.1.1 Impact of upper replacement position The cracking load and ultimate load of concrete flexural members are two key indicators for evaluating their flexural performance. The cracking load specifically refers to the load value when visible cracks begin to appear on the surface of the member as the bending force gradually increases. The ultimate load represents the maximum load that the member can withstand under the action of bending force. If this load value is exceeded, the member will be damaged or lose stability. The cracking load is not only an important precursor to the ultimate load, but also an important basis for evaluating the crack resistance of the member. In the design and evaluation process of the member, the size of the cracking load and its impact must be fully considered to ensure that the member will not crack or crack prematurely under normal use conditions. At the same time, as a core indicator of member design and safety assessment, the ultimate load directly determines the bearing capacity and safety reserve of the member.

[0033] The cracking and ultimate load data of the components with different modified bamboo reinforcement replacement positions in the upper part are shown in Table 2. KW12 is a plain concrete flexural member, KW01 has 2 modified bamboo reinforcements in the upper part and 3 steel bars in the lower part; KW02 and KW03 have bamboo reinforcement-steel and steel bar-bamboo reinforcement in the upper part and three steel bars in the lower part, and KW04 has 2 steel bars in the upper part and 3 steel bars in the lower part.

[0034] Table 2 Bending performance of components at different replacement positions in the upper part

[0035] It can be seen from Table 2 that when the concrete strength remains the same, the cracking loads of each component show a high degree of similarity, and the difference between them is within the range of 2kN. Comparing the cracking loads of components with different concrete strengths, it can be seen that the cracking load of flexural components shows a significant increasing trend with the increase of concrete strength grade, such as Figure 4 Obviously, the cracking load of concrete flexural members mainly depends on the concrete strength, and the type and performance of the member reinforcement have limited influence on it. In order to study the change trend of the ultimate load of the modified bamboo bars replacing the steel bars at different positions on the upper part of the flexural members, the table data were sorted and analyzed, and the results were obtained. Figure 5 .

[0036] like Figure 5As shown in the figure, as the concrete strength grade gradually increases from C20 to C30 and C40, the ultimate load of the corresponding components also shows an increasing trend. This phenomenon reveals the positive effect of the increase in concrete strength on enhancing the flexural bearing capacity of components under the ultimate state. On the other hand, the ultimate load fluctuations of the four components KW01 to KW04 with the same concrete strength grade are small, showing similar ultimate bearing capacities. Compared with the KW04 component which is all steel bars, the ultimate load of the flexural component with concrete strength grade C20 of the KW01 component which is all modified bamboo bars differs by 9.3kN, that is, a difference of 6.9%; the ultimate load of the flexural component with concrete strength grade C30 differs by 9.1kN, that is, a difference of 6.5%; the ultimate load of the flexural component with concrete strength grade C40 differs by 8.5kN, that is, a difference of 10kN. The maximum difference in ultimate load does not exceed 10kN, that is, a difference of 7%. In summary, by changing the replacement position of the upper modified bamboo bars, the cracking and ultimate load changes of the components are limited. When the lower reinforcement conditions are the same, the change of upper reinforcement has limited effect on the flexural bearing capacity of concrete.

[0037] The reason is that when a concrete flexural member is subjected to four-point bending loading, the upper area of ​​the member is mainly subjected to compressive stress, and this part of the stress is mainly borne by the concrete itself. As for the upper reinforcement, its main function is to partially enhance the bearing capacity, resist negative bending moment, prevent cracking and improve ductility. Whether it is modified bamboo reinforcement or steel reinforcement, its performance is sufficient to meet the requirements. When the modified bamboo reinforcement replaces the upper reinforcement, the ultimate load of all specimens is similar. The decrease in ultimate load caused by the change in the upper reinforcement does not exceed 7%. It shows that under the current test conditions, the modified bamboo reinforcement can completely replace the upper reinforcement of the flexural member while ensuring a small loss in bearing capacity.

[0038] 1.1.2 Impact of the number of upper substitutions When the lower part is all steel bars, the average value of KW02 and KW03 data is taken as the representative value of cracking and ultimate load when the number of modified bamboo bars is 1. The influence of the change in the replacement number of modified bamboo bars in the upper part on the load of the flexural member is shown in Table 3.

[0039] Table 3 Bending performance of components with different replacement numbers in the upper part

[0040] As shown in Table 3, the cracking loads of modified bamboo-reinforced concrete flexural members with the same concrete strength are basically the same, while the cracking loads of members with different concrete strengths are quite different, and the change in the number of modified bamboo reinforcement replacements has limited effect on them. As the concrete strength gradually increases, the cracking load of the flexural member also gradually increases, such as Figure 6This shows that concrete strength is the key to determining the cracking load, and the number and type of reinforcement have relatively limited influence on the cracking load. In order to study the ultimate load variation trend of modified bamboo reinforcement replacing different numbers of steel bars in the upper part of the flexural member, the table data is sorted out. Figure 7 .

[0041] like Figure 7 As shown in the figure, from the overall trend, with the increase of the number of upper replacements, the ultimate load of the component shows a downward trend. When the number of upper modified bamboo bars is 0, the flexural member shows the highest ultimate load. As the number of upper modified bamboo bars gradually increases to 2, the ultimate load of the component gradually decreases and reaches the lowest value. Under the condition of keeping the lower reinforcement unchanged, the ultimate load of the flexural member in this test shows a downward trend with the increase of the number of upper modified bamboo bars, but the load curve changes relatively smoothly. The ultimate flexural load of components with concrete strength grades of C20, C30 and C40 increases successively, indicating that the increase in concrete strength helps to enhance the flexural bearing capacity of the component to a certain extent.

[0042] In summary, the change in the number of modified bamboo bars replaced in the upper part has little effect on the cracking load of the flexural member, and the effect on the ultimate load is also limited. The maximum difference between the ultimate load of the flexural member with 2 modified bamboo bars and the member with 0 bamboo bars is no more than 9.3kN, 6.9 percentage points. Within the current test parameter range, changing the number of modified bamboo bars replaced in the upper part, the flexural member shows a slight reduction in strength, indicating that modified bamboo bars have the potential to replace the upper steel bars of flexural members.

[0043] 1.2 Impact of replacing lower reinforcement 1.2.1 Impact of the lower replacement position The main function of the lower reinforcement of a concrete flexural member is to withstand the tensile force generated by the bending moment. In a flexural member, when bending occurs under the action of an external load, the upper part of the member is compressed and the lower part is tensile. Since the tensile strength of concrete is very low and it cannot resist this tensile force alone, reinforcements need to be arranged at the lower part of the member to withstand this tensile force. In this way, the reinforcement and concrete can work together to resist the external load and ensure the strength and stability of the member. In addition, the lower reinforcement can also enhance the integrity and ductility of the member and improve the seismic performance of the member. Under the action of horizontal forces such as earthquakes, the lower reinforcement can effectively transmit and disperse the seismic force to avoid brittle failure of the member. At the same time, the arrangement of the lower reinforcement also helps to reduce the deformation of the member and ensure the normal use and safety of the member. It is the "skeleton" of the entire member and plays a vital role in the strength and stability of the member.

[0044] Two modified bamboo bars are longitudinally arranged at the upper part of the flexural members, and the lower reinforcement is used as the test variable. The flexural performance data of the members with different modified bamboo bars at the lower part are shown in Table 4. In the table, the lower part of KW05 is arranged with bamboo bars-rebars-rebars, the lower part of KW06 is arranged with rebars-bamboo bars-rebars, the lower part of KW07 is arranged with rebars-rebars-bamboo bars, the lower part of KW08 is arranged with bamboo bars-bamboo bars-rebars, the lower part of KW09 is arranged with bamboo bars-rebars-bamboo bars, the lower part of KW10 is arranged with rebars-bamboo bars-bamboo bars, and the lower part of KW11 is arranged with bamboo bars-bamboo bars-bamboo bars (see Table 1 for specific reinforcement conditions).

[0045] Table 4 Bending performance of components at different replacement positions in the lower part

[0046] As shown in Table 4, when the upper reinforcement is the same (bamboo bars are configured), for members with the same concrete strength, the cracking load shows a slight change trend with the change of the lower reinforcement position. Only when the lower part of the flexural member is all steel bars, the cracking load is slightly larger, but this difference also has a certain limit, and the maximum difference does not exceed 4.9kN. The cracking load of flexural members with different concrete strengths shows a regular change, that is, the cracking load of the member increases with the increase of concrete strength. This is consistent with the change law when the modified bamboo bars replace the upper steel bars, indicating that the cracking load of the flexural member has limited correlation with the type, quantity and position of its reinforcement, and mainly depends on the strength of the concrete.

[0047] In order to further study the ultimate load variation trend of concrete flexural members with modified bamboo bars replacing steel bars at different positions at the bottom, the data were sorted out. Figure 8 .

[0048] like Figure 8 As shown in the figure, the influence of modified bamboo bars replacing lower steel bars on the bearing capacity of components is quite significant, and the ultimate load change curve fluctuates greatly. When modified bamboo bars completely replace steel bars, the ultimate load of components with concrete strength grade C20 is 49.6kN different from that of the configuration of lower full steel bars, which is a relative decrease of 39.0%; the difference of bending members with concrete strength grade C30 is 46.5kN, which is a relative decrease of 35.4%; the difference of bending members with concrete strength grade C40 is 44.2kN, which is a decrease of 30.8%. The maximum difference between the ultimate loads of the two does not exceed 50kN, that is, the difference does not exceed 40%. With the increase of concrete strength grade, the ultimate load of the component shows an increasing trend. It shows that the increase of concrete strength has a certain positive effect on the bending performance of the component.

[0049] When only one modified bamboo bar is arranged at the bottom of the flexural member, its ultimate load will change accordingly with the different replacement positions of the bamboo bar. When one modified bamboo bar replaces different outer steel bars at the bottom of the member, the ultimate load of the flexural member shows significant consistency, with a difference of no more than 2kN. However, when the reinforcement pattern of the lower part is changed to steel-bamboo-steel (that is, the modified bamboo bar is arranged in the middle), the ultimate load is relatively reduced. The reason for this phenomenon is that under the bending loading of the current test conditions, the longitudinal force-bearing reinforcement in the middle of the tension zone can withstand greater tensile stress. When two modified bamboo bars are arranged at the bottom, their ultimate load also changes with the different replacement positions of the modified bamboo bars. Specifically, when two modified bamboo bars replace the middle and outer steel bars of the member respectively, the change in the position of the outer modified bamboo bar (whether on the left or right side) has no significant effect on the ultimate load of the flexural member, so the ultimate load of the member will not change significantly due to this position change. However, when the modified bamboo bars replaced all the outer steel bars, the ultimate load of the member reached a relatively high value, which indicated that the modified bamboo bars were more suitable for replacing the lower outer steel bars of concrete flexural members.

[0050] In summary, the lower part of the modified bamboo-reinforced concrete flexural member is mainly subjected to tensile stress by the configured reinforcement. The change of reinforcement will significantly affect the bearing capacity of the flexural member. Therefore, the modified bamboo reinforcement replacing the lower reinforcement has a significant effect on the ultimate bearing capacity of the concrete flexural member. The ultimate load of the flexural member with modified bamboo reinforcement replacing the different outer reinforcements in the table below remains basically unchanged, while the load is relatively reduced when the middle part is replaced.

[0051] 1.2.2 Impact of the number of lower replacements The number of lower reinforcements is a key factor affecting the flexural capacity of concrete flexural members. As the main tensile component, reinforcements bear the tensile stress generated by the bending moment at the bottom of the member. Increasing the number of lower reinforcements can effectively improve the flexural capacity of the member because its higher tensile strength can share more tensile stress. However, the configuration of reinforcements must be moderate. Too much reinforcement will increase costs and may cause structural problems.

[0052] This section mainly studies the influence of modified bamboo bars replacing different numbers of steel bars in the lower part of flexural members on their bearing capacity, and explores the law of member bearing capacity changing with the number of modified bamboo bars replaced. The purpose is to seek a solution for efficient steel bar replacement under the premise of reducing the bearing capacity of flexural members as much as possible. From the conclusion of Section 1.1, it can be seen that the modified bamboo bars replacing the upper steel bars have little effect on the bearing capacity of concrete flexural members. Therefore, the upper reinforcement of concrete members in this section is set to modified bamboo bars, and the average value of flexural load with the same number of modified bamboo bars is taken as its representative value. The bearing capacity of flexural members with different numbers of modified bamboo bars replaced in the lower part is shown in Table 5.

[0053] Table 5 Bending performance of components with different replacement numbers in the lower part

[0054] It can be seen from Table 5 that, under the premise of the same upper reinforcement, the change in the number of modified bamboo bars in the lower part has a slight effect on the cracking load of the flexural member. Specifically, with the increase in the number of modified bamboo bars in the lower part, the cracking load of the flexural member decreases, but the load reduction is not large, and the maximum difference does not exceed 4.5 kN.

[0055] With the increase of concrete strength, the cracking load of modified bamboo-reinforced concrete flexural members increases significantly, such as Fig. 9 In order to further analyze the law of the ultimate load of the flexural member changing with the replacement amount of the lower modified bamboo reinforcement, the table data is sorted into Fig.10 .

[0056] As the number of modified bamboo bars in the lower part increases, the ultimate load of the flexural member gradually decreases, and the rate of decrease of the ultimate load of the flexural member with 0 to 1 bamboo bar is significantly lower than that with 1 to 3 bamboo bars. Fig.10 For example, in C20 concrete flexural members, the ultimate load of the flexural member with 1 modified bamboo bar is reduced by 10.5% compared with 0 modified bamboo bars; the ultimate load of the flexural member with 2 modified bamboo bars is reduced by 17.5% compared with 1 modified bamboo bar; the ultimate load of the flexural member with 3 modified bamboo bars is reduced by 49.6% compared with 0 modified bamboo bars. Therefore, the change in the number of lower modified bamboo bars has a significant effect on the ultimate bearing capacity of the flexural member. When the modified bamboo bar replaces one lower steel bar, the ultimate load of the flexural member can be maintained at a relatively high level.

[0057] 1.3 Impact of replacing lower reinforcement 1.3.1 Impact of the overall replacement quantity The following strategies are adopted to determine the load values ​​of flexural members with different numbers of modified bamboo bars: when the number of modified bamboo bars is 1, the mean of the two groups of data KW02 and KW03 is taken as the representative value of the number of modified bamboo bars 1; when the number is 2, the data of KW01 is taken; if the number is 3, the mean of the three groups of data KW05, KW06 and KW07 is taken as the representative value of the number of modified bamboo bars 3; for the case of 4, the mean of KW08, KW09 and KW10 is taken as the representative value of the number of modified bamboo bars 4; when the number of modified bamboo bars is 5, the value of KW11 is directly used. The cracking load and ultimate load values ​​of flexural members are sorted out in Table 6 below.

[0058] Table 6 Bending performance of components with different replacement numbers

[0059] From the analysis of Table 6, it can be seen that, under the premise of keeping the upper reinforcement unchanged, the number of modified bamboo bars in the lower part has limited effect on the cracking load of the flexural member. Specifically, as the number of modified bamboo bars in the lower part increases, the cracking load of the flexural member decreases, but the decrease is small, and the decrease curve is stable without obvious fluctuations. The change in concrete strength has a significant positive effect on the cracking load of the flexural member, such as Fig.11 (a). The ultimate load of the component shows a significant and stable change pattern with the increase in the number of modified bamboo bars. As the number of modified bamboo bars gradually increases, the ultimate load of the component shows a trend of gradually decreasing. When the number of modified bamboo bars replaced increases to 5, the ultimate load of the component decreases to the minimum value. This shows that the flexural bearing capacity of the specimen under the ultimate state gradually decreases with the increase in the overall replacement number of modified bamboo bars, but when the overall replacement number is 3, the flexural members of different concrete strengths still have relatively high ultimate loads, such as Fig.11 (b). With the increase of concrete strength, the cracking load of flexural members shows a steady upward trend, while the ultimate load increases relatively slowly. This trend shows that increasing concrete strength has a certain gain on the ultimate load of enhanced members and has a significant positive effect on increasing the cracking load of flexural members.

[0060] 1.3.2 Overall alternatives and their load reduction rates The ultimate load of modified bamboo-reinforced concrete components is related to the number and replacement position of modified bamboo bars and steel bars. Taking the load of fully reinforced concrete components as the benchmark, the ultimate load difference between modified bamboo-reinforced concrete components and fully reinforced concrete components is calculated by ratio with the ultimate load of fully reinforced concrete components to obtain the load reduction rate. The smaller the load reduction rate, the closer it is to the ultimate load of reinforced concrete flexural members. The ultimate load reduction rates of different components are shown in Table 7 (the specific reinforcement conditions of the components are shown in Table 1).

[0061] Table 7 Reduction rate of ultimate load of bending members

[0062] It can be seen from Table 7 that the change trends of the ultimate load reduction rate of flexural members with different concrete strengths are basically the same, and all reach the maximum value at KW11. The change curves of the ultimate load reduction rate of members with concrete strength grades of C20, C30 and C40 are basically fitted, as shown in Fig.12As shown. When the horizontal coordinates in the curve are KW01~KW04, the load reduction rate curve is gentle and the reduction rate is small. At this time, the maximum load reduction rate of the flexural members of each concrete strength is: 6.8% for C20 concrete members, 6.5% for C30 concrete members, and 5.6% for C40 concrete members. KW01~KW04 all represent flexural members with steel bars at the bottom and modified bamboo bars of different numbers or positions at the top. This shows that it is feasible to replace steel bars with modified bamboo bars at the top when the ultimate load is allowed to be reduced by no more than 7%.

[0063] KW05~KW11 are members with bamboo reinforcements in the upper part and different reinforcements in the lower part. KW05~KW07 have only one modified bamboo reinforcement in the lower part. At this time, the ultimate load of KW05 and KW07 is a smaller value, indicating that the load loss is small and the ultimate load is large. If one modified bamboo reinforcement is required in the lower part, the bamboo reinforcement configuration of KW05 and KW07 can be adopted, that is, one modified bamboo reinforcement is arranged on the outer side of the lower part. At this time, the strength reduction rates are respectively 14.6% and 14.1% for C20 concrete members, 12.2% and 13.0% for C30 concrete members, and 10.5% and 11% for C40 concrete members.

[0064] KW08~KW10 are concrete bending members with two modified bamboo bars at the bottom. At this time, KW09 is the minimum point, indicating that its reduction rate is small and the ultimate load is large. If two modified bamboo bars are required at the bottom, this reinforcement method can be used, that is, the modified bamboo bars are arranged on the outside of the bottom. At this time, the load reduction rates are: 28.2% for C20 concrete members, 23.8% for C30 concrete members, and 22.7% for C40 concrete members. The maximum value of the curve is KW11. At this time, modified bamboo bars are configured at both the upper and lower parts of the member, and their load reduction rates are: C20 concrete components account for 43.2%, C30 concrete components account for 39.6%, and C40 concrete components account for 34.7%.

[0065] Therefore, the modified bamboo bars can completely replace two upper steel bars of concrete flexural members under the premise of a load reduction rate of no more than 7%, and replace three steel bars, that is, replace the upper steel bars and one lower outer steel bar, under the premise of a load reduction rate of no more than 15%. The load reduction rate of concrete flexural members replacing four steel bars is between 22% and 29%, and the ultimate load reduction rate of concrete flexural members that completely replace steel bars exceeds 34%.

[0066] Combined with the conclusion of 1.3.1, under the premise that the ultimate load of the flexural member is not greatly reduced, the optimal solution for the modified bamboo bar to replace the steel bars of the flexural member is: if only 2 steel bars are replaced, the upper steel bars can be completely replaced, and the ultimate load reduction rate does not exceed 7%. If 3 steel bars need to be replaced, the upper two steel bars can be completely replaced and 1 lower outer steel bar can be replaced. At this time, the ultimate load of the flexural member is allowed to be reduced by no more than 15%. Therefore, when the ultimate load of the concrete member with equal cross-section is allowed to be reduced by no more than 7%~15%, the modified bamboo bar can replace the upper and lower parts of the steel bars in the reinforced concrete member with equal areas.

[0067] In summary, in this embodiment, when replacing three beam reinforcements 6 in the modified bamboo-steel concrete beam, specifically replacing two beam reinforcements 6 on the upper part of the steel stirrups 7 and the beam reinforcement 6 on the lower outer side (any one on the left or right of the lower end), the maximum number of replacement reinforcements can be used under the premise that the ultimate load of the bending member is allowed to be reduced by no more than 15%, so as to minimize the amount of reinforcement.

[0068] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for replacing steel bars in bending-resistant members with modified bamboo bars, characterized in that: The method for replacing steel bars in bending-resistant members with modified bamboo bars comprises the following steps: S1. Modifying natural bamboo tendons by chemical and physical methods to produce modified bamboo tendons; S2, making steel hoops to fix the beam modified bamboo bars and beam steel bars to the steel hoops; S3, the modified bamboo bars and beam steel bars are reserved with anchorage lengths to be bent and anchored on the steel bars of the reinforced concrete main beam; S4, making formwork, pouring modified bamboo-steel concrete slabs, modified bamboo-steel concrete beams, reinforced concrete beams, and reinforced concrete columns; S5. After the concrete hardens, the formwork is removed to form a steel-modified bamboo reinforced concrete structure.

2. The method for replacing steel bars in bending-resistant members with modified bamboo bars according to claim 1, characterized in that: Step S1 specifically includes: S11. Material selection: select multi-year-old bamboo as raw material, clean the branches and tips of the bamboo, and cut the bamboo into bamboo pieces of specific sizes; and remove the green and yellow parts of the bamboo pieces by machine or manual method; S12, boiling and soaking, putting bamboo slices into water and boiling to remove water-soluble organic matter and potential residual air; S13, delignification, using peroxyformic acid solution to delignify the bamboo chips under the catalytic action of sulfuric acid until the bamboo chips turn white, so that the molecular structures of lignin and hemicellulose are effectively removed, while the molecular structure of cellulose is well preserved; S14, neutralization extraction, using an alkaline solution to neutralize the bamboo chips after delignification treatment, and then washing the bamboo fibers with deionized water to remove the residual lignin and hemicellulose components on the bamboo chips; S15, post-processing, subjecting the bamboo fiber obtained in S14 to microwave heating, screening and inspection sub-processes; S16, screening, screening the post-processed bamboo fibers to obtain modified bamboo tendons.

3. The method for replacing steel bars in bending-resistant members with modified bamboo bars according to claim 1, characterized in that: The modified bamboo-steel concrete slab comprises a concrete slab body and slab-modified bamboo bars and slab steel bars arranged inside the concrete body; The plate steel bars are arranged on the upper and lower sides of the concrete plate body, the plate modified bamboo bars are arranged between the plate steel bars, and the plate modified bamboo bars and the plate steel bars are perpendicular to each other; Before pouring the modified bamboo-steel concrete slab, the slab modified bamboo reinforcement is tied and fixed on the slab reinforcement.

4. The method for replacing steel bars in bending-resistant members with modified bamboo bars according to claim 1, characterized in that: The modified bamboo-steel concrete beam comprises a concrete beam body and the steel bar hoop arranged in the concrete beam body; The steel stirrups include beam modified bamboo bars, beam steel bars, and steel stirrups; The modified bamboo bars, beam steel bars and steel stirrups are all located inside the main body of the concrete beam. The steel stirrups are rectangular in structure. The beam steel bars are arranged on the inner side of the bottom angle of the steel stirrups. The modified bamboo bars are arranged on the inner side of the top angle of the steel stirrups. The modified bamboo bars are also arranged at the bottom of the steel stirrups. The modified bamboo bars and beam steel bars are both perpendicular to the plane where the steel stirrups are located.

5. The method for replacing steel bars in bending-resistant members with modified bamboo bars according to claim 4, characterized in that: The beam-modified bamboo reinforcement at the bottom of the steel stirrup is arranged on one side of the bottom of the steel stirrup.

6. The method for replacing steel bars in bending-resistant members with modified bamboo bars according to claim 1, characterized in that: The steel-modified bamboo reinforced concrete structure includes reinforced concrete columns, reinforced concrete main beams, modified bamboo-steel concrete slabs, and modified bamboo-steel concrete beams; wherein the reinforced concrete columns are arranged at four corners, the two ends of the reinforced concrete main beams are connected to the reinforced concrete columns to form a rectangular frame, the two ends of the modified bamboo-steel concrete beams are fixed on the reinforced concrete main beams, and the modified bamboo-steel concrete slabs are laid on the modified bamboo-steel concrete beams and the reinforced concrete main beams.

7. The method for replacing steel bars in bending-resistant members with modified bamboo bars according to claim 1, characterized in that: The modified bamboo reinforcement obtained in S1 is further processed by brushing epoxy resin on the surface of the bamboo reinforcement and air-drying it naturally; after air-drying, epoxy resin and polyamide resin curing agent are brushed on the surface of the bamboo reinforcement again, and corundum particles are evenly sprayed on the surface of the bamboo reinforcement to enhance the roughness, corrosion resistance and water resistance of the bamboo reinforcement; the treated modified bamboo reinforcement is left to stand at room temperature and away from light for at least 3 days to ensure that the epoxy resin is fully cured and bonds the bamboo reinforcement and corundum.

8. The method for replacing steel bars in bending-resistant members with modified bamboo bars according to claim 1, characterized in that: In S4, before pouring concrete, the mold needs to be thoroughly cleaned to ensure that it is flat, free of cracks and wear, and the mold should be moistened with a release agent and padded with paper in advance to facilitate demoulding.

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