KR20220156773A - Method and System for Estimating Tensile Behavior of Reinforced Concrete Member - Google Patents

Abstract

The present invention relates to a method and a system for predicting a tensile behavior of reinforced concrete members. In predicting the tensile behavior of the reinforced concrete member by performing a detailed analysis of the tensile behavior of the reinforced concrete member, based on results of a rebar attachment test, a rebar attachment model is idealized, and then based on an initial average crack spacing at the time of first crack occurrence in reinforced concrete members, a rebar attachment stress-slip amount relationship, which directly reflects the effect of rebar attachment characteristics, is considered to derive the structural relationship between tensile stress and strain of reinforced concrete members. The method for predicting a tensile behavior of reinforced concrete members includes steps of: setting up a mathematical model for the rebar attachment stress-slip amount relationship; idealizing the mathematical model for the rebar attachment stress-slip amount relationship using data acquired through rebar attachment experiments; calculating rebar stress on a crack surface when a first crack occurs in a reinforced concrete member, and calculating an initial average crack interval from the idealized rebar attachment stress-slip amount relationship model; and calculating a rebar strain at the crack surface.

Description

Method and system for predicting tensile behavior of reinforced concrete members directly considering the characteristics of attachment behavior of reinforcing bars and concrete based on reinforcement attachment experiments {Method and System for Estimating Tensile Behavior of Reinforced Concrete Member}

The present invention analytically analyzes the tensile behavior of reinforced concrete members after cracking in concrete by directly considering the characteristics of the attachment behavior of reinforcing bars and concrete after concrete cracks occur in a state where the reinforced concrete member is subjected to tensile force using the results of the reinforcement attachment test. It is about predictable methods and systems.

Specifically, in the present invention, in predicting the tensile behavior of a reinforced concrete member by performing a detailed analysis of the tensile behavior of the reinforced concrete member, the first crack occurs in the reinforced concrete member after idealizing the rebar attachment model based on the results of the rebar attachment test. Tensile behavior of reinforced concrete members was derived by deriving a structural relationship between tensile stress and strain of reinforced concrete members by considering the relationship between reinforcement attachment stress-slip amount, which directly reflected the effect of reinforcement attachment characteristics, based on the initial average crack interval at the time of application. It is about a predictive method and system.

Safety, usability, and durability are reviewed when designing reinforced concrete members. Among these reviews, when examining the usability of reinforced concrete members, deflection and cracks should be considered. Eurocode 2 (British Standard, "Eurocode 2: Design of concrete structures - Part 1-1: General rules and rules for buildings", BS EN 1992-1-1:2004, 2014, p. 225), the current European design standard In the domestic design standard KDS 14 20 30 (Ministry of Land, Infrastructure and Transport, "KDS 14 20 30:2021 Concrete Usability Design Standard", 2021, p. 15), the crack width of reinforced concrete is multiplied by the average strain considering the attachment characteristics of the reinforcement by the crack interval. is proposed to calculate. However, these existing design standards suggest a method for calculating the crack width by dividing only circular reinforcing bars and deformed reinforcing bars, so the reinforcement attachment characteristics are considered indirectly.

On the other hand, in order to predict the behavior of reinforced concrete members, nonlinear structural analysis must be performed, and in the nonlinear structural analysis of reinforced concrete members, it is necessary to reflect the "tensile strengthening effect" due to the attachment between reinforcing bars and concrete after cracks occur. . Regarding the tensile strengthening effect of reinforced concrete members, a tensile strengthening effect model is presented based on the panel experiment results at the University of Toronto, Canada (Evan C. Bentz, "Explaining the Riddle of Tension Stiffening Models for Shear Panel Experiments", Journal of Structural Engineering, ASCE, 2005, pp. 1422-1425), these models are widely used for nonlinear behavior analysis of reinforced concrete members (members). However, this existing tensile strengthening effect model is limited to general reinforced concrete only, and has a limitation in that it cannot directly consider the reinforcement attachment characteristics.

In particular, recently, concrete with high-strength concrete and new construction materials is being developed, and new material reinforcing bars such as FRP are being applied to concrete structures. For these new concrete structures, crack width review and design for conventional general reinforced concrete members There is a limit to reasonably predicting the tensile behavior of reinforced concrete members with the standard and tensile strengthening effect. Therefore, it is necessary to develop a tensile behavior analysis technique of reinforced concrete members that can directly consider not only the existing reinforcement attachment characteristics in reinforced concrete, but also the reinforcement attachment characteristics differently exhibited when new construction materials are applied.

Republic of Korea Patent Publication No. 10-2011-0094619 (published on August 24, 2011).

The present invention was developed to overcome the limitations of the prior art as described above, and specifically, in order to more reasonably predict the tensile behavior of reinforced concrete members, directly considering the attachment behavior characteristics of reinforcing bars and concrete in reinforced concrete members The purpose of this study is to provide a tensile behavior prediction method and prediction system through detailed analysis of the tensile behavior of reinforced concrete members.

Specifically, in the present invention, the tensile behavior of the reinforced concrete member is predicted by directly considering the attachment behavior characteristics of the reinforcing bar and concrete in the reinforced concrete member so that the tensile behavior of the reinforced concrete member can be interpreted and predicted more rationally, that is, An object of the present invention is to provide a method and system for deriving a relationship between tensile stress and strain (tensile strain) of a reinforced concrete member.

In order to achieve the above object, in the present invention, a specific analysis technique that can reasonably predict the tensile behavior of a reinforced concrete member subjected to tension is provided by directly considering the reinforcement attachment test or the reinforcement attachment model presented in domestic and foreign design standards. do.

In the present invention, setting a mathematical model for the rebar attachment stress-slip amount relationship; Idealizing a mathematical model for a relationship between rebar attachment stress and slip amount using data acquired through a rebar attachment experiment; Calculating reinforcing bar stress on the crack surface when a first crack occurs in a reinforced concrete member, and calculating an initial average crack interval from an idealized reinforcing bar attachment stress-slip amount relationship model; And calculating the reinforcing strain at the crack surface; by including, a correlation between the tensile stress and the tensile strain of the reinforced concrete member is derived, thereby predicting the tensile behavior of the reinforced concrete member. A tensile behavior prediction method is provided.

In addition, in the present invention, in order to achieve the above object, a "rebar attachment stress-slip amount relationship mathematical model setting module" for setting a mathematical model for the rebar attachment stress-slip amount relationship; "Idealization module of mathematical model of rebar attachment stress-slip amount relationship" that idealizes a mathematical model for rebar attachment stress-slip amount relationship using data acquired through rebar attachment experiments; "Initial average crack spacing calculation module" that calculates the reinforcing bar stress on the crack surface when a first crack occurs in a reinforced concrete member and calculates the initial average crack spacing from the idealized reinforcing bar attachment stress-slip amount relationship model; and a "rebar strain calculation module at the crack surface" that calculates the reinforcing bar strain at the crack surface; A tensile behavior prediction system of a reinforced concrete member is provided, characterized in that the tensile behavior of the reinforced concrete member is predicted by deriving a correlation between the tensile stress and the tensile strain of the reinforced concrete member.

Current domestic and foreign design standards and conventional analysis models proposed by foreign researchers are very limited models that can only be applied to general reinforced concrete, and have the disadvantage of not being able to directly consider the attachment behavior of reinforcing bars.

However, according to the present invention, it is possible to analytically predict the tensile behavior of reinforced concrete members more rationally by directly considering the reinforcement attachment behavior. In addition, recently, development of new construction materials for concrete and reinforcing bars as well as high-strength concrete is actively progressing, and the analysis technique presented in the present invention can be applied to these new construction materials. In addition, based on the analysis technique presented in the present invention, it is possible to calculate the tensile strength effect of a reinforced concrete member in which the reinforcement attachment behavior characteristics are reflected, and from this, it is possible to perform a more rational analysis of the nonlinear structural behavior of reinforced concrete.

1 is a schematic flow chart of a method according to the present invention.
2 is a schematic block diagram of a system according to the present invention.
3 is a graph showing a rebar attachment stress-slip amount relationship model presented in CEB-FIP Model Code 2010.
4 is a schematic diagram sequentially showing crack behavior of reinforced concrete members subjected to tension.
5 is a schematic diagram showing the behavior of crack generation in a reinforced concrete member under tension.
6 is a schematic flowchart showing a process of analyzing the tensile behavior of a reinforced concrete member in direct consideration of the reinforcement attachment behavior.
7 (a) and (b) are schematic graphs showing examples of tensile behavior of reinforced concrete predicted by the method of the present invention, respectively.
8 (a) and (b) are schematic graphs showing examples of concrete average tensile stress-strain behavior predicted by the method of the present invention, respectively.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. The present invention has been described with reference to the embodiments shown in the drawings, but this is described as one embodiment, and thereby the technical idea of the present invention and its core configuration and operation are not limited.

The method according to the present invention directly considers the attachment behavior characteristics of reinforcing bars and concrete and derives the relationship between tensile stress and strain (tensile strain) in reinforced concrete members ("tensile stress-strain relationship of reinforced concrete members"), It is a method that can reasonably predict the tensile behavior of reinforced concrete members.

Fig. 1 shows a schematic flow chart for a method according to the present invention, and Fig. 2 shows a schematic flow chart for a system according to the present invention. As illustrated in the drawings, the method for deriving the tensile stress-strain relationship of a reinforced concrete member according to the present invention includes, in detail, (a) setting a mathematical model for a rebar attachment stress-slip amount relationship; (b) idealizing a mathematical model for the relationship between rebar attachment stress and slip amount using data acquired through rebar attachment experiments; (c) calculating the reinforcing bar stress at the crack surface when the first crack occurs in the reinforced concrete member, and calculating the initial average crack spacing from the idealized reinforcing bar attachment stress-slip amount relationship model; and (d) the reinforcing bar strain at the crack surface considering the equilibrium of force at each cross section between cracks, the equation expressed as the reinforcing bar attachment stress-slip amount relationship, and the reinforcing bar and concrete deformation relationship between cracks. It has a configuration including a; through which the correlation between the tensile stress and tensile strain of the reinforced concrete member is derived, and the manager calculates the tensile stress of the reinforced concrete member thus derived. Using the stress-strain relationship, it is possible to more reasonably predict the tensile behavior of reinforced concrete members.

The system according to the present invention is for executing the method of the present invention as described above, and as illustrated in FIG. 2, the rebar attachment stress-slip relation mathematical model setting module 1, the rebar attachment stress-slip relation mathematical It is composed of a model idealization module (2), an initial average crack spacing calculation module (3), and a reinforcing bar strain calculation module at the crack surface (4).

As illustrated in the drawing, in the present invention, first, a mathematical model for simulating <rebar attachment stress-slip amount relationship> is selected for a reinforced concrete member to grasp and predict tensile behavior (Step S1 - Rebar attachment stress-slip amount) Selection step of the quantity relationship model). Specifically, the user selects a mathematical model for simulating the <rebar attachment stress-slip amount relationship> using the mathematical model setting module (1) for the relationship between rebar attachment stress and slip amount.

Here, <rebar attachment stress-slip amount relationship> is the degree of attachment of reinforcing bars to concrete in reinforced concrete members, that is, "rebar attachment stress", and the degree of slip of reinforcing bars to concrete in reinforced concrete members, that is, " In step S1, a model that can mathematically simulate this <rebar attachment stress-slip amount relationship>, that is, a "rebar attachment stress-slip amount relationship model" is selected.

As a method to mathematically simulate the rebar attachment stress-slip amount relationship, there is a method using the model presented in the CEB-FIP Model Code 2010, which is widely used at home and abroad. 3 is a graph showing a rebar attachment stress-slip amount relationship model presented in CEB-FIP Model Code 2010. The "rebar attachment stress-slip amount relationship model" proposed in the CEB-FIP Model Code 2010 is expressed by Equations 1 to 3 below.

는 철근의 부착응력을 의미하고,

는 소정의 슬립이 발생하였을 때의 철근 부착응력을 의미하며,

는 철근의 최대 부착응력을 의미한다. 그리고 수학식 1 내지 수학식 3에서

는 철근 슬립량을 의미하며,

와

는 각각

와

에 상응하는 철근 슬립량을 의미한다. 일반적인 콘크리트 및 이형철근이 사용된 철근콘크리트 부재에 대해서는

,

,

, 그리고

이다. 여기서

은 콘크리트 평균압축강도를 의미하며,

는 철근 부착강도와 슬립량의 관계에 대한 그래프에서의 곡선 형태를 반영하는 계수이다. 위 기호에 대한 설명은 후술하는 다른 수학식에도 동일하게 적용된다.In the above equations 1 to 3

is the attachment stress of the reinforcing bar,

Means the reinforcement attachment stress when a predetermined slip occurs,

is the maximum bond stress of the reinforcing bar. And in Equations 1 to 3

is the reinforcing bar slip amount,

Wow

are respectively

Wow

It means the rebar slip amount corresponding to For reinforced concrete members using general concrete and deformed reinforcing bars,

,

,

, and

to be. here

is the average compressive strength of concrete,

is a coefficient reflecting the shape of the curve in the graph of the relationship between the rebar attachment strength and the amount of slip. The description of the above symbols is equally applicable to other equations to be described later.

After the rebar attachment stress-slip amount relationship model is selected, the mathematical model for the rebar attachment stress-slip amount relationship is idealized using the results obtained through subsequent rebar attachment experiments (data on the relationship between rebar attachment stress and slip). (idealize) (step S2 - idealization step of the rebar attachment stress-slip amount relationship model). The idealization of the rebar attachment stress-slip amount relationship model in step S2 is performed in the "idealization module (2) of the mathematical model of the rebar attachment stress-slip amount relationship".

), 철근 최대부착강도일 때의 슬립량(

), 그리고 실험에서 측정된 데이터로부터 철근 부착강도와 슬립량의 관계를 보여주는 그래프를 도출하고, 상기 그래프의 곡선 형태를 반영하는 계수(

)를 도출하여, 위 수학식 1의 형태로 표현된 철근 부착응력-슬립량 관계 모델을 완성하는 것이다. For example, when the mathematical model represented by Equation 1 is selected as the rebar attachment stress-slip amount relationship model, the above Equation 1 is more than obtained using the rebar attachment stress-slip amount result measured by a standardized experiment. it is to anger Specifically, in the idealization stage of the rebar attachment stress-slip amount relationship model, a standardized test for rebar attachment stress-slip amount (for example, a pull-out test for reinforcing bars placed in a rectangular parallelepiped concrete specimen) ) to acquire the measured result (data on the relationship between the reinforcement attachment stress and slip, that is, data including the value of the reinforcement attachment stress according to the amount of slip), and obtain the maximum attachment strength of the reinforcement from the acquired data (

), the amount of slip at the maximum attachment strength of the rebar (

), and a graph showing the relationship between the reinforcing bar attachment strength and the amount of slip is derived from the data measured in the experiment, and the coefficient reflecting the curve shape of the graph (

) to complete the rebar attachment stress-slip amount relationship model expressed in the form of Equation 1 above.

Subsequently, in the initial average crack spacing calculation module 3, the reinforcing bar stress at the crack surface is calculated when the first crack occurs in the reinforced concrete member, and the initial average crack spacing is calculated from the idealized reinforcing bar attachment stress-slip amount relationship model ( Step S3 - Calculation of initial mean crack spacing and reinforcing stress).

)로부터 아래의 수학식 4 및 수학식 5를 활용하여 산정할 수 있다.When the tensile stress acting on the concrete by the load reaches the tensile strength of the concrete, the first crack occurs in the concrete. The crack spacing at the time of the first crack occurrence in a reinforced concrete member is the transmission length considering the attachment characteristics of the reinforcing bars (

) can be calculated using Equations 4 and 5 below.

은 첫 균열 발생 시의 평균 균열 간격을 의미하고,

는 콘크리트 탄성계수에 대한 철근의 탄성계수 비를 의미하며,

는 철근비를 의미하고,

는 첫 균열 발생시 균열면에서의 철근 응력을 의미하고,

는 철근 지름을 의미하며,

는 철근 부착 거동 곡선의 형태를 반영하는 계수를 의미한다. 이와 같은 각 기호는 본 명세서의 다른 수학식에도 동일하게 적용된다. In Equation 4 and Equation 5 above,

Means the average crack interval at the time of the first crack occurrence,

is the ratio of the modulus of elasticity of reinforcing steel to the modulus of elasticity of concrete,

means the rebar cost,

means the reinforcing bar stress at the crack surface at the time of the first crack occurrence,

is the diameter of the reinforcing bar,

is the coefficient reflecting the shape of the rebar attachment behavior curve. Each symbol like this is equally applied to other equations in this specification.

는 응력 단위를 갖는 것으로서 다음의 수학식 6에 의해 계산될 수 있다. Coefficient in Equation 5 above

Has a unit of stress and can be calculated by Equation 6 below.

는 철근의 탄성계수를 의미하고

는 철근비를 의미한다. In Equation 6 above

is the modulus of elasticity of the reinforcing bar

means the rebar cost.

는 첫 균열 발생시 균열면에서의 철근 응력을 의미하는데, 이는 아래의 수학식 7에 의하여 산출할 수 있다. as explained above

Means the reinforcing bar stress at the crack surface when the first crack occurs, which can be calculated by Equation 7 below.

는 콘크리트 단면적을 의미하며,

는 철근 단면적을 의미하고,

은 콘크리트 인장강도를 의미하며,

는 철근비를 의미한다. In Equation 7 above

is the concrete cross-sectional area,

is the cross-sectional area of the reinforcing bar,

is the concrete tensile strength,

means the rebar cost.

와, 초기 평균 균열간격이 산정된 후에는, 균열면에서의 철근 변형률 연산 모듈(4)에서, 균열과 균열 사이 각 단면에서의 힘의 평형, 철근 부착응력-슬립량 관계로 표현되는 구성방정식, 및 균열과 균열 사이에서의 철근과 콘크리트 변형에 대한 적합조건을 고려하여 철근콘크리트 부재의 균열면에서의 철근 변형률을 연산한다(단계 S4 - 균열면에서의 철근 변형률을 연산하는 단계). Reinforcing bar stress at the crack surface when the first crack occurs in a reinforced concrete member by the above process

And, after the initial average crack spacing is calculated, in the reinforcement strain calculation module 4 at the crack surface, the equilibrium of force at each cross section between cracks, the constitutive equation expressed by the reinforcement attachment stress-slip amount relationship, and calculating the reinforcing bar strain at the crack surface of the reinforced concrete member in consideration of the suitable conditions for the reinforcing bar and concrete deformation between cracks (step S4 - calculating the reinforcing bar strain at the crack surface).

After the first crack occurs in a reinforced concrete member, the tensile stress of the concrete between cracks increases locally as the tensile load or deformation increases. Later, when the tensile stress of concrete between cracks reaches the tensile strength of concrete, new cracks are generated between cracks, and the crack spacing is reduced to half of the existing crack spacing. 4 is a schematic diagram sequentially depicting the cracking behavior of a reinforced concrete member subjected to tension. Figure 5 is a schematic diagram showing the behavior of crack occurrence stages in a reinforced concrete member subjected to tension. After dividing the crack stabilization phase before the reinforcing bar yielding (Fig. 5(b)) and the crack stabilization phase after the reinforcing bar yielding (Fig. 5(c)), the tensile strength of each position of the reinforcing bar and concrete It shows stress, tensile strain, slip amount and bond stress.

As shown in (a) of FIG. 5, in the crack generation step, the crack interval is greater than twice the transmission length, and in the crack generation step, it can be seen that new cracks can occur between cracks as the load increases. have. Subsequently, as new cracks are created, the crack interval decreases, and when the crack stabilization step shown in FIG. 5 (b) and (c) is entered, new cracks do not occur due to the decrease in attachment length (crack stabilization phase). In particular, in the crack stabilization step, the adhesion stress of the reinforcing bar due to slip is different before and after the reinforcing bar yielding, so the local bonding behavior effect appears differently according to the yielding of the reinforcing bar. In order to simulate the behavior of rebar attachment stress-slip amount for each position, the present invention uses the form of the model presented in CEB-FIP Model Code 1990, as summarized in FIG. 3 and Equation 1.

After the reinforcing bar yields, a relatively large tensile stress occurs in the surrounding concrete surrounding the reinforcing bar due to the shape of the deformed reinforcing bar, and the attachment ability of the reinforcing bar decreases compared to before the reinforcing bar yielding due to a rapid increase in the reinforcing bar strain due to the reinforcing bar yielding.

를 철근 부착응력에 곱함으로써 철근콘크리트 부재의 인장 거동 해석 즉, 철근콘크리트 부재의 인장응력-인장 변형률의 상관 관계를 도출함에 있어서 철근 부착응력 감소효과를 반영한다. In identifying and analyzing the tensile behavior of these reinforced concrete members, when applying the rebar attachment stress-slip amount relationship model, the reinforcement attachment stress reduction effect according to the strain of the reinforcement after yielding the reinforcement is expressed by Equation 8 below Coefficient

By multiplying by the reinforcing bar attachment stress, the effect of reducing the reinforcement attachment stress is reflected in the tensile behavior analysis of the reinforced concrete member, that is, in deriving the correlation between the tensile stress and tensile strain of the reinforced concrete member.

는 철근의 항복변형률을 의미하고,

는 철근 변형률을 의미한다.In Equation 8 above

is the yield strain of the reinforcing bar,

is the reinforcing bar strain.

For the tensile load or deformation at which the first crack occurred, the concrete strain at the central section between cracks was assumed, and from this, the tensile stress in concrete, the tensile stress in reinforcing bars, and the strain in reinforcing bars were calculated at the same location. The concrete tensile stress at the crack surface is calculated through the known 4th order Runge Kutta numerical analysis method.

In principle, the concrete tensile stress calculated for the crack surface should be zero. Therefore, if the concrete tensile stress calculated for the crack surface is not zero, after adjusting or re-assuming the previously assumed concrete strain value between cracks and cracks, as described above, the concrete tensile stress at the corresponding location, reinforcing bar Calculate the tensile stress and the strain of the reinforcing bar, and calculate the tensile stress in the concrete at the crack surface again by the numerical analysis method.

The above calculation is repeated until the concrete tensile stress at the crack surface becomes zero. In other words, if the calculated concrete tensile stress at the crack surface is not zero, the previously assumed concrete strain value between cracks and cracks is re-assumed, and then the pre-assumed concrete strain value is used to determine the crack and stress as described above. The tensile stress of concrete, the stress of reinforcing bars, and the strain of reinforcing bars in the cross section between cracks are calculated, and the concrete strain and tensile stress of concrete at the crack surface are calculated through numerical analysis methods. This is repeated until the concrete tensile stress becomes zero.

On the other hand, when the tensile stress of concrete between cracks is smaller than the tensile strength of concrete, the average stress and average strain of concrete and reinforcing bars are calculated from the stress and strain of concrete and reinforcing bars for each location calculated from the above process. On the other hand, if the concrete stress between cracks is greater than the concrete tensile strength, it can be considered that a new crack has occurred. At this time, the crack interval is set to half of the existing crack interval, and the above calculation is repeated again.

As such, assuming the concrete strain at the central section between cracks, calculating the tensile stress of concrete, the tensile stress of reinforcing bars, and the strain of reinforcing bars at the corresponding location, and calculating the tensile stress of concrete at the crack surface through the numerical analysis method. Calculate and check whether the concrete tensile stress at the crack surface becomes zero> is referred to as "rebar strain calculation at the target section" for convenience.

The target cross section, that is, the cross section for which the reinforcing bar strain is to be calculated is initially set as the central cross section between cracks, and then the target cross section is gradually moved to the crack surface, performing the above "calculation of reinforcing bar strain at the target cross section", and finally By performing "rebar strain calculation at target cross section" at the crack surface, "rebar strain at crack surface" is calculated. And, the above "calculation of reinforcing bar strain at the target section" is continuously performed until the calculated "strain of reinforcing bar at the crack surface" reaches the strain corresponding to the fracture of the reinforcing bar.

By finally performing this process, the tensile stress-strain relationship of the reinforced concrete member is derived for the reinforced concrete member subjected to the tensile load, and accordingly, the tensile behavior of the reinforced concrete member for each load stage can be predicted. . 6 is a schematic flow chart showing an analysis sequence for a detailed analysis technique of a reinforced concrete member subjected to tension, that is, a schematic flowchart showing a process of analyzing the tensile behavior of a reinforced concrete member directly considering the reinforcement attachment behavior.

<Specific embodiments of the present invention>

As a specific embodiment of the present invention, the method of the present invention described above was applied to a real reinforced concrete member under tensile load, and its detailed behavior was analyzed.

In this example, reinforced concrete members in which reinforcing bars with a yield strength of 400 MPa were placed in concrete with compressive strengths of 65.1 MPa and 150.7 MPa were analyzed. Furthermore, in order to apply the method of the present invention to reinforced concrete members having various reinforcement ratios, reinforced concrete members having a total of five reinforcement ratios of 1.0, 1.5, 2.0, 2.5, and 3.0% were included in the examples.

As for the above example, the tensile behavior was identified using the method of the present invention, and a correlation between tensile stress and tensile strain was derived as an indicator of tensile behavior. It is shown in the graphs of FIG. 7 (a) and (b), respectively. In each of (a) and (b) of FIG. 7 , the horizontal axis represents “average tensile strain” and the vertical axis represents “average tensile stress”.

As shown in (a) and (b) of FIG. 7, it was found that the tensile behavior of the reinforced concrete member was significantly different from the tensile behavior of the reinforcing bar itself due to the tensile strengthening effect according to the reinforcing bar attachment behavior. In particular, as the concrete compressive strength increases, the concrete tensile strength also increases, which is reflected in the analysis. Therefore, in the case of members with high concrete compressive strength, it can be seen that the contribution of concrete to the tensile stress after cracking also increases. In addition, it can be seen that as the load and strain increase, cracks occur sequentially in the reinforced concrete member, resulting in a stepwise decrease in the tensile strengthening effect. In particular, it can be seen that the contribution of concrete to tensile behavior due to the tensile strength effect after yielding the reinforcing bar is significantly reduced compared to before yielding the reinforcing bar.

When the tensile contribution of the reinforcing bar itself is excluded from the tensile behavior of the reinforced concrete member predicted from the method for analyzing the tensile behavior of reinforced concrete proposed in the present invention, the average stress of concrete, which is the tensile contribution of concrete, as shown in (a) and (b) of FIG. Strain curves can be derived. In each of FIG. 8 (a) and (b), the abscissa axis represents "average tensile strain" and the ordinate axis represents "average tensile stress".

As shown in (a) and (b) of FIG. 8, whenever a new crack occurs in a reinforced concrete member, the concrete tensile stress decreases step by step, and when no new crack occurs and only deformation increases, the concrete tensile stress temporarily It can be seen that this increases In addition, it can be seen that as the average strain is closer to the yield strain of the reinforcing bar, the average tensile stress of concrete decreases rapidly as the reinforcing bar yields first at the crack surface. After the overall yielding of the reinforcing bars, it was found that the tensile stress of the concrete increased to some extent due to the attachment behavior of the reinforcing bars that still existed, but the magnitude was found to be relatively small compared to the tensile stress of concrete before the reinforcing bar yielding. In addition, since the tensile strength of concrete increases as the compressive strength of concrete increases, it can be seen that the average tensile stress of concrete also increases due to the tensile strengthening effect after crack generation.

In the detailed analysis results, the average tensile stress of concrete increases and decreases repeatedly depending on the time of crack occurrence, but as the average strain increases until the reinforcing bar yields, the average tensile stress of concrete generally decreases. This tendency is similar to the form presented in several existing models to reflect the tensile strengthening effect in general reinforced concrete members. However, since the tensile reinforcement effect is greatly affected by the reinforcement attachment characteristics, the method for analyzing the tensile behavior of reinforced concrete proposed in the present invention has the advantage of directly considering the reinforcement attachment characteristics. In addition, unlike conventional general analysis models, it has the advantage of being able to predict tensile behavior using only the results of adhesion behavior experiments even when new construction materials such as fiber-reinforced concrete and FRP bars are applied.

100: system
One; Rebar attachment stress-slip amount relationship mathematical model setting module
2: Idealization module of mathematical model of rebar attachment stress-slip amount relationship
3: Initial Average Crack Spacing Module
4: Rebar strain calculation module at the crack surface

Claims (2)

Setting up a mathematical model for the rebar attachment stress-slip relationship;
Idealizing a mathematical model for a relationship between rebar attachment stress and slip amount using data acquired through a rebar attachment experiment;
Calculating reinforcing bar stress on the crack surface when a first crack occurs in a reinforced concrete member, and calculating an initial average crack interval from an idealized reinforcing bar attachment stress-slip amount relationship model; and
Calculating the reinforcing bar strain at the crack surface; by including,
A method for predicting tensile behavior of a reinforced concrete member, characterized in that the tensile behavior of the reinforced concrete member is predicted by deriving a correlation between tensile stress and tensile strain of the reinforced concrete member. "rebar attachment stress-slip amount relationship mathematical model setting module (1)" for setting a mathematical model for the rebar attachment stress-slip relationship;
"Idealization module (2) of mathematical model of rebar attachment stress-slip amount relationship" idealizing a mathematical model for rebar attachment stress-slip amount relationship using data acquired through rebar attachment experiments;
"Initial average crack spacing calculation module (3)" that calculates the reinforcing bar stress on the crack surface when a first crack occurs in a reinforced concrete member and calculates the initial average crack spacing from the idealized reinforcing bar attachment stress-slip amount relationship model; and
It is configured to include a "rebar strain calculation module 4 at the crack surface" that calculates the reinforcing bar strain at the crack surface;
A tensile behavior prediction system for reinforced concrete members, characterized in that the tensile behavior of reinforced concrete members is predicted by deriving a correlation between tensile stress and tensile strain of reinforced concrete members.

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