Dimension design and thermal bridge influence prediction method for multilayer composite connecting piece

Abstract

The invention discloses a size design and thermal bridge influence prediction method for a multi-layer composite connecting piece, and belongs to the field of heat preservation and energy conservation. According to the method, a mathematical model for the size design of the multi-layer composite connecting piece is established, and an efficient numerical calculation basis is provided for the size design of the composite connecting piece. The defect that the size of the multi-layer composite connecting piece depends on tedious tests and experience is overcome, and the size design efficiency of the multi-layer composite connecting piece is remarkably improved. The invention provides a mathematical prediction method for the thermal bridge influence of the multi-layer composite connecting piece. Due to the fact that mechanical and thermal parameters of a multi-layer composite connecting piece have a coupling effect on the influence of a thermal bridge, the mechanical and thermal parameters of the composite connecting piece need to be considered at the same time for determining the influence of the thermal bridge in a sandwich wallboard, however, related technologies are in a blank state at present, and the influence of the thermal bridge of the composite connecting piece cannot be accurately evaluated. The prediction method is provided for evaluating the influence of the thermal bridge by establishing a related mathematical model, and development and evaluation of the multi-layer composite connecting piece can be guided.

Description

Technical Field

[0001] The invention belongs to the field of thermal insulation and energy saving, and in particular relates to a method for dimension design of a multi-layer composite connector and a prediction method for thermal bridge influence. Background Art

[0002] Building energy consumption accounts for about 50% of the country's total energy consumption, among which operating energy consumption is the key to determining the total energy consumption of buildings. Studies have found that building envelope walls can effectively reduce operating energy consumption. Considering the structure, fire protection and thermal insulation requirements of the envelope wall, sandwich wall panels have become one of the most popular forms of building envelope walls. However, in order to meet the structural requirements, it is necessary to arrange connectors to connect the inner and outer concrete layers of the sandwich wall panels as a whole. Due to the high thermal conductivity of the connectors relative to the insulation layer, this forms a thermal bridge phenomenon, causing significant energy loss.

[0003] In order to reduce the impact of thermal bridges, multilayer composite connectors that combine high-strength materials and low thermal conductivity materials have been proposed. However, the current assessment of its thermal bridge impact is limited to experimental means, and there is no thermal bridge impact assessment model. This makes the thermal bridge impact assessment of multilayer composite connectors inefficient and costly, and it cannot effectively guide its design and development. The key difficulty in establishing a thermal bridge impact assessment model for multilayer composite connectors is that the mechanical and thermal parameters of multilayer composite connectors have a coupled effect on the thermal bridge effect, and there is currently no mathematical model to calculate this coupling effect. (Connectors mainly play a mechanical role in sandwich wall panels. Connectors made of different materials have different mechanical parameters, which will affect the size (diameter) of the connectors, and the size and thermal parameters jointly determine the degree of thermal bridge impact.) In order to accurately evaluate the thermal bridge impact of multilayer composite connectors, it is necessary to first establish a size calculation model for multilayer composite connectors, and then consider the size and thermal parameters of multilayer composite connectors to evaluate their thermal bridge impact.

[0004] Since the mechanical properties of multi-layer composite connectors determine the size of the connectors, the mechanical parameters and thermal parameters of multi-layer composite connectors jointly determine the thermal bridge effect. Establishing a method for sizing and thermal bridge effect prediction of multi-layer composite connectors not only helps predict the thermal bridge effect of composite connectors in sandwich wall panels, but also helps guide the design and development of multi-layer composite connectors, thereby saving more energy. Summary of the invention

[0005] The purpose of the present invention is to solve the problem that the existing multi-layer composite connectors cannot quickly calculate their thermal bridge effects due to the lack of mathematical models, and to provide a method for size design and thermal bridge effect prediction of multi-layer composite connectors. Through numerical calculation, the optimal size of the multi-layer composite connector can be quickly obtained, and then its thermal bridge effect can be accurately predicted.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] A method for sizing and thermal bridge impact prediction of a multi-layer composite connector, characterized in that: the method comprises:

[0008] Step 1: Obtain thermal and mechanical parameters of multi-layer composite connectors

[0009] Step 2: Calculation model of multi-layer composite connector size

[0010] ① Calculation of tensile strength

[0011] Ultimate tensile strength of composite connectors:

[0012] Among them, N p is the ultimate axial tensile strength of the composite connector, f T is the tensile strength of the sandwich panel material, h an is the effective anchorage depth of the composite connector, h d is the diameter of the composite connector;

[0013] For the tensile strength of composite connectors N T , should satisfy N T ≤N p ;

[0014] ②Shear strength calculation

[0015] Experimental research has found that when the sandwich wall panel undergoes vertical displacement, the failure mode of the connector is bending-shear failure because the composite connector connects the inner and outer wall panels of the sandwich wall panel.

[0016] Therefore, under the vertical load of the sandwich panel, the ultimate shear strength of the composite connector is:

[0017]

[0018] Among them, F v is the maximum shear strength design value of the composite connector, f b is the bending strength of the composite connector, I is the section inertia moment of the composite connector, S z is the moment of inertia of the composite connector, δ is the thickness of the sandwich panel cavity (or insulation layer), W z is the area moment of the connector, f TT is the ultimate tensile strength of the composite connector;

[0019] Among them, the shear strength of the connector should meet F≤F v ;

[0020] ③Displacement calculation

[0021] Vertical displacement of the composite connector under the deadweight of the sandwich panel (η):

[0022]

[0023] Among them, D w is the load applied by the outer leaf of the sandwich wall panel to the composite connector, and M is the bending stiffness of the composite connector;

[0024] ④ Calculation of connector diameter

[0025] The strength condition of the composite connector can be obtained as follows: The diameter h of the composite connector d The following conditions should be met:

[0026]

[0027] According to the displacement conditions, the diameter of the single-layer composite connector should meet the following conditions:

[0028]

[0029] Where E represents the elastic modulus of the material, I represents the moment of inertia of the material, and h d1 、h d2 , ...represent the diameters of the multi-layer composite connector from the innermost layer to the outermost layer respectively;

[0030] The cross-sectional stiffness of the multi-layer composite connector is as follows:

[0031] EI=E1I1+E2I2+……+E n I n

[0032]

[0033]

[0034]

[0035] …

[0036]

[0037]

[0038] Therefore, the calculation model of the diameter of multi-layer connectors is as follows:

[0039]

[0040]

[0041] The above two constraints are satisfied at the same time, that is, the optimal diameter of the multi-layer composite connector (i.e., the minimum connector diameter) is obtained;

[0042] Step 3: Calculation of heat transfer coefficient

[0043] ① Establish a heat transfer balance equation (as shown below) to obtain the temperature gradient ▽T and heat flux α of the sandwich wall panel containing multi-layer composite connectors, and calculate it by numerical iteration method or using finite element software;

[0044]

[0045] Where ρ is the density of each material, C p is the heat capacity of each material, ▽T is the temperature gradient of the research object, t represents time, λ is the thermal conductivity of each material, and J is the external environmental heat source;

[0046] ②After obtaining the temperature change gradient ▽T and heat flux α, the heat transfer coefficient ω is obtained by the following formula:

[0047] λ▽T=ω(T exter -T)

[0048]

[0049] Among them, T exter is the outdoor ambient temperature, T inter represents the indoor ambient temperature, T is the temperature of the sandwich wall panel, and A is the surface area of ​​the sandwich wall panel;

[0050] ③ Thermal bridge effect: Subtract the heat transfer coefficient of the sandwich wall panel with connectors from the heat transfer coefficient of the sandwich wall panel without connectors, that is, use the difference in heat transfer coefficients to evaluate the thermal bridge effect;

[0051] Step 4: Energy consumption calculation

[0052] ① Annual energy consumption of multi-layer composite connectors C an The calculation formula is: an =24×60×60ωT d ; Among them, T d is the total degree days for the whole year;

[0053] ② Impact of thermal bridges: Subtract the energy consumption of sandwich wall panels with connectors from the energy consumption of sandwich wall panels without connectors, that is, use the difference in energy consumption to evaluate the impact of thermal bridges.

[0054] Furthermore, the step one is specifically as follows: obtaining the density, thermal conductivity, constant pressure heat capacity, axial ultimate tensile strength, ultimate shear strength, flexural strength, and elastic modulus of each material of the multilayer composite connector through thermal and mechanical experiments or by referring to a material parameter manual.

[0055] Furthermore, in step 4, T d The calculation formula is: Among them, CT d and HT dThe total degree days for summer and winter respectively can be obtained by referring to the local climate manual or by collecting local annual climate data.

[0056] The beneficial effects of the present invention compared to the prior art are:

[0057] 1. The present invention establishes a mathematical model for the dimensional design of multi-layer composite connectors, which provides an efficient numerical calculation basis for the dimensional design of composite connectors. Compared with the prior art, it solves the drawback that the dimensional determination of multi-layer composite connectors depends on cumbersome experiments and experience, and significantly improves the dimensional design efficiency of multi-layer composite connectors.

[0058] 2. The present invention provides a mathematical prediction method for the thermal bridge effect of multi-layer composite connectors. Since the mechanical and thermal parameters of multi-layer composite connectors have a coupling effect on the thermal bridge effect, the determination of the thermal bridge effect in sandwich wall panels needs to consider the mechanical and thermal parameters of the composite connectors at the same time. However, the relevant technology is currently blank and it is impossible to accurately evaluate the thermal bridge effect of the composite connector. The present invention provides a prediction method for the evaluation of the thermal bridge effect by establishing a relevant mathematical model, which can guide the development and evaluation of multi-layer composite connectors, thereby saving more energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 The figure is a flow chart of the method of the present invention. DETAILED DESCRIPTION

[0060] The specific embodiments of the present invention are described in detail below, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the protection scope of the present invention. The experimental methods described in the embodiments of the present invention are conventional methods unless otherwise specified.

[0061] Embodiment 1:

[0062] Three types of three-layer composite connectors are made of steel, FRP and nylon, and the amount of the three materials is required to be the same. From the inside to the outside, the material composite forms of the three composite connectors are FRP-steel-nylon, steel-nylon-FRP and nylon-FRP-steel. The thickness of the inner and outer leaf concrete slabs of the sandwich wall panel where the composite connector is located is 15cm and 5cm respectively, the thickness of the middle insulation layer is 8cm, and 4 composite connectors are arranged per square meter. Taking Harbin as the application location, the optimal diameter of the composite connector is calculated, and its thermal bridge effect is evaluated.

[0063] Solution: First, consult the material parameter manual and substitute the mechanical and thermal performance parameters of the three materials in the composite connector into the calculation model to obtain the optimal diameter of the connector (i.e. the minimum diameter, because the larger the diameter of the connector, the more significant the thermal bridge effect, which is not conducive to energy saving); then consult the thermal engineering manual to obtain Harbin's HT d and CT d The values ​​are 5032℃·d and 14℃·d respectively. The heat transfer coefficient and energy consumption are calculated to evaluate the thermal bridge effect from the perspectives of thermal performance and energy consumption.

[0064] After calculation, the optimal diameter of the three-layer composite connector is shown in the following table:

[0065] Composite connector type FRP-Steel-Nylon Steel-Nylon-FRP Nylon-FRP-Steel Optimum diameter 18mm 15mm 24mm

[0066] After calculation, the thermal bridge impact assessment of the three-layer composite connector is as follows:

[0067] Composite connector type FRP-Steel-Nylon Steel-Nylon-FRP Nylon-FRP-Steel Difference in heat transfer coefficient <![CDATA[0.137W / (m 2 ·K)]]> <![CDATA[0.110W / (m 2 ·K)]]> <![CDATA[0.152W / (m 2 ·K)]]> Difference in energy consumption 2910.8kJ 2337.2kJ 3229.6kJ

Claims

1. A method for dimension design and thermal bridge impact prediction of a multi-layer composite connector, characterized in that: The method is: Step 1: Obtain thermal and mechanical parameters of multi-layer composite connectors Step 2: Dimensional calculation model of multi-layer composite connector ① Calculation of tensile strength Ultimate tensile strength of composite connectors: Among them, N p is the ultimate axial tensile strength of the composite connector, f T is the tensile strength of the sandwich panel material, h an is the effective anchorage depth of the composite connector, h d is the diameter of the composite connector; For the tensile strength of composite connectors N T , should satisfy N T ≤N p ; ② Calculation of shear strength The ultimate shear strength of the composite connector under the vertical load of the sandwich panel: Among them, F v is the maximum shear strength design value of the composite connector, f b is the bending strength of the composite connector, I is the section inertia moment of the composite connector, S z is the moment of inertia of the composite connector, δ is the thickness of the sandwich panel cavity (or insulation layer), W z is the area moment of the connector, f TT is the ultimate tensile strength of the composite connector; Among them, the shear strength of the connector should meet F≤F v ; ③Displacement calculation Vertical displacement of the composite connector under the deadweight of the sandwich panel (η): Among them, D w is the load applied by the outer leaf of the sandwich wall panel to the composite connector, and M is the bending stiffness of the composite connector; ④ Calculation of connector diameter The strength condition of the composite connector can be obtained as follows: The diameter h of the composite connector d The following conditions should be met: According to the displacement conditions, the diameter of the single-layer composite connector should meet the following conditions: Where E represents the elastic modulus of the material, I represents the moment of inertia of the material, and h d1 、h d2 , ...represent the diameters of the multi-layer composite connector from the innermost layer to the outermost layer respectively; The cross-sectional stiffness of the multi-layer composite connector is as follows: EI=E1I1+E2I2+……+E n THE n Therefore, the calculation model of the diameter of multi-layer connectors is as follows: The above two constraints are satisfied at the same time, that is, the optimal diameter of the multi-layer composite connector (i.e., the minimum connector diameter) is obtained; Step 3: Calculation of heat transfer coefficient ① Establish a heat transfer balance equation (as shown below) to obtain the temperature gradient of the sandwich wall panel containing multi-layer composite connectors and heat flux α, calculated by numerical iteration method or using finite element software; Where ρ is the density of each material, C p is the heat capacity of each material, is the temperature change gradient of the research object, t represents time, λ is the thermal conductivity of each material, and J is the external environmental heat source; ②Get the temperature gradient After calculating the heat flux α, the heat transfer coefficient ω is obtained by the following formula: Among them, T exter is the outdoor ambient temperature, T inter represents the indoor ambient temperature, T is the temperature of the sandwich wall panel, and A is the surface area of ​​the sandwich wall panel; ③ Thermal bridge effect: Subtract the heat transfer coefficient of the sandwich wall panel with connectors from the heat transfer coefficient of the sandwich wall panel without connectors, that is, use the difference in heat transfer coefficients to evaluate the thermal bridge effect; Step 4: Energy consumption calculation ① Annual energy consumption of multi-layer composite connectors C an The calculation formula is: an =24×60×60ωT d ; Among them, T d is the total degree days for the whole year; ② Impact of thermal bridges: Subtract the energy consumption of sandwich wall panels with connectors from the energy consumption of sandwich wall panels without connectors, that is, use the difference in energy consumption to evaluate the impact of thermal bridges.

2. The method for dimension design and thermal bridge impact prediction of a multi-layer composite connector according to claim 1, characterized in that: The step one is specifically as follows: obtaining the density, thermal conductivity, constant pressure heat capacity, axial ultimate tensile strength, ultimate shear strength, flexural strength, and elastic modulus of each material of the multilayer composite connector through thermal and mechanical experiments or by referring to a material parameter manual.

3. The method for dimension design and thermal bridge impact prediction of a multi-layer composite connector according to claim 1, characterized in that: In step 4, T d The calculation formula is: Among them, CT d and HT d are the total degree days for summer and winter, respectively.

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