A novel design method and system for outer-wrapped lightweight concrete box columns of folding houses

Abstract

The present invention discloses a novel design method and system for an outer lightweight concrete box column of a folding house, which relates to the field of steel component design, wherein the method comprises: constructing a bearing capacity analysis finite element model of an outer lightweight concrete box steel column, and based on the bearing capacity analysis finite element model, performing structural parameter analysis on the box steel column to obtain bearing capacity; constructing a heat transfer performance analysis finite element model of an outer lightweight concrete box steel column, and based on the heat transfer performance analysis finite element model, performing heat transfer performance analysis on the box steel column to obtain heat transfer performance; based on the structural parameters and heat transfer performance, completing the design of a novel outer lightweight concrete box column. The present invention can achieve the same service life as the steel column, well protect the built-in box steel column, improve the fire resistance and durability of the structure, overcome the weaknesses of steel, and can also improve the mechanical properties of the steel column by outer protective layer, reduce the possibility of local buckling deformation of the box steel column, and retain the easy assembly characteristics of the traditional steel column.

Description

Technical Field

[0001] The invention relates to the field of steel component design, and in particular to a novel design method and system for outer-wrapped lightweight concrete box columns of a folding house. Background Art

[0002] With the progress of society, the residential construction area in my country is increasing. Under the influence of promoting the development of green buildings, it is particularly important for residential buildings, which are ranked first in the building volume, to adopt green assembly forms. On the other hand, steel structure buildings have the characteristics of assembly in terms of structural characteristics, manufacturing and construction technology, and construction technology. Therefore, it is necessary to analyze and study steel structure houses to promote the construction of steel structure houses.

[0003] Ordinary steel structures are widely used in buildings due to their advantages such as light weight, high strength and good toughness. Due to the poor corrosion resistance and fire resistance of steel components, necessary protective measures need to be taken when using steel components in actual structures. Through systematic investigation and research, it is found that although there are many external factors that hinder the industrialization and promotion of steel structure housing, the fact that fireproof and anti-corrosion protective materials cannot have the same lifespan as the main structure is one of the important reasons affecting the industrialization of steel structures. It can be seen that steel structures need regular maintenance after they are built, and the later maintenance costs are high and inconvenient to handle. In addition, the commonly used protective materials (such as fire retardant coatings, fireproof boards, etc.) have poor mechanical properties. When an earthquake occurs, the fire retardant coatings and fireproof boards coated on the steel structure are prone to cracking, damage or even falling off under the action of reciprocating loads, which has a great impact on the effectiveness of fire protection of steel components. Summary of the invention

[0004] In steel structures, steel columns are important load-bearing components. If there is a problem with the steel column, it will have a great impact on the mechanical properties of the entire structure. Therefore, in order to avoid and solve the technical problems in the above background, the present invention proposes a new design method and system for hollow steel lightweight concrete column (HSLCC).

[0005] To achieve the above object, the present invention provides a novel design method for outer-wrapped lightweight concrete box columns of a folding house, the steps comprising:

[0006] Constructing a bearing capacity analysis finite element model of an outsourced lightweight concrete box-type steel column, and based on the bearing capacity analysis finite element model, performing structural parameter analysis on the box-type steel column to obtain the bearing capacity; the structural parameters include: lightweight concrete thickness, width-to-thickness ratio, and bonding degree between lightweight concrete and the box-type steel column;

[0007] Constructing a finite element model for heat transfer performance analysis of a box-type steel column wrapped with lightweight concrete, and performing heat transfer performance analysis on the box-type steel column based on the finite element model to obtain heat transfer performance;

[0008] Based on the structural parameters and the heat transfer performance, the design of a new type of outer-clad lightweight concrete box column is completed.

[0009] Preferably, the method for analyzing the thickness of the lightweight concrete includes: using a pure box-type steel column specimen to wrap lightweight concrete of different thicknesses to analyze the influence of the thickness of lightweight concrete on the mechanical properties of the pure box-type steel column specimen; wherein the pure box-type steel column specimen includes a pure long steel column and a pure short steel column, and the pure long steel column and the pure short steel column have the same width-to-thickness ratio, but different specimen heights.

[0010] Preferably, the method for analyzing the width-to-thickness ratio includes: performing axial compression analysis on outsourced lightweight concrete box column specimens with different width-to-thickness ratios and the same lightweight concrete thickness, extracting the load-displacement curve, buckling load and ultimate load of the outsourced lightweight concrete box column specimens, and analyzing the influence of the width-to-thickness ratio on the axial bearing capacity of the outsourced lightweight concrete box column.

[0011] Preferably, the method for analyzing the degree of bonding between the lightweight concrete and the box-type steel column includes: reflecting the degree of bonding between the lightweight concrete and the built-in box-type steel column by selecting different friction coefficients between the contact interface between the lightweight concrete and the built-in box-type steel column; and selecting outsourced lightweight concrete box column specimens with the same width-to-thickness ratio, different lightweight concrete thicknesses, and different friction coefficients to analyze the degree of bonding between the lightweight concrete and the box-type steel column.

[0012] Preferably, based on the thickness of the lightweight concrete, the width-to-thickness ratio and the bonding degree between the lightweight concrete and the box-type steel column, a calculation formula for the bearing capacity includes:

[0013] ,

[0014] In the formula, N cr For carrying capacity; is the stability coefficient; f c , f y Both are the design values ​​of compressive strength of lightweight concrete and steel components; A. A S Both are the cross-sectional area of ​​the component and the cross-sectional area of ​​the steel component.

[0015] Preferably, by constructing the heat transfer performance analysis finite element model, the heat transfer performance of the box-type steel column is analyzed to obtain the heat transfer coefficient formula of the lightweight concrete box-type steel column:

[0016] ,

[0017] In the formula, K represents the heat transfer coefficient; t Indicates the thickness of lightweight concrete; e Represents a natural constant.

[0018] The present invention also provides a novel outsourcing lightweight concrete box column design system for folding houses, the system is used to implement the above method, including: a bearing capacity model construction module, a heat transfer performance model construction module and a design module;

[0019] The bearing capacity model building module is used to build a bearing capacity analysis finite element model of the box-type steel column wrapped with lightweight concrete, and based on the bearing capacity analysis finite element model, perform structural parameter analysis on the box-type steel column to obtain the bearing capacity; the structural parameters include: lightweight concrete thickness, width-to-thickness ratio and bonding degree between lightweight concrete and box-type steel column;

[0020] The heat transfer performance model building module is used to build a finite element model for heat transfer performance analysis of a box-type steel column wrapped with lightweight concrete. Based on the heat transfer performance analysis finite element model, a heat transfer performance analysis is performed on the box-type steel column to obtain heat transfer performance.

[0021] The design module is used to complete the design of a new type of externally wrapped lightweight concrete box column based on the structural parameters and the heat transfer performance.

[0022] Preferably, the process for analyzing the thickness of the lightweight concrete includes: using pure box-type steel column specimens to wrap lightweight concrete of different thicknesses to analyze the influence of lightweight concrete thickness on the mechanical properties of pure box-type steel column specimens; wherein the pure box-type steel column specimens include pure long steel columns and pure short steel columns, and the pure long steel columns and pure short steel columns have the same width-to-thickness ratio, but different specimen heights.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The design method of the present invention can not only achieve the same service life as that of steel columns, but also well protect the built-in box-type steel columns, improve the fire resistance and durability of the structure, overcome the weaknesses of steel, but also improve the mechanical properties of steel columns by outsourcing the protective layer, reduce the possibility of local buckling deformation of the box-type steel columns, and retain the easy assembly characteristics of traditional steel columns. It has important research significance and good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings required for use in the embodiments. 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 labor.

[0026] Figure 1 : is the load-displacement curve of short column specimens with different lightweight concrete thicknesses according to an embodiment of the present invention; Figure 1 (a) shows the load-displacement curve of specimen HSLCSC-30-15; Figure 1 (b) shows the load-displacement curve of HSLCSC-30-25; Figure 1 (c) shows the load-displacement curve of specimen HSLCSC-30-35; Figure 1 (d) indicates comprehensive comparison;

[0027] Figure 2 : is the load-displacement curve of long column specimens with different lightweight concrete thicknesses according to the embodiment of the present invention; wherein, Figure 2 (a) shows the load-displacement curve of specimen HSLCLC-30-15; Figure 2 (b) shows the load-displacement curve of HSLCLC-30-25; Figure 2 (c) shows the load-displacement curve of specimen HSLCLC-30-35; Figure 2 (d) indicates comprehensive comparison;

[0028] Figure 3 : is the load-displacement curve of short column specimens with different friction coefficients according to the embodiment of the present invention; wherein, Figure 3 (a) indicates an outsourced 15 mm short column specimen; Figure 3 (b) indicates a 25 mm short column specimen;

[0029] Figure 4 : is the load-displacement curve of the long column specimens with different friction coefficients according to the embodiment of the present invention; wherein, Figure 4 (a) indicates an outsourced 15 mm long column specimen; Figure 4 (b) indicates an outsourced 25 mm long column specimen;

[0030] Figure 5 Schematic diagram of the relationship between the outer package coefficient and the thickness of lightweight concrete in an embodiment of the present invention; Figure 5 (a) represents the outsourcing coefficient when the width-to-thickness ratio is 15; Figure 5 (b) represents the outsourcing coefficient when the width-to-thickness ratio is 25;

[0031] Figure 6 is the heat transfer coefficient of the test pieces with different thickness of the outer lightweight concrete according to the embodiment of the present invention;

[0032] Figure 7 The heat transfer coefficient curve and fitting curve of the outer lightweight concrete box-type steel column of the embodiment of the present invention; wherein, Figure 7 (a) represents the heat transfer coefficient curve of the specimen; Figure 7 (b) represents the linear function fitting curve; Figure 7 (c) represents the quadratic function fitting curve; Figure 7 (d) shows the exponential function fitting curve. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] Embodiment 1

[0036] The following is a novel design method for a folding house with a lightweight concrete box column according to an embodiment of the present invention, the steps comprising:

[0037] S1. Construct a bearing capacity analysis finite element model for the box-type steel column wrapped with lightweight concrete, and based on the bearing capacity analysis finite element model, perform structural parameter analysis on the box-type steel column to obtain the bearing capacity.

[0038] This embodiment uses ABAQUS finite element software to construct different bearing capacity analysis finite element models of lightweight concrete box-shaped steel columns according to different requirements for subsequent analysis and research. The displacement load curve, buckling load and ultimate load that appear in the subsequent structural parameter analysis in this step are all obtained through comprehensive analysis based on the bearing capacity analysis finite element model constructed in this step.

[0039] In this embodiment, the structural parameter analysis mainly includes the following parameters: lightweight concrete thickness, width-to-thickness ratio, and bonding degree between lightweight concrete and box-type steel columns.

[0040] Lightweight concrete thickness

[0041] The thickness of lightweight concrete is one of the main factors affecting the axial bearing capacity of the new type of box-type steel column wrapped with lightweight concrete (HSLCC for short). In this embodiment, the width-to-thickness ratio of the pure box-type steel column specimen is set to 15-40, of which the height of the pure long steel column (HSLC) specimen is 1500mm and the height of the pure short steel column (HSSC) specimen is 400mm. In the process of setting the comparison, different thicknesses of lightweight concrete are selected to wrap HSLC and HSSC, and the thickness of lightweight concrete is 15mm-40mm respectively, so as to analyze the influence of lightweight concrete thickness on the mechanical properties of HSSC specimens and HSLC specimens.

[0042] In order to obtain the influence of different lightweight concrete thicknesses on the axial bearing capacity of HSSC specimens, this embodiment sets the width-to-thickness ratio of the HSSC specimen to 30, and the lightweight concrete thicknesses to 15 mm, 25 mm, and 35 mm, respectively. The load-displacement curve is obtained through comprehensive analysis, as shown in Figure 1 As shown. Figure 1 It can be seen that the load-displacement curve trend of the specimen with lightweight concrete box-shaped steel short column (HSLCSC for short) is similar to that of the HSSC specimen. This stage is the elastic stage. The built-in box-shaped steel column is the main load-bearing body, and the deformation is the same as that of the pure steel specimen. The axial bearing capacity of the HSLCSC is improved compared with the pure steel specimen. The lightweight concrete produces a small deformation and fewer cracks. With the increase of vertical loading displacement, the built-in box-shaped steel column reaches the yield load and begins to buckle. Due to the presence of lightweight concrete, the displacement of the HSLCSC specimen when buckling occurs is higher than that of the HSSC specimen, indicating that the constraint effect of lightweight concrete affects the built-in box-shaped steel Buckling performance of the column, lightweight concrete and built-in box-type steel column begin to bear stress together, the slope of the load-displacement curve decreases, the axial bearing capacity of the specimen is slightly improved, more cracks are produced in the middle lightweight concrete and the width continues to extend, a small number of cracks are produced at both ends, this stage is the elastic-plastic stage, indicating the improvement and proportion of lightweight concrete in the axial bearing capacity of the specimen; when the vertical displacement continues to load, after the specimen reaches the ultimate load, more cracks are produced in the lightweight concrete and the width is larger, part of the lightweight concrete on the surface of the specimen begins to fall off, the bending degree of the built-in box-type steel column is larger, the displacement in the middle of the specimen is the largest, and it enters the plastic failure stage, and the bearing capacity of the specimen begins to decrease.

[0043] Depend on Figure 1 The buckling load and ultimate load of the HSLCSC specimen were extracted from the curve and compared with those of the HSSC specimen of the same specification, as shown in Table 1.

[0044] Table 1

[0045] ,

[0046] In Table 1, the specimen names are the English abbreviations-width-thickness ratio-outer thickness.

[0047] Through analysis, we can conclude that:

[0048] (1) The thickness of lightweight concrete has little effect on the axial bearing capacity and failure mode of the short column specimens. Due to the low strength of lightweight concrete, the increase is within 7%~9%. This shows that in the short column specimens, the built-in box-type steel column is still the main body of the load. The lightweight concrete has little effect on the buckling load of the short column specimens, but has a more obvious effect on the ultimate load, which is increased by about 9%.

[0049] (2) With the increase of the thickness of lightweight concrete, the increase in the buckling load and ultimate load of the short column specimen under the same condition also increases. However, when the width-to-thickness ratio of the box-type steel column increases, the proportion of the increase in the axial bearing capacity of lightweight concrete decreases. This means that for short columns, when the thickness of the box-type steel column side plate is thinner, the effect of lightweight concrete on the improvement of the axial bearing capacity of the specimen is better. When the thickness of the box-type steel column side plate is larger, the strength of the built-in box-type steel column is large, and the lightweight concrete only plays a restraining effect.

[0050] HSLC specimens with the same specifications as HSSC were selected and analyzed, and the load-displacement curves of HSLC specimens were comprehensively analyzed, such as Figure 2 As shown. It can be seen that the overall change trend of the curve is the same as that of HSSC. The main difference is in the buckling mode. When the thickness of lightweight concrete is above 25 mm, the buckling mode of HSLC changes from local buckling to overall instability. At the same time, the increase effect of lightweight concrete on the axial bearing capacity of HSLC specimens is also reduced, indicating that at this time, the lightweight concrete has been subjected to stress together with the box-type steel column, and the material is fully utilized.

[0051] The buckling load and ultimate load of the HSLCLC specimens are analyzed and are shown in Table 2.

[0052] Table 2

[0053] ,

[0054] In Table 2, the specimen names are the English abbreviations-width-thickness ratio-outer thickness.

[0055] Through analysis, we can conclude that:

[0056] (1) The thickness of lightweight concrete has a significant impact on the long column specimens, with the increase ranging from 8% to 20%. This indicates that lightweight concrete affects the buckling mode of the HSLC specimens and greatly increases the axial bearing capacity of the specimens. The lightweight concrete and the box-type steel column share the load and share the stress for the built-in box-type steel column.

[0057] (2) As the thickness of lightweight concrete increases, the improvement of the HSLC specimen increases, but the improvement of the axial bearing capacity decreases. When the thickness of the built-in box-type steel column side plate of the HSLC specimen decreases, the influence of lightweight concrete on the axial bearing capacity of the specimen becomes greater. This means that when the thickness of the built-in box-type steel column side plate is thin, lightweight concrete is more likely to affect its buckling mode and to improve the overall axial bearing capacity of the HSLC specimen.

[0058] Width ratio

[0059] By performing axial compression analysis on HSLCC specimens with width-to-thickness ratios of 15 to 40 and the same lightweight concrete thickness, the load-displacement curves, buckling loads and ultimate loads of the HSLCC specimens were extracted, and the effect of the width-to-thickness ratio on the axial bearing capacity of HSLCC was studied.

[0060] Table 3 lists the effects of different width-to-thickness ratios on HSSC specimens when the thickness of lightweight concrete is 25 mm and 35 mm. Through analysis, it can be concluded that when the thickness of lightweight concrete is the same, the increase in the width-to-thickness ratio tends to a constant value for the axial bearing capacity of HSSC specimens, indicating that the change in the width-to-thickness ratio has little effect on the axial bearing capacity of HSSC specimens, among which the lightweight concrete plays the main role in increasing the capacity. With the increase of the width-to-thickness ratio, the buckling load and ultimate load of HSSC are reduced, but the increase is slightly increased.

[0061] Table 3

[0062] ,

[0063] In Table 3, the specimen names are the English abbreviations-width-thickness ratio-outer thickness.

[0064] In order to study the influence of the width-to-thickness ratio on the axial bearing capacity of long column specimens, the same analysis process as that of HSSC was adopted, as shown in Table 4. Through analysis, it can be concluded that when the thickness of lightweight concrete is the same, increasing the width-to-thickness ratio will increase the axial bearing capacity of HSLC specimens less, and the improvement effect is increased compared with HSSC; with the increase of the width-to-thickness ratio, the buckling load and ultimate load of the HSLC specimens decrease, but the improvement amplitude increases, indicating that the width-to-thickness ratio state also has an impact on the HSLC specimens. When the thickness of lightweight concrete is small, HSLC is locally buckled and the improvement effect is not obvious. However, when the buckling mode of HSLC is transformed into overall instability, the width-to-thickness ratio significantly improves the axial bearing capacity of long column specimens.

[0065] Table 4

[0066] ,

[0067] The specimen names in Table 4 are English abbreviations-width-thickness ratio-outer thickness.

[0068] Through comprehensive analysis of HSSC and HSLC specimens, it can be concluded that the effect of the width-to-thickness ratio on the axial bearing capacity of the HSLCC specimens is lower than that of the lightweight concrete thickness. However, when the HSLC buckling mode changes, the effect of the width-to-thickness ratio on the axial bearing capacity increases significantly.

[0069] The current specifications have clear provisions on the width-to-thickness ratio limit of pure steel specimens. However, when the steel structure is wrapped with lightweight concrete, the mechanical properties of the specimens are improved and the requirements in the specifications are no longer applicable.

[0070] By analyzing the load displacement curves and failure modes of HSLCC specimens under different width-to-thickness ratios and lightweight concrete thicknesses, it is found that the side panels of built-in box-shaped steel columns are affected by the constraints of the surrounding panels and lightweight concrete. In the HSSC specimens, with the loading of vertical displacement, the side panels buckle locally, the out-of-plane normal displacement of the lower part of the web increases, and the out-of-plane normal displacement of the upper part of the flange also increases; in the HSLC specimens, the deformation is the same as that of the HSSC specimens. This shows that the nonlinear behaviors of the built-in box-shaped steel columns affect each other, thereby reducing the plastic development of the HSLCC specimens.

[0071] In order to obtain the width-to-thickness ratio limit of the HSLCC specimen wall panel, it was simplified to a slab constrained on one side by concrete. Based on the elastic-plastic local buckling theory of thin plates, the elastic-plastic buckling stress of the slab constrained on one side under uniformly distributed compressive stress was derived, and the analytical solution for the width-to-thickness ratio limit of the HSLCC specimen wall panel was obtained. a , the width is b , thickness is η The wall panel is placed on the lightweight concrete, ignoring the friction between the two and the deformation of the lightweight concrete, and applying the mid-surface force on the steel plate. According to the small deflection theory, the equilibrium equation under the elastic state can be obtained, as shown in formula (1):

[0072] , (1)

[0073] Where: D is the bending stiffness; ω is the out-of-plane deformation function; x , y All are coordinate axis directions; N x for x Directional pressure.

[0074] Since lightweight concrete has little effect on the axial bearing capacity of the specimen, but when the thickness of lightweight concrete reaches a certain level, it can change the buckling mode of the specimen. Therefore, it can be derived according to the width-to-thickness ratio formula of pure steel specimens, as shown in formula (2):

[0075] , (2)

[0076] Where: k is the buckling coefficient; E is the elastic modulus; is Poisson’s ratio; σ xcr represents the critical stress; N xcr Indicates critical pressure.

[0077] This embodiment simulates the HSLCC specimen and analyzes it using the thin plate theory and the standard calculation method. Through theoretical derivation, the width-to-thickness ratio of the short column specimen and the long column specimen is finally obtained. The results obtained by the two methods are compared and analyzed. It can be concluded that the buckling mode will affect the width-to-thickness ratio limit of the specimen, but the effect is small. At the same time, it can be concluded that the maximum width-to-thickness ratio limit of the HSLCSC specimen is 58, and the maximum width-to-thickness ratio limit of the HSLCLC specimen is 55.

[0078] Bonding degree between lightweight concrete and box-type steel columns

[0079] In the process of analyzing the load-displacement curve of the HSLCC specimen, it was found that when the specimen reaches the buckling load and the ultimate load, a smooth section will appear, and this stage also determines the size of the ultimate load. In order to explore the influencing factors of this stage, different friction coefficients are selected between the contact interface of lightweight concrete and the built-in box-type steel column to reflect the degree of bonding between the two. This embodiment lists lightweight concrete with a thickness of 15mm and 25mm, a width-to-thickness ratio of 30, and friction coefficients of 0.6, 0.8 and binding states, respectively, to study the influence of the degree of bonding on short column specimens and long column specimens.

[0080] like Figure 3 As shown in the figure, the load-displacement curves of HSSC specimens with different friction coefficients are shown. Since lightweight concrete does not change the buckling mode of HSSC, the influence of different buckling modes is excluded. Through analysis, it can be concluded that:

[0081] (1) As the friction coefficient gradually increases, the bonding between the lightweight concrete and the built-in box-type steel column becomes stronger. During the stress process of the HSSC specimen, the joint stress stage of the lightweight concrete and the box-type steel column becomes longer, and the ultimate load of the specimen is also slightly increased. However, the effect of increasing the buckling load is small.

[0082] (2) When the specimen is in the elastic stage, the change in the friction coefficient has little effect on the trend of the load-displacement curve of the short column specimen. When the HSSC specimen enters the elastic-plastic stage, the built-in box-type steel column begins to buckle, and the lightweight concrete and the box-type steel column begin to bear force together. A smooth section appears in the load-displacement curve. As the friction coefficient increases, this stage becomes longer and the slope of the curve increases, increasing the ultimate load by a small margin. When the HSSC specimen enters the plastic stage, the friction coefficient has little effect on the HSSC specimen, and the trend is the same.

[0083] (3) By analyzing the load-displacement curve, it can be concluded that when the thickness of lightweight concrete is less than 25 mm, the load-displacement curve of the HSSC specimen is quite different and the influence is more obvious. When the thickness of lightweight concrete is greater than 25 mm, the friction coefficient has little effect on the load-displacement curve of the HSSC specimen.

[0084] Same as HSSC, Figure 4 The load-displacement curves of HSLC specimens with different friction coefficients are listed. Through analysis, it can be concluded that:

[0085] (1) When the thickness of lightweight concrete is less than 25 mm, the HSLC specimen is still partially buckled, and its load-displacement curve changes in the same way as the short column. The change in friction coefficient has no effect on the overall trend of the load-displacement curve. Before the specimen reaches the buckling load, the overall buckling load of the HSLC specimen increases slightly by about 2%. When the HSLC specimen enters the elastic-plastic stage, this stage increases compared to the HSSC specimen, indicating that the influence of lightweight concrete on the HSLC specimen is greater than that on the short column specimen. When the HSLC specimen enters the plastic stage, the increase in friction coefficient will slow down the speed of specimen failure.

[0086] (2) When the thickness of lightweight concrete is greater than 25 mm, the buckling mode of the HSLC specimen changes to overall instability. It can be concluded from the load-displacement curve that the stage of joint stress of lightweight concrete and box-type steel column becomes smaller, but the increase in buckling load and ultimate load is greater, indicating that the lightweight concrete better constrains the local buckling of the built-in box-type steel column, affects the buckling mode of the HSLC specimen, and delays the buckling failure process. The rest of the changes are the same as when the thickness of lightweight concrete is 15 mm.

[0087] By comparing and analyzing HSLC specimens with different thicknesses, it can be concluded that the improvement of the axial bearing capacity of the HSLC specimens by the friction coefficient will not change due to the change of the buckling mode of the HSLC specimens. After changing the friction coefficient, the load-displacement curve trends of the HSLC specimens are the same. The larger the friction coefficient, the better the improvement effect.

[0088] Through a comprehensive analysis of HSLCC in terms of lightweight concrete thickness, width-to-thickness ratio, and degree of bonding between lightweight concrete and box-type steel columns, it can be concluded that due to the low strength of lightweight concrete, the effect of improving the axial bearing capacity and buckling performance of HSLCSC specimens is not obvious. The main function of lightweight concrete is to protect the box-type steel columns, and it does not affect its key performance such as buckling mode. Therefore, in order to simplify the design process, HSLCSC specimens with small improvement effects can be designed as pure steel specimens.

[0089] For the HSLCLC specimen, lightweight concrete affects the buckling mode of the HSLCLC specimen and has a greater impact on the axial bearing capacity of the HSLCLC specimen. Since its design process is the same as that of the short column, the calculation formula of its axial bearing capacity needs to be changed and modified based on the calculation formula of the axial bearing capacity of the pure steel specimen. Here, an outsourcing coefficient is introduced β , and finally the formula is obtained, as shown in formula (3):

[0090] , (3)

[0091] In the formula, N cr For carrying capacity; is the stability coefficient; f c , f y Both are the design values ​​of compressive strength of lightweight concrete and steel components; A. A S Both are the cross-sectional area of ​​the component and the cross-sectional area of ​​the steel component; β is the outsourcing coefficient.

[0092] The HSLCLC specimens are analyzed. It can be seen from formula (3) that the envelope coefficient of long column specimens under different lightweight concrete thicknesses is related to the lightweight concrete thickness and stability coefficient. When the lightweight concrete thickness is the same, the width-to-thickness ratio has little effect on the stability coefficient, and the stability coefficient at the same thickness can be unified. Through the above research, the lightweight concrete thickness of 25mm has the greatest impact on the long column specimens. In this implementation, the stability coefficient when the lightweight concrete thickness is 25mm is selected, and the value is 0.895. By analyzing long column specimens with different width-to-thickness ratios and lightweight concrete thicknesses, the envelope coefficient of each group of specimens is derived, such as Figure 5 shown.

[0093] By comparing the relationship between the external package coefficient and lightweight concrete under different width-to-thickness ratios, it can be concluded that the external package coefficient increases with the increase of lightweight concrete thickness, but the change range is small and controlled between 0.1; when the width-to-thickness ratio increases, the external package coefficient decreases; under different width-to-thickness ratios, the external package coefficient of the same lightweight concrete thickness is small, about 3%, and the change trend is also the same, so the average external package coefficient of each thickness is selected for fitting. According to the actual situation, the difference between the lightweight concrete thickness of 15mm and 20mm is small, so the 15mm case can be ignored, and the relationship between the external package coefficient and the lightweight concrete thickness is simplified, as shown in formula (4):

[0094] , (4)

[0095] in, t Indicates the thickness of lightweight concrete

[0096] Finally, the outsourcing coefficient formula is substituted into formula (3), and the final calculation formula for the axial bearing capacity of the HSLCC specimen is obtained, as shown in formula (5):

[0097] , (5)

[0098] In the formula, N cr For carrying capacity; is the stability coefficient; f c , f y Both are the design values ​​of compressive strength of lightweight concrete and steel components; A. A S Both are the cross-sectional area of ​​the component and the cross-sectional area of ​​the steel component; t Indicates the thickness of lightweight concrete.

[0099] S3. Construct a finite element model for heat transfer performance analysis of box-type steel columns wrapped with lightweight concrete. Based on the finite element model for heat transfer performance analysis, perform heat transfer performance analysis on the box-type steel columns to obtain the heat transfer performance.

[0100] As a finite element simulation software, ABAQUS can not only solve a large number of structural problems, but also solve problems such as heat transfer, thermoelectric coupling analysis, and acoustic analysis. This embodiment mainly uses the heat transfer analysis function of the software to simulate and analyze the influence of different lightweight concrete thicknesses on the heat transfer performance of HSLCC.

[0101] By studying the heat transfer performance of HSLCC, we can find out the advantages of its thermal insulation performance and the influence of lightweight concrete thickness on heat transfer performance. According to the simulation results and relevant specifications, the heat transfer coefficient is compared and the calculation formula of HSLCC heat transfer coefficient is derived. Considering that the heat transfer of components in actual engineering is relatively complex, in order to ensure the correctness of the simulation results and improve the calculation efficiency, the following three assumptions will be proposed and a finite element model for heat transfer performance analysis of box-type steel columns wrapped with lightweight concrete will be established:

[0102] (1) Assuming constant temperature inside and outside

[0103] In actual environments, temperature will change over time, but there are many influencing factors. At the same time, the heat transfer performance of HSLCC is relatively stable and related to the material properties. Therefore, a constant temperature is used in the interaction conditions of the model, and the heat transfer is defined as steady-state heat transfer.

[0104] (2) Ignore the contact thermal resistance between materials

[0105] Contact thermal resistance is generated when different materials come into contact. This is related to factors such as surface contact and material properties, but has little effect on the heat transfer performance of components. To simplify the heat transfer analysis process, the contact thermal resistance in the model is ignored during modeling, that is, the temperatures on the contact surfaces of different materials are the same.

[0106] (3) Radiation heat transfer is not considered

[0107] In actual engineering, heat transfer mainly includes heat conduction, heat convection and heat radiation. Among them, heat radiation has little effect on components and is greatly affected by the environment. Therefore, radiation heat transfer is not considered in the simulation process.

[0108] After the model was established, the inner and outer surface temperature values ​​were extracted from the HSLCC specimens with different lightweight concrete thicknesses, as shown in Table 5. Through comparative analysis, it can be concluded that with the increase of lightweight concrete thickness, the maximum temperature difference of the outer surface decreased from 0.539℃ to 0.326℃, a decrease of 39.5%, and the maximum temperature difference of the inner surface decreased from 0.897℃ to 0.673℃, a decrease of 25%, which weakened the thermal bridge and cold bridge effects to a certain extent; due to the existence of lightweight concrete, the temperature difference of the outer surface and the temperature difference of the inner surface were both within 1℃. At the same time, the greater the thickness of the lightweight concrete, the more the overall temperature of the inner and outer surfaces tended to the set temperature, showing better thermal insulation performance. When the thickness of lightweight concrete is less than 25mm, the impact on the overall surface temperature is greater, increasing by about 19%, and the thermal insulation effect is enhanced. When the thickness of lightweight concrete is more than 25mm, the impact on the overall surface temperature gradually decreases, increasing by about 10%. The internal and external surface temperatures tend to a fixed value and are close to the set temperature. At this time, it can be concluded that lightweight concrete with a thickness of 25mm is the most economical and has a better thermal insulation effect. It can be used as a recommended thickness value. Increasing the thickness will result in the material failing to fully exert its performance and wasting materials.

[0109] Table 5

[0110] .

[0111] The heat transfer coefficient of HSLCC under different lightweight concrete thicknesses is extracted, such as Figure 6 As shown, through comparative analysis, it can be concluded that with the increase of lightweight concrete thickness, the heat transfer coefficient decreases by about 25%, indicating that the thermal insulation effect is better; when the lightweight concrete thickness is before 25mm, the heat transfer coefficient of the corresponding specimen changes by about 10%, and when the lightweight concrete thickness is after 25mm, with the increase of lightweight concrete thickness, the heat transfer coefficient does not change much, all within 5%, which verifies some of the above conclusions, that is, the lightweight concrete thickness of 25mm can be used as the recommended thickness value, at this time the thermal insulation performance of lightweight concrete materials is fully exerted.

[0112] From the data collected above, it can be seen that the heat transfer coefficient of HSLCC specimens under different lightweight concrete thicknesses is shown in formula (6):

[0113] , (6)

[0114] In the formula, K represents the heat transfer coefficient; q represents the average heat flux density of the cross section; Represents the difference between the mean inner and outer surface temperatures.

[0115] According to the three assumptions made when establishing the finite element model for heat transfer performance analysis, it is assumed that the heat flux density of the specimen is consistent along the thickness direction during the heat transfer process. Therefore, the heat flux density in equation (6) can be taken as the average heat flux density of any cross section in the thickness direction. At the same time, the temperature value of each node on the inner and outer surfaces is derived through ABAQUS, and the average value is obtained by integrating and averaging to obtain the average temperature of the inner and outer surfaces of the specimen.

[0116] Through calculation, the heat transfer coefficient of HSLCC under different lightweight concrete thicknesses is obtained and the curve is drawn, such as Figure 7 (a) Observation Figure 7 (a) It can be seen that there is a certain functional relationship between the heat transfer coefficient of the specimen and the thickness of lightweight concrete. Different functions are used to fit the relevant data, such as Figure 7 (b) Figure 7 (c) and Figure 7 (d) shown.

[0117] The HSLCC heat transfer coefficient curve was fitted with linear function, quadratic function and exponential function respectively, and the error analysis of the fitting function was carried out according to the correlation coefficient, relative error and relative standard deviation. The results are shown in Table 6:

[0118] Table 6

[0119] .

[0120] Through analysis, it can be concluded that the linear function does not meet the specification requirements and the error is too large, the errors of the quadratic function and the exponential function meet the specification requirements, but the exponential function has a higher accuracy than the quadratic function, so the exponential function is selected for fitting. The heat transfer coefficient formula of HSLCC is determined as shown in formula (7):

[0121] , (7)

[0122] In the formula, K represents the heat transfer coefficient; t Indicates the thickness of lightweight concrete; e Represents a natural constant.

[0123] S4. Complete the design of new type of externally wrapped lightweight concrete box column based on structural parameters and heat transfer performance.

[0124] After obtaining the structural parameters and heat transfer performance according to the above steps, this embodiment designs a 6m long, 3m wide, and 2.8m high folding box house based on the above data. The folding box house adopts a new type of outer lightweight concrete box column, in which the outer lightweight concrete thickness is 25mm and the outer concrete density is 800kg / m 3The compressive strength is 7.6MPa, the box column size is 100mm×100mm, the thickness is 5mm, Q235 steel is used, and the compressive strength design value is 375MPa.

[0125] Embodiment 2

[0126] The present invention also provides a novel design system for outsourced lightweight concrete box columns of folding houses, comprising: a bearing capacity model construction module, a heat transfer performance model construction module and a design module; the bearing capacity model construction module is used to construct a bearing capacity analysis finite element model of outsourced lightweight concrete box-type steel columns, and based on the bearing capacity analysis finite element model, perform structural parameter analysis on the box-type steel columns to obtain the bearing capacity; the structural parameters include: lightweight concrete thickness, width-to-thickness ratio and degree of bonding between lightweight concrete and box-type steel columns; the heat transfer performance model construction module is used to construct a heat transfer performance analysis finite element model of outsourced lightweight concrete box-type steel columns, and based on the heat transfer performance analysis finite element model, perform heat transfer performance analysis on the box-type steel columns to obtain heat transfer performance; the design module is used to complete the design of the novel outsourced lightweight concrete box columns based on the structural parameters and heat transfer performance.

[0127] Among them, the workflow for analyzing the thickness of lightweight concrete includes: using pure box-type steel column specimens to outsource lightweight concrete of different thicknesses to analyze the influence of lightweight concrete thickness on the mechanical properties of pure box-type steel column specimens; wherein the pure box-type steel column specimens include pure long steel columns and pure short steel columns, and the pure long steel columns and pure short steel columns have the same width-to-thickness ratio, but different specimen heights, the pure long steel column specimen is 1500mm high, and the pure short steel column specimen is 400mm high.

[0128] The process of analyzing the width-to-thickness ratio includes: performing axial compression analysis on externally wrapped lightweight concrete box column specimens with different width-to-thickness ratios and the same lightweight concrete thickness, extracting the load-displacement curve, buckling load and ultimate load of the externally wrapped lightweight concrete box column specimens, and analyzing the influence of the width-to-thickness ratio on the axial bearing capacity of the externally wrapped lightweight concrete box column.

[0129] The process of analyzing the bonding degree between concrete and box-type steel columns includes: selecting different friction coefficients between the contact interface of lightweight concrete and built-in box-type steel columns to reflect the bonding degree between the two; and selecting outsourced lightweight concrete box column specimens with the same width-to-thickness ratio, different lightweight concrete thicknesses, and different friction coefficients to analyze the bonding degree between the concrete and the box-type steel columns.

[0130] Based on the thickness of the lightweight concrete, the width-to-thickness ratio and the bonding degree of the box-type steel column, the calculation formula for the bearing capacity includes:

[0131] , (8),

[0132] In the formula,N cr For carrying capacity; is the stability coefficient; f c , f y Both are the design values ​​of compressive strength of lightweight concrete and steel components; A. A S Both are the cross-sectional area of ​​the component and the cross-sectional area of ​​the steel component; t is the thickness of lightweight concrete.

[0133] The heat transfer performance model building module constructs the heat transfer performance analysis finite element model to analyze the heat transfer performance of the box-type steel column and obtains the heat transfer coefficient formula of the lightweight concrete box-type steel column:

[0134] , (9)

[0135] In the formula, K represents the heat transfer coefficient; t Indicates the thickness of lightweight concrete; e Represents a natural constant.

[0136] After the design module obtains the structural parameters and heat transfer performance according to the above process, this embodiment designs a 6m long, 3m wide and 2.8m high folding box house based on the above data. The folding box house adopts a new type of outer lightweight concrete box column, in which the outer lightweight concrete thickness is 25mm and the outer concrete density is 800kg / m 3 The compressive strength is 7.6MPa, the box column size is 100mm×100mm, the thickness is 5mm, Q235 steel is used, and the compressive strength design value is 375MPa.

[0137] The embodiments described above are only descriptions of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A novel design method for outer lightweight concrete box columns of a folding house, characterized in that the steps include: Constructing a bearing capacity analysis finite element model for a box-shaped steel column wrapped with lightweight concrete, and based on the bearing capacity analysis finite element model, performing structural parameter analysis on the box-shaped steel column to obtain the bearing capacity; The structural parameters include: lightweight concrete thickness, width-to-thickness ratio, and bonding degree between lightweight concrete and box-type steel column; the method for analyzing the lightweight concrete thickness includes: using pure box-type steel column specimens to wrap lightweight concrete of different thicknesses to analyze the influence of lightweight concrete thickness on the mechanical properties of pure box-type steel column specimens; wherein, the pure box-type steel column specimens include pure long steel columns and pure short steel columns, and the pure long steel columns and pure short steel columns have the same width-to-thickness ratio, but different specimen heights; the method for analyzing the width-to-thickness ratio includes: performing axial compression analysis on wrapped lightweight concrete box column specimens with different width-to-thickness ratios and the same lightweight concrete thickness, and extracting the outer lightweight concrete box column thickness. The load displacement curve, buckling load and ultimate load of the column specimen are analyzed to analyze the influence of the width-to-thickness ratio on the axial bearing capacity of the outer lightweight concrete box column; the method for analyzing the bonding degree between the lightweight concrete and the box-type steel column includes: by selecting different friction coefficients between the contact interface of the lightweight concrete and the built-in box-type steel column, the bonding degree between the two is reflected; and the outer lightweight concrete box column specimens with the same width-to-thickness ratio, different lightweight concrete thickness and different friction coefficient are selected to analyze the bonding degree between the lightweight concrete and the box-type steel column; based on the lightweight concrete thickness, the width-to-thickness ratio and the bonding degree of the box-type steel column, the calculation formula for the bearing capacity includes: ， Where N cr For carrying capacity; is the stability factor; f c 、f y are the design values ​​of compressive strength of lightweight concrete and steel components respectively; A, A S are the cross-sectional area of ​​the component and the cross-sectional area of ​​the steel component, respectively; where t represents the thickness of lightweight concrete; Constructing a finite element model for heat transfer performance analysis of a box-type steel column wrapped with lightweight concrete, and performing heat transfer performance analysis on the box-type steel column based on the finite element model to obtain heat transfer performance; Based on the structural parameters and the heat transfer performance, the design of a new type of outer-clad lightweight concrete box column is completed.

2. The novel design method of outer-wrapped lightweight concrete box columns of a folding house according to claim 1 is characterized in that: By constructing the heat transfer performance analysis finite element model, the heat transfer performance of the box-type steel column is analyzed, and the heat transfer coefficient formula of the box-type steel column wrapped with lightweight concrete is obtained: ， Where K represents the heat transfer coefficient; t represents the thickness of lightweight concrete; and e represents a natural constant.

3. A novel design system for outer-wrapped lightweight concrete box columns of a folding house, the system being used to implement the method described in any one of claims 1-2, characterized in that: include: Load-bearing capacity model building module, heat transfer performance model building module and design module; The bearing capacity model building module is used to build a bearing capacity analysis finite element model of the box-type steel column wrapped with lightweight concrete, and based on the bearing capacity analysis finite element model, perform structural parameter analysis on the box-type steel column to obtain the bearing capacity; The structural parameters include: lightweight concrete thickness, width-to-thickness ratio, and bonding degree between lightweight concrete and box-type steel column; the method for analyzing the lightweight concrete thickness includes: using pure box-type steel column specimens to wrap lightweight concrete of different thicknesses to analyze the influence of lightweight concrete thickness on the mechanical properties of pure box-type steel column specimens; wherein, the pure box-type steel column specimens include pure long steel columns and pure short steel columns, and the pure long steel columns and pure short steel columns have the same width-to-thickness ratio, but different specimen heights; the method for analyzing the width-to-thickness ratio includes: performing axial compression analysis on wrapped lightweight concrete box column specimens with different width-to-thickness ratios and the same lightweight concrete thickness, and extracting the outer lightweight concrete box column thickness. The load displacement curve, buckling load and ultimate load of the column specimen are analyzed to analyze the influence of the width-to-thickness ratio on the axial bearing capacity of the outer lightweight concrete box column; the method for analyzing the bonding degree between the lightweight concrete and the box-type steel column includes: by selecting different friction coefficients between the contact interface of the lightweight concrete and the built-in box-type steel column, the bonding degree between the two is reflected; and the outer lightweight concrete box column specimens with the same width-to-thickness ratio, different lightweight concrete thickness and different friction coefficient are selected to analyze the bonding degree between the lightweight concrete and the box-type steel column; based on the lightweight concrete thickness, the width-to-thickness ratio and the bonding degree of the box-type steel column, the calculation formula for the bearing capacity includes: ， Where N cr For carrying capacity; is the stability factor; f c 、f y are the design values ​​of compressive strength of lightweight concrete and steel components respectively; A, A S are the cross-sectional area of ​​the component and the cross-sectional area of ​​the steel component, respectively; where t represents the thickness of lightweight concrete; The heat transfer performance model building module is used to build a finite element model for heat transfer performance analysis of a box-type steel column wrapped with lightweight concrete. Based on the heat transfer performance analysis finite element model, a heat transfer performance analysis is performed on the box-type steel column to obtain heat transfer performance. The design module is used to complete the design of a new type of externally wrapped lightweight concrete box column based on the structural parameters and the heat transfer performance.

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