Study on Safety Performance of Building Finish Layer under Thermomechanical Coupling Condition

The building ﬁnish layer is a comprehensive structural system including the building exterior insulation system and building exterior ﬁnish. Combining with buildings has the advantage of reducing wall heat loss and building deformation caused by large temperature diﬀerences. Since the building ﬁnish layer is prone to cracking, hollowing, and peeling, during the application process, its safety needs to be studied and certiﬁed. This study prepares 20 groups of specimens, 15 anchor bolts in each group. The anchor bolt pull-out strength test is carried out. Anchoring damage evolution law and failure mode of anchor bolts are in-vestigated. And the inﬂuence of anchoring methods on the pull-out bearing capacity is analyzed. In addition, ABAQUS ﬁnite element data simulation is carried out. The stress state of ﬁnish in thermomechanical coupling condition and without the eﬀect of temperature are compared and analyzed. The inﬂuence factors of anchor bolt pull-out strength and the inﬂuence of temperature load on the long-term performance of building ﬁnish layer are obtained. The durability of the building ﬁnish layer is analyzed. The results show that the anchoring strength of the anchor bolt is positively correlated with the anchoring depth. The anchoring strength is inﬂuenced signiﬁcantly by anchoring construction sequence and temperature. The stress under the coupled eﬀect of temperature and load is greater than that of the single eﬀect of load, and the stress distribution changes signiﬁcantly. Due to thermal expansion and contraction, the anchor bolt would loosen, which is more prone to damage the building ﬁnish layer in a low temperature environment. The weight relationship of each inﬂuencing factor of the building ﬁnish layer is proposed. A systematic evaluation index system is established. The results of this study provide a basis for subsequent related research work and engineering applications.


Introduction
e building finish layer is a comprehensive structural system including the building exterior insulation system and building exterior finish. As one of the building envelope, it can enhance the beauty of the building. It also helps to reduce the heat loss [1,2] and the deformation of the building caused by the temperature difference. erefore, it can help in energy conservation and increase the service life of buildings. According to relevant statistics, more than 95% of new buildings in China have used building finish layers. e building finish layer is widely used in new residential buildings, and the renovation of old communities has developed into an industry. Under the influence of temperature, humidity, load, material property degradation, and service life, there will be various degrees of cracking, hollowing, peeling, and other phenomena. e building finish layer cannot fully meet the requirements of the specification [3] during use. is problem caused casualties and economic looses, which need to be solved urgently in the finish layer of the building.
ere are many factors that damage the building finish layer, and the current research [4][5][6] is limited to the influence of individual factors on the building finish layer system [7,8]. Some scholars have conducted research on a specific thermal insulation material, and systematic research on the building finish layer is still blank [9][10][11][12]. For the anchoring performance of anchor bolts [13], the main focus is on fatigue failure and bearing capacity [14,15]. e existing codes have limitations on the safety evaluation of the building finish layer, which are too absolute, and the quantitative and qualitative indicators are blurred.
Based on the research status of the above building finish layer, this study carried out anchor bolt pull-out strength tests and finite element analysis results. is study prepares 20 groups of specimens, 15 anchor bolts in each group. e influence of anchoring depth, anchoring construction sequence, and temperature on anchoring strength is obtained. To verify the accuracy of the test results, compare the results of the anchor bolt pull-out strength test with the refined model analysis results. is work studies the influence of the building finish layer under the condition of temperatureload coupling. For the rigid finish layer, semirigid finish layer, and flexible finish layer, the results of temperature field analysis, no-temperature stress field analysis, and temperature-load coupling analysis are carried out, respectively, to obtain the influence of temperature load on the finish layer. Regarding the long-term performance of the building finish layer, combined with related literature [16,17], the effects of heat-humidity cycles, heat-cold cycles and heat-rain cycles on the building finish layer are summarized. Finally, in view of the problems existing in the engineering application of the classification boundaries in the existing specifications for building finish layers, this study proposes a fuzzy evaluation method. e evaluation method adopts the method of engineering experience survey; through the method of frequency statistics, the weight value and membership degree of each material are obtained. After that, the calculation formulas of related quantitative indicators and qualitative indicators are put forward, and an evaluation method for the building finish layer is established. e aerated concrete blocks used in the test are the same batch of materials. e section size is 600 mm × 200 mm × 250 mm as shown in Figure 1. e plastic anchor bolt uses a percussive disc anchor, the disc diameter is 50 mm, the expansion sleeve diameter is 10 mm, and the expansion sleeve has a total length of 162 mm, as shown in Figure 2. e anchoring depth is set to four types: 50 mm, 60 mm, 70 mm, and 80 mm. ere are two ways of construction sequence: normal construction sequence (inserting the plastic expansion sleeve into the drilled hole and then driving the steel nail into the plastic expansion sleeve) and simultaneous anchoring (driven plastic expansion sleeve and steel nails into the block together). Temperature changes mainly considered the temperature difference between construction and use. is study prepares 20 groups of specimens, 15 anchor bolts in each group. e spot layout of the test piece is shown in Figure 3. In order to avoid the difference of aerated concrete block materials from affecting the test results, different anchorage depths are arranged on the same block in this test.

Anchor Bolt Pull-Out Strength Test and Simulation Analysis
In the main view, considering that the puller is constrained by distance requirements during operation, it is impossible to implant anchor bolts at 10 measuring points at the same time. us, the test is divided into two batches: the location of the first batch of measuring points is 1, 2, 5, 6, 9, and 10, and the second batch is 3, 4, 7, and 8. In the side view, the measuring point are implanted with 5 anchor bolts at a time. e anchor bolt layout after anchoring is shown in Figure 4.

Test Setup.
e loading instrument for this test is the HC-MD60 high-precision rivet puller as shown in Figure 5.
e force loading mode is adopted during the test. A unidirectional tensile load is applied to the anchor casing, as shown in Figure 6. When loading, the puller and the anchor bolt are in the same straight line. When the load displayed by the puller remains unchanged, the anchor bolt is pulled out.

Result and Discussion.
During the test, there are three results: the anchor bolt is pulled out as a whole. e plastic expansion, the casing is pulled off, and the metal anchor bolt is not pulled out. e plastic expansion sleeve is pulled off, and the metal anchor bolt is pulled out. e typical test results of anchor bolts are shown in Figure 7.
e construction sequence of all anchor bolts in this group is normal. e relevant drawing test data are given in Table 1. e results show that the pull-out strength of the   Advances in Materials Science and Engineering anchor bolt is positively correlated with the anchoring depth. For every 10 mm increase in anchorage depth, the anchoring force of the anchor bolt will increase by about 21.4%. In order to study the influence of the anchoring construction sequence on the anchoring strength of the anchor bolt, the normal construction sequence and simultaneous anchoring are carried out, and the results are given in Table 2. It can be found that the anchoring strength of simultaneous anchoring is reduced by about 70% compared with the normal construction sequence.
Considering the influence of temperature changes on the anchoring strength of anchor bolts, the anchor bolt pull-out strength tests under different ambient temperatures are designed. e anchor bolts are constructed at ambient temperatures of 20°C and 38°C, respectively, and then, the anchor bolt pull-out strength tests are carried out in the season when the ambient temperature is 20°C, 38°C, and −5°C.
e results are given in Table 3. e greater the temperature difference between the driving of the rivet and the pull-out strength test, the more obvious the reduction in the anchoring strength of the anchor bolts. is is because the thermal expansion coefficients of the aerated concrete block and the anchor bolt are different, resulting in temperature deformation, the extrusion force between the anchor bolt and the block is reduced, and the pull-out resistance is also reduced. e anchor bolt is prone to loosening under long-term action, which affects the stability and safety of the finish layer.  Advances in Materials Science and Engineering

Anchor Bolt Drawing Simulation.
Modeling and analyzing anchor bolts of different depths. Both anchor bolts and blocks use C3D8R entities to establish unit models, and the stress field element uses a C3D20 R: 20 node quadratic reduction integral hexahedral element. When building the model, the diameter of the anchor bolt is 10 mm, and the diameter of the reserved hole of the block is 10 mm. e variable of the anchor pull simulation test is the anchoring depth, which is 60 mm, 70 mm, and 80 mm, respectively. e boundary conditions around the model are completely fixed. e material properties of anchor bolts and blocks are given in Table 4. e constitutive relationship is shown in Figure 8. e schematic diagram of anchor bolt anchoring is shown in Figure 9, and the model mesh is shown in Figure 10.
e simulation results show that the influence range of a single anchor bolt can reach 70 mm, which is 7 times the diameter of the anchor bolt. Its maximum principal stress can reach 0.54 MPa and the maximum bond stress is 0.32 MPa. e distribution of Mises principal stress inside the aerated concrete block before and after anchor bolt drawing is shown in Figure 11, and 12 shows the distribution of the bond stress. e comparison of pull-out strength test data and simulated data under different anchoring depths is shown in Figure 13. e comparison shows that the simulation data iare 4.82% larger than the test data, and the simulation analysis agrees with the test data. erefore, it can provide data support for the subsequent modeling and analysis of the finish layer. According to the different softness and hardness of the internal insulation material of the finish layer, it can be divided into three types of structural forms: rigid finish layer, semirigid finish layer, and flexible finish layer. is article analyzes the modeling of three types of the finish layer. In order to simplify the modeling, it is divided into seven parts: masonry wall, interface layer, insulation layer, bonding layer, facing brick, casing, and metal nails. e rigid finish layer has no external wall insulation anchor bolts, and the material is a vitrified microbead insulation mortar. e semirigid finish layer adopts external wall insulation anchor bolts, and the material is mainly semirigid materials such as polystyrene board. e flexible material also uses anchor bolts, but the materials are mainly flexible materials such as thermal insulation rock wool. e simplified model structure diagram is shown in Figure 14.

Model Parameter Setting and Material Property
Definition. e model size of the rigid finish layer is set to 1 × 1 m 2 , and the model size of the semirigid finish layer and flexible finish layer is 0.3 × 0.3 m 2 . e material properties under heating-cooling cycles [18] are adopted. In addition, relevant specifications such as JGJ144-2017 technical specification for external wall thermal insulation engineering [19], JGT 366-2012 anchor bolt for external wall thermal insulation [20], national standard, and GB 11968-2006 autoclaved aerated concrete block [21] are taken as the basis for selection and comparison of relevant material parameters. e material parameters used are given in Table 5.

Mesh Division and Boundary Conditions.
e threedimensional solid element model is adopted in this modeling. e element type of temperature field is DC3D20: 20 node secondary heat transfer hexahedron, and the element type of stress field is C3D20 R: 20 node secondary reduced integral hexahedron. e mesh generation of the model is shown in Figure 15. Among them, the semirigid finish layer and the flexible finish layer both use insulation anchor bolts, so the same model is constructed.

Analysis of Temperature Field Results.
e temperature field of rigid veneer, semirigid veneer, and flexible veneer was simulated. e simulation analysis has obtained the heating curve of each layer of the building finish layer in 2.5 h. It is found that there is a difference in the ultimate temperature of each layer for materials, and the temperature difference in the insulation layer is large. e temperature load of the rigid surface layer is 50°C, the maximum temperature difference before and after the insulation layer is 23.6°C, and the temperature difference between the inside and outside of the surface layer reaches 29.5°C. At −20°C, the temperature difference between before and after is 6.6°C and 39.2°C, respectively. e semirigid finish layer anchor bolt has an obvious thermal bridge effect, which causes the temperature difference of the insulation layer to reach 11.5°C. For semirigid materials at 50°C, the gradient of the limit temperature of different materials is shown in Figure 16.      Advances in Materials Science and Engineering e flexible material is similar to the semirigid material, and the anchor bolt also has a thermal bridge effect. is makes the temperature difference between the inside and outside of the insulation layer reach 13.4°C, and the insulation effect is better than that of the semirigid finish layer; the difference is about 3°C. e temperature field distribution of some materials is shown in Figures 17 and 18.
e results show that the building finish layer can reduce the heat exchange between the wall and the external environment, which is beneficial to reduce the influence of the external hot and cold environment on the indoor temperature. e external wall thermal insulation material has a significant thermal insulation effect, which is conducive to maintaining the comfort of the indoor environment. At the same time, the temperature change of the building is reduced, which is conducive to its durability.

Analysis of Stress Field
Results. Temperature and load will affect the finish layer of the building and cause it to produce stress and deformation.
is article studies and discusses its durability. e three types of the finish layer were analyzed in the nontemperature stress field and coupled with the temperature load. e influence of the temperature load on the building finish layer is obtained.
is article carried out the following simulation: under the action of 2000 Pa surface load and gravity load, the Mises principal stress and normal bonding stress were compared and analyzed under three conditions of no temperature, 50°C, and −20°C. e following results are obtained through the comparative analysis under three temperature conditions: for no-temperature load, the surface load is 2000 Pa, and the maximum surface stress is 0.04 MPa. But under 50°C and −20°C temperature load, its maximum stress reached 2.8 MPa and 10.3 MPa, respectively. e results show that the temperature load has a significant effect on the stress changes of each layer of materials.
e stress under the coupled temperature load is higher than the stress under the separate load. e simulation results show that the stress situation in low temperature environment is significantly higher than that in high temperature environment. In winter, the building finish layer is more prone to damage, which is consistent with the realization of simulation results.
is verifies the correctness of the simulation results. Figure 19 shows the principal stress distribution of some materials of the finish layer under different working conditions. e principal stress curve changes of some materials are shown in Figure 20. e results show that the temperature load will increase the Mises principal stress of each layer of material, more obvious in low temperature environment. e materials of all layers are in the same direction except for the face brick. Facing bricks appear under the stress concentration phenomenon in low temperature environment, which will destroy the stability of the building finish layer.   Advances in Materials Science and Engineering Figure 21 shows the cloud diagram of the bond stress distribution. e bonding strength between the materials of each layer determines the stability of the building finish layer. e stress of the building finish layer material will be greatly reduced before and after the insulation layer. It is obviously affected by gravity load. is is consistent with the phenomenon of engineering damage. At the boundary conditions, there are triple effects of boundary conditions, load, and temperature. e stress change caused by temperature is more obvious. Figure 22 shows the bond stress curve of each layer of the semirigid building finish layer at different temperatures. e stress distribution is consistent under three load conditions, and the temperature load has little effect on the bond stress.
ere are constraints at the boundary conditions. Temperature load will cause the direction of bond stress to change. At the boundary of the principle, the bonding stresses of the facing brick, the bonding layer, the interface layer, and the masonry wall tend to be consistent. e insulation layer has a thermal bridge effect at the anchor bolt; this makes the magnitude and direction of the bond stress at the anchor bolt greatly affected by the temperature load.

Durability Analysis of the Finish Layer.
At present, some related research studies [22] have been conducted on factors such as humidity and durability. Sun [23] carried out a study on the thermal and moisture coupling of the flexible finish layer. Based on the performance of flexible materials, they established a coupled heat-moisture migration model for the flexible finish layer and established relevant evaluation indicators and methods. e result shows that the tensile bond strength of the finish layer will decrease under the effect of heat-moisture coupling. e intensity reduction is related to the duration of action, serious with time.
Liu [24] carried out comparative experiments between humidity-controlling materials and the ordinary mortar at 25°C and 60%-85% relative humidity and concluded that the moisture absorption capacity of the humidity-conditioning mortar is 6 times that of ordinary mortar. At the same time, it is highly sensitive to temperature, and as the temperature rises, the humidity control effect is significant. rough the test results, a new system combining the external wall insulation structure system and the internal plastering and humidity-controlling mortar is proposed. It has the effect of heat preservation and humidity control at the same time.
Xiang [25] studied the surface mortar under the cycle of heat-rain and carried out 20 times, 40 times, 60 times, and 80 heat-rain cycle tests respectively, also 2 times and 5 times the heat-cold cycle test. Tests        Advances in Materials Science and Engineering strength). Analyze the failure mechanism by comparing the magnitude of stress in each case. Part of the test results is given in Table 6. e bond strength test of the polymerbonded mortar is given in Table 7. In Tables 6 and 7, H-R is the heat-rain cycle, and D is the curing age. For example, 28d + 20H-R means that the blocks undergo 20 heat-rain cycles tests after 28 days of standard curing. e test results show that weather resistance has a great influence on the building finish layer. e flexural strength, compressive strength, and bonding strength of the polymer mortar surface are reduced.
Huo et al. [26] studied the durability of the thermal insulation mortar finish layer and modified polystyrene board finish layer through experiments. e heat-cold cycle and hotrain cycle tests were carried out on the specimens and gained its bond strength. e curve change is shown in Figure 23.
e test results show that the heat-rain cycle has a greater impact on the finish layer. With the increase of the number of tests, the plastic deformation of the building finish layer increases. e deformation of the polystyrene board is greater than that of the vitrified bead insulation mortar, and heat-cold cycles cause greater strength attenuation than heat-humidity cycles.
Due to the influence of temperature, humidity, and load, the long-term performance of building finish layers cannot meet the requirements of the specification. e temperature    +5.296e+00 +5.274e+00 +5.252e+00 +5.230e+00 +5.208e+00 +5.186e+00 +5.164e+00 +5.142e+00 +5.120e+00 +5.098e+00 +5.076e+00 +5.054e+00 +5.032e+00 Advances in Materials Science and Engineering change causes cracks in the material, thereby reducing the anchoring force of the anchor bolt, and ultimately affects the long-term performance of the building finish layer. As the number of heat and humidity cycles increases, the plastic deformation of the material becomes larger, and the bonding strength between the materials decreases. e reason is that the heat-humidity cycle causes the material to expand or contract, resulting in varying degrees of deformation. is leads to the destruction of the long-term performance of the material. And the heat-cold cycle is more harmful than the heat-humid cycle. Due to weather resistance, it is impossible to accurately analyze the plastic deformation of the building finish layer; this has resulted in an insufficient weather resistance analysis of the building finish layer, still in the preliminary exploration stage.

Evaluation Index
System. e existing comprehensive safety assessment method for the finish layer is essentially an analytic hierarchy process, which mainly includes classification of grades and weight determination. With reference to relevant specifications, an evaluation index system has been established for the building finish layer, from appearance and structure, material performance, and bearing capacity. e appearance and structure are obtained through on-site inspection. Material performance indicators are obtained through material testing. e bearing capacity index is obtained through the bearing capacity detection test, including two aspects of the bearing capacity test and review. e relevant test indicators are given in Tables 8-10.

Fuzzy Evaluation Method.
ere are some problems in the practical engineering application, such as absoluteness of classification boundaries, uncertainty of qualitative indicators, and complexity of influencing factors. Combined with relevant specifications [27][28][29], this study proposes a systematic fuzzy evaluation method for the building finish layer. e building finish layers are divided into four fuzzy grades: from good to severe, it can be divided into I, II, III, and IV, as given in Table 11.

Determination of Weight.
is article uses a questionnaire to survey relevant personnel on engineering experience.
rough the frequency statistics method, the six weights of thermal insulation panels, structural adhesives, anchor bolts, facing bricks, material properties, and bearing capacity are obtained. e weight relationship of the underlying indicators is determined. According to the questionnaire survey results of the weight (u i ⟶ w ij , i,       ≥ 30), the corresponding safety impact score is divided into group p (p is generally 5-10), the group distance is h � (max w ij − min w ij )/p, and calculate the frequency and frequency of the score value in each group; then, the corresponding weight of the evaluation index is

Membership Degree and Qualitative Index.
e building finish layer system is evaluated in the form of an evaluation set, and the safety evaluation of the building finish layer is directly affected by the accuracy of the basic indicators. is article proposes a corresponding index system for different types of building finish layers, gives a level division interval of basic parameters, and determines the degree of membership.
In order to meet the fuzzy comprehensive evaluation combining quantitative and qualitative indicators, the quantification of the safety qualitative indicators of the building finish layer has been studied. ere are four levels of subjective evaluation indicators, namely, I, II, III, and IV. e subjective evaluation index membership degree matrix is quantified in Table 12.
e hypothesis still needs to satisfy the following relations: For the subjective evaluation index u ij , if the evaluation results of all components are i level, (i � 1, 2, 3, 4), it can be obtained that the index u ij of the component subunits are all i level. e results are as follows: x 11 + 2x 12 + < 1.5, x 11 + x 12 � 1, For situations that do not contain three or four-level components, the second secondary components are less than 30%. en, the subunit level of the component is the first level. For the situations where the fourth-level components are not included and the third-level components are less than 20%, the subunit level of the component is the second level. For the case with four-level components, if the fourthlevel component is less than 10%, it is a third-level component, and if it is greater than 10%, it is a fourth-level component. e first-level evaluation rules are as follows: 0.7 0.3 .
According to the same judgment rules, similar inequality relations can be obtained at the second, third, and fourth levels. is article combines all the above inequality relations. rough trial calculations, a set of solutions given in Table 13 can be obtained. e membership level used for subjective evaluation index is given in Table 13.
To sum up, the structural characteristics of the building finish layer are analyzed, and three relevant detection indexes, such as appearance and structure, material performance, and bearing capacity, of the building finish layer are determined.
e comprehensive evaluation levels of the safety performance of the finish layer are divided, and the corresponding fuzzy evaluation methods are proposed for different structural levels and index systems. Use the method of questionnaire and frequency statistics to determine the weight and membership degree of the relevant detection index of the building decoration layer and determine the quantitative index and qualitative index.  Table 11: Safety classification of the finish layer.
Overall structure of the finish layer I e bearing capacity is enough, which meets the requirements of the specification. II e safety is slightly low, which meets the requirements of the specification. III e degradation of bearing capacity is large, and the safety does not meet the specification.

IV
Bearing capacity degradation is serious, safety is very low, neither meets the specification.

Conclusions
(1) e anchoring strength of the anchor bolt is positively correlated with the anchoring depth of the anchor bolt. e diameter of the influence of a single anchor bolt can reach 70 mm, which is seven times the diameter of the anchor bolt. e maximum principal stress is 0.54 MPa, and the maximum bonding stress is 0.32 MPa. In addition, the simulation results are in good agreement with the results of anchor bolt pull-out tests.
(2) For the safety performance of the building finish layer, the temperature load has a significant effect. e coupling conditions of temperature-free stress field and temperature load are compared and analyzed. e results show that the temperature load not only increases the stress of the building finish layer but also affects its stress distribution. For low temperature environments, the influence of temperature load is more significant. It is consistent with the phenomenon that the building finish layer is more susceptible to damage in winter.
(3) Based on actual engineering and related literature, the influence of the heat-humidity cycle on the safety performance of the building finish layer is obtained. As the number of heat-moisture cycles increases, the plastic deformation of the material increases and the bond strength decreases to damage. At the same time, the heat-cold cycle damages the building finish layer more than the heat-humidity cycle. (4) According to the appearance and structure, material performance, and bearing capacity, the weight relationship and membership relationship of the influencing factors of the finish layer are determined. e calculation formulas of the relevant quantitative and qualitative indexes are summarized, and the evaluation method for the finish layer is established.

Data Availability
e data used to support the findings of this study are included within the article.

Conflicts of Interest
e authors declare that they have no conflicts of interest.