Simulation analysis of the entire construction process of the sunflower shaped continuous arch bridge

At present, there is a lot of research on the structural system of the completion stage of the Kuihua arch bridge in China, but there is a lack of research on the risks existing in each stage of the construction of the Kuihua arch bridge. Therefore, it is necessary to conduct a full process simulation analysis of the construction process of the sunflower shaped continuous arch bridge. The following conclusions were drawn from this study: (1) After analysis, the construction method of first removing the support below the main arch ring and then pouring the main beam can ensure the safety of construction. (2) The maximum axial force of the support pole below the main arch is -17.67kN, located in rows 10 and 50. The maximum vertical displacement of the main arch is -4.998mm, which is much smaller than the allowable deflection. Therefore, the shape of the main arch is within the safe range. (3) The tensile stress of the main arch and continuous longitudinal beam are both less than the design value of C40 concrete tensile strength of 1.71MPa, so the main arch and continuous longitudinal beam have not cracked, and are in a safe state throughout the construction process.


Introduction
The sunflower shaped continuous arch bridge is a new type of irregular arch structure with reasonable stress and beautiful shape, most of which are reinforced concrete arch bridges.Compared with traditional open spandrel arch bridges, the sunflower shaped continuous arch bridge eliminates columns or transverse walls on the arch and adopts a web arch directly connected to the main arch.The load on the arch is transmitted to the main arch in a concentrated manner through the web arch ring, using a "large arch stacked with small arches" method [1].The sunflower shaped arch bridge greatly reduces the structural weight, increases the overall integrity of the bridge, and from the appearance, the sunflower shaped continuous arch bridge is transparent and beautiful, resembling sunflower petals with a strong sense of rhythm.However, the structural system of the sunflower shaped continuous arch bridge is subjected to complex forces, and the continuous transformation of the structural system during the construction process leads to many problems.Therefore, it is necessary to study and analyze the risks that exist during the construction process of the sunflower shaped continuous arch bridge.
The sunflower shaped continuous arch bridge is highly favored by people due to its beautiful shape and economical cost.At present, a large number of sunflower shaped continuous arch bridges have been built and put into use across the country.There are significant differences in form between the sunflower shaped continuous arch bridge and the traditional arch bridge, and their stress performance is relatively complex.The research on the mechanical properties of their structural system is not detailed and comprehensive enough.Therefore, further in-depth research on the sunflower shaped continuous arch bridge is of great significance.At present, some scholars in China have conducted research on sunflower shaped continuous arch bridges, and the main research content is as follows: Wang and Xin [2] established an 8-hole continuous sunflower shaped arch bridge model using finite element analysis software Midas/Civil, and analyzed the influence of the connection method of the main arch ring on the stress performance, deformation performance, and stability of the sunflower shaped arch structure.Jin Wencheng, Zhao Hongyao, Bai Jinzeng, Qin Bo [3] used the Sanhegou Bridge in Xuan'en County as the engineering background and conducted simulation analysis of its structural system using finite element software Bridge Doctor.Jin Wencheng, Zhao Hongyao, Bai Jinzeng, and Qin Bo [4] compared and analyzed the characteristics and shortcomings of non integral tied sunflower arch bridges and integral prestressed sunflower arch bridges, and combined with engineering examples, analyzed the stress characteristics of sunflower shaped arch bridges in urban Fushuihe Bridge, and proposed key control sections for the design of such bridges.Liang Qingxue [5] used finite element analysis software Midas/Civil combined with engineering examples to study the influence of the main arch connection form, main arch ring span loss ratio, and belly arch ring span loss ratio on the structural performance of the sunflower shaped arch bridge.He also studied the influence of different main arch connection forms on the stability of the structural system and conducted preliminary analysis and research on the vibration effect of the sunflower shaped arch bridge.Kang Juntao, Liang Qingxue, and Zhou Hansheng [6] used a prestressed sunflower arch bridge as an example and established a calculation model using finite element software Midas/Civil.They analyzed the influence of the main web arch connection method and the loss to span ratio on the structural stress performance of the prestressed sunflower arch bridge, as well as the influence of the main web arch connection method on the stability of the arch ring.
Yang Zhulin, Wang Panfeng, Zhao Hui, and Zhao Shunbo [7] introduced the coordination ideas of various factors such as the selection of bridge type schemes and elevation settings using the Beiguan West Kuihua Arch Bridge in Neiqiu County as the background, and conducted simulation analysis on it using finite element software Bridge Doctor.
At present, there is a lot of research on the structural system of the completion stage of the Kuihua arch bridge in China, but there is a lack of research on the construction control of each stage of the Kuihua arch bridge construction, and a lack of research on the risks existing in each stage of construction.Therefore, this article conducts a full process simulation analysis of the construction process of the joint sunflower shaped continuous arch bridge based on ANSYS and Midas/Civil finite element software, conducts risk analysis on the main arch ring shape and support system during the construction process, and analyzes the stress state of the main and auxiliary arch rings and continuous longitudinal beams.

Background
This article takes the Jiulonghu Bridge in Huangpu District, Guangzhou City as the background project to carry out risk control research on the construction of the sunflower shaped continuous arch bridge.The Jiulonghu Bridge consists of 10m continuous beams on both sides and three span continuous arches, with a span combination of (10+3x40+10) and a total length of 146m.The bridge has a total width of 40m and is divided into two sections: left and right.The width of a single section is 17.5m, and a net width of 5m is reserved in the middle of the two sections.The three span continuous arch is a solid web slab arch, with a web arch above the main arch.The building above the web arch is a continuous reinforced concrete slab beam, as shown in Figure 1.
Due to the fact that this bridge is a three span sunflower shaped continuous arch bridge with a symmetrical structure on both sides, a comprehensive model is established for it.When analyzing the results, only 1/2 of the spans need to be extracted.For the convenience of statistical analysis of the results of finite element analysis, the full support poles below the main arch are numbered, and the control sections of the 1/2 span main arch and longitudinal beams are defined.The numbering of the support poles below the main arch is shown in Figure 2; The definition of the main arch control section is shown in Figure 3; The definition of the longitudinal beam control section is shown in Figure 4.

Establishing ANSYS finite element analysis model for sunflower shaped continuous arch bridge
Due to the complex stress on the arch structure and support system, the support system analysis uses beam element BEAM188 to simulate the support members.The main arch and web arch are modeled using SOLID65 solid elements, with 95221 model nodes and 175012 elements.
The longitudinal beam structure is simple and the arch structure is two different structural systems.The main beam structure is simulated using Midas/Civil beam elements, with 229 model nodes and 158 elements.
The calculation is divided into two parts for coupling.The ANSYS model converts the longitudinal beam load into node load acting on the top of the main beam support frame.In addition, the displacement value of the support position after removing all supports is used as the settlement value of the supports in Midas/Civil.
Based on the symmetry principle of a three span sunflower shaped continuous arch bridge, a 1/2 modeling method is adopted.The ANSYS geometric entity model is shown in Figure 5, and the Midas/Civil longitudinal beam geometric model is shown in Figure 6.The finite element model based on ANSYS is divided using the BEAM188 element and LMESH one-dimensional line element, while the SOLID65 element is divided using the VSWEEP threedimensional sweep mesh based on parallel or equal face mesh.Local refinement is performed at the connection between the web arch and the main arch, as shown in Figure 7.The reinforcement in the dispersed model is shown in Figure 8.

Results
The construction method of first removing the support below the main arch ring and then pouring the main beam is adopted.The extraction of results is mainly divided into four parts, namely the axial force of the control section under the main arch ring, the displacement value of the control section of the main arch ring, the stress value of the control section of the main web arch ring, and the stress value of the continuous longitudinal beam in each construction stage.
According to the structural system transformation, the construction steps are divided into five steps, which are:

Safety analysis of the main arch shape and support system
The axial force values of the control section vertical pole below the main arch are shown in Table 1.The displacement values of the main arch control section are shown in Table 2, and the vertical displacement of the main arch beam is analyzed as shown in Figure 9.The following conclusions can be drawn from the analysis of the above data: (1) The maximum axial force of the upright pole of the full hall support below the main arch is -17.67kN,located in rows 10 and 50.According to the calculation results in Chapter 2, the maximum axial force value does not exceed the allowable value, so the full hall support system is in a safe state.
(2) The main arch ring produces significant displacement at sections G3, G4, G5, G10, and G11, with a maximum displacement value of -4.998mm.The increase in displacement during construction stages (1), (2), and ( 4) is relatively small, while the increase in displacement during construction stages (3) and ( 5) is relatively large.Analysis shows that the vertical displacement of the section between the main arch ring and the longitudinal beam support is relatively large.Removing the support below the main arch ring and pouring the longitudinal beam increases the displacement of the main arch ring.After removing the support below the main beam, the displacement value of the section between the main arch ring and the longitudinal beam support will slightly decrease, and the displacement value of the section between the main arch ring and the main beam support will slightly increase.
(3) According to regulations, the deflection of reinforced concrete arch bridges should not exceed 1/1000 of the bridge span.This bridge has a single span of 30m, so the maximum allowable deflection should be less than -30mm.The maximum vertical displacement of the main arch ring is -4.998mm, which is much smaller than the allowable deflection.Therefore, the main arch ring shape is within the safe range.

Stress state analysis of the main and abdominal arch rings
The stress values of the control section of the main arch ring are shown in Table 3, and the stress analysis of the main arch ring beam is shown in Figure 10 as shown.
(2) The main arch ring produces significant displacement at sections G3, G4, G5, G10, and G11, with a maximum displacement value of -4.998mm.The increase in displacement during construction stages (1), (2), and (4) is relatively small, while the increase in displacement during construction stages (3) and ( 5) is relatively large.Analysis shows that the vertical displacement of the section between the main arch ring and the longitudinal beam support is relatively large.Removing the support below the main arch ring and pouring the longitudinal beam increases the displacement of the main arch ring.After removing the support below the main beam, the displacement value of the section between the main arch ring and the longitudinal beam support will slightly decrease, and the displacement value of the section between the main arch ring and the main beam support will slightly increase.
(3) According to regulations, the deflection of reinforced concrete arch bridges should not exceed 1/1000 of the bridge span.This bridge has a single span of 30m, so the maximum allowable deflection should be less than -30mm.The maximum vertical displacement of the main arch ring is -4.998mm, which is much smaller than the allowable deflection.Therefore, the main arch ring shape is within the safe range.

Stress state analysis of continuous longitudinal beams
The stress values of the control section of the continuous longitudinal beam are shown in Table 4, and the analysis of the stress of the continuous longitudinal beam is shown in Figure 11.upper edge 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 The following conclusions can be drawn from the analysis of the above data: (1) The stress value on the upper edge of the continuous longitudinal beam is very small and negligible during construction stage (4), while tensile stress is generated during construction stage (5) in Z1, Z3, Z5, Z7, Z9, and Z11, with a maximum tensile stress value of 0.80MPa.The lower edge of the continuous longitudinal beam generates tensile stress during the construction stage (4) at Z2, Z4, Z6, Z10, and Z12, with a maximum tensile stress value of 0.30MPa.During the construction stage (5) at Z2, Z4, Z6, Z10, and Z12, tensile stress is generated, with a maximum tensile stress value of 0.60MPa.Analysis shows that during the construction process, when the support below the continuous longitudinal beam is not removed after pouring the continuous longitudinal beam, tensile stress occurs at the lower edge of the mid span section of the continuous longitudinal beam, with a maximum tensile stress of 0.30MPa; After dismantling the support below the continuous longitudinal beam, tensile stress occurred at the support point section of the continuous longitudinal beam, with a maximum tensile stress of 0.60MPa.Compression stress occurred at the mid span section, with a maximum compressive stress of 1.00MPa.
(2) According to the longitudinal variation diagram of normal stress along the beam body, the maximum tensile stress of the beam body during the construction process is 1.00 MPa, which is less than the design value of C40 concrete tensile strength of 1.71 MPa.Therefore, the continuous longitudinal beam body has not cracked and is in a safe state throughout the construction process 5. Conclusions (1) The ANSYS finite element model can more accurately simulate the overall state of the bridge during the actual construction process than the Midas/Civil finite element model.Therefore, ANSYS was chosen to carry out the full process simulation modeling method for the construction method of first removing the actual lower part of the main arch ring and then pouring the main beam.
(2) The ANSYS finite element simulation method is applied to calculate the axial force of the full support pole below the main arch ring, the displacement value of the main arch ring, the stress value of the arch structure system, and the stress value of the continuous longitudinal beam in each stage of the demolition method construction.
(3) Conduct a full process simulation analysis of the construction of the sunflower shaped continuous arch bridge, analyzing the safety of the main arch ring shape and support system, the safety of the main web arch ring stress state, and the safety of the continuous longitudinal beam stress state during the construction process.After analysis, the construction method of first removing the support below the main arch ring and then pouring the main beam can ensure the safety of the construction.

Figure 2 .
Figure 2. The number of bracket poles under the main arch circle

Figure 3 .
Figure 3.The main arch ring controls the section definition

Figure 4 .
Figure 4.The stringer controls the section definition

Figure 5 .
Figure 5.Model of arch structure Figure 6.Model of the stringer beam body

Figure 7 .
Figure 7.Unit display Figure 8.Display of rebar in diffusion model

( 1 )
Erect the support below the main arch ring and pour the main arch ring; (2) Close the main arch with the bridge pier, set up the support below the belly arch, set up the support below the longitudinal beam, pour the belly arch (3), and remove the support below the main arch; (4) Pouring longitudinal beams; (5) Remove the bracket below the longitudinal beam and the bracket below the abdominal arch ring.

Figure 11 .
Figure 11.Diagram of the change of longitudinal beam stress along the beam body

Table 1 .
Control the axial force value of the cross-section pole

Table 2 .
Controls the displacement value of the main arch ring of the cross-section

Table 4 .
The continuous stringer controls the cross-sectional stress value(MPa)