60 Structural Finite Element Analysis of A Novel Lifting Formwork for Thin-walled High Piers with Variable Cross-section Weidong Zhao1, a, *, Changqiong Yang1, b, *, Yongxing Wang1, c, *, Feiyue Li1, d, * 1Yunling construction Co, ltd of YCIC group, Kunming, Yunnan Province 6500041, PR China a562598783@qq.com, b664147995@qq.com, c83158301@qq.com, d438093812@qq.com * Corresponding Author Email Abstract. According to the background of the construction project, a new type of formwork structure for thin-walled high piers with variable cross-section is proposed, which realizes safe and efficient reversal of the formwork by lifting the outer frame as a whole and introduces the construction technology of the formwork structure system. Through the finite element software modeling of the overturning structure, the corresponding load conditions are established according to the actual working conditions of the project, and the force and deformation of the overturning structure are thus calculated, which ensures the quality of the project very well. Keywords: Variable section structures, high bridge pier, formwork construction, mechanical analysis. 1. Introduction In order to meet the urgent development of ground transportation in mountainous areas and other complex landscapes, high-level highway construction will appear high-altitude large-scale pier structure, often higher than 50 meters, which brings certain difficulties to the main structure construction safety, structural construction technology programs need to meet the requirements of safety, economy, practicality and so on [1-4]. The key to the construction of the template system innovation and technology iteration, combined with the characteristics of the project, the use of a new type of thin-walled high piers for variable cross-section of the new template structure, the template system through the overall lifting of the outer frame to achieve the template of the safety and efficiency of the inversion, compared to other technical solutions [5-8], has a very high safety and breakthrough construction efficiency, to ensure that the construction of high and large-scale piers structure is completed successfully. 2. Project Overview and Formwork Solution Selection Located in Huize County, Yunnan Province, China, this project is a key construction node and a major difficult construction task for the highest grade highway. This project in order to ensure safety, improve quality, quality assurance in the construction of high piers, so the project department to carry out technical attacks put forward high piers as a whole to enhance the outer frame to realize the safety of the template and efficient inversion of the construction process. In the construction formwork solution selection, the program should meet the following requirements: (1) to ensure construction safety; (2) to solve the problem of variable slope, variable diameter, variable cross-section construction; (3) a better solution to the problem of vertical transportation; (4) to solve the problem of multi-point control and communication of electrical equipment; (5) affordable. On the basis of traditional climbing mold, we have developed the overall frame lifting and in the gap between the frame and the outer wall of the pier to carry out efficient and safe formwork inversion system, the formwork to increase the horizontal long openings and articulated rods to achieve the high piers of the variable slope, the requirements of the variable cross-section. The fixed angle steel ring is changed to adjustable truss ring to meet the requirements of different curvatures of the tower body, and avoid the use of through the hall tensile screw, significantly improve the quality of the outer surface of the pier construction and aesthetics, and improve the durability of high piers in mountainous areas in complex climatic conditions. 61 3. Principles of Formwork Construction Figure 1. Variable-section thin-walled pier lifting form inverted molding system elevation and site construction drawings Figure 2. Variable cross-section thin-walled pier lifting frame inverted mode double-layer formwork construction flowchart Variable cross-section thin-walled pier lifting frame inverted mold technology for Yunnan Jiaotou Group Yunling Construction Co., Ltd. science and technology research and development project (YLJS-KF-2024-01) of the patented template technology. The outer frame of the stress system is mainly composed of crawler frame fixed 10T wedge jack and supported on 6 48*3.5 steel pipe crawler bars. The constant load of truss, climbing frame, suspension platform and hydraulic equipment is 14.5 62 tons. Variable load is calculated according to the area all uniform load is not allowed to exceed 4 tons. Constant load of 5 tons for internal mold and its support as well as hydraulic equipment, etc. Variable load is allowed not to exceed 3 tons, as showing in Fig 1. The construction process is divided from the pier column part mainly has the pier bottom solid section construction, standard thin wall section construction, cross partition construction and pier top solid section construction, the corresponding template system is completed in the pier bottom section of the first layer of template installation, circle truss installation, the second template installation, operation platform installation, internal mold installation, the pier top is gradually complete the removal of the internal mold, the demolition of the two layers of templates, the removal of the circle trusses and platforms, the flowchart is shown in Fig. 2. After pouring the bearing platform, the outer edge line of the pier column should be measured and placed, and the first layer of outer formwork can be assembled after the reinforcement is finished, because the technology has canceled the tie bar, the formwork can't withstand the lateral pressure of the concrete pouring, and it is necessary to install the ring truss to support the formwork laterally. The main point of this stage is that temporary support (steel bench) is needed under the hoop truss to support the hoop truss, the installation position of the formwork should be accurate and accurate, and it is necessary to ensure that the formwork is installed vertically by using a wire hammer, and the bolt top support is fixed firmly. Crawling pole, wedge jack, lifting frame can be poured concrete after installation and debugging. The slope between the templates through the small-surface template “clamped” large-surface template way to close the break, which in the large-surface template end of the flange and oblong holes, the corresponding small- surface template plane perpendicular to the large-surface template and open the spacing of 120- 140mm bolt holes through the high-strength bolts and the large-surface bolted to the oblong holes. The first cycle of the external formwork, i.e. the cumulative lifting of the operating platform to a height of 4.8m and the completion of the remaining reinforcement binding of the second mold, meanwhile, the installation of the internal formwork system and debugging of the hydraulic system for slope closing and lifting of the internal mold. 4. Model Analytics In this case, variable cross-section thin-walled hollow pier lifting frame inverted mold is divided into outer truss and outer double-layer template, as well as the inner mold and the corresponding slope adjustment cylinder hydraulic system, template system main parameters are as follows. Table 1. Main structural parameters of the formwork system Structures Material/Specifications Amount Note 1 Long side trusses Q235, H-W-D m: 11*1.16*1.7 2 Chord L100*10, web L63*5 2 Short side trusses Q235, H-W-D m: 7.6*1.16*1.45 2 Chord L100*10, web L63*5 3 Exterior Climbing Frame Q235, 4.8m/3.72m 4/2 18a# double channel welded with inverted triangle diagonal bracing, rigidity control 4 Internal Mold Crawler Q235, 3m 4 18a# Channel Welded 10mm Steel Plate with Triangle Tie Rods 5 Outer Form / Adjustment Form Q235, THK 5mm 4 10# channel steel reinforcement plate spacing 0.4m, peripheral L100*10 angle steel flange. 14 tons. 6 Internal Form Q235, THK 5mm 80# channel steel reinforcement plate spacing 0.35-0.37m, peripheral L80*8 angle steel flange, 4 tons 7 Operating platforms 2.5mm patterned steel plate Load shall not be greater than 3KN/㎡ 8 Suspension platforms 2.5mm patterned steel plate Load shall not be greater than 2KN/㎡ 63 According to the “safety technical specification for formwork of building construction” (JGJ162- 2008), when internal vibrator is used, the standard value of lateral pressure of the newly poured concrete acting on the formwork can be calculated according to the following formula, and take the lesser of these values: F=0.22γCt0β1β2V1/2 F=γCH Concrete lateral pressure calculations: F=0.22γCt0β1β2V1/2=0.22×25×200/35×1.2×1.15×21/2=61.34KN/m2 F=γCH=25×2.4=60KN/m2 Take the smaller value between the two, so the standard value of lateral pressure of freshly poured concrete on the formwork F = 60kN/m2. The standard value of the load generated when dumping concrete is 2kN/m2 for vertical face formwork. According to “building construction template safety technical specification” (JGJ162-2008) and stent load effect combination of the standard value of the load combination: Strength checking: Fma×=1.2×F+1.4×Q3k=1.2×60+1.4×2=74.8kN/m2 Stiffness checking: Fma×=F=60kN/m2. Hollow thin-walled pier formwork panel adopts 5mm thick steel plate, after the panel set [10 channel steel, channel steel maximum spacing of 1264mm. panel according to three equal span continuous beam calculation, calculation span diameter take 493mm, 1264mm, 493mm, take the width of the plate 1m. 5mm thick panel calculation parameter: unit weight 19.65KN/m3, f = 215MPa, fv = 125MPa, modulus of elasticity E = 2.06×105MPa, W = 6.0×103mm3, I = 1.8×104mm4, A = 6×103mm2. Modulus of elasticity E=2.06×105MPa, W=6.0×103mm3, I=1.8×104mm4, A=6×103mm2. Take the width of the panel as 1m, the panel is subjected to the homogeneous load q=Fma××1=74.8kN/m, the panel is a multi-span continuous beam, the net span is 0.35m, and the calculation is in accordance with the 3 equal spanning check. The result of internal force calculation is shown in Fig. 3- 5. Figure 3. Bending moment envelope diagram. Figure 4. Shear force envelope diagram. 64 Figure 5. Panel deflection resultant diagram. Besides, the vertical ribs of the formwork are made of [10 channel steel, the maximum spacing of channel steel is 371mm. after the channel steel, double splicing [14 channel steel back flute is set up, the spacing of back flute is 300mm. the calculation of vertical ribs is carried out by MIDAS CIVIL, and modeling is carried out in accordance with the actual support situation, and the vertical ribs calculation model is made of 273mm +371mm +331mm +301mm + 331mm + 371mm + 273mm double cantilever beam, the calculation model is shown in Figure 3.3. 273mm double cantilever beam, the calculation model is shown in Figure 6 and 7. Figure 6. Bending stress diagram of vertical rib Figure 7. Shear stress diagram of vertical rib 65 From Figs. 6 and 7, the maximum value of bending stress of vertical rib is 21.5MPa