Abstract
With the development of large span bridges, the height of the pylon is getting higher and higher, and the cross-sectional form of the pylon is getting more and more complicated, the construction of the pylon is a high-risk operation. The traditional pylon reinforcement construction uses manual asembling on the pylon, which is a labor-intensive high-altitude operation with high labor intensity, low construction efficiency, and not easy to guarantee quality. The pylon of Yanji Yangtze River Bridge is in the form of an octagonal outer cavity with a circular cross section, and the main reinforcement is arranged in four layers from outside to inside. The maximum diameter of the outer main reinforcement is 50 mm, the outer two layers and the third layer main reinforcement are connected by hoop reinforcement, and staggered arrangement of height directions. Based on the construction of the pylon of Yanji Yangtze River Bridge, the research on the construction technology of reinforcement bar was carried out for the characteristics of the pylon reinforcement, which solved the technical problems such as assembling of reinforcement parts, overall lifting and alignment docking on the pylon, which greatly reduced the labor intensity of operators, reduced the safety risk of overhead work and improved the quality of the pylon construction.
You have full access to this open access chapter, Download conference paper PDF
Keyword
1 Overview
The pylon of Yanji Yangtze River Bridge is a portal frame structure with a height of 184 m. The pylon adopts an octagonal outer section with a circular inner cavity, the outer dimensions of the pylon section are chamfered to 2 m, the inner cavity is circular, the diameter of the upper beam is 3.6 m, the diameter of the middle beam is 5 m, and the diameter of the rest of the section is 6 m. The different diameters adopt a gradual transition in the form of a circular platform. The pylon cross-section is arranged with double layers of vertical reinforcement, of which the outer ring main reinforcement is divided into 50 mm and 40 mm according to different heights. The inner circle is arranged with one layer of vertical reinforcement, and the diameter of the main reinforcement of the inner circle is divided into 40 mm and 32 mm according to different heights. A layer of 32 mm diameter vertical reinforcement is arranged between the inner and outer circles. The hoop reinforcement is divided into 20 mm and 16 mm diameter, and the vertical spacing of hoop reinforcement is 10 cm in the encrypted area of the lower pylon and 15 cm in the rest of the column. The outer and middle layers of the main reinforcing bars are connected by a chain of hoops, and the height direction is arranged according to the plum blossom. The pylon standard section reinforcement plan is shown in Fig. 1.
Standard section steel plan of the Pylon
The most common way of steel reinforcement construction in the pylon is to process the unit parts in the steel processing yard and tie and form all manually on the pylon on site. This project pylon main reinforcement diameter is 50 mm, a 6 m long reinforcement weighs about 93 kg, workers work at height with high risk, high labor intensity, low construction efficiency, quality is not easy to ensure. In the intelligent development trend of modern bridge construction [1,2,3], we proposed the special action of “mechanization for human, automation for human reduction” and carried out research on the key technology of the pylon reinforcement.
2 Study on the Overall Construction Process of Reinforced bar Product on Pylon
After investigation and research, the pylon reinforced bar product construction process mainly has the following three kinds: 1, based on the steel mesh overall bending forming parts grouping production process; 2, based on the steel piece and block production forming parts grouping production process; 3, The production process of assembing reinforcement by workers under the pylon using moulding frame. As the pylon of this project is a round section with octagonal outer and inner cavity, the outer and middle layers of main reinforcing bars are connected with rings and hoops, and the height direction is arranged according to plum blossom, considering the difficulty of steel parts production, production efficiency and actual production situation on site, there are significant advantages of using the third steel parts construction process [4,5,6].
The overall construction process of pylon reinforced bar product adopts the intelligent steel processing equipment in the steel processing plant to process the semi-finished products, transport them to the moulding frame in site for assmbling, lift them by special spreader, and use the tapered sleeve to lock the reinforcing steel joint to connect with the pylon reinforcing steel.
3 Key Technology for Construction of Reinforced bar Product on Pylon
3.1 The Design for Moulding Frame
According to the height of the pylon section, the length and width of each section are changing with the slope, after calculation, it can be seen that the length of the 4 large faces of the 6 m standard section of the pylon is reduced by 82 mm per section. The spacing of the reinforcement in each chamfered part of the pylon section is unchanged, and the reinforcement in the middle area of the 4 large faces is closed and divided. The inner cavity is a 6m diameter circle with the same reinforcement spacing. There are 4 layers of main reinforcement in the standard section of the pylon, except for the outer 2 layers where the relative spacing of the main reinforcement position is unchanged, and the relative spacing of the main reinforcement position in the other layers changes with the change of section height [7].
In order to meet the requirements of the above-mentioned changes in the production of reinforcing bars product, a detailed research and design was carried out for the reinforcing bar section moulding frame. The moulding frame mainly includes: outer operating platform, inner ring operating platform, telescopic platform, bottom positioning system, top positioning system, climbing ladder, travel system and strong skeleton. The outer operating platform is moved along the guiding track by the walking motor, and the inner operating platform is fixed to the ground by expansion bolts. Since the spacing of the main reinforcement in the middle layer is 45 cm and the quantity is small, in order to improve the overall stiffness of the reinforcement parts, a strong skeleton is set up between the middle layer and the main reinforcement of the inner ring, with one horizontal connection every 1.9 m, three in total, and each horizontal connection is welded to the main reinforcement of the middle layer and the inner ring. The size of the strong skeleton is adjusted according to the closing of the reinforcement in every other section. The structural layout of the steel bar component binding jig frame is shown in Figs. 2 and 3.This moulding frame can meet the whole pylon reinforcement assembling requirements by adjusting the position of operation platform, bottom positioning system and top positioning system, which has the characteristics of simple operation, strong adaptability and low construction cost [8,9,10].
Elevation layout of moulding frame for reinforced bar product
Plan layout of the top of the moulding frame for assembling reinforced bar product.
The rebar bottom positioning system mainly consists of positioning channel steel, outer ring rebar positioning device, middle ring rebar positioning device and inner ring rebar positioning device. The positioning device is composed of 70 × 5 mm square steel and round steel pipe, which is made according to the steel design drawing. According to each section of the pylon reinforcement bottom section layout, the bottom reinforcement positioning device is placed by total station, adjusted in place and fixed with the positioning channel steel.
The rebar top positioning system is mainly composed of comb plate support beam, outer ring rebar positioning comb plate, middle ring rebar positioning comb plate and inner ring rebar positioning comb plate. The comb plate is composed of 75 × 8 mm angle steel, which is made according to the steel design drawing. According to the top section layout of each section of pylon reinforcement, a total station is used to place the top reinforcement positioning device, which is adjusted in place and fixed with the comb plate support beam.
3.2 Design of Overall Lifting Spreader for Reinforced bar Product
According to the situation of each section of the pylon reinforcement, the spreader was studied and designed in detail to meet the requirements of the overall lifting of reinforcement parts. The spreader is composed of adjustable frame, main load bearing frame, movable distribution beam and movable lifting point, and each part is locked by fine-rolled rebar. The overall lifting structure of the steel reinforcement component in the steel reinforcement department is shown in Fig. 4. The adjustable frame moves along the main load-bearing frame to accommodate the change of center of gravity of the pylon section. The movable distribution beam moves along the main load bearing frame and the movable lifting point moves along the movable distribution beam to accommodate changes in profile and rebar take-up.
Schematic diagram of the overall lifting spreader structure of the reinforced bar product.
3.3 Fabrication of Reinforced bar Product
According to the elevation position of the top reinforcement of the Nth section on the pylon, the bottom and top section layout of the N + 1th section of pylon reinforcement is drawn, and the initial positioning of moulding frame is done according to the requirement of 50 cm spacing between the outer operation platform and the main reinforcement. Through the N + 1 pylon reinforcement bottom and top cross-sectional layout, the bottom reinforcement positioning device and the top reinforcement positioning comb plate are placed by total station, and after precise positioning, the bottom positioning device is fixed with the bottom positioning channel, and the top comb plate is fixed on the positioning support of the tied tire frame. The reinforcement installation is assisted by pylon crane or truck crane, and the hoop bars are positioned and tied by hoop positioning tooling, and the main bars and hoop bars are welded and reinforced after the assembling is completed. According to the reinforcement assembling process, after the N + 1th section of reinforcement parts are tied, the top surface of the reinforcement parts are remeasured to check the deviation of the reinforcement position from the design position.
3.4 Integral Lifting of Reinforced bar Product
The spreader is connected with the reinforced bar product by 48 lifting points, including 24 lifting points in the outer circle, 16 lifting points in the middle circle and 8 lifting points in the inner circle, and the spacing between lifting points is controlled within 2 m. According to the change of the cross-sectional dimension of the pylon, the FEA software is used to establish the calculation model of the pylon section reinforcement, and the vertical deformation cloud diagram of the whole reinforcement part is shown in Fig. 5. Through the calculation and analysis, it can be seen that the maximum stress of the reinforced parts structure is 127 MPa, the maximum vertical displacement is 9.1 mm, and its structural strength and stiffness meet the requirements of the code. The multiple lifting points arrangement can effectively reduce the lifting deformation and facilitate the adjustment of the parts attitude.
Cloud diagram of vertical deformation of the whole lifting of reinforced bar product (mm).
The calculation model of lifting spreader is established by finite element analysis software, as shown in Fig. 6. The calculation results of the main components of the spreader are shown in Table 1. From the calculation results, it is known that the maximum stress of the spreader is 145 MPa, the maximum vertical displacement is 7 mm, and its structural strength and stiffness meet the specification requirements.
Calculation model of overall lifting spreader for reinforced bar product.
Before lifting, the adjustable frame of the spreader is adjusted to ensure that the center of gravity of the spreader is the same as the center of gravity of the reinforced bar product. The steel reinforcement parts are connected to the main reinforcement by removable steel fixture, which is fixed on the spreader beam. The connection by steel fixture can effectively improve the connection efficiency of lifting points, facilitate disassembly and reusability, and reduce the welding workload of traditional welding lugs as lifting points. The movable lifting point of spreader adopts 5t unloading buckle + wire rope + 5t basket bolt to connect with the lugs of spreader beam, and the horizontal position of the bottom opening of spreader is controlled by adjusting the length of the basket bolt, and the parts are connected after leveling. By controlling the plane relative position relationship between the spreader and the parts, the center of gravity of the parts and the center of gravity of the spreader basically coincide, and the attitude of the parts is adjusted at first, and the attitude of the parts is precisely adjusted by the flower basket bolts.
The reinforced bar product was lifted by XGT2850-120S pylon crane, which has a lifting capacity of 107 tons within 28 m of the working radius, and the actual lifting weight of the steel reinforcement parts is 99 tons, and the performance of the pylon crane can meet the lifting requirements. The spreader was raised to the state that most of the steel ropes were tensed and straightened, and the flower basket bolts were adjusted to ensure that all 48 steel ropes were tensed and stressed. Lift the part slowly off the ground to observe the attitude of the bottom of the part, to ensure that the height difference of the bottom of the part is within 5cm, if it exceeds 5 cm, the part will fall and adjust the flower basket bolt until it meets the requirements. Hang 4 cables at the bottom of the part and lift the part to the pylon.
3.5 Integral Lifting of Reinforced bar Product
In order to improve the efficiency of the alignment on the pylon of the reinforced bar product, 12 positioning flares are set on the pylon reinforcing steel, which are used to guide the precise alignment, including 2 on each large surface of the outermost ring reinforcing steel, 8 in total, and 4 on the inner ring reinforcing steel. One prism is set at each of the 8 corner locations on the top of the reinforced bar product for real-time measurement during the alignment of the reinforced bar product, which is used to guide the precise positioning of the reinforced bar product. By adjusting the flower basket bolts, the radial height difference of all the main bars is controlled within 1cm. Borrowing the cross beam on top of the integrated intelligent pylon building machine, a 5t hand chain hoist was used to match the rebar parts for precise alignment until the design requirements were met. After all measurement points are within the allowable range, taper sleeve and clamp are installed. The taper sleeve connection joint grade is I, the percentage of taper sleeve locking joint area in the same connection section can be 100%, which provides favorable conditions for the construction of parts [11,12,13].
The four chamfered surfaces are connected simultaneously using the tapered sleeve squeezer to ensure that there is no change in the butt joint attitude of the reinforced bar product. The connection of steel reinforcement components on the tower is shown in Fig. 7. After completion, the main reinforcing bars are then extruded and joined symmetrically along both sides. By pulling white lines to ensure that the sleeve is at the same level after the extrusion is completed. The main reinforcing bars are horizontally corrected by means of auxiliary facilities such as crowbars or hand-held hoists to meet the tapered sleeve connection conditions. Connect all the outermost main reinforcement before loosening the structure, and the remaining tapered sleeves are connected as soon as possible in the subsequent continuous operation of loosening the structure. For the extruded completed sleeve, small calipers are used to test the quality of extrusion.
Schematic diagram of the connection on the pylon of the reinforced bar product.
3.6 Measurement of Reinforced bar Product
According to the location of the tied tire frame of the reinforced bar product, an independent coordinate system and a measurement-specific observation pier were established to reduce the errors generated by the turning points as well as the external environment, so as to reduce the accumulation of errors during the release process. In order to summarize the changes in the posture of the middle part of the connection process, five measurements were taken during the unconnected, connected 25%, 50%, 75% and 100% processes of the reinforced bar product. The overall deviation was (0 to 15) mm before connection and (5 to 20) mm after unhooking, and the overall deviation was basically unchanged (considering the measurement error). It was initially determined that the accuracy at the time of starting positioning had a greater impact on the part, and that the part basically stopped deviating during the connection process as the connection stiffness increased.
4 Conclusion
The pylon of Yanji Yangtze River Bridge has an octagonal cross-section and a circular inner cavity, with 4 layers of reinforcement in the standard section and a maximum diameter of 50 mm. Through the pylon steel parts construction technology research, developed a very large variable cross-section pylon steel parts moulding frame and steel parts overall lifting spreader, mastered this kind of cross-section steel parts production method and the pylon buttress precision alignment method, realize the pylon steel parts factory standardized processing, let steel parts assembling does not occupy the pylon construction key line, effectively reduce the labor intensity and overhead construction operation risk, improve the pylon construction quality and quality. Improve the quality and efficiency of pylon construction. Practice shows that the pylon using steel parts construction is conducive to quality improvement and rapid construction, with good social and economic benefits.
References
Doi, F., Seto, K., Minami, M., et al.: Vibration control of model structure of large bridge tower: 4th report, intelligent control under construction. J. Antibiot. 63(609), 1428–1434 (1997). https://doi.org/10.1299/kikaic.63.1428
Petroski, H.: Tower bridge. Am. Sci. 83(2), 121–124 (1995)
Ohuchi, H., Scordelis, A.C.: Slender reinforced concrete bridge towers under cyclic lateral load. J. Struct. Eng. 117(2), 325–342 (1991). https://doi.org/10.1061/(ASCE)0733-9445(1991)117:2(325)
Zhang, A., Li, Z.: Key construction techniques for pier reinforcement in long sections and with variable cross-section. World Bridges 47(4), 37–41 (2019)
Wang, X.: Overall design of Zhongshan bridge in Shenzhen-Zhongshan link. Bridge Constr. 49(1), 83–88 (2019)
Chen, S.: Key techniques for construction of substructure of non-navigable span bridge of Hong Kong-Zhuhai-Macao bridge over shallow water area. Bridge Constr. 46(1), 6–11 (2016)
Peng, Y., Ding, S., Ren, M., Li, Z., Zhang, W.: System conception and overall design of the Yanji Yangtze River Bridge in Hubei. Bridge Constr. 52(03), 1–7 (2022)
Yuan, H., Huo, D., Wu, Z.: Key technology of assembling steel reinforcement parts of the cable tower of Lingdingyang bridge for the Shenzhen-China passage. Highway 67(04), 147–151 (2022)
Zhou, M.S., Zeng, W., Feng, S.D., Wang, Y.: Research on forming and component assembly technology of ultra-high cable tower reinforcement mesh. Constr. Technol. 50(09), 41–44 (2021)
Cheng Mao-Lin, W., Zhong-Zheng, Y.-L., Bin, C.: Construction method of assembling super-high steel reinforcement parts based on mesh bending and forming. Highway 67(01), 145–150 (2022)
Wei, L., Cao, M., Cui, B., Xiong, W.: Study of construction method for installing superstructure of Wangdong Changjiang river highway bridge. Bridge Constr. 49(1), 6 (2019)
Wang, D., Han, B.: Key techniques for construction of pylon of channel bridge of Pingtan straits rail-cum-road bridge. Bridge Constr. 49(3), 5 (2019)
Li, J.: Key construction techniques for pylons of main navigational channel bridge of Hutong Changjiang river bridge. Bridge Constr. 49(6), 6 (2019)
Author information
Authors and Affiliations
Corresponding author
Editor information
Editors and Affiliations
Rights and permissions
Open Access This chapter is licensed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license and indicate if changes were made.
The images or other third party material in this chapter are included in the chapter's Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the chapter's Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.
Copyright information
© 2024 The Author(s)
About this paper
Cite this paper
Ruan, M., Luo, H., Wu, D. (2024). Study of the Construction Technique of Reinforced Bar Product on Large and Variable Section Pylon. In: Xiang, P., Zuo, L. (eds) Novel Technology and Whole-Process Management in Prefabricated Building. PBSFTT 2023. Lecture Notes in Civil Engineering, vol 382. Springer, Singapore. https://doi.org/10.1007/978-981-97-5108-2_34
Download citation
DOI: https://doi.org/10.1007/978-981-97-5108-2_34
Published:
Publisher Name: Springer, Singapore
Print ISBN: 978-981-97-5107-5
Online ISBN: 978-981-97-5108-2
eBook Packages: EngineeringEngineering (R0)