The large lifting capacity of 10 tons and a maximum lifting height of 42 meters are sufficient to meet the requirements for truss lifting. The vehicle is heavy, with an unloaded walking ground pressure of 79012. The floor's design bearing capacity is suitable for the first floor. Therefore, it is necessary to use steel plates as the walking path for crawler cranes. According to calculations, each section of the basement should be supported with a cross-section of 250x25 mm, using wooden columns composed of 2.5x2.51 m to form the main grid.
The installation sequence of components includes the stiff columns of the shaft and the ⑧ axis, along with components ①, ②, and ③. These are constructed as part of the podium and main building structural system up to an elevation of 30.000 m. Combined with the beam and slab system of each level, the concrete in the columns is poured. At this stage, the stiff column also functions as part of the truss, forming the truss with cross braces and large joints. Component number 2 indicates the installation order. Due to the size and weight of the components, the truss is nearly 3 meters long, requiring it to be fabricated in sections in the factory. A major challenge during the on-site assembly is that the No. ⑤ brace lacks a fulcrum.
For the installation of the No. 4 diagonal brace, the lower end is connected to the stubs attached to the stiff column 1, while the upper end is a free end, which tends to move out of plane. To prevent instability during splicing, a No. 40 I-beam is installed between the two at a height of 13 bars from the upper end, with temporary support connections made at the intersection with the diagonal brace. The connection sequence begins by connecting the lower end of the diagonal brace with a connecting plate and corbel. Then, the door is moved out and aligned with the structural column. Once the column has enough rigidity to resist displacement, a manual hoist is used to adjust the diagonal brace to the design angle. Finally, 17 steel for hidden connection is applied, ensuring the rod remains in place. The same method is used for the other diagonal brace, completing the assembly in order.
During the correction phase, the measurement and welding calibration principle ensures that each truss member lies within its axis plane and that the deviation of the 1-axis column position does not exceed 30 mm. All member connections must follow the steel member connection standards, including weld seam width and verticality. These do not adhere to the overall steel truss inspection standards. Initially, single-chip calibration is performed using jacks, followed by continuous measurement until the acceptance standard is met. Only after passing inspection is the welding applied.
The truss welding is full penetration welding, with all welds rated as grade 1. A reasonable welding sequence is essential to reduce and control deformation. The principle is: first weld inclined rods, then straight rods; weld same rod parts first, then the other ends after cooling; welds are done first, followed by flat welding. Anti-deformation measures or intermittent welding are adopted during construction. Throughout the welding process, the shrinkage value and change law of the weld are monitored, with anti-deformation measures implemented accordingly.
Weld seams are inspected using ultrasonic flaw detection, with the first party conducting self-inspection. Any unqualified welds are cut using carbon arc gouging, re-welded, and re-inspected, but no more than two repair times are allowed.
Concrete is poured into the slant bar and large joints of the truss-pressed bar. This significantly improves load-bearing capacity, but the construction difficulty arises due to stiffeners and partitions inside the bar. Ensuring compactness of vertical rods is challenging, and since the rods are sealed, it's hard to monitor the pouring situation. Core pulling is not permitted. To address this, the following measures were taken: improve concrete workability, pre-open a round hole in the appropriate location, perform initial pouring, and then complete the second pour from the top after closing. Additionally, 3-meter-long, 10-mm-diameter, and 5-mm-thick elements were used.
At the Shenzhen World Trade Center Building Preparation Office, Zhang Jinglin introduced the single-sided treatment technology for the friction surface of steel structures. Steel structures require high-strength bolt friction-type connections. When the pre-tension remains constant, increasing the load-bearing capacity of the joint structure requires raising the friction coefficient on the contact surface according to design specifications. Surface sandblasting is typically double-sided, but factors like large blasting areas, handling difficulties, and blasting technology often hinder construction quality and schedule. In the dry coal shed project of Wuhan Yangluo Power Plant, the friction coefficient did not meet design requirements due to improper surface treatment.
Later, a single-sided treatment method using composite sandblasting was employed, effectively solving the issue. The steel structure of the dry coal shed hinged arch in Wuhan Yangluo Power Plant consists of 7 arch trusses, 84 auxiliary trusses, 2 connecting trusses, 14 ground schools, and 7 sets of natural hinges connected by 14,000 high-strength bolts. Each arch frame weighs approximately 30 tons and is divided into 16 sections, with connections using 2 or elbow 16 torsion shear type high-strength bolts.
In Luozun Village, high-strength bolt connections require sandblasting on the contact surface to achieve a friction coefficient of at least 0.45. However, production personnel used grinding wheels, resulting in insufficient friction coefficients. To address this, pickling treatment was proposed. The method involved wiping rust from the friction surface using No. 1 coarse sand cloth without cleaning to a bright finish, followed by washing with 15% dilute sulfuric acid. After washing, the surface showed a grayish-black color with a rough texture, equivalent to the roughness of No. 0.4–0.6 emery cloth. Composite sandblasting was used for certain areas to meet the required friction coefficient.
The sandblasting process was adjusted based on the friction coefficient. Different sand materials were used, such as aluminum sand, steel sand, and quartz sand. By changing the material to quartz sand, the design requirements could be met. The method primarily aimed to increase the friction coefficient of one surface. The compound sandblasting technique changed the process from secondary to secondary construction. Components were heated to 700°C before sandblasting, cooled completely, and then cleaned with a wire brush to remove loose sand. After reheating to about 600°C, another sandblasting was performed. Special attention was given to areas around bolt holes and critical parts to avoid leakage spray. The treated surface appeared grayish-white with uniform spots and a rough feel, meeting the required roughness level.
Random sampling of the treated friction surfaces showed average friction coefficients of 0.503 and 0.483, exceeding the design value of 0.450. The dry coal shed project was successfully completed, and the single-sided friction surface treatment scheme proved effective. It saved 350,000 yuan in material costs and processing time. The splint connection part of the large steel structure is mostly located on the main truss and is often operated in open-air conditions.
The sandblasting process of the friction surface is affected by weather and other factors, leading to unstable processing quality and friction coefficients not meeting design requirements. Using the above method, the core plate part is mainly used in the webs of the brace bar and auxiliary truss. These have small geometric sizes, light weight, and convenient transfer, allowing them to be processed in a special blasting room without external interference.
Huaneng Power Generation Co., Ltd. Wuhan Yangluo Power Plant, rtf.431415
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