The design calculation for this project is based on a space bar finite element method program. The grid is divided into seven distinct areas, with the A, D, and G zones classified as the first type of frame based on their structural dimensions, while the B, C, E, and F zones are categorized as the second type. Each joint is treated as a hinge, and all members are analyzed as axial force bars. The yield strength of the steel used is 235 N/mm², the design stress is set at 200 N/mm², and the allowable slenderness ratio for the members is limited to 150.
For the structural components, high-frequency welded pipes are used in the bolt ball node grid system, with various sizes such as 60×3.5, 76×3.75, 89×4.0, 114×4.0, and 159×6. The bolt balls are forged from 45 steel, and high-strength bolts are made of 40Cr steel. The sealing plates, supports, and support blocks are fabricated from A3 steel, while the sleeves are made from Q235, 16Mn, or 45 steel. The grid's support system plays a critical role in its design, utilizing a pressure-bearing mechanism that can handle both compression and tension forces, ensuring the hinge behavior of the upper grid structure.
The large grandstand roof of the Zhuhai International Circuit features a long cantilever structure with an asymmetrical layout and a 22-meter span. To ensure the safety and performance of the grid, deflection tests were conducted. The coordinates of the grid supports were measured using a Leica TC1700 total station, with horizontal angles observed in two rounds and side lengths measured four times to obtain an average. The elevation of the grid supports was measured using a Soka BZ precision level, following the fourth-level accuracy standards.
Deflection observations included three main steps: (1) measuring the elevation, axis coordinates, and offset of the grid support after completion; (2) measuring the deflection of the truss before and after the roof covering; and (3) monitoring settlement and displacement every half month, especially after strong typhoons. Measuring points were placed on the upper chord nodes, with each zone divided into four deflection lines along the longitudinal direction. The deflection data showed close agreement with the design calculations, with a maximum error of 28 mm. Some areas exhibited slight asymmetry, with the right side showing slightly more deflection than the left, indicating a minor tilt.
Since the upper chord was not visible, measuring points were installed on the roof. Each section had two edges and three deflection lines, with numbering similar to the roof covering but not identical. Due to reference point loss, relative deflections were calculated based on the elevation difference between the average of points 2 and 4 and the middle point. The results showed some discrepancies at individual points, likely due to deformation caused by strong typhoons, but overall, the deflections remained within acceptable limits.
In conclusion, the Zhuhai International Circuit's grandstand grid is a large cantilever bolt ball node structure that can be accurately modeled and analyzed using space bar finite element methods. Deflection measurements were taken before and after roof installation, revealing smaller observed errors compared to calculated values. Although some tilting was observed in certain areas, the entire grid structure remains safe and stable.
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