Installation method analysis and characteristic detection of anchor bolts

The pre-tightening force required for the anchor bolts is calculated based on the flange dimensions: inner diameter D1 = 4.09 m, outer diameter D2 = 5.315 m, and bolt center circle diameter D0 = 5.015 m. The load combinations include vertical load N, horizontal load H, and bending moment M. There are seven working conditions, but only the most dangerous one is considered—where one side is fully loaded, and the impact coefficient for P2 is 1.4. The known loads include an empty tank weight of P1 = 1200 kN, full tank weight of P2 = 4500 kN, and fork arm weight of 3100 kN. The combined vertical load N is 9400 kN, and the bending moment M is 38745 kN/m. The flange area A is calculated as (π/4)(D2² - D1²) = 9.049 m², and the equivalent bending section modulus W is calculated as π/64(D2⁴ - D1⁴)/D0/2 = 10.144 m³. Since the turntable can rotate 360°, the overturning moment can act in any direction. To calculate the required preload, the distance from each bolt to the tipping centerline must be determined. Assuming maximum overturning moment around the Y-axis, the distance from each bolt to the Y-axis is Lk = 0.5 * D0 * cos(8° * k), where k = 0, 1, 2, ..., 45.

The stiffness of the joint is calculated based on the 2-meter-long anchor bolts, which are manufactured in two sections, with the lower part embedded in reinforced concrete. Bolt stiffness c1 is calculated considering that the lower section has minimal deformation, so only the upper section's deformation is taken into account. The threaded and non-threaded sections have different cross-sectional areas, so their compliance is calculated separately and converted to stiffness values. Using the formula ΔL = FL / EA, the deformation constants D1 and D2 are calculated, resulting in a total compliance D = D1 + D2 = 1.54 × 10⁻⁶ mm/N, leading to a bolt stiffness c1 = 6.493 × 10⁵ N/mm. Flange stiffness c2 and gasket stiffness c3 are also calculated. The flange flexibility coefficient K2 = 6.52 × 10⁻⁸ mm/N, resulting in c2 = 1.53 × 10⁷ N/mm. The gasket flexibility coefficient K3 = 1.083 × 10⁻⁷ mm/N, giving c3 = 9.24 × 10⁶ N/mm.

The required pre-tightening force for the bolt is calculated based on the principle that the joint should not slip. Using the formula Pv = (NZ + MAZW) * (c1c2 + c2c3 + c3c1), with Z = 45 bolts, the calculated pre-tightening force is Pv = 537.7 kN. The original design’s pre-tightening force of 540 kN exceeds this value, meeting the requirements. The maximum external load Fmax at the bolt is calculated as 422.9 kN, and the working maximum pulling force Pmax is 556.9 kN. The anchor bolts have a high strength grade (12.9), but the safety factor is low at only 1.06. Manufacturing such high-strength bolts is challenging, so imported professional-grade bolts are typically used in critical applications. Alternatively, larger diameter bolts (e.g., 42 mm) could be used, reducing the strength level, making manufacturing easier, and improving the safety factor.

Pre-tightening Force Detection Method After several years of using the rotating table, it becomes essential to determine how much pre-tightening force remains and whether it is sufficient to ensure safe equipment operation. This poses a practical challenge for equipment managers. To address this, an experimental study was conducted. Based on the principle of compressive deformation after the nut is tightened, a new method was explored to measure residual pre-tightening force by attaching a resistance strain gauge to the side of the nut. Experimental results showed that the strain gauge is sensitive and provides good correspondence between tightening and loosening. The residual pre-tightening force can be directly measured without altering the actual preload, and the measurement process is reversible, ensuring no loss of the initial tightening force.