Pre-tightening Method for Anchor Bolts
Anchor bolts are composed of two parts. The middle section is connected by a threaded sleeve, and the total length is approximately 2 meters. The lower part is fixedly embedded in reinforced concrete, while the upper part can be disassembled. There are 45 bolts evenly distributed around a circle with a circumference of 5.015 meters. These anchor bolts are installed using hydraulic extension. The construction process involves first elongating the bolt with a 1TH hydraulic tensioner, then tightening the nut by hand, and finally releasing the tensioner to achieve pre-tightening. During the process, the length of the bolt head beyond the nut should be about (0.6–1.0) times the diameter of the bolt. A dial gauge is mounted on the top of the piston to measure the displacement of the head. While pulling, the readings from both the dial gauge and the hydraulic pressure gauge are observed, and the pressurization is stopped when the oil pressure reaches a predetermined value. The displacement serves as a reference.
The pre-tightening force required for the anchor bolts is calculated based on the flange inner diameter D1 = 4.09 m, outer diameter D2 = 5.315 m, and bolt center circle diameter D0 = 5.015 m. N represents the sum of vertical loads, H the sum of horizontal loads, and M the bending moment. There are seven combinations of load conditions, but only the most dangerous one is considered here: one side fully loaded with an impact coefficient of P2 at 1.4. The empty tank weight is P1 = 1200 kN, the full tank weight is P2 = 4500 kN, and the fork arm weight is 3100 kN. The combined vertical load N = 9400 kN, M = 38745 kN/m, and H = 0.
The geometric properties of the flange include an area A = (Ï€/4)(D2² - D1²) = 9.049 m² and an equivalent bending section modulus W = Ï€/64(D2â´ - D1â´) * D0/2 = 10.144 m³. Since the turntable can rotate 360 degrees, the overturning moment can occur in any direction. To calculate the required preload, the distance from each bolt to the tipping axis must be determined. Assuming the maximum overturning moment occurs 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 considering the 2-meter-long anchor bolts, which are manufactured in two sections, with the lower part embedded in the reinforced concrete. The bolt stiffness c1 is calculated by considering the deformation of the upper section only, as the lower section has minimal deformation. The compliance of the threaded portion and the bolted rod is calculated separately and converted into stiffness values. Using the formula ΔL = FL / EA, we calculate the deformation of each segment. For the optical axis segment (d1 = 32 mm, L1 = 135 mm, A1 = 1024 mm²) and the thread segment (d2 = 30 mm, L2 = 130 mm, A2 = 708.9 mm²), the total compliance D = 1.54 × 10â»â¶ mm/N, resulting in a stiffness c1 = 6.493 × 10âµ N/mm.
The flange stiffness c2 and pad stiffness c3 are calculated using the flexibility coefficient K. For the flange, K2 = 6.52 × 10â»â¸ mm/N, so c2 = 1.53 × 10â· N/mm. For the backing plate, K3 = 1.083 × 10â»â· mm/N, so c3 = 9.24 × 10ⶠN/mm. The required pre-tightening force Pv is calculated using the formula:
Pv = (NZ + MAZW) × [c1c2 + c2c3 + c3c1] / (c1c2 + c2c3 + c3c1).
With Z = 45 bolts, the calculation yields Pv = 537.7 kN. The original design pre-tightening force is 540 kN, which is slightly higher and meets the requirements.
The maximum external load Fmax on the bolt is calculated as Fmax = -NZ + MLmax / (iEL2k) = 422.9 kN, where i = 2 (number of bolt rows) and Lmax = 2.51 m. The working maximum pulling force Pmax is calculated as:
Pmax = [c1c3 / (c1c2 + c2c3 + c3c1)] × Fmax + Pv = 556.9 kN.
The strength of the anchor bolts (grade 12.9) is sufficient, but the safety factor is low at 1.06. Manufacturing such high-strength bolts is challenging, and in critical applications, imported professional manufacturers are typically used. In practice, larger bolts (e.g., 42 mm diameter) could be used, reducing the strength level and improving the safety factor while simplifying manufacturing.
Pre-tightening Force Detection Method
After several years of using the rotary table, it became essential to determine how much pre-tightening force remains and whether it's sufficient to ensure safe operation. This led to the need for a reliable method to check residual pre-tightening force. To address this, an experimental study was conducted. Based on the principle of compressive deformation after tightening, a new method was explored: attaching a resistance strain gauge to the side of the nut to measure residual preload. Experimental results showed that the strain gauge is sensitive and provides consistent readings when the nut is tightened or loosened. The residual pre-tightening force can be directly measured without affecting the original preload. After measurement, the nut can be re-tightened, ensuring no change in the preload value. Formwork System,Flat Surface Formwork System,Concrete Formwork,Customizable Formwork Systems RILICO , https://www.rilico.com