Pre-tightening method for anchor bolts The anchor bolts are composed of two parts. The middle bolts are connected by a threaded sleeve. The total length is about 2m. The lower part is fixedly embedded in the reinforced concrete, and the upper part can be disassembled. There are 45 bolts that are evenly distributed over a circumference of 5.015 m. The anchor bolts are mounted by hydraulic extension. The construction process is to first lengthen the bolt with a pulling tool) 1TH hydraulic tensioner, and then tighten the nut by hand to loosen the tensioner to pre-tighten the bolt. During construction, the length of the bolt head beyond the nut is about (0.61.0) times the diameter of the bolt, and the displacement of the head is measured by a dial gauge mounted on the top of the piston. While pulling, observe the dial gauge reading and the hydraulic gauge reading, and stop the pressurization when the oil pressure (ie, the pulling force) reaches a predetermined value. The displacement is for reference. The pre-tightening force required for the anchor bolts is calculated as the flange inner diameter D1=4.09m; the flange outer diameter D2=5.315m; the bolt center circle diameter D0=5.015m. N is the sum of the loads (forces) in the vertical direction; H is the sum of the loads (forces) in the horizontal direction; M is the sum of the bending moments. There are 7 kinds of working conditions for the load combination. Only the most dangerous one is considered here: one side is full load, and the impact coefficient of P2 is 1.4. It is known that the empty tank weight is P1=1200kN, the full tank weight is P2=4500kN, the fork arm weight is 3100kN. The combined load N=9400kN, M=38745kN/m, H=0. Geometric property flange area A = (P / 4) (D2-D21) = 9.049 m2. Flange equivalent bending section modulus (farth bolt) W=P64D42-D41D0/2=10.144m3. Since the turntable can rotate 360b, the overturning moment can be in any direction. In order to calculate the required preload, the distance from the center of each bolt to the tipping center line needs to be calculated. Assuming that there is a maximum overturning moment around the Y axis, the distance from each bolt to the Y axis is Lk = 0.5 D0cos (8 k) (k = 0, 1, 2, 3, 45). The stiffness of the joint is calculated by the anchor bolt 2m long, manufactured in two sections, and the lower part is buried in the reinforced concrete. 1) Bolt stiffness c1. Considering that the following section is buried, there is very little deformation, so only the deformation of the above section is calculated. The cross-sectional area of ​​the threaded portion and the bolted rod are not the same, so their compliance should be calculated separately and converted to the stiffness value. From R = F / A = EE = E $ L / L, then $ L = (L / EA) # F = DF. Therefore, $L1=D1F, $L2=D2F, $L=(D1+D2)F. The optical axis segment d1 = 32 mm, L1 = 135 mm, and A1 = (P / 4) d21 = 1024 mm2. Thread segment d2 = 30 mm, L2 = 130 mm, A2 = (P / 4) d2 = 708.9 mm2. The modulus of elasticity E=2.05@105N/mm2D=D1+D2=1E(L1A1)+L2A2=1.54@10-6mm/N, c1=1/D=6.493@105N/mm. 2) Flange stiffness c2 and pad stiffness c3. The area affected by the rigidity of the coupling member, the coupling member flexibility coefficient K = 1 PEdtan Aln (a + 2ltan A - d) (a + d) (a + 2ltan A + d) (ad). Flange K2=6.52@10-8mm/N, c2=1/K2=1.53@107N/mm. Backing plate K3=1.083@10-7mm/N, c3=1/K3=9.24@106N/mm. The pre-tightening force required for the bolt is based on the principle that the joint is not slitted Pv(NZ+MAZW)c1c2+c2c3c1c2+c2c3+c3c1. Among them, the number of bolts Z=45. Substituting each data into the above formula, Pv537.7kN; the bolt pre-tightening force of the original design is 540kN, which is greater than the calculation pre-tightening force and meets the requirements. The maximum external load Fmax at the bolt is in accordance with the load combination state 7Fmax=-NZ+MLmax2iEL2k=422.9kN, where i is the number of bolt rows, and i=2; Lmax=L0=2.51 m. The bolt working maximum pulling force PmaxPmax=c1c3c1c2+c2c3+c3c1Fmax+Pv=556.9kN. The strength of the anchor bolts is the highest (12.9) to meet the strength requirements, and the safety factor is relatively small, only 1.06. The manufacture of such bolts is relatively difficult. In such important occasions, the products of imported professional manufacturers are generally used. In fact, the anchor bolts can be made larger. For example, the diameter of the bolts is 42 mm, which reduces the strength level, which makes the manufacturing difficulty less and improves the safety factor. Pre-tightening force detection method After discussing the use of the rotary table for several years, how much pre-tightening force remains, whether to continue to ensure the safe operation of the equipment, how to check the residual pre-tightening force is a realistic problem placed in front of the equipment management personnel. For this reason, the author conducted an experimental study. According to the principle of compressive deformation after the nut is tightened, a new method of measuring the residual preload force by sticking a resistance strain gauge to the side of the nut is explored. Experiments show that after the nut is tightened, the strain gauge is sensitive; the correspondence from slack to tightening and from tightening to slack is good, that is, the nut is tightened and then relaxed, and the strain gauge is better. The residual pre-test can be directly measured. The value of the tightening force; it can be restored after the measurement, and does not change the magnitude of the preload.
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