Bolted structural anchor bolts are 1920mm in length and manufactured in two sections, with the lower part embedded in reinforced concrete. When calculating the stiffness of the bolt (c1), it is assumed that the lower section is fixed within the concrete, resulting in minimal deformation. Therefore, only the deformation of the upper section is considered during analysis. The performance grade of the bolt is 1219 (GB3098.1-82), with a nominal yield strength (R0.2) of 1080MPa and a guaranteed stress (Sp) of 970MPa, which serves as the permissible stress. Since the actual working stress (R) is less than Sp, both the maximum operating and installation stresses are within acceptable limits, confirming that the anchor bolt meets the required strength criteria.
During production and maintenance, gap bolts are used to check for looseness in anchor bolts. Tensioning cylinders can also be used to stretch the bolts. During maintenance, the residual preload force is denoted as Pvc, and the residual deformation is calculated as vLc = Pvc(1/C1 + 1/C2 + 1/C3). When the applied tensile force P equals Pvc, the bolt enters a critical state: if P ≤ Pvc, the deformation remains zero; however, when P ≥ Pvc, the deformation increases significantly. This sudden change allows for an accurate judgment of the residual preload. If the displacement increases gradually with a small increase in pulling force, it indicates that the residual preload is still sufficient. However, if the displacement jumps abruptly, it suggests that the actual residual preload has dropped below the required level, and the bolt should be replaced at this point.
The theoretical pre-tension force required for the anchor bolt is 158.3kN. The original design specification of 220kN is more than sufficient to meet the actual requirements. During installation, the tensioning cylinder is used to apply pre-tension through elongation, with the applied force serving as the control parameter. This method of controlling the installation based on displacement is considered reasonable and effective.
However, the safety factor for the ground screw inspection is only 1.188, which is relatively low, indicating that the strength margin is not substantial. Therefore, during operation, regular checks of the pre-tightening force are essential to prevent potential equipment failures. Ensuring consistent and proper preloading is crucial for maintaining the integrity and reliability of the anchor bolt system over time.
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