1High strength bolts cannot be used as temporary bolts for installation. This is easy to cause the hole is not straight, or forced on the hole, so that the connecting plate fits, the screw thread damage of the bolt, the torque coefficient changes, the bolt shaft force is uneven, or the connecting plate produces internal stress.
2, foundation pit supporting steel supportThe friction surface can not be treated carelessly or installed without high strength bolts, so that there will be a sandwich between the friction surface,If the friction surface is not properly protected and corroded, the friction surface will be concave and uneven, which will greatly reduce the friction coefficient and reduce the connection strength. In this case, the friction surface must be retreated to ensure quality.
3There can be no gap between the steel support connecting plates of foundation pit supporting. Installing a high strength bolt, due to the defect on the operation, such as hole reamer repair, not bolt screw tightly around the stick, make the iron into friction surface, or joint of steel plates, steel buckling, deformation, a burr hole, sundry between have not been thoroughly remove installation bolt, or improper construction order, taken from bolt group of lateral to the order of the intermediate fastening, etc., Often lead to friction surface between most or local space so that the friction coefficient is close to zero, the bolt can not reach the specified pre-tightening shaft force, and greatly reduce the connection strength, force will make the connection sliding.
4If bolts of different specifications are available, bolts, nuts and washers cannot be used interchangeably. The nuts and washers of high strength bolts have been tested to match each other, so that the torque coefficient is a fixed value, and the mutual use will make the torque coefficient change, but not up to the required preload, when used, the preload is greatly reduced, and affect the quality of the connection.
5The steel support of foundation pit support cannot make the fastening torque or axial force of high strength bolts insufficient. During the installation, the electric and manual wrench is often faulty or has a large error, and is used without correction, so that the torque is not enough; Or the connection plate is not smooth, not corrected on the preloading force, so that part of the torque value consumed to overcome the deformation; Or the operation is not good, although the wrench reading torque is reached, but the actual preload is not reached; Or some bolts miss the initial or final twist, so that the bolt group force imbalance; Or the final screw does not meet the design requirements of the preload shaft force value, which will affect the preload force, and reduce the connection strength, should pay attention to prevent.
6High strength bolts can not be cut by a final screw or not in accordance with the requirements of the order of fastening. In this way, part of the axial force of the bolt will be consumed to overcome the deformation of the steel plate. When the bolts around it are tightened, the axial force is apportioned and reduced. In addition, to make the bolt group to receive strength evenly in the bolt, screw in the early and final screw should be according to the order from middle to outside fastening, some violation operations to reverse order, from both ends to the middle, often cause between the drum, the part of the axial force consumption on overcome the deformation, the pre-tightening force, reduce the friction coefficient, and influence the connection strength.
7, the steel support of foundation pit support can not appear the bolt is not satisfied with the buckle. This will make the nut under long-term or vibration load, easy to tripping loose, reduce the preload, and make the connection strength is not enough, this bolt must be replaced.
8The friction surface between the steel support connecting plate and the connecting surface of foundation pit shall not be polluted by oil and paint after treatment.
9, foundation pit supporting steel Angle brace and fish belly beam hoisting
In this project, the Angle brace and fish belly beam are assembled by standard parts, and two-point crane is used for on-site installation. After being in place, the bolt holes are clamped with punching nails first, and the mounting bolts are inserted. The number of mounting bolts shall not be less than one third of the total number of bolts. No reaming is allowed when installing connecting bolts, and the connecting surface must be flat.
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