(1) The deviation of the position of the girder center line from the designed positioning axis shall not be greater than 5 мм.
The alignment of the girder’s center line is crucial as it serves as the central axis for the entireкранstructure. Even a minor deviation exceeding 5 mm can cause misalignment of the crane components during installation. This misalignment may lead to uneven stress distribution when the crane is in operation, potentially resulting in premature wear of certain parts, and even compromising the overall stability and safety of the crane. During the construction process, precise surveying and alignment techniques are used to ensure this tolerance is met. Workers may use high-precision theodolites or laser alignment tools to mark and verify the position of the center line, comparing it with the design blueprints at multiple points along the length of the girder.
(2) The deviation of the elevation of the girder top surface from the designed elevation shall be between -5 mm and +10 мм.
This elevation tolerance range is carefully defined to guarantee the proper operation of theкран. If the elevation is too low, it might limit the clearance for the lifting equipment, increasing the risk of collisions between the lifted loads and the surrounding structures. От друга страна, if it’s too high, it could disrupt the smooth running of the trolley along the girder, affecting theкран‘s load handling efficiency. Builders need to account for factors like foundation settlement and construction inaccuracies when setting the elevation. They use leveling instruments such as automatic levels to measure and adjust the height at various points across the girder, ensuring compliance with this specification.
(3) The relative elevation difference of the girder plane at the columns shall not be greater than 10 мм, and at other locations, it shall not be greater than 15 мм.
At the column positions, the girder needs to be more precisely leveled because this is where the main support forces are transferred. A larger elevation difference here could cause uneven loading on the columns, potentially leading to structural damage over time. Away from the columns, a slightly more lenient tolerance of 15 mm is allowed, but still, careful attention must be paid. Construction teams will take multiple elevation measurements at regular intervals along the girder, especially around the columns, and use shims or adjustable supports to correct any excessive differences.
(4) The dimensional deviation of the center position of the stud holes reserved on the girder shall not be greater than 5 мм.
The accurate positioning of the stud holes is essential for the proper bolting together of components. If these holes are misaligned by more than 5 мм, it will be difficult, if not impossible, to insert and tighten the studs correctly. This can cause loose connections, which under the dynamic loads of crane operation, can quickly lead to component failures. To ensure the holes are in the right place, templates are often used during the manufacturing or construction process. These templates are precisely fabricated according to the design drawings and are fixed in place to guide the drilling or punching of the stud holes.
(5) For the top surface of the leveling layer on the girder, the following requirements must be ensured: within a 400-mm-wide range at the bolt locations, the levelness of the top surface shall not be greater than 2 мм; within any 6-meter length, the elevation difference of the top surfaces at each bolt location shall not be greater than 3 мм; along the entire length of the workshop, the elevation difference of the top surfaces at each bolt location shall not be greater than 5 мм.
The leveling of the girder’s top surface, especially around the bolt areas, is vital for even load distribution across the bolts. If the surface is uneven, bolts will bear uneven forces, which can cause bolt fatigue and failure. For the 400-mm-wide areas around bolts, workers use small spirit levels to check the levelness during the construction of the leveling layer. Over longer lengths, more sophisticated surveying equipment like total stations may be used to measure and control the elevation differences, ensuring the stability of the entire crane structure.
(6) The top surface of the leveling layer must be leveled and troweled smooth, with no exposed stones or unevenness. Въпреки това, it is not permitted to use the method of spreading additional cement slurry on the surface for smoothing.
A smooth and even top surface of the leveling layer is necessary to provide a stable base for the crane components. Exposed stones can cause stress concentrations, and an uneven surface can disrupt the alignment of parts placed on it. Banning the addition of extra cement slurry on the surface prevents potential delamination issues, as a thin layer of added slurry may not bond properly with the underlying layer, leading to peeling or cracking over time. Construction workers will use proper troweling techniques, often multiple passes with different grades of trowels, to achieve the required smoothness.
In addition to these key inspection points, other aspects also demand attention during the pre-installation phase of the overhead crane. The material quality of the girder needs to be thoroughly examined. Metallurgical tests can be carried out to verify the strength, hardness, and ductility of the steel used, ensuring it meets the design requirements. Any internal defects, such as voids or inclusions, can weaken the girder’s load-bearing capacity. Nondestructive testing methods like ultrasonic testing or magnetic particle inspection are commonly used for this purpose.
The environmental conditions of the installation site also play a role. High humidity or corrosive atmospheres can accelerate the corrosion of the girder. If the installation site is near a chemical plant or a coastal area, additional anti-corrosion measures may need to be considered, such as applying special coatings or using corrosion-resistant alloys. Temperature fluctuations can also affect the expansion and contraction of the girder. In regions with large temperature variations, expansion joints may need to be designed and installed properly to accommodate these changes without causing structural damage.
The connection details between the girder and other components, like the end connections to the columns or the attachment points for the trolley system, require meticulous inspection. Welds should be inspected for integrity, looking for any signs of cracking, porosity, or incomplete fusion. Bolts should be checked for the correct torque, as insufficient or excessive torque can lead to joint failures. Освен това, during the transportation of the girder to the installation site, care must be taken to avoid any accidental impacts or deformations. Specialized lifting and transportation equipment, along with proper padding and restraint, are used to safeguard the girder’s integrity. All these additional considerations, combined with the strict inspection of the girder itself, contribute to the overall safety and reliable operation of the overhead crane.
