Construction of Long Span Cantilevered Truss Structures ( Part 2)

( 4 ) Hoisting steel trusses

When hoisting the truss of the facade wall frame section, each truss is a hoisting unit, because there is no lower chord in the wall frame section, it is necessary to adjust the facade wall frame during the hoisting operation, which is realized by setting up the chain on both sides, after accurate alignment, it should be welded in time to fix it with the support, and then reinstall the connecting rods between the two adjacent wall frames. When welding connecting rods, it should be carried out in the order from the middle to the two ends, so as to reduce the influence of welding shrinkage stress and control the error to the minimum range. Cantilever beam segment trusses can only be installed after the installation of facade wall frames and connecting rods in a construction area is completed. Every 2 pieces when hoisting.

It is a unit, forming a space frame structure form, and the center of gravity cannot be accurately grasped when ascending. For this, the location and quantity of the lifting points, as well as the length, diameter and binding method of the wire rope should be determined through simulation and calculation. In order to ensure the accuracy of hoisting alignment, it is necessary to check the interface again, and use the code plate and temporary connection plate to fix the interface position, so as to avoid large errors. Place the cantilevered end on the supporting tire frame, adjust the position of the truss with the help of chains and jacks, replace the jack after confirming that it is correct, take measures to fix the truss, and select steel as the reinforcement material.

( 5 ) Unloading the pipe truss

During the process of unloading the pipe truss, the stress of the entire structural system will change, its load will gradually decrease to 0, the original construction state will be converted to the use state, and the overall structure will be redistributed. When the unloading sequence and unloading scheme are different, the reaction force of the support point of the tire frame is also different. When unloading, the calculation results should be strictly followed, and the deformation of the entire structure should be scientifically coordinated under the premise of ensuring the safety of the structure and support. monitoring to determine the best uninstall method. Both the proportional method and the equidistance method are the most commonly used unloading methods, and the realization methods include air cushion, hydraulic jack and screw jack. The unloading of the pipe truss in this project is carried out step by step and in stages. Using MIDAS/Gen software to conduct finite element analysis on the unloading process through simulation, it is found that after the unloading is completed, the maximum vertical movement distance of the entire structure is 58mm, and the displacement point is near the temporary support at the short end of the inner ring, and the long end of the inner ring The support position also has a displacement phenomenon, and the position change is 25mm. The method used in the actual unloading operation is the equidistant method with jacks, each unloading volume is 8mm, and 88 jacks act at the same time. If the stroke is insufficient, a fixed device can be used to switch until the unloading is completed.

( 6 ) Construction monitoring

During the construction process, do a good job in real-time monitoring to understand structural stress changes and structural deformation, and obtain relevant information such as vibration and temperature, so as to make timely adjustments to the construction and ensure that the expected construction effect can be achieved. First of all, according to the obtained stress changes, the structural strain should be controlled within a reasonable range, and the key construction points, maximum stress points and minimum stress points can be used as monitoring points.