Steel truss hoisting
Lifting segmentation principle
During the hoisting of two-way truss, the following principles shall be followed in construction segmentation and construction sequence:
(1) meets the field performance of the crane and is convenient to install;
(2) Rationality and economy of factory division;
(3) Requirements on the weight and transportation conditions of individual parts;
(4) Requirements on the weight and transportation conditions of individual parts;
(5) Requirements on the weight and transportation conditions of individual parts;
(6) When cutting, the butt joint position of steel bars should not be on the same plane, but should be staggered by a distance of not less than 500mm.
Quality control measures
(1) Control the weld size in strict accordance with the design requirements, and do not arbitrarily increase or decrease the height and width of the weld.
(2) Using small line energy, small weld bead and multi-pass and multi-layer welding methods to reduce shrinkage.
(3) When assembling and welding, the components should have shrinkage allowance, and the components should be corrected in sections (blocks) to control the welding deformation of the assembly blocks.
(4) When assembling and welding, carry out multi-person symmetrical reverse welding to minimize welding deformation.
(5) When assembling and welding, the components should have shrinkage allowance, and the components should be corrected in sections (blocks) to control the welding deformation of the assembly blocks.
(6) When welding, the free end should be selected according to the characteristics of symmetrical arrangement of bars to avoid excessive internal force caused by welding error accumulation.
(7) Improve the manufacturing accuracy of components, and the length of components shall be accepted according to the positive deviation.
(8) For the measurement of span, centerline, displacement, elevation and camber, steel rule, theodolite, level and total station shall be used for accurate measurement, and possible position deviation shall be found and corrected in time to ensure the overall assembly accuracy.
Welding of steel truss
Preparatory work/about to start work
Before welding, the range of 10 ~ 15 mm at the interface should be cleaned to remove corrosion and surface stains of steel. Before formal welding, the starting point and arc closing place of tack welding should be polished into a gentle slope shape, and no defects such as incomplete fusion and shrinkage cavity should be confirmed. Welding shrinkage should be reserved at both ends of the steel truss. Due to errors in processing and manufacturing, deformation may occur during transportation, which must be corrected before welding.
Matters needing attention
Precautions for the first layer welding: Before welding, remove the raised part of the first layer and check whether there is fusion and depression at the edge of the groove. If there is, it must be removed. When grinding solder joints and other parts, pay attention to avoid touching the edge of the groove. Large diameter covered electrode is selected for middle current vertical welding, and high current is selected for flat welding. Precautions for welding the surface layer: when welding the surface layer, low current should be selected, and the melting time should be extended at the edge of the groove. When replacing covered electrode, the time should be as short as possible to prevent welding interruption.
quality management
(1) steel truss is preheated before welding to remove moisture and moisture; (2) Controlling the welding speed can appropriately increase the heat input; (3) controlling the fusion ratio to reduce the proportion of harmful substances in the base metal and molten metal in the weld metal; (4) As far as possible, the welding material of the root weld should be low sulfur, low phosphorus and high manganese content, so as to increase the toughness and improve the hot cracking resistance.
safety program
(1) Establish a security alert zone. Improper operation during hoisting will cause safety accidents and affect the project. Therefore, it is necessary to set up a warning zone, which is the scope of hoisting operation, set up a special person to guard the warning zone, clearly and uniformly establish a 24-hour duty system, and prohibit personnel from walking around the site during hoisting.
(2) During hoisting, assign special personnel to detect the jack, and report the operation of the jack with communication equipment to prevent the jack from slipping and other faults.
(3) While checking the jack, assign special personnel to check the oil pump. If there is overheating, oil leakage, unstable pressure output, etc., it should also be reported in time. With the consent of the commander-in-chief, the whole site will stop working for inspection and maintenance. Unilateral orders are strictly prohibited.
(4) During hoisting, ropes should be set at both ends of the truss to ensure the stability of the truss and prevent the truss from shaking.
(5) Welding shall be carried out after hoisting to the designated position. During welding, electric arc burns should be prevented, and steel strand and anchorage should be insulated.
(6) In order to ensure the smooth progress of the hoisting project, in line with the principle of safety first and prevention first, emergency preparations should be made before hoisting, and corresponding preventive measures should be formulated.
(7) Hoisting personnel should wear safety helmets when entering the hoisting site, and fasten their safety belts when working high above the ground. Professionals wear full-time signs and always pay attention to the instructions of signalmen to prevent danger. Signalers should carry flags, whistles and communication equipment with them.
(8) Before crane operation, it is necessary to know the weight of the working object to avoid overload operation. When lifting components, the sliding rope must be tied at a reasonable position. First, lift it to a height of half a meter, and check its binding to ensure that it is firm before lifting it. Pay attention to slow rise and slow fall when lifting parts. It is forbidden to stand on components or place other components to prevent safety accidents.
(9) The signalman's language and signal must be consistent with that of the driver, and the commander should enunciate clearly to avoid misunderstanding. The tower crane driver should obey the signalman's command to ensure the coordinated operation of all parties and avoid mistakes.
(10) When the steel member falls, the speed slows down, and the construction personnel hold the member outside the member. It is forbidden to put your hands on the bottom of the component or the joint of the component.
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