Installation deviation problem
This chapter focuses on the problems such as the out-of-tolerance of steel column installation elevation size, the out-of-tolerance of steel column verticality, the deviation of crane beam verticality and levelness, etc.
1. The installation elevation dimension of steel column is out of tolerance.
phenomenon
The elevation dimension of steel column after installation affects the installation and adjustment difficulty of other components.
cause
The foundation elevation is incorrect, and the foundation coordinates and elevation are not checked and accepted before installation or handled improperly.
Prevention and treatment
(1) The construction shall be carried out in strict accordance with the design drawings to ensure the inspection and acceptance of the steel column foundation before installation, and the selection shall be made according to the foundation elevation or the actual length of the steel column or the supporting surface of the support, so that the elevation dimensions of each steel column after installation will be consistent and will not be too high or too low.
(2) The adjustment of foundation elevation shall be handled as follows:
1) The total length of steel column should meet the quality requirements, and the foundation bearing surface can be poured to the design elevation at one time, and it will be placed directly without adjustment during installation;
2) The steel column foundation should be watered to 40~60mm higher than the design standard, and then leveled to the design elevation with fine stone concrete. The secondary watering leveling layer should make the new and old concrete closely combined to achieve the design strength of foundation and not form interlayer;
3) Pouring the foundation to 40~60mm higher than the design standard, and then pouring concrete after the steel column is installed on the adjusting shim;
4) according to the design elevation, the column foot support (steel, railings, etc. ) embedded in advance, steel column after installation pouring cement mortar.
2. The verticality of steel column is out of tolerance
After installation, the verticality deviation of the steel column exceeds the allowable value in the code, which not only affects the compressive strength of the structure itself, but also affects the installation of other components.
cause
(1) The deformation control measures of the steel column itself were improper during manufacture, and the height and deflection of the column were not treated.
(2) Before installation, check the quality of the steel column. If there are deformation defects, they should be treated before installation.
(3) Under the action of external force, the strength and stability of easily deformable steel columns are not calculated, and no reinforcement measures are taken during hoisting. In addition, environmental temperature difference, wind force, sunshine and other external influences are related to welding deformation and other factors.
Prevention and treatment
(1) Anti-deformation measures should be taken during fabrication, installation and welding operations, and the fabricated and to-be-installed steel columns should be supported and cushioned during placement and transportation to prevent deformation due to bending moment caused by dead weight; Generally, the lifting point for vertical lifting should be 2/3 of the total length of the column.
(2) When correcting the verticality of steel columns, first fix the side columns at both ends as reference columns, and then correct the rest columns according to the vertical and horizontal axes. When adjusting the verticality, we can calculate the required pad thickness through the formula according to the actual inclination value and size of the steel column, so as to adjust its verticality.
(3) When adjusting the verticality of steel columns, attention should be paid to the deformation under the action of temperature difference and wind, which should generally be carried out in the morning or in an environment with low solar radiation temperature. When lifting the roof panel after the steel column is connected with the roof truss, it is forbidden to do it from one slope, and it should be done symmetrically from the edges of the two slopes in the center of the upper chord to the middle.
3. Deviation of verticality and levelness of crane beam
phenomenon
In construction, it is often encountered that the verticality and levelness of crane beams and the relative elevation of two crane beams exceed the allowable deviation, which affects the installation of crane tracks.
cause
(1) The production quality of the crane beam itself does not meet the requirements.
(2) The fabrication and installation of steel columns do not meet the requirements.
(3) The elevation and levelness of the support surface of the crane beam supported by the steel column lead to the out-of-tolerance of the plane height or levelness of the crane beam and the relative elevation of the two crane beams.
Prevention and treatment
(1) When making steel columns, strictly control the size and deformation from the bottom surface of steel columns to the support surface.
(2) Adjust the verticality of the steel column and the levelness of the bracket when installing and positioning, measure the height of the crane beam support and the height of the bracket from the bottom of the column in advance, and use the pad iron to adjust it in advance on the foundation plane or the support surface.
(3) During installation, the center line drawn on the upper flange plane of the beam in advance should be aligned and leveled. When the relevant dimensions can meet the requirements of crane track installation after careful retest, the control of this value should generally be based on the fact that the installed crane beam has no load and no deflection. If the upper arch is too large after installation, it will affect the next crane track installation.
Improper installation method
This chapter focuses on the problems that the quality of foundation grouting does not meet the requirements, the camber of steel roof truss does not meet the requirements, and the installation quality of crane track does not meet the requirements.
1. The quality of foundation grouting does not meet the requirements.
phenomenon
After the secondary grouting, there is a gap between the foundation surface of the steel column and the bottom surface of the steel column, and the mortar is not filled, especially in the center of the plane under the bottom plate, and the edge of the plane on the foundation is not treated with aproll.
cause
The distance between the bottom surface of the steel column and the foundation surface is too small, the mortar is not easy to fill, the grouting material is not selected properly, the operation technology is not correct, and the tools are not selected properly.
Prevention and treatment
(1) When adjusting the elevation with shim, keep the distance between the foundation bearing surface and the lower surface of steel column bottom plate not less than 40mm, so as to facilitate grouting and gap filling.
(2) The cement mortar for secondary grouting should be one level higher than the original foundation concrete grade, and antifreeze and early strength agent should be mixed into the mortar during winter construction to prevent freezing injury or slow strength growth; Before pouring, the dirt on the foundation surface should be cleaned up, and the original foundation surface should be wetted with clear water before pouring mortar.
(3) For some steel column foundations with small grouting gaps, holes can be drilled on the steel plate at the column foot for grouting, and the foundation steel plate with the length and width exceeding 1m can be treated by this method. After the curing period, the holes in the bottom plate of the steel column can be covered with small steel plates and welded to death.
(4) If the design requires post-grouting strength test, four kinds of materials, the same mixture ratio and the same construction method should be used in the same batch of construction to make two sets of mortar specimens, one for strength test before steel structure hoisting and the other for 28d standard curing, so as to make age strength for future reference.
2. The camber of steel roof truss does not meet the requirements.
The phenomenon of excessive arching affects the connection of steel columns, resulting in negative deviation of the upper span size; The camber deflection not only affects the stress load, but also increases the deviation of the upper span size and verticality of the steel column.
cause
(1) The camber is not processed according to the specified camber or the camber deformation is not processed.
(2) The roof truss is not rigidly reinforced, and the selection of lifting points is incorrect.
Prevention and treatment
(1) When making, the span should be compared with the arch according to the regulations.
(2) In the production process, when the arch frame and other structures are deformed, they should be corrected and hoisted after meeting the requirements.
(3) Before hoisting, choose a reasonable hoisting scheme, reinforce according to the size of different spans, and choose the correct hoisting point to avoid the problem of excessive arching or deflection deformation of steel roof truss camber.
3. The installation quality of crane track does not meet the requirements.
phenomenon
After installation, the levelness, straightness and relative elevation of the two tracks are out of tolerance, and the coincidence degree between the center of crane track and the center of crane beam is out of tolerance.
cause
(1) Due to the installation quality defect of crane beam, the elevation and levelness of crane track are out of tolerance.
(2) Before installation, the crane track is not corrected or does not meet the requirements after correction.
(3) The elevation, levelness and centerline coordinates of the crane beam were not accepted before the crane track installation.
Prevention and treatment
(1) Before installing the crane rail, check and accept the elevation, levelness and centerline of the crane beam, and stagger the joints of the two rails along the whole length of the rail to avoid being concentrated in the same position.
(2) Correct the bending deformation of crane track before installation.
(3) The bolts for fixing the track shall be provided with locking measures. Generally, a spring washer or locknut should be added under the nut to prevent the crane from loosening due to external force and vibration during use.
(4) When the track is installed on the concrete crane beam, the pad iron under the track should be flat to ensure close contact with the bottom of the track, and the contact area should be greater than 60%; The gap between the cushion block and the concrete crane beam should be greater than 25mm, and it should be filled with non-shrinkage cement mortar; The gasket should be welded firmly. If steel beams and pads are tied together, they should be welded to the crane beam.
Welding problem
This chapter focuses on the problems that the cutting edge is unprocessed or does not meet the requirements of the specification, and the weld connection is defective.
1. The cutting edge is not machined or does not meet the specification requirements.
phenomenon
There are some defects in the steel cutting surface, such as lack of edge and uneven bending greater than1mm.
cause
The gas cutting process is not standardized, and the cutting process does not meet the requirements.
Prevention and treatment
(1) Before gas cutting, check that all equipment of the whole gas cutting system is operating normally, the pressure gauge is normal without damage, the gas flow of the cutting nozzle is smooth, and the cutting torch angle is correct.
(2) Select the correct process parameters according to the machine and plate thickness.
(3) During gas cutting, adjust the shape of oxygen jet to make its outline clear, and the cutting torch moves at a uniform speed. The surface of the cutting nozzle should be 2 ~ 5mm away from the central tip of the flame.
2. Welding connection defects
Poor weld formation, arc pit, crack, flash, incomplete fusion, incomplete penetration, meat biting, slag inclusion, porosity, parent metal wear and so on.
(1) stomata
cause
1) covered electrode is affected with damp;
2) The baking temperature of acid covered electrode is too high, and the weldment is not clean;
3) Excessive current turns covered electrode red;
4) impure protective gas;
5) The welding wire is rusted.
Prevention and treatment
1) Before welding, the impurities on the weld groove surface must be cleaned up;
2) Reasonable selection of welding method;
3) Welding materials must be baked properly;
4) When welding in high wind speed environment, windproof measures should be taken.
(2) Slag inclusion
cause
1) The welding material is of poor quality and the slag is too thick;
2) Corrosion or other impurities on the weldment or in the groove are not cleaned up;
3) When welding by layers, the slag of each layer in the welding project is not cleared, and then the next layer is welded; 4) The current is too small and the welding speed is too fast.
Prevention and treatment
Adopt 1) covered electrode with good process performance;
2) Choose a reasonable welding specification and groove size before welding;
3) Both sides of the groove shall be cleaned;
4) During multi-layer welding, the slag of each layer shall be thoroughly cleaned.
(3) Biting meat
cause
1) The current is too large;
2) The arc is too long or the transmission angle is improper;
3) Improper welding position.
prevent
1) Correct selection of welding current and welding speed during welding;
2) adopt the correct method of transporting strips;
3) Adopt appropriate covered electrode angle and arc length.
(4) Incomplete penetration
cause
1) The welding current is too small and the welding speed is too fast;
2) The bevel angle is too small and the welding angle is improper;
3) covered electrode is eccentric;
4) When welding on both sides, the back root is not completely cleaned;
5) There are uncleared impurities such as rust on the weldment;
6) During tack welding, the welding materials are not matched, the size of welding angle is irregular, and the spacing of welding spots is irregular, which affects the weld formation and causes incomplete penetration and fusion defects.
Prevention and treatment
1) Choose a reasonable welding specification;
2) Correct selection of groove type, size, angle and clearance;
3) Adopt appropriate technology and correct operation method;
4) tack welding must be carried out by welders with corresponding certificates, and tack welding shall use the same welding materials as formal welding. It is required to conduct tack welding on the outside of the joint groove. When there are pores and cracks in tack welding, they should be removed and re-welded.
Material problem
This chapter focuses on the transportation, stacking deformation and span inaccuracy of components.
1. Transportation and stacking deformation of components
Significant parts will be deformed during transportation or stacking, resulting in complete bending or slow bending.
cause
(1) members generally bend slowly due to welding deformation;
(2) The components are deformed due to collision during transportation, which generally shows dead bending;
(3) The component pads are unreasonable, for example, the upper and lower pads are not vertical. And the stacking position sinks, resulting in complete bending or slow bending deformation of the assembly.
Prevention and treatment
The dead bending deformation of (1) members is generally corrected mechanically, that is, by using jacks or other tools or by baking with oxyacetylene flame. Depending on the structural stiffness, generally, tool correction is the main method, supplemented by oxyacetylene baking, which can achieve better results.
(2) When the structure is slowly bent and deformed, oxyacetylene flame can be used for correction, and large oxyacetylene flame gun is generally used for baking. In the process of flame baking, linear heating is often used to correct structures with large deformation or rigidity; Triangular heating is often used to correct the bending deformation of members with large thickness and strong stiffness.
2. The member span is inaccurate
phenomenon
The member span value is greater than or less than the design value.
cause
(1) The manufacturing size of the assembly is too large or too small;
(2) The accumulated deviation of small assembled components leads to inaccurate span;
(3) The steel rule is not uniform.
Prevention and treatment
(1) If there is a contradiction between the springing value and the span value due to the fabrication deviation of components, the springing value should be met first. In order to ensure the accuracy of springing and span values, the accuracy of component fabrication dimensions must be checked in strict accordance with GB 50205—200 1 Code for Acceptance of Construction Quality of Steel Structure Engineering.
(2) The deviation of small assembly parts must be eliminated during assembly;
(3) The steel ruler used for component fabrication, assembly and hoisting shall be unified.
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