steel structure engineering
Because of its own advantages, steel structure has been widely used in modern buildings such as Bridges, industrial plants and high-rise buildings. In the process of a large number of engineering construction, steel structure engineering has also exposed a lot of common quality problems.
After the foundation concrete pouring is completed, the anchor bolts have overall offset, relative position offset, and bolt top elevation deviation; resulting in axial position deviation of the upper steel structure, screw rods and column bottom plate holes cannot be aligned, or steel columns are completed, the exposed length of the screw thread is insufficient, and the nut cannot be tightened.
(a) The original coordinate points given by the owner or the general contractor were not reviewed, resulting in deviations in the measurement coordinate system.
(b) After the bolt pre-embedding is completed, the follow-up review is not carried out in time.
(c) The positioning scheme of the embedded parts is not selected properly.
(d) There is a collision between the embedded bolt and the foundation steel bar, which affects the positioning.
(a) The measurement coordinate points given by the general contractor or the owner must be strictly reviewed to ensure that the error of the measurement coordinate system is within the allowable range.
(b) Check the civil engineering foundation drawings, clarify the relative relationship between the steel structure embedded parts and them, solve the contradiction between the two, and determine a reasonable steel structure embedded insertion process.
(c) Timely review and correction during the foundation construction process, especially during the concrete pouring process must be tracked and measured.
(d) Choose a suitable positioning scheme during the construction of embedded parts, such as adding positioning boards or positioning brackets.
When the anchor bolts are fixed, they are excessively welded with the foundation steel bars or positioning plates, which damages the screw base material and the foundation steel bars, resulting in a decrease in the mechanical properties of the screws and steel bars, and a decrease in the performance of the foundation concrete structure.
(a) There was no special construction technology exchange before the operation
(b) Insufficient operating experience of construction workers
(c) Lack of on-site management and control
(a) Before the pre-embedding operation, make a comprehensive disclosure to the operators.
(b) Welding operators must hold a certificate to work
(c) Spot welding is sufficient when the anchor bolts are fixed to the positioning plate, no full welding is required.
After the anchor bolts are pre-embedded, no protective measures are taken, the threaded fasteners are contaminated by concrete, or are damaged during backfilling, resulting in the adjustment nuts being unable to adjust the height of the column bottom. After the steel column is completed, the fastening nuts cannot be screwed in.
(a) The finished product protection construction technology was not disclosed before the operation, and no protection measures were taken after the embedded parts were pre-embedded.
(b) During the cross-operation, no disclosure was made to the relevant units.
(a) After the pre-embedding of the screw is completed, apply anti-rust butter to the screw thread, and then wrap it with tape for protection.
(b) After the infrastructure is completed, set eye-catching warning signs to prevent construction machinery from rolling
(c) Provide written reminders to cross-construction units.
The flatness of the surface is not strictly controlled when the steel plate embedded parts are fixed. After the concrete pouring is completed, the surface of the embedded parts is inclined, resulting in too large or too small gaps when the exposed steel components are connected to the buried plate, which affects the quality of joint welding construction.
(a) During the construction of buried slabs, no surface smoothness control measures were taken.
(b) The buried slab is not fixed firmly, and after being disturbed by the construction of other professional units, the deviation was not reviewed and corrected in time.
(c) Failure to review in time during concrete pouring.
(a) Before the buried plate is welded and fixed, the surface flatness must be checked with a ruler before it can be fixed.
(b) Review and correct deviations in time during the process of interspersed operations.
(c) Strictly implement on-site monitoring and review.
During the installation of the steel structure, the base material of the steel component is burned by welding temporary pallets, lifeline columns, and ladder lugs, which leads to a decline in structural performance.
(a) During the installation of steel components, welding is applied randomly, which makes the size of the welding feet too large, which easily causes the phenomenon of “overburning” of the base metal, causing warping, deformation and large welding shrinkage of the components, which affects the connection quality.
(b) In the process of welding the temporary plate and the base metal, the welding material is not selected correctly, and the welding rod with the strength and performance of the base metal is widely different.
(c) When cutting the lifting lugs and other plates on the component, the gas cutting nozzle is too close to the base material, leaving no cutting allowance.
(a) During the installation of steel structures, random welding of components is not allowed to avoid damage to the base metal.
(b) Strictly inspect the material of the weldment, control the content of sulfur and phosphorus within the allowable range, and correctly select the welding rod, welding wire and flux that match the base metal.
(c) The lifeline uprights should be tool-type uprights connected with bolts to avoid damage to the base metal of the component.
(d) When cutting the lifting lug and the code plate on site, in order to avoid damage to the base material, a cutting allowance of about 3-5mm is reserved.
During the installation of the steel structure, the splicing of the connecting plates is not tight, resulting in gaps in the contact surfaces of the connected components, which seriously affects the structural strength of the bolted connection.
(a) There is bending deformation of the connecting plate, and the contact surface with the component cannot be completely fitted.
(b) There are sundries between the contact surfaces or the burrs on the edge of the hole are not cleaned during factory processing
(c) Before installation, the unevenness of the contact surface of the component and the connecting plate has not been adjusted or the treatment method is unreasonable.
(d) The specifications, types and thickness of connecting components are not uniform
(a) Various deformations of connecting components and connecting plates should be corrected before installation.
(b) Before the components are installed, the corrosion, welding slag, burrs and oil stains on the contact surface and the periphery of the hole wall should be cleaned in advance to ensure a tight connection.
(c) When connecting steel flanges with slopes and unequal thickness plates, in order to keep the contact surfaces close together and to ensure uniform force transmission of the connected structural parts, it should be based on the difference in slope and thickness. Use the flat backing plate and the inclined backing plate to adjust the leveling respectively.
In the process of steel structure installation, the butt fault of steel column and steel beam is too large, which makes the actual thickness of weld after welding fails to meet the design requirements and affects the structural strength of the joint; For the bolted joint, it will make the floor slab lay not dense. If the butt groove is too small, the welding cannot be penetrated and the welding quality will be affected.
(a) During the processing of steel members, the hole position and aperture of the bolt on the connecting node plate are deviated.
(b) Material size deviation and welding deformation during factory processing and production.
(c) In the field installation, the wrong mouth is not adjusted in strict accordance with the specification requirements before the high-strength bolt is screwed.
(d) The factory processing does not open the groove according to the design Angle.
(1) During factory processing, strictly control the quality of each process such as feeding, assembling, coal connecting, drilling, etc. (2) During site installation, coal connecting positioning code plate is advanced.
(3) The small butt groove is adjusted by air trauma.
During the installation process, the steel member is cut randomly by hand, resulting in many defects such as cut marks and grooves at the incision, and there may be defects such as non-fusion, porosity, slag inclusion at the edge of the welding, which will lead to the reduction of the connection strength of the welded part and affect the quality of the weld.
(a) The length of the steel component is too long when it is made, and it can not be installed on site, and the site is manually cut by gas cutting.
(b) The installation error of the steel structure leads to the normal installation of the components, and the onsite gas cutting is manually cut at will. (3) During on-site gas cutting, the operating level of workers is uneven, which makes the incision more defective.
(a) Strictly control the cutting size to ensure the quality of component processing. For on-site installation errors, revise and deepen the drawings in advance and digest them at the factory processing stage.
(b) If it is necessary to trim steel components on site, choose workers with high operating level to use semi-automatic flame cutting machine.
(c) If after cutting the steel member, the incision is not smooth and the flame cut marks are more, the Angle grinder should be used on site to polish and smooth the parts with deep cut marks, and the welding material matching with the base metal should be welded and filled and then polished and smooth.
High strength bolts are piled up at will, without any protective measures, resulting in high strength bolts pollution, rust and can not be used; The specifications of high-strength bolts are mixed, resulting in serial use when used, resulting in unnecessary waste.
(a) The high-strength bolt has been contaminated and corroded when entering the field, and has not been treated.
(b) There is no special warehouse to store high-strength bolts, no rain and moisture prevention measures.
(c) High-strength bolts are not used according to the daily demand plan.
(d) The remaining high-strength bolts on the day are thrown around.
(a) High-strength bolts enter the site for acceptance, and the bolt connection pairs should be kept in boxes in the indoor warehouse, and the ground should have moisture-proof measures, and stacked according to the batch number and specifications. Shall not be mixed in storage or use.
(b) Do not open the box as much as possible before use, so as not to damage the sealing of the package: After unpacking some bolts, they should also be packed again, so as not to be contaminated with dust and rust.
(c) The storage time of high-strength bolt connection shall not exceed 6 months: when the storage period exceeds 6 months, torque coefficient test or fastening axial force test shall be carried out according to the requirements, and it can be used after passing the inspection.
(d) When the high-strength bolt connection pair is installed and used, the site shall receive it according to the specifications and quantity planned to be used on the day, install the remaining bolts and put them back into a dry and clean container for proper storage, and shall not be put or thrown away carelessly.
The high-strength bolt is also used as the installation bolt, the high-strength bolt from the start of use to the final completion of the time interval is long, during this time due to the impact of the environment and other winter factors (such as rain, etc.), its torque coefficient or fastening axial force will change, especially resulting in thread damage and the change of the surface state of the connection of the torque coefficient or fastening axial force, there are structural safety risks
(a) Failure to disclose the team’s approach techniques.
(b) The quality management of the project was slack and did not attract attention.
(c) Team construction lazy.
(a) Technical disclosure of the team before construction of high-strength bolts.
(b) Attention should be paid to the quality management of the project schedule. When installing high-strength bolts, mounting bolts and punching nails should be used first. The number of mounting bolts and punching nails inserted into each node should be determined according to the load borne during the installation process, and should comply with the following provisions. Should not be less than 1/3 of the total number of mounting holes; Mounting bolts should not be less than 2; The number of piercing nails should not be more than 30% of the number of mounting bolts; Do not use high-strength bolts as mounting bolts.
High strength bolt screws do not meet the requirements (should be exposed 2~3 thread), too little thread exposed will make the nut stress is not uniform; The thread exposed is too long, in addition to uneconomical, it also brings difficulties when screwing high-strength bolts.
(a) The length of high-strength bolts is incorrectly calculated before construction.
(b) Steel component installation error.
(c) high-strength bolt specifications mixed.
(d) The nut is not tightened.
(e) Deformation of the high-strength bolt connection surface of the component
(a) Technical disclosure of the team before construction of high-strength bolts.
(b) Before the construction of high-strength bolts, the bolt length should be reviewed, and the bolt specifications corresponding to each node should be sent to the team.
(c) When the component is installed, it is fixed and corrected by punching nails and mounting bolts first.
(d) When the joint surface of the high-strength bolt is deformed, it shall be corrected in time before installation.
The direction of the high-strength bolt, nut, or washer is incorrect, which affects the fastening effect of the bolt and causes potential structural safety risks. The surface of the chamfered side of the washer is flat and smooth, and the torque coefficient is small when tightened, and the dispersion rate is also small, so the chamfered side should be oriented towards the nut, for the large hexagonal head high-strength bolt connection pair, the washer set internal chamfering is to match the transition arc under the bolt head, so the chamfered side of the washer must be oriented towards the bolt head, otherwise the bolt head cannot be well attached to the washer. Affect the mechanical performance of the bolt: the marked side of the nut faces outward for easy acceptance, and the smooth surface of the unmarked side of the nut should face inward.
(a) No technical disclosure of high-strength bolt construction or no targeted mention of technical disclosure.
(b) The project management is relaxed, and such details are not paid attention to, and special acceptance inspections are not carried out.
(c) The worker’s sense of responsibility is not strong and the operation is casual.
(a) Technical disclosure of the team before construction of high-strength bolts.
(b) Attention should be paid to the quality management of project schedule.
(c) When the torsional high-strength bolt is installed, the side of the nut with a round table surface (the side with a mark and the side with a chamfer of the washer are oriented towards the side with a plum head.
(d) When installing a large hexagon head high-strength bolt, the chamfered side of the washer under the bolt head faces the bolt head, the side of the nut with a round table surface (marked side) and the chamfered side of the washer face the side with a club head.
Cracks are usually cold or hot. Welding cracks directly affect weld quality and structure safety.
(a) The main reasons for cold cracks are unreasonable welding structure design, improper weld layout, unreasonable welding process measures, such as no preheating before welding, welding bean cold zone.
(b) The main causes of hot cracking are poor cracking resistance of the base material, poor quality of the welding material, improper selection of welding process parameters, and excessive welding internal stress.
(a) Treatment method: The crack holes should be drilled at both ends of the crack or the weld metal should be removed for repair welding.
(b) For cold cracks, steel with good crack resistance should be selected, low hydrogen or ultra-low hydrogen, low strength electrode should be used, and the preheating temperature and line energy should be controlled to reduce the tendency of cold cracks.
(c) For hot cracks, steel with high nickel content should be selected, the method of refining should be used to improve the purity of steel, reduce the content of impurities, and control the concave of the weld less than 1㎜, reduce the line energy, in order to reduce the tendency of low heat cracks.
Welding does not use the arc quenching plate, so that the weld arc and arc quenching is easy to produce non-fusion, slag inclusion, porosity, cracks and other defects, in the multi-layer welding at both ends of the weld defects accumulation, defects are more prominent, and cause local stress concentration.
(a) The project does not disclose the construction technology to the workers or disclose the targeted content.
(b) Project personnel have weak quality awareness and do not pay attention to this phenomenon.
(c) The lack of supervision of the project arc extinguishing board, which is discarded at will, resulting in insufficient quantity.
(a) The strength of the arc extinguishing plate should not be greater than the strength of the welded steel, and should have a similar weldability to the welded steel.
(b) The end of the welded joint shall be provided with a welding arc starting plate and a drawing plate, and the weld shall be arc starting and terminating on the provided extension section. After the parts that are prone to defects at both ends are led outside the workpiece, the defective parts are cut off to ensure the quality of the weld. The length of welding arc plate and extraction plate should be greater than 25mm, and the length of submerged arc welding arc plate and extraction plate should be greater than 80mm.
(c) The arc guide plate and the lead plate should be removed by flame cutting, carbon arc gouging or mechanical methods. The base material should not be damaged during removal and the cutting edge should be polished until it is even with the weld end. Do not use hammer to remove the arc plate and the lead plate.
The causes of non-fusion and non-penetration are basically the same, mainly due to the process parameters, measures and groove to the end of the groove and the surface of the weld is not clean enough or there are impurities such as oxide and welding slag, and the welder’s technology is poor.
(a) Treatment method: For non-fusion, the weld metal at the non-fusion should be removed and repaired! The single side of the structure with good openness can be repaired directly on the back of the weld; For important coal parts that cannot be directly filled with coal, the unhardened metal should be shoveled and re-welded.
(b) Preventive measures: Before welding, the groove form and assembly gap should be determined, and the dirt on both sides of the groove edge should be carefully removed: reasonable selection of welding current, coal strip Angle and strip speed for weldparts with fast thermal conductivity and large heat dissipation area, flame heating can be used before preheating or welding. Long arc preheating and then welding can be selected: For the welding seam requiring full penetration, the single-sided coal double-sided forming process should be used as far as possible to avoid magnetic bias phenomenon, so that the arc is not biased to one side and ensure that the groove can be heated.
Solid inclusions are mainly composed of slag inclusion and tungsten inclusion. The main reasons for slag inclusion are poor quality of welding materials, too small welding current, too fast welding speed, too large slag density, preventing slag floating, multi-layer welding is not clean slag, etc. The main reason of tungsten clamping is the contact between tungsten electrode and molten pool metal during argon arc welding.
(a) Treatment method: for slag inclusion, the weld metal at the slag inclusion should be removed, and then welded; For tungsten clamping, the defect metal at the tungsten should be dug out and welded again.
(b) Preventive measures: before welding, the welding parts should be carefully cleaned, and the previous layer of slag must be cleaned when multi-layer welding; Correct selection of welding specifications, welding current should not be too small, welding speed should not be too fast; The method of transporting bar should be correctly adopted, and the flow direction of slag should be observed during operation to prevent the formation of solid inclusions.
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