Steel structures, due to their inherent advantages, are widely used in modern buildings such as bridges, industrial plants, and high-rise buildings. However, numerous quality defects have been exposed in numerous construction projects involving steel structures. This article mainly discusses some opinions on common problems and improvement measures found in the acceptance and completion acceptance of steel structure main bodies in recent years.

 

　　I. Some problems and solutions in the construction process of steel structure engineering

 

　　1. Problems in the production and manufacturing of components

 

　　The plates used in gantry steel frames are very thin, with the thinnest being 4 mm. For cutting thinner plates, shearing should be the preferred method, avoiding flame cutting. Flame cutting can cause significant wave deformation at the plate edges. Currently, most manufacturers use submerged arc automatic welding or semi-automatic welding for H-steel welding. If not well controlled, welding deformation may occur, causing the components to bend or warp.

 

　　2. Column base installation problems

 

　　(1) Embedded parts (anchor bolts) problems: overall or layout offset; incorrect elevation; no protection measures for threads. This directly causes misalignment of the steel column base plate bolt holes and insufficient thread length.

 

　　Measures: The steel structure construction unit and the civil construction unit collaborate to complete the embedded parts work before concrete pouring. Related dimensions must be verified and securely fixed.

 

　　(2) Non-vertical anchor bolts: poor levelness of the frame column base plate, non-vertical anchor bolts, and large horizontal errors of pre-embedded anchor bolts after foundation construction. After the columns are installed, they are not in a straight line, leaning in different directions, making the appearance of the building unsightly. This introduces errors in steel column installation, affecting structural force and failing to meet the requirements of construction acceptance standards.

 

　　Measures: Anchor bolt installation should adhere to the principle of first leveling the base plate with lower adjustment bolts and then filling with secondary grouting using non-shrinkage mortar, a method commonly used abroad. Therefore, during anchor bolt construction, steel bars or angle steel can be used to fix the anchor bolts. They are welded into a cage-like structure for enhanced support, or other effective measures are taken to prevent the anchor bolts from shifting during concrete pouring.

 

　　(3) Anchor bolt connection problems: anchor bolts at the column base are not tightened, the base plate is not welded to the base plate; some anchor bolts do not show 2-3 threads.

 

　　Measures: Welding anchor rods and nuts should be adopted; fire-retardant coatings and heat insulation treatment should be added to the outside of chemical anchor bolts to prevent damage to anchoring performance in case of fire; foundation settlement observation data should be supplemented.

 

　　3. Connection problems

 

　　(1) High-strength bolt connection

 

　　1) The bolt equipment surface does not meet the requirements, making it difficult to install the bolts or the bolt tightening degree does not meet the design requirements.

 

　　Cause analysis:

 

　　① Surface has floating rust, oil stains, and other impurities; burrs and weld beads are present on the bolt hole wall.

 

　　② Defects remain on the bolt installation surface even after treatment.

 

　　Solution:

 

　　① Floating rust, oil stains, and defects on the high-strength bolt surface and bolt hole wall should be thoroughly cleaned. Before use, rust prevention treatment must be performed. Bolts used for assembly should not be used during formal assembly. Bolts should be stored and issued by designated personnel.

 

　　② When processing the assembly surface, consider the construction and installation sequence to prevent repetition, and process as much as possible before hoisting.

 

　　2) Bolt thread damage; the bolt cannot be freely screwed into the nut, affecting bolt assembly.

 

　　Cause analysis: Severe thread corrosion.

 

　　Solution:

 

　　① Before use, bolts should be selected, cleaned, derusted, and pre-matched.

 

　　② Bolts with damaged threads cannot be used as temporary bolts and must not be forcibly driven into the bolt holes.

 

　　③ Pre-selected bolt assemblies should be stored in sets and should not be interchanged during use.

 

　　(2) On-site weld phenomenon: difficult to ensure quality; ultrasonic flaw detection was not used for first and second-level welds requiring full penetration according to the design; no welding between the floor main beam and the column; no arc plate was used for welding.

 

　　Solution: Before welding the steel structure, check the qualification certificate of the welding rods, select the welding rods according to the design requirements, and use the welding rods according to the instructions and operating procedures. The weld surface should not have cracks or weld beads. First and second-level welds should not have pores, slag inclusions, or crater cracks. First-level welds should not have undercut or incomplete welds. First and second-level welds should undergo non-destructive testing as required. The welder's steel stamp should be checked at the specified welds and locations. Unqualified welds must not be arbitrarily processed; a modified process should be determined before processing. The number of rework times for welds in the same location should not exceed twice.

 

　　4. Component deformation problems

 

　　(1) Component deformation during transportation, resulting in dead bends or gentle bends, making component installation impossible.

 

　　Cause analysis:

 

　　1) Deformation caused by welding during component manufacturing, generally exhibiting gentle bending.

 

　　2) During component transportation, unreasonable support points, such as non-vertical upper and lower padding wood, or settlement of the stacking site, can cause dead bends or gentle deformation in the components.

 

　　3) Deformation caused by collisions during component transportation, generally exhibiting dead bends.

 

　　Preventive measures:

 

　　1) During component manufacturing, measures to reduce welding deformation should be adopted.

 

　　2) During assembly and welding, measures such as reverse deformation should be adopted. The assembly sequence should follow the welding sequence, assembly jigs should be used, and sufficient supports should be set up to prevent deformation.

 

　　3) During transportation and storage, attention should be paid to the reasonable configuration of support points.

 

　　Solution:

 

　　1) For components with dead bends, mechanical rectification is generally used, i.e., correction using jacks or other tools, or correction with oxyacetylene flame heating.

 

　　2) When the structure undergoes slow bending deformation, oxyacetylene flame heating is used for correction.

 

　　(2) After the steel beam components are assembled, the full-length twist exceeds the allowable value, resulting in poor installation quality of the steel beam.

 

　　Cause analysis:

 

　　1) Unreasonable splicing process.

 

　　2) The dimensions of the assembled nodes do not meet the design requirements.

 

　　Solution:

 

　　1) For assembled components, an assembly workbench should be set up. When welding, the bottom surface of the component should be leveled to prevent warping. The assembly workbench should have horizontal support points at each point, and welding deformation should be prevented during assembly welding. Especially for the final assembly of beam sections or ramps, deformation should be adjusted after positioning welding, and attention should be paid to ensuring that the node dimensions meet the design requirements; otherwise, component twisting is likely to occur.

 

　　2) For components with poor self-rigidity, reinforcement should be carried out before turning over for welding, and the components should also be leveled after turning over; otherwise, the components cannot be corrected after welding.

 

　　(3) Component arching, the value is greater than or less than the design value. When the arching value of the component is small, the beam will deflect downward after installation; when the arching value is large, it is easy to cause the elevation of the squeezed surface to exceed the standard.

 

　　Cause analysis:

 

　　1) The dimensions of the components do not meet the design requirements.

 

　　2) During the erection process, the deviation between the measured value and the calculated value was not corrected.

 

　　3) For bridges with small spans, the arching degree is small and ignored during assembly.

 

　　Solution:

 

　　1) Strictly inspect each step according to the allowable deviations in the fabrication of steel structural components.

 

　　2) During the erection process, after the members are assembled, and after the on-site joint construction is completed, the upward arching degree is measured, and other adjustments are made during construction.

 

　　3) In the process of small assembly, the cumulative deviation should be strictly controlled, and measures should be taken to eliminate the influence of weld shrinkage.

 

　　5. Steel structure installation problems

 

　　(1) Pre-control measures for gaps at the base of steel columns Before hoisting steel columns, the base elevation should be strictly controlled and accurately measured, and the base surface should be carefully leveled according to the measured value; if the secondary grouting method is used, grouting holes (also acting as vent holes) should be opened at the bottom of the column base plate, and steel shims should be used to level the uneven parts at the bottom of the steel column, and the column base support steel plates should be installed in advance according to the design elevation, and then secondary grouting should be carried out.

 

　　(2) Pre-control measures for steel column displacement Before pouring the concrete foundation, the pre-embedded bolts should be clamped in place according to the design position using a fixed chuck to prevent displacement during concrete pouring; the holes reserved for the lower steel plate of the column should be enlarged, and the hole position should be determined before making the reserved holes.

 

　　(3) Pre-control measures for excessive vertical deviation of columns Steel columns should be hoisted and positioned according to the calculated hanging points, and at least two hoisting methods must be used. Temporary fixation should be carried out during hoisting to prevent hoisting deformation; temporary supports should be added promptly after the columns are in place; vertical deviations should be corrected before fixation.

 

　　II. Conclusion

 

　　Only by strengthening the training of technical personnel and workers on specifications, standards, and operating procedures during construction management, effectively doing the pre-construction preparation, strengthening quality control and supervision during the construction process, actively playing the role of various aspects such as construction and supervision, and doing a good job in the process acceptance of each sub-project can the overall quality of the steel structure project be ensured.