Due to its own advantages, steel structures are widely used in modern buildings such as bridges, industrial plants, and high-rise buildings. In a large number of engineering construction processes, steel structure engineering has also exposed many quality problems. This paper mainly focuses on Liaoning's recent problems in the main experience of steel structure acceptance and completion acceptance and rectification measures.
1. Production problems of components
The plate used for the portal steel frame is very thin and can be used up to 4 mm. The cutting of multiple sheets should be preferred for cutting and avoiding flame cutting. Because cutting with flame will cause great wave deformation at the edge of the board. At present, most manufacturers of H-beam welding use submerged arc welding or semi-automatic welding. If the control is not good, the welding deformation should occur, causing the member to bend or twist.
2. Column foot installation problem
(1) Pre-embedded parts (anchor bolts) Problem phenomenon: overall or layout offset; the elevation is incorrect; the threaded fasteners are not protected. Directly causing the bolt holes in the steel column bottom plate to be misaligned, resulting in insufficient thread length.
Measures: The steel structure construction unit cooperates with the civil construction unit to complete the work of the embedded parts before the concrete is poured. The relevant dimensions must be reviewed and secured.
(2) The anchor bolt is not vertical: the horizontalness of the bottom of the frame column is not the same, the anchor bolt is not vertical, and the horizontal error of the pre-embedded anchor is too large after the foundation construction. After the column is installed, it is not in a straight line, and it is difficult to see the appearance of the house. It brings errors to the installation of the steel column, and the structural stress is affected, which does not meet the requirements of the construction acceptance specification.
Measures: The installation of anchor bolts should be carried out by first leveling the bottom plate with the lower adjusting bolts, and then filling it with secondary grouting without shrinking mortar. Therefore, when anchor bolt construction, fixed anchor bolts such as steel bars or angle steel can be used. Welding into cages, perfecting the support, or taking other effective measures to avoid moving the anchor bolt one bit when pouring the foundation concrete.
(3) Anchor bolt connection problem: the column foot anchor bolt is not tightened, the pad plate is not welded to the bottom plate; some anchor bolts that do not expose 2 to 3 thread buttons.
Measures: Welding bolts and nuts should be adopted; outside the chemical anchors, fireproof coatings and heat insulation should be thickened to prevent anchoring performance during fire; the 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, resulting in poor bolt installation, or the degree of bolt fastening does not meet the design requirements.
1. There are impurities such as floating rust and oil on the surface, and there are burrs and welds in the bolt holes.
2. The bolt mounting surface is still defective after being processed.
1. The surface of high-strength bolts, such as floating rust, oil stains and bolt holes, should be cleaned one by one. It must be rust-proofed before use, so that the bolts for assembly should not be used in the formal assembly. Bolts should be kept and distributed by a special person.
2. Handling the assembly surface should take into account the construction and installation sequence, prevent repeated, and try to handle it before lifting.
2) The bolt thread is damaged, and the screw cannot be screwed into the nut freely, which affects the assembly of the bolt.
Analysis of the cause: The thread is severely rusted.
1. Before use, the bolts should be selected, cleaned and rusted for pre-matching.
2. The bolts damaged by the thread cannot be used as temporary bolts. It is strictly forbidden to force the screw holes.
3. Pre-opted bolt assemblies shall be stored in sets and shall not be interchangeable during use.
(2) On-site weld phenomenon: the quality is difficult to guarantee; the design requires full penetration of the first and second welds without ultrasonic flaw detection; the main beam and column of the floor are not welded; the arc runner is not used for welding.
Solution: Before welding the steel structure, check the welding certificate. Select the welding strip according to the design requirements. Use the welding rod according to the instructions and operating procedures. There must be no cracks or welds on the surface of the weld. First and second welds. There shall be no stomata, slag inclusions or crater cracks. The first-order weld shall not have any defects such as undercut and under-welding. The first and second welds shall be non-destructively tested as required. The welder's steel shall be inspected at the specified welds and parts. . Unqualified welds shall not be disposed of without authorization. After the modification process is determined, the number of weld repairs in the same part shall not exceed two times.
4. Component deformation problem
(1) The component is deformed during transportation, and there is a dead bend or a slow bend, which makes the component unable to be installed.
1) The deformation caused by welding during the production of the component generally exhibits a gentle bend.
2) When the component is to be transported, the support point is unreasonable, such as the underlay is not vertical, or the stacking site is sunken, causing the component to produce a dead bend or a slow deformation.
3) The deformation of the component during transportation due to collision, generally showing a dead bend.
1) When manufacturing components, measures to reduce welding distortion are used.
2) In assembly welding, measures such as deformation in the opposite direction are adopted. The assembly sequence should be in accordance with the welding sequence. The assembled tires should be used to set up enough brackets to prevent deformation.
3) Pay attention to the reasonable arrangement of the pads during transportation and transportation.
1) The deformation of the member is usually bent by mechanical correction. Use a jack or other tool to correct or supplement with oxyacetylene flame after grilling.
2) When the structure is subjected to slow bending deformation, it is corrected by oxyacetylene flame heating.
(2) The full-length distortion of the steel beam members after assembly is more than the allowable value, resulting in poor installation quality of the steel beams.
1) The splicing process is unreasonable.
2) The size of the assembled node does not meet the design requirements.
1) Assemble the components to be assembled, and the bottom surface of the components should be leveled to prevent warpage. The assembly workbench shall be at the level of each fulcrum, and welding deformation shall be prevented during the welding. In particular, the final assembly of the beam section or the stairway should be adjusted after the positioning welding. Note that the size of the joint should conform to the design, otherwise the component may be distorted.
2) The components with poor rigidity should be reinforced before turning over the welding. After the components are turned over, they should be leveled, otherwise the components cannot be corrected after welding.
(3) The member is arched, the value is large or less than the design value. When the value of the arching of the component is small, the beam is bent downward after installation; when the value of the arching is large, the elevation of the extruded surface is likely to exceed the standard.
1) The component size does not meet the design requirements.
2) During the erection process, it is not corrected based on the measured value and the calculated value.
3) Bridges with small spans have a small degree of arching and are ignored during assembly.
1) Perform each step of inspection strictly according to the allowable deviation of steel structural members.
2) During the erection process, the rods are installed and the construction of the joints at the site is completed, and the upper crown is measured, and other adjustments are made during the construction.
3) In the small assembly process, the cumulative deviation should be strictly controlled, and measures should be taken to eliminate the influence of the welding shrinkage.
5. Steel structure installation problem
(1) Pre-control measures for the foot of the steel column Before the steel column is hoisted, the basic elevation should be strictly controlled, the measurement should be accurate, and the basic surface should be carefully leveled according to the measured value; if the secondary grouting method is used, the bottom of the column foot should be watered. Hole (also used as vent hole), use steel pad to flatten the bottom of the steel column, and pre-position the steel plate of the column foot according to the design elevation, and then take the secondary grout.
(2) Pre-control measures for steel column displacement Before pouring the concrete foundation, the pre-embedded bolts are clamped according to the design position by the shaping chuck to prevent displacement when the concrete is poured; the reserved holes of the lower steel plate should be enlarged to determine the hole position. Make a reserved hole.
(3) The vertical deviation of the column is too large. The pre-control measures shall be hoisted in accordance with the calculated hanging point, and the lifting method of two points or more shall be adopted. Temporary fixing shall be carried out during lifting to prevent hoisting deformation; after the column is in place Temporary support should be added in time; vertical deviation should be corrected before fixing.
Only in the process of construction management, strengthen the training and training of technical personnel and workers on the standardization and operation procedures, effectively prepare for the start of construction, strengthen the quality control and supervision and inspection during the construction process, and actively exert various aspects such as construction and supervision. The role of the sub-projects in the process of acceptance, in order to ensure the overall quality of steel structure engineering.