Common problems and solutions in steel structure construction
1. Production and manufacture of components
The plates used in the portal steel frame are very thin, the thinnest can be used up to 4mm. Cutting method should be preferred for multi sheet cutting, instead of flame cutting. Because cutting with flame will cause great wave deformation on the edge of the plate. At present, most manufacturers of H-beam welding adopt submerged arc automatic welding or semi-automatic welding. If the control is not good, the welding deformation should occur to make the component bend or twist.
2. Column base installation problems
(1) Problems of embedded parts (anchor bolts): overall or layout deviation; elevation error; no protection measures for screw thread. The bolt holes of the steel column base plate are not aligned directly, resulting in insufficient screw thread length.
Measures: the steel structure construction unit shall cooperate with the civil construction unit to complete the work of embedded parts before concrete pouring and vibrating. The relevant dimensions must be checked and fixed firmly.
(2) The phenomenon that anchor bolt is not vertical: the levelness of frame column base plate is poor, the anchor bolt is not vertical, and the horizontal error of embedded anchor bolt after foundation construction is large. After the column is installed, it is not in a straight line, which makes the appearance of the house difficult to see, brings errors to the steel column installation, affects the structural stress, and does not meet the requirements of the construction acceptance specification.
Measures: for the installation of anchor bolt, the bottom plate shall be leveled with the lower adjusting bolt first, and then filled with non shrinkage mortar by secondary grouting. This method is used abroad. Therefore, during the construction of anchor bolt, the steel bar or angle steel can be used to fix the anchor bolt. Weld into cages, improve supports, or take other effective measures to avoid anchor bolt displacement when pouring foundation concrete.
(3) Problems of anchor bolt connection: the anchor bolt of column base is not tightened, the base plate is not welded with the base plate; some anchor bolts with 2-3 threads are not exposed.
Measures: bolts and nuts shall be welded; outside chemical bolts, fireproof coating and heat insulation shall be thickened to prevent the anchoring performance from being affected in case of fire; foundation settlement observation data shall be supplemented.
3. Connection problems
(1) High strength bolt connection
1) The bolt equipment surface does not meet the requirements, resulting in poor installation of bolts, or the degree of bolt fastening does not meet the design requirements.
① There are impurities such as floating rust and oil stain on the surface, and there are burrs and weld beading on the bolt hole wall.
② The bolt installation surface is still defective after treatment.
① The surface of high-strength bolts shall be cleaned one by one for floating rust, oil stain and bolt hole defects. Rust proof treatment must be carried out before use, so that the bolts used for assembly shall not be used during formal assembly. Bolts shall be kept and distributed by special personnel.
② The construction and installation sequence shall be taken into account for handling the assembly surface to prevent repetition, and handling shall be conducted before hoisting as far as possible.
2) The screw thread of the bolt is damaged, and the screw cannot screw into the nut freely, which affects the assembly of the bolt.
Cause analysis: the screw thread is seriously rusted.
① Bolts shall be selected before use and pre assembled after cleaning and derusting.
② Bolts with damaged screw threads shall not be used as temporary bolts, and it is strictly forbidden to force into screw holes.
③ The pre selected bolt components shall be stored in sets and shall not be interchanged during use.
(2) On site weld phenomenon: quality is difficult to be guaranteed; ultrasonic flaw detection is not used for the primary and secondary welds with full penetration required by the design; the main beam and column of the floor are not welded; arc strike plate is not used for welding.
Solution: before the welding of steel structure, check the qualification certificate of the welding rod, select the welding rod according to the design requirements, use the welding rod according to the instructions and operation procedures, the weld surface shall be free of cracks and weld beading, the first and second level welds shall be free of porosity, slag inclusion and crater cracks, the first level welds shall be free of undercut, incomplete welding and other defects, and the first and second level welds shall be subject to NDT as required The welder’s steel seal shall be checked at the specified weld and position. Unqualified welds shall not be treated without authorization, and shall be treated after the modification process is determined. The weld repair times of the same part shall not exceed twice.
4. Deformation of components
(1) During transportation, the components are deformed, dead or slow bending occurs, which makes the components unable to be installed.
1) The deformation caused by welding during the fabrication of components generally presents slow bending.
2) When the components are to be transported, the supporting points are unreasonable, the upper and lower skids are not vertical, etc., or the stacking site is sunk, resulting in dead bending or slow deformation of the components.
3) In the transportation of components, there is deformation due to collision, which generally presents dead bend.
1) When making components, measures to reduce welding deformation shall be taken.
2) During assembly and welding, measures such as reverse deformation shall be taken. The assembly sequence shall follow the welding sequence. The assembly mould shall be used and enough supports shall be set to prevent deformation.
3) Pay attention to the reasonable allocation of cushion points during transportation.
1) The dead bending deformation of components is generally controlled by mechanical correction method. That is, use jack or other tools to rectify or assist with oxyacetylene flame to rectify.
2) In case of slow bending deformation of the structure, oxyacetylene flame shall be used for correction.
(2) After assembly, the whole length of the steel beam is twisted beyond the allowable value, resulting in poor installation quality of the steel beam.
1) The splicing process is unreasonable.
2) The size of assembled joint does not meet the design requirements.
1) The assembling worktable shall be set for assembling components, and the bottom surface of components shall be leveled to prevent warpage when welding. Each fulcrum of the assembly workbench shall be horizontal, and welding deformation shall be prevented during assembly welding. In particular, the final assembly of beam segments or staircases should be adjusted after positioning and welding. Attention should be paid to the size of the nodes to conform to the design, otherwise the components will be distorted.
2) For members with poor rigidity, they shall be reinforced before turning over for welding and leveled after turning over, otherwise they cannot be rectified after welding.
(3) When the component is arched, the value is large or less than the design value. When the arching value of the component is small, the beam will deflect after installation; when the arching value is large, the extrusion surface elevation will easily exceed the standard.
1) The dimension of the component does not meet the design requirements.
2) During the erection process, no correction was made according to the difference between the measured value and the calculated value.
3) For bridges with small span, the camber is small, which is ignored in assembly.
1) The inspection shall be carried out in strict accordance with the allowable deviation of steel structure components.
2) In the process of erection, the camber measurement shall be carried out after the installation of members and the construction of site joints, and other adjustments shall be made during the construction.
3) In the process of small assembly, the accumulated deviation shall be strictly controlled, and measures shall be taken to eliminate the influence of welding shrinkage.
5. Steel structure installation problems
(1) Pre control measures for the gap at the bottom of the steel column before hoisting the steel column, the foundation elevation shall be strictly controlled, the measurement shall be accurate, and the foundation surface shall be carefully leveled according to the measurement value; if the secondary grouting method is adopted, the pouring hole (also as the exhaust hole) shall be opened at the bottom of the column base, the uneven part at the bottom of the steel column shall be leveled by the steel plate, and the steel plate of the column base support shall be placed according to the design elevation in advance, and then the secondary grouting method shall be adopted Grouting.
(2) Pre control measures for displacement of steel column before pouring the concrete foundation, the embedded bolts shall be blocked by the fixed chuck according to the design position to prevent displacement during pouring the concrete; the reserved holes of low steel plate of the column shall be enlarged, and the reserved holes shall be made after the hole position is determined.
Pre control measures for excessive vertical deviation of column: the steel column shall be hoisted in place according to the calculated hanging point, and the hoisting method of more than two points shall be adopted. During hoisting, temporary fixation shall be carried out to prevent hoisting deformation; after the column is in place, temporary support shall be added in time; the vertical deviation shall be corrected before fixation.
All in all, only in the process of construction management, strengthen the training and study of technical personnel and workers on the standards and operation procedures, do a good job in preparation before construction, strengthen the quality control, supervision and inspection during construction, actively play the role of construction, supervision and other aspects, and do a good job in the process acceptance of each sub project, can the overall quality of the steel structure project be guaranteed.
Post time: Mar-24-2020