Common problems and preventive measures of steel structure installation

1. The elevation of positioning axis and supporting surface of foundation is out of tolerance.

The elevation of the positioning axis and supporting steel cylinder surface of the foundation exceeds the allowable deviation value of the specification.

The causes are as follows:

There are errors and deviations in the foundation survey control network, foundation survey setting out and elevation finding.

The foundation formwork is not set firmly, the pouring concrete is too high, and the concrete is vibrated and hit, which causes the formwork displacement and the datum line deviation.

Or the steel ruler, theodolite and level are not calibrated, so there is error.

Or construction stuff read the wrong drawings, axis wrong, without strict inspection.

Or the foundation bearing surface has not been plastered and leveled twice, and the concrete settlement shrinks and sinks.

Or the embedded steel plate (or support) is not fixed.

As the foundation positioning axis and supporting surface are out of tolerance, the column installation axis and supporting elevation will be out of tolerance, which will affect the quality of the whole steel structure installation project.

Precautions:

(1) The accuracy of the instruments and measuring tools used in the basic survey control network, basic survey setting out and leveling shall be accurate. Before use, they must be checked or verified by the measurement department. If problems are found, they shall be adjusted in time to prevent errors or accumulated errors, resulting in axis and elevation exceeding the allowable deviation.

(2) The foundation formwork must be firmly erected with sufficient strength and rigidity. When pouring concrete and vibrating, it is necessary to prevent striking the formwork and generating displacement. In the process of concrete pouring, the positioning axis and elevation shall be checked regularly with measuring tools or suspension lines. In case of any deviation, the pouring and vibration shall be stopped and the reinforcement and adjustment shall be carried out after elimination. Before the final setting of concrete, the surface of foundation concrete shall be plastered and leveled twice. For the embedded steel plate or support, the elevation and levelness shall be aligned twice, and the bottom concrete shall be ensured to be dense. The steel plate or support of the foundation support column shall be provided with necessary fixing devices to ensure the correct position and elevation.

(3) If the vertical and horizontal axis of the foundation, the steel plate of the column bearing surface or the elevation and levelness of the support are out of tolerance, it shall be raised according to the deviation. When the out of tolerance is not serious, it can be solved by shifting the column base, expanding the hole and filling the base plate. If the out of tolerance is serious and cannot be adjusted, it shall be studied together with relevant departments, and the feasible correction scheme shall be determined before handling.

2. Foundation anchor bolt thread is damaged

The foundation anchor bolt thread is damaged, and the column cannot be screwed and tightened during installation.

The causes of bolt thread damage are as follows:

The anchor bolt is impacted or improperly kept during transportation when loading and unpacking, which causes serious corrosion of the thread.

Or the bolts are damaged by external scale without protection measures.

Or the bolt is used as the electric welding zero line on site, and the thread is damaged by the arc burn.

Or use the bolt as the binding point of traction rope tension.

Because the bolt thread is damaged, it is impossible to screw in the nut to fasten the steel column and other components, which affects the transmission and stability of structural force

Precautions:

(1) During the transportation, loading and unpacking of anchor bolts, the protection of the threads shall be strengthened. After the application of industrial vaseline oil, the threads shall be wrapped and bound with plastic film to prevent damage and corrosion. It shall be stored separately and shall not be mixed with other parts to avoid damage to threads due to mutual impact.

(2) After the anchor bolt is buried, it shall not be used as the fulcrum of bending processing or as the neutral line of electric welding machine or the binding point of traction force. When hoisting components, proper operation shall be carried out to prevent the horizontal lateral impact force from damaging the thread.

(3) If the thread of the bolt has been damaged, the following measures can be taken: when the damaged length of the thread does not exceed its effective length, the thread can be trimmed with a steel file until the nut is screwed in smoothly. If the damaged length of the thread of the local foot bolt exceeds the specified effective length, the length of the large original thread section can be cut off by gas cutting; then, one end of the same material and specification as the original bolt can be processed into a thread, and a groove of 30 ° - 45 ° can be made on the cross section of the butt end and the lower end can be butt welded, and then the steel sleeve of corresponding diameter, specification and length can be put into the joint Welding reinforcement and reinforcement shall be carried out. After reinforcement by casing, the diameter of bolt will be larger than the hole diameter of base plate, which can be solved by appropriately expanding the diameter of column base plate.

3. The setting of base plate of column base is not in conformity with the requirements

The mortar base plate of column base is set at will, and the elevation, levelness and position do not meet the design and specification requirements.

The causes are as follows:

The pad is laid on the foundation surface without treatment and leveling, so that the pad can not be stably stressed, and the surface is uneven with different heights;

The base plate is not arranged reasonably according to the stress requirements, so that the base, the base plate and the foundation can not bear the uniform pressure, so that the base slurry sinks unevenly, and the elevation and levelness can not meet the requirements.

If the setting of the opening base plate is not in accordance with the requirements and the load is not evenly transferred, the mechanical performance of the column will be reduced and the stability of the superstructure will be affected.

Precautions:

(1) In order to make the base plate group transmit force to the foundation smoothly, the base plate should be closely combined with the base mortar of the foundation surface. The uneven foundation surface shall be chiseled and leveled.

(2) The setting position and distribution of the base plate shall be correct. Generally, it shall be arranged in the center of the steel plate and the stress concentration part on both sides or near both sides of the anchor bolt according to the stress area of the steel column base plate, so that the base plate and the foundation can fully bear the pressure load, uniformly bear the force together, and avoid partial bias, concentrated stress or fastening stress of the base plate on the anchor bolt Deformation occurs.

(3) The area of the base plate directly bearing the load shall meet the stress requirements, which shall be determined by calculation. The area shall not be too large or too small. Too large causes waste, too small easily causes local concentrated overload of the foundation, which affects the overall and even stress of the foundation. The thickness of the base plate is generally used within 4-25 mm, with no more than 3 plates in each group. There is an additional 10-12 mm thick steel plate for the mortar base plate, with the length of 100-300 mm and the width of 50-120 mm. The strength of 30 MPa non shrinkage cement mortar shall not be lower than that of the base mortar. Since the steel column is installed with the main backing plate to adjust the elevation and levelness, the elevation and levelness shall be found well when setting the slurry, and the allowable deviation shall meet the specifications, and the supervision shall be strengthened. The rust, oil stain and processing burr on the surface of the base plate shall be cleaned before the base plate is grouted, so that it can be firmly combined with the concrete when the base plate is grouted and grouted; the length of the base plate group exposed to the outside of the edge of the base plate after the base plate is grouted is about 10 ~ 20mm.

4. Install the steel column directly without checking the foundation before installation

Before the installation of steel column, the axis, elevation, position and elevation of foundation bolt and concrete quality of foundation shall be directly installed without prior inspection. In this way, it is possible that the out of tolerance will not be repaired, which will make the structure installation difficult, increase the installation stress of steel column, affect the installation accuracy, and even cause quality problems.

Precautions:

Before the installation of steel column, the positioning control line, foundation axis, elevation, anchor bolt position, elevation and concrete quality of the foundation of the building shall be checked in advance. If the deviation is found, measures shall be taken to correct it and adjust it to the allowable deviation range of the specification. For elevation inspection, the measured data shall be compared with the measured data of steel column size and elevation pre inspection one by one, and the error between the two shall be eliminated during the adjustment of bearing pedestal slurry base plate or anchor bolt nut. The allowable deviation of foundation bearing surface, anchor bolt position and pedestal slurry base plate shall meet the requirements of specifications. The quality problems of foundation concrete shall be handled according to relevant regulations.

5. Do not check the external dimension of steel members, handle deformation and quality defects before installation

Before the installation of the steel structure, the external dimensions of the steel members shall not be inspected, and the deformation and quality defects of the members shall be handled. Since the steel members have passed the quality inspection before they are processed and delivered from the factory. However, it is possible to miss the inspection, or new deformation and damage may occur in the delivery, transportation and stacking of components. If there is no recheck before installation, these problems can not be dealt with in time before installation, which will affect the installation quality of steel structure, causing installation difficulties or permanent quality defects.

Precautions:

Before the installation of steel members, the steel members shall be carefully pre inspected:

It includes checking the model and quantity of the component, the external dimension of the component and the relevant dimensions between the supporting surfaces and the installation holes, and marking the reference line of the component axis. Check whether there is deformation in the component, and correct and repair the deformation error.

Whether the connecting plate, splint and other accessories of the component are complete, and whether the position and size are accurate. Inspect whether the surface quality of component welding area and friction surface of high-strength bolt connection meet the requirements and are polluted.

Whether the component nodes are complete and whether the center of gravity position of main components is marked.

Whether the component surface is polluted, whether the paint falls off, etc.

Pre inspection records shall be made for component pre inspection; components with deformation and defects exceeding the allowable deviation shall be corrected and repaired on the ground before installation, and can be installed only after they are qualified.

6. Steel column installation perpendicularity out of tolerance

The perpendicularity deviation of steel column exceeds the value allowed by the design or code. The causes are as follows:

During the fabrication of steel column, no deformation control measures have been taken or bending deformation has not been straightened.

Or the length of the column is large, the rigidity is poor, and elastic or plastic deformation occurs under the action of external force.

Or due to the unreasonable hoisting process and procedures, the roof slab is bent and deformed due to the effects of temperature, wind force and external force.

Or there is deviation in the span size of the roof truss, and the external force is used to force the connection during the installation, which causes the verticality of the steel column to exceed the deviation.

The results show that the steel column will shift when it is loaded, which will affect the bearing capacity and stability.

Precautions:

(1) Anti deformation measures shall be taken for the assembly and welding of steel column during the fabrication, and the deformation during the fabrication shall be corrected in time. For transportation and stacking of steel columns, the supporting points shall be appropriate to prevent bending and deformation under the action of self weight. The out of plane rigidity of the long column is poor. The lifting point should be 2 / 3 of the total length of the column to prevent deformation. If the span size of steel roof truss exceeds the deviation, it shall be corrected before installation to prevent forced connection and bending deformation of column body.

(2) When the steel column is hoisted to the foundation plane in place, the vertical and horizontal axis on the column base plate shall be aligned with the foundation line to prevent the deviation of span size, resulting in the horizontal tension or thrust when the column head and roof truss are installed and connected, resulting in the bending and deformation of the column body, and proper control shall be carried out.

(3) When the roof panel is hoisted after the steel column is connected and installed with the tailstock, it shall be carried out symmetrically and synchronously from the two slope edges in the center of the upper chord to the middle, so as to prevent the side concentrated pressure caused by one slope, resulting in the bending deformation of the steel column. Steel columns and other connected components shall not be used for horizontal dragging or vertical hoisting of heavy components and equipment without design permission, and bending deformation of columns or damage of connecting structures shall be prevented.

(4) For the bending steel column with installed fixed perpendicularity out of tolerance, if it is elastic deformation, it can be restored to its original state after the removal of external pressure, and it can be corrected without external force; if it is plastic deformation, it can be corrected by adding temporary support above or at the top of the bending part of the steel column before the correction, so as to reduce the load-bearing gravity, and then fix one side of the bending to the reaction frame, using the jack If the rigidity of the steel column is large, it needs to be supplemented by heating the curved convex surface with oxyacetylene flame, and then applying the jacking force to get the correction.

7. Steel column installation height out of tolerance

The height dimension or relative position (±) elevation dimension of the steel column after installation is out of tolerance, so that the total height of each column and the height deviation value at the bracket are inconsistent.

The causes are as follows:

The foundation elevation is incorrect or deviated.

The length and size of the steel column in the manufacturing stage are out of tolerance.

Or when the foundation elevation is adjusted and treated during the installation, it is not combined with the actual length (height) of the steel column, which will cause the height or elevation dimension of the steel column after installation to produce positive or negative deviation.

Because of the out of tolerance, it is difficult to install and adjust the components connected with it, and it is very difficult to rectify, which is time-consuming.

Precautions:

(1) During the foundation construction, the elevation size shall be strictly controlled to ensure the elevation accuracy. The surface elevation dimension of the foundation shall be adjusted in combination with the actual length of the steel column or the elevation dimension of the bracket bearing surface, so as to make the height and elevation dimension of the steel column consistent after installation.

(2) The length dimension (including the total length specified in the design and the length dimension of each position, the length dimension controlled within the allowable plus and minus deviation range and the positive and extra difference not allowed to be generated) and the length of steel column without joint and the dimension of bracket are correct in the manufacturing process of steel column. The latter can adopt welding the column body first, and the column base plate and column head plate are not welded temporarily. Once it occurs, it is necessary to weld the column body first In case of out of tolerance. Making adjustment before welding the base plate or the upper column head plate of the column, and finally weld the column base plate and the column head plate.