1、 The positioning axis and supporting surface elevation of foundation are out of tolerance

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

The causes are as follows:

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

The foundation formwork support is not firm, the pouring concrete blanking is too high, the concrete vibration and impact, so that the formwork displacement, resulting in the datum line deviation.

Or the use of steel ruler, theodolite, level without verification, there is error.

Or the construction of wrong drawings, axis wrong, not strictly checked.

Or the bearing surface of the foundation has not been plastered and leveled for the second time, and the concrete settlement shrinks and sinks.

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

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

Preventive measures:

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

(2) The foundation formwork must be firmly supported with sufficient strength and rigidity.When pouring concrete and vibrating, it is necessary to prevent the impact of formwork and displacement.In the process of concrete pouring, the positioning axis and elevation shall be checked regularly with measuring tools or suspension wire. If any deviation is found, 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.The elevation and levelness of the embedded steel plate or support shall be adjusted twice, and the bottom concrete shall be dense.The steel plate or support of foundation supporting column shall be provided with necessary fixing device to ensure the correct position and elevation.

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

2、 Foundation anchor bolt thread damage

The screw thread of foundation anchor bolt is damaged, and it is impossible to screw nut and fasten during column installation.

The causes of bolt thread damage are as follows:

The anchor bolts are seriously rusted due to impact or improper storage during transportation, loading and unpacking.

Or the bolt was damaged by external scale without protective measures after embedding.

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

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

Due to the damage of bolt thread, 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.

Preventive measures:

(1) When the anchor bolts are transported, packed and unpacked, the thread protection shall be strengthened. After being smeared with industrial vaseline oil, it shall be wrapped and bound with plastic film to prevent thread damage and corrosion.They should be stored separately and should not be mixed with other parts or components to avoid damaging the thread due to mutual impact.

(2) After the anchor bolt is embedded, it shall not be used as the fulcrum for bending processing, 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 thread from being damaged by horizontal lateral impact force.

(3) The bolt thread has been damaged, the following treatment methods can be taken: when the damaged length of the thread does not exceed its effective length, the steel file can be used to trim the thread until the nut is smoothly screwed in.When the damaged length of the local foot bolt thread exceeds the effective length specified, the length of the original thread can be cut by gas cutting; one end of the thread is processed into a thread with the same material and specification as the original bolt, and a 30 ° – 45 ° groove is made at the end section of the butt joint. After butt welding with the lower end, the steel sleeve with the corresponding diameter, specification and length is sheathed into the jointWelding reinforcement is carried out.After casing reinforcement, the diameter of bolt will be larger than the hole diameter of base plate, so the diameter of column base plate can be enlarged appropriately.

3、 The setting of grouting base plate of column base does not meet the requirements

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

The causes are as follows:

If the foundation surface is not treated and leveled, the base plate can not be stably stressed, and the surface is uneven and uneven;

The base plate is not reasonably arranged according to the stress requirements, so that the base, the base plate and the foundation can not bear uniform pressure, resulting in uneven settlement of the base slurry, and the elevation and levelness can not meet the requirements.

The bearing capacity of the column will be reduced and the stability of the upper structure will be affected if the setting of the open base plate does not meet the requirements and the effect of uniform load transfer can not be achieved.

Preventive measures:

(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 slurry on the foundation surface.The uneven foundation surface shall be chiseled and leveled.

(2) The location and distribution of the base plate should be correct. Generally, according to the stress area of the steel column base plate, it should be arranged in the center of the steel plate and the stress concentration parts on both sides or near the two sides of the anchor bolt, so that the base plate, the base plate and the foundation can fully bear the pressure load and bear the force uniformly together, so as to avoid partial bias pressure, concentrated stress or the bottom plate under the anchor bolt fastening stressThe deformation occurs when.

(3) The area of the base plate directly bearing the load should meet the stress demand and be determined by calculation. The area should not be too large or too small.If it is too large, it will cause waste, and if it is too small, it will overload the foundation locally, which will affect the overall and uniform stress of the foundation.The thickness of the base plate is generally within the range of 4 ~ 25 mm, with no more than 3 pieces in each group. The base plate has a steel plate with a thickness of 10 ~ 12 mm, with a length of 100 ~ 300 mm and a width of 50 ~ 120 mm.Non shrinkage cement mortar with strength not lower than 30MPa is used for grouting.Since the steel column is mainly installed against the cushion plate to adjust the elevation and levelness, the elevation and levelness shall be found during grouting, and the allowable deviation shall comply with the specification, and the supervision shall be strengthened.Before grouting, the rust, oil stain and processing burr on the surface of the base plate shall be cleaned, so as to ensure that the base plate can be firmly combined with the concrete during grouting and grouting; the length of the base plate group exposed to the outside of the base plate edge is about 10 ~ 20 mm.

4、 Before the installation of steel column, the foundation is directly installed without inspection

Before the installation of steel column, the axis and elevation of the foundation, the position and elevation of the anchor bolt and the concrete quality of the foundation are not checked in advance, and the installation is carried out directly.In this way, it may be out of tolerance and not be repaired, which will cause structural installation difficulties, increase the steel column installation stress and affect the installation accuracy, and even cause quality hazards.

Preventive measures:

Before the installation of steel column, the positioning control line, foundation axis, elevation, anchor bolt position, elevation and concrete quality of foundation shall be inspected in advance. Measures shall be taken to correct the out of tolerance and adjust it to the allowable deviation range of the specification.For elevation inspection, the measured data shall be compared with the pre inspection measured data of steel column size and elevation, and the error between the two shall be eliminated during the adjustment of bearing base plate or anchor bolt nut. The allowable deviation of foundation bearing surface, anchor bolt position and grouting base plate shall meet the requirements of specification.The quality problems of foundation concrete should be treated according to relevant regulations.

5、 Before installation, do not check the overall dimensions of steel members, handle deformation and quality defects

Before structural installation, the overall dimensions of steel members are not checked to deal with the deformation and quality defects of components.

Although the steel members have passed the quality inspection before leaving the factory, they may be missed inspection, or the components may have new deformation and damage during the delivery, transportation and stacking. If they are not rechecked before installation, these problems can not be handled in time before installation, which will affect the installation quality of steel structures and cause installation difficulties or permanent quality defects. 

Preventive measures:

Before the installation of steel members, the steel members shall be carefully inspected in advance

It includes checking the model and quantity of components, the overall dimensions of components and the relevant dimensions between bearing surfaces and installation holes, and marking the datum line of component axis.Check whether there is deformation of the component, and correct and repair the deformation error.

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

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

Whether the surface of the component is polluted and whether the paint falls off.

The pre inspection record shall be made for the pre inspection of components; for the components with deformation and defects exceeding the allowable deviation, rectification and repair shall be carried out on the ground before installation, and the installation can be carried out only after the components are qualified.

6、 Steel column installation verticality out of tolerance

The perpendicularity deviation of steel column exceeds the value allowed by design or specification

No deformation control measures were taken during the fabrication of steel column, or the bending deformation was not straightened.

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

Or due to the unreasonable hoisting technology and hoisting procedure of roof panel, the bending deformation is caused by temperature, wind force and external force.

Or roof truss span size deviation, installation with external force forced connection, resulting in steel column verticality deviation.

This will lead to the deviation of the steel column when it is stressed, and affect the bearing capacity and stability.

Preventive measures:

(1) Anti deformation measures shall be taken for assembly and welding of steel column, and the deformation during fabrication shall be corrected in time.During transportation and stacking of steel columns, the supporting points shall be appropriate to prevent bending deformation under self weight.The stiffness of the long column out of plane is poor, so the lifting point should be selected at 2 / 3 of the total length of the column to prevent deformation.If the span size of the steel roof truss is out of tolerance, it should be corrected first and then installed to prevent forced connection and bending deformation of the column body.

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

(3) When the roof panel is hoisted after the steel column is connected with the tailstock, the two slope edges of the center of the upper chord should be symmetrically and synchronously moved to the middle to prevent the bending deformation of the steel column caused by the lateral concentrated pressure caused by the one slope.Without design permission, steel columns and other connected components shall not be used for horizontal dragging or vertical hoisting of heavier components and equipment. Bending deformation of columns or damage of connection structures shall be prevented.

(4) If it is elastic deformation, it can be restored to its original state after cutting off the external pressure, and it can be corrected without external force; if it is plastic deformation, temporary support can be added above or at the top of the bending part of the steel column before correction to reduce its bearing gravity, and then fix one side of the counter force frame at the bending position, using the kilogramIf the rigidity of the steel column is large, it needs to be corrected by heating the curved convex surface with oxyacetylene flame and then applying jacking force.

7、 Steel column installation height out of tolerance

After installation, the height dimension or relative position (±) elevation dimension of the steel column is out of tolerance, which makes the total height of each column and the height deviation of corbel inconsistent.

The causes are as follows:

The foundation elevation is incorrect or has deviation.

The length of steel column is 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 lead to the positive or negative out of tolerance of the height or elevation dimension of the steel column after installation.

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

Preventive measures:

(1) During the foundation construction, the elevation size should be strictly controlled to ensure the elevation accuracy.The elevation size of the foundation surface should be adjusted according to the actual length of the steel column or the elevation dimension of the bracket bearing surface, so that the height and elevation dimension of the steel column after installation are consistent.

(2) During the production process of steel column, the length size (including the total length specified in the design and the length size of each position, the length size within the allowable positive and negative deviation range and the positive out of tolerance difference) and the full length of steel column without joint and the size of bracket shall be correct. The latter can be welded first, and the column base plate and column head plate shall not be welded temporarilyIn case of out of tolerance, the adjustment shall be made before welding the base plate or upper column head plate of the column, and finally the column base plate and column head plate shall be welded.