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How to avoid mistakes in steel structure construction

Views: 0     Author: Site Editor     Publish Time: 09-10-2017      Origin: Site

1. The positioning axis and supporting surface elevation of the foundation are out of tolerance:

The positioning axis of the foundation and the elevation of the supporting steel cylinder exceed the allowable deviation.


The reasons are as follows:

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

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

Or the use of steel ruler, theodolite, level without calibration, there are errors.

Or construction wrong drawings, axis wrong, without strict inspection.

Or if the foundation bearing surface is not plastered and leveled twice, the concrete will shrink and sink.

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

Because 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 structural steel construction installation project.


Avoiding measures:

(1) The accuracy of basic survey control network, instruments and measuring tools used for 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 for steel structure construction must be firmly supported with sufficient strength and rigidity. When pouring concrete, cutting and vibrating, it is necessary to prevent from striking the formwork and causing displacement. In the process of concrete pouring, the positioning axis and elevation shall be checked regularly with measuring tools or suspension lines. If any deviation is found, the pouring and vibration shall be stopped, and the work shall be carried out after reinforcement and adjustment. Before the final setting of concrete, the surface of foundation concrete shall be plastered and leveled twice. For the embedded steel plate or bearing, the elevation and levelness shall be aligned twice, and the concrete at the bottom shall be dense. The steel plate or support of foundation support column shall be provided with necessary fixing devices to ensure correct position and elevation.

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


2. Foundation anchor bolt thread damage:

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


The causes of bolt thread damage are as follows:

Anchor bolts are impacted or improperly kept during transportation, loading and unpacking, resulting in serious thread corrosion.

Or the bolts were not protected after burying and were damaged by outside.

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

Or the bolt is used as the binding point of the pulling force of the traction rope.

Due to the damage of bolt thread, it is impossible to screw in nuts to fasten steel columns and other components, which affects the transmission and stability of structural force.


Avoiding measures:

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

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

(3) The screw thread of the bolt has been damaged, and the following treatment methods can be adopted: when the damaged length of the screw thread does not exceed its effective length, the steel file can be used to trim the screw thread, so as to smoothly screw in the nut. When the length of thread damage of local foot bolt exceeds the specified effective length, the length of original thread section can be cut by gas cutting; Then, with the same material and specification as the original bolt, one end of the bolt is processed into thread, and the butt end section is made into 30º-- 45º. After butt welding with the lower end of the groove, the corresponding diameter specification and length of the steel casing sleeve into the joint, welding reinforcement. After casing reinforcement for steel work in construction, the diameter of the bolt will be larger than that of the base plate, which can be solved by appropriately enlarging the diameter of the base plate.


3. The setting of mortar 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 reasons are as follows:

The surface of the foundation is not treated and leveled, so that the base plate can not bear the force smoothly, and the surface is uneven and uneven;

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

If the setting of open base plate does not meet the requirements, it can not transfer the load evenly, which will reduce the mechanical performance of the column and affect the stability of the superstructure.


Avoiding measures:

(1) In order to make the base plate group transmit the 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, the base plate, the base plate and the foundation should be arranged in the center of the steel plate and the stress concentration position 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 to avoid partial bias Concentrated stress or deformation of the base plate occurs when the anchor bolts are tightened.

(3) The area of the base plate directly bearing the load should meet the needs of the stress, which should be determined by calculation, and the area should not be too large or too small. Too large will cause waste, too small will cause local concentrated overload of foundation and affect the overall and uniform stress of foundation. The thickness of the base plate is generally within the range of 4 ~ 25 mm, each group is no more than 3 pieces. The base plate has a 10 ~ 12 mm thick steel plate, the length of the base plate is 100 ~ 300 mm, and the width is 50 ~ 120 mm. When setting the mortar, use non shrinkage cement mortar with strength not lower than 30MPa. As the steel column is mainly installed with cushion plate to adjust the elevation and levelness, the elevation and levelness shall be found when grouting, and the allowable deviation shall comply with the specification, and the supervision shall be strengthened. Before the base plate is grouted, the rust, oil stain and burr on the surface of the base plate shall be cleaned, so that the base plate can be firmly combined with the concrete when grouted and grouted; 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, so the installation is carried out directly. In this way, there may be out of tolerance without repair, which will cause structural installation difficulties, increase the steel column installation stress and affect the installation accuracy, and even cause quality hazards.


Avoiding 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 pre checked. If the deviation is found, measures shall be taken to correct and adjust to the allowable deviation range of the specification. For elevation inspection, the measured data shall be compared with the pre inspection data of steel column size and elevation, and the error of the two shall be eliminated when the support base slurry pad or anchor bolt nut is adjusted. The allowable deviation of foundation support surface, anchor bolt position and base slurry pad shall meet the requirements of the specification. The quality of foundation concrete shall be dealt with in accordance with relevant regulations.


5. Don't check the dimension of steel members, deal with deformation and quality defects before installation

Before the installation of the structure, the external dimensions of the steel members are not checked, and the deformation and quality defects of the members are handled.

Although the steel components have passed the quality inspection before they are processed in the factory, they may fail to be inspected, or new deformation and damage may occur in the transportation and stacking of the components. If the review is not carried out before the installation, these problems can not be dealt with in time before the installation, which will affect the installation quality of the steel structure and cause installation difficulties or permanent quality defects.


Avoiding measures:

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

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

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 the welding area of the component and the friction surface of the high-strength bolt connection meet the requirements and whether it is polluted.

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

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

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


6. The perpendicularity of steel column installation is out of tolerance:

The verticality deviation of steel column exceeds the allowable value in design or code

When the steel column is manufactured, the deformation control measures are not taken or the bending deformation is 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 procedure, the roof panel is bent and deformed under the action of temperature, wind and external force.

Or there is deviation in the span size of the roof truss, the external force is used to force the connection during the installation, resulting in the over deviation of the verticality of the steel column.

This will lead to the deflection of the steel column and affect the bearing capacity and stability.


Avoiding 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. When transporting and stacking steel columns, the supporting points should be appropriate to prevent bending deformation under the action of self weight. The out of plane stiffness of long column 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 steel roof truss exceeds the deviation, it should 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 above the column base plate should be aligned with the foundation line, so as to prevent the deviation of span size, which will lead to the horizontal tension or thrust when the column head is installed and connected with the roof truss, so as to make the column body bending and deformation, and carry out appropriate control.

(3) When the roof slab is hoisted after the connection and installation of the steel column and the tail-stock, it should be carried out symmetrically and synchronously from the edge of the two slopes in the center of the top chord to the middle, so as to prevent the bending deformation of the steel column caused by the lateral concentrated pressure generated by the one slope. Without the permission of the design, the steel column and other connected components shall not be used for horizontal dragging or vertical hoisting of heavy components and equipment, and the column bending deformation or damage to the connecting structure shall be prevented.

(4) If the bending steel column is elastic deformation, it can be restored to its original state after the external pressure is removed; 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 correction, so as to reduce the load-bearing gravity, and then fixing one side reaction frame at the bending part, and using jack for correction. If the rigidity of the steel column is large, it can be corrected by heating the bending convex surface with oxyacetylene flame, and then applying jacking force.


7. Steel column installation height is out of tolerance

Height dimension or relative position of steel column after installation (±) The elevation dimension is out of tolerance, which makes the difference between the total height of each column and the height deviation of the bracket.

The reasons are as follows

Foundation elevation is incorrect or deviation occurs.

The length and dimension of steel column during the production stage are out of tolerance.

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

Because of the over tolerance, it is difficult to install and adjust the components connected with it, which makes it difficult to correct and takes time.

Avoiding measures:

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

(2) During the manufacturing process of steel column, the length and size (including the total length and the length of each position specified in the design, the length and size within the allowable positive and negative deviation range, and the positive excess value not allowed) and the correct size of the total length and bracket of the steel column without contact point shall be strictly controlled. The latter can be adopted to weld the column body first, and the column base plate and column head plate shall not be welded temporarily, In case of out of tolerance, adjust before welding the base plate or upper column head plate of the column, and finally weld the base plate and column head plate of the column.

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