Nowadays, steel structure projects are increasingly favored by more construction units. When undertaking the steel structure installation project, how can we ensure the construction is fast and good? Here is a summary of your common disease prevention methods, take a look at it.

 

 

Installation deviation problem

      This chapter focuses on the steel column installation elevation oversized, column verticality out of tolerance, crane beam verticality and horizontal deviation.

1. Steel column installation elevation size difference

【Phenomenon】 After the installation of steel column elevation size, affect the installation of other components of the difficulty of adjustment.

【Reason】 The basic elevation is not correct, before installation, the coordinates and elevation inspection of the foundation are not accepted or handled properly.

Prevention

(1) The construction shall be carried out in strict accordance with the provisions of the design drawings to ensure the inspection and acceptance of the steel column foundation before installation and the matching of the basic elevation and the actual length of the steel columns or the support surface of the bracket so that the elevation of each steel column after installation The same size, not too high or too low.

(2) According to the following methods to deal with the adjustment of the basic elevation: 1) The total length of the steel column should meet the quality requirements, the basic support surface can be irrigated to the design elevation, the installation does not make direct adjustments in place; 2) Watering first to the design elevation 40 ~ 60mm lower than the location, and then use fine stone concrete leveling to the design elevation, the second watering leveling layer should make the old and new concrete closely combined to achieve the basic design strength, will not form a sandwich; 3) Lower than the design elevation 40 ~ 60mm, the steel column installed in the adjustment of the horn and then pouring concrete; 4) according to the design elevation embedment of the column foot bearing (steel, rail, etc.) until the column after installation Watering cement mortar.

2. Steel column over tolerance

【Phenomenon】 Vertical deviation after installation of steel column exceeds the allowable value of the standard, in addition to its own structure to withstand the impact of pressure intensity, but also affect the other components of the installation.

【the reason】

(1) The steel column itself is improperly controlled by deformation during manufacture, and the upper bend of the column body is not treated.

(2) Check the quality of the steel column before installation, if deformation defects should be dealt with before installation.

(3) Under the action of external force, the strength and stability of the easily deformed steel column are not calculated, and no reinforcement measures are taken during hoisting. In addition, environmental temperature, wind, sunlight and other external influences and welding deformation and other factors are related.

Prevention

(1) In the production, installation, welding operations should take measures to prevent deformation of the steel columns have been produced and to be installed in place when the support pad is good, the process of transport so as to prevent bending due to self-weight Moment caused by deformation; lifting the vertical lifting point should generally choose the full length of the column 2/3 position.

(2) When correcting the verticality of the steel column, fix the two side columns as the reference column and correct the remaining columns with respect to the vertical and horizontal axes. When adjusting the verticality, calculate the actual value of the steel column and its size according to the formula Horn to increase or decrease the thickness, to adjust its verticality.

(3) When adjusting the verticality of steel columns, it should be noted that the deformation under the effect of temperature difference and wind force should generally be carried out in the morning when the temperature is low or at low sun exposure. It is forbidden to carry out the roofing when the steel column is connected with the roof trusses. It should be carried out synchronously from the two slope edges of the winding center to the middle.

3. Crane vertical and horizontal deviation degree

【Phenomenon】 In construction, the verticality of crane beam is often encountered. The horizontalness and the relative elevation of two crane beams exceed the allowable deviation, which affects the installation of crane track.

【the reason】

(1) The quality of crane beam itself does not meet the requirements.

(2) steel production and installation did not meet the requirements.

(3) The elevation and horizontality of the bracket surface of the steel column supporting crane beam lead to the height or horizontalness of the plane of the crane beam and the relative elevation difference between the two crane beams.

Prevention

(1) In the production of steel columns, the bottom of the steel column to the seat surface size and distortion control strictly.

(2) Adjust the verticality of the steel column and the level of the bracket when installing and positioning. Pre-measure the height of the support of the crane beam and the height of the bracket from the bottom of the column. Use the horn on the foundation plane or the support surface of the bracket Pre-adjusted.

(3) During installation, the centerline of the upper flange plane of the beam should be properly aligned and adjusted. When the relevant dimensions are meticulously re-tested to meet the requirements of the crane track installation, the general control of this value should be based on the installed Crane beam no load, without bending under prevail, if the arch after installation is too large, will affect the next crane track installation.

 

Improper installation method

      This section focuses on the quality of the foundation grout does not meet the requirements, steel truss arch does not meet the requirements, the quality of the crane track installation does not meet the requirements.

1. The quality of the basic grout does not meet the requirements

【Phenomenon】 There are gaps between the steel column foundation and the steel column bottom after the secondary grouting. The mortar does not fill well, especially in the center of the bottom plane.

【Reason】 The distance between the bottom surface of the steel column and the surface on the base is too small, the mortar is not easy to fill, improper matching of the grouted material, improper operation technology and inappropriate selection of tools.

Prevention

(1) Maintain the basic support surface When using horns to adjust the elevation so that the distance between the underside of the steel column floor and not less than 40mm, in order to facilitate grouting and filling the gap.

(2) The cement mortar used for secondary grouting should be one grade higher than that of the original basic concrete. In winter construction, antifreeze and early strength admixture should be incorporated into the mortar to prevent the occurrence of frost damage or the slow increase of strength. The basic surface of the dirt treatment clean, wet with water and then the original surface of the original watering the mortar.

(3) For some of the grouting gap smaller steel column foundation, the column can be used as a hole in the perforated steel plate, the base plate length and width are more than 1m can be so dealt with, when the health period is reached, and then Steel column floor openings with a small steel cover welding death.

(4) According to the design requirements of the need to do the grout strength test, the same batch of construction should be based on the use of four materials, the same mix, the same method of construction two mortar specimens, a group of steel structures before lifting for strength test, Another group of specimens for 28d standard conservation, age strength for future reference.

2. Steel roof truss does not meet the requirements

【Phenomenon】 The crown is too large, affecting the connection of steel columns, so that the size of the upper part of the negative deviation; camber deflection under the load not only affects the force, but also increase the upper span of the steel span size and vertical deviation.

【the reason】

(1) Production is not processed according to the provisions of the camber or camber deformation untreated.

(2) Roof truss is not reinforced, the choice of lifting point is not correct.

Prevention

(1) In the production of the required span should be arch.

(2) In the production of all cambers and other structural deformation, to be corrected to meet the requirements before lifting.

(3) Select a reasonable hoisting scheme before hoisting, reinforce according to different span sizes, and select the correct hoisting point to avoid the problem of overlarge or undergone deformation on the arch of the steel truss.

3. Crane track installation quality does not meet the requirements

【Phenomenon】 After installing the crane track, level, straightness and the relative elevation difference between the two tracks, the center of the crane track center and crane beam super-tolerance and so on.

【the reason】

(1) Due to the quality defects of the crane beam installation, the elevation of the crane track will lead to exceeding the level error.

(2) Crane tracks are installed without correction prior to installation or have not been rectified, but not required.

(3) The elevation, horizontalness and centerline coordinates of the crane beam are not checked before installation of the crane track.

Prevention

(1) Prior to the installation of the crane track, check and check the elevation, horizontalness and straight line of the crane beam. At the same time, the joints of the two tracks should be staggered with each other along the whole length of the track, and should not be concentrated in the same position.

(2) Correct the bending deformation of the track before the installation of the crane track.

(3) Loose bolts should be used to fix the rail. Generally, add a spring washer or anti-loosening nut under the nut to prevent the crane from being loosened by external force and vibration during use.

(4) When the track is installed on the concrete crane beam, the horn under the track should be flat to ensure close contact with the bottom of the track. The contact area should be more than 60%. The clearance between the cushion and the concrete crane beam should be more than 25mm. Shrinkage of cement mortar filling; should be welded between the solid plate. In the case of steel beams, the horn should be welded to the crane beam.

 

Welding problems

      This section focuses on cutting edge unprocessed or up to the specification requirements, weld defects.

1. Cutting edge unprocessed or up to the specification

【Phenomenon】 steel cutting surface exists more than 1mm of the edge, bending inequality defects.

【Reason】 Gas cutting process is not standardized, cutting process does not meet the requirements.

Prevention

(1) Check before gas cutting Confirm that the entire gas cutting system equipment is operating normally, the pressure gauge is normal and nondestructive, the cutting nozzle airflow is smooth and the torch angle is correct.

(2) Select the correct process parameters based on the machine and plate thickness.

(3) Gas cutting to adjust the shape of the oxygen jet, so that its outline is clear, high-power, cutting torch move to maintain uniform speed, cutting nozzle surface from the tip of flame heart 2 ~ 5mm is appropriate.

Weld connection defects

【Phenomenon】 Bad forming of weld, crater, crack, welding knob, unmelted, incomplete penetration, bite meat, slag inclusion, stoma, base material abrasion and so on.

(1) Stoma

【Reason】 1) Electrode damp; 2) Acidic electrode baking temperature is too high, the weldment is not clean; 3) The current is too large to make the electrode red; 4) The protective gas is impure;

[Control] 1) Before welding the surface of the weld groove must be cleaned of impurities; 2) a reasonable choice of welding methods; 3) welding materials must be properly baked; 4) wind speed in the environment should take measures to prevent wind welding.

(2) slag

【Reason】 1) The quality of the welding material is not good, the slag is too thick; 2) The corrosion or other impurities in the weldment or groove is not cleaned; 3) When the layering welding, Clean it to the next level of welding; 4) current is too small, the welding speed too fast.

[Control] 1) the use of good performance welding rod; 2) choose a reasonable welding before welding specifications and groove size; 3) bevel on both sides to be cleaned; 4) in the multi-layer welding to thoroughly clean each layer slag.

(3) bite the meat

【Reason】 1) The current is too large; 2) The arc is too long or wrong angle; 3) The welding position is improper.

[Prevention] 1) Correct choice of welding current and welding speed during welding; 2) Correct transport method; 3) Appropriate welding rod angle and arc length.

(4) not welded

【Reason】 1) The welding current is too small, the welding speed is too fast; 2) The groove angle is too small, the welding angle is improper; 3) The electrode is eccentric; 4) There are rust and other unclean clean impurities; 6) When positioning welding welding material does not match the size of the welding horn and solder joint spacing is not standardized, affecting the weld forming, resulting in incomplete penetration, not fusion defects.

[Control] 1) Select a reasonable welding specifications; 2) Correct choice of groove type, size, angle and gap; 3) The appropriate process and the correct method of operation; 4) Welding, positioning welding using the same welding materials and formal welding requirements of the root of the weld should be welded to the outside of the groove groove positioning welding, weld seam with holes and cracks, after the eradication of re-welding.

 

Material problems

     This chapter focuses on component transportation, stacking deformation, component span inaccuracy.

1. Component transport, stacking deformation

【Phenomenon】 Deformation of components during transportation or stacking, appear dead or slow bend.

【Reason】 (1) The components are deformed due to welding and generally appear to be crooked; (2) The components are deformed due to collision during transportation, and generally show dead curves; (3) The component pads are unreasonable, Mat is not vertical, etc., sinking place deposition, so that the components have dead or slow bending deformation.

Prevention

(1) dead bending deformation of components, the general use of mechanical correction of governance, that is, with jack or other tools to be corrected or supplemented by oxyacetylene flame roasting, depending on the stiffness of the structure may be, the main tool should be corrected mainly oxyacetylene Baking supplemented, can achieve good results.

(2) When the structure is bent and deformed gently, the oxyacetylene flame can be used for heating and correcting. Generally, large oxyacetylene flame gun is used for roasting. Flame baking, the linear heating and more for the correction of large deformation or greater rigidity of the structure; Triangle heating is often used to correct thicker, more rigid components of the bending deformation.

2. Component span is not accurate

[Phenomenon] component span value is greater than or less than the design value.

【Reason】 (1) The size of the component is too large or too small; (2) The cumulative deviation of the small component causes the span not to be allowed; (3) The steel ruler is not unified.

[Prevention] (1) due to the production of components deviations, arch and span values ​​conflict, we should first meet the arch value. In order to ensure the accuracy of arch-span and span value, the precision of the size of components must be inspected in strict accordance with GB 50205-2001 "Code for Construction Quality Acceptance of Steel Structures"; (2) Members in the production, assembly, lifting the steel used in the ruler should be unified.

Source: Steel Structure Online