In the construction of steel structure engineering, it is found that many steel structure practitioners have many blind spots and even misunderstandings on the construction quality control of steel structure on site, which leads to the actual quality control requirements not effectively implemented, and there are many quality problems in the construction process of some projects.By sorting out the relevant specifications and technical standards, and consulting the relevant senior personnel of steel structure design and construction, the common quality problems found in the construction are summarized and sorted out in order to sort out the problems, find the countermeasures, and make necessary explanations for the relevant problems combined with personal understanding, hoping to improve the construction quality of steel structure engineering together with the front-line engineering and technical personnel Quantity control level. 

Steel structure engineering construction

1、 The current steel structure codes and standards and the scope of application are not complete

 Quite a lot of steel structure front-line construction and supervision personnel know little about the steel structure related specifications, and some on-site supervisors often do not know the content and requirements of the specification; in addition, they are not familiar with the acceptance data of steel structure construction quality, and do not know how to collect, sort out and improve the process control data.

 　　1Main specifications and standards at present

 At present, China’s steel structure specifications and technical standards mainly include design and construction acceptance. Combined with the main structural forms of steel structure engineering, the main specifications involved are as follows:

 　　1）Design class

 It mainly includes code for design of steel structures (GB 50017-2003), technical code for cold-formed thin-walled steel structures (GB 50018-2002), technical specification for steel structures of light-weight buildings with gabled frames (cecs102:2002), and code for design and construction of grid structures (jgj7-91).

 It should be specially pointed out that: at present, portal frame is widely used as light steel structure type in single storey industrial buildings, and the design is mainly based on cecs102:2002. The scope of application of the code is: it is applicable to medium and light-weight steel structures with single span or multi span solid web portal frame, light roof and light external wall, no bridge crane or only lifting capacity of no more than 20tSteel structure of single storey house with working bridge crane or 3T? Suspension crane.For those structural systems which only use light steel roof or multi-storey, the code is not applicable and can not be arbitrarily applied.In addition, the scope of steel structures other than light steel is very wide, which can include all kinds of steel structures, regardless of the load, and even many contents of light steel structures. The corresponding design standards are mainly based on GB 50017-2003 (the grid structure shall be based on the grid structure design code).

 　　2）Acceptance

 It mainly includes code for acceptance of construction quality of steel structures (GB 50205-2001), standard for quality inspection and evaluation of grid structures (jgj78-91), bolt ball joints of steel grid structures (jg10-1999), welded ball joints of steel grid structures (jg11-1999), inspection and acceptance standards for steel grids (jg12-1999), design and construction acceptance specification for high strength bolt connections of steel structures (jgj82-91) and construction and Construction Engineering (jgj82-91)Technical specification for welding of steel structures (jgj81-2002).The quality acceptance of all kinds of steel structures shall be carried out according to GB 50205-2001; for grid structures, other codes and standards can be combined on the basis of GB 50205.In particular, jgj78-91 is still in effect at present. The relationship between jgj78-91 and GB 500205 can be considered as the parent code, which is very low requirement, while jgj78-91 focuses more on grid structure engineering.

　　2Construction quality control data sorting

 Many steel structure construction units are very confused about the management of construction data, and make their own acceptance forms at will. Each mode is quite different, and there is no fixed format, which is not convenient for the sorting, review and preservation of engineering data.The participating units shall strictly check the contents and requirements of “GJ: steel structure engineering” in the “construction quality acceptance data of Construction Engineering” issued by Jiangsu Provincial Construction Department.

 2、 Problems in construction drawing review

 　　1Construction drawing review opinions are not effectively implemented

 In principle, the on-site construction drawings should be the drawings that have passed the examination and have been sealed and confirmed by the review organization. However, due to the limited number of drawings confirmed by stamping, and some design units reply to the review opinions with the mode of separate design changes and original drawings, if the construction site adopts the design drawings without seal confirmation, the contents of drawing review may not be coveredImproper use of drawings.In addition, many construction units do not pay attention to the drawing review opinions, and the review documents are not sent to the construction and supervision units in time, which leads to some construction and supervision personnel working according to the incorrect drawings without knowing the contents of the drawing review.Therefore, it is necessary for the construction, construction and supervision units to take measures to strengthen the quality control in this respect, so as to ensure that the construction review content is effectively implemented in the construction process.

　　2The qualified drawings are not re submitted for review after being “optimized”

 In some large-scale steel structure projects, in order to reduce the cost and the steel structure construction unit to lower the quotation and then win the bid, there is often the so-called “optimization” phenomenon: that is, the steel structure construction unit modifies the structural design of qualified drawings, reduces the amount of steel, and then processes, manufactures and installs according to the modified drawings.As such “optimization” may lead to a significant reduction in the original safety of the structure, in order to ensure the structural safety, the “optimized” structural design drawings must be re submitted to the original construction drawing review organization for review, and the construction can be carried out only after it is qualified.

 3、 The raw materials used in steel structure engineering do not conform to the design or specification

 　　1Wrong use of steel

 Steel structure steel mainly includes carbon structural steel Q235, Low Alloy Steel 16Mn steel (Q345 steel), 15MnV steel and so on. Q235 steel is divided into four grades: A, B, C and D.Q235B steel is often used in many engineering designs. This kind of steel can meet the requirements of impact toughness at room temperature, and it is suitable for the steel structure workshop with crane beam. However, in the actual project quality inspection, we often find that the project participants simply think that Q235 steel is enough. Therefore, Q235A steel which does not meet the design requirements is often used. In fact, the steel grade only ensures the tensile strength However, the impact toughness is not guaranteed due to the high carbon content, and the weldability is poor due to the high carbon content.In addition, if the design unit only indicates Q235 steel on the design drawing, but does not indicate the grade, it must be clear in the joint review of drawings.

 　　2Wrong welding rod

 　　Q235 steel is connected with Q345 steel and E50 series is wrongly used.This situation often occurs when there is no design requirement.Ordinary people’s habitual thinking is that the welding rod or flux suitable for high strength steel should be used for the connection between high-strength steel and low-strength steel. On the contrary, for the welding between different steels, considering the toughness and economy of the connection, the welding rod and flux suitable for low-strength steel should be selected, only to ensure that the final weld strength is equal to that of the base metal.For eq35 series steel, it should be selected for Q345 series steel.In this regard, we must realize that using the wrong electrode is equivalent to using the wrong steel. Therefore, we must be careful in the selection of welding rod.

4、 Defects in column base treatment

 The common quality problems of column base include inaccurate positioning of embedded bolts, random reaming of column foot plate, lack of shear key (or shear key groove is not reserved for short concrete column), and the gap under column foot plate cannot be filled effectively.

 　　1The positioning of embedded bolts is not accurate

 The inaccurate positioning of embedded bolts often leads to the following problems, such as the need for reaming of column foot plate.Common temporary installation and fixing method: the position of embedded bolt is attached to the template.

 The main reasons for the deviation of embedded bolts are as follows: 1. Measurement error, each measurement error, and the measurement error before and after two times. This is very small, that is, within one or two millimeters, which can be tolerated.2. The displacement in the pouring process is now mechanized. The concrete flow rate is large, the flow rate is greater, and the impact force on the formwork is large; and the concrete is not evenly distributed around the formwork, and the force difference on each side of the formwork is large, which will cause the deformation and displacement of the formwork, resulting in the overall displacement of the bolt and the inclination of the bolt, which is often measured in cm,It is often difficult for the column to reach the accurate position.

 Base plate method

 In general, double nuts shall be used to prevent the embedded bolts from loosing (cecs102:2002).If only one nut can be installed due to elevation problem, the nut shall be firmly welded with the pressing plate below, and the pressing plate shall be firmly welded with the column bottom plate.The hole diameter of the bolt is usually 40-3% of the diameter of the bolt, and the diameter of the bolt is usually 40-2mm.

 Shear key or shear groove missing

 It is often found that shear keys or shear grooves are left out during construction.The anchor bolt of column base is designed according to the bearing tension, and the horizontal force of anchor bolt is not considered in calculation.If there is no shear member, almost all the shear forces at the bottom of the column caused by lateral wind load, horizontal seismic load and crane horizontal load are borne by the anchor bolt at the column base, which will destroy the anchor bolt at the column base.

 To solve these problems, we need to strengthen the sense of responsibility, strictly compare the construction with the drawings, and strengthen the process inspection.

 Second filling of column base gap

 The gap between the bottom plate of the column base and the top of the concrete column is generally required to be 50 mm, but sometimes it is too small in the actual construction, which makes the grouting material difficult to fill or fill.In addition, generally, the secondary grouting material is required to be one grade higher than the column concrete strength. Due to the high strength and small amount of secondary grouting material, the actual mix proportion and strength can not be well controlled on site, which often leads to insufficient strength and compactness (especially in the shear groove).Therefore, in order to avoid such problems, it is suggested that high strength self leveling finished grouting materials should be preferred for secondary filling materials.

5、 Quality problems in weld treatment

 　　1The weld deformation is too large

 Improper control of welding deformation often leads to plane warping of welded H-beam or steel column end plate, and the mechanical performance of the component will be affected due to the contact surface not close to each other when the warped end plate is spliced.There are some strong technical force of professional steel manufacturers in this point to control better.Generally, there are several methods to control welding deformation: (1) select reasonable welding sequence and weld symmetrically as far as possible, for example, layered welding can be used for thicker weld; (2) deviation in the opposite direction of welding deformation shall be reserved; (3) fixture or special fixture shall be used to fix the weldment, and the end plate can be fixed on a support with high rigidity by bolts; (4) heat correction。

 　　2The weld quality of field installation is poor

 The construction units of steel structure often do not pay enough attention to the inspection of field installation weld, and even ignore the quality of field installation weld, which brings unstable factors to the normal bearing and use of components.On site welding conditions are more uncertain due to poor welding quality.For the full penetration welds with design requirements above grade II, some projects do not carry out flaw detection according to the specification requirements.To solve this kind of problems, we should strengthen the on-site management, strengthen the process quality control, and carry out the third-party verification test in strict accordance with the specification requirements.

 　　3The number of weld flaw detection does not meet the requirements

 The welding seam in building steel structure can be divided into three levels: the first level weld is full penetration, which is used for the butt weld with equal strength under dynamic load, the second level weld is the full penetration constant strength weld under static load tension and compression and the third level weld is the common fillet weld and combined weld without equal strength.

 　　Article 5.2.4 (mandatory) of GB 50205-2001 clearly requires that “100% of the first level weld inspection and 20% of the second level weld inspection.”However, in actual operation, the number of detection often does not meet the requirements, especially for the secondary weld detection, the percentage is calculated by the number of weld, which leads to the number of detection does not meet the requirements of the specification.It is stipulated in the specification as follows: 20% of the secondary weld inspection spot check, for the factory made weld, the percentage shall be calculated according to each weld, that is, 20% of the length of each weld, and not less than 200 mm; and for the field installed weld, the percentage can be calculated according to the number of welds, that is, 20% of the total number. 

 Therefore, many engineering construction, supervision units and even some inspection personnel can not correctly grasp the essence of this specification. For secondary welds, no matter what type, they do not distinguish between factory made and on-site installed welds, and unify 20% of the total number of flaw detection, resulting in insufficient detection quantity.

 In the actual supervision and control, the following principles can be followed: for those steel member manufacturers who are not strong in their own technical strength, do not have the ability of non-destructive testing of welds, and have not commissioned an independent third party to carry out weld inspection on the ex factory components, the third party must be entrusted to carry out on-site flaw detection according to the requirements of article 5.2.4 of GB 50205 after the products enter the site; however, for those steel members which have no technical strength, do not have the ability of nondestructive testing of welds, and have not entrusted an independent third party to carryFor the steel member manufacturing unit with damage detection capability and the components have carried out self inspection according to article 5.2.4 of GB 50205 before leaving the factory, or although they do not have the self inspection ability, they have entrusted an independent third party to carry out flaw detection according to the quantity requirements of article 5.2.4 of GB 50205, and their products must also entrust a third party to carry out safety sampling inspection after their products enter the site, but the sampling proportion meets the requirements of appendix g of GB 50205-20013% of the first and second level welds shall be randomly inspected according to the number of welds, and no less than 3 places.

 6、 Treatment of butt welding groove

 Code for design of steel structures (GB 50017-2003) clearly stipulates: when thin plate and thick plate or narrow plate and wide plate are connected, if the width or thickness of weldment is different, and the difference is more than 4mm on the same side, oblique angle with slope no more than 1:2.5 shall be made from one side or both sides in the direction of width or thickness.In the daily steel structure engineering, it is found that most of the butt welds at flange plate and end plate are directly butt welded instead of making the transition of inclination angle as required.

 On the treatment of this problem, some steel structure design and installation units also have different opinions. They say that light steel designed according to technical specification for steel structure of light-weight buildings with gabled frames (cecs102) may not be implemented.For this reason, we have also consulted the article of Professor Cai Yiyan of cecs102 management group: “different from the centralized management department of cecs102, if the project is designed according to cecs102 instead of according to GB 50017, the relevant components and connections do not need to comply with the provisions of GB 50017, so this requirement can not be implemented.”

For this point of view, the author has different views.First of all, this only represents an academic point of view, and informal codes or technical standards; in addition, as a national standard, GB 50017 does not say that it is not applicable to light steel structures, so it is understood to be applicable to conventional steel structures; in addition, this requirement is a constructive provision, which is intended to avoid the problems such as excessive stress concentration caused by sudden change of butt weld (refer to the code for design of steel structures)Therefore, even light steel structure should not be an exception.Therefore, the treatment of butt welding groove should be carried out according to GB 50017.

7、 Single side fillet weld is adopted at random for T-joint

 In some large-scale industrial buildings, the fillet weld between flange plate and web of H-beam is usually designed as single-sided fillet weld by steel structure design and construction unit.

 According to article 7.1.1.2 of technical specification for steel structures of light-weight buildings with gabled frames (cecs102:2002), when the web thickness of T-joint is less than 8 mm and full penetration is not required, automatic or semi-automatic submerged arc welding single-sided fillet weld can be adopted if the technical equipment and other technical conditions meet the requirements of Appendix F after process qualification.

 　　F. 0.1 single side fillet weld shall meet the following requirements:

 (1) The single side fillet weld is suitable for the weld only bearing shear force;

 (2) The single side fillet weld can only be used for the structure which bears static load and indirect dynamic load, and is not exposed to strong corrosive medium;

 (3) The requirements of fillet size, throat and small root penetration should be met;

 (4) The welding parameters and methods passing the process assessment shall not be changed;

 (5) The connection between column and base plate, column and bracket, end plate of beam, crane beam and hanger supporting local suspended load shall not be used with single fillet weld unless specially specified.

 Therefore, for this type of T-joint with single-sided fillet weld, the stress characteristics and parts of the weld shall be checked to see whether they conform to the scope specified in the specification (Appendix f.0.1), and then the welding procedure qualification report shall be checked to see whether the technical equipment and conditions in the evaluation report are consistent with the actual selection of the processing and manufacturing unit, and then the physical welding quality shall be checked to see whether it meets the requirements.

 8、 Defects in inspection and construction quality control of high strength bolt connection

 　　1Wrong understanding of the concept of high strength bolt connection pair

 Many engineers have not formed a correct understanding of what high strength bolt is, and even some people mistakenly believe that the torsional shear high-strength bolt is friction type, while the large hexagon high-strength bolt is pressure bearing type.

 The full name of high-strength bolt in production is high-strength bolt connection pair, which is not generally referred to as high-strength bolt.Each connecting pair includes a bolt, a nut and two washers, which are produced in the same batch and processed in the same heat treatment process.According to the installation characteristics, it is divided into large hexagon head bolt and torsion shear bolt.According to the performance grade of high strength bolt, it can be divided into 8.8 grade and 10.9 grade, and the torsion shear type is only used in grade 10.9.In the marking method, the number before the decimal point represents the tensile strength after heat treatment, and the number after the decimal point represents the yield ratio, that is, the ratio between the measured yield strength and the measured ultimate tensile strength.Grade 8.8 indicates that the tensile strength of the bolt rod is not less than 800MPa and the yield ratio is 0.8; grade 10.9 indicates that the tensile strength of the bolt rod is not less than 1000MPa and the yield ratio is 0.9.In structural design, the diameter of high-strength bolts is generally M16 / M20 / M22 / M24 / M27 / M30, but M22 / M27 is the second choice series, and under normal circumstances, M16 / M20 / M24 / M30 is the main choice. 

 　　GB 131-2006 specification for large hexagon high strength bolts stipulates: under the premise of the same batch, if the bolt length is ≤ 100 mm, the length difference is ≤ 15 mm; or when the bolt length is ≥ 100 mm, the length difference is ≤ 20 mm, which can be regarded as the same length.)

 The tightening of high strength bolts should be divided into initial tightening and final tightening.For large joints, it should be divided into initial tightening, re tightening and final tightening.The initial tightening torque is about 50% of the construction torque, and the re tightening torque is equal to the initial tightening torque.In order to prevent omission, color shall be used to mark the nuts of high strength bolts after initial or re tightening.For the high strength bolt after final tightening, mark the nut with another color.It is strictly forbidden to expand the hole by gas cutting during the field installation of high strength bolts.Generally, the exposure of high-strength bolts shall not be less than 2-3 buckles, and 1 or 4 buckles of 10% exposed bolts are allowed.

 During the initial tightening, re tightening and final tightening of high-strength bolts, the bolts at the joints shall be tightened in a certain order, and generally, the bolts shall be tightened outwards in the central sequence of the bolt group.The initial tightening, re tightening and final tightening of high strength bolts should be completed on the same day, and the final tightening should not be completed after the next day.In the process of supervision, it is often found that some projects have such construction units, and the final twisting time is one day or even a week or a month after the completion of re twisting.Therefore, construction and supervision units need special attention.

 　　2）Incorrect calculation of construction torque

 Quite a lot of engineers don’t know how to calculate the construction torque.According to the code GB 50205-2001, the calculation formula of the initial tightening torque is as follows: the torsional shear type t0 = 0.065pc * D and the large hexagonal type t0 = 0.05tc. When the final tightening, the screwing off of the plum blossom head is taken as the tightening mark.For those that cannot be unscrewed with tools due to structural reasons, the number of plum heads that cannot be removed in the final tightening shall not exceed 5% of the total number of bolts in the node, and the torque method shall be used for marking according to the specification requirements, and the final tightening torque shall be checked.The construction torque of large hexagon head high strength bolt is determined by the following formula: TC = k · PC · D Tc – construction torque (n · m); K – average value of torque coefficient of high-strength bolt connection pair (Note: the actual test value of testing organization shall prevail); PC – standard value of construction pre tension of high-strength bolt (KN)(Note: it is specified in the acceptance code of GB 50205 that this is the standard value of construction pretension of high-strength bolt connection, which is about 10% higher than that in the design specification of GB 50017, mainly considering the pretension loss.)D-diameter of high strength bolt (mm);

 (Note: some senior construction experts suggest to use TC = 1.05k · PC · d to calculate the construction torque, in which 1.05 is the attenuation coefficient, which is to consider the appropriate existence of certain over tension in the pre tightening tension.As there is no specific requirement in the specification, it is only for reference.)

 According to the above formula, in order to facilitate the reference of the majority of engineering and technical personnel, the reference table of construction torque value of common high-strength bolt is sorted out, and the approximate construction torque of each specification of bolt is provided for reference. The column of “actual torque coefficient” should be adjusted and determined according to the re test results of the actual selection of high-strength bolt torque coefficient in the specific project.

 　　3）The configuration of torque wrench in construction does not meet the requirements

 Quite a number of projects can not correctly configure the torque wrench for construction (including manual and electric type).Some projects have no configuration at all, and ordinary spanners are used to construct high-strength bolts at random; some projects are configured but not calibrated regularly according to the regulations, resulting in failure; some projects are equipped with torque wrench, but the range does not match the engineering requirements (as can be seen from the above “construction torque value reference table”, the construction torque of each type of high-strength bolt is different, and the field configuration is manualOr the electric torque wrench shall be able to cover all kinds of high strength bolts selected in the project design).Such problems lead to high intensity

 The torque control of bolt connection construction has become empty talk; and the supervision personnel also know little about it. Basically, the construction unit is allowed to do it by themselves, and then sign on the data.

 Generally speaking, the torque wrench used in the construction of high-strength bolts must be corrected before use, and its torque error shall not be greater than ± 5%. It can be used only after it is qualified.The torque wrench with too large deviation of torque value can not be used continuously.It is not allowed to use ordinary wrench or electric ordinary wrench for construction.

 For such problems, the key is to increase the intensity of inspection and punishment, and supervise and urge the construction and supervision units to fulfill their own responsibilities.

 9、 The friction surface clearance of the end plate is larger than the specification requirement

 In the construction of steel structure engineering, it is often found that the high strength bolt connecting plate warps and the contact surface cannot be closely attached together.Due to the friction type high strength bolt connection method is to press the joint between components by bolts, and use friction to prevent sliding between components to achieve internal force transfer.Therefore, when there is a gap on the surface of the spliced plate, the pressure between the friction surfaces with clearance decreases after fixation, which affects the bearing capacity.According to the specification, the contact surface of the top tight joint should not be less than 70% close to each other, and the edge is very large, and the gap should not be greater than 0.8mm. The detection methods are 0.3mm and 0.8mm feeler gauges.In fact, it often exceeds the standard or even seriously exceeds the standard.(Note: article 10.3.2 of code GB 50205 stipulates that the joint contact surface shall not be less than 70%, which is the requirement for steel structure on-site installation and must be controlled by the steel structure installation unit; while article 8.3.3 of the Code stipulates that the contact surface tightening shall not be less than 75%, which is the requirement for the assembly of steel components in the factory and the requirement that the processing and manufacturing unit shall implement.Therefore, the two top tight requirements should be distinguished.) 

 The test results show that when the clearance is less than or equal to 1 mm, it has little effect on the sliding of the friction surface, and can basically achieve the normal transmission of internal force; when the clearance is greater than 1 mm, the anti sliding force will decrease by 10%.Therefore, when there is a gap between the contact surfaces, the following treatment should be taken: s ≤ 1.0mm can not be treated; 1.0mm < s ≤ 3.0mm, the higher part should be ground into a 1:10 inclined plane; the grinding direction should be vertical to the stress direction; when s > 3.0mm, a backing plate should be added, and both sides of the base plate should be treated with friction surface, the method is the same as that of components.

 Once the high-altitude installation of steel members is completed, it is difficult to rectify such problems.Therefore, it is necessary to strengthen the inspection in the stage of ground pre assembly so as to find out the problems and deal with them as soon as possible.

10、 Improper treatment of component deformation

 　　1Arch problem of steel beam

 The main purpose of steel beam arched is to offset part of the deformation of roof steel beam after loading deformation, and the roof can still maintain a certain slope.If the camber of steel beam is too large, the roof slope near the roof ridge will become smaller, and if the steel beam deformation is too large, the roof slope near the cornice will become too small.

 It is not appropriate to change the slope too much.Whether the arch is arched or not and how large it should be arched should be a design problem.Therefore, when the arch camber is not required in the design, the allowable deviation of camber in the schedule c.0.5 (for welded solid web steel beam) and schedule c.0.6 (for steel truss) in the code for acceptance of construction quality of steel structures (GB 50205) is – 5 ~ 10 mm, that is, the construction party is not required to determine the camber.Generally speaking, the design does not require, and the construction party does not arch. 

 The method of arching includes parabola arch and broken line arch.For portal frames, the broken line arch is often used, that is, at the joint of steel beam, the angle of connecting end plate is controlled to achieve the purpose of arching.For the truss, only when setting out the arch.

 　　2Improper installation of roof purlin, tie bar and brace leads to excessive deformation

 In some projects, the connection plate of rigid tie bar and wind tie rod is set at different positions, which makes the horizontal support system not in the same plane, thus affecting the overall stability of the rigid frame.The rigid tie rod and the wind rod constitute a horizontal support system, and the setting height of the system should be consistent in the same slope direction.

 In the installation of roof or wall purlin, some construction units increase and lengthen the bolt hole diameter of purlin or purlin supporting plate at will for the convenience of installation.Purlin is not only a member supporting roof panel or hanging wall panel, but also a supporting body set by the beam column corner brace of rigid frame. Setting a certain number of corner braces can reduce the calculation length out of plane of rigid frame, and effectively ensure the overall stability of rigid frame out of plane.If the hole diameter of purlin or purlin supporting plate is too large and too long, the corner brace will lose its due function

 In order to increase the compressive capacity, casing is often added at the slope direction near the gutter.However, it is often found that there is a gap between the two ends of the casing and the purlin, which can not be close to each other, which can not play a role. If necessary, repair spot welding can be used to solve the problem.

 In addition, some units arbitrarily increase the roof load. The original design did not consider the suspended load such as suspended ceiling or equipment pipeline, but arbitrarily increased the suspended load such as ceiling in construction, which led to excessive deflection or collapse of steel beam.No unit shall arbitrarily increase the load beyond the design scope.In the process of construction, if such problems are found, it must be required to send the increased load and whether the design requirements should be checked according to a certain proportion.For the public building grid structure with safety level I and span of more than 40m, or in case of quality doubt, the site must be re inspected “.

 For this difference, because the two norms are currently effective, I personally understand that:

 The national standard GB 50205-2001 focuses on the inspection and acceptance requirements of important structural materials at the construction site, which is a sampling re inspection requirement on the construction site based on the inspection of factory certification materials. The inspection shall be carried out by an independent third party; while jgj78-91 focuses more on the quality assurance of the processing and manufacturing of the grid frame. The above mentioned inspection requirements are for materials and componentsAccording to the inspection requirements before leaving the factory, the manufacturer must test the products to be qualified according to the requirements before leaving the factory, and the inspection can be completed by the manufacturer with test conditions.In engineering practice, according to the actual situation, the specific inspection requirements can be determined by comprehensively considering the source of components and parts, the technical level and strength of grid manufacturer, and the grid installation and construction unit.

 12、 Coating quality of steel structure

 　　1Coating quality problems of anticorrosive coatings

 The rust removal and coating protection of steel members are important means to ensure the durability of the structure. The anti rust method and derusting grade of the component surface should be suitable for the anti rust coating used in the design, and the specific adaptability specification has been clearly indicated.The coating shall be provided with certificate (pay attention to the validity period) or retest report. The coating thickness shall be checked to see if it meets the design requirements. If there is no design requirement, the coating thickness shall be 150 μ m outdoors and 125 μ m indoor, and the allowable deviation shall be – 25 μ M. in addition, attention shall be paid to the climatic conditions during coating, and the coating shall not be applied where it is not required, otherwise, the coating shall be removed to meet the requirements according to the derusting method (such as end plate friction of high strength bolt connection)Wipe the surface, etc.).Special attention should be paid to the fact that if welding is carried out directly on the surface of the painted steel, dense pores will appear at the root of the weld, which will seriously affect the welding quality. Therefore, welding on the surface of the painted steel is strictly prohibited. If welding is necessary, paint removal must be carried out.This is a lot of engineering problems, especially after the steel components enter the site inspection found problems, many construction units on-site rectification, operation conditions are not available, it is very easy to appear the above problems.

 　　2Coating quality of fire retardant coating

 In the daily inspection, it is found that many engineering fire retardant coatings are not sampled and rechecked, or the re inspection indexes are not complete; another common problem is that the thickness of fire retardant coatings does not meet the design requirements.

 Fire retardant coatings are divided into thin coating type and thick coating type.As for the re inspection batch, it is stipulated in GB 50205 that the bonding strength of thin coating fire retardant coating shall be inspected once every 100t, and the bonding strength and compressive strength of thick coating fire retardant coating shall be inspected once every 500t. The corresponding indexes shall meet the requirements of technical specification for application of fire retardant coatings for steel structures (cecs24:90).

 The thickness of thin coating fire retardant coating shall meet the design requirements of fire resistance.The thickness of the thick fire retardant coating, 80% or more of the area should meet the design requirements of the fire resistance limit, and the thickness of the very thin part should not be less than 85% of the design requirements.

 The above content involves the analysis and treatment of quality problems in the process of steel structure construction. I hope readers can put forward valuable opinions.