Key points of construction quality control

1

Construction preparation

Construction preparation is a necessary condition for construction. It plays an important role in giving full play to people’s positive factors, reasonably organizing human and material resources, speeding up project progress, providing construction quality, saving investment and materials, and playing an important role in successfully completing the task of steel structure construction.

1.1Do a good job in joint examination and disclosure of construction drawings

Drawings are the basis of engineering construction. The technical director of the project shall organize relevant technical personnel to review and digest the drawings. The first purpose is to make the construction unit and all participating units familiar with the design drawings, understand the engineering characteristics and design intent, find out the technical problems to be solved and formulate solutions; the second is to solve the problems existing in the drawings and reduce the drawingsThe quality hidden danger in the drawing will be eliminated in the bud.At the same time, do a good job in technical disclosure, the combination of construction and design, steel structure hoisting and civil construction, steel structure and concrete structure prefabrication.

1.2Conscientiously compile the construction organization design of steel structure engineering

Construction organization design is an important comprehensive technical document prepared by the construction unit to guide all activities in the whole process of project construction, and is a scientific management method.When preparing the construction organization and construction scheme, the construction unit shall formulate practical and feasible detailed implementation rules from five aspects of personnel, machine, material, method and environment, implement the plan, organize personnel, implement self inspection, mutual inspection and special inspection, bring all the quality problems that are easy to occur into the controlled state, and ensure that the technical measures of the scheme are effective and feasible.In the process of compiling and implementing the construction organization design, extensive and in-depth research should be done, and the disclosure should be made to the construction personnel, so that everyone can check.For steel structure engineering, the fabrication process and installation construction organization design shall be prepared respectively for the fabrication stage and the installation stage.The content of production process should include the quality standards and technical requirements of each process and sub item in the production stage, as well as the specific measures formulated to ensure the product quality.The construction organization design of steel structure installation engineering includes the establishment of quality assurance system and technical management system, measures and methods of quality and progress control, and arrangement of construction period.

2

Pay attention to the quality control of steel structure foundation engineering

The quality control of steel structure foundation engineering generally refers to the quality control of steel structure foundation embedded bolt. The embedded bolt is the first step of the whole project construction, is also a very critical step, and is the foundation of the whole project.When the bolts are embedded in the construction foundation, first of all, be familiar with the drawings, understand the intention of the drawings, and make the installation template.The embedded bolt is positioned on the main reinforcement and formwork of the column with two installation templates and steel bars to ensure that the embedded bolt will not be displaced due to the construction of pouring concrete.In this way, the spacing and height between each group of bolts can be controlled within the allowable error range; at the same time, the screw thread of bolts shall be protected from damage during concrete pouring.After the completion of civil engineering, the elevation and axis of anchor bolts shall be rechecked with theodolite and level gauge and recorded.And submit to the next process for acceptance.

3

Quality control of steel structure fabrication engineering

The construction of steel structure engineering usually goes through two stages: Factory fabrication and site installation.Most of the time of steel structure engineering is carried out in the factory workshop. Because the quality of steel structure components processed and manufactured in the factory is good or bad, it is very important for the on-site installation of steel structure engineering and the safety and stability of the overall structure.Therefore, the steel structure manufacturer must have the corresponding enterprise qualification, production scale, technical ability, mechanical equipment and advanced technology level.

The general manufacturing process of steel structure is divided into: lofting → blanking → assembling → cutting → assembling → submerged arc welding → drilling → assembly → correction and molding → riveter parts blanking → fabrication and assembly → welding and welding inspection → antirust treatment, coating and numbering → component acceptance and delivery.In the production of steel structure, we should grasp the key process for quality control according to the steel structure manufacturing process, such as controlling the processing of key parts, the technology and measures of main components, the processing equipment and process equipment used.

4

Pay attention to welding engineering quality control

Welding engineering is the most important link in steel structure fabrication and installation engineering, so we must pay attention to the quality control of welding engineering.At present, most of the steel structure in the production process with automatic submerged arc welding machine, some with semi-automatic gas shielded welding machine, some parts of the manual welding.

There are many welding quality problems existing in manual welding seam. These problems include: weld bead, slag inclusion, air hole, incomplete penetration, undercut, wrong side, large deviation of weld size, no need of arc striking plate, no correction of welding deformation, and unclean cleaning of spatter.In view of this situation, before welding of steel structure, the qualification certificate of welding rod shall be inspected and used according to the requirements of the manual. The welder must have the certificate, and the weld surface shall be free of cracks and weld beading, the first and second level welds shall be free of porosity, slag inclusion, arc pit crack, undercut, incomplete welding and other defectsThe welder’s steel seal shall be checked on the weld and parts.Unqualified welds shall not be treated without authorization, and shall be treated after modification of the process. The number of weld repair at the same part shall not be more than 2 times.

5

Quality control of steel member installation

After the completion of the project, the steel structure will be installed on site.Before the installation of the steel structure, the quality of the components should be checked. When the permanent deformation and defects of the components exceed the allowable value, they should be treated.

For steel column installation, check whether the pad iron under the column bottom plate is padded and leveled to prevent the instability of the anchor bolt under the column bottom plate; whether the control column is vertical and whether there is displacement; in the installation project, temporary support measures should be taken before the structure has formed a stable system.

When the steel structure is installed to form a space fixed unit, and the acceptance is qualified, the construction unit is required to timely pour the space of column bottom plate and foundation top surface with expansion concrete for secondary compaction.Finally, the verticality and overall plane bending of the main structure of the steel structure should be checked.

6

Quality control of fastener connection in steel structure

The quality control of steel structure fastener connection mainly emphasizes the quality control of high strength bolt connection.The construction quality control of high strength bolt connection project is completed from the following aspects:

6.1 First of all, steel structure engineering must pay attention to the processing quality of high-strength bolt friction surface and protection before installation to prevent pollution and corrosion.Before installation, the anti sliding coefficient test of friction surface of high-strength bolt is carried out, the factory certificate and batch number of high-strength bolt are checked, and the axial force test of high-strength bolt with different batch number is conducted regularly.

 6.2 The installation of high-strength bolts requires free penetration, and no tapping and reaming are allowed; therefore, certain jig frame mould shall be prepared to control its deformation during the fabrication of steel structure, and feasible fixing measures shall be taken to ensure the dimensional stability of components during transportation.

6.3 During the installation of steel structure, the contact surface of plate stack should be flat, the contact surface must be greater than 75%, and the edge gap should not be greater than 0.8mm.The installation process of high-strength bolts, including operation sequence, installation method, tightening sequence, initial tightening and final tightening, shall be strictly controlled and inspected, and the torque wrench for tightening bolts shall be calibrated.After the final tightening, check one by one, and make up or replace the under tightening and over tightening.

7

Rust removal and painting of steel structure

Steel structure rust removal and coating is the most easily neglected link in steel structure engineering.The rust removal of steel structure is divided into manual rust removal and mechanical rust removal. The construction personnel shall adopt different derusting methods according to the drawing requirements and rust removal grade.The quality control of painting project should be such that before the painting of steel structure, there should be no welding slag, oil, water, burr and other foreign matters on the surface of the painted components, and the brushing times and thickness should meet the design requirements.The coating materials must have a certificate, and the fire-retardant coating project must be constructed by the construction unit approved by the fire-fighting parts.

8

Construction quality control of color steel plate

Color steel plate engineering is another important part of steel structure engineering.Its construction quality directly affects the use of steel structure engineering.At present, there are many kinds of color steel plate.

However, the construction problems of color steel plate are relatively concentrated, such as: the joint of color plate, the manufacture and installation of color plate accessories are not fine and unreliable, the maintenance structure leakage, the appearance quality of color plate is uneven, deformation, scratch, pollution, etc.

Therefore, the quality control of profiled color plate installation mainly includes: after the profiled color plate enters the site, the appearance and certificate of conformity shall be inspected, and the installation accuracy of steel components related to the profiled plate construction and installation shall be rechecked, and the welding seam coating and splash during the installation of purlin shall be removed, and anti-corrosion treatment shall be carried out by applying anti-corrosion paint.When the color plate is installed, a reasonable installation process sequence should be worked out.

How to implement the quality control in the construction of steel structure engineering production and installation unit is mainly through the full-time and part-time personnel with quality control function of relevant departments to perform their own responsibilities in the quality control.The quality control method is mainly through the preparation and audit of relevant technical documents and reports, through on-site process inspection and final inspection and necessary tests.

1、 Prepare and review relevant technical documents and reports

The preparation and review of technical quality documents and reports is an important means for comprehensive control of project quality. The specific contents are as follows:

1Production project

(1) Review construction drawings, design changes and modification drawings.

(2) Test and compile the technical appraisal certificate of new technology, new material and new structure.

(3) Prepare and review technical process documents (such as manufacturing essentials, technical instructions, painting essentials, packaging and transportation essentials, process procedures), etc., and quality inspection documents (such as quality inspection essentials, quality inspection form, etc.).

(4) Quality inspection form for relevant materials and semi-finished products.

(5) Timely feedback the statistical data or management chart reflecting the dynamic process quality.

(6) Timely deal with the quality accidents of relevant engineering projects, make treatment reports, and put forward appropriate corrective and preventive measures. 

(7) Do a good job in product acceptance and delivery data.

2Installation items

(1) Prepare and review the construction scheme and construction organization design to ensure the project quality with reliable technical measures.

(2) Review the formal commencement report and issue the commencement instruction.

(3) Review the technical qualification certificate and personnel qualification certificate of each Subcontractor entering the construction site.

(4) Review the quality inspection guide, material certificate and test report of relevant materials, finished products and semi-finished products.

(5) Review construction drawings, design changes, modification drawings and notices, agreements and instructions.

(6) Prepare the technical appraisal of new process, new technology, new material and new structure related to the test.

(7) Make process handover inspection and quality inspection report of subdivisional and divisional works.

(8) Deal with the quality accident in time, make the treatment report, and put forward the appropriate corrective and preventive measures.

(9) Timely feedback process quality dynamic statistical data or management chart.

(10) Timely complete the project acceptance data.

2、 Process inspection and final inspection

1Inspection contents

(1) Material preparation inspection.Whether the appearance and size of the products provided by customers meet the technical quality standards for the purchased materials and steel components entering the site, and whether the machine tool rollers are in good working condition.

(2) Inspection before construction.Whether the site has the starting conditions and whether the project quality can be guaranteed after the commencement.

(3) Process handover inspection.On the basis of self inspection and mutual inspection, quality inspection personnel inspection and process handover inspection should be strengthened for important processes or processes with significant impact on project quality.

(4) Inspection of concealed works.All concealed works can only be covered up after being certified by quality inspection personnel.The work on the installation site must be certified by the customer supervision.

(5) Follow up, supervise and inspect.Follow up supervision and inspection shall be carried out for engineering structures with great difficulty in construction or construction with special requirements and easy to produce quality problems.

(6) After the completion of subdivisional and divisional works, the acceptance record shall be signed after self inspection and approval by the supervisor.

2Methods of inspection

The inspection method is divided into on-site quality inspection and test inspection

(1) On site quality inspection methods include visual inspection method and actual measurement method

a. Visual inspection

The means of visual inspection can be summed up as four words: look, touch, knock and photograph.

[look] is to visually inspect the appearance according to the quality standard.For example, the appearance of steel should be free of cracks, scabs, folds, hemp lines, bubbles and inclusions; the construction process should be carried out in a reasonable construction sequence, the workers’ operation is normal, and the instrument indication is correct; the weld surface quality should be free of cracks, weld beading, spatter, undercut, slag inclusion, air hole, poor joint, etc., which should meet the relevant provisions of the code for construction and acceptance。

The quality of coating construction should be derusting to the level specified in the design and contract. No rain should be allowed 4 hours after coating. The surface of paint film should be uniform, meticulous, without obvious color difference, sagging, tarnish, wrinkling, pinhole, bubble, shedding, dirt adhesion, missed coating, etc.

Touch is a feeling check.It is mainly applicable to the internal corners of steel structure engineers, such as the smoothness of the corner cutting of stiffening plate of steel components and the welding cladding angle can be identified by hand.

[knock] is to check the sound sense with tools.For example, if the steel structure engineering column angle pad is padded firmly, and the high-strength screw inspection joint is close and tight, the knocking inspection can be used to determine whether it is close to the actual or not through the sound.

For parts that are difficult to see or have dark light, the method of mirror reflection or light illumination can be used for inspection.

B it’s impossible

The actual measurement inspection method is to judge whether the quality is qualified by comparing the measured data with the allowable deviation specified in the construction specifications and evaluation standards. The means of the actual measurement inspection method can be summarized into four words: measurement, pulling, measuring and plugging.

[measurement] is to check the manufacturing accuracy with steel tape, steel ruler, angle ruler, vernier caliper and weld inspection ruler, measure the installation deviation, and measure the weld appearance size.

[pulling] is to check the bending and twisting of components with the method of pulling wires.

[measurement] is to detect the deviation of axis, elevation, perpendicularity, internal quality of weld, temperature and humidity with measuring tools and measuring instruments.

[plug] is to check with feeler gauge, hole tester and arc-shaped mould.If a feeler gauge is used to check the contact surface clearance of high-strength bolts, the hole passing rate is checked with a hole tester, and the grid steel ball is checked with arc-shaped sleeve die.

(2) Test and inspection

Test inspection refers to the inspection method which can judge the quality only by means of test.For example, the mechanical strength test, welding test, welding test, welding test, etc.