The steel structure is widely used in large-scale factories, stadiums, super high-rise buildings, and other fields because of its lightweight and simple construction. However, most of the reasons why companies implement steel structures are to optimize the structure, save resources, and recycle. At the same time, it pays attention to promoting the advantages of steel structure, while ignoring its defects and hidden dangers. There are many reasons why steel structure engineering quality is difficult to guarantee, and they are also very complicated. There are problems caused by improper workmanship, problems caused by violating process operations, problems caused by the technical level and sense of responsibility of the constructors, and decision-makers. Quality problems caused by mistakes. Below, the editor will analyze some quality problems of steel structure engineering.
01 Problems in the steel itself
When a unit was processing a 1200*1200*60 box-shaped column in a building, it suddenly found that the 60mm thick plate as the web was torn during the welding process. The clear crack was visible to the naked eye and the plate was divided into two halves from the thickness direction. After NDT inspection, it was found that the crack depth occurred at a depth of about 3mm. At the same time, the parts cut from several other plates of the same type and batch number were inspected, and it was found that there was an interlayer in the plate, and poor rolling quality was the main cause of quality problems. During the welding process, the material of the sandwich layer is pulled apart due to the welding stress generated by the welding. As a result, the thick plate tears in the thickness direction.
Due to the particularity of the part used, this part is used as a web in the component. The parts welded in the vertical up and down directions are welded in the form of the full penetration grooved stiffener, due to the delamination inside the plate, The welding stress generated by welding is released outwards and the board is torn in the thickness direction.
The following measures can be taken according to the actual situation:
(1) A large number of interlayers in the steel are quality problems caused by the steel mill itself during the rolling process, which have exceeded the requirements of the national standards and specifications. You can ask the steel mill to send someone to verify and negotiate with the steel mill for return or replacement. deal with;
(2) If the number of interlayers is small, the opinions of the technical department and the owner can be solicited, the information will be fed back to the steel mill, and construction remedial measures can be taken for the problems that have occurred. According to the results of the non-destructive testing, gouging can be used for all the problematic parts. Open, exceed its own depth, and then fill it with equal-strength welding materials. After completion, the surface will be treated, and NDT testing will be performed after the specified time. At the same time, the same components will be sampled for physical and chemical testing, and they can continue to be used when they meet the design specifications;
(3) Cut off the parts under the witness of the supervisor, replace them with plates that meet the conditions, use the replaced parts for non-load-bearing and non-important parts or use them as auxiliary materials, and do it after the specified time after completion of NDT test, make a record.
02 Problems in the construction process
Quality problems are more likely to occur in the process of processing and post-processing is difficult. Special processes and important processes are the main ones. The proportion of quality problems in general processes is very small. During the construction process, special procedures include welding and painting, and important procedures include blanking and assembly.
1. Welding process
This process is a hidden project and one of the processes most prone to quality problems. According to statistics from a company’s product quality report in 2004, among the quality problems that occurred in this process, the repair rate of welds caused by welding quality was as high as 80%, followed by improper operation of the previous process and technical problems of the operators. Weld quality problems account for about 10%. These problems are the main problems that directly affect the quality of the project. Therefore, this type of problem can only be detected and judged by a professional inspection company using professional inspection tools. Generally, based on the defects in the weld Types are divided into slag inclusion, unfused, pores, etc.
2. Painting process
This process is also a hidden process, and the impact on the structure is less than the impact on the building function. It is also a process that is more prone to quality problems. The quality problems of the process are mainly manifested in: large area and partial peeling of the paint film on the surface of the component, peeling of the paint film on the surface of the component, sagging phenomenon, the insufficient thickness of the paint film, uneven distribution of the paint film thickness, and color difference of the paint film Larger.
3. Stakeout and blanking process
This process belongs to the leading part before component processing, and its quality has a direct impact on the next process, and even leads to the scrapping of all the blanking parts. This situation is very common, so it is very common before the blanking. It is very important and necessary to strengthen the quality control of the process.
The quality problems caused by this process are mainly manifested in:
For long strip and thin plate type parts, the deformation is severe during cutting;
Horse teeth, nodules, and cut depths on the cutting surface caused by cutting gas or slag inclusions and uneven distribution of ingredients in the plate are beyond the standard;
Gas cutting or sawing of parts does not take into account the shrinkage and deformation of subsequent processes and the size of parts exceeds the standard;
Batch parts are scrapped due to errors in process documentation;
The size of the blanking cutting seriously exceeds the standard requirements.
4. Assembly process
This process occupies an important position in the quality of component processing, and its quality is greatly affected by the previous process, so it is very important to strengthen the monitoring of the process before assembly.
The quality problems caused by this process are mainly manifested in:
The position of the assembled parts is wrong, such as 3450mm installed into 4350mm;
The parts are used incorrectly. 2# parts should be assembled, but 3# other parts were assembled;
The parts are assembled incorrectly in the correct position. For example, the hole 45mm on the board is originally facing outward, but the 45mm is actually installed inward;
The assembly gap of the assembled parts exceeds the requirements of the specifications and technical documents, and the gap of 3mm is now 7mm;
Some parts are assembled without correction, and the existing deformation after the assembly is completed cannot be eliminated;
The operator cuts without permission for the sake of saving trouble, causing the size of the hole on the part to exceed the standard;
There is no surface treatment in the welding area; assembly errors caused by errors in the drawing dimensions.