When carrying out daily management and maintenance of steel structure building, attention should be paid to the following aspects of inspection.
Weld, bolts, rivets and other connections whether there are cracks, loosening, fractures and other phenomena.
Whether the webs, connection plates and other components appear to have excessive local deformation, there is no damage phenomenon.
Whether the deformation of the whole structure is abnormal, and whether there is beyond the normal range of deformation.
1. Inspection and treatment of weld defects
1.1 Common inspection methods for weld defects
a. Appearance inspection. Inspection will first remove the debris on the weld, with a magnifying glass (5 ~ 20 times) to observe the appearance of the quality of the weld. In addition to the requirements of the weld must, no defects, but also requires a good appearance of the weld. Good appearance of the weld should have a fine scaled surface. Free of crease interruptions and unfilled traps, and gently connected to the base metal.
b. Drilling inspection. This is a kind of broken ring weld inspection method. In the knot important components of the weld seam for external to view inspection into. In order to further confirm, you can use the drilling method again where there is a doubt to check whether the weld has pores, slag, not welded through and other defects, and after the inspection is completed, fill the eye with the same welding rod as the original weld.
c. Nitric acid alcohol leaching method of inspection. This method is generally used to check the cracks that are not easily observed. The method is to clean the suspicious place thoroughly, light, wash with acetone or benzene, drop on the content of about 8% of nitric acid alcohol solution for erosion, if the weld has cracks that have brown hooks show. Ultrasonic, x-ray, r-ray inspection for important components of the main weld, must be used ultrasonic, x-ray, r-ray and other inspection methods to check whether there are defects inside the whip, must also be taken when x, r two kinds of radiographic negatives for analysis and inspection with.
d. Special considerations. Power load and alternating load and tension can make defective welds crack quickly, causing serious consequences, so the steel structure project subject to power load, members on the tension area, should be strictly checked to prevent omissions.
1.2 Welding seam disease treatment method
Regardless of the method of inspection, such as the existence of defects found in the weld should be taken to deal with the corresponding measures.
a. For weld cracking phenomenon, the nature of the crack should be analyzed, where the cracks are generated in the use of the stage, must identify the causes, comprehensive management, to completely eliminate the disease. Cracks left over from the construction can be directly patched weld.
b. For defects belonging to the design of the weld, such as the size of the weld or insufficient size of the weld foot, it should be redesigned to a reasonable size after correct theoretical calculations. If necessary, the same welding conditions as the structure can be used to construct the weld on the test piece, and then carry out the same mechanical test as the steel structure engineering force to confirm the reasonable weld and foot size.
c. For the weld that has not welded through, slag, porosity and other defects, should be re-welded.
d. For weld seam with nibbles and arc pits should be welded.
e. For the weld tumor should be completely eradicated and rewelded.
2. Inspection and maintenance of bolts and rivet connections
For the recent new steel structure project, in addition to the weld connection, a large number of connection methods used is the bolt connection. Because the high-strength bolt connection method has been very mature technology, its operation method has the advantages of simplicity, speed, low labor intensity, and maintenance and replacement is also very convenient. At present, except for special occasions, the rivet connection has the tendency to be replaced by high-strength bolts. For the owners, their management and maintenance of the steel structure project is not necessarily new, so the owners should learn the inspection and maintenance of bolts and rivet connections at the same time.
For the inspection of bolts and rivets even, should pay attention to the bolts and rivets in the subject and the use of shearing and loosening phenomenon, the focus of the inspection is the part subject to alternating load and dynamic load action. In the inspection, also take into account the discovery of design and construction defects left behind.
2.1 Inspection methods
a. For the inspection of the bolt, generally use visual inspection, hand hammer tapping, wrench test wrench and other methods to carry out. Mainly check whether the bolt is loose and whether the bolt rod is fractured. For bolts subjected to dynamic load, the nut should be removed periodically, using a magnifying glass to carefully check whether there are micro cracks on the bolt rod, if necessary, physical flaw detection methods such as X-rays can be used to check, and strive to expand when eliminating hidden problems.
b. For cracked or fractured bolts, identify the cause of the broken ring, make detailed records and timely replacement. If the bolt to be tightened is a high-strength bolt, according to the type of nut (friction type or pressure type) and the requirements of the strength level, use the power wrench to screw the bolt to the specified torque.
c. For the inspection of rivets, one hand can be close to the nail head, the other hand hammer from the side of the nail head knocking, if you feel the nail head beating, it means that the rivet has a loose need to replace the processing, there is a rotten head, missing edge or cracked rivets also need to replace the processing. Replacement can be used in place of high-strength bolts, the bolt diameter must be converted according to the principle of equal strength decision, to ensure that the replacement rivets do not affect the bearing capacity of the steel structure project.
In the actual inspection, to correctly determine whether the rivet is loose or sheared off dimension is large, not only requires that the inspector should have a certain amount of practical experience, but also requires a high sense of responsibility. For important structures, it is generally required to change and re-inspect at least once to prevent large oversights.
2.2 The repair and treatment of bolt and rivet connection
Generally is carried out without unloading the situation. In order to avoid causing overloading of other bolts and rivets, the replacement of bolts should be carried out each; when replacing rivets, if the total number of a group of stressed rivets does not exceed 10, each should be replaced.
If the damage to the bolts and rivets on the steel structure project is large and the number to be replaced is large, the repair should be carried out in the unloaded condition to ensure safety.