Metal structures connected with bolts and nuts are considered one of the most modern types of structures in construction industry because it has been determined by scientific research and numerous tests on the structures connected with bolts and nuts that this type of structure is suitable for preventing natural disasters. In countries such as Japan and New Zealand, which have been exposed to the most severe earthquakes, it has been shown that bolted connection structures are very efficient, and hence other countries have thought of mandating metal constructions with bolted connections.
One of the advantages of using structures with bolts and nuts connections, especially in tall and huge structures, is that during strong shocks due to wind or earthquake, a distance is created between the bolts and nuts and the skeleton, and this leads to no destruction and failure. And as a result, the efficiency of bolts and nuts is very impressive at this time, and the difference between bolt and weld connections is in the same direction, because during vibration, weld connections fail and lead to skeleton destruction and collapse, but in bolt and nut connections in The effect of the distance created between the bolt and the skeleton will not collapse.
Also, in the structure that use bolts and nuts instead of welding in connections, the installation time, execution time, and material waste are significantly less, and on the other hand, the construction quality and safety of the structure are higher by the same amount. Due to the fact that the parts are made in the factory under strict supervision and inspection, the quality of the construction is much higher compared to the welded metal structures that are made and installed on site.
Also, in the discussion of structural corrosion, bolted and bolted structures are ahead of welding because in bolted and bolted structures, the parts are de-rusted before painting, while this is not done in welded structures, and metal structures are enriched with welding instead of paint. Anti-rust is used with zinc, which is used in bolt and nut structures, which causes rapid corrosion of the structure.
The only defect that may exist in bolted structures is that the joints are not closed with enough precision and skill, or that the holes and the amount of twisting of the joints are inappropriate.
Now, the important point is that for the use of bolts and nuts in the joints of metal skeletons, quality is the first word, and the security of the structure requires the use of high-quality bolts and nuts, for this purpose, factory bolts and nuts can be used instead of workshop ones. Because in the factory, the products are evaluated and checked by various tests so that the experts can ensure their accuracy and quality. Some of these tests are as follows:
Tensile tests, bending tests (visual inspection for the absence of cracks), shear tests, fatigue tests and some tests that are performed by existing robots.
The use of bolts and nuts in the industry must be in full compliance with the standards that in building construction and metal frameworks, municipal rules and regulations must also be observed, some of which are as follows:
1/ Before the implementation of the construction of metal structures, the map of all the details must be clear and all the information of the connections, including welds, rivets and screws, must be mentioned in detail.
2/All factory screws must be distinguished from workshop screws and the type of high resistance screws connection (reliable or friction) must be clearly defined and the tightening limit of the screws must be specified.
3/ All the parts that are connected by bolts and nuts must be completely fixed to each other during installation by using pins or temporary bolts. The use of temporary installation and maintenance tools should not damage or widen the screw holes.
4/ If the holes of the parts in a connection are not exactly opposite each other, it will be possible to blow (non-acceptance) and reject the connection.
5/ In general, drilling holes in sheets thicker than 12 mm or sheets made of special strong and hard steel should be done with a drill.
6/ The parts that are connected to each other with high-strength screws must be completely fastened together and no filling washers or any other compressible materials should be placed between them.
7/ When the parts are assembled and installed, all the connection surfaces (including the surfaces adjacent to the screw head and the side of the nut) must be free from peeled parts and other waste materials, especially the contact surfaces of the friction joints must be completely clean and have no traces of paint. , varnish, oils and other materials should not be present in them.
8/ High strength screws should be used according to the specifications in the relevant standard.