Specifications of ordinary screws
Common screws are mild steel or low carbon. The characteristics of these screws can be described as follows:
The total capacity of these screws is provided by the shear or tensile strength throughout the diameter. This screw is relatively less resistant and they are used under low and static loads in cases such as light structures, secondary members of structures such as lapes and shafts of harnesses, small trusses and assembly aids in joints.
Typical bolts are called A307 bolts in the ASTM standard. The materials of these screws are soft or low carbon steel and their minimum breaking stress is around 60KSI, equivalent to 4200kg/cm2.
3.6, 4.6, 4.8, 5.6 screws are considered normal screws in the German DIN standard.
Common screws are available in the market from 12mm to 36mm in diameter.
It is possible that these screws will separate from each other due to forces such as swing and impact, so it is necessary to use equipment such as metal washers, grooved sheets or bent spikes behind the nut to prevent this from happening.
Strong screws
As their name suggests, these screws have high resistance and are very popular. These screws are made of quality steel with medium carbon, which are made resistant by heating. The characteristics of these screws can be described as follows.
The total capacity of these screws is the sum of two things: the shear strength across the diameter of the screw and the friction created between the nut and the metal surfaces attached.
To obtain the frictional capacity, these screws must be prestressed to 70% of the ultimate tensile strength of the steel of the screws.
All kinds of standard high strength screws
A325 A449 bolts with a yield stress of about 5600kg/cm2 to 6300kg/cm2, which are made of medium carbon steel and heat treated.
A490 screws with a yield stress of about 8000kg/cm2 to 9000kg/cm2, which are made of alloy steel and heat treated.
In the DIN standard, 8.8 screws are seen as high strength screws and 10.9 and 12.9 screws as 20mm and 22mm diameters are seen in construction works.
High-strength screws can withstand intermittent and large loads.
Nowadays, the use of bolt and nut skeleton in new structures is not rare. In the past, the use of bolted structures was only limited to sheds and industrial complexes as well as in oil and gas industries, but today we see the widespread use of these structures in office, residential and commercial buildings. These structures are very popular due to the high installation speed and no need for difficult welding operations. In the following, we will examine the advantages and disadvantages of bolt and nut skeleton.