Difference of tensile strength between

Chinese high strength

bolts and DIN

The reasons are as follows:
1. In our country's code, it is required to apply pretension P, P = 0.9 * 0.9 * fu * AE / 1.2.
Among them, Fu is the smaller tensile strength and AE is the useful area of bolt.
The planned pretension of high strength bolt is determined by material strength and useful section of bolt
A. when tightening the bolt, the shear stress caused by the torque will reduce the tensile ability of the bolt, so the tensile strength of the material is divided by a coefficient of 1.2;
B. in order to compensate the slack of pretension, the bolt should be over tensioned by 5% ~ 10%, so the coefficient should be multiplied by 0.9;
C. The variation of material resistance is multiplied by a coefficient of 0.9;
D. an additional safety factor of 0.9 is introduced for tensile strength.
The conflict type is based on the resistance between the connected members, and the ultimate bearing capacity is the shear force equal to the resistance. In order to avoid slack after unloading when the external force is greater than the bolt pretension, the planned value of tensile bearing capacity should not be greater than 0.8p.
Taking grade 10.9 bolt as an example, the smaller tensile strength is 1040n2, and the planned value of tensile bearing capacity is 1040 * 0.9 * 0.9 * 0.9 * 0.8 / 1.2 = 500n2
2. The planning value of tensile bearing capacity of bearing type high-strength bolt in Chinese code is also determined according to 0.8p, but the sliding of contact surface is allowed. At this time, the stress situation is the same as that of ordinary bolt, and the bearing capacity is the strength of bolt itself. The bearing type is that when the shear force exceeds the resistance force, the screw is subject to shear failure or the hole wall is damaged under pressure. Although the shear deformation of bearing type high-strength bolt is larger than that of conflict type bolt, the bearing capacity of bearing type high-strength bolt is higher than that of conflict type bolt.

This kind of bolt cannot be used in the structure under dynamic load.
3. According to the din code, the high strength bolt with high resistance can not be used in seismic area, so it is planned according to the strength of bolt itself, and only the partial factor and safety factor of material are reduced, which is higher than the standard value in China.
Taking M20 high strength bolt of grade 10.9 as an example, the pre tension is controlled according to the Chinese code, and the planned tensile capacity is 124kn; according to the strength of the material itself, the din specification is 178kn. The accounting process is as follows:
N < = 314 * 900 / 1.1 / 1.1 = 234kn, in which 314 is the sectional area, 900 is the yield strength, 1.1 and 1.1 are the additional safety factor and material partial factor respectively;
N < = 245 * 1000 / 1.25 / 1.1 = 178kn, in which 245 is the net sectional area, 1000 is the smaller tensile strength, 1.25 and 1.1 are the additional safety factor and material partial factor respectively;
The smaller value of both is 178kn.
             Therefore, if the planning value of China's code is selected, the small deformation of the overall structure under normal working conditions (non earthquake) is ensured; if the planning value in DIN code is selected, the structure is also safe (we will still apply pre tightening force during construction to ensure the contact surface with certain resistance force and small deformation of the overall structure. Only in earthquake can bolts play a greater effect Its strength resists).  
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