The change of pre-tension force when high-strength bolt connection is under tension

The working condition of high-strength bolts under tension is shown in the figure. Figure (a) shows the force state of a high-strength bolt that has been pre-tensioned before being subjected to external tension. At this time, the bolt rod is subjected to a pre-tension P, and a pressure C is acting on the friction surface. According to the equilibrium conditions, Cu003dP. That is, the pressure C on the friction surface is equal to the pretension P.

Picture (b) shows the force state of the high-strength bolt when it bears the external tension N0t. It is assumed that the bolts and the connected plates maintain elastic properties. After the bolt receives the external tension N0t, the tension in the bolt rod increases from the original P to Pf. At this time, the bolt rod is stretched again, that is, the bolt rod is elongated by an increment; because the bolt rod is stretched, the plate that was originally compressed by P has a corresponding compression recovery amount, and the pressure between the plates is changed from the original The C is reduced to Cf. In other words, when the bolt is subjected to the external tension N0t, the tension in the bolt rod will increase, while the pressure between the contact surfaces will decrease. According to the balance conditions, get (Guide: The processing method of anchor bolt hooks directly use the bending machine)

The deformation of the bolt rod and the plate is the same within the plate thickness range:

That is, the extension increment of the bolt rod is equal to the recovery amount of the plate compression.

Suppose the cross-sectional area of u200bu200bthe bolt rod is Ab, the friction surface area is Au, the elastic modulus of the bolt and the connected plate are both E, then Cu003dP, Cfu003dPf－N0t are substituted into the above formula, after finishing Generally, Au is many times larger than Ab. For example, if Au/Abu003d10 and substituting it into the above formula, the tension term N0t in the above formula can be divided by the average value of the load factor 1.3 to obtain the design external tension Nt, namely: Nt u003d1.0N0t.

When the design external tension Ntu003dP, Ptu003d1.07P. That is to say, when the external tension applied to the bolt connection does not exceed P, the tension in the high-strength bolt rod does not increase much, and it can be considered that the original pre-tension in the bolt rod is basically unchanged.

More related hardware stamping parts industry news: