Experts, please proceed: Two questions regarding the calculation of load on connection bolts of pressure vessels
Thread Content
This post was last edited by mikech on 2009-11-6 15:37. According to mechanical design literature: bolt preload F`； The container is subjected to a working load of F while in operation ； Total tensile force of the bolt F0 ； The remaining preload is F" ； c1 and c2 represent the stiffness of the bolt and the flange, respectively ； F0=F"+F ； F0 = F` + Fc1/(c1 + c2) ； The bolt is subjected to a pre-tightening force F`, and during operation it is also subjected to an operating load F. Under normal circumstances, the total tensile force on the bolt, F0, is not equal to the sum of F and F’. Two questions: 1. The preload on the bolt, F’, is the force that causes the bolt to stretch; the working load, F, is also a force that causes the bolt to stretch. Since these forces act in the same direction, why can’t they be simply added together, i.e., F0 = F’ + F? Rather, F0 = F” + F; so where does the rest of the lost force go? 2. According to the formula F0 = F’ + Fc1/(c1+c2), the total pulling force F0 on the container when it is under load is certainly greater than the pre-tensioning force F’. However, according to Figure 15.8(c) or the formula F0 = F” + F, F0 will only be equal to or greater than the bolt pre-tensioning force F’ when the working load F reaches a certain value. Isn’t this contradictory? Please ask Haiyou for advice!
“Where does the rest of the lost force go? ” The reduced compression of the connected components results in them being \"relaxed,\" but the total load on the bolts still increases; it is simply not equal to the preload plus the working load. Evidence for this can be found in the chapter on \"Calculation of Indeterminate Structures\" in mechanics of materials.