Calculation of screw assemblies

This booklet deals with the problem of dimensioning connections between thin, flat parts, i.e. parts whose thickness is small compared to other dimensions, such as the splices of aeronautical structures and structural steel connections.

What characterizes these connections, compared with those studied in previous issues of [BM 5 561][BM 5 562][BM 5 563] , is that they practically always comprise several rows of bolts, and that the strength of the connection is no longer determined by that of the most heavily loaded bolt, but by that of the assembled parts.

We won't go into detail here on the calculations specific to the various types, which are covered in specialized calculation codes (Eurocode 3 for steel structures) or in calculation manuals for aeronautical structures. We have tried to give a unified presentation, to show the influence of the various parameters and to derive the main design rules applicable to general mechanical engineering.

However, we have chosen to deal in detail with the consideration of clamping prestressing in the calculation of assemblies working in shear-hardening and the search for optimum clamping.

In fact, this point is often overlooked by engineers (and wrongly neglected), even though it can be a simple way of significantly increasing fatigue life, in the same way as interference assemblies.

This first part deals with the behavior of joints under static loading, and in particular with the tricky problem of calculating the load distribution between the rows of fasteners on a joint bar.

The second part is essentially devoted to the behavior of assemblies under time-varying loads, and the calculation of their service life.