VDI 2230 - Eccentrically Loaded Joints

[wnmascare]

Hi everyone!

According to VDI 2230, there are two kinds of loading joints: concentric and eccentric. For the case of eccentric loading joints, the variable "a" (the substitutional line of action of the axial working load) must be determined. According to section 5.2.1, the variable "a" is obtained from the position of the zero point of the bending moment characteristic in the system closest to the bolt. The text explanation in the standard is not precise and very difficult to understand.

Thus, does anyone here know why the variable "a" must be determined according to the previous explanation?

Many thanks in advance.

 

[RolMec]

Hello,

section 5.2.1 needs to be read in conjunction with section 3.2.2. The basic idea is to expand the (theoretical) calc. solution for the ideal centrically loaded joint to the more practical issue of an excentrically designed or loaded joint. This is done by establishing a "replacement moment" which brings back the centrically loaded basis solution, superimposing an additional loading by this "replacement moment". The "replacement moment" is derived from the axial load FA multiplied by the distance from the load vector to the centerline of the ideal and regular deformation body.
Specifically for the case of section 5.2.1 you look at figure 15: The distance a is between the centerline of the interlace (where there's an equal distance between the inner and outer edges of the rod's joint) and the line of action of the reactive force in the plane of the interlace. The reactive force's line of action in this plane is located, where the bending moment is zero (appl. mech. basic). Concluding: In order to find the calculation value of a for this problem, one needs at first to determine the distribution / curve of the bending moment in the interlaces's plane.

This is however quite highend applied mechanics esp. when it comes to more complicated geometries and load situations, so perhaps you seek some guidance fom people who do this in everyday's engineering life.
;-) imo the possession as such of a mech. design & calculation + a FEA software is not enough, practical skills & expertise are the crucial factors here.
Regards

Roland Heilmann
Lpz FRG

 

[wnmascare]

Dear RolMec, thank you for your reply.

I'm sorry, but I can stil understand why the reactive force line of action "F[sub]A[/sub]" will be located, where the bending moment is zero. Is there a specific reason?

Thanks in advance.

 

[RolMec]

Hello,

basic point is, where the bending moment (distribution) is zero, this means that at this place the bending effect from the eccentric clamping is now "equalized". As for a concentric load situation there would be no such bending effect, this model assumption allows to virtually place the reactive force at this specific location at distance a and thus to obtain again a calculation based on an "equalized system", by adding the "re-placement" moment to the bolt connection loading. Refer equations (71) ff.

I hope i could clarify this, but it's not easily done in words. Perhaps you could connect to some people of the applied design profession who could show you an example how it's done, or else ultimately by discussing VDI 2230 with a professor of applied mechanics or mech. engineering.
Kind regards
R.

Roland Heilmann
Lpz FRG