VDI 2230 - Substitutional Line of Action of the Axial Force

[wnmascare]

Hi everyone!

VDI 2230 states that 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. Additionally, the standard doesn't make clear why we should replace the line of action of the actual axial working load by a substitutional line of action (calculation of the variable "a").

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

Does it have to do with prying effect?

Many thanks in advance.

 

[Agent666]

Not familiar with the standard, but can you post the relevant clauses, any relevant figures and a sketch of the type of connection being referred to, as I'm having a hard time determining exactly what type of bolted connection is being talked about here.

 

[wnmascare]

Dear Agent666

See the bolted connection in the figure attached. FB is the axial working load and "a" is the substitutional line of action of the axial working load. This strategy is applied to any kind of bolted connection.

 

[TLHS]

It's hard to say without knowing what they do with it, but it's a force and location that does a good job defining the moment diagram as simple systems. If you take the system including Fa and look left, it's a cantilever beam with a point load of Fa. If you look at the system including Fa to the right, including the symmetrical Fa on the other side, it's a simply supported beam with a point load of Fb and reaction forces of Fa. There's lots of ways this could be convenient in formulating things.

 

[Agent666]

Seems to just be a way of simplifying the system down to a force times a lever arm from the point of inflection as TLHS has noted.

The fact that your bolt carries the tension from the moment through the joint with bearing on the outer edge through the steel assembly takes care of the prying action.