Learning Forum

[Lambrescu]

I do not understant why I get negative values for workload in some bolts. The pretensions are all positive (It is about a Flange with 8 bolts tightned sequentialy in three steps:30kn, 60 kn, 90 kn

[Avnish Pandey]

Hi Lambrescu,

In ANSYS, the Working Load reported by the Bolt Tool is the reaction force at the pretension section after the bolt has been pretensioned and subjected to operational loads.

A typical workflow is:

1. Apply the bolt pretension.
2. Lock the pretension in the next load step.
3. Apply the operational loads.

The Working Load then represents the resulting force in the bolt during each load step.

A negative Working Load can occur even when the pretension value is positive. This simply indicates that the operational loads have reduced or reversed the reaction force at the pretension section relative to the original pretension direction. In bolted flange assemblies, load redistribution, contact behavior, and gasket stiffness can cause some bolts to experience reduced or reversed reactions in certain load steps.

Therefore, negative Working Load values do not necessarily indicate a modeling issue; they often reflect the actual force redistribution occurring within the joint during loading.

Regards,