Alp – How might I avoid ‘Incremental deflection > limit at iteration %d’ errors during analysis?
Analysis may fail at a particular limit of lateral load with the message “Incremental deflection > limit at iteration %d”.
The incremental deflection limit is set in ALP under “Convergence Control”. This is a reasonably large number by default (2m), so if you are exceeding it there may be a problem with the design. Unless you have the wrong soil/pile stiffnesses entered, excessive displacement probably indicates the soil has gone fully passive and still not reached equilibrium.
It can sometimes also help Alp to converge if you apply your load in increments, rather than all at once. This allows you to look at the pile and adjacent soil behaviour with increasing lateral load. From the tabular output, you should be able to observe at what loading the soil passive resistance limit is reached and the soil goes plastic.
ALP assumes a linear elastic behaviour for the pile, so no structural failure is modelled. You will have to do a structural check separately.