A common problem in bolted connections is the self-loosening effect of bolts over time. Therefore the remaining strength in a slip resistant connection can only roughly be estimated for a certain point of time. A possible solution ot avoid self-loosening is the use of lockbolts, which have been studied in order to achieve recommendations for connections which are "free from maintenance". The pretension force in the bolt unavoidably reduces over time due to creep of primer, forces in bolts and in plates. These effects are experimentally studied. For all types of connections this effect is very important and in this paper the focus is brought on lap joints, where the influence of various types of loading is examined.