Interference in stochastic flow-line models

The nature of the variability of construction activity duration is described and its effects on sequential repetitive activities investigated. The central limit theorem is used to argue that the distribution of activity durations containing sufficient sequential repetitions of an operation will be approximately normal. Based on this assumption of normality, the probability of an activity interfering with the progress of the next activity in the sequence is investigated. It is shown that this is a function of the probability of independent activities overlapping on the final operations and a heuristic method of evaluating this function is described. The assumptions inherent in this heuristic method are tested by comparing the results of such calculations with the results from a digital simulation model. It is shown that the calculated probabilities of interference compare very well with the estimated probabilities from the simulation results except for the results for activities whose average rates of progress diverge in time. These discrepancies are, however, unimportant in the anticipated uses of the model, where convergent activities have much greater significance.