Construction error and optimal inspection rate

Discussion of error rates in construction involves issues ranging from the origins of error; to error detection, planning for repairs and optimisation of inspection costs. The problem of determining optimum rates of inspection for simple tasks has not received a great deal of attention from researchers. To address this issue a rework model is presented by means of a flowchart. Fault Tree Analysis (FTA) is then used for the systematic break-down of error and calculation of the probability of error of the top event. A simulation model is developed which incorporates learning and forgetting effects and calculates the predicted number of errors requiring rework for a completed task. A Minimum Cost Model (MCM) has been applied to calculate the total cost of inspection and rejection for a simple reinforced concrete slab. Results are presented for three circumstances; 100% inspection; less than 100% inspection; and less than 100% inspection but incorporating learning and forgetting effects. The evidence suggests that incorporation of both MCM and learning and forgetting effects on error rate is the most appropriate strategy.