cncPave is a computer simulation program whose purpose is to facilitate competent decision-making when designing concrete pavement. cncPave assumes that input values are uncertain and calculates the consequence - uncertainty about the output.

The main output variables are the areas of the road that has shattered, has pumping, has faulting in excess of 5 mm and, in case of continuously reinforced concrete, also the crack spacing.

Risk of failure is the probability of load exceeding the bearing capacity of pavement. Load is expressed in terms of expected heavy-vehicle (HV) axles in a given period. The HV axle loads follow a frequency distribution that is indicated by the user. Bearing capacity of pavement is the number of HV axles that are distributed as mentioned above, under which the pavement becomes unserviceable. Serviceability is defined in terms of the area that has shattered, is pumping and is showing faulting at the transverse joints. Standards of serviceability are determined by the road engineer. When a road becomes unserviceable it has failed.

cncPave treats input and output values as random variables. It assumes that input variables follow so-called triangular probability distribution, which is determined by three parameters - the minimum practical value, the best estimate and the maximum practical value. From these cncPave derives the probability distribution of cumulative damage CD (expected number of HV axles divided by the bearing capacity of pavement). The area of pavement failed is then deduced from the distribution of CD - it is the proportion of CD values that exceed 1.

The distributions of output variable are obtained by means of Monte Carlo simulation. The user specifies that, say, 100 000 cases are to be created and analysed. In each case a generator of random numbers is used repeatedly, to create a value for each individual input variable, according to the triangular distribution specified for this variable. Values thus generated are then used in formulas that comprise the design procedure. In each case the output values are obtained from the procedure and recorded by computer. At the end of simulation, there is a record of 100 000 such output variables, from which their respective failure distributions are plotted. The decision on the quality and acceptability of pavement design is based on the evaluation of these distributions and their parameters.

Detailed description of input and output variables, formulas and procedures used can be found in the cncPave Help file. Please refer to this document if you need additional information.