Traffic

The design ADTT (Average Daily Truck Traffic) accounts for directional and lane distribution factors, design life, and traffic growth:

Total trucks over the design life (free trucks per day calculator):

Load repetitions for axle type N:

Cracking

Per Westergaard 1927, the relative stiffness of the slab and support system is:

For single and tandem axles, the equivalent stress equations are documented in Ioannides, et. al 1992; Lee and Carpenter 2001; and ERES 2004a, while these equations are repeated along with those for tridem axles in ERES 2004b. Note that there are some differences in signs and other issues in the presentation of these equations in some of these references, and the following is confirmed to match StreetPave.

There are four adjustment factors to the equivalent stress equation:

The maximum equivalent moment due to an axle load is:

For single axles without edge support:

For single axles with edge support:

For tandem axles without edge support:

For tandem axles with edge support:

For tridem axles without edge support:

For tridem axles with edge support:

The maximum moment is combined with the four adjustment factors and concrete thickness to arrive at the equivalent stress for a given axle load:

To account for the structural enhancement of macrofibers or steel fibers:

The stress ratio is computed for each axle load:

The fatigue equation to be used in the StreetPave framework per ERES 2004a is:

Where the probability of failure is calculated as:

From which the fatigue damage from each individual axle load is computed:

Lastly, the total fatigue damage by all traffic is determined by summing the fatigue damage from all individual axle loads:

Faulting

The faulting model developed from Packard and Tyabji 1983 to CTL 1992 and into ERES 2004a. There are three adjustment factors to the maximum pressure:

The maximum pressure at the slab-foundation interface is:

For single axles without edge support and without dowels:

For single axles without edge support and with dowels:

For single axles with edge support and without dowels:

For single axles with edge support and with dowels:

For tandem axles without edge support and without dowels:

For tandem axles without edge support and with dowels:

For tandem axles with edge support and without dowels:

For tandem axles with edge support and with dowels:

For tridem axles without edge support and without dowels:

For tridem axles without edge support and with dowels:

For tridem axles with edge support and without dowels:

For tridem axles with edge support and with dowels:

The power (or rate of work) is determined. Note: the square on p_c is missing in ERES 2004a but is present in the prior references; ACPA also added the adjustment factors:

To determine the allowable repetitions, two more adjustment factors are required:

If C₁ × P_N ≤ 9, there are unlimited allowable erosion repetitions; otherwise:

From which the erosion damage from each individual axle load is computed:

Lastly, the total erosion damage for a given set of inputs by all traffic is determined by summing the erosion damage from all individual axle loads: