What is the peak-to peak voltage of a 56 Vrms ac voltage?

For a sine wave, the form factor is the square root of 2. Thus, the effective voltage of 56 V (56 Vrms) is 2-1/2 times the peak-to-peak voltage. Thus, the peak-to-peak voltage Vpp = Vrms * sqrt(2)

In this example:

Vpp = 56V * 1.4142... = 79.2V (rounded to one decimal place)