Rectification voltage
The 24 V AC voltage you are measuring is 24 VRMS or root-mean squared. It is the equivalent DC voltage that will give the same heating power into a load. It's peak voltage is &radic;2VRMS.

The rectifier and smoothing capacitors will give &radic;2 x 24 = 34 V. You will lose 2 x 0.7 V on the diodes so that results in 32.6 V. 

When you load up the circuit the DC voltage will fall as the capacitor will discharge somewhat while the AC voltage is low.