You have not connected the output enable pin to anything, this is pin 13 and needs to be connected to ground.
You also have your code wrong:-
const int ShiftPWM_latchPin=10; const int ShiftPWM_dataPin = 11; const int ShiftPWM_clockPin = 12;
The way it is wired it should read:-
const int ShiftPWM_latchPin=11; const int ShiftPWM_dataPin = 12; const int ShiftPWM_clockPin = 10;
And you need decoupling capacitors.
Not really sure why you have diodes across your piezos.
To cut out the negative ringing.
Or 1M resistors.
To provide a load and so limit the peak voltage.