There are a few problems with the circuit.
A full bridge rectifier should not be grounded on both sides. Float the source (the sinewave current source). Connect the return path of the bridge to the current source (in the model it is unconnected).
The impedance of the load (C1 and R2) is too low. The peak source current is 45uA, you cannot drive a 1ohm resistor and see more than 45uV. Increase it to something much higher, say 1Mohm. C1 should be much smaller, maybe 1nF.
At 40Hz (the frequency of the sine wave), the impedance of the 171nF cap is 23e3, which limits the peak voltage to about 1V. I'm not familar with piezoelectric devices, so have no idea whether the model is reasonable, but to get a significant voltage out of it in that configuration the capacitance has to be much smaller.
Make all the diodes the same; you can do this by selecting all of them and using the common parameter tool. Currently they have a mix of values. Set Vknee to 0.7 and Goff to 0.
A useful way to debug this, and other circuits, is to test in pieces. With MapleSim this is fairly easy. For example, you can disable everything to the right of the piezoelectric model (select the parts and click the enable/disable icon on the toolbar), add a temporary ground, then check whether the voltage across the piezoelectric device produced is reasonable.