Maximum disturbance to space time of gravitational waves, and will this affect humans? Do we have a theory that can tell us how much change gravitational waves can make to space time. If it is infinite then I think any time we can see biggest change in space time and how much could it affect to humans?
Gravitational waves cause a stretch and squeeze in space-time. It has two polarizations Plus and Cross polarization. This serves as an axis for the stretch and squeeze when a gravitational wave hits a body. However, the order of stretching and squeezing is actually really small. It changes space-time by an order of $10^{-21}$m. That's around the diameter of a proton. There are Numerical relativity simulations where you can see for yourself how much the change in space-time occurs for a certain pair of mass collisions. 

Check out the Waveforms for SEOBNR, Taylor etc. You might get a good idea. 

FYI : Question belongs in physics.stackexchange