thread strategy and test delay

Hi,
I am learning to use SoapUI as a performance testing tool. I have seen the different strategies available in SoapUI for the load test e.g. Simple, Burst, Variance, Thread etc.

My requirement is to ramp up the number of threads and, for achieve this, I think that the thread strategy is the right one.

I need to change test delay (like in a simple strategy scenario) in thread strategy, how i can do it??

thank in advance,
Roberto