[css3-animation] keyframes without animations

How can I define "keyframes" without animation?
I don't want an "animation-timing-function" controlled animation, instead I
would like to simply change CSS properties in the key frames (without any
animation effects).

It would be usable if the "animation-timing-function" property had a "none"
value.

# @keyframes 'frames' {
#
#     from {
#         top: 0;
#         animation-timing-function: none;
#     }
#
#     50% {
#         top: 50px;
#         animation-timing-function: none;
#     }
#
#     to {
#         top: 150px;
#     }
#
# }

In the upper case, the "animated" element would jumps from 0 to  50px, then
from 50px to 150px without any animation.

Is there any CSS based solution to this problem? (or do I still need
javascript to do a simple 3 (or more) step CSS value change?)

Thanks,
Andras Nemeseri