It's disabled by default.

ttt_ragdoll_collide (def. 0):
By default ragdolls will not collide with other ragdolls and some small physics objects (or doors set not to collide with debris). Enabling ragdoll collision will change that. Earlier versions of TTT had ragdoll collision, but this allowed griefers to create situations where ragdolls were physics-glitched to constantly collide, causing serious lag. Some maps may expect ragdolls to collide though. Use with care.