[JohnPaulB]

Hexagram #4. Kicking Down the Door by David Pulver

TFT Official rules that you can convert to your needs.

"It’s possible to force open a door on a successful ST roll. Prying it open with crowbars (see Crowbars Can Help, ITL, p. 71) requires tools and a 3/ST roll. Similarly, brute force (Knocking the Door Open, ITL, p. 71) by slamming into it with a shoulder, feet, or battering ram requires a 5/ST roll (if using a ram, against the wielders’ combined ST). If the door isn’t a regular ST 30 door, assume the ST roll is (door ST/10) dice to pry it open, or two ST higher to knock it open, rounding up to the nearest die. Thus, a ST 60 door would be 6/ST to pry and 8/ST to knock open.

An alternative to totally destroying the door is to burst it open through the sheer impact of missile spells (or siege artillery or explosions). The regular ST 30 door will burst open after taking 10 hits from a missile attack. Assume higher or lower ST doors will burst open if any single attack inflicts at least 1/3 their ST in damage (before applying armor). Thus, a ST 60 door would burst open if a hit by a Lightning Bolt, etc., rolled 20+ damage."

The article gives ST of doors and gates.