LOL, settle down, EoN
.
The math of a fortified pikeman on a forest is:
2 - Base Defense
1 - Fortification Bonus (50 %)
1 - Forest Bonus (50%)
--
4
Ironclad: Attack = 4
Though it appears the ironclad has a 50-50 shot (assuming it is 100% healthy), in fact the odds favor the Ironclad because it has 30 hit points, vs. the pikeman's 10.
So it is possible, but not probably, the pikeman will defeat the ironclad.
If the pikeman is a veteran, the pikeman's odds are still less than 50-50, even though he defends with 5 and the ironclad attacks with 4.
If the ironclad is Veteran, the chance is remote that the pikeman will survive... but the ironclad will take some damage and be "slowed" in future movement and/or number of attacks in a turn... so the death of the pikeman may not be in vain, esp. since a pikeman costs only 20 shields.
A long time ago, I faced AIs that had ironclads attacking my cities for about 12 turns before I stole gunpowder. The best I could manage against the ironclad onslaught was rapid replacement of my pikemen. It was fortunate for me I was not facing a human player who could have taken advantage of a coordinated assault... 3 of my cites were empty after almost every ironclad bombardment.
Conclusion: Unless your city is on a hill (or river/forest or mountain), it will likely lose to a healthy ironclad. So just use (vet) musketeers to defend!