Does Citadel stack if multiple heroes on the same team use it???

I've tried looking online for the answer but cannot find it anywhere.. basically, I want to know if all 5 of my team put citadel on and get into a 5v5 team fight, does the enemy team only get the initial 20% physical armor decreased from one of our cards, or do they lose 100% physical armor because of 5 of us are running citadel? Thanks in advance!