Strong Grip

You have advantage on tests of Strength to grab, pull, or avoid being disarmed.

You may wield a heavy melee weapon in one hand,
BUT
you have a -5 penalty to hit with heavy melee weapons wielded in one hand,
and for the purposes of casting spells heavy melee weapons wielded in one hand do not count as heavy
(You must use both hands to get any bonuses for casting a spell with a heavy weapon).

Since you do not need both hands to wield a heavy melee weapon, you may wield a heavy melee weapon in one hand with another weapon (which may also be a heavy melee weapon) in the other,
but the -5 penalty to hit with a weapon that is not light or unarmed while it is being dual wielded applies.

(Bonuses to attacks and spells from a weapon only apply to attacks or spells using that weapon. If you are dual-wielding, each attack or spell can only get the bonuses from one weapon.)

Normally, two hands are required to wield a heavy melee weapon.