A curtain wall structure that can provide a continuous sealing plane through the use of a dual density gasket and that offers improved sealing and thermal insulation properties. The curtain wall structure also provides a structural reinforcement element assembly that is integrated into a mullion of the curtain wall structure to provide a better load bearing capacity. A curtain wall water drainage cross element assembly is also provided to prevent water from flowing vertically inside the curtain wall system. An expansion joint assembly is also provided and designed as two movable parts allowing provides a sound free vertical displacement of components by means of no direct metal to metal contact between sliding parts.