Siege Carpentry is a unique technology in Age of Empires IV: The Sultans Ascend available to the Ayyubids that can be researched at the Siege Workshop starting in the Castle Age. Researching the technology gives all siege engines the Structural Reinforcements ability.
While in Golden Age Tier 2 or higher, the research speed of this technology is +25%.
Structural Reinforcements (Active): Siege unit gains +20 melee armor and +5 fire armor for 10 seconds. The ability costs 50 wood to activate and is only useable on one unit at a time, but has a global 90 second cooldown.