In a steel arch shoe detail for a timber canopy, what long-term issue is expected?

• A. Glulam decay due to end grain being in direct contact with steel.
• B. Glulam decay due to moisture buildup inside arch shoe.
• C. Glulam split due to material expansion perpendicular to grain.
• D. Glulam split due to tension parallel to grain.

Answer: (B)

Moisture management is the critical factor in timber-to-steel canopy details. The steel arch shoe can trap and limit drying of the glulam at the interface, creating a microclimate where moisture persists inside the arch seat. When moisture content stays high over time, wood-decay fungi can colonize the glulam, leading to progressive rot and loss of strength.

This decay mechanism isn’t primarily caused by end-grain contact with steel or by simple mechanical splitting from moisture. The long-term concern is the buildup of moisture inside the arch shoe, which promotes fungal decay in the glulam.