What is the purpose of large surface area washers when used on wooden structures?

• A. Provide additional bearing area to help preclude damage to the wood when the hardware is tightened.
• B. Improve corrosion resistance of the hardware.
• C. Reduce friction in the joint.
• D. Change the load direction of the bolt.

Answer: (D)

The main idea is to spread the load over a larger area to protect the wood. When a bolt or screw is tightened against wood, the contact pressure can crush or split the fibers if the bearing surface is small. A large surface area washer increases the area in contact with the wood, lowering the local pressure and helping prevent damage or pull-through as the fastener is tightened. That’s why this washer is used on wooden structures—to preserve the wood and keep the joint secure over time.

It doesn’t change the direction of the load on the bolt, which is why it won’t alter the load path. It isn’t primarily for corrosion resistance, and while it might influence slight friction at the contact surface, that isn’t its main purpose.