What are the three fastener failure modes?

• A. Pull-out, pull-over, and tensile break.
• B. Pull-out, pull-over, and shear failure.
• C. Pull-out only.
• D. Tensile break and pull-over.

Answer: (C)

When assessing fastener performance in roofing under uplift, there are three distinct ways a fastener can fail. Pull-out means the fastener withdraws from the substrate because the surrounding material can’t resist withdrawal, so the threads or core pull free. Pull-over occurs when the fastener head or washer pulls through the membrane or substrate, reducing clamping and allowing uplift to continue. Shear failure happens when the fastener shank or the joint between materials shears in the substrate, letting the panel slide past the fastener under load. These are the main mechanisms to consider because they cover the common directions of loading and loss of restraint in roofing assemblies. Tensile break of the fastener itself is a different, less typical event in standard roof fastening scenarios. Therefore, the three primary fastener failure modes are pull-out, pull-over, and shear failure.