Tornadoes: Walls, Connections, and Continuous Load Path

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Failures of connections anchoring homes to foundations, roof to wall connection failures, penetration of walls by wind blown debris, and gable end failures from lack of adequate bracing are examples of structural failures that occur in high wind events, especially in non- coastal areas that don’t typically incorporate high wind construction practices in home building.

In a tornado, if the connections of the home to the foundation are inadequate, the home can slide or lift off the foundation.

Tips:

• Anchor base or sill plates to the foundation with anchor bolts and washers at no more than 4’ on center

When roof to wall connections fail in high wind events, significant damage occurs to the roof structure, up to the loss of the entire roof.

Tips:

• Ensure a continuous load path from the roof to the foundation by connecting the roof to the wall with a metal anchor, connecting components of the wall together with appropriate metal connectors, and anchoring the walls to the foundation with anchor bolts or other suitable embedded anchors.

In tornadoes and other high wind events, wind borne debris can penetrate walls with fiberboard or rigid insulation board sheathing and create openings that allow air pressure to build up inside the house, increasing the wind pressure on all structural elements.

Tips

• Sheath walls with plywood or OSB sheathing to prevent penetration from debris and to strengthen walls against lateral wind loads.

Unbraced gable end walls collapse or rotate, causing loss of the roof system. This can often lead to the loss of larger sections of the building.

Tips

• Ensure adequate sheathing connection at the top of the gable end

• Sheath the outside of the gable with plywood or OSB

• Anchor the bottom of the triangular gable end to the top of the wall below

• Brace the bottom of the triangular gable end for wind blowing both into and away from the gable

Benefits of Using This Mitigation Strategy

• Helps to prevent damage to a structure and its contents

• Helps to prevent injuries to occupants

Technical Information Provided by FEMA





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