1995 Building Publications - Recommended Performance-Based Criteria for the Design of Manufactured Home Foundation Systems to Resist Wind and Seismic Loads.

Recommended Performance-Based Criteria for the Design of Manufactured Home Foundation Systems to Resist Wind and Seismic Loads.

NISTIR 5664; 74 p. August 1995.

Sponsor:

Department of Housing and Urban Development, Washington, DC

Available from:

National Technical Information Service
Order number: PB96-128111

Keywords:

building technology; codes; standards; earthquake engineering; foundations; manufactured housing; mobile homes; soil anchors; structural engineering; wind engineering; wind loads; windstorm protection; structural systems

Abstract:

This report addresses the issue of tornadoes as a basis for the design of manufactured homes and compares base shears due to wind loading with base shears due to earthquake excitation for various wind and seismic zones. Only for annual exceedance probabilities less than about 2.5 x 10-4 will tornadic wind speeds govern the design for wind loading. In view of the accepted probabilities of attaining or exceeding design limit states for ordinary buildings, it is concluded that tornadoes should not be a part of the wind load design criteria for manufactured homes. Also, it is concluded that transverse base shear due to wind loading will always exceed the base shear due to earthquake loading, regardless of the wind or seismic zone in which the manufactured home is sited. In the longitudinal direction the ranges of base shear for wind and earthquake are approximately equal. These comparisons are based on the assumption that the structural system is properly detailed to resist earthquake forces and is capable of accommodating inelastic deformations several times greater than the deformation at first yield. In view of the uncertainty regarding the dynamic properties of manufactured homes and their support systems, a simplified equation for the determination of seismic base shear is proposed. Traditional anchor/tie/pier systems and current installation practice do not provide adequate windstorm protection for manufactured homes. Even with preloading, the effectiveness of traditional shallow, helix-plate soil anchors is limited to basic wind speeds of approximately 44.7 m/s (100 mph). However, there are several alternative anchoring and support systems on the market or under development that can provide the required resistance to wind and earthquake loads. Finally, a set of performance-based criteria for anchoring manufactured homes against wind and earthquake loads is proposed.

Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899