Christine E. Wittich
Date of this Version
Ouoba, S.T.A. (2021). Fragility Functions of Manufactured Houses under Earthquake Loads. M.S. Thesis, Department of Civil and Environmental Engineering, University of Nebraska-Lincoln, Lincoln, NE.
Manufactured homes are factory-built homes made of wooden structural members, then transported and installed on a given site. Manufactured housing is used in many countries, such as in Australia, and in New Zealand but remain mostly popular in the United States. In 2020, nearly 22 million people were estimated to live in manufactured homes in the United States, with an increase of more than fifty percent in the shipment over the past seven years. However, performance observations from the last decades have shown the vulnerability of manufactured homes to extreme events, like windstorms and earthquakes. Damage assessments and post-event evaluations have highlighted that the foundations play an important role in the vulnerability of manufactured homes to the lateral forces generated by these events. Manufactured homes are typically installed on stacked concrete masonry unit (CMU) blocks that are not anchored to the ground. Because the CMU blocks are unanchored and squat, they respond in a rigid-body motion under earthquake loads, leading to a permanent displacement or overturning of the home. Given that most manufactured homes in the United States are not required to anchor their foundations to the ground, there is a need to quantify the risk associated with these foundations given future earthquake scenarios. The present thesis aims to develop seismic fragility functions for typical manufactured homes that relate the level of damage sustained by manufactured homes to an earthquake’s intensity. To this end, finite element models of a manufactured home accounting for various typical foundation configurations, installation techniques, and home geometries were modeled using SAP2000. A nonlinear dynamic analysis was then performed for a set of earthquake records to predict the home’s response. Fragility curves were then generated to correlate the level of damage to the Peak Ground Acceleration (PGA) of the earthquake. Manufactured homes’ response to earthquake ground motions, is found to be particularly sensitive to their dimensions, the material isolating their foundations from the soil, and the number of blocks making up the foundations.
Advisor: Christine E. Wittich