Civil and Environmental Engineering
Empirical Fragility Functions and Numerical Parametric Study for Buckling of Steel Grain Bins under High Wind Loads
Dr. Christine E. Wittich Ph.D.
Date of this Version
Ruder, A.S. (2022). Empirical Fragility Functions and Numerical Parametric Study for Buckling of Steel Grain Bins Under High Wind Loads [Master's thesis, University of Nebraska-Lincoln].
While rural infrastructure is critical to the agricultural industry, it has been historically more susceptible to damage and slower to recover following natural disasters than its urban and suburban counterparts. This has been made evident most recently by the events of the August 10, 2020, derecho in which rural regions in Iowa were among the hardest hit areas with sustained windspeeds exceeding 120 mph. Among the most frequently damaged structures in this event were corrugated steel grain bins, which farmers and co-ops use to dry and store certain commodities. Unlike most other critical structures, steel grain bins are not designed and constructed to consistent design standards for wind loads resulting in a wide range of performance and impact to individual farmers and the economy. Therefore, the overarching goal of this thesis is to enhance knowledge of steel grain bin performance under wind loads, which is accomplished by field reconnaissance, empirical fragility analysis, and finite element modeling.
A survey of over 600 standard construction corrugated steel grain bins was carried out over a large area of eastern and central Iowa in the immediate aftermath of the August 2020 storm. Physical characteristics, configuration, construction, and damage severity were observed and recorded. Windspeed data from the National Weather Service and point estimates from observed damage indicators were used to build a more detailed estimate of peak windspeeds across the region. Empirical fragility curves were developed to relate the probability of various steel grain bin damage states to windspeed. This fragility analysis considered the effects of the physical characteristics, configuration, and construction of the grain bins. The results of this analysis showed that grain bin diameter and exposure of the terrain they are located on are the most significant factors when it comes to their susceptibility to damage.
Finite element modelling was used to carry out a parametric analysis of the effects of a wide range of physical characteristics of empty steel grain bins on their buckling strength under wind loads. The finite element software LS-DYNA was utilized to construct three-dimensional numerical models using shell elements. Critical wind load was determined by a nonlinear buckling analysis by the arc-length method. The parametric analysis was carried out by looking at the effects of diameter, height, number of vertical stiffeners, number of wind rings, presence of wind on the roof of the structure, analysis as vented or unvented, wavelength of the corrugation profile, depth of the corrugation profile, thickness of the cylinder wall, and thickness of vertical stiffeners. The results of this analysis were compared to empirical results from the data collected during the August 2020 derecho in order to confirm the trends observed during the parametric analysis. The conclusions drawn from this were that grain bin height, diameter, and openness of terrain have the greatest influence on susceptibility to damage from high winds regardless of other characteristics. Parameters such as presence of stiffeners, wind rings, and roof vents had more influence on the theoretical buckling wind load than they had on observed performance in the field.
Advisor: Christine E. Wittich
A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of the Requirements For the Degree of Master of Science, Major: Civil Engineering, Under the Supervision of Professor Christine E. Wittich. Lincoln, Nebraska: December 2022
Copyright © 2022 Andrew S. Ruder